Recent Postings from Galaxies

Cosmic Galaxy-IGM HI Relation at ${\it{z}}\sim 2-3$ Probed in the COSMOS/UltraVISTA $1.6$ deg$^2$ Field

We present spatial correlations of galaxies and IGM neutral hydrogen HI in the COSMOS/UltraVISTA 1.62 deg$^2$ field. Our data consist of 13415 photo-$z$ galaxies at $z\sim2-3$ with $K_s<23.4$ and the Ly$\alpha$ forest absorptions in the background quasar spectra selected from SDSS data with no signature of damped Ly$\alpha$ system contamination. We estimate a galaxy overdensity $\delta_{gal}$ in an impact parameter of 2.5 pMpc, and calculate the Ly$\alpha$ forest fluctuations $\delta_{\langle F\rangle}$ whose negative values correspond to the strong Ly$\alpha$ forest absorptions. We identify a weak anti-correlation between $\delta_{gal}$ and $\delta_{\langle F\rangle}$ with a Spearman's rank correlation coefficient of $-0.39$ suggesting that the galaxy overdensities and the Ly$\alpha$ forest absorptions positively correlate in space at the $\sim90\%$ confidence level. This positive correlation indicates that high-$z$ galaxies exist around an excess of HI gas in the Ly$\alpha$ forest. We find four cosmic volumes, dubbed $A_{obs}$-$D_{obs}$, that have extremely large (small) values of $\delta_{gal} \simeq0.8$ ($-1$) and $\delta_{\langle F\rangle}$ $\simeq0.1$ ($-0.4$), three out of which, $B_{obs}$-$D_{obs}$, significantly depart from the correlation, and weaken the correlation signal. We perform cosmological hydrodynamical simulations, and compare with our observational results. Our simulations reproduce the correlation, agreeing with the observational results. Moreover, our simulations have model counterparts of $A_{obs}$-$D_{obs}$, and suggest that the observations pinpoint, by chance, a galaxy overdensity like a proto-cluster, gas filaments lying on the sightline, a large void, and orthogonal low-density filaments. Our simulations indicate that the significant departures of $B_{obs}$-$D_{obs}$ are produced by the filamentary large-scale structures and the observation sightline effects.

Infalling-Rotating Motion and Associated Chemical Change in the Envelope of IRAS 16293-2422 Source A Studied with ALMA

We have analyzed rotational spectral line emission of OCS, CH3OH, HCOOCH3, and H2CS observed toward the low-mass Class 0 protostellar source IRAS 16293-2422 Source A at a sub-arcsecond resolution (~0".6 x 0".5) with ALMA. Significant chemical differentiation is found at a 50 AU scale. The OCS line is found to well trace the infalling-rotating envelope in this source. On the other hand, the CH3OH and HCOOCH3 distributions are found to be concentrated around the inner part of the infalling-rotating envelope. With a simple ballistic model of the infalling-rotating envelope, the radius of the centrifugal barrier (a half of the centrifugal radius) and the protostellar mass are evaluated from the OCS data to be from 40 to 60 AU and from 0.5 to 1.0 Msun, respectively, assuming the inclination angle of the envelope/disk structure to be 60 degrees (90 degrees for the edge-on configuration). Although the protostellar mass is correlated with the inclination angle, the radius of the centrifugal barrier is not. This is the first indication of the centrifugal barrier of the infalling-rotating envelope in a hot corino source. CH3OH and HCOOCH3 may be liberated from ice mantles due to weak accretion shocks around the centrifugal barrier, and/or due to protostellar heating. The H2CS emission seems to come from the disk component inside the centrifugal barrier in addition to the envelope component. The centrifugal barrier plays a central role not only in the formation of a rotationally-supported disk but also in the chemical evolution from the envelope to the protoplanetary disk.

A Monte-Carlo Method for Estimating Stellar Photometric Metallicity Distributions [Replacement]

Based on the Sloan Digital Sky Survey (SDSS), we develop a new monte-carlo based method to estimate the photometric metallicity distribution function (MDF) for stars in the Milky Way. Compared with other photometric calibration methods, this method enables a more reliable determination of the MDF, in particular at the metal-poor and metal-rich ends. We present a comparison of our new method with a previous polynomial-based approach, and demonstrate its superiority. As an example, we apply this method to main-sequence stars with $0.2<g-r<0.6$, $6$ kpc$<R<9$ kpc, and in different intervals in height above the plane, $|Z|$. The MDFs for the selected stars within two relatively local intervals ($0.8$ kpc$<|Z|<1.2$ kpc, $1.5$ kpc$<|Z|<2.5$ kpc) can be well-fit by two Gaussians, with peaks at [Fe/H] $\approx-0.6$ and $-1.2$ respectively, one associated with the disk system, the other with the halo. The MDFs for the selected stars within two more distant intervals ($3$ kpc$<|Z|<5$ kpc, $6$ kpc$<|Z|<9$ kpc) can be decomposed into three Gaussians, with peaks at [Fe/H] $\approx-0.6$, $-1.4$ and $-1.9$ respectively, where the two lower peaks may provide evidence for a two-component model of the halo: the inner halo and the outer halo. The number ratio between the disk component and halo component(s) decreases with vertical distance from the Galactic plane, consistent with the previous literature.

A Monte-Carlo Method for Estimating Stellar Photometric Metallicity Distributions

Based on the Sloan Digital Sky Survey (SDSS), we develop a new monte-carlo based method to estimate the photometric metallicity distribution function (MDF) for stars in the Milky Way. Compared with other photometric calibration methods, this method enables a more reliable determination of the MDF, in particular at the metal-poor and metal-rich ends. We present a comparison of our new method with a previous polynomial-based approach, and demonstrate its superiority. As an example, we apply this method to main-sequence stars with $0.2<g-r<0.6$, $6$ kpc$<R<9$ kpc, and in different intervals in height above the plane, $|Z|$. The MDFs for the selected stars within two relatively local intervals ($0.8$ kpc$<|Z|<1.2$ kpc, $1.5$ kpc$<|Z|<2.5$ kpc) can be well-fit by two Gaussians, with peaks at [Fe/H] $\approx-0.6$ and $-1.2$ respectively, one associated with the disk system, the other with the halo. The MDFs for the selected stars within two more distant intervals ($3$ kpc$<|Z|<5$ kpc, $6$ kpc$<|Z|<9$ kpc) can be decomposed into three Gaussians, with peaks at [Fe/H] $\approx-0.6$, $-1.4$ and $-1.9$ respectively, where the two lower peaks may provide evidence for a two-component model of the halo: the inner halo and the outer halo. The number ratio between the disk component and halo component(s) decreases with vertical distance from the Galactic plane, consistent with the previous literature.

Chemical history of isolated dwarf galaxies of the Local Group: I. dSphs: Cetus and Tucana

For the first time, we obtain chemical evolution models (CEMs) for Tucana and Cetus, two isolated dwarf spheroidal galaxies (dSphs) of the Local Group. The CEMs have been built from the star formation histories (SFHs) and the metallicity histories, both obtained independently by the LCID project from deep color-magnitude dia- grams. Based on our models, we find that the chemical histories were complex and can be divided into different epochs and scenarios. In particular, during 75 percent of the SFH, the galaxies behaved as closed boxes and, during the remaining 25 percent, either received a lot of primordial gas by accretion or they lost metals through metal-rich winds. In order to discriminate between these two scenarios, abundances ratios in old stars are needed. At t approximately 4.5 Gyr, the galaxies lost most of their gas due to a short-strong, well-mixed wind. We obtain very similar CEMs for both galaxies, although Cetus is twice as massive as Tucana. We conclude that the star formation in both galaxies began with only 1.5 percent of the baryonic mass fraction predicted by lambda CDM.

ALMA Science Verification Data: Millimeter Continuum Polarimetry of the Bright Radio Quasar 3C 286

We present full-polarization observations of the compact, steep-spectrum radio quasar 3C~286 made with the ALMA at 1.3~mm. These are the first full-polarization ALMA observations, which were obtained in the framework of Science Verification. A bright core and a south-west component are detected in the total intensity image, similar to previous centimeter images. Polarized emission is also detected toward both components. The fractional polarization of the core is about 17\%, this is higher than the fractional polarization at centimeter wavelengths, suggesting that the magnetic field is even more ordered in the millimeter radio core than it is further downstream in the jet. The observed polarization position angle (or EVPA) in the core is $\sim$\,$39^{\circ}$, which confirms the trend that the EVPA slowly increases from centimeter to millimeter wavelengths. With the aid of multi-frequency VLBI observations, we argue that this EVPA change is associated with the frequency-dependent core position. We also report a serendipitous detection of a sub-mJy source in the field of view, which is likely to be a submillimeter galaxy.

Recommended Thermal Rate Coefficients for the C + H$_3^+$ Reaction and Some Astrochemical Implications

We have incorporated our experimentally derived thermal rate coefficients for C + H$_3^+$ forming CH$^+$ and CH$_2^+$ into a commonly used astrochemical model. We find that the Arrhenius-Kooij equation typically used in chemical models does not accurately fit our data and use instead a more versatile fitting formula. At a temperature of 10 K and a density of 10$^4$ cm$^{-3}$, we find no significant differences in the predicted chemical abundances, but at higher temperatures of 50, 100, and 300 K we find up to factor of 2 changes. Additionally, we find that the relatively small error on our thermal rate coefficients, $\sim15\%$, significantly reduces the uncertainties on the predicted abundances compared to those obtained using the currently implemented Langevin rate coefficient with its estimated factor of 2 uncertainty.

The Hawaii SCUBA-2 Lensing Cluster Survey: Number Counts and Submillimeter Flux Ratios

We present deep number counts at 450 $\mu$m and 850 $\mu$m using the SCUBA-2 camera on the James Clerk Maxwell Telescope. We combine data for six lensing cluster fields and three blank fields to measure the counts over a wide flux range at each wavelength. Thanks to the lensing magnification, our measurements extends to fluxes fainter than 1 mJy and 0.2 mJy at 450 $\mu$m and 850 $\mu$m, respectively. Our combined data highly constrain the faint end of the number counts. Integrating our counts shows that the majority of the extragalactic background light (EBL) at each wavelength is contributed by faint sources with $L_{\rm IR} < 10^{12} L_{\odot }$, corresponding to luminous infrared galaxies (LIRGs) or normal galaxies. By comparing our result with the 500 $\mu$m stacking of $K$-selected sources from the literature, we conclude that the $K$-selected LIRGs and normal galaxies still cannot fully account for the EBL that originates from sources with $L_{\rm IR} < 10^{12} L_{\odot }$. This suggests that many faint submillimeter galaxies may not be included in the UV star formation history. We also explore the submillimeter flux ratio between the two bands for our 450 $\mu$m and 850 $\mu$m selected sources. At 850 $\mu$m, we find a clear relation between the flux ratio and the observed flux. This relation can be explained by a redshift evolution, where galaxies at higher redshifts have higher luminosities and star formation rates. In contrast, at 450 $\mu$m, we do not see a clear relation between the flux ratio and the observed flux.

A large difference in the progenitor masses of active and passive galaxies in the EAGLE simulation

Cumulative number density matching of galaxies is a method to observationally connect descendent galaxies to their typical main progenitors at higher redshifts and thereby to assess the evolution of galaxy properties. The accuracy of this method is limited due to galaxy merging and scatter in the stellar mass growth history of individual galaxies. Behroozi et al. (2013) have introduced a refinement of the method, based on abundance matching of observed galaxies to the Bolshoi dark-matter-only simulation. The EAGLE cosmological hydro-simulation is well suited to test this method, because it reproduces the observed evolution of the galaxy stellar mass function and has a representative sample of passive/active galaxies. We find agreement with the Behroozi et al. (2013) method for the complete sample of main progenitors of z = 0 galaxies, but we also find a strong dependence on the current star formation rate. Passive galaxies with a stellar mass up to 10^10.75 Msun have a completely different median mass history than active galaxies of the same mass. This difference persists if we only select central galaxies. This means that the cumulative number density method should be applied separately to active and passive galaxies. Even then, the typical main progenitor of a z = 0 galaxy already spans two orders of magnitude in stellar mass at z = 2. Any observational analysis using cumulative number density matching therefore needs to be tested on a range of simulations.

The multiplicity of 250-$\mu$m Herschel sources in the COSMOS field

We investigate the multiplicity of extragalactic sources detected by the Herschel Space Observatory in the COSMOS field. Using 3.6- and 24-$\mu$m catalogues, in conjunction with 250-$\mu$m data from Herschel, we seek to determine if a significant fraction of Herschel sources are composed of multiple components emitting at 250 $\mu$m. We use the XID+ code, using Bayesian inference methods to produce probability distributions of the possible contributions to the observed 250-$\mu$m flux for each potential component. The fraction of Herschel flux assigned to the brightest component is highest for sources with total 250-$\mu$m fluxes < 45 mJy; however, the flux in the brightest component is still highest in the brightest Herschel sources. The faintest 250-$\mu$m sources (30-45 mJy) have the majority of their flux assigned to a single bright component; the second brightest component is typically significantly weaker, and contains the remainder of the 250-$\mu$m source flux. At the highest 250-$\mu$m fluxes (45-110 mJy), the brightest and second brightest components are assigned roughly equal fluxes, and together are insufficient to reach 100 per cent of the 250-$\mu$m source flux. This indicates that additional components are required, beyond the brightest two components, to reproduce the observed flux. 95 per cent of the sources in our sample have a second component that contains more than 10 per cent of the total source flux. Particularly for the brightest Herschel sources, assigning the total flux to a single source may overestimate the flux contributed by around 150 per cent.

Tidal stirring of satellites with shallow density profiles prevents them from being too big to fail

The "too big to fail" problem is revisited by studying the tidal evolution of populations of dwarf satellites with different density profiles. The high resolution cosmological $\rm \Lambda CDM$ "ErisMod" set of simulations is used. These simulations can model both the stellar and dark matter components of the satellites, and their evolution under the action of the tides of a MW-sized host halo at a force resolution better than 10 pc. The stronger tidal mass loss and re-shaping of the mass distribution induced in satellites with $\gamma=0.6$ dark matter density distributions, as those resulting from the effect of feedback in hydrodynamical simulations of dwarf galaxy formation, is sufficient to bring the circular velocity profiles in agreement with the kinematics of MW's dSphs. In contrast, in simulations in which the satellites retain cusps at $z=0$ there are several "massive failures" with circular velocities in excess of the observational constraints. Various sources of deviations in the conventionally adopted relation between the circular velocity at the half light radius and the one dimensional line-of-sight velocity dispersions are found. Such deviations are caused by the response of circular velocity profiles to tidal effects, which also varies depending on the initially assumed inner density profile, and by the complexity of the stellar kinematics, which include residual rotation and anisotropy. In addition tidal effects naturally induce large deviations in the stellar mass-halo mass relation for halo masses below $\rm 10^9 ~ M_{\odot}$, preventing any reliable application of the abundance matching technique to dwarf galaxy satellites.

The HI Content of Galaxies in Groups and Clusters as Measured by ALFALFA

We present the HI content of galaxies in nearby groups and clusters as measured by the 70% complete Arecibo Legacy Fast-ALFA (ALFALFA) survey, including constraints from ALFALFA detection limits. Our sample includes 22 systems at distances between 70-160 Mpc over the mass range 12.5<log M/M_sun<15.0, for a total of 1986 late-type galaxies. We find that late-type galaxies in the centers of groups lack HI at fixed stellar mass relative to the regions surrounding them. Larger groups show evidence of a stronger dependence of HI properties on environment, despite a similar dependence of color on environment at fixed stellar mass. We compare several environment variables to determine which is the best predictor of galaxy properties; group-centric distance r and r/R_200 are similarly effective predictors, while local density is slightly more effective and group size and halo mass are slightly less effective. While both central and satellite galaxies in the blue cloud exhibit a significant dependence of HI content on local density, only centrals show a strong dependence on stellar mass, and only satellites show a strong dependence on halo mass. Finally, we see evidence that HI is deficient for blue cloud galaxies in denser environments even when both stellar mass and color are fixed. This is consistent with a picture where HI is removed or destroyed, followed by reddening within the blue cloud. Our results support the existence of pre-processing in isolated groups, along with an additional rapid mechanism for gas removal within larger groups and clusters, perhaps ram-pressure stripping.

Multi-wavelength landscape of the young galaxy cluster RXJ1257.2+4738 at z=0.866. II. Morphological properties

The study of the evolution of the morphological distribution of galaxies in different environments can provide important information about the effects of the environment and the physical mechanisms responsible for the morphological transformations. As part of a complete analysis of the young cluster RXJ1257+4738 at z$\sim$0.9, we studied in this work the morphological properties of its galaxies. We used non-parametric methods of morphological classification, as implemented in the galSVM code. The classification with the applied method was possible even using ground-based observations: r'-band imaging from OSIRIS/GTC. We defined very conservative probability limits, taking into account the probability errors, in order to obtain a trustworthy classification. In this way we were able to classify about the 30% of all cluster members, and to separate between LT and ET galaxies. Additionally, when analysing the colour-magnitude diagram, we observed a significant population of blue ET galaxies between the classified ones. We discussed possible explanations for the finding of this population. Moreover, we studied different physical properties of LT, ET, and blue ET galaxies. They turn out to be comparable, with the exception of the stellar mass that shows that the red ET population is more massive. We also analysed the morphology-density and morphology-radius relations, observing that, only when considering the morphological separation between ET and LT galaxies, a mild classical behaviour is obtained. RXJ1257+4738 is a young galaxy cluster, showing a clumpy structure and being still in the process of formation, which could explain the lack of some of the standard morphological relations. This makes this cluster a very attractive case for obtaining the higher resolution data and for studying in more details the morphological properties of the entire cluster and relation with the environment.

An accurate and self-consistent chemical abundance catalogue for the APOGEE/Kepler sample

Context. The APOGEE survey has obtained high-resolution infrared spectra of more than 100,000 stars. Deriving chemical abundances patterns of these stars is paramount to piecing together the structure of the Milky Way. While the derived chemical abundances have been shown to be precise for most stars, some calibration problems have been reported, in particular for more metal- poor stars. Aims. In this paper, we aim to (1) re-determine the chemical abundances of the APOGEE+Kepler stellar sample (APOKASC) with an independent procedure, line list and line selection, and high quality surface gravity information from astroseismology, and (2) extend the abundance catalogue by including abundances that are not currently reported in the most recent APOGEE release (DR12). Methods. We fixed the Teff and log g to those determined using spectrophotometric and asteroseismic techniques, respectively. We made use of the Brussels Automatic Stellar Parameter (BACCHUS) code to derive the metallicity and broadening parameters for the APOKASC sample. In addition, we derived differential abundances with respect to Arcturus. Results. We have validated the BACCHUS code on APOGEE data using several well-known stars, and stars from open and globular clusters. We also provide the abundances of C, N, O, Mg, Ca, Si, Ti, S, Al, Na, Ni, Mn, Fe, K, P, Cr, Co, Cu, Rb, Yb and V for every star, line, and show the impact of line selection on the final abundances. These include abundances of five new elements and improved abundances for Si, Ti, S, and V. Conclusions. In this paper, we present an independent analysis of the APOKASC sample and provide abundances of up to 21 elements. This catalogue can be used not only to study chemical abundance patterns of the Galaxy but also to train data driven spectral approaches which can improve the abundance precision in a restricted dataset, but also full APOGEE sample.

Detecting components spectrally localized at astrophysical process frequencies in time series of the electric field vertical component of the earth atmosphere boundary layer

Signal eigenvectors and components analyser (RF Utility model patent 116242) was used to explore the time-series of the electric field vertical component Ez in the Earth atmosphere boundary layer. There have been detected non-coherent complex-periodic components localized at the frequencies of gravity-wave impact of binary stars and at the frequency of axion-photon interaction. These components cannot be detected by means of quadrature scheme of spectral analysis and have RMS values from 0.05 V/m to 0.5 V/m at binary stars gravity-wave impact frequencies and from 0.7 V/m to 2.7 V/m at axion-photon interaction frequency. It was also demonstrated that the axion-photon interaction frequency modulates the amplitude

Comparing [CII], HI, and CO dynamics of nearby galaxies

The HI and CO components of the interstellar medium (ISM) are usually used to derive the dynamical mass M_dyn of nearby galaxies. Both components become too faint to be used as a tracer in observations of high-redshift galaxies. In those cases, the 158 $\mu$m line of atomic carbon [CII] may be the only way to derive M_dyn. As the distribution and kinematics of the ISM tracer affects the determination of M_dyn, it is important to quantify the relative distributions of HI, CO and [CII]. HI and CO are well-characterised observationally, however, for [CII] only very few measurements exist. Here we compare observations of CO, HI, and [CII] emission of a sample of nearby galaxies, drawn from the HERACLES, THINGS and KINGFISH surveys. We find that within R_25, the average [CII] exponential radial profile is slightly shallower than that of the CO, but much steeper than the HI distribution. This is also reflected in the integrated spectrum ("global profile"), where the [CII] spectrum looks more like that of the CO than that of the HI. For one galaxy, a spectrally resolved comparison of integrated spectra was possible; other comparisons were limited by the intrinsic line-widths of the galaxies and the coarse velocity resolution of the [CII] data. Using high-spectral-resolution SOFIA [CII] data of a number of star forming regions in two nearby galaxies, we find that their [CII] linewidths agree better with those of the CO than the HI. As the radial extent of a given ISM tracer is a key input in deriving M_dyn from spatially unresolved data, we conclude that the relevant length-scale to use in determining M_dyn based on [CII] data, is that of the well-characterised CO distribution. This length scale is similar to that of the optical disk.

The Local Universe: Galaxies in 3D

Here I present results from individual galaxy studies and galaxy surveys in the Local Universe with particular emphasis on the spatially resolved properties of neutral hydrogen gas. The 3D nature of the data allows detailed studies of the galaxy morphology and kinematics, their relation to local and global star formation as well as galaxy environments. I use new 3D visualisation tools to present multi-wavelength data, aided by tilted-ring models of the warped galaxy disks. Many of the algorithms and tools currently under development are essential for the exploration of upcoming large survey data, but are also highly beneficial for the analysis of current galaxy surveys.

Post-Newtonian Evolution of Massive Black Hole Triplets in Galactic Nuclei: I. Numerical Implementation and Tests

Massive black-hole binaries (MBHBs) are thought to be the main source of gravitational waves (GWs) in the low-frequency domain surveyed by ongoing and forthcoming Pulsar Timing Array campaigns and future space-borne missions, such as {\it eLISA}. However, many low-redshift MBHBs in realistic astrophysical environments may not reach separations small enough to allow significant GW emission, but rather stall on (sub)pc-scale orbits. This "last-parsec problem" can be eased by the appearance of a third massive black hole (MBH) -- the "intruder" -- whose action can force, under certain conditions, the inner MBHB on a very eccentric orbit, hence allowing intense GW emission eventually leading to coalescence. A detailed assessment of the process, ultimately driven by the induced Kozai-Lidov oscillations of the MBHB orbit, requires a general relativistic treatment and the inclusion of external factors, such as the Newtonian precession of the intruder orbit in the galactic potential and its hardening by scattering off background stars. In order to tackle this problem, we developed a three-body Post-Newtonian (PN) code framed in a realistic galactic potential, including both non-dissipative 1PN and 2PN terms, and dissipative terms such as 2.5PN effects, orbital hardening of the outer binary, and the effect of the dynamical friction on the early stages of the intruder dynamics. In this first paper of a series devoted at studing the dynamics of MBH triplets from a cosmological perspective, we describe, test and validate our code.

Post-Newtonian Evolution of Massive Black Hole Triplets in Galactic Nuclei: I. Numerical Implementation and Tests [Cross-Listing]

Massive black-hole binaries (MBHBs) are thought to be the main source of gravitational waves (GWs) in the low-frequency domain surveyed by ongoing and forthcoming Pulsar Timing Array campaigns and future space-borne missions, such as {\it eLISA}. However, many low-redshift MBHBs in realistic astrophysical environments may not reach separations small enough to allow significant GW emission, but rather stall on (sub)pc-scale orbits. This "last-parsec problem" can be eased by the appearance of a third massive black hole (MBH) -- the "intruder" -- whose action can force, under certain conditions, the inner MBHB on a very eccentric orbit, hence allowing intense GW emission eventually leading to coalescence. A detailed assessment of the process, ultimately driven by the induced Kozai-Lidov oscillations of the MBHB orbit, requires a general relativistic treatment and the inclusion of external factors, such as the Newtonian precession of the intruder orbit in the galactic potential and its hardening by scattering off background stars. In order to tackle this problem, we developed a three-body Post-Newtonian (PN) code framed in a realistic galactic potential, including both non-dissipative 1PN and 2PN terms, and dissipative terms such as 2.5PN effects, orbital hardening of the outer binary, and the effect of the dynamical friction on the early stages of the intruder dynamics. In this first paper of a series devoted at studing the dynamics of MBH triplets from a cosmological perspective, we describe, test and validate our code.

The 2X-HI disks of spiral galaxies

The outskirts of galaxies - especially the very extended HI disks of galaxies - are strongly affected by their local environment. I highlight the giant 2X-HI disks of nearby galaxies (M 83, NGC 3621, and NGC 1512), studied as part of the Local Volume HI Survey (LVHIS), their kinematics and relation to XUV disks, signatures of tidal interactions and accretion events, the MHI - DHI relation as well as the formation of tidal dwarf galaxies. - Using multi-wavelength data, I create 3D visualisations of the gas and stars in galaxies, with the shape of their warped disks obtained through kinematic modelling of their HI velocity fields.

Spectroscopic Confirmation of a Protocluster at z=3.786

We present new observations of the field containing the z=3.786 protocluster, PC217.96+32.3. We confirm that it is one of the largest and most overdense high-redshift structures known. Such structures are rare even in the largest cosmological simulations. We used the Mayall/MOSAIC1.1 imaging camera to image a 1.2x0.6 deg area (~150x75 comoving Mpc) surrounding the protocluster's core and discovered 165 candidate Lyman Alpha emitting galaxies (LAEs) and 788 candidate Lyman Break galaxies (LBGs). There are at least 2 overdense regions traced by the LAEs, the largest of which shows an areal overdensity in its core (i.e., within a radius of 2.5 comoving Mpc) of 14+/-7 relative to the average LAE spatial density in the imaged field. Further, the average LAE spatial density in the imaged field is twice that derived by other field LAE surveys. Spectroscopy with Keck/DEIMOS yielded redshifts for 164 galaxies (79 LAEs and 85 LBGs); 65 lie at a redshift of 3.785+/-0.010. The velocity dispersion of galaxies near the core is 350+/-40 km/s, a value robust to selection effects. The overdensities are likely to collapse into systems with present-day masses of >10^{15} solar masses and >6x10^{14} solar masses. The low velocity dispersion may suggest a dynamically young protocluster. We find a weak trend between narrow-band (Lyman Alpha) luminosity and environmental density: the Lyman Alpha luminosity is enhanced on average by 1.35X within the protocluster core. There is no evidence that the Lyman Alpha equivalent width depends on environment. These suggest that star-formation and/or AGN activity is enhanced in the higher density regions of the structure. PC217.96+32.3 is a Coma cluster analog, witnessed in the process of formation.

Inflow, Outflow, Yields, and Stellar Population Mixing in Chemical Evolution Models

Chemical evolution models are powerful tools for interpreting stellar abundance surveys and understanding galaxy evolution. However, their predictions depend heavily on the treatment of inflow, outflow, star formation efficiency (SFE), the IMF, the SNIa delay time distribution, stellar yields, and mixing of stellar populations. Using flexCE, a new, flexible one-zone chemical evolution code, we investigate the effects of individual parameters and the trade-offs between them. Two of the most important parameters are the SFE and outflow mass-loading parameter, which shift the knee in [O/Fe]-[Fe/H] and the equilibrium abundances, respectively. One-zone models with simple star formation histories follow narrow tracks in [O/Fe]-[Fe/H] that do not match the observed bimodality in this plane. A mix of one-zone models with variations in their inflow timescales and outflow mass-loading parameters, as motivated by the inside-out galaxy formation scenario with radial mixing, reproduces the high- and low-alpha sequences better than a single model with two infall epochs. We present [X/Fe]-[Fe/H] tracks for 20 elements assuming three different SN yield models and find some significant discrepancies with observations, especially for elements with strongly metallicity-dependent yields. Analyzing the high dimensional abundance space probed by surveys like APOGEE, GALAH, and Gaia-ESO will require more advanced statistical techniques. We applied one such technique, principal component abundance analysis, to the simulations and data to reveal the main correlations amongst abundances and quantify their contributions to variation in abundance space. PC1 and PC2 of the stellar population mixing scenario are dominated by alpha-elements and elements with metallicity-dependent yields, respectively, and they collectively explain 99% of the variance. flexCE is available at https://github.com/bretthandrews/flexCE.

Tidal stripping as a test of satellite quenching in redMaPPer clusters

When dark matter halos are accreted by massive host clusters, strong gravitational tidal forces begin stripping mass from the accreted subhalos. This stripping eventually removes all mass beyond a subhalo's tidal radius, but the unbound mass remains in the vicinity of the satellite for at least a dynamical time t_dynamical. The N-body subhalo study of Chamberlain et al. verified this picture and pointed out a useful observational consequence: measurements of subhalo correlations beyond the tidal radius are sensitive to the infall time, t_infall, of the subhalo onto its host. We perform this cross-correlation measurement using ~ 160,000 red satellite galaxies in SDSS redMaPPer clusters and find evidence that subhalo correlations do persist well beyond the tidal radius, suggesting that many of the observed satellites fell into their current host less than a dynamical time ago, t_infall < t_dyn. Combined with estimated dynamical times t_dynamical ~ 3-5 Gyr and SED fitting results for the time at which satellites stopped forming stars, t_quench ~ 6 Gyr, we infer that for a significant fraction of the satellites, star formation quenched before those satellites entered their current hosts. The result holds for red satellites over a large range of cluster-centric distances 0.1 - 0.6 Mpc/h. We discuss the implications of this result for models of galaxy formation.

Supersymmetric Theory of Stochastic ABC Model: A Numerical Study [Cross-Listing]

In this paper, we investigate numerically the stochastic ABC model, a toy model in the theory of astrophysical kinematic dynamos, within the recently proposed supersymmetric theory of stochastics (STS). STS characterises stochastic differential equations (SDEs) by the spectrum of the stochastic evolution operator (SEO) on elements of the exterior algebra or differentials forms over the system's phase space, X. STS can thereby classify SDEs as chaotic or non-chaotic by identifying the phenomenon of stochastic chaos with the spontaneously broken topological supersymmetry that all SDEs possess. We demonstrate the following three properties of the SEO, deduced previously analytically and from physical arguments: the SEO spectra for zeroth and top degree forms never break topological supersymmetry, all SDEs possesses pseudo-time-reversal symmetry, and each de Rahm cohomology class provides one supersymmetric eigenstate. Our results also suggests that the SEO spectra for forms of complementary degrees, i.e., k and dim X -k, may be isospectral.

Large-scale environmental dependence of gas-phase metallicity in dwarf galaxies

We study how the cosmic environment affects galaxy evolution in the Universe by comparing the metallicities of dwarf galaxies in voids with dwarf galaxies in more dense regions. Ratios of the fluxes of emission lines, particularly those of the forbidden [OIII] and [SII] transitions, provide estimates of a region's electron temperature and number density. From these two quantities and the emission line fluxes [OII] 3727, [OIII] 4363, and [OIII] 4959,5007, we estimate the abundance of oxygen with the Direct Te method. We estimate the metallicity of 37 void dwarf galaxies and 75 dwarf galaxies in more dense regions using spectroscopic observations from the Sloan Digital Sky Survey Data Release 7, as re-processed in the MPA-JHU value-added catalog. We find very little difference between the two sets of galaxies, indicating little influence from the large-scale environment on their chemical evolution. Of particular interest are a number of extremely metal-poor dwarf galaxies that are equally abundant in both voids and denser regions.

The Star Formation Rate Efficiency of Neutral Atomic-dominated Hydrogen Gas in the Outskirts of Star Forming Galaxies from z~1 to z~3

Current observational evidence suggests that the star formation rate (SFR) efficiency of neutral atomic hydrogen gas measured in Damped Ly-alpha Systems (DLAs) at z~3 is more than 10 times lower than predicted by the Kennicutt-Schmidt (KS) relation. To understand the origin of this deficit, and to investigate possible evolution with redshift and galaxy properties, we measure the SFR efficiency of atomic gas at z~1, z~2, and z~3 around star-forming galaxies. We use new robust photometric redshifts in the Hubble Ultra Deep Field to create galaxy stacks in these three redshift bins, and measure the SFR efficiency by combining DLA absorber statistics with the observed rest-frame UV emission in the galaxies' outskirts. We find that the SFR efficiency of HI gas at z>1 is ~1-3% of that predicted by the KS relation. Contrary to simulations and models that predict a reduced SFR efficiency with decreasing metallicity and thus with increasing redshift, we find no significant evolution in the SFR efficiency with redshift. Our analysis instead suggests that the reduced SFR efficiency is driven by the low molecular content of this atomic-dominated phase, with metallicity playing a secondary effect in regulating the conversion between atomic and molecular gas. This interpretation is supported by the similarity between the observed SFR efficiency and that observed in local atomic-dominated gas, such as in the outskirts of local spiral galaxies and local dwarf galaxies.

Are Some Milky Way Globular Clusters Hosted by Undiscovered Galaxies?

The confirmation of a globular cluster (GC) in the recently discovered ultrafaint galaxy Eridanus II (Eri II) motivated us to examine the question posed in the title. After estimating the halo mass of Eri II using a published stellar mass - halo mass relation, the one GC in this galaxy supports extending the relationship between the number of GCs hosted by a galaxy and the galaxy's total mass about two orders of magnitude in stellar mass below the previous limit. For this empirically determined specific frequency of between 0.06 and 0.39 globular clusters per 10$^9$ $M_\odot$ of total mass, the surviving Milky Way (MW) subhalos with masses smaller than $10^{10} M_\odot$ could host as many as 5 to 31 GCs, broadly consistent with the actual population of outer halo MW GCs, although matching the radial distribution in detail remains a challenge. Using a subhalo mass function from published high resolution numerical simulations and a Poissonian model for populating those halos with the aforementioned empirically constrained frequency, we find that about 90$\%$ of these GCs lie in lower-mass subhalos than that of Eri II. From what we know about the stellar mass-halo mass function, the subhalo mass function, and the mass-normalized GC specific frequency, we conclude that some of the MW's outer halo GCs are likely to be hosted by undetected subhalos with extremely modest stellar populations.

Deep imaging of Eridanus II and its lone star cluster

We present deep imaging of the most distant dwarf discovered by the Dark Energy Survey, Eridanus II (Eri II). Our Magellan/Megacam stellar photometry reaches $\sim$$3$ mag deeper than previous work, and allows us to confirm the presence of a stellar cluster whose position is consistent with Eri II's center. This makes Eri II, at $M_V=-7.1$, the least luminous galaxy known to host a (possibly central) cluster. The cluster is partially resolved, and at $M_V=-3.5$ it accounts for $\sim$$4\%$ of Eri II's luminosity. We derive updated structural parameters for Eri II, which has a half-light radius of $\sim$$280$ pc and is elongated ($\epsilon$$\sim$$0.48$), at a measured distance of $D$$\sim$$370$ kpc. The color-magnitude diagram displays a blue, extended horizontal branch, as well as a less populated red horizontal branch. The presence of the latter, together with a central concentration of stars brighter than the old main sequence turnoff, hints at a possible intermediate-age ($\sim$$3$ Gyr) population. Alternatively, these sources could be blue straggler stars. A deep Green Bank Telescope observation of Eri II reveals no associated atomic gas.

Interpreting the subtle spectral variations of the 11.2 and 12.7 {\mu}m polycyclic aromatic hydrocarbon bands

We report new properties of the 11 and 12.7 {\mu}m emission complexes of polycyclic aromatic hydrocarbons (PAHs) by applying a Gaussian-based decomposition technique. Using high-resolution \textit{Spitzer} Space Telescope data, we study in detail the spectral and spatial characteristics of the 11 and 12.7 {\mu}m emission bands in maps of reflection nebulae NGC 7023 and NGC 2023 (North and South) and the star-forming region M17. Profile variations are observed in both the 11 and 12.7 {\mu}m emission bands. We identify a neutral contribution to the traditional 11.0 {\mu}m PAH band and a cationic contribution to the traditional 11.2 {\mu}m band, the latter of which affects the PAH class of the 11.2 {\mu}m emission in our sample. The peak variations of the 12.7 {\mu}m complex are explained by the competition between two underlying blended components. The spatial distributions of these components link them to cations and neutrals. We conclude that the 12.7 {\mu}m emission originates in both neutral and cationic PAHs, lending support to the use of the 12.7/11.2 intensity ratio as a charge proxy.

Semi-implicit anisotropic cosmic ray transport on an unstructured moving mesh

In the interstellar medium of galaxies and the intracluster gas of galaxy clusters, the charged particles making up cosmic rays are moving almost exclusively along (but not across) magnetic field lines. The resulting anisotropic transport of cosmic rays in the form of diffusion or streaming not only affects the gas dynamics but also rearranges the magnetic fields themselves. The coupled dynamics of magnetic fields and cosmic rays can thus impact the formation and evolution of galaxies and the thermal evolution of galaxy clusters in critical ways. Numerically studying these effects requires solvers for anisotropic diffusion that are accurate, efficient, and robust, requirements that have proven difficult to satisfy in practice. Here, we present an anisotropic diffusion solver on an unstructured moving mesh that is conservative, does not violate the entropy condition, allows for semi-implicit time integration with individual timesteps, and only requires solving a single linear system of equations per timestep. We apply our new scheme to a large number of test problems and show that it works as well or better than previous implementations. Finally, we demonstrate for a numerically demanding simulation of the formation of an isolated disk galaxy that our local time-stepping scheme reproduces the results obtained with global time-stepping at a fraction of the computational cost.

Spatially resolved integral field spectroscopy of the ionized gas in IZw18

We present a detailed 2D study of the ionized ISM of IZw18 using new PMAS-IFU optical observations. IZw18 is a high-ionization galaxy which is among the most metal-poor starbursts in the local Universe. This makes IZw18 a local benchmark for understanding the properties most closely resembling those prevailing at distant starbursts. Our IFU-aperture (~ 1.4 kpc x 1.4 kpc) samples the entire IZw18 main body and an extended region of its ionized gas. Maps of relevant emission lines and emission line ratios show that higher-excitation gas is preferentially located close to the NW knot and thereabouts. We detect a Wolf-Rayet feature near the NW knot. We derive spatially resolved and integrated physical-chemical properties for the ionized gas in IZw18. We find no dependence between the metallicity-indicator R23 and the ionization parameter (as traced by [OIII]/[OII]) across IZw18. Over ~ 0.30 kpc^2, using the [OIII]4363 line, we compute Te[OIII] values (~ 15000 - 25000 K), and oxygen abundances are derived from the direct determinations of Te[OIII]. More than 70% of the higher-Te[OIII] (> 22000 K) spaxels are HeII4686-emitting spaxels too. From a statistical analysis, we study the presence of variations in the ISM physical-chemical properties. A galaxy-wide homogeneity, across hundreds of parsecs, is seen in O/H. Based on spaxel-by-spaxel measurements, the error-weighted mean of 12 + log(O/H) = 7.11 +/- 0.01 is taken as the representative O/H for IZw18. Aperture effects on the derivation of O/H are discussed. Using our IFU data we obtain, for the first time, the IZw18 integrated spectrum.

Massive Quiescent Cores in Orion: VI. The Internal Structures and a Candidate of Transiting Core in NGC 2024 Filament

We present a multi-wavelength observational study of the NGC 2024 filament using infrared to sub-millimeter continuum and the \nht\ $(1,1)$ and $(2,2)$ inversion transitions centered on FIR-3, the most massive core therein. FIR-3 is found to have no significant infrared point sources in the Spitzer/IRAC bands. But the \nht\ kinetic temperature map shows a peak value at the core center with $T_{\rm k}=25$ K which is significantly higher than the surrounding level ($T_{\rm k}=15-19$ K). Such internal heating signature without an infrared source suggests an ongoing core collapse possibly at a transition stage from first hydrostatic core (FHSC) to protostar. The eight dense cores in the filament have dust temperatures between 17.5 and 22 K. They are much cooler than the hot ridge ($T_{\rm d}=55$ K) around the central heating star IRS-2b. Comparison with a dust heating model suggests that the filament should have a distance of $3-5$ pc from IRS-2b. This value is much larger than the spatial extent of the hot ridge, suggesting that the filament is spatially separated from the hot region along the line of sight.

Ultraviolet Fe II Emission in Fainter Quasars: Luminosity Dependences, and the Influence of Environments

We investigate the strength of ultraviolet Fe II emission in fainter quasars compared with brighter quasars for 1.0 <= z <= 1.8, using the SDSS (Sloan Digital Sky Survey) DR7QSO catalogue and spectra of Schneider et al., and the SFQS (SDSS Faint Quasar Survey) catalogue and spectra of Jiang et al. We quantify the strength of the UV Fe II emission using the W2400 equivalent width of Weymann et al., which is defined between two rest-frame continuum windows at 2240-2255 and 2665-2695 Ang. The main results are the following. (1) We find that for W2400 >~ 25 Ang. there is a universal (i.e. for quasars in general) strengthening of W2400 with decreasing intrinsic luminosity, L3000. (2) In conjunction with previous work by Clowes et al., we find that there is a further, differential, strengthening of W2400 with decreasing L3000 for those quasars that are members of Large Quasar Groups (LQGs). (3) We find that increasingly strong W2400 tends to be associated with decreasing FWHM of the neighbouring Mg II {\lambda}2798 broad emission line. (4) We suggest that the dependence of W2400 on L3000 arises from Ly{\alpha} fluorescence. (5) We find that stronger W2400 tends to be associated with smaller virial estimates from Shen et al. of the mass of the central black hole, by a factor ~ 2 between the ultrastrong emitters and the weak. Stronger W2400 emission would correspond to smaller black holes that are still growing. The differential effect for LQG members might then arise from preferentially younger quasars in the LQG environments.

A new star-forming region in Canis Major

A new southern star-formation region, located at an estimated distance of ~1.5 kpc in the Lynds 1664 dark cloud in Canis Major, is described. Lynds 1664 contains several compact star clusters, small stellar groups, and young stars associated with reflection nebulae. Narrow-band H{\alpha} and [SII] images obtained with 4-m CTIO telescope reveal more than 20 new Herbig-Haro objects associated with several protostellar outflows.

Using deep images and simulations to trace collisional debris around massive galaxies

Deep imaging programs, such as MATLAS which has just been completed at the CFHT, allows us to study with their diffuse light the outer stellar populations around large number of galaxies. We have carried out a systematic census of their fine structures, i.e. the collisional debris from past mergers. We have identified among them stellar streams from minor mergers, tidal tails from gas-rich major mergers, plumes from gas-poor major mergers, and shells from intermediate mass mergers. Having estimated the visibility and life time of each of these structures with numerical simulations, we can reconstruct the past mass assembly of the host galaxy. Preliminary statistical results based on a sample of 360 massive nearby galaxies are presented.

On the limits of measuring the bulge and disk properties of local and high-redshift massive galaxies

A considerable fraction of the massive quiescent galaxies at \emph{z} $\approx$ 2, which are known to be much more compact than galaxies of comparable mass today, appear to have a disk. How well can we measure the bulge and disk properties of these systems? We simulate two-component model galaxies in order to systematically quantify the effects of non-homology in structures and the methods employed. We employ empirical scaling relations to produce realistic-looking local galaxies with a uniform and wide range of bulge-to-total ratios ($B/T$), and then rescale them to mimic the signal-to-noise ratios and sizes of observed galaxies at \emph{z} $\approx$ 2. This provides the most complete set of simulations to date for which we can examine the robustness of two-component decomposition of compact disk galaxies at different $B/T$. We confirm that the size of these massive, compact galaxies can be measured robustly using a single S\'{e}rsic fit. We can measure $B/T$ accurately without imposing any constraints on the light profile shape of the bulge, but, due to the small angular sizes of bulges at high redshift, their detailed properties can only be recovered for galaxies with $B/T$ \gax\ 0.2. The disk component, by contrast, can be measured with little difficulty.

Cosmological Galaxy Evolution with Superbubble Feedback II: The Limits of Supernovae

We explore when supernovae can (and cannot) regulate the star formation and bulge growth in galaxies based on a sample of 18 simulated galaxies. The simulations include key physics such as evaporation and conduction, neglected in prior work, and required to correctly model superbubbles resulting from stellar feedback. We show that for galaxies with virial masses $>10^{12}\;M_\odot$, supernovae alone cannot prevent excessive star formation. This failure occurs due to a shutdown of galactic winds, with wind mass loadings falling from $\eta\sim10$ to $\eta<1$. In more massive systems, this transfer of baryons to the circumgalactic medium falters earlier on and the galaxies diverge significantly from observed galaxy scaling relations and morphologies. The decreasing efficiency is simply due to a deepening potential well preventing gas escape. This implies that non-supernova feedback mechanisms must become dominant for galaxies with stellar masses greater than $\sim4\times10^{10}\;M_\odot$. The runaway growth of the central stellar bulge, strongly linked to black hole growth, suggests that feedback from active galactic nuclei is the probable mechanism. Below this mass, supernovae alone are able to produce a realistic stellar mass fraction, star formation history and disc morphology.

Cosmological Galaxy Evolution with Superbubble Feedback II: The Limits of Supernovae [Replacement]

We explore when supernovae can (and cannot) regulate the star formation and bulge growth in galaxies based on a sample of 18 simulated galaxies. The simulations include key physics such as evaporation and conduction, neglected in prior work, and required to correctly model superbubbles resulting from stellar feedback. We show that for galaxies with virial masses $>10^{12}\;M_\odot$, supernovae alone cannot prevent excessive star formation. This failure occurs due to a shutdown of galactic winds, with wind mass loadings falling from $\eta\sim10$ to $\eta<1$. In more massive systems, this transfer of baryons to the circumgalactic medium falters earlier on and the galaxies diverge significantly from observed galaxy scaling relations and morphologies. The decreasing efficiency is simply due to a deepening potential well preventing gas escape. This implies that non-supernova feedback mechanisms must become dominant for galaxies with stellar masses greater than $\sim4\times10^{10}\;M_\odot$. The runaway growth of the central stellar bulge, strongly linked to black hole growth, suggests that feedback from active galactic nuclei is the probable mechanism. Below this mass, supernovae alone are able to produce a realistic stellar mass fraction, star formation history and disc morphology.

Clustering, Cosmology and a New Era of Black Hole Demographics -- II. The Conditional Luminosity Functions of Type 2 and Type 1 Active Galactic Nuclei

The orientation-based unification model of active galactic nuclei (AGNs) posits that the principle difference between obscured (Type 2) and unobscured (Type 1) AGNs is the line-of-sight into the central engine. If this model is correct than there should be no difference in many of the properties of AGN host galaxies (e.g., the mass of the surrounding dark matter haloes). However, recent clustering analyses of Type 1 and Type 2 AGNs have provided some evidence for a difference in the halo mass, in conflict with the orientation-based unified model. In this work, a method to compute the Conditional Luminosity Function (CLF) of Type 2 and Type 1 AGNs is presented. The CLF allows many fundamental halo properties to be computed as a function of AGN luminosity, which we apply to the question of the host halo masses of Type 1 and 2 AGNs. By making use of the total AGN CLF, the Type 1 X-ray luminosity function, and the luminosity-dependent Type 2 AGN fraction, the CLFs of Type 1 and 2 AGNs are calculated at $z\approx 0$ and $0.9$. At both $z$, there is no statistically significant difference in the mean halo mass of Type 2 and 1 AGNs at any luminosity. There is marginal evidence that Type 1 AGNs may have larger halo masses than Type 2s, which would be consistent with an evolutionary picture where quasars are initially obscured and then subsequently reveal themselves as Type 1s. As the Type 1 lifetime is longer, the host halo will increase somewhat in mass during the Type 1 phase. The CLF technique will be a powerful way to study the properties of many AGNs subsets (e.g., radio-loud, Compton-thick) as future wide-area X-ray and optical surveys substantially increase our ability to place AGNs in their cosmological context.

Clustering, Cosmology and a New Era of Black Hole Demographics -- I. The Conditional Luminosity Function of Active Galactic Nuclei

Deep X-ray surveys have provided a comprehensive and largely unbiased view of active galactic nuclei (AGN) evolution stretching back to $z \sim 5$. However, it has been challenging to use the survey results to connect this evolution to the cosmological environment that AGNs inhabit. Exploring this connection will be crucial to understanding the triggering mechanisms of AGNs and how these processes manifest in observations at all wavelengths. In anticipation of upcoming wide-field X-ray surveys that will allow quantitative analysis of AGN environments, this paper presents a method to observationally constrain the Conditional Luminosity Function (CLF) of AGNs at a specific $z$. Once measured, the CLF allows the calculation of the AGN bias, mean dark matter halo mass, AGN lifetime, halo occupation number, and AGN correlation function -- all as a function of luminosity. The CLF can be constrained using a measurement of the X-ray luminosity function and the correlation length at different luminosities. The method is demonstrated at $z \approx 0$ and $0.9$, and clear luminosity dependence in the AGN bias and mean halo mass is predicted at both $z$, supporting the idea that there are at least two different modes of AGN triggering. In addition, the CLF predicts that $z\approx 0.9$ quasars are hosted by haloes with $M_{\mathrm{h}} \sim 10^{14}$ M$_{\odot}$. These `young cluster' environments may provide the necessary interactions between gas-rich galaxies to fuel luminous accretion. The results derived from this method will be useful to populate AGNs of different luminosities in cosmological simulations.

Galaxy-scale gravitational lens candidates from the Hyper Suprime-Cam imaging survey and the Galaxy And Mass Assembly spectroscopic survey

We present a list of galaxy-scale lens candidates including a highly probable interacting galaxy-scale lens in the Hyper Suprime-Cam (HSC) imaging survey. We combine HSC imaging with the blended-spectra catalog from the Galaxy And Mass Assembly (GAMA) survey to identify lens candidates, and use lens mass modeling to confirm the candidates. We find 46 matches between the HSC S14A_0b imaging data release and the GAMA catalog. Ten of them are probable lens systems according to their morphology and redshifts. There is one system with an interacting galaxy pair, HSC J084928+000949, that has a valid mass model. We predict the total mass enclosed by the Einstein radius of $\sim0.72$" ($\sim1.65$kpc) for this new expected lens system to be $\sim10^{10.59}M_{\odot}$. Using the photometry in the {\it grizy} bands of the HSC survey and stellar population synthesis modeling with a Salpeter stellar initial mass function, we estimate the stellar mass within the Einstein radius to be $\sim10^{10.46}\,M_{\odot}$. We thus find a dark matter mass fraction within the Einstein radius of $\sim25\%$. Further spectroscopy or high-resolution imaging would allow confirmation of the nature of these lens candidates. The particular system with the interacting galaxy pair, if confirmed, would provide an opportunity to study the interplay between dark matter and stars as galaxies build up through hierarchical mergers.

A Distant Echo of Milky Way Central Activity closes the Galaxy's Baryon Census

We report on the presence of large amounts of million-degree gas in the Milky Way's interstellar and circum-galactic medium. This gas (1) permeates both the Galactic plane and the halo, (2) extends to distances larger than 60-200 kpc from the center, and (3) its mass is sufficient to close the Galaxy's baryon census. Moreover, we show that a vast, $\sim 6$ kpc radius, spherically-symmetric central region of the Milky Way above and below the 0.16 kpc thick plane, has either been emptied of hot gas or the density of this gas within the cavity has a peculiar profile, increasing from the center up to a radius of $\sim 6$ kpc, and then decreasing with a typical halo density profile. This, and several other converging pieces of evidence, suggest that the current surface of the cavity, at 6 kpc from the Galaxy's center, traces the distant echo of a period of strong nuclear activity of our super-massive black-hole, occurred about 6 Myrs ago.

The LyA-LyC Connection: Evidence for an Enhanced Contribution of UV-faint Galaxies to Cosmic Reionization

The escape of ionizing Lyman Continuum (LyC) photons requires the existence of low-N_HI sightlines, which also promote escape of Lyman-Alpha (Lya). We use a suite of 2500 Lya Monte-Carlo radiative transfer simulations through models of dusty, clumpy interstellar (`multiphase') media from Gronke & Dijkstra (2016), and compare the escape fractions of Lya [f_esc(Lya)] and LyC radiation [f_esc(LyC)]. We find that f_esc(LyC) and f_esc(Lya) are correlated: galaxies with a low f_esc(Lya) consistently have a low f_esc(LyC), while galaxies with a high f_esc(Lya) exhibit a large dispersion in f_esc(LyC). We argue that there is increasing observational evidence that Lya escapes more easily from UV-faint galaxies. The correlation between f_esc(LyC) and f_esc(Lya) then implies that UV-faint galaxies contribute more to the ionizing background than implied by the faint-end slope of the UV-luminosity function. In multiphase gases, the ionizing escape fraction is most strongly affected by the cloud covering factor, f_cl, which implies that f_esc(LyC) is closely connected to the observed Lya spectral line shape. Specifically, LyC emitting galaxies typically having narrower, more symmetric line profiles. This prediction is qualitatively similar to that for `shell models'.

Zooming in on major mergers: dense, starbursting gas in cosmological simulations

We introduce the `Illustris zoom simulation project', which allows the study of selected galaxies forming in the $\Lambda$CDM cosmology with a 40 times better mass resolution than in the parent large-scale hydrodynamical Illustris simulation. We here focus on the starburst properties of the gas in four cosmological simulations of major mergers. The galaxies in our high-resolution zoom runs exhibit a bursty mode of star formation with gas consumption timescales 10 times shorter than for the normal star formation mode. The strong bursts are only present in the simulations with the highest resolution, hinting that a too low resolution is the reason why the original Illustris simulation showed a dearth of starburst galaxies. Very pronounced bursts of star formation occur in two out of four major mergers we study. The high star formation rates, the short gas consumption timescales and the morphology of these systems strongly resemble observed nuclear starbursts. This is the first time that a sample of major mergers is studied through self-consistent cosmological hydrodynamical simulations instead of using isolated galaxy models setup on a collision course, thereby greatly reducing the parameter freedom involved in this traditional modelling technique. We also study the orbits of the colliding galaxies and find that the starbursting gas preferentially appears in head-on mergers with very high collision velocities. Encounters with large impact parameters do typically not lead to the formation of starbursting gas.

Revisiting the Contributions of Supernova and Hypernova Remnants to the Diffuse High-Energy Backgrounds: Constraints on Very-High-Redshift Injections [Cross-Listing]

Star-forming and starburst galaxies are considered as one of the viable candidate sources of the high-energy cosmic neutrino background detected in IceCube. We revisit contributions of supernova remnants (SNRs) and hypernova remnants (HNRs) in such galaxies to the diffuse high-energy neutrino and gamma-ray backgrounds, in light of the latest Fermi data above 50GeV. We also take into account possible time dependent effects of the cosmic-ray (CR) acceleration during the SNR evolution. CRs accelerated by the SNR shocks can produce high-energy neutrinos up to $\sim100$ TeV energies, but CRs from HNRs can extend the spectrum up to PeV energies. We show that, only if HNRs are dominant over SNRs, the diffuse neutrino background above 100 TeV can be explained without contradicting the gamma-ray data. However, the neutrino data around 30 TeV remain unexplained, which might suggest a different population of gamma-ray dark CR sources. Alternatively, we consider possible contributions of Pop-III HNRs up to $z\lesssim10$, and show that they are not constrained by the gamma-ray data, and thus could contribute to the diffuse high-energy backgrounds if their explosion energy reaches ${\mathcal E}_{\rm POP-III}\sim{\rm a~few}\times10^{53}$erg. More conservatively, our results suggest that the explosion energy of POP-III HNRs is ${\mathcal E}_{\rm POP-III}\lesssim7\times{10}^{53}$erg.

The stellar metallicity gradients in galaxy discs in a cosmological scenario

The stellar metallicity gradients of disc galaxies provide information on the disc assembly, star formation processes and chemical evolution. They also might store information on dynamical processes which could affect the distribution of chemical elements in the gas-phase and the stellar components. We studied the stellar metallicity gradients of stellar discs in a cosmological simulation. We explored the dependence of the stellar metallicity gradients on stellar age and the size and mass of the stellar discs. We used galaxies selected from a cosmological hydrodynamical simulation performed including a physically-motivated Supernova feedback and chemical evolution. The metallicity profiles were estimated for stars with different ages. We confront our numerical findings with results from the CALIFA Survey. The simulated stellar discs are found to have metallicity profiles with slopes in global agreement with observations. Low stellar-mass galaxies tend to have a larger variety of metallicity slopes. When normalized by the half-mass radius, the stellar metallicity gradients do not show any dependence and the dispersion increases significantly, regardless of galaxy mass. Galaxies with stellar masses around $10^{10}$M$_{\odot}$ show steeper negative metallicity gradients. The stellar metallicity gradients correlate with the half-mass radius. However, the correlation signal is not present when they are normalized by the half-mass radius. Stellar discs with positive age gradients are detected to have negative and positive metallicity gradients, depending on the relative importance of the recent star formation activity in the central regions. The large dispersions in the metallicity gradients as a function of stellar mass could be ascribed to the effects of dynamical processes such as mergers/interactions and/or migration as well as those regulating the conversion of gas into stars. [abridged]

Globular clusters indicate ultra diffuse galaxies are dwarfs

We present an analysis of archival {\it HST/ACS} imaging in the F475W ($g_{475}$), F606W ($V_{606}$) and F814W ($I_{814}$) bands of the globular cluster (GC) system of a large (3.4 kpc effective radius) ultra-diffuse galaxy (DF17) believed located in the Coma Cluster of galaxies. We detect 11 GCs down to the 5$\sigma$ completeness limit of the imaging ($I_{814}=$27 mag). Correcting for background and our detection limits yields a total population of GCs in this galaxy of $32\pm6$ and a $V$-band specific frequency, $S_N=33\pm6$. Based on comparisons to the GC systems of Local galaxies, we show that both the absolute number and the colors of the GC system of DF17 are consistent with the GC system of a dark-matter dominated dwarf galaxy with virial mass $\sim1.0\times10^{11}$~\msun and a dark-to-stellar mass ratio, $M_{vir} / M_{ star}\sim 1300$. Based on the stellar mass-growth of the Milky Way, we show that DF17 cannot be understood as a failed Milky Way-like system, but is more similar to quenched Large Magellanic Cloud-like systems. We find that the mean color of GC population, $g_{475}-I_{814}$ = $0.91\pm0.05$ mag, coincides with the peak of the color distribution of intracluster GCs and are also similar to those of the blue GCs in the outer regions of massive galaxies. We suggest that both the intracluster GC population in Coma and the blue-peak in the GC populations of massive galaxies may be fed - at least in part - by the disrupted equivalents of systems such as DF17.

Geometric and Kinematic Structure of the Outflow/Envelope System of L1527 Revealed by Subarcsecond-resolution Observation of CS

Subarcsecond-resolution images of the rotational line emissions of CS and c-C$_3$H$_2$ obtained toward the low-mass protostar IRAS 04368$+$2557 in L1527 with the Atacama Large Millimeter/submillimeter Array are investigated to constrain the orientation of the outflow/envelope system. The distribution of CS consists of an envelope component extending from north to south and a faint butterfly-shaped outflow component. The kinematic structure of the envelope is well reproduced by a simple ballistic model of an infalling rotating envelope. Although the envelope has a nearly edge-on configuration, the inclination angle of the rotation axis from the plane of the sky is found to be 5$^\circ$, where we find that the western side of the envelope faces the observer. This configuration is opposite to the direction of the large-scale ($\sim$ 10$^4$ AU) outflow suggested previously from the $^{12}$CO ($J$=3$-$2) observation, and to the morphology of infrared reflection near the protostar ($\sim$ 200 AU). The latter discrepancy could originate from high extinction by the outflow cavity of the western side, these discrepancies or may indicate that the outflow axis is not parallel to the rotation axis of the envelope. Position-velocity diagrams show the accelerated outflow cavity wall, and its kinematic structure in the 2000 AU scale is explained by a standard parabolic model with the inclination angle derived from the analysis of the envelope. The different orientation of the outflow between the small and large scale implies a possibility of precession of the outflow axis. The shape and the velocity of the outflow in the vicinity of the protostar are compared with those of other protostars.

Using Leaked Power to Measure Intrinsic AGN Power Spectra of Red-Noise Time Series

Fluxes emitted at different wavebands from active galactic nuclei (AGNs) fluctuate at both long and short timescales. The variation can typically be characterized by a broadband power spectrum, which exhibits a red-noise process at high frequencies. The standard method of estimating power spectral density (PSD) of AGN variability is easily affected by systematic biases such as red-noise leakage and aliasing, in particular, when the observation spans a relatively short period and is gapped. Focusing on the high-frequency PSD that is strongly distorted due to red-noise leakage and usually not significantly affected by aliasing, we develop a novel and observable normalized leakage spectrum (NLS), which describes sensitively the effects of leaked red-noise power on the PSD at different temporal frequencies. Using Monte Carlo simulations, we demonstrate how an AGN underlying PSD sensitively determines the NLS when there is severe red-noise leakage and thereby how the NLS can be used to effectively constrain the underlying PSD.

Occurrence of instability through the protostellar accretion disks by landing of low-mass condensations

Low-mass condensations (LMCs) are observed inside the envelope of the collapsing molecular cloud cores. In this research, we investigate the effects of landing LMCs for occurrence of instability through the protostellar accretion disks. We consider some regions of the disk where duration of infalling and landing of the LMCs are shorter than the orbital period. In this way, we can consider the landing LMCs as density bumps and grooves in the azimuthal direction of an initial thin axisymmetric steady state self-gravitating protostellar accretion disk (nearly Keplerian). Using the linear effects of the bump quantities, we obtain a characteristic equation for growth/decay rate of bumps; we numerically solve it to find occurrence of instability. We also evaluate the minimum-growth-time-scale (MGTS) and the enhanced mass accretion rate. The results show that infalling and landing of the LMCs in the inner regions of the protostellar accretion disks can cause faster unstable modes and less enhanced accretion rates relative to the outer regions. Also, more fragmentation of landed LMCs in the azimuthal direction have less chance for instability, and then can produce more values of enhanced mass accretion rate.

 

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