Posts Tagged structure lines

Recent Postings from structure lines

The physical characteristics of the gas in the disk of Centaurus A using the Herschel Space Observatory

We search for variations in the disk of Centaurus A of the emission from atomic fine structure lines using Herschel PACS and SPIRE spectroscopy. In particular we observe the [C II](158 $\mu$m), [N II](122 and 205 $\mu$m), [O I](63 and 145 $\mu$m) and [O III](88 $\mu$m) lines, which all play an important role in cooling the gas in photo-ionized and photodissociation regions. We determine that the ([C II]+[O I]$_{63}$)/$F_{TIR}$ line ratio, a proxy for the heating efficiency of the gas, shows no significant radial trend across the observed region, in contrast to observations of other nearby galaxies. We determine that 10 – 20% of the observed [C II] emission originates in ionized gas. Comparison between our observations and a PDR model shows that the strength of the far-ultraviolet radiation field, $G_0$, varies between $10^{1.75}$ and $10^{2.75}$ and the hydrogen nucleus density varies between $10^{2.75}$ and $10^{3.75}$ cm$^{-3}$, with no significant radial trend in either property. In the context of the emission line properties of the grand-design spiral galaxy M51 and the elliptical galaxy NGC 4125, the gas in Cen A appears more characteristic of that in typical disk galaxies rather than elliptical galaxies.

Gas lines from the 5-Myr old optically thin disk around HD141569A. Herschel observations and modeling

At the distance of 99-116 pc, HD141569A is one of the nearest HerbigAe stars that is surrounded by a tenuous disk, probably in transition between a massive primordial disk and a debris disk. We observed the fine-structure lines of OI at 63 and 145 micron and the CII line at 157 micron with the PACS instrument onboard the Herschel Space Telescope as part of the open-time large programme GASPS. We complemented the atomic line observations with archival Spitzer spectroscopic and photometric continuum data, a ground-based VLT-VISIR image at 8.6 micron, and 12CO fundamental ro-vibrational and pure rotational J=3-2 observations. We simultaneously modeled the continuum emission and the line fluxes with the Monte Carlo radiative transfer code MCFOST and the thermo-chemical code ProDiMo to derive the disk gas- and dust properties assuming no dust settling. The models suggest that the oxygen lines are emitted from the inner disk around HD141569A, whereas the [CII] line emission is more extended. The CO submillimeter flux is emitted mostly by the outer disk. Simultaneous modeling of the photometric and line data using a realistic disk structure suggests a dust mass derived from grains with a radius smaller than 1 mm of 2.1E-7 MSun and from grains with a radius of up to 1 cm of 4.9E-6 MSun. We constrained the polycyclic aromatic hydrocarbons (PAH) mass to be between 2E-11 and 1..4E-10 MSun assuming circumcircumcoronene (C150H30) as the representative PAH. The associated PAH abundance relative to hydrogen is lower than those found in the interstellar medium (3E-7) by two to three orders of magnitude. The disk around HD141569A is less massive in gas (2.5 to 4.9E-4 MSun or 67 to 164 MEarth) and has a flat opening angle (<10%). [abridged]

Mid-Infrared Atomic Fine-Structure Emission Line Spectra of Luminous Infrared Galaxies: Spitzer/IRS Spectra of the GOALS Sample

We present the data and our analysis of MIR fine-structure emission lines detected in Spitzer/IRS high-res spectra of 202 local LIRGs observed as part of the GOALS project. We detect emission lines of [SIV], [NeII], [NeV], [NeIII], [SIII]18.7, [OIV], [FeII], [SIII]33.5, and [SiII]. Over 75% of our galaxies are classified as starburst (SB) sources in the MIR. We compare ratios of the emission line fluxes to stellar photo- and shock-ionization models to constrain the gas properties in the SB nuclei. Comparing the [SIV]/[NeII] and [NeIII]/[NeII] ratios to the Starburst99-Mappings III models with an instantaneous burst history, the line ratios suggest that the SB in our LIRGs have ages of 1-4.5Myr, metallicities of 1-2Z_sun, and ionization parameters of 2-8e7cm/s. Based on the [SIII]/[SIII] ratios, the electron density in LIRG nuclei has a median electron density of ~300cm-3 for sources above the low density limit. We also find that strong shocks are likely present in 10 SB sources. A significant fraction of the GOALS sources have resolved neon lines and 5 show velocity differences of >200km/s in [NeIII] or [NeV] relative to [NeII]. Furthermore, 6 SB and 5 AGN LIRGs show a trend of increasing line width with ionization potential, suggesting the possibility of a compact energy source and stratified ISM in their nuclei. We confirm a strong correlation between the [NeII]+[NeIII] emission, as well as [SIII]33.5, with both the IR luminosity and the 24um warm dust emission measured from the spectra. Finally, we find no correlation between the hardness of the radiation field or the line width and the ratio of the total IR to 8um emission (IR8). This may be because the IR luminosity and the MIR fine-structure lines are sensitive to different timescales over the SB, or that IR8 is more sensitive to the geometry of the warm dust region than the radiation field producing the HII region emission.

Two high-redshift DLAs towards a z~5 gamma-ray burst

Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A from which we can measure abundance patterns, metallicity, dust content and extinction of the GRB host galaxy (z=5.0) as well as a Damped Lyman-alpha Absorber (DLA) galaxy along the line of sight (z=4.6). These systems have column densities of log N =22.30 +/- 0.06 and 21.34 +/- 0.10, respectively. The GRB host galaxy has a metallicity of 2% solar (based on sulfur), and a lower limit of the metallicity for the intervening DLA is 3% (based on silicon). For the intervening absorber we also measure -1.73<[Fe/H]<-1.09, but the true metallicity can be higher, because it is unclear how much the abundances are affected by dust depletion. The presence and variability of fine-structure lines confirms the z=5.0 system as the GRB host. This is the highest redshift where Fe II fine-structure lines have been detected. The afterglow is only mildly reddened with A_V = 0.11 +/- 0.04 mag, and the host galaxy has a dust-to-metals ratio which is consistent with being equal to or lower than typical values in the Local Group.

Towards A Removal of Temperature Dependencies from Abundance Determinations

The metal content of a galaxy is a key property for distinguishing between viable galaxy evolutionary scenarios, and it strongly influences many of the physical processes in the interstellar medium. An absolute and robust determination of extragalactic metallicities is essential in constraining models of chemical enrichment and chemical evolution, however, current gas phase abundance determinations from optical fine-structure lines are uncertain to 0.8 dex as conversion of these optical line fluxes to abundances is strongly dependent on the electron temperature of the ionized gas. In contrast, the far-IR emission lines can be used to derive an O++ abundance that is relatively insensitive to temperature, while the ratio of the optical to far-IR lines provides a consistent temperature to be used in the derivation of an O$^+$ abundance. We present observations of the [O III] 88 \micron\ fine-structure line in NGC 628 that were obtained as part of the KINGFISH program. These data are combined with optical IFU data to derive oxygen abundances for seven HII regions. We find the abundance of these regions to all lie between the high and low values of strong line calibrations and in agreement with estimates that assume temperature fluctuations are present in the HII regions.

Far-infrared Fine-Structure Line Diagnostics of Ultraluminous Infrared Galaxies

We present Herschel observations of six fine-structure lines in 25 Ultraluminous Infrared Galaxies at z<0.27. The lines, [O III]52, [N III]57, [O I]63, [N II]122, [O I]145, and [C II]158, are mostly single gaussians with widths <600 km s-1 and luminosities of 10^7 – 10^9 Solar. There are deficits in the [O I]63/L_IR, [N II]/L_IR, [O I]145/L_IR, and [C II]/L_IR ratios compared to lower luminosity systems. The majority of the line deficits are consistent with dustier H II regions, but part of the [C II] deficit may arise from an additional mechanism, plausibly charged dust grains. This is consistent with some of the [C II] originating from PDRs or the ISM. We derive relations between far-IR line luminosities and both IR luminosity and star formation rate. We find that [N II] and both [O I] lines are good tracers of IR luminosity and star formation rate. In contrast, [C II] is a poor tracer of IR luminosity and star formation rate, and does not improve as a tracer of either quantity if the [C II] deficit is accounted for. The continuum luminosity densities also correlate with IR luminosity and star formation rate. We derive ranges for the gas density and ultraviolet radiation intensity of 10^1 < n < 10^2.5 and 10^2.2 < G_0 < 10^3.6, respectively. These ranges depend on optical type, the importance of star formation, and merger stage. We do not find relationships between far-IR line properties and several other parameters; AGN activity, merger stage, mid-IR excitation, and SMBH mass. We conclude that these far-IR lines arise from gas heated by starlight, and that they are not strongly influenced by AGN activity.

Uncertainties in water chemistry in disks: An application to TW Hya

Context. This paper discusses the sensitivity of water lines to chemical processes and radiative transfer for the protoplanetary disk around TW Hya. The study focuses on the Herschel spectral range in the context of new line detections with the PACS instrument from the Gas in Protoplanetary Systems project (GASPS). Aims. The paper presents an overview of the chemistry in the main water reservoirs in the disk around TW Hya. It discusses the limitations in the interpretation of observed water line fluxes. Methods. … (abbreviated) Results. We report new line detections of p-H2O (3_22-2_11) at 89.99 micron and CO J=18-17 at 144.78 micron for the disk around TW Hya. Disk modeling shows that the far-IR fine structure lines ([OI], [CII]) and molecular submm lines are very robust to uncertainties in the chemistry, while the water line fluxes can change by factors of a few. The water lines are optically thick, sub-thermally excited and can couple to the background continuum radiation field. The low-excitation water lines are also sensitive to uncertainties in the collision rates, e.g. with neutral hydrogen. The gas temperature plays an important role for the [OI] fine structure line fluxes, the water line fluxes originating from the inner disk as well as the high excitation CO, CH+ and OH lines. Conclusions. Due to their sensitivity on chemical input data and radiative transfer, water lines have to be used cautiously for understanding details of the disk structure. Water lines covering a wide range of excitation energies provide access to the various gas phase water reservoirs (inside and outside the snow line) in protoplanetary disks and thus provide important information on where gas-phase water is potentially located. Experimental and/or theoretical collision rates for H2O with atomic hydrogen are needed to diminish uncertainties from water line radiative transfer.

DIGIT survey of far-infrared lines from protoplanetary disks I

[abridged] We present far-infrared spectroscopic observations of PMS stars taken with Herschel/PACS as part of the DIGIT key project. The sample includes 22 Herbig AeBe and 8 T Tauri sources. Multiple atomic fine structure and molecular lines are detected at the source position: [OI], [CII], CO, OH, H_2O, CH^+. The most common feature is the [OI] 63micron line detected in almost all of the sources followed by OH. In contrast with CO, OH is detected toward both Herbig AeBe groups (flared and non-flared sources). An isothermal LTE slab model fit to the OH lines indicates column densities of 10^13 < N_OH < 10^16 cm^-2, emitting radii 15 < r < 100 AU and excitation temperatures 100 < T_ex < 400 K. The OH emission thus comes from a warm layer in the disk at intermediate stellar distances. Warm H_2O emission is detected through multiple lines toward the T Tauri systems AS 205, DG Tau, S CrA and RNO 90 and three Herbig AeBe systems HD 104237, HD 142527, HD 163296 (through line stacking). Overall, Herbig AeBe sources have higher OH/H_2O abundance ratios across the disk than do T Tauri disks, from near- to far-infrared wavelengths. Far-infrared CH^+ emission is detected toward HD 100546 and HD 97048. The slab model suggests moderate excitation (T_ex ~ 100 K) and compact (r ~ 60 AU) emission in the case of HD 100546. The [CII] emission is spatially extended in all sources where the line is detected. This suggests that not all [CII] emission is associated with the disk and that there is a substantial contribution from diffuse material around the young stars. The flux ratios of the atomic fine structure lines are consistent with a disk origin for the oxygen lines for most of the sources.

The ionizing sources of luminous compact HII regions in the RCW106 and RCW122 clouds [Replacement]

Given the rarity of young O star candidates, compact HII regions embedded in dense molecular cores continue to serve as potential sites to peer into the details of high-mass star formation. To uncover the ionizing sources of the most luminous and compact HII regions embedded in the RCW106 and RCW122 giant molecular clouds, known to be relatively nearby (2-4 kpc) and isolated, thus providing an opportunity to examine spatial scales of a few hundred to a thousand AU in size. High spatial resolution (0.3"), mid-infrared spectra (R=350), including the fine structure lines [ArIII] and [NeII], were obtained for four luminous compact HII regions, embedded inside the dense cores within the RCW106 and RCW122 molecular cloud complexes. At this resolution, these targets reveal point-like sources surrounded by nebulosity of different morphologies, uncovering details at spatial dimensions of <1000AU. The point-like sources display [ArIII] and [NeII] lines – the ratios of which are used to estimate the temperature of the embedded sources. The derived temperatures are indicative of mid-late O type objects for all the sources with [ArIII] emission. Previously known characteristics of these targets from the literature, including evidence of disk or accretion suggest that the identified sources may grow more to become early-type O stars by the end of the star formation process.

The ionizing sources of luminous compact HII regions in the RCW106 and RCW122 clouds

Given the rarity of young O star candidates, compact HII regions embedded in dense molecular cores continue to serve as potential sites to peer into the details of high-mass star formation. To uncover the ionizing sources of the most luminous and compact HII regions embedded in the RCW106 and RCW122 giant molecular clouds, known to be relatively nearby (2-4 kpc) and isolated, thus providing an opportunity to examine spatial scales of a few hundred to a thousand AU in size. High spatial resolution (0.3"), mid-infrared spectra (R=350), including the fine structure lines [ArIII] and [NeII], are obtained for four luminous compact HII regions, embedded inside the dense cores within the RCW106 and RCW122 molecular cloud complexes. At this resolution, these targets reveal point-like sources surrounded by nebulosity of different morphologies, uncovering details at spatial dimensions of <1000AU. The point-like sources display [ArIII] and [NeII] lines – the ratios of which are used to estimate the temperature of the embedded sources. The derived temperatures are indicative of mid-late O type objects for all the sources with [ArIII] emission. Previously known characteristics of these targets from the literature, such as evidences of disk and/or accretion suggest that the identified sources may grow further to become early type O stars by the end of the star formation process.

Probing the Interstellar Medium of z~1 Ultra-luminous Infrared Galaxies through Interferometric Observations of CO and Spitzer Mid-infrared Spectroscopy

We explore the relationship between gas, dust and star formation in a sample of 12 ultra-luminous infrared galaxies (ULIRGs) at high redshift compared to a similar sample of local galaxies. We present new CO observations and/or Spitzer mid-IR spectroscopy for 6 70 micron selected galaxies at z~1 in order to quantify the properties of the molecular gas reservoir, the contribution of an active galactic nuclei (AGN) to the mid-IR luminosity and the star formation efficiency (SFE=LIR/L’CO). The mid-IR spectra show strong polycyclic aromatic hydrocarbon (PAH) emission and our spectral decomposition suggests that the AGN makes a minimal contribution (<25%) to the mid-IR luminosity. The 70 micron selected ULIRGs which we find to be spectroscopic close pairs, are observed to have high SFE, similar to local ULIRGs and high redshift submillimeter galaxies, consistent with enhanced IR luminosity due to an ongoing major merger. Combined with existing observations of local and high redshift ULIRGs, we further compare the PAH, IR and CO luminosities. We show that the ratio LPAH6.2/LIR decreases with increasing IR luminosity for both local and high redshift galaxies but the trend for high redshift galaxies is shifted to higher IR luminosities; the average LPAH6.2/LIR ratio at a given LIR is ~3 times higher at high redshift. When we normalize by the molecular gas, we find this trend to be uniform for galaxies at all redshifts and that the molecular gas is correlated with the PAH dust emission.The similar trends seen in the [CII] to molecular gas ratios in other studies suggests that PAH emission, like [CII], continues to be a good tracer of photodissociation regions even at high redshift. Together the CO, PAH and far-IR fine structure lines should be useful for constraining the interstellar medium conditions in high redshift galaxies.

Probing the Interstellar Medium of z~1 Ultra-luminous Infrared Galaxies through Interferometric Observations of CO and Spitzer Mid-infrared Spectroscopy [Replacement]

We explore the relationship between gas, dust and star formation in a sample of 12 ultra-luminous infrared galaxies (ULIRGs) at high redshift compared to a similar sample of local galaxies. We present new CO observations and/or Spitzer mid-IR spectroscopy for 6 70 micron selected galaxies at z~1 in order to quantify the properties of the molecular gas reservoir, the contribution of an active galactic nuclei (AGN) to the mid-IR luminosity and the star formation efficiency (SFE=LIR/L’CO). The mid-IR spectra show strong polycyclic aromatic hydrocarbon (PAH) emission and our spectral decomposition suggests that the AGN makes a minimal contribution (<25%) to the mid-IR luminosity. The 70 micron selected ULIRGs which we find to be spectroscopic close pairs, are observed to have high SFE, similar to local ULIRGs and high redshift submillimeter galaxies, consistent with enhanced IR luminosity due to an ongoing major merger. Combined with existing observations of local and high redshift ULIRGs, we further compare the PAH, IR and CO luminosities. We show that the ratio LPAH6.2/LIR decreases with increasing IR luminosity for both local and high redshift galaxies but the trend for high redshift galaxies is shifted to higher IR luminosities; the average LPAH6.2/LIR ratio at a given LIR is ~3 times higher at high redshift. When we normalize by the molecular gas, we find this trend to be uniform for galaxies at all redshifts and that the molecular gas is correlated with the PAH dust emission.The similar trends seen in the [CII] to molecular gas ratios in other studies suggests that PAH emission, like [CII], continues to be a good tracer of photodissociation regions even at high redshift. Together the CO, PAH and far-IR fine structure lines should be useful for constraining the interstellar medium conditions in high redshift galaxies.

An Overview of the Dwarf Galaxy Survey

The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galaxies using 230h of far-infrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws to this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Zsun, and spans 4 orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially on their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 mic with the highest sensitivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158 mic, [OI] 63 mic, [OI] 145 mic, [OIII] 88 mic, [NIII] 57 mic and [NII] 122 and 205 mic have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines (J=4-3 to J=13-12), [NII] 205 mic and [CI] lines at 370 and 609 mic. This paper describes the sample selection and global properties of the galaxies, the observing strategy as well as the vast ancillary database available to complement the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.

An Overview of the Dwarf Galaxy Survey [Replacement]

The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galaxies using 230h of far-infrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws to this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Zsun, and spans 4 orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially on their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 mic with the highest sensitivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158 mic, [OI] 63 mic, [OI] 145 mic, [OIII] 88 mic, [NIII] 57 mic and [NII] 122 and 205 mic have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines (J=4-3 to J=13-12), [NII] 205 mic and [CI] lines at 370 and 609 mic. This paper describes the sample selection and global properties of the galaxies, the observing strategy as well as the vast ancillary database available to complement the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.

Far-Infrared Spectroscopy of the Galactic Center. Hot Molecular Gas: Shocks versus Radiation near SgrA*

We present a 52-671um spectral scan toward SgrA* taken with the PACS and SPIRE spectrometers onboard Herschel. The achieved angular resolution allows us to separate, for the first time at far-IR wavelengths, the emission toward the central cavity (gas in the inner central parsec of the galaxy) from that of the surrounding circum-nuclear disk. The spectrum toward SgrA* is dominated by strong [OIII], [OI], [CII], [NIII], [NII], and [CI] fine structure lines (in decreasing order of luminosity) arising in gas irradiated by UV-photons from the central stellar cluster. In addition, rotationally excited lines of 12CO (from J=4-3 to 24-23), 13CO, H2O, OH, H3O+, HCO+ and HCN, as well as ground-state absorption lines of OH+, H2O+, H3O+, CH+, H2O, OH, HF, CH and NH are detected. The excitation of the 12CO ladder is consistent with a hot isothermal component at Tk ~ 10^{3.1} K and n(H2)< 10^4 cm^{-3}. It is also consistent with a distribution of temperature components at higher density with most CO at Tk<300 K. The detected molecular features suggest that, at present, neither very enhanced X-ray, nor cosmic-ray fluxes play a dominant role in the heating of the hot molecular gas. The hot CO component (either the bulk of the CO column or just a small fraction depending on the above scenario) results from a combination of UV- and shock-driven heating. If irradiated dense clumps/clouds do not exist, shocks likely dominate the heating of the hot molecular gas. This is consistent with the high-velocity gas detected toward SgrA*.

Fine structure collision strengths and line ratios for [Ne V] in infrared and optical sources [Cross-Listing]

Improved collisions strengths for the mid-infrared and optical transitions in Ne V are presented. Breit-Pauli R-Matrix calculations for electron impact excitation are carried out with fully resolved near-threshold resonances at very low energies. In particular, the fine structure lines at 14 micron and 24 micron due to transitions among the ground state levels 1s^22s^22p^3 (^3P_{0,1,2}), and the optical/near-UV lines at 2973, 3346 and 3426 Angstrom transitions among the ^3P_{0,1,2}, ^1D_2, ^1S_0 levels are described. Maxwellian averaged collision strengths are tabulated for all forbidden transistion within the ground configuration. Significant differences are found in the low temperature range Te < 10000 K for both the FIR and the opitcal transitions compared to previous results. An analysis of the 14/24 line ratio in low-energy-density (LED) plasma conditions reveals considerable variation; the effective rate coefficient may be dominated by the very low-energy behaviour rather than the maxwellian averaged collision strengths. Computed values suggest a possible solution to the anomalous mid-IR ratios found to be lower than theoretical limits observed from planetary nebulae and Seyfert galaxies. While such LED conditions may be present in infrared sources, they might be inconsistent with photoionization equilibrium models.

Herschel/SPIRE Sub-millimeter Spectra of Local Active Galaxies

We present the sub-millimeter spectra from 450 GHz to 1550 GHz of eleven nearby active galaxies observed with the SPIRE Fourier Transform Spectrometer (SPIRE/FTS) onboard Herschel. We detect CO transitions from J_up = 4 to 12, as well as the two [CI] fine structure lines at 492 and 809 GHz and the [NII] 461 GHz line. We used radiative transfer models to analyze the observed CO spectral line energy distributions (SLEDs). The FTS CO data were complemented with ground-based observations of the low-J CO lines. We found that the warm molecular gas traced by the mid-J CO transitions has similar physical conditions (n_H2 ~ 10^3.2 – 10^3.9 cm^-3 and T_kin ~ 300 – 800 K) in most of our galaxies. Furthermore, we found that this warm gas is likely producing the mid-IR rotational H2 emission. We could not determine the specific heating mechanism of the warm gas, however it is possibly related to the star-formation activity in these galaxies. Our modeling of the [CI] emission suggests that it is produced in cold (T_kin < 30 K) and dense (n_H2 > 10^3 cm^-3) molecular gas. Transitions of other molecules are often detected in our SPIRE/FTS spectra. The HF J=1-0 transition at 1232 GHz is detected in absorption in UGC05101 and in emission in NGC7130. In the latter, near-infrared pumping, chemical pumping, or collisional excitation with electrons are plausible excitation mechanisms likely related to the AGN of this galaxy. In some galaxies few H2O emission lines are present. Additionally, three OH+ lines at 909, 971, and 1033 GHz are identified in NGC7130.

Evidence for CO shock excitation in NGC 6240 from Herschel SPIRE spectroscopy

We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines are detected, including CO J=4-3 through J=13-12, 6 H2O rotational lines, and [CI] and [NII] fine-structure lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the CO ladders of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the excitation of the gas in NGC 6240. We applied both C and J shock models to the H2 v=1-0 S(1) and v=2-1 S(1) lines and the CO rotational ladder. The CO ladder is best reproduced by a model with shock velocity v_s=10 km s^-1 and a pre-shock density n_H=5 * 10^4 cm^-3. We find that the solution best fitting the H2 lines is degenerate: The shock velocities and number densities range between v_s = 17 – 47 km s^-1 and n_H=10^7 – 5 * 10^4 cm^-3, respectively. The H2 lines thus need a much more powerful shock than the CO lines. We deduce that most of the gas is currently moderately stirred up by slow (10 km s^-1) shocks while only a small fraction (< 1 percent) of the ISM is exposed to the high velocity shocks. This implies that the gas is rapidly loosing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.

The complete far-infrared and submillimeter spectrum of the Class 0 protostar Serpens SMM1 obtained with Herschel. Characterizing UV-irradiated shocks heating and chemistry

We present the first complete 55-671 um spectral scan of a low-mass Class 0 protostar (Serpens SMM1) taken with the PACS and SPIRE spectrometers on board Herschel. More than 145 lines have been detected, most of them rotationally excited lines of 12CO (full ladder from J=4-3 to 42-41), H2O, OH, 13CO, HCN and HCO+ . Bright [OI]63,145um and weaker [CII]158 and [CI]370,609um lines are also detected. Mid-IR spectra retrieved from the Spitzer archive are also first discussed here, they show clear detections of [NeII], [FeII], [SiII] and [SI] fine structure lines as well as weaker H2 S(1) and S(2) pure rotational lines. The observed line luminosity is dominated by CO (~54%), H2O (~22%), [OI] (~12%) and OH (~9%) emission. A non-LTE model allowed us to quantify the contribution of the 3 different temperature components suggested by the 12CO rotational ladder (Tk(hot)~800 K, Tk(warm)~375 K and Tk(cool)~150 K). Gas densities n(H2)~5×10^6 cm^-3 are needed to reproduce the observed far-IR lines arising from shocks in the inner protostellar envelope for which we derive upper limit abundances of x(CO)~10^-4, x(H2O)~0.2×10^-5 and x(OH)~10^-6. The lower energy submm 12CO and H2O lines show more extended emission that we associate with the cool entrained outflow gas. Fast dissociative J-shocks (v_s > 60 km s^-1) as well as lower velocity non-dissociative shocks (v_s < 20 km s^-1) are needed to explain both the atomic lines and the hot CO and H2O lines respectively. Observations also show the signature of UV radiation and thus, most observed species likely arise in UV-irradiated shocks. Dissociative J-shocks produced by an atomic jet are the most probable origin of [OI] and OH emission and of a significant fraction of the warm CO emission. In addition, H2O photodissociation in UV-irradiated non-dissociative shocks can also contribute to the [OI] and OH emission.

The complete far-infrared and submillimeter spectrum of the Class 0 protostar Serpens SMM1 obtained with Herschel. Characterizing UV-irradiated shocks heating and chemistry [Replacement]

We present the first complete 55-671 um spectral scan of a low-mass Class 0 protostar (Serpens SMM1) taken with the PACS and SPIRE spectrometers on board Herschel. More than 145 lines have been detected, most of them rotationally excited lines of 12CO (full ladder from J=4-3 to 42-41), H2O, OH, 13CO, HCN and HCO+ . Bright [OI]63,145um and weaker [CII]158 and [CI]370,609um lines are also detected. Mid-IR spectra retrieved from the Spitzer archive are also first discussed here, they show clear detections of [NeII], [FeII], [SiII] and [SI] fine structure lines as well as weaker H2 S(1) and S(2) pure rotational lines. The observed line luminosity is dominated by CO (~54%), H2O (~22%), [OI] (~12%) and OH (~9%) emission. A non-LTE radiative transfer model allowed us to quantify the contribution of the 3 different temperature components suggested by the 12CO rotational ladder (Tk(hot)~800 K, Tk(warm)~375 K and Tk(cool)~150 K). Gas densities n(H2)~5×10^6 cm^-3 are needed to reproduce the observed far-IR lines arising from shocks in the inner protostellar envelope for which we derive upper limit abundances of x(CO)~10^-4, x(H2O)~0.2×10^-5 and x(OH)~10^-6. The lower energy submm 12CO and H2O lines show more extended emission that we associate with the cool entrained outflow gas. Fast dissociative J-shocks (v_s > 60 km s^-1) as well as lower velocity non-dissociative shocks (v_s < 20 km s^-1) are needed to explain both the atomic lines and the hot CO and H2O lines respectively. Observations also show the signature of UV radiation and thus, most observed species likely arise in UV-irradiated shocks. Dissociative J-shocks produced by an atomic jet are the most probable origin of [OI] and OH emission and of a significant fraction of the warm CO emission. In addition, H2O photodissociation in UV-irradiated non-dissociative shocks can also contribute to the [OI] and OH emission.

On the Excitation and Formation of Circumstellar Fullerenes

We compare and analyze the Spitzer mid-infrared spectrum of three fullerene-rich planetary nebulae in the Milky Way and the Magellanic Clouds; Tc1, SMP SMC16, and SMP LMC56. The three planetary nebulae share many spectroscopic similarities. The strongest circumstellar emission bands correspond to the infrared active vibrational modes of the fullerene species C60 and little or no emission is present from Polycyclic Aromatic Hydrocarbons (PAHs). The strength of the fullerene bands in the three planetary nebulae is very similar, while the ratio of the [NeIII]15.5um/[NeII]12.8um fine structure lines, an indicator of the strength of the radiation field, is markedly different. This raises questions about their excitation mechanism and we compare the fullerene emission to fluorescent and thermal models. In addition, the spectra show other interesting and common features, most notably in the 6-9um region, where a broad plateau with substructure dominates the emission. These features have previously been associated with mixtures of aromatic/aliphatic hydrocarbon solids. We hypothesize on the origin of this band, which is likely related to the fullerene formation mechanism, and compare it with modeled Hydrogenated Amorphous Carbon that present emission in this region.

Submillimeter Line Emission from LMC 30Dor: The Impact of a Starburst on a Low Metallicity Environment

(Abridged) The 30 Dor region in the Large Magellanic Cloud (LMC) is the most vigorous star-forming region in the Local Group. Star formation in this region is taking place in low-metallicity molecular gas which is exposed to an extreme far–ultraviolet (FUV) radiation field powered by the massive compact star cluster R136. We used the NANTEN2 telescope to obtain high-angular resolution observations of the 12CO 4-3, 7-6, and 13CO 4-3 rotational lines and [CI] 3P1-3P0 and 3P2-3P1 fine-structure sub-millimeter transitions in 30Dor-10, the brightest CO and FIR-emitting cloud at the center of the 30Dor region. We derive the properties of the low-metallicity molecular gas using an excitation/radiative transfer code and find a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. We compare the derived properties with those in the N159W region, which is exposed to a more moderate far-ultraviolet radiation field compared with 30Dor-10, but has similar metallicity. We also combine our CO detections with previously observed low-J CO transitions to derive the CO spectral-line energy distribution in 30Dor-10 and N159W. The separate excitation analysis of the submm CO lines and the neutral carbon fine structure lines shows that the mid-J CO and [CI]-emitting gas in the 30Dor-10 region has a temperature of about 160 K and a H2 density of about 10^4 cm^-3. We find that the molecular gas in 30Dor-10 is warmer and has a smaller beam filling factor compared to that of N159W, which might be a result of the effect of a strong FUV radiation field heating and disrupting the low–metallicity molecular gas. We use a clumpy PDR model (including the [CII] line intensity reported in the literature) to constrain the FUV intensity to about chi_0 ~ 3100 and an average total H density of the clump ensemble of about 10^5 cm^-3 in 30Dor-10.

Submillimeter Line Emission from LMC 30Dor: The Impact of a Starburst on a Low Metallicity Environment [Replacement]

(Abridged) The 30 Dor region in the Large Magellanic Cloud (LMC) is the most vigorous star-forming region in the Local Group. Star formation in this region is taking place in low-metallicity molecular gas that is exposed to an extreme far–ultraviolet (FUV) radiation field powered by the massive compact star cluster R136. We used the NANTEN2 telescope to obtain high-angular resolution observations of the 12CO 4-3, 7-6, and 13CO 4-3 rotational lines and [CI] 3P1-3P0 and 3P2-3P1 fine-structure submillimeter transitions in 30Dor-10, the brightest CO and FIR-emitting cloud at the center of the 30Dor region. We derived the properties of the low-metallicity molecular gas using an excitation/radiative transfer code and found a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. We compared the derived properties with those in the N159W region, which is exposed to a more moderate far-ultraviolet radiation field compared with 30Dor-10, but has similar metallicity. We also combined our CO detections with previously observed low-J CO transitions to derive the CO spectral-line energy distribution in 30Dor-10 and N159W. The separate excitation analysis of the submm CO lines and the neutral carbon fine structure lines shows that the mid-J CO and [CI]-emitting gas in the 30Dor-10 region has a temperature of about 160 K and a H2 density of about 10^4 cm^-3. We find that the molecular gas in 30Dor-10 is warmer and has a lower beam filling factor compared to that of N159W, which might be a result of the effect of a strong FUV radiation field heating and disrupting the low–metallicity molecular gas. We use a clumpy PDR model (including the [CII] line intensity reported in the literature) to constrain the FUV intensity to about chi_0 ~ 3100 and an average total H density of the clump ensemble of about 10^5 cm^-3 in 30Dor-10.

Probing the time variability of five Fe low broad absorption line quasars

We study the time variability of five Fe Low ionization Broad Absorption Line (FeLoBAL) QSOs using repeated spectroscopic observations with the 2m telescope at IUCAA Girawali observatory (IGO) spanning an interval of upto 10 years. We report a dramatic variation in Al III and Fe III fine-structure lines in the spectra of SDSS J221511.93-004549.9 (z_em ~ 1.478). However, there is no such strong variability shown by the C IV absorption. This source is known to be unusual with (i) the continuum emission dominated by Fe emission lines, (ii) Fe III absorption being stronger than Fe II and (iii) the apparent ratio of Fe III UV 48 to Fe III UV 34 absorption suggesting an inverted population ratio. This is the first reported detection of time variability in the Fe III fine-structure lines in QSO spectra. There is a strong reduction in the absorption strength of these lines between year 2000 and 2008. Using the template fitting techniques, we show that the apparent inversion of strength of UV lines could be related to the complex spectral energy distribution of this QSO. The observed variability can be related to change in the ionization state of the gas or due to transverse motion of this absorbing gas. The shortest variability timescale of Al III line gives a lower limit on the electron density of the absorbing gas as n_e >= 1.1 x 10^4 cm^-3. The remaining 4 FeLoBALs do not show any changes beyond the measurement uncertainties either in optical depth or in the velocity structure. We present the long-term photometric light curve for all of our sources. Among them only SDSS J221511.93-004549.9 shows significant (>= 0.2 mag) variability.

The warm gas atmosphere of the HD 100546 disk seen by Herschel (Evidence of a gas-rich, carbon-poor atmosphere?)

(Abridged) Context. With the Herschel Space Observatory, lines of simple molecules (C+, O, and CO) have been observed in the atmosphere of protoplanetary disks. When combined with ground-based [CI], all principle forms of carbon can be studied. The absence of neutral carbon [CI], which is predicted by models to be strong, can then be interpreted together with [CII] and carbon monoxide. Aims. We study the gas temperature, excitation, and chemical abundance of the simple carbon-bearing species by the method of chemical-physical modeling. We explore the sensitivity of the lines to the entering parameters and constrain the region from which the line radiation emerges. Methods. Numerical models of the radiative transfer are used together with a chemical network simulation and a calculation of the gas energetics to obtain the gas temperature. We present our new model, which is based on our previous models but includes several improvements. Results. A model of the disk around the Herbig Be star HD 100546 is able to reproduce the CO ladder together with the atomic fine-structure lines of [OI] and either [CI] or [CII]. We find that the high-J lines of CO can only be reproduced by a warm atmosphere with Tgas>>Tdust. The high-J CO observable with PACS are dominated from regions within some tens of AU. Conclusions. Only a warm atmosphere with Tgas>>Tdust can reproduce the CO ladder. The CO ladder together with [O I] and the upper limit to [CI] can be reproduced by models with a high gas/dust ratio and a low abundance of volatile carbon. These models however produce too small amounts of [CII]. Models with a low gas/dust ratio and more volatile carbon also reproduce CO and [OI], are in closer agreement with observations of [CII], but overproduce [CI]. Due to the uncertain origin of the [CII] emission, we prefer the high gas/dust ratio models, indicating a low abundance of volatile carbon.

Resolving the Far-IR Line Deficit: Photoelectric Heating and Far-IR Line Cooling in NGC 1097 and NGC 4559

The physical state of interstellar gas and dust is dependent on the processes which heat and cool this medium. To probe heating and cooling of the ISM over a large range of infrared surface brightness, on sub-kiloparsec scales, we employ line maps of [C \ii] 158 $\mu$m, [O \one] 63 $\mu$m, and [N \ii] 122 $\mu$m in NGC 1097 and NGC 4559, obtained with the PACS spectrometer onboard {\it Herschel}. We matched new observations to existing Spitzer-IRS data that trace the total emission of polycyclic aromatic hydrocarbons (PAHs). We confirm at small scales in these galaxies that the canonical measure of photoelectric heating efficiency, ([C \ii] + [O \one])/TIR, decreases as the far-infrared color, $\nu f_\nu$(70 $\mu$m)/$\nu f_\nu$(100 $\mu$m), increases. In contrast, the ratio of far-infrared (far-IR) cooling to total PAH emission, ([C \ii] + [O \one])/PAH, is a near constant $\sim$6% over a wide range of far-infrared color, 0.5 \textless\ $\nu f_\nu$(70 $\mu$m)/$\nu f_\nu$(100 $\mu$m) $\lesssim$ 0.95. In the warmest regions, where $\nu f_\nu$(70 $\mu$m)/$\nu f_\nu$(100 $\mu$m) $\gtrsim$ 0.95, the ratio ([C \ii] + [O \one])/PAH drops rapidly to 4%. We derived representative values of the local UV radiation density, $G_0$, and the gas density, $n_H$, by comparing our observations to models of photodissociation regions. The ratio $G_0/n_H$, derived from fine-structure lines, is found to correlate with the mean dust-weighted starlight intensity, $<U>$ derived from models of the IR SED. Emission from regions that exhibit a line deficit is characterized by an intense radiation field, indicating that small grains are susceptible to ionization effects. We note that there is a shift in the 7.7 / 11.3 $\mu$m PAH ratio in regions that exhibit a deficit in ([C \ii] + [O \one])/PAH, suggesting that small grains are ionized in these environments.

Spatial variation of the cooling lines in the Orion Bar from Herschel/PACS

We present spatially resolved Herschel/PACS observations of the Orion Bar. We have characterise the emission of the far-infrared fine-structure lines of [CII] (158um), [OI] (63 and 145um), and [NII] (122um) that trace the gas local conditions. The observed distribution and variation of the lines are discussed in relation to the underlying geometry and linked to the energetics associated with the Trapezium stars. These observations enable us to map the spatial distribution of these fine-structure lines with a spatial resolution between 4″ and 11″ and covering a total square area of about 120″x105″. The spatial profile of the emission lines are modelled using the radiative transfer code Cloudy. We find that the spatial distribution of the [CII] line coincides with that of the [OI] lines. The [NII] line peaks closer to the ionising star than the other three lines, but with a small region of overlap. We can distinguish several knots of enhanced emission within the Bar indicating the presence of an inhomogenous and structured medium. The emission profiles cannot be reproduced by a single photo-dissociation region, clearly indicating that, besides the Bar, there is a significant contribution from additional photo-dissociation region(s) over the area studied. The combination of both the [NII] and [OI] 145um lines can be used to estimate the [CII] emission and distinguish between its ionised or neutral origin. We have calculated how much [CII] emission comes from the neutral and ionised region, and find that at least 82% originates from the photo-dissocciation region. Together, the [CII] 158um and [OI] 63 and 145um lines account for 90% of the power emitted by the main cooling lines in the Bar (including CO, H2, etc…), with [OI] 63um alone accounting for 72% of the total.

Infrared spectroscopy of intermediate mass young stellar objects

In this paper we present Spitzer Infrared Spectrograph spectroscopy for 14 intermediate-mass young stellar objects. We use Spitzer spectroscopy to investigate the physical properties of these sources and their environments. Our sample can be divided into two types of objects: young isolated, embedded objects with spectra that are dominated by ice and silicate absorption bands, and more evolved objects that are dominated by extended emission from polycyclic aromatic hydrocarbons (PAHs) and pure H2 rotational lines. We are able to constrain the illuminating FUV fields by classifying the PAH bands below 9micron. For most of the sources we are able to detect several atomic fine structure lines. In particular, the [NeII] line appearing in two regions could originate from unresolved photodissociation regions (PDRs) or J-shocks. We relate the identified spectral features to observations obtained from NIR through submillimeter imaging. The spatial extent of several H2 and PAH bands is matched with morphologies identified in previous Spitzer/IRAC observations. This also allows us to distinguish between the different H2 excitation mechanisms. In addition, we calculate the optical extinction from the silicate bands and use this to constrain the spectral energy distribution fit, allowing us to estimate the masses of these YSOs.

Far-IR/Submillimeter Spectroscopic Cosmological Surveys: Predictions of Infrared Line Luminosity Functions for z<4 Galaxies

Star formation and accretion onto supermassive black holes in the nuclei of galaxies are the two most energetic processes in the Universe, producing the bulk of the observed emission throughout its history. We simulated the luminosity functions of star-forming and active galaxies for spectral lines that are thought to be good spectroscopic tracers of either phenomenon, as a function of redshift. We focused on the infrared (IR) and sub-millimeter domains, where the effects of dust obscuration are minimal. Using three different and independent theoretical models for galaxy formation and evolution, constrained by multi-wavelength luminosity functions, we computed the number of star-forming and active galaxies per IR luminosity and redshift bin. We converted the continuum luminosity counts into spectral line counts using relationships that we calibrated on mid- and far-IR spectroscopic surveys of galaxies in the local universe. Our results demonstrate that future facilities optimized for survey-mode observations, i.e., the Space Infrared Telescope for Cosmology and Astrophysics (SPICA) and the Cerro Chajnantor Atacama Telescope (CCAT), will be able to observe thousands of z>1 galaxies in key fine-structure lines, e.g., [SiII], [OI], [OIII], [CII], in a half-square-degree survey, with one hour integration time per field of view. Fainter lines such as [OIV], [NeV] and H_2 (0-0)S1 will be observed in several tens of bright galaxies at 1<z<2, while diagnostic diagrams of active-nucleus vs star-formation activity will be feasible even for normal z~1 galaxies. We discuss the new parameter space that these future telescopes will cover and that strongly motivate their construction.

A view of the narrow-line region in the infrared: active galactic nuclei with resolved fine-structure lines in the Spitzer archive [Replacement]

We queried the Spitzer archive for high-resolution observations with the Infrared Spectrograph of optically selected active galactic nuclei (AGN) for the purpose of identifying sources with resolved fine-structure lines that would enable studies of the narrow-line region (NLR) at mid-infrared wavelengths. By combining 298 Spitzer spectra with 6 Infrared Space Observatory spectra, we present kinematic information of the NLR for 81 z<=0.3 AGN. We used the [NeV], [OIV], [NeIII], and [SIV] lines, whose fluxes correlate well with each other, to probe gas photoionized by the AGN. We found that the widths of the lines are, on average, increasing with the ionization potential of the species that emit them. No correlation of the line width with the critical density of the corresponding transition was found. The velocity dispersion of the gas, sigma, is systematically higher than that of the stars, sigma_*, in the AGN host galaxy, and it scales with the mass of the central black hole, M_BH. Further correlations between the line widths and luminosities L, and between L and M_BH, are suggestive of a three dimensional plane connecting log(M_BH) to a linear combination of log(sigma) and log(L). Such a plane can be understood within the context of gas motions that are driven by AGN feedback mechanisms, or virialized gas motions with a power-law dependence of the NLR radius on the AGN luminosity. The M_BH estimates obtained for 35 type 2 AGN from this plane are consistent with those obtained from the M_BH-sigma_* relation.

A view of the narrow-line region in the infrared: active galactic nuclei with resolved fine-structure lines in the Spitzer archive

We queried the Spitzer archive for high-resolution observations with the Infrared Spectrograph of optically selected active galactic nuclei (AGN) for the purpose of identifying sources with resolved fine-structure lines that would enable studies of the narrow-line region (NLR) at mid-infrared wavelengths. By combining 298 Spitzer spectra with 6 Infrared Space Observatory spectra, we present kinematic information of the NLR for 81 z<=0.3 AGNs. We used the [NeV], [OIV], [NeIII], and [SIV] lines, whose fluxes correlate well with each other, to probe gas photoionized by the AGN. We found that the widths of the lines are, on average, increasing with the ionization potential of the species that emit them. No correlation of the line width with the critical density of the corresponding transition was found. The velocity dispersion of the gas, sigma, is systematically higher than that of the stars, sigma_*, in the AGN host galaxy, and it scales with the mass of the central black hole, M_BH. Further correlations between the line widths and luminosities L, and between L and M_BH, are suggestive of a three dimensional plane connecting log(M_BH) to a linear combination of log(sigma) and log(L). Such a plane can be understood within the context of gas motions that are driven by AGN feedback mechanisms, or virialized gas motions with a power-law dependence of the NLR radius on the AGN luminosity. The M_BH estimates obtained for 35 type 2 AGN from this plane are consistent with those obtained from the M_BH-sigma_* relation.

The Illusive ISM of Dwarf Galaxies: Excess Submillimetre Emission and CO-Dark Molecular Gas

The Herschel Dwarf Galaxy Survey investigates the interplay of star formation activity and the the metal-poor gas and dust of dwarf galaxies using FIR and submillimetre imaging spectroscopic and photometric observations in the 50 to 550mu window of the Herschel Space Observatory. The dust SEDs are well constrained with the new Herschel and MIR Spitzer data. A submillimetre excess is often found in low metallicity galaxies, which,if tracing very cold dust, would highlight large dust masses not easily reconciled in some cases, given the low metallicities and expected gas-to-dust mass ratios. The galaxies are also mapped in the FIR fine-structure lines (63 and 145mu OI, 158mu CII, 122 and 205mu NII, 88mu OIII) probing the low density ionised gas, the HII regions and photodissociation regions. While still early in the Herschel mission we can already see, along with earlier studies, that line ratios in the metal-poor ISM differ remarkably from those in the metal-rich starburst environments. In dwarf galaxies, L[CII]/L(CO) (>10^4) is at least an order of magnitude greater than in the most metal-rich starburst galaxies. The enhanced [CII] arises from the larger photodissociation region where H2, not traced by the CO, can exist. The 88mu [OIII] line usually dominates the FIR line emission over galaxy-wide scales in dwarf galaxies, not the 158mu [CII] line which is the dominant FIR cooling line in metal-rich galaxies. All of the FIR lines together can contribute 1% to 2% of the L(TIR). The Herschel Dwarf Galaxy survey will provide statistical information on the nature of the dust and gas in low metallicity galaxies, elucidating the origin of the submm excess in dwarf galaxies, and help determine a ([CII] +CO) to H2 conversion factor, thus providing observational constraints on chemical evolution models of galaxies.

The Elusive ISM of Dwarf Galaxies: Excess Submillimetre Emission and CO-Dark Molecular Gas [Replacement]

The Herschel Dwarf Galaxy Survey investigates the interplay of star formation activity and the the metal-poor gas and dust of dwarf galaxies using FIR and submillimetre imaging spectroscopic and photometric observations in the 50 to 550mu window of the Herschel Space Observatory. The dust SEDs are well constrained with the new Herschel and MIR Spitzer data. A submillimetre excess is often found in low metallicity galaxies, which,if tracing very cold dust, would highlight large dust masses not easily reconciled in some cases, given the low metallicities and expected gas-to-dust mass ratios. The galaxies are also mapped in the FIR fine-structure lines (63 and 145mu OI, 158mu CII, 122 and 205mu NII, 88mu OIII) probing the low density ionised gas, the HII regions and photodissociation regions. While still early in the Herschel mission we can already see, along with earlier studies, that line ratios in the metal-poor ISM differ remarkably from those in the metal-rich starburst environments. In dwarf galaxies, L[CII]/L(CO) (>10^4) is at least an order of magnitude greater than in the most metal-rich starburst galaxies. The enhanced [CII] arises from the larger photodissociation region where H2, not traced by the CO, can exist. The 88mu [OIII] line usually dominates the FIR line emission over galaxy-wide scales in dwarf galaxies, not the 158mu [CII] line which is the dominant FIR cooling line in metal-rich galaxies. All of the FIR lines together can contribute 1% to 2% of the L(TIR). The Herschel Dwarf Galaxy survey will provide statistical information on the nature of the dust and gas in low metallicity galaxies, elucidating the origin of the submm excess in dwarf galaxies, and help determine a ([CII] +CO) to H2 conversion factor, thus providing observational constraints on chemical evolution models of galaxies.

Discovery of interstellar anions in Cepheus star-forming region

We report the detection of microwave emission lines from the hydrocarbon anion C6H- and its parent neutral C6H in the star-forming region L1251A (in Cepheus), and the pre-stellar core L1512 (in Auriga). The carbon-chain-bearing species C4H, HC3N, HC5N, HC7N and C3S are also detected in large abundances. The observations of L1251A constitute the first detections of anions and long-chain polyynes and cyanopolyynes (with more than 5 carbon atoms) in the Cepheus Flare star-forming region, and the first detection of anions in the vicinity of a protostar outside of the Taurus molecular cloud complex, highlighting a wider importance for anions in the chemistry of star formation. Rotational excitation temperatures have been derived from the HC3N hyperfine structure lines, and are found to be 6.2 K for L1251A and 8.7 K for L1512. The anion-to-neutral ratios are 3.6% and 4.1%, respectively, which are within the range of values previously observed in the interstellar medium, and suggest a relative uniformity in the processes governing anion abundances in different dense interstellar clouds. This research contributes towards the growing body of evidence that carbon chain anions are relatively abundant in interstellar clouds throughout the Galaxy, but especially in the regions of relatively high density and high depletion surrounding pre-stellar cores and young, embedded protostars.

Probing Reionization with Intensity Mapping of Molecular and Fine Structure Lines

We propose observations of the molecular gas distribution during the era of reionization. At $z \sim $ 6 to 8, $^{12}$CO$(J=1-0)$ line intensity results in a mean brightness temperature of about 0.5 $\mu$K with rms fluctuations of 0.1 $\mu$K at 1 to 10 Mpc spatial scales, corresponding to 30 arcminute angular scales. This intensity fluctuations can be mapped with an interferometer, similar to existing and planned 21-cm background experiments, but operating at $\sim$ 12 to 17 GHz. We discuss the feasibility of detecting the cross-correlation between HI and CO molecular gas since such a cross-correlation has the advantage that it will be independent of systematics and most foregrounds in each of the 21-cm and CO$(1-0)$ line experiments. Additional instruments tuned to higher-order transitions of the CO molecule or an instrument operating with high spectral resolution at mm-wavelengths targeting 158 $\mu$m CII could further improve the reionization studies with molecular gas. The combined 21-cm and CO line observations has the potential to establish the relative distribution of gas in the inter-galactic medium and molecular gas that are clumped in individual first-light galaxies that are closely connected to the formation of massive stars in these galaxies.

Far-Infrared Line Deficits in Galaxies with Extreme Lfir/MH2 Ratios

We report initial results from the far-infrared fine structure line observations of a sample of 44 local starbursts, Seyfert galaxies and infrared luminous galaxies obtained with the PACS spectrometer on board Herschel. We show that the ratio between the far-infrared luminosity and the molecular gas mass, Lfir/MH2, is a much better proxy for the relative brightness of the far-infrared lines than Lfir alone. Galaxies with high Lfir/MH2 ratios tend to have weaker fine structure lines relative to their far-infrared continuum than galaxies with Lfir/MH2 < 80 Lsun/Msun. A deficit of the [C II] 158 micron line relative to Lfir was previously found with the ISO satellite, but now we show for the first time that this is a general aspect of all far-infrared fine structure lines, regardless of their origin in the ionized or neutral phase of the interstellar medium. The Lfir/MH2 value where these line deficits start to manifest is similar to the limit that separates between the two modes of star formation recently found in galaxies on the basis of studies of their gas-star formation relations. Our finding that the properties of the interstellar medium are also significantly different in these regimes provides independent support for the different star forming relations in normal disk galaxies and major merger systems. We use the spectral synthesis code Cloudy to model the emission of the lines. The expected increase of the ionization parameter with Lfir/MH2 can simultaneously explain the line deficits in the [C II], [N II] and [O I] lines.

Metallicity Diagnostics with Infrared Fine-Structure Lines

Although measuring the gas metallicity in galaxies at various redshifts is crucial to constrain galaxy evolutionary scenarios, only rest-frame optical emission lines have been generally used to measure the metallicity. This has prevented us to accurately measure the metallicity of dust-obscured galaxies, and accordingly to understand the chemical evolution of dusty populations, such as ultraluminous infrared galaxies. Here we propose diagnostics of the gas metallicity based on infrared fine structure emission lines, which are nearly unaffected by dust extinction even the most obscured systems. Specifically, we focus on fine-structure lines arising mostly from HII regions, not in photo-dissociation regions, to minimize the dependence and uncertainties of the metallicity diagnostics from various physical parameters. Based on photoionization models, we show that the emission-line flux ratio of ([OIII]51.80+[OIII]88.33)/[NIII]57.21 is an excellent tracer of the gas metallicity. The individual line ratios [OIII]51.80/[NIII]57.21 or [OIII]88.33/[NIII]57.21 can also be used as diagnostics of the metallicity, but they suffer a stronger dependence on the gas density. The line ratios [OIII]88.33/[OIII]51.80 and [NII]121.7/[NIII]57.21 can be used to measure and, therefore, account for the dependences on the of the gas density and ionization parameter, respectively. We show that these diagnostic fine-structure lines are detectable with Herschel in luminous infrared galaxies out z=0.4. Metallicity measurements with these fine-structure lines will be feasible at relatively high redshift (z=1 or more) with SPICA, the future infrared space observatory.

Multi-wavelength diagnostic properties of Galactic Planetary Nebulae detected by GLIMPSE-I

We uniformly analyze 136 optically detected PNe and candidates from the GLIMPSE-I survey in order to to develop robust, multi-wavelength, classification criteria to augment existing diagnostics and provide pure PN samples. PNe represent powerful astrophysical probes. They are important dynamical tracers, key sources of ISM chemical enrichment, windows into late stellar evolution, and potent cosmological yardsticks. But their utility depends on separating them unequivocally from the many nebular mimics which can strongly resemble bona fide PNe in traditional optical images and spectra. We merge new PNe from the carefully evaluated, homogeneous MASH-I and MASH-II surveys, which offer a wider evolutionary range of PNe than hitherto available, with previously known PNe classified by SIMBAD. Mid-infrared (MIR) measurements vitally complement optical data because they reveal other physical processes and morphologies via fine-structure lines, molecular bands and dust. MIR colour-colour planes, optical emission line ratios and radio fluxes show the unambiguous classification of PNe to be complex, requiring all available evidence. Statistical trends provide predictive value and we offer quantitative MIR criteria to determine whether an emission nebula is most likely to be a PN or one of the frequent contaminants such as compact HII regions or symbiotic systems. Prerequisites have been optical images and spectra but MIR morphology, colours, environment and a candidate’s MIR/radio flux ratio provide a more rigorous classification. Our ultimate goal is to recognize PNe using only MIR and radio characteristics, enabling us to trawl for PNe effectively even in heavily obscured regions of the Galaxy.

The Origin of Dust in the Early Universe: Probing the Star Formation History of Galaxies by their Dust Content

Two distinct scenarios for the origin of the ~ 4 \times 10^8 M\odot of dust observed in the high-redshift (z = 6.4) quasar J1148+5251 have been proposed. The first assumes that this galaxy is much younger than the age of the universe at that epoch so that only supernovae (SNe) could have produced this dust. The second scenario assumes a significantly older galactic age, so that the dust could have formed in lower-mass asymptotic giant branch (AGB) stars. Presenting new integral solutions for the chemical evolution of metals and dust in galaxies, we offer a critical evaluation of these two scenarios, and observational consequences that can discriminate between the two. We show that AGB stars can produce the inferred mass of dust in this object, however, the final mass of surviving dust depends on the galaxy’s star formation history (SFH). In general supernovae cannot produce the observed amount of dust unless the average SN event creates over ~ 1 M\odot of dust in its ejecta. However, special SFHs can be constructed in which SNe can produce the inferred dust mass with a reasonable average dust yield of ~ 0.15 M\odot. The two scenarios propose different origins for the galaxy’s spectral energy distribution, different star formation efficiencies and stellar masses, and consequently different comoving number densities of J1148+5251-type hyperluminous infrared (IR) objects. The detection of diagnostic mid-IR fine structure lines, and more complete surveys determining the comoving number density of these objects can discriminate between the two scenarios.

Star Formation in Extreme Environments: The Effects of Cosmic Rays and Mechanical Heating

Context: Molecular data of extreme environments, such as Arp 220, but also NGC 253, show evidence for extremely high cosmic ray (CR) rates (10^3-10^4 * Milky Way) and mechanical heating from supernova driven turbulence. Aims: The consequences of high CR rates and mechanical heating on the chemistry in clouds are explored. Methods: PDR model predictions are made for low, n=10^3, and high, n=10^5.5 cm^-3, density clouds using well-tested chemistry and radiation transfer codes. Column densities of relevant species are discussed, and special attention is given to water related species. Fluxes are shown for fine-structure lines of O, C+, C, and N+, and molecular lines of CO, HCN, HNC, and HCO+. A comparison is made to an X-ray dominated region model. Results: Fine-structure lines of [CII], [CI], and [OI] are remarkably similar for different mechanical heating and CR rates, when already exposed to large amounts of UV. HCN and H2O abundances are boosted for very high mechanical heating rates, while ionized species are relatively unaffected. OH+ and H2O+ are enhanced for very high CR rates zeta > 5 * 10^-14 s^-1. A combination of OH+, OH, H2O+, H2O, and H3O+ trace the CR rates, and are able to distinguish between enhanced cosmic rays and X-rays.

Three-dimensional chemically homogeneous and bi-abundance photoionization models of the "super-metal-rich" planetary nebula NGC 6153

Deep spectroscopy of the planetary nebula (PN) NGC\,6153 shows that its heavy element abundances derived from optical recombination lines (ORLs) are ten times higher than those derived from collisionally excited lines (CELs), and points to the existence of H-deficient inclusions embedded in the diffuse nebula. In this study, we have constructed chemically homogeneous and bi-abundance three-dimensional photoionization models, using the Monte Carlo photoionization code {\sc mocassin}. We attempt to reproduce the multi-waveband spectroscopic and imaging observations of NGC\,6153, and investigate the nature and origin of the postulated H-deficient inclusions, as well as their impacts on the empirical nebular analyses assuming a uniform chemical composition. Our results show that chemically homogeneous models yield small electron temperature fluctuations and fail to reproduce the strengths of ORLs from C, N, O and Ne ions. In contrast, bi-abundance models incorporating a small amount of metal-rich inclusions ($\sim 1.3$ per cent of the total nebular mass) are able to match all the observations within the measurement uncertainties. The metal-rich clumps, cooled down to a very low temperature ($\sim 800$~K) by ionic infrared fine-structure lines, dominate the emission of heavy element ORLs, but contribute almost nil to the emission of most CELs. We find that the abundances of C, N, O and Ne derived empirically from CELs, assuming a uniform chemical composition, are about 30 per cent lower than the corresponding average values of the whole nebula, including the contribution from the H-deficient inclusions. Ironically, in the presence of H-deficient inclusions, the traditional standard analysis of the optical helium recombination lines, assuming a chemically homogeneous nebula, overestimates the helium abundance by 40 per cent.

Submillimeter absorption from SH+, a new widespread interstellar radical, 13CH+ and HCl

We have used the Atacama Pathfinder Experiment 12 m telescope (APEX) to carry out an absorption study of submillimeter wavelength rotational ground-state lines of H35Cl, H37Cl, 13CH+, and, for the first time, of the SH+ radical (sulfoniumylidene or sulfanylium). We detected the quartet of ground-state hyperfine structure lines of SH+ near 683 GHz with the CHAMP+ array receiver against the strong continuum source Sagittarius B2, which is located close to the center of our Galaxy. In addition to absorption from various kinematic components of Galactic center gas, we also see absorption at the radial velocities belonging to intervening spiral arms. This demonstrates that SH+ is a ubiquitous component of the diffuse interstellar medium. We do not find clear evidence for other SH+ lines we searched for, which is partially due to blending with lines from other molecules. In addition to SH+, we observed absorption from H35Cl, H37Cl, and 13CH+. The observed submillimeter absorption is compared in detail with absorption in 3 mm transitions of H13CO+ and c-C3H2 and the CO J = 1-0 and 3-2 transitions.

Understanding Physical Conditions in High Redshift Galaxies through C I Fine Structure Lines: Data and Methodology

We probe the physical conditions in high redshift galaxies, specifically, the Damped Lyman-alpha Systems (DLAs) using neutral carbon (CI) fine structure lines and molecular hydrogen (H2). We report five new detections of CI and analyze the CI in an additional 2 DLAs with previously published data. We also present one new detection of H2 in a DLA. We present a new method of analysis that simultaneously constrains \emph{both} the volume density and the temperature of the gas, as opposed to previous studies that a priori assumed a gas temperature. We use only the column density of CI measured in the fine structure states and the assumption of ionization equilibrium in order to constrain the physical conditions in the gas. We present a sample of 11 CI velocity components in 6 DLAs and compare their properties to those derived by the global CII* technique. The resulting median values for this sample are: <n(HI)> = 69 cm^{-3}, <T> = 50 K, and <log(P/k)> = 3.86 cm^{-3} K, with standard deviations, sigma_{n(HI)} = 134 cm^{-3}, sigma_T = 52 K, and sigma_{log(P/k)} = 3.68 cm^{-3} K. This can be compared with the integrated median values for the same DLAs : <n(HI)> = 2.8 cm^{-3}, <T> = 139 K, and <log(P/k)> = 2.57 cm^{-3} K, with standard deviations sigma_{n(HI)} = 3.0 cm^{-3}, sigma_T = 43 K, and sigma_{log(P/k)} = 0.22 cm^{-3} K. Interestingly, the pressures measured in these high redshift CI clouds are similar to those found in the Milky Way. We conclude that the CI gas is tracing a higher-density, higher-pressure region, possibly indicative of post-shock gas or a photodissociation region on the edge of a molecular cloud. We speculate that these clouds may be direct probes of the precursor sites of star formation in normal galaxies at high redshift.

Low-ionization Line Emission from Starburst Galaxies: A New Probe of Galactic-Scale Outflows

We study the kinematically narrow, low-ionization line emission from a bright, starburst galaxy at z = 0.69 using slit spectroscopy obtained with Keck/LRIS. The spectrum reveals strong absorption in MgII and FeII resonance transitions with Doppler shifts of -200 to -300 km/s, indicating a cool gas outflow. Emission in MgII near and redward of systemic velocity, in concert with the observed absorption, yields a P Cygni-like line profile similar to those observed in the Ly alpha transition in Lyman Break Galaxies. Further, the MgII emission is spatially resolved, and extends significantly beyond the emission from stars and HII regions within the galaxy. Assuming the emission has a simple, symmetric surface brightness profile, we find that the gas extends to distances > ~7 kpc. We also detect several narrow FeII* fine-structure lines in emission near the systemic velocity, arising from energy levels which are radiatively excited directly from the ground state. We suggest that the MgII and FeII* emission is generated by photon scattering in the observed outflow, and emphasize that this emission is a generic prediction of outflows. These observations provide the first direct constraints on the minimum spatial extent and morphology of the wind from a distant galaxy. Estimates of these parameters are crucial for understanding the impact of outflows in driving galaxy evolution.

Measuring the 3D Clustering of Undetected Galaxies Through Cross Correlation of their Cumulative Flux Fluctuations from Multiple Spectral Lines [Replacement]

We discuss a method for detecting the emission from high redshift galaxies by cross correlating flux fluctuations from multiple spectral lines. If one can fit and subtract away the continuum emission with a smooth function of frequency, the remaining signal contains fluctuations of flux with frequency and angle from line emitting galaxies. Over a particular small range of observed frequencies, these fluctuations will originate from sources corresponding to a series of different redshifts, one for each emission line. It is possible to statistically isolate the fluctuations at a particular redshift by cross correlating emission originating from the same redshift, but in different emission lines. This technique will allow detection of clustering fluctuations from the faintest galaxies which individually cannot be detected, but which contribute substantially to the total signal due to their large numbers. We describe these fluctuations quantitatively through the line cross power spectrum. As an example of a particular application of this technique, we calculate the signal-to-noise ratio for a measurement of the cross power spectrum of the OI(63 micron) and OIII(52 micron) fine structure lines with the proposed Space Infrared Telescope for Cosmology and Astrophysics. We find that the cross power spectrum can be measured beyond a redshift of z=8. Such observations could constrain the evolution of the metallicity, bias, and duty cycle of faint galaxies at high redshifts and may also be sensitive to the reionization history through its effect on the minimum mass of galaxies. As another example, we consider the cross power spectrum of CO line emission measured with a large ground based telescope like CCAT and 21-cm radiation originating from hydrogen in galaxies after reionization with an interferometer similar in scale to MWA, but optimized for post-reionization redshifts.

Measuring the 3D Clustering of Undetected Galaxies Through Cross Correlation of their Cumulative Flux Fluctuations from Multiple Spectral Lines

We discuss a method for detecting the emission from high redshift galaxies by cross correlating flux fluctuations from multiple spectral lines. If one can fit and subtract away the continuum emission with a smooth function of frequency, the remaining signal contains fluctuations of flux with frequency and angle from line emitting galaxies. Over a particular small range of observed frequencies, these fluctuations will originate from sources corresponding to a series of different redshifts, one for each emission line. It is possible to statistically isolate the fluctuations at a particular redshift by cross correlating emission originating from the same redshift, but in different emission lines. This technique will allow detection of clustering fluctuations from the faintest galaxies which individually cannot be detected, but which contribute substantially to the total signal due to their large numbers. We describe these fluctuations quantitatively through the line cross power spectrum. As an example of a particular application of this technique, we calculate the signal-to-noise ratio for a measurement of the cross power spectrum of the OI(63 micron) and OIII(52 micron) fine structure lines with the proposed Space Infrared Telescope for Cosmology and Astrophysics (SPICA). We find that the cross power spectrum can be measured beyond a redshift of z=8. Such observations could constrain the evolution of the metallicity, bias, and duty cycle of faint galaxies at high redshifts and may also be sensitive to the reionization history through its effect on the minimum mass of galaxies.

Excitation of the molecular gas in the nuclear region of M82

We present high resolution HIFI spectroscopy of the nucleus of the archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4 fine-structure lines are detected. Besides showing the effects of the overall velocity structure of the nuclear region, the line profiles also indicate the presence of multiple components with different optical depths, temperatures and densities in the observing beam. The data have been interpreted using a grid of PDR models. It is found that the majority of the molecular gas is in low density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and a relatively low UV radiation field (GO = 10^2). The remaining gas is predominantly found in clouds with higher densities (n=10^5 cm^-3) and radiation fields (GO = 10^2.75), but somewhat lower column densities (N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1% relative surface filling) component, with an even higher density (n=10^6 cm^-3) and UV field (GO = 10^3.25). These results show the strength of multi-component modeling for the interpretation of the integrated properties of galaxies.

Excitation of the molecular gas in the nuclear region of M82 [Replacement]

We present high resolution HIFI spectroscopy of the nucleus of the archetypical starburst galaxy M82. Six 12CO lines, 2 13CO lines and 4 fine-structure lines are detected. Besides showing the effects of the overall velocity structure of the nuclear region, the line profiles also indicate the presence of multiple components with different optical depths, temperatures and densities in the observing beam. The data have been interpreted using a grid of PDR models. It is found that the majority of the molecular gas is in low density (n=10^3.5 cm^-3) clouds, with column densities of N_H=10^21.5 cm^-2 and a relatively low UV radiation field (GO = 10^2). The remaining gas is predominantly found in clouds with higher densities (n=10^5 cm^-3) and radiation fields (GO = 10^2.75), but somewhat lower column densities (N_H=10^21.2 cm^-2). The highest J CO lines are dominated by a small (1% relative surface filling) component, with an even higher density (n=10^6 cm^-3) and UV field (GO = 10^3.25). These results show the strength of multi-component modeling for the interpretation of the integrated properties of galaxies.

Spitzer spectral line mapping of the HH211 outflow

Aims: We employ archival Spitzer slit-scan observations of the HH211 outflow in order to investigate its warm gas content, assess the jet mass flux in the form of H2 and probe for the existence of an embedded atomic jet. Methods: Detected molecular and atomic lines are interpreted by means of emission line diagnostics and an existing grid of molecular shock models. The physical properties of the warm gas are compared against other molecular jet tracers and to the results of a similar study towards the L1448-C outflow. Results: We have detected and mapped the v=0-0 S(0) – S(7) H2 lines and fine-structure lines of S, Fe+, and Si+. H2 is detected down to 5" from the source and is characterized by a "cool" T~300K and a "warm" T~1000 K component, with an extinction Av ~ 8 mag. The amount of cool H2 towards the jet agrees with that estimated from CO assuming fully molecular gas. The warm component is well fitted by C-type shocks with a low beam filling factor ~ 0.01-0.04 and a mass-flux similar to the cool H2. The fine-structure line emission arises from dense gas with ionization fraction ~0.5 – 5 x 10e-3, suggestive of dissociative shocks. Line ratios to sulfur indicate that iron and silicon are depleted compared to solar abundances by a factor ~10-50. Conclusions: Spitzer spectral mapping observations reveal for the first time a cool H$_2$ component towards the CO jet of HH211 consistent with the CO material being fully molecular and warm at ~ 300 K. The maps also reveal for the first time the existence of an embedded atomic jet in the HH211 outflow that can be traced down to the central source position. Its significant iron and silicon depletion excludes an origin from within the dust sublimation zone around the protostar. The momentum-flux seems insufficient to entrain the CO jet, although current uncertainties on jet speed and shock conditions are too large for a definite conclusion.

Herschel-PACS observation of the 10 Myr old T Tauri disk TW Hya: Constraining the disk gas mass

Planets are formed in disks around young stars. With an age of ~10 Myr, TW Hya is one of the nearest T Tauri stars that is still surrounded by a relatively massive disk. In addition a large number of molecules has been found in the TW Hya disk, making TW Hya the perfect test case in a large survey of disks with Herschel-PACS to directly study their gaseous component. We aim to constrain the gas and dust mass of the circumstellar disk around TW Hya. We observed the fine-structure lines of [OI] and [CII] as part of the Open-time large program GASPS. We complement this with continuum data and ground-based 12CO 3-2 and 13CO 3-2 observations. We simultaneously model the continuum and the line fluxes with the 3D Monte-Carlo code MCFOST and the thermo-chemical code ProDiMo to derive the gas and dust masses. We detect the [OI] line at 63 micron. The other lines that were observed, [OI] at 145 micron and [CII] at 157 micron, are not detected. No extended emission has been found. Preliminary modeling of the photometric and line data assuming [12CO]/[13CO]=69 suggests a dust mass for grains with radius < 1 mm of ~1.9 times 10^-4 Msun (total solid mass of 3 times 10^-3 Msun) and a gas mass of (0.5–5) times 10^-3 Msun. The gas-to-dust mass may be lower than the standard interstellar value of 100.

 

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