Recent Postings from Galaxies

Testing Quasar Unification: Radiative Transfer in Clumpy Winds

Various unification schemes interpret the complex phenomenology of quasars and luminous active galactic nuclei (AGN) in terms of a simple picture involving a central black hole, an accretion disc and an associated outflow. Here, we continue our tests of this paradigm by comparing quasar spectra to synthetic spectra of biconical disc wind models, produced with our state-of-the-art Monte Carlo radiative transfer code. Previously, we have shown that we could produce synthetic spectra resembling those of observed broad absorption line (BAL) quasars, but only if the X-ray luminosity was limited to $10^{43}$ erg s$^{-1}$. Here, we introduce a simple treatment of clumping, and find that a filling factor of $\sim0.01$ moderates the ionization state sufficiently for BAL features to form in the rest-frame UV at more realistic X-ray luminosities. Our fiducial model shows good agreement with AGN X-ray properties and the wind produces strong line emission in, e.g., Ly \alpha\ and CIV 1550\AA\ at low inclinations. At high inclinations, the spectra possess prominent LoBAL features. Despite these successes, we cannot reproduce all emission lines seen in quasar spectra with the correct equivalent-width ratios, and we find an angular dependence of emission-line equivalent width despite the similarities in the observed emission line properties of BAL and non-BAL quasars. Overall, our work suggests that biconical winds can reproduce much of the qualitative behaviour expected from a unified model, but we cannot yet provide quantitative matches with quasar properties at all viewing angles. Whether disc winds can successfully unify quasars is therefore still an open question.

Comparing Young Massive Clusters and their Progenitor Clouds in the Milky Way

Young massive clusters (YMCs) have central stellar mass surface densities exceeding $10^{4} M_{\odot} pc^{-2}$. It is currently unknown whether the stars formed at such high (proto)stellar densities. We compile a sample of gas clouds in the Galaxy which have sufficient gas mass within a radius of a few parsecs to form a YMC, and compare their radial gas mass distributions to the stellar mass distribution of Galactic YMCs. We find that the gas in the progenitor clouds is distributed differently than the stars in YMCs. The mass surface density profiles of the gas clouds are generally shallower than the stellar mass surface density profiles of the YMCs, which are characterised by prominent dense core regions with radii ~ 0.1 pc, followed by a power-law tail. On the scale of YMC core radii, we find that there are no known clouds with significantly more mass in their central regions when compared to Galactic YMCs. Additionally, we find that models in which stars form from very dense initial conditions require surface densities that are generally higher than those seen in the known candidate YMC progenitor clouds. Our results show that the quiescent, less evolved clouds contain less mass in their central regions than in the highly star-forming clouds. This suggests an evolutionary trend in which clouds continue to accumulate mass towards their centres after the onset of star formation. We conclude that a conveyor-belt scenario for YMC formation is consistent with the current sample of Galactic YMCs and their progenitor clouds.

Sub-mm Emission Line Deep Fields: CO and [CII] Luminosity Functions out to z = 6

Now that ALMA is reaching its full capabilities, observations of sub-mm emission line deep fields become feasible. Deep fields are ideal to study the luminosity function of sub-mm emission lines, ultimately tracing the atomic and molecular gas properties of galaxies. We couple a semi-analytic model of galaxy formation with a radiative transfer code to make predictions for the luminosity function of CO J=1-0 up to CO J=6-5 and [CII] at redshifts z=0-6. We find that: 1) our model correctly reproduces the CO and [CII] emission of low- and high-redshift galaxies and reproduces the available constraints on the CO luminosity function at z<2.75; 2) we find that the CO and [CII] luminosity functions of galaxies increase from z = 6 to z = 4, remain relatively constant till z = 1 and rapidly decrease towards z = 0. The galaxies that are brightest in CO and [CII] are found at z~2; 3) the CO J=3-2 emission line is most favourable to study the CO luminosity and global H2 mass content of galaxies, because of its brightness and observability with currently available sub-mm and radio instruments; 4) the luminosity functions of high-J CO lines show stronger evolution than the luminosity functions of low-J CO lines; 5) our model barely reproduces the available constraints on the CO and [CII] luminosity function of galaxies at z>1.5 and the CO luminosity of individual galaxies at intermediate redshifts. We argue that this is driven by a lack of cold gas in galaxies at intermediate redshifts as predicted by cosmological simulations of galaxy formation. This may lay at the root of other problems theoretical models face at the same redshifts.

A Slippery Slope: Systematic Uncertainties in the Baryonic Tully-Fisher Relation

The baryonic Tully-Fisher relation (BTFR) is both a valuable observational tool and a critical test of galaxy formation theory. We explore the systematic uncertainty in the slope and the scatter of the observed BTFR utilizing a homogeneously measured dataset of 930 isolated galaxies. We measure a fiducial relation of log_10 M_baryon = 3.24 log_10 V_rot + 3.21 with a scatter of 0.25 dex over the baryonic mass range of 10^7.4 to 10^11.3 M_sun. We then conservatively vary the definitions of M_baryon and V_rot, the sample definition and the linear fitting algorithm used to fit the BTFR. We obtain slopes ranging from 2.64 to 3.46 and scatter measurements ranging from 0.16 to 0.41 dex. We next compare our fiducial slope to literature measurements, where reported slopes range from 3.0 to 4.3 and scatter is either unmeasured, unmeasurable or as large as 0.4 dex. Measurements derived from unresolved HI line-widths tend to produce slopes of 3.2, while measurements derived strictly from resolved asymptotic rotation velocities produce slopes of 4.0. The largest factor affecting the BTFR slope is the definition of rotation velocity. Sample definition, mass range and linear fitting algorithm also significantly affect the measured BTFR. Galaxies with V_rot < 100 km/s are consistent with the BTFR of more massive galaxies, but these galaxies drive most of the scatter in the BTFR. This is most likely due to the diversity in rotation curve shapes of low-mass galaxies and underestimated systematic uncertainties. It is critical when comparing predictions to an observed BTFR that the rotation velocity definition, the sample selection and the fitting algorithm are similarly defined. Fitting a power-law model to the BTFR is an oversimplification and we recommend direct statistical comparisons between datasets with commensurable properties.

The CALYMHA survey: Ly$\alpha$ escape fraction and its dependence on galaxy properties at $z=2.23$

We present the first results from our CAlibrating LYMan-$\alpha$ with H$\alpha$ (CALYMHA) pilot survey at the Isaac Newton Telescope. We measure Ly$\alpha$ emission for 488 H$\alpha$ selected galaxies at $z=2.23$ from HiZELS in the COSMOS and UDS fields with a specially designed narrow-band filter ($\lambda_c$ = 3918 {\AA}, $\Delta\lambda$= 52 {\AA}). We find 17 dual H$\alpha$-Ly$\alpha$ emitters ($f_{\rm Ly\alpha} >5\times10^{-17}$ erg s$^{-1}$ cm$^{-2}$, of which 5 are X-ray AGN). For star-forming galaxies, we find a range of Ly$\alpha$ escape fractions (f$_{\rm esc}$, measured with 3$"$ apertures) from $2$\%$-30$\%. These galaxies have masses from $3\times10^8$ M$_{\odot}$ to 10$^{11}$ M$_{\odot}$ and dust attenuations E$(B-V)=0-0.5$. Using stacking, we measure a median escape fraction of $1.6\pm0.5$\% ($4.0\pm1.0$\% without correcting H$\alpha$ for dust), but show that this depends on galaxy properties. The stacked f$_{\rm esc}$ tends to decrease with increasing SFR and dust attenuation. However, at the highest masses and dust attenuations, we detect individual galaxies with f$_{\rm esc}$ much higher than the typical values from stacking, indicating significant scatter in the values of f$_{\rm esc}$. Relations between f$_{\rm esc}$ and UV slope are bimodal, with high f$_{\rm esc}$ for either the bluest or reddest galaxies. We speculate that this bimodality and large scatter in the values of f$_{\rm esc}$ is due to additional physical mechanisms such as outflows facilitating f$_{\rm esc}$ for dusty/massive systems. Ly$\alpha$ is significantly more extended than H$\alpha$ and the UV. f$_{\rm esc}$ continues to increase up to at least 20 kpc (3$\sigma$, 40 kpc [2$\sigma$]) for typical SFGs and thus the aperture is the most important predictor of f$_{\rm esc}$.

Star Formation in Luminous Quasars at 2<z<3

We investigate the relation between star formation rates ($\dot{M}_{s}$) and AGN properties in optically selected type 1 quasars at $2<z<3$ using data from Herschel and the SDSS. We find that $\dot{\rm{M}}_s$ remains approximately constant with redshift, at $300\pm100~\rm{M}_{\odot}$yr$^{-1}$. Conversely, $\dot{\rm{M}}_s$ increases with AGN luminosity, up to a maximum of $\sim600~\rm{M}_{\odot}$yr$^{-1}$, and with CIV FWHM. In context with previous results, this is consistent with a relation between $\dot{\rm{M}}_s$ and black hole accretion rate ($\dot{\rm{M}}_{bh}$) existing in only parts of the $z-\dot{\rm{M}}_{s}-\dot{\rm{M}}_{bh}$ plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between $\dot{\rm{M}}_s$ and both AGN luminosity and CIV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing CIV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; $M_i$ is not a linear tracer of L$_{2500}$, the Baldwin effect changes form at high AGN luminosities, and high CIV EW values signpost a change in the relation between $\dot{\rm{M}}_s$ and $\dot{\rm{M}}_{bh}$. Finally, there is no strong relation between $\dot{\rm{M}}_s$ and Eddington ratio, or the asymmetry of the CIV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with CIV asymmetries arising from orientation effects.

Dust Destruction by the Reverse Shock in the Cassiopeia A Supernova Remnant

Core collapse supernovae (CCSNe) are important sources of interstellar dust, potentially capable of producing one solar mass of dust in their explosively expelled ejecta. However, unlike other dust sources, the dust has to survive the passage of the reverse shock, generated by the interaction of the supernova blast wave with its surrounding medium. Knowledge of the net amount of dust produced by CCSNe is crucial for understanding the origin and evolution of dust in the local and high-redshift universe. Our aim is to identify the dust destruction mechanisms in the ejecta, and derive the net amount of dust that survives the passage of the reverse shock. We use analytical models for the evolution of a supernova blast wave and of the reverse shock, with special application to the clumpy ejecta of the remnant of Cassiopeia A. We assume that the dust resides in cool oxygen-rich clumps that are uniformly distributed within the remnant and surrounded by a hot X-ray emitting plasma, and that the dust consists of silicates (MgSiO3) and amorphous carbon grains. The passage of the reverse shock through the clumps gives rise to a relative gas-grain motion and also destroys the clumps. Inside the ejecta clouds, dust is processed via kinetic sputtering, which is terminated either when the grains escape the clumps, or when the clumps are destroyed by the reverse shock. In either case, grain destruction proceeds thereafter by thermal sputtering in the hot ambient gas. We find that 11.8% and 15.9% of, respectively, the silicate and carbon dust survives the passage of the reverse shock by the time the shock has reached the center of the remnant. These fractions depend on the morphology of the ejecta and the medium into which the remnant is expanding, as well as the composition and size distribution of the grains that formed in the ejecta. Results will therefore differ for different types of supernovae.

Dark matter fraction of low-mass cluster members probed by galaxy-scale strong lensing

We present a strong lensing system, composed of 4 multiple images of a source at z = 2.387, created by two lens galaxies, G1 and G2, belonging to the galaxy cluster MACS J1115.9+0129 at z = 0.353. We use observations taken as part of the Cluster Lensing and Supernova survey with Hubble, CLASH, and its spectroscopic follow-up programme at the Very Large Telescope, CLASH-VLT, to estimate the total mass distributions of the two galaxies and the cluster through strong gravitational lensing models. We find that the total projected mass values within the half-light radii, R_{e}, of the two lens galaxies are M_{T,G1}(< R_{e,G1}) = (3.6 +/- 0.4) x 10^{10}M_{Sun} and M_{T,G2}(< R_{e,G2}) = (4.2 +/- 1.6) x 10^{10}M_{Sun}. The effective velocity dispersion values of G1 and G2 are (122 +/- 7) km/s and (137 +/- 27) km/s, respectively. We remark that these values are relatively low when compared to those of ~200-300 km/s, typical of lens galaxies found in the field by previous surveys. By fitting the spectral energy distributions of G1 and G2, we measure projected luminous over total mass fractions within R_{e} of 0.11 +/- 0.03, for G1, and 0.73 +/- 0.32, for G2. The fact that the less massive galaxy, G1, is dark-matter dominated in its inner regions raises the question of whether the dark matter fraction in the core of early-type galaxies depends on their mass. Further investigating strong lensing systems will help us understand the influence that dark matter has on the structure and evolution of the inner regions of galaxies.

The Time-Domain Spectroscopic Survey: Understanding the Optically Variable Sky with SEQUELS in SDSS-III

The Time-Domain Spectroscopic Survey (TDSS) is an SDSS-IV eBOSS subproject primarily aimed at obtaining identification spectra of ~220,000 optically-variable objects systematically selected from SDSS/Pan-STARRS1 multi-epoch imaging. We present a preview of the science enabled by TDSS, based on TDSS spectra taken over ~320 deg^2 of sky as part of the SEQUELS survey in SDSS-III, which is in part a pilot survey for eBOSS in SDSS-IV. Using the 15,746 TDSS-selected single-epoch spectra of photometrically variable objects in SEQUELS, we determine the demographics of our variability-selected sample, and investigate the unique spectral characteristics inherent in samples selected by variability. We show that variability-based selection of quasars complements color-based selection by selecting additional redder quasars, and mitigates redshift biases to produce a smooth quasar redshift distribution over a wide range of redshifts. The resulting quasar sample contains systematically higher fractions of blazars and broad absorption line quasars than from color-selected samples. Similarly, we show that M-dwarfs in the TDSS-selected stellar sample have systematically higher chromospheric active fractions than the underlying M-dwarf population, based on their H-alpha emission. TDSS also contains a large number of RR Lyrae and eclipsing binary stars with main-sequence colors, including a few composite-spectrum binaries. Finally, our visual inspection of TDSS spectra uncovers a significant number of peculiar spectra, and we highlight a few cases of these interesting objects. With a factor of ~15 more spectra, the main TDSS survey in SDSS-IV will leverage the lessons learned from these early results for a variety of time-domain science applications.

Chemistry and Kinematics of Red Supergiant Stars in the Young Massive Cluster NGC 2100

We have obtained K-band Multi-Object Spectrograph (KMOS) near-IR spectroscopy for 14 red supergiant stars (RSGs) in the young massive star cluster NGC 2100 in the Large Magellanic Cloud (LMC). Stellar parameters including metallicity are estimated using the J-band analysis technique, which has been rigorously tested in the Local Universe. We find an average metallicity for NGC 2100 of [Z]=$-$0.38$\pm$0.20 dex, in good agreement with estimates from the literature for the LMC. Comparing our results in NGC 2100 with those for a Galactic cluster (at Solar-like metallicity) with a similar mass and age we find no significant difference in the location of RSGs in the Hertzsprung--Russell diagram. We combine the observed KMOS spectra to form a simulated integrated-light cluster spectrum and show that, by analysing this spectrum as a single RSG, the results are consistent with the average properties of the cluster. Radial velocities are estimated for the targets and the dynamical properties are estimated for the first time within this cluster. The data are consistent with a flat velocity dispersion profile, and with an upper limit of 3.9 \kms, at the 95\% confidence level, for the velocity dispersion of the cluster. However, the intrinsic velocity dispersion is unresolved and could, therefore, be significantly smaller than the upper limit reported here. An upper limit on the dynamical mass of the cluster is derived as $M_{dyn}$ $\le$ $15.2\times10^{4}M_{\odot}$ assuming virial equilibrium.

SDSS-II Supernova Survey: An Analysis of the Largest Sample of Type Ia Supernovae and Correlations with Host-Galaxy Spectral Properties

Using the largest single-survey sample of Type Ia supernovae (SNe Ia) to date, we study the relationship between properties of SNe Ia and those of their host galaxies, focusing primarily on correlations with Hubble residuals (HR). Our sample consists of 345 photometrically-classified or spectroscopically-confirmed SNeIa discovered as part of the SDSS-II Supernova Survey (SDSS-SNS). This analysis utilizes host-galaxy spectroscopy obtained during the SDSS-I/II spectroscopic survey and from an ancillary program on the SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS) that obtained spectra for nearly all host galaxies of SDSS-II SN candidates. In addition, we use photometric host-galaxy properties from the SDSS-SNS data release (Sako et al. 2014) such as host stellar mass and star-formation rate. We confirm the well-known relation between HR and host-galaxy mass and find a 3.6{\sigma} significance of a non-zero linear slope. We also recover correlations between HR and host-galaxy gas-phase metallicity and specific star-formation rate as they are reported in the literature. With our large dataset, we examine correlations between HR and multiple host-galaxy properties simultaneously and find no evidence of a significant correlation. We also independently analyze our spectroscopically-confirmed and photometrically-classified SNe Ia and comment on the significance of similar combined datasets for future surveys.

The ESO UVES Advanced Data Products Quasar Sample - VI. Sub-Damped Lyman-$\alpha$ Metallicity Measurements and the Circum-Galactic Medium

The Circum-Galactic Medium (CGM) can be probed through the analysis of absorbing systems in the line-of-sight to bright background quasars. We present measurements of the metallicity of a new sample of 15 sub-damped Lyman-$\alpha$ absorbers (sub-DLAs, defined as absorbers with 19.0 < log N(H I) < 20.3) with redshift 0.584 < $\rm z_{abs}$ < 3.104 from the ESO Ultra-Violet Echelle Spectrograph (UVES) Advanced Data Products Quasar Sample (EUADP). We combine these results with other measurements from the literature to produce a compilation of metallicity measurements for 92 sub-DLAs as well as a sample of 362 DLAs. We apply a multi-element analysis to quantify the amount of dust in these two classes of systems. We find that either the element depletion patterns in these systems differ from the Galactic depletion patterns or they have a different nucleosynthetic history than our own Galaxy. We propose a new method to derive the velocity width of absorption profiles, using the modeled Voigt profile features. The correlation between the velocity width delta_V90 of the absorption profile and the metallicity is found to be tighter for DLAs than for sub-DLAs. We report hints of a bimodal distribution in the [Fe/H] metallicity of low redshift (z < 1.25) sub-DLAs, which is unseen at higher redshifts. This feature can be interpreted as a signature from the metal-poor, accreting gas and the metal-rich, outflowing gas, both being traced by sub-DLAs at low redshifts.

The mosaic multiple stellar populations in $\omega$ Centauri : the Horizontal Branch and the Main Sequence

We interpret the stellar population of $\omega$ Centauri by means of a population synthesis analysis, following the most recent observational guidelines for input metallicities, helium and [(C+N+O)/Fe] contents. We deal at the same time with the main sequences, sub-giant and horizontal branch data. The reproduction of the observed colour magnitude features is very satisfying and bears interesting hints concerning the evolutionary history of this peculiar stellar ensemble. Our main results are: 1) no significant spread in age is required to fit the colour-magnitude diagram. Indeed we can use coeval isochrones for the synthetic populations, and we estimate that the ages fall within a $\sim 0.5$ Gyr time interval; in particular the most metal rich population can be coeval (in the above meaning) with the others, if its stars are very helium--rich (Y$\sim$0.37) and with the observed CNO enhancement ([(C+N+O)/Fe] = + 0.7); 2) a satisfactory fit of the whole HB is obtained, consistent with the choice of the populations providing a good reproduction of the main sequence and sub giant data. 3) the split in magnitude observed in the red HB is well reproduced assuming the presence of two stellar populations in the two different sequences observed: a metal poor population made of stars evolving from the blue side (luminous branch) and a metal richer one whose stars are in a stage closer to the zero age HB (dimmer branch). This modelization also fits satisfactorily the period and the [Fe/H] distribution of the RR Lyrae stars.

High-Resolution Imaging of Water Maser Emission in the active galaxies NGC 6240 and M51

We present the results of observations of 22GHz H2O maser emission in NGC 6240 and M51 made with the Karl G. Jansky Very Large Array. Two major H2O maser features and several minor features are detected toward the southern nucleus of NGC 6240. These features are redshifted by about 300 km/s from the galaxy's systemic velocity and remain unresolved at the synthesized beam size. A combination of our two-epoch observations and published data reveals an apparent correlation between the strength of the maser and the 22GHz radio continuum emission, implying that the maser excitation relates to the activity of an active galactic nucleus in the southern nucleus rather than star-forming activity. The star-forming galaxy M51 hosts H2O maser emission in the center of the galaxy; however, the origin of the maser has been an open question. We report the first detection of 22GHz nuclear radio continuum emission in M51. The continuum emission is co-located with the maser position, which indicates that the maser arises from active galactic nucleus-activity and not from star-forming activity in the galaxy.

The white dwarf population within 40 pc of the Sun

The white dwarf luminosity function is an important tool to understand the properties of the Solar neighborhood, like its star formation history, and its age. Here we present a population synthesis study of the white dwarf population within 40~pc from the Sun, and compare the results of this study with the properties of the observed sample. We use a state-of-the-art population synthesis code based on Monte Carlo techniques, that incorporates the most recent and reliable white dwarf cooling sequences, an accurate description of the Galactic neighborhood, and a realistic treatment of all the known observational biases and selection procedures. We find a good agreement between our theoretical models and the observed data. In particular, our simulations reproduce a previously unexplained feature of the bright branch of the white dwarf luminosity function, which we argue is due to a recent episode of star formation. We also derive the age of the Solar neighborhood employing the position of the observed cut-off of the white dwarf luminosity function, obtaining ~8.9+-0.2 Gyr. We conclude that a detailed description of the ensemble properties of the population of white dwarfs within 40pc of the Sun allows us to obtain interesting constraints on the history of the Solar neighborhood.

Metallicity gradients in Local Universe galaxies: time evolution and effects of radial migration

Our knowledge of the shape of radial metallicity gradients in disc galaxies has recently improved. Conversely, the understanding of their time evolution is more complex, since it requires analysis of stellar populations with different ages, or systematic studies of galaxies at different redshifts. In the Local Universe, Hii regions and planetary nebulae (PNe) are important tools to investigate it. We present an in-depth study of all nearby spiral galaxies (M33, M31, NGC300, and M81) with direct-method nebular abundances of both populations. For the first time, we also evaluate the radial migration of PN populations. We analyse Hii region and PN properties to: determine whether oxygen in PNe is a reliable tracer for past interstellar medium (ISM) composition; homogenise the published datasets; estimate the migration of the oldest stellar populations; determine the overall chemical enrichment and slope evolution. We confirm that oxygen in PNe is a reliable tracer for the past ISM metallicity. We find that PN gradients are flatter than or equal to those of Hii regions. When radial motions are negligible, this result provides a direct measurement of the time evolution of the gradient. For galaxies with dominant radial motions, we provide upper limits on the gradient evolution. Finally, the total metal content increases with time in all target galaxies, with early morphological type having a larger increment Delta(O/H) than late-type galaxies. Our findings provide important constraints to discriminate among different galactic evolutionary scenarios, favouring cosmological models with enhanced feedback from supernovae. The advent of extremely large telescopes will allow us to include galaxies in a wider range of morphologies and environments, thus putting firmer constraints to galaxy formation and evolution scenarios.

Probing the Dragonfish star-forming complex: the ionizing population of the young massive cluster Mercer 30

The Dragonfish Nebula has been recently claimed to be powered by a superluminous but elusive OB association. Instead, systematic searches in near-infrared photometric surveys have found many other cluster candidates on this sky region. Among these, the first confirmed young massive cluster was Mercer 30, where Wolf-Rayet stars were found. We perform a new characterization of Mercer 30 with unprecedented accuracy, combining NICMOS/HST and VVV photometric data with multi-epoch ISAAC/VLT H- and K-band spectra. Stellar parameters for most of spectroscopically observed cluster members are found through precise non-LTE atmosphere modeling with the CMFGEN code. Our spectrophotometric study for this cluster yields a new, revised distance of d = (12.4 +- 1.7) kpc and a total of Q = 6.70 x 10^50 Lyman ionizing photons. A cluster age of (4.0 +- 0.8) Myr is found through isochrone fitting, and a total mass of (1.6 +- 0.6) x 10^4 Msol is estimated thanks to our extensive knowledge of the post-main-sequence population. As a consequence, membership of Mercer 30 to the Dragonfish star-forming complex is confirmed, allowing us to use this cluster as a probe for the whole complex, which turns out to be extremely large (400 pc across) and located at the outer edge of the Sagittarius-Carina spiral arm (11 kpc from the Galactic Center). The Dragonfish complex hosts 19 young clusters or cluster candidates (including Mercer 30 and a new candidate presented in this work) and an estimated minimum of 9 field Wolf-Rayet stars. The sum of all these contributions accounts for, at least, 73% of the Dragonfish Nebula ionization and leaves little or no room for the alleged superluminous OB association; alternative explanations are discussed.

What is controlling the fragmentation process in the Infrared Dark Cloud G14.225-0.506? Differet level of fragmentation in twin hubs

We present observations of the 1.3 mm continuum emission toward hub-N and hub-S of the infrared dark cloud G14.225-0.506 carried out with the Submillimeter Array, together with observations of the dust emission at 870 and 350 microns obtained with APEX and CSO telescopes. The large scale dust emission of both hubs consists of a single peaked clump elongated in the direction of the associated filament. At small scales, the SMA images reveal that both hubs fragment into several dust condensations. The fragmentation level was assessed under the same conditions and we found that hub-N presents 4 fragments while hub-S is more fragmented, with 13 fragments identified. We studied the density structure by means of a simultaneous fit of the radial intensity profile at 870 and 350 microns and the spectral energy distribution adopting a Plummer-like function to describe the density structure. The parameters inferred from the model are remarkably similar in both hubs, suggesting that density structure could not be responsible in determining the fragmentation level. We estimated several physical parameters such as the level of turbulence and the magnetic field strength, and we found no significant differences between these hubs. The Jeans analysis indicates that the observed fragmentation is more consistent with thermal Jeans fragmentation compared with a scenario that turbulent support is included. The lower fragmentation level observed in hub-N could be explained in terms of stronger UV radiation effects from a nearby HII region, evolutionary effects, and/or stronger magnetic fields at small scales, a scenario that should be further investigated.

Binary Black Hole Mergers from Globular Clusters: Masses, Merger Rates, and the Impact of Stellar Evolution

Expanding upon our previous work (Rodriguez et al., 2015), we study merging binary black holes formed in globular clusters using our Monte Carlo approach to stellar dynamics. We have created a new set of 52 cluster models with different masses, metallicities, and radii to fully characterize the binary black hole merger rate. These models include all the relevant dynamical processes (such as two-body relaxation, strong encounters, and three-body binary formation) and agree well with detailed direct N-body simulations. In addition, we have enhanced our stellar evolution algorithms with updated metallicity-dependent stellar wind and supernova prescriptions, allowing us to compare our results directly to the most recent population synthesis predictions for merger rates from isolated binary evolution. We explore the relationship between a cluster's global properties and the population of binary black holes that it produces. In particular, we derive a numerically calibrated relationship between the merger times of ejected black hole binaries and a cluster's mass and radius. We explore the masses and mass ratios of these binaries as a function of redshift, and find a merger rate of ~5 Gpc$^{-3}$ yr$^{-1}$ in the local universe, with 90% of sources having total masses from $32M_{\odot}$ to $64M_{\odot}$. Under standard assumptions, approximately 1 out of every 7 binary black hole mergers in the local universe will have originated in a globular cluster, but we also explore the sensitivity of this result to different assumptions for binary stellar evolution. If black holes were born with significant natal kicks, comparable to those of neutron stars, then the merger rate of binary black holes from globular clusters would be comparable to that from the field, with approximately 1/2 of mergers originating in clusters [Abridged].

The Science Case for ALMA Band 2 and Band 2+3

We discuss the science drivers for ALMA Band 2 which spans the frequency range from 67 to 90 GHz. The key science in this frequency range are the study of the deuterated molecules in cold, dense, quiescent gas and the study of redshifted emission from galaxies in CO and other species. However, Band 2 has a range of other applications which are also presented. The science enabled by a single receiver system which would combine ALMA Bands 2 and 3 covering the frequency range 67 to 116 GHz, as well as the possible doubling of the IF bandwidth of ALMA to 16 GHz, are also considered.

Studying the Outflow-Core Interaction with ALMA Cycle 1 Observations of the HH 46/47 Molecular Outflow

We present ALMA Cycle 1 observations of the HH 46/47 molecular outflow using combined 12m array and 7m array observations. We use 13CO and C18O emission to correct for the 12CO optical depth, to accurately estimate the outflow mass, momentum and kinetic energy. Applying the optical depth correction increases the mass estimate by a factor of 14, the momentum by a factor of 6, and the kinetic energy by a factor of about 2. The new 13CO(1-0) and C18O(1-0) data also allow us to trace denser and slower outflow material than that traced by 12CO. These species are only detected within about 1~2 km/s from the cloud velocity. The cavity wall of the red lobe appears at very low velocities (~0.2 km/s). Combing the material traced only by 13CO and C18O, the measured total mass of the CO outflow is 1.4 Msun, the total momentum is 1.7 Msun km/s and the total energy is 4.7e43 erg, assuming Tex=15 K. The improved angular resolution and sensitivity in 12CO reveal more details of the outflow structure. Specifically, we find that the outflow cavity wall is composed of multiple shells entrained in a series of jet bow-shock events. The outflow kinetic energy distribution shows that even though the red lobe is mainly entrained by jet bow-shocks, more outflow energy is being deposited into the cloud at the base of the outflow cavity rather than around the heads of the bow shocks. The estimated outflow mass, momentum, and energy indicate that the outflow is capable to disperse the parent core within the typical lifetime of the embedded phase of a low-mass protostar, and regulating a core-to-star efficiency of 1/4~1/3. The 13CO and C18O emission also trace a circumstellar envelope with rotation and infall motions. In CS, we found possible evidence for a slowly-moving rotating outflow, which we believe is entrained not only poloidally but also toroidally by a wind launched from relatively large radii on the disk.

The off-centered Seyfert-like compact emission in the nuclear region of NGC 3621

We analyze an optical data cube of the nuclear region of NGC 3621, taken with the integral field unit of the Gemini Multi-object Spectrograph. We found that the previously detected central line emission in this galaxy actually comes from a blob, located at a projected distance of 2.14" +/- 0.08" (70.1 +/- 2.6 pc) from the stellar nucleus. Only diffuse emission was detected in the rest of the field of view, with a deficit of emission at the position of the stellar nucleus. Diagnostic diagram analysis reveals that the off-centered emitting blob has a Seyfert 2 spectrum. We propose that the line-emitting blob may be a "fossil" emission-line region or a light "echo" from an active galactic nucleus (AGN), which was significantly brighter in the past. Our estimates indicate that the bolometric luminosity of the AGN must have decreased by a factor of ~13 - 500 during the last ~230 years. A second scenario to explain the morphology of the line-emitting areas in the nuclear region of NGC 3621 involves no decrease of the AGN bolometric luminosity and establishes that the AGN is highly obscured toward the observer but not toward the line-emitting blob. The third scenario proposed here assumes that the off-centered line-emitting blob is a recoiling supermassive black hole, after the coalescence of two black holes. Finally, an additional hypothesis is that the central X-ray source is not an AGN, but an X-ray binary. This idea is consistent with all the scenarios we proposed.

The physical and chemical structure of Sagittarius B2, I. Three-dimensional thermal dust and free-free continuum modeling on 100 au to 45 pc scales

We model the dust and free-free continuum emission in the high-mass star-forming region Sagittarius B2 in order to reconstruct the three-dimensional density and dust temperature distribution, as a crucial input to follow-up studies of the gas velocity field and molecular abundances. We employ the three-dimensional radiative transfer program RADMC-3D to calculate the dust temperature self-consistently, provided a given initial density distribution. This density distribution of the entire cloud complex is then recursively reconstructed based on available continuum maps, including both single-dish and high-resolution interferometric maps covering a wide frequency range (40 GHz - 4 THz). The model covers spatial scales from 45 pc down to 100 au, i.e. a spatial dynamic range of 10^5. We find that the density distribution of Sagittarius B2 can be reasonably well fitted by applying a superposition of spherical cores with Plummer-like density profiles. In order to reproduce the spectral energy distribution, we position Sgr B2(N) along the line of sight behind the plane containing Sgr B2(M). We find that the entire cloud complex comprises a total gas mass of 8.0 x 10^6 Msun within a diameter of 45 pc, corresponding to an averaged gas density of 170 Msun/pc^3. We estimate stellar masses of 2400 Msun and 20700 Msun and luminosities of 1.8 x 10^6 Lsun and 1.2 x 10^7 Lsun for Sgr B2(N) and Sgr B2(M), respectively. We report H_2 column densities of 2.9 x 10^24 cm^-2 for Sgr B2(N) and 2.5 x 10^24 cm^-2 for Sgr B2(M) in a 40" beam. For Sgr B2(S), we derive a stellar mass of 1100 Msun, a luminosity of 6.6 x 10^5 Lsun and a H_2 column density of 2.2 x 10^24 cm^-2 in a 40" beam. We calculate a star formation efficiency of 5% for Sgr B2(N) and 50% for Sgr B2(M), indicating that most of the gas content in Sgr B2(M) has already been converted to stars or dispersed.

Bayesian analysis of cosmic-ray propagation: evidence against homogeneous diffusion

We present the results of the most complete ever scan of the parameter space for cosmic ray (CR) injection and propagation. We perform a Bayesian search of the main GALPROP parameters, using the MultiNest nested sampling algorithm, augmented by the BAMBI neural network machine learning package. This is the first such study to separate out low-mass isotopes ($p$, $\bar p$ and He) from the usual light elements (Be, B, C, N, O). We find that the propagation parameters that best fit $p$, $\bar p$, He data are significantly different from those that fit light elements, including the B/C and $^{10}$Be/$^9$Be secondary-to-primary ratios normally used to calibrate propagation parameters. This suggests each set of species is probing a very different interstellar medium, and that the standard approach of calibrating propagation parameters using B/C can lead to incorrect results. We present posterior distributions and best fit parameters for propagation of both sets of nuclei, as well as for the injection abundances of elements from H to Si. The input GALDEF files with these new parameters will be included in an upcoming public GALPROP update.

The Infrared Medium-Deep Survey. V. A New Selection Strategy for Quasars at z > 5 based on Medium-Band Observation with SQUEAN

Multiple color selection techniques have been successful in identifying quasars from wide-field broad-band imaging survey data. Among the quasars that have been discovered so far, however, there is a redshift gap at $5 \lesssim {\rm z} \lesssim 5.7$ due to the limitations of filter sets in previous studies. In this work, we present a new selection technique of high redshift quasars using a sequence of medium-band filters: nine filters with central wavelengths from 625 to 1025 nm and bandwidths of 50 nm. Photometry with these medium-bands traces the spectral energy distribution (SED) of a source, similar to spectroscopy with resolution R $\sim$ 15. By conducting medium-band observations of high redshift quasars at 4.7 $\leq$ z $\leq$ 6.0 and brown dwarfs (the main contaminants in high redshift quasar selection) using the SED camera for QUasars in EArly uNiverse (SQUEAN) on the 2.1-m telescope at the McDonald Observatory, we show that these medium-band filters are superior to multi-color broad-band color section in separating high redshift quasars from brown dwarfs. In addition, we show that redshifts of high redshift quasars can be determined to an accuracy of $\Delta{\rm z}/(1+{\rm z}) = 0.002$ -- $0.026$. The selection technique can be extended to z $\sim$ 7, suggesting that the medium-band observation can be powerful in identifying quasars even at the re-ionization epoch.

The start of the Sagittarius spiral arm (Sagittarius origin) and the start of the Norma spiral arm (Norma origin) - model-computed and observed arm tangents at galactic longitudes -20 degrees < l < +23 degrees

Here we fitted a 4-arm spiral structure to the more accurate data on global arm pitch angle and arm longitude tangents, to get the start of each spiral arm near the Galactic nucleus. We find that the tangent to the 'start of the Sagittarius' spiral arm (arm middle) is at l= -17 degrees +/- 0.5 degree, while the tangent to the 'start of the Norma' spiral arm (arm middle) is at l= +20 degrees +/- 0.5 degree. Earlier, we published a compilation of observations and analysis of the tangent to each spiral arm tracer, from longitudes +23 degrees to +340 degrees; here we cover the arm tracers in the remaining longitudes +340 degrees (=- 20 degrees) to +23 degrees. Our model arm tangents are confirmed through the recent observed masers data (at the arm's inner edge). Observed arm tracers in the inner Galaxy show an offset from the mid-arm; this was also found elsewhere in the Milky Way disk (Vallee 2014c). In addition, we collated the observed tangents to the so-called '3-kpc-arm' features; here they are found statistically to be near l= -18 degrees +/- 2 degrees and near l= +21 degrees +/- 2 degrees, after excluding misidentified spiral arms. We find that the model-computed arm tangents in the inner Galaxcy are spatially coincident with the mean longitude of the observed tangents to the '3-kpc-arm' features (same galactic longitudes, within the errors). These spatial similarities may be suggestive of a contiguous space.

The Herschel Virgo Cluster Survey. XIX. Physical properties of low luminosity FIR sources at $z <$ 0.5

The Star formation rate (SFR) is a crucial parameter to investigate galaxy evolution. At low redshift the cosmic SFR density declines smoothly, and massive active galaxies become passive, reducing their star formation activity. This implies that the bulk of the SFR density at low redshift is mainly driven by low mass objects. We investigate the properties of a sample of low luminosity Far-Infrared (FIR) sources selected at 250 microns from Pappalardo et al. (2015). We have collected data from Ultraviolet to FIR to perform a multi-wavelengths analysis. The main goal is to investigate the correlation between SFR, stellar mass, and dust mass for a galaxy population with a wide range in dust content and stellar mass, including the low mass regime that most probably dominates the SFR density at low z. We define a main sample of ~800 sources with full Spectral Energy Distribution (SED) coverage between 0.15 < lambda < 500 microns and an extended sample with ~5000 sources in which we remove the constraints on the Ultraviolet and Near-Infrared bands. We analyze both samples with two different SED fitting methods: MAGPHYS and CIGALE. In the SFR versus stellar mass plane our samples occupy a region included between local spirals and higher redshift star forming galaxies. The galaxies subsample with the higher masses (M* > 3e10 Msol) does not lie on the main sequence, but shows a small offset, as a consequence of the decreased star formation. Low mass galaxies (M* < 1e10 Msol) settle in the main sequence with SFR and stellar mass consistent with local spirals. Deep Herschel data allow the identification of a mixed galaxy population, with galaxies still in an assembly phase, or galaxies at the beginning of their passive evolution. We find that the dust luminosity is the parameter that discriminates these two galaxy populations.

Keck/MOSFIRE Spectroscopy of z=7-8 Galaxies: Lyman-alpha Emission from a Galaxy at z=7.66

We report the results from some of the deepest Keck/MOSFIRE data yet obtained for candidate $z \gtrsim 7$ galaxies. Our data show one significant line detection with 6.5$\sigma$ significance in our combined 10 hours of integration which is independently detected on more than one night, ruling out the possibility that the detection is spurious. The asymmetric line profile and non-detection in the optical bands strongly imply that the detected line is Ly$\alpha$ emission from a galaxy at $z$(Ly$\alpha)=7.6637 \pm 0.0011$, making it the fourth spectroscopically confirmed galaxy at $z>7.5$. This galaxy is bright in the rest-frame ultraviolet (UV; $M_{\rm UV} \sim -21.2$) with a moderately blue UV slope ($\beta=-2.2^{+0.3}_{-0.2}$), and exhibits a rest-frame Ly$\alpha$ equivalent width of EW(Ly$\alpha$) $\sim 15.6^{+5.6}_{-3.6}$ \AA. The non-detection of the 11 other $z \sim$ 7--8 galaxies in our long 10 hr integration, reaching a median 5$\sigma$ sensitivity of 28 \AA\ in the rest-frame EW(Ly$\alpha$), implies a 1.3$\sigma$ deviation from the null hypothesis of a non-evolving distribution in the rest-frame EW(Ly$\alpha$) between $3<z<6$ and $z=$ 7--8. Our results are consistent with previous studies finding a decline in Ly$\alpha$ emission at $z>6.5$, which may signal the evolving neutral fraction in the intergalactic medium at the end of the reionization epoch, although our weak evidence suggests the need for a larger statistical sample to allow for a more robust conclusion.

The low-mass end of the baryonic Tully-Fisher relation

The scaling of disk galaxy rotation velocity with baryonic mass (the "Baryonic Tully-Fisher" relation, BTF) has long confounded galaxy formation models. It is steeper than the M ~ V^3 scaling relating halo virial masses and circular velocities and its zero point implies that galaxies comprise a very small fraction of available baryons. Such low galaxy formation efficiencies may in principle be explained by winds driven by evolving stars, but the tightness of the BTF relation argues against the substantial scatter expected from such vigorous feedback mechanism. We use the APOSTLE/EAGLE simulations to show that the BTF relation is well reproduced in LCDM simulations that match the size and number of galaxies as a function of stellar mass. In such models, galaxy rotation velocities are proportional to halo virial velocity and the steep velocity-mass dependence results from the decline in galaxy formation efficiency with decreasing halo mass needed to reconcile the CDM halo mass function with the galaxy luminosity function. Despite the strong feedback, the scatter in the simulated BTF is smaller than observed, even when considering all simulated galaxies and not just rotationally-supported ones. The simulations predict that the BTF should become increasingly steep at the faint end, although the velocity scatter at fixed mass should remain small. Observed galaxies with rotation speeds below ~40 km/s seem to deviate from this prediction. We discuss observational biases and modeling uncertainties that may help to explain this disagreement in the context of LCDM models of dwarf galaxy formation.

The Fornax Deep Survey with VST. I. The extended and diffuse stellar halo of NGC~1399 out to 192 kpc

[Abrigded] We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside two square degrees around the bright galaxy NGC1399 in the core of the cluster. We found a very extended and diffuse envelope surrounding the luminous galaxy NGC1399: we map the surface brightness out to 33 arcmin (~ 192 kpc) from the galaxy center and down to about 31 mag/arcsec^2 in the g band. The deep photometry allows us to detect a faint stellar bridge in the intracluster region between NGC1399 and NGC1387. By analyzing the integrated colors of this feature, we argue that it could be due to the ongoing interaction between the two galaxies, where the outer envelope of NGC1387 on its east side is stripped away. By fitting the light profile, we found that it exists a physical break radius in the total light distribution at R=10 arcmin (~58 kpc) that sets the transition region between the bright central galaxy and the outer exponential stellar halo. We discuss the main implications of this work on the build-up of the stellar halo at the center of the Fornax cluster. By comparing with the numerical simulations of the stellar halo formation for the most massive BCGs, we find that the observed stellar halo mass fraction is consistent with a halo formed through the multiple accretion of progenitors with a stellar mass in the range 10^8 - 10^11 M_sun. This might suggest that the halo of NGC1399 has also gone through a major merging event. The absence of a significant number of luminous stellar streams and tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around NGC1399 is characterised by a more diffuse and well-mixed component, including the ICL.

Accuracy requirements to test the applicability of the random cascade model to supersonic turbulence

A model, which is widely used for inertial rang statistics of supersonic turbulence in the context of molecular clouds and star formation, expresses (measurable) relative scaling exponents Z_p of two-point velocity statistics as a function of two parameters, beta and Delta. The model relates them to the dimension D of the most dissipative structures, D=3-Delta/(1-beta). While this description has proved most successful for incompressible turbulence (beta=Delta=2/3, and D=1), its applicability in the highly compressible regime remains debated. For this regime, theoretical arguments suggest D=2 and Delta=2/3, or Delta=1. Best estimates based on 3D periodic box simulations of supersonic isothermal turbulence yield Delta=0.71 and D=1.9, with uncertainty ranges of Delta in [0.67, 0.78] and D in [2.04,1.60]. With these 5-10\% uncertainty ranges just marginally including the theoretical values of Delta=2/3 and D=2, doubts remain whether the model indeed applies and, if it applies, for what values of beta and Delta. We use a Monte Carlo approach to mimic actual simulation data and examine what factors are most relevant for the fit quality. We estimate that 0.1% (0.05%) accurate Z_p, with p=1...5, should allow for 2% (1%) accurate estimates of beta and Delta in the highly compressible regime, but not in the mildly compressible regime. We argue that simulation-based Z_p with such accuracy are within reach of today's computer resources. If this kind of data does not allow for the expected high quality fit of beta and Delta, then this may indicate the inapplicability of the model for the simulation data. In fact, other models than the one we examine here have been suggested.

DHIGLS: DRAO H I Intermediate Galactic Latitude Survey

Observations of Galactic H I gas for seven intermediate Galactic latitude fields are presented at 1' angular resolution using data from the DRAO Synthesis Telescope (ST) and the Green Bank Telescope (GBT). The DHIGLS data are the most extensive arcminute resolution measurements of the diffuse atomic interstellar medium beyond those in the Galactic plane. The acquisition, reduction, calibration, and mosaicking of the DRAO ST data and the cross calibration and incorporation of the short-spacing information from the GBT are described. The high quality of the DHIGLS data enables a variety of new studies in directions of low Galactic column density. We find evidence for dramatic changes in the structures in channel maps over even small changes in velocity. This narrow line emission has counterparts in absorption spectra against bright background radio sources, quantifying that the gas is cold and dense and can be identified as the cold neutral medium phase. We analyze the angular power spectra of maps of the integrated H I emission (column density) from the mosaics for several distinct velocity ranges. Fitting power spectrum models based on a power law, but including the effects of the synthesized beam and noise at high spatial frequencies, we find exponents ranging from -2.5 to -3.0. Power spectra of maps of the centroid velocity for these components give similar results. These exponents are interpreted as being representative of the 3D density and velocity fields of the atomic gas, respectively. Fully reduced DHIGLS H I data cubes and other data products are available at www.cita.utoronto.ca/DHIGLS.

On the inconsistency between cosmic stellar mass density and star formation rate up to $z\sim8$

In this paper, we test the discrepancy between the stellar mass density and instantaneous star formation rate in redshift range $0<z<8$ using a large observational data sample. We first compile the measurements of the stellar mass densities up to $z\sim 8$. Comparing the observed stellar mass densities with the time-integral of instantaneous star formation history, we find that the observed stellar mass densities are lower than that implied from star formation history at $z<4$. We also use Markov chain monte carlo method to derive the best-fitting star formation history from the observed stellar mass density data. At $0.5<z<6$, the observed star formation rate densities are larger than the best-fitting one, especially at $z\sim2$ where by a factor of about two. However, at lower ($z<0.5$) and higher redshifts ($z>6$), the derived star formation history is consistent with the observations. This is the first time to test the discrepancy between the observed stellar mass density and instantaneous star formation rate up to very high redshift $z\approx8$ using the Markov chain monte carlo method and a varying recycling factor. Several possible reasons for this discrepancy are discussed, such as underestimation of stellar mass density, initial mass function and cosmic metallicity evolution.

SALT long-slit spectroscopy of HE 0435-4312: fast change in the Mg II emission line shape

The MgII emission line is visible in the optical band for intermediate redshift quasars (0.4<z<1.6) and it is thus an extremely important tool to measure the black hole mass and to understand the structure of the Broad Line Region. We aim to determine the substructure and the variability of the MgII line with the aim to identify which part of the line comes from a medium in Keplerian motion. Using SALT telescope we performed ten spectroscopic observation of a quasar HE 0435-4312 (z=1.2231) over the period of 3 years (Dec 23/24, 2012 to Dec 7/8, 2015). We find that the line is well modeled by two Lorentzian components, and the relative strength of these components vary with time. The line maximum is shifted in a time-dependent way from the position of the Fe II pseudo-continuum, although the effect is not very strong, and the line asymmetry varies in time. We also note very different local conditions in the formation region of Mg II and FeII. The timescale for the line shape variability is of the order of the light travel time to the emitting region, therefore the changes are most likely due to the varying irradiation patterns and the presence of the two components does not imply two distinct emission regions.

Infalling clouds on to supermassive black hole binaries - II. Binary evolution and the final parsec problem

The formation of massive black hole binaries (MBHBs) is an unavoidable outcome of galaxy evolution via successive mergers. However, the mechanism that drives their orbital evolution from parsec separations down to the gravitational wave (GW) dominated regime is poorly understood and their final fate is still unclear. If such binaries are embedded in gas-rich and turbulent environments, as observed in remnants of galaxy mergers, the interaction with gas clumps (such as molecular clouds) may efficiently drive their orbital evolution. Using numerical simulations, we test this hypothesis by studying the dynamical evolution of an equal-mass, circular MBHB accreting infalling molecular clouds. We investigate different orbital configurations, modelling a total of 13 systems to explore different possible pericentre distances and relative inclinations of the cloud-binary encounter. We show that the evolution of the binary orbit is dominated by the exchange of angular momentum through gas accretion during the first stages of the interaction for all orbital configurations. Building on these results, we construct a simple model for evolving a MBHB interacting with a sequence of clouds, which are randomly drawn from reasonable populations with different levels of anisotropy in their angular momenta distributions. We show that the binary efficiently evolves down to the GW emission regime within a few hundred million years, overcoming the 'final parsec' problem regardless of the stellar distribution.

The cosmic evolution of massive black holes in the Horizon-AGN simulation

We analyze the demographics of black holes (BHs) in the large-volume cosmological hydrodynamical simulation Horizon-AGN. This simulation statistically models how much gas is accreted onto BHs, traces the energy deposited into their environment and, consequently, the back-reaction of the ambient medium on BH growth. The synthetic BHs reproduce a variety of observational constraints such as the redshift evolution of the BH mass density and the mass function. Yet there seem to be too many BHs with mass~ 1e7 Msun at high redshift, and too few BHs with similar mass at z=0 in intermediate-mass galaxies. Strong self-regulation via AGN feedback, weak supernova feedback, and unresolved internal process are likely to be responsible for this, and for a tight BH-galaxy mass correlation. Starting at z~2, tidal stripping creates a small population of BHs over-massive with respect to the halo. The fraction of galaxies hosting a central BH or an AGN increases with stellar mass. The AGN fraction agrees better with multi-wavelength studies, than single-wavelength ones, unless obscuration is taken into account. The most massive halos present BH multiplicity, with additional BHs gained by ongoing or past mergers. In some cases, both a central and an off-center AGN shine concurrently, producing a dual AGN. This dual AGN population dwindles with decreasing redshift, as found in observations. Specific accretion rate and Eddington ratio distributions are in good agreement with observational estimates. The BH population is dominated in turn by fast, slow, and very slow accretors, with transitions occurring at z=3 and z=2 respectively.

Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. VI. Velocity-resolved Reverberation Mapping of H$\beta$ Line

In the sixth of the series of papers reporting on a large reverberation mapping (RM) campaign of active galactic nuclei (AGNs) with high accretion rates, we present velocity-resolved time lags of H$\beta$ emission lines for nine objects observed in the campaign during 2012$-$2013. In order to correct the line-broadening caused by seeing and instruments before the analysis of velocity-resolved RM, we adopt Richardson-Lucy deconvolution to reconstruct their H$\beta$ profiles. The validity and effectiveness of the deconvolution are checked out by Monte Carlo simulation. Five among the nine objects show clear dependence of time delay on velocity. Mrk 335 and Mrk 486 show signatures of gas inflow whereas the clouds in the broad-line regions (BLRs) of Mrk 142 and MCG +06-26-012 tend to be radial outflowing. Mrk 1044 is consistent with the case of virialized motions. The lags of the rest four are not velocity-resolvable. The velocity-resolved RM of super-Eddington accreting massive black holes (SEAMBHs) shows that they have diversity of the kinematics in their BLRs. Comparing with the AGNs with sub-Eddington accretion rates, we do not find significant differences in the BLR kinematics of SEAMBHs.

The ATLAS-SPT Radio Survey of Cluster Galaxies

Using a high-performance computing cluster to mosaic 4,787 pointings, we have imaged the 100 sq. deg. South Pole Telescope (SPT) deep-field at 2.1 GHz using the Australian Telescope Compact Array to an rms of 80 $\mu$Jy and a resolution of 8". Our goal is to generate an independent sample of radio-selected galaxy clusters to study how the radio properties compare with cluster properties at other wavelengths, over a wide range of redshifts in order to construct a timeline of their evolution out to $z \sim 1.3$. A preliminary analysis of the source catalogue suggests there is no spatial correlation between the clusters identified in the SPT-SZ catalogue and our wide-angle tail galaxies.

Ca II triplet spectroscopy of RGB stars in NGC 6822: kinematics and metallicities

We present a detailed analysis of the chemistry and kinematics of red giants in the dwarf irregular galaxy NGC 6822. Spectroscopy at 8500 Angstroms was acquired for 72 red giant stars across two fields using FORS2 at the VLT. Line of sight extinction was individually estimated for each target star to accommodate the variable reddening across NGC 6822. The mean radial velocity was found to be v_helio = (52.8 +/- 2.2) km/s with dispersion rms = 24.1 km/s, in agreement with other studies. Ca II triplet equivalent widths were converted into [Fe/H] metallicities using a V magnitude proxy for surface gravity. The average metallicity was [Fe/H] = (-0.84 +/- 0.04) with dispersion rms = 0.31 dex and interquartile range 0.48. Our assignment of individual reddening values makes our analysis more sensitive to spatial variations in metallicity than previous studies. We divide our sample into metal-rich and metal-poor stars; the former are found to cluster towards small radii with the metal-poor stars more evenly distributed across the galaxy. The velocity dispersion of the metal-poor stars is higher than that of the metal-rich stars; combined with the age-metallicity relation this indicates that older populations have either been dynamically heated or were born in a less disclike distribution. The low ratio (v_rot/v_rms) suggests that within the inner 10', NGC 6822's stars are dynamically decoupled from the HI gas, possibly in a thick disc or spheroid.

Solo Dwarfs I: Survey introduction and first results for the Sagittarius Dwarf Irregular Galaxy

We introduce the Solitary Local Dwarfs Survey (Solo), a wide field photometric study targeting every isolated dwarf galaxy within 3 Mpc of the Milky Way. Solo is based on (u)gi multi-band imaging from CFHT/MegaCam for northern targets, and Magellan/Megacam for southern targets. All galaxies fainter than Mv = -18 situated beyond the nominal virial radius of the Milky Way and M31 (>300 kpc) are included in this volume-limited sample, for a total of 42 targets. In addition to reviewing the survey goals and strategy, we present results for the Sagittarius Dwarf Irregular Galaxy (Sag DIG), one of the most isolated, low mass galaxies, located at the edge of the Local Group. We analyze its resolved stellar populations and their spatial distributions. We provide updated estimates of its central surface brightness and integrated luminosity, and trace its surface brightness profile to a level fainter than 30 mag./sq.arcsec. Sag DIG is well described by a highly elliptical (disk-like) system following a single component Sersic model. However, a low-level distortion is present at the outer edges of the galaxy that, were Sag DIG not so isolated, would likely be attributed to some kind of previous tidal interaction. Further, we find evidence of an extremely low level, extended distribution of stars beyond 5 arcmins (>1.5 kpc) that suggests Sag DIG may be embedded in a very low density stellar halo. We compare the stellar and HI structures of Sag DIG, and discuss results for this galaxy in relation to other isolated, dwarf irregular galaxies in the Local Group.

Dispersion of Magnetic Fields in Molecular Clouds. IV - Analysis of Interferometry Data

We expand on the dispersion analysis of polarimetry maps toward applications to interferometry data. We show how the filtering of low-spatial frequencies can be accounted for within the idealized Gaussian turbulence model, initially introduced for single-dish data analysis, to recover reliable estimates for correlation lengths of magnetized turbulence, as well as magnetic field strengths (plane-of-the-sky component) using the Davis-Chandrasekhar-Fermi method. We apply our updated technique to TADPOL/CARMA data obtained on W3(OH), W3 Main, and DR21(OH). For W3(OH) our analysis yields a turbulence correlation length $\delta\simeq19$ mpc, a ratio of turbulent-to-total magnetic energy $\left\langle B_{\mathrm{t}}^{2}\right\rangle /\left\langle B^{2}\right\rangle \simeq0.58$, and a magnetic field strength $B_{0}\sim1.1\:\mathrm{mG}$; for W3 Main $\delta\simeq22$ mpc, $\left\langle B_{\mathrm{t}}^{2}\right\rangle /\left\langle B^{2}\right\rangle \simeq0.74$, and $B_{0}\sim0.7\:\mathrm{mG}$; while for DR21(OH) $\delta\simeq12$ mpc, $\left\langle B_{\mathrm{t}}^{2}\right\rangle /\left\langle B^{2}\right\rangle \simeq0.70$, and $B_{0}\sim1.2\:\mathrm{mG}$.

The clustering amplitude of X-ray selected AGN at z=0.8: Evidence for a negative dependence on accretion luminosity

The northern tile of the wide-area and shallow XMM-XXL X-ray survey field is used to estimate the average dark matter halo mass of relatively luminous X-ray selected AGN [$\rm log\, L_X (\rm 2-10\,keV)= 43.6^{+0.4}_{-0.4}\,erg/s$] in the redshift interval $z=0.5-1.2$. Spectroscopic follow-up observations of X-ray sources in the XMM-XXL field by the Sloan telescope are combined with the VIPERS spectroscopic galaxy survey to determine the cross-correlation signal between X-ray selected AGN (total of 318) and galaxies (about 20,\,000). We model the large scales (2-25\,Mpc) of the correlation function to infer a mean dark matter halo mass of $\log M / (M_{\odot} \, h^{-1}) = 12.50 ^{+0.22} _{-0.30}$ for the X-ray selected AGN sample. This measurement is about 0.5\,dex lower compared to estimates in the literature of the mean dark matter halo masses of moderate luminosity X-ray AGN [$L_X (\rm 2-10\,keV)\approx 10^{42} - 10^{43}\,erg/s$] at similar redshifts. Our analysis also links the mean clustering properties of moderate luminosity AGN with those of powerful UV/optically selected QSOs, which are typically found in halos with masses few times $10^{12}\,M_{\odot}$. There is therefore evidence for a negative luminosity dependence of the AGN clustering. This is consistent with suggestions that AGN have a broad dark matter halo mass distribution with a high mass tail that becomes sub-dominant at high accretion luminosities. We further show that our results are in qualitative agreement with semi-analytic models of galaxy and AGN evolution, which attribute the wide range of dark matter halo masses among the AGN population to different triggering mechanisms and/or black hole fueling modes.

APOGEE strings: a fossil record of the gas kinematic structure

We compare APOGEE radial velocities (RVs) of young stars in the Orion A cloud with CO line gas emission and find a correlation between the two at large-scales, in agreement with previous studies. However, at smaller scales we find evidence for the presence of substructure in the stellar velocity field. Using a Friends-of-Friends approach we identify 37 stellar groups with almost identical RVs. These groups are not randomly distributed but form elongated chains or strings of stars with five or more members with low velocity dispersion, across lengths of 1-1.5~pc. The similarity between the kinematic properties of the APOGEE strings and the internal velocity field of the chains of dense cores and fibers recently identified in the dense ISM is striking and suggests that for most of the Orion A cloud, young stars keep memory of the parental gas substructure where they originated.

The cosmic assembly of stellar haloes in massive Early-Type Galaxies

Using the exquisite depth of the Hubble Ultra Deep Field (HUDF12 programme) dataset, we explore the ongoing assembly of the outermost regions of the most massive galaxies (M_{stellar} > 5x10^{10} M_{Sun}) at z < 1. The outskirts of massive objects, particularly Early-Types Galaxies (ETGs), are expected to suffer a dramatic transformation across cosmic time due to continuous accretion of small galaxies. HUDF imaging allows us to study this process at intermediate redshifts in 6 massive galaxies, exploring the individual surface brightness profiles out to 25 effective radii. We find that 10-30% of the total stellar mass for the galaxies in our sample is contained within 10 < R < 50 kpc. These values are in close agreement with numerical simulations, and at least 2-3 times higher than those reported for late-type galaxies. The fraction of stellar mass stored in the outer envelopes/haloes of Massive Early-Type Galaxies increases with decreasing redshift, being 28.7% at < z > = 0.1, 22.6% at < z > = 0.65 and 3.5% at < z > = 2. The fraction of mass in diffuse features linked with ongoing minor merger events is > 1-3%, very similar to predictions based on observed close pair counts. Therefore, our results suggest that the size and mass growth of the most massive galaxies have been solely driven by minor and major merging from z = 1 to today.

The very wide-field $gzK$ galaxy survey -- II. The relationship between star-forming galaxies at $z \sim 2$ and their host haloes based upon HOD modelling

We present the results of an halo occupation distribution (HOD) analysis of star-forming galaxies at $z \sim 2$. We obtained high-quality angular correlation functions based on a large sgzK sample, which enabled us to carry out the HOD analysis. The mean halo mass and the HOD mass parameters are found to increase monotonically with increasing $K$-band magnitude, suggesting that more luminous galaxies reside in more massive dark haloes. The luminosity dependence of the HOD mass parameters was found to be the same as in the local Universe; however, the masses were larger than in the local Universe over all ranges of magnitude. This implies that galaxies at $z \sim 2$ tend to form in more massive dark haloes than in the local Universe, a process known as downsizing. By analysing the dark halo mass evolution using the extended Press--Schechter formalism and the number evolution of satellite galaxies in a dark halo, we find that faint Lyman break galaxies at $z \sim 4$ could evolve into the faintest sgzKs $(22.0 < K \leq 23.0)$ at $z \sim 2$ and into the Milky-Way-like galaxies or elliptical galaxies in the local Universe, whereas the most luminous sgzKs $(18.0 \leq K \leq 21.0)$ could evolve into the most massive systems in the local Universe. The stellar-to-halo mass ratio (SHMR) of the sgzKs was found to be consistent with the prediction of the model, except that the SHMR of the faintest sgzKs was smaller than the prediction at $z \sim 2$. This discrepancy may be attributed that our samples are confined to star-forming galaxies.

The very wide-field $gzK$ galaxy survey -- I. Details of the clustering properties of star-forming galaxies at $z \sim 2$

We present the results of clustering analysis on the $z \sim 2$ star-forming galaxies. By combining our data with data from publicly available archives, we collect $g$-, $\zb / z$-, and $K$-band imaging data over 5.2 deg$^{2}$, which represents the largest area BzK/gzK survey. We apply colour corrections to translate our filter-set to those used in the original BzK selection for the gzK selection. Because of the wide survey area, we obtain a sample of 41,112 star-forming gzK galaxies at $z \sim 2$ (sgzKs) down to $\KAB < 23.0$, and determine high-quality two-point angular correlation functions (ACFs). Our ACFs show an apparent excess from power-law behaviour at small angular scale $(\theta \la 0.01^{\circ})$, which corresponds the virial radius of a dark halo at $z \sim 2$ with a mass of $\sim 10^{13} \Msun$. We find that the correlation lengths are consistent with the previous estimates over all magnitude range; however, our results are evaluated with a smaller margin of error than that in previous studies. The large amount of data enables us to determine ACFs differentially depending on the luminosity of the subset of the data. The mean halo mass of faint sgzKs $(22.0 < K \leq 23.0)$ was found to be $\Mh = (1.32^{+0.09}_{-0.12}) \times 10^{12} h^{-1} \Msun$, whereas bright sgzKs ($18.0 \leq K \leq 21.0)$ were found to reside in dark haloes with a mass of $\Mh = (3.26^{+1.23}_{-1.02}) \times 10^{13} h^{-1} \Msun$.

The Launching of Cold Clouds by Galaxy Outflows II: The Role of Thermal Conduction

We explore the impact of electron thermal conduction on the evolution of radiatively-cooled cold clouds embedded in flows of hot and fast material, as occur in outflowing galaxies. Performing a parameter study of three-dimensional adaptive mesh refinement hydrodynamical simulations, we show that electron thermal conduction causes cold clouds to evaporate, but it can also extend their lifetimes by compressing them into dense filaments. We distinguish between low column-density clouds, which are disrupted on very short times, and high-column density clouds with much-longer disruption times that are set by a balance between impinging thermal energy and evaporation. We provide fits to the cloud lifetimes and velocities that can be used in galaxy-scale simulations of outflows, in which the evolution of individual clouds cannot be modeled with the required resolution. Moreover, we show that the clouds are only accelerated to a small fraction of the ambient velocity because compression by evaporation causes the clouds to present a small cross-section to the ambient flow. This means that either magnetic fields must suppress thermal conduction, or that the cold clouds observed in galaxy outflows are not formed of cold material carried out from the galaxy.

The VIMOS Ultra Deep Survey First Data Release: spectra and spectroscopic redshifts of 698 objects up to z~6 in CANDELS

This paper describes the first data release (DR1) of the VIMOS Ultra Deep Survey (VUDS). The DR1 includes all low-resolution spectroscopic data obtained in 276.9 arcmin2 of the CANDELS-COSMOS and CANDELS-ECFDS survey areas, including accurate spectroscopic redshifts z_spec and individual spectra obtained with VIMOS on the ESO-VLT. A total of 698 objects have a measured redshift, with 677 galaxies, two type-I AGN and a small number of 19 contaminating stars. The targets of the spectroscopic survey are selected primarily on the basis of their photometric redshifts to ensure a broad population coverage. About 500 galaxies have z_spec>2, 48 with z_spec>4, and the highest reliable redshifts reach beyond z_spec=6. This dataset approximately doubles the number of galaxies with spectroscopic redshifts at z>3 in these fields. We discuss the general properties of the sample in terms of the spectroscopic redshift distribution, the distribution of Lyman-alpha equivalent widths, and physical properties including stellar masses M_star and star formation rates (SFR) derived from spectral energy distribution fitting with the knowledge of z_spec. We highlight the properties of the most massive star-forming galaxies, noting the large range in spectral properties, with Lyman-alpha in emission or in absorption, and in imaging properties with compact, multi-component or pair morphologies. We present the catalogue database and data products. All data are publicly available and can be retrieved from a dedicated query-based database available at http://cesam.lam.fr/vuds.

The extended epoch of galaxy formation: age dating of ~3600 galaxies with 2<z<6.5 in the VIMOS Ultra-Deep Survey

We aim at improving constraints on the epoch of galaxy formation by measuring the ages of 3597 galaxies with spectroscopic redshifts 2<z<6.5 in the VIMOS Ultra Deep Survey (VUDS). We derive ages and other physical parameters from the simultaneous fitting with the GOSSIP+ software of observed UV rest-frame spectra and photometric data from the u-band up to 4.5 microns using composite stellar population models. We conclude from extensive simulations that at z>2 the joint analysis of spectroscopy and photometry combined with restricted age possibilities when taking into account the age of the Universe substantially reduces systematic uncertainties and degeneracies in the age derivation. We find galaxy ages ranging from very young with a few tens of million years to substantially evolved with ages up to ~1.5-2 Gyr. The formation redshifts z_f derived from the measured ages indicate that galaxies may have started forming stars as early as z_f~15. We produce the formation redshift function (FzF), the number of galaxies per unit volume formed at a redshift z_f, and compare the FzF in increasing redshift bins finding a remarkably constant 'universal' FzF. The FzF is parametrized with (1+z)^\zeta, with \zeta~0.58+/-0.06, indicating a smooth 2 dex increase from z~15 to z~2. Remarkably this observed increase is of the same order as the observed rise in the star formation rate density (SFRD). The ratio of the SFRD with the FzF gives an average SFR per galaxy of ~7-17Msun/yr at z~4-6, in agreement with the measured SFR for galaxies at these redshifts. From the smooth rise in the FzF we infer that the period of galaxy formation extends from the highest possible redshifts that we can probe at z~15 down to redshifts z~2. This indicates that galaxy formation is a continuous process over cosmic time, with a higher number of galaxies forming at the peak in SFRD at z~2 than at earlier epochs. (Abridged)

Size evolution of star-forming galaxies with $2<z<4.5$ in the VIMOS Ultra-Deep Survey

We measure galaxy sizes on a sample of $\sim1200$ galaxies with confirmed spectroscopic redshifts $2 \leq z_{spec} \leq 4.5$ in the VIMOS Ultra Deep Survey (VUDS), representative of star-forming galaxies with $i_\mathrm{AB} \leq 25$. We first derive galaxy sizes applying a classical parametric profile fitting method using GALFIT. We then measure the total pixel area covered by a galaxy above a given surface brightness threshold, which overcomes the difficulty of measuring sizes of galaxies with irregular shapes. We then compare the results obtained for the equivalent circularized radius enclosing 100\% of the measured galaxy light $r_T^{100}$ to those obtained with the effective radius $r_{e,\mathrm{circ}}$ measured with GALFIT. We find that the sizes of galaxies computed with our non-parametric approach span a large range but remain roughly constant on average with a median value $r_T^{100}\sim2.2$ kpc for galaxies with $2<z<4.5$. This is in stark contrast with the strong downward evolution of $r_e$ with increasing redshift, down to sizes of $<1$ kpc at $z\sim4.5$. We analyze the difference and find that parametric fitting of complex, asymmetric, multi-component galaxies is severely underestimating their sizes. By comparing $r_T^{100}$ with physical parameters obtained through SED fitting we find that the star-forming galaxies that are the largest at any redshift are, on average, more massive and more star-forming. We discover that galaxies present more concentrated light profiles as we move towards higher redshifts. We interpret these results as the signature of several, possibly different, evolutionary paths of galaxies in their early stages of assembly, including major and minor merging or star-formation in multiple bright regions. (abridged)

 

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