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We employ several galaxy formation models, in particular, L-GALAXIES, IllustrisTNG, and EAGLE, as well as observational samples from SDSS and DESI, to investigate galactic conformity, the observed large-scale correlation between the star-formation properties of central (primary) galaxies and those of their neighbours. To analyse the models and observations uniformly, we introduce CENSAT, a new algorithm to define whether a galaxy is a central or a satellite system based on an isolation criterion. We find that the conformity signal is present, up to at least 5 Mpc from the centres of low- and intermediate-mass centrals in the latest version of L-GALAXIES (Ayromlou et al. 2021), IllustrisTNG, and EAGLE, as well as in SDSS and DESI observational samples. In comparison, the conformity signal is substantially weaker in an older version of L-GALAXIES (Henriques et al. 2020). One of the main differences between this older model and the other models is its neglect of ram-pressure stripping of the gas reservoirs of galaxies except within the boundaries of massive cluster haloes. Our observational comparisons demonstrate that this difference significantly affects the observed large-scale conformity signal. Furthermore, by examining the contribution of backsplash, fly-by, central, and satellite galaxies to the conformity signal, we show that much, but not all, of it arises from primary galaxies near massive systems. Remaining tensions between the models and observations may be solved by modifying the physical prescriptions for how feedback processes affect the distribution and kinematics of gas and the environment around galaxies out to scales of several Megaparsecs., Comment: Submitted to MNRAS

Integral field unit (IFU) spectra of face-on star-forming galaxies from the MaNGA survey are stacked in radial bins so as to reach a S/N high enough to measure emission lines and Lick indices out to 2.5-3 R_e. Two thirds of galaxies have stellar populations in the outer disks that are older, more metal poor and less dusty than in the inner disks. Recent bursts of star formation have occurred more frequently in the outer disk, but extinction-corrected Halpha equivalent widths are significantly lower at fixed D_n(4000) in these regions. I examine the properties of a subset of galaxies with the the most H$\alpha$ deficient outer disks. These regions contain young stellar populations that must have formed within the last 0.5 Gyr, but extinction-corrected Halpha values well below the values predicted for a standard Kroupa IMF. The Halpha deficient galaxies have flat D_n(4000) and Hdelta_A profiles with little radial fluctuation, indicating that star formation has occurred extremely uniformly across the entire disk. The H$\alpha$ line profiles indicate that the ionized gas kinematics is also very regular across the disk. The main clue to the origin of the Halpha deficiency is that it sets in at the same radius where the dust extinction abruptly decreases, suggesting a mode of star formation deficient in massive stars in quiescent, HI-dominated gas. Finally, I have carried out a search for galaxies with signatures of unusual Halpha kinematics and find that 15% of the sample exhibit evidence for significant ionized gas that is displaced from the systemic velocity of the disk., Comment: 16 pages, 15 figures, accepted for publication in MNRAS

With the aim of bringing substantial insight to the fundamental question of how galaxies acquire their material for star-formation, we present the first comprehensive characterisation of the galaxy connectivity (i.e. the number of small-scale filamentary streams connected to a galaxy) in relation with the cosmic environment, and a statistical exploration of the impact of connectivity on the star-formation rate at z=2. We detect kpc-scale filaments directly connected to galaxies by applying the DisPerSE filament finder to the DM density around 2942 central galaxies ($M_* > 10^{8}$ $\mathrm{M}_\odot / h$) of the TNG50-1 simulation. Our results demonstrate that galaxy connectivity spans a broad range (from 0 to 9), with more than half of the galaxies connected to two or three streams. We examine a variety of factors that could influence the connectivity finding out that it increases with mass, decreases with local density for low mass galaxies, and does not depend on local environment, estimated by the Delaunay tessellation, for high mass galaxies. We further classify galaxies according to their location in different cosmic web environments, and we highlight the influence of the large-scale structure on the number of connected streams. Our results reflect the different strengths of the cosmic tides, which can prevent the formation of coherent streams feeding the galaxies, or even disconnect the galaxy from its local web. Finally, we show that, at fixed local density, the star-formation rate (SFR) of low mass galaxies is up to $5.9\sigma$ enhanced due to connectivity. This SFR boost is even more significant ($6.3\sigma$) for galaxies embedded in cosmic filaments, where the available matter reservoirs are large. A milder impact is found for high mass galaxies, hinting at different relative efficiencies of matter inflow via small-scale streams in galaxies of different masses., Comment: published in A&A

We study the radial motions of cold, star-forming gas in the secular evolution phase of a set of 14 magnetohydrodynamical cosmological zoom-in simulations of Milky Way-mass galaxies. We study the radial transport of material within the disc plane in a series of concentric rings. For the gas in each ring at a given time we compute two quantities as a function of time and radius: 1) the radial bulk flow of the gas; and 2) the radial spread of the gas relative to the bulk flow. Averaging the data from all the halos, we find that the radial spread increases with radius in the form of a power law with strong secondary dependencies on the fraction of accreted material and the local radial velocity dispersion of the gas. We find that the bulk motion of gas is well described in the inner disc regions by a radially-independent mean inward flow speed of $-$2.4 km s$^{-1}$. The spread around this value relates to the change in angular momentum of the gas and also the amount of accreted material. These scalings from fully cosmological, MHD simulations of galaxy formation can then be used in semi-analytic models to better parameterise the radial flow of gas in discs., 17 pages, 13 figures, Accepted for publication in MNRAS

In order to study the circumgalactic medium (CGM) of galaxies we develop an automated pipeline to estimate the optical continuum of quasars and detect intervening metal absorption line systems with a matched kernel convolution technique and adaptive S/N criteria. We process $\sim$ one million quasars in the latest Data Release 16 (DR16) of the Sloan Digital Sky Survey (SDSS) and compile a large sample of $\sim$ 160,000 MgII absorbers, together with $\sim$ 70,000 FeII systems, in the redshift range $0.35, Comment: 23 pages, 20 Figures, 3 Appendices, MNRAS accepted. The MgII absorber catalogue is publicly available at https://wwwmpa.mpa-garching.mpg.de/SDSS/MgII/

We perform a comparison, object-by-object and statistically, between the Munich semi-analytical model, L-Galaxies, and the IllustrisTNG hydrodynamical simulations. By running L-Galaxies on the IllustrisTNG dark matter-only merger trees, we identify the same galaxies in the two models. This allows us to compare the stellar mass, star formation rate and gas content of galaxies, as well as the baryonic content of subhaloes and haloes in the two models. We find that both the stellar mass functions and the stellar masses of individual galaxies agree to better than $\sim0.2\,$dex. On the other hand, specific star formation rates and gas contents can differ more substantially. At $z=0$ the transition between low-mass star-forming galaxies and high-mass, quenched galaxies occurs at a stellar mass scale $\sim0.5\,$dex lower in IllustrisTNG than in L-Galaxies. IllustrisTNG also produces substantially more quenched galaxies at higher redshifts. Both models predict a halo baryon fraction close to the cosmic value for clusters, but IllustrisTNG predicts lower baryon fractions in group environments. These differences are due primarily to differences in modelling feedback from stars and supermassive black holes. The gas content and star formation rates of galaxies in and around clusters and groups differ substantially, with IllustrisTNG satellites less star-forming and less gas-rich. We show that environmental processes such as ram-pressure stripping are stronger and operate to larger distances and for a broader host mass range in IllustrisTNG. We suggest that the treatment of galaxy evolution in the semi-analytic model needs to be improved by prescriptions which capture local environmental effects more accurately., Comment: Submitted to MNRAS. The catalogue of L-Galaxies run on TNG is publicly available at https://tng-project.org/ayromlou20

We select 1076 galaxies with extinction-corrected Halpha equivalent widths too large to be explained with a Kroupa (2001) IMF, and compare these with a control sample of galaxies that is matched in stellar mass, redshift and 4000 AA break strength, but with normal Halpha equivalent widths. Our goal is to study how processes such as black hole growth and energetic feedback processes from massive stars differ between galaxies with extreme central Halpha emission and galaxies with normal young central stellar populations. The stellar mass distribution of Halpha excess galaxies is peaked at 3 \times 10^10 Msun and almost all fall well within the star-forming locus in the [OIII]/Hbeta versus [NII]/Halpha BPT disgram. Halpha excess galaxies are twice as likely to exhibit Halpha line asymmetries and 1.55 times more likely to be detected at 1 GHz in the VLA FIRST survey compared to control sample galaxies. The radio luminosity per unit stellar mass decreases with the stellar age of the system. Using stacked spectra, we demonstrate that [NeV] emission is not present in the very youngest of the radio-quiet Halpha excess galaxies with detectable Wolf-Rayet features, suggesting that black hole growth has not yet commenced in such systems. [NeV] emission is detected in Halpha excess galaxies with radio detections and the strength of the line correlates with the radio luminosity. This is the clearest indication for a possible population of black holes that may be forming in a subset of the Halpha excess population., 17 pages, 22 figures, accepted in MNRAS

We present an analysis of the origin and properties of the circum-galactic medium (CGM) in a suite of 11 cosmological zoom simulations resembling present day spiral galaxies. On average the galaxies retain about 50\% of the cosmic fraction in baryons, almost equally divided into disc (interstellar medium) gas, cool CGM gas and warm-hot CGM gas. At radii smaller than 50 kpc the CGM is dominated by recycled warm-hot gas injected from the central galaxy, while at larger radii it is dominated by cool gas accreted onto the halo. The recycled gas typically accounts for one-third of the CGM mass. We introduce the novel publicly available analysis tool \textsc{pygad} to compute ion abundances and mock absorption spectra. For Lyman-${\alpha}$ absorption we find good agreement of the simulated equivalent width (EW) distribution and observations out to large radii. Disc galaxies with quiescent assembly histories show significantly more absorption along the disc major axis. By comparing the EW and HI column densities we find that CGM Lyman-${\alpha}$ absorbers are best represented by an effective line-width $b\approx 50 - 70$ km s$^{-1}$ that increases mildly with halo mass, larger than typically assumed., Comment: 18 pages, 20 figures

We investigate the cool gas absorption in galaxy clusters by cross-correlating MgII absorbers detected in quasar spectra from Data Release 16 of the Sloan Digital Sky Survey (SDSS) with galaxy clusters identified in the Dark Energy Spectroscopic Instrument (DESI) survey. We find significant covering fractions ($1-5\, \%$ within $r_{500}$, depending on the chosen redshift interval), $\sim 4-5$ times higher than around random sightlines. While the covering fraction of cool gas in clusters decreases with increasing mass of the central galaxy, the total MgII mass within $r_{\rm 500}$ is nonetheless $\sim 10$ times higher than for SDSS luminous red galaxies (LRGs). The MgII covering fraction versus impact parameter is well described by a power law in the inner regions and a exponential function at larger distances. The characteristic scale of the transition between these two regimes is smaller for large equivalent width absorbers. Cross-correlating MgII absorption with photo-z selected cluster member galaxies from DESI reveals a statistically significant connection. The median projected distance between MgII absorbers and the nearest cluster member is $\sim200$ kpc, compared to $\sim500$ kpc in random mocks with the same galaxy density profiles. We do not find a correlation between MgII strength and the star formation rate of the closest cluster neighbour. This suggests that cool gas in clusters, as traced by MgII absorption, is: (i) associated with satellite galaxies, (ii) dominated by cold gas clouds in the intracluster medium, rather than by the interstellar medium of galaxies, and (iii) may originate in part from gas stripped from these cluster satellites in the past., Comment: 19 pages, revised version accepted for publication in MNRAS

We present, for the first time, the relationship between local stellar mass surface density, $\mathrm{\Sigma_{*}}$, and N/O derived from SDSS-IV MaNGA data, using a sample of $792765$ high signal-to-noise ratio star-forming spaxels. Using a combination of phenomenological modelling and partial correlation analysis, we find that $\mathrm{\Sigma_{*}}$ alone is insufficient to predict the N/O in MaNGA spaxels, and that there is an additional dependence on the local star formation rate surface density, $\mathrm{\Sigma_{SFR}}$. This effect is a factor of $3$ stronger than the dependence of 12+log(O/H) on $\mathrm{\Sigma_{SFR}}$. Surprisingly, we find that the local N/O scaling relations also depend on the total galaxy stellar mass at fixed $\Sigma_{*}$ as well as the galaxy size at fixed stellar mass. We find that more compact galaxies are more nitrogen rich, even when $\mathrm{\Sigma_{*}}$ and $\mathrm{\Sigma_{SFR}}$ are controlled for. We show that $\sim50\%$ of the variance of N/O is explained by the total stellar mass and size. Thus, the evolution of nitrogen in galaxies is set by more than just local effects and does not simply track the build up of oxygen in galaxies. The precise form of the N/O-O/H relation is therefore sensitive to the sample of galaxies from which it is derived. This result casts doubt on the universal applicability of nitrogen-based strong-line metallicity indicators derived in the local universe., Comment: 22 pages, 14 figures. Accepted for publication in the Astrophysical Journal

We report the discovery of two kinematically anomalous atomic hydrogen (HI) clouds in M 100 (NGC 4321), which was observed as part of the Deciphering the Interplay between the Interstellar medium, Stars, and the Circumgalactic medium (DIISC) survey in HI 21 cm at 3.3 km s$^{-1}$ spectroscopic and 44 arcsec$\times$30 arcsec spatial resolution using the Karl G. Jansky Very Large Array. These clouds were identified as structures that show significant kinematic offsets from the rotating disk of M100. The velocity offsets of 40 km s$^{-1}$ observed in these clouds are comparable to the offsets seen in intermediate-velocity clouds (IVCs) in the circumgalactic medium (CGM) of the Milky Way and nearby galaxies. We find that one anomalous cloud in M 100 is associated with star-forming regions detected in H$\alpha$ and far-ultraviolet imaging. Our investigation shows that anomalous clouds in M 100 may originate from multiple mechanisms, such as star formation feedback-driven outflows, ram-pressure stripping, and tidal interactions with satellite galaxies. Moreover, we do not detect any cool CGM at 38.8 kpc from the center of M 100, giving an upper limit of N(HI) $\le$ $1.7\times10^{13}$ cm$^{-2}$ (3$\sigma$). Since M 100 is in the Virgo cluster, the non-existence of neutral/cool CGM is a likely pathway for turning it into a red galaxy., Comment: 19 pages, 3 tables, 7 figures, Accepted for publication at ApJ

This paper describes a search for galaxy centers with clear indications of unusual stellar populations with an initial mass function flatter than Salpeter at high stellar masses. Out of a sample of 668 face-on galaxies with stellar masses in the range 10^10- 10^11 M_sol, I identify 15 galaxies with young to intermediate age central stellar populations with unusual stellar population gradients in the inner regions of the galaxy. In these galaxies, the 4000 Angstrom break is either flat or rising towards the center of the galaxy, indicating that the central regions host evolved stars, but the H$\alpha$ equivalent width also rises steeply in the central regions. The ionization parameter [OIII]/[OII] is typically low in these galactic centers, indicating that ionizing sources are stellar rather than AGN. Wolf Rayet features characteristic of hot young stars are often found in the spectra and these also get progressively stronger at smaller galactocentric radii. These outliers are compared to a control sample of galaxies of similar mass with young inner stellar populations, but where the gradients in Halpha equivalent width and 4000 Angstrom break follow each other more closely. The outliers exhibit central Wolf Rayet red bump excesses much more frequently, they have higher central stellar and ionized gas metallicities, and they are also more frequently detected at 20 cm radio wavelengths. I highlight one outlier where the ionized gas is clearly being strongly perturbed and blown out either by massive stars after they explode as supernovae, or by energy injection from matter falling onto a black hole., Comment: 16 pages, 16 figures, accepted for publication in MNRAS

We introduce a Local Background Environment (LBE) estimator that can be measured in and around every galaxy or its dark matter subhalo in high-resolution cosmological simulations. The LBE is designed to capture the influence of environmental effects such as ram-pressure stripping on the formation and evolution of galaxies in semi-analytical models. We define the LBE directly from the particle data within an adaptive spherical shell, and devise a Gaussian mixture estimator to separate background particles from previously unidentified subhalo particles. Analyzing the LBE properties, we find that the LBE of satellite galaxies is not at rest with respect to their host halo, in contrast to typical assumptions. The orientations of the velocities of a subhalo and its LBE are well aligned in the outer infall regions of haloes, but decorrelated near halo center. Significantly, there is no abrupt change in LBE velocity or density at the halo virial radius. This suggests that stripping should also happen beyond this radius. Therefore, we use the time-evolving LBE of galaxies to develop a method to better account for ram-pressure stripping within the Munich semi-analytical model, L-Galaxies. Overall, our new approach results in a significant increase in gas stripping across cosmic time. Central galaxies, as well as satellites beyond the virial radius, can lose a significant fraction of their hot halo gas. As a result, the gas fractions and star formation rates of satellite galaxies are suppressed relative to the fiducial model, although the stellar masses and global stellar mass functions are largely unchanged., Submitted to MNRAS

We have carried out a controlled comparison of the structural and kinematic properties of the circumgalactic medium (CGM) around Milky Way mass galaxies in the Illustris and IllustrisTNG simulations. Very striking differences are found. At z=0, gas column density and temperature profiles at large radii ($\sim 100$ kpc) correlate strongly with disk gas mass fraction in Illustris, but not in TNG. The neutral gas at large radii is preferentially aligned in the plane of the disk in TNG, whereas it is much more isotropic in Illustris. The vertical coherence scale of the rotationally supported gas in the CGM is linked to the gas mass fraction of the galaxy in Illustris, but not in TNG. A tracer particle analysis allows us to show how these differences can be understood as a consequence of the different sub-grid models of feedback in the two simulations. A study of spatially matched galaxies in the two simulations shows that in TNG, feedback by supernovae and AGN helps to create an extended smooth reservoir of hot gas at high redshifts, that then cools to form a thin, rotationally-supported disk at later times. In Illustris, AGN dump heat in the form of hot gas bubbles that push diffuse material at large radii out of the halo. The disk is formed by accretion of colder, recycled material, and this results in more vertically extended gas distributions above and below the Galactic plane. We conclude that variations in the structure of gas around Milky Way mass galaxies are a sensitive probe of feedback physics in simulations and are worthy of more observational consideration in future., Comment: 16 pages, 14 figures, accepted for publication in MNRAS

We study an idealized one-dimensional model for the evolution of hot gas in darkmatter haloes for redshifts z = 0, 6]. We introduce a numerical set-up incorporating cosmological accretion of gas, along with the growth of the halo, based on the Van den Bosch model for the average growth of haloes as a function of cosmic time. We evolve one-dimensional Lagrangian shells with radiative cooling of the gas and heating due to feedback from the gas cooling and moving in towards the centre. A simple Bondi accretion model on to a central black hole is used to include feedback heating. The set-up captures some of the key characteristics of spherically symmetric accretion on to the haloes: formation of virial shocks slightly outside r(200) and long-term thermal balance in the form of cooling and heating cycles. The gas density outside our initial haloes at z = 6 is constrained by requiring that the baryon fraction within the virial radius for non-radiative evolution be equal to the universal value at almost all times. The total mass in the cold phase (taken to be similar to 10(4) K) within 40 kpc is tracked as a function of the halo mass and redshift. We compare the evolution of the cold gas mass to the observed stellar mass versus halo mass relations, following which, we can constrain the feedback energy required for different halo masses and redshifts. We also compare and match the hot gas density and temperature profiles for our most massive halo to those of clusters observed upto redshift 2. Our model is thus an improvement over the semi-analytic models in which isothermal condition and rho proportional to r(-2) are assumed.

We examine the stellar haloes of the Auriga simulations, a suite of thirty cosmological magneto-hydrodynamical high-resolution simulations of Milky Way-mass galaxies performed with the moving-mesh code AREPO. We study halo global properties and radial profiles out to $\sim 150$ kpc for each individual galaxy. The Auriga haloes are diverse in their masses and density profiles; mean metallicity and metallicity gradients; ages; and shapes, reflecting the stochasticity inherent in their accretion and merger histories. A comparison with observations of nearby late-type galaxies shows very good agreement between most observed and simulated halo properties. However, Auriga haloes are typically too massive. We find a connection between population gradients and mass assembly history: galaxies with few significant progenitors have more massive haloes, possess large negative halo metallicity gradients and steeper density profiles. The number of accreted galaxies, either disrupted or under disruption, that contribute 90% of the accreted halo mass ranges from 1 to 14, with a median of 6.5, and their stellar masses span over three orders of magnitude. The observed halo mass--metallicity relation is well reproduced by Auriga and is set by the stellar mass and metallicity of the dominant satellite contributors. This relationship is found not only for the accreted component but also for the total (accreted + in-situ) stellar halo. Our results highlight the potential of observable halo properties to infer the assembly history of galaxies., Comment: Accepted to MNRAS. 30 pages, 19 figures

We present a modified version of the L-GALAXIES 2020 semi-analytic model of galaxy evolution, which includes significantly increased direct metal enrichment of the circumgalactic medium (CGM) by supernovae (SNe). These more metal-rich outflows do not require increased mass-loading factors, in contrast to some other galaxy evolution models. This modified L-GALAXIES 2020 model is able to simultaneously reproduce the gas-phase metallicity $(Z_{\rm g})$ and stellar metallicity $(Z_{*})$ radial profiles observed in nearby disc galaxies by MaNGA and MUSE, as well as the observed mass - metallicity relations for gas and stars at $z=0$ and their evolution back to $z\sim{}2-3$. A direct CGM enrichment fraction of $\sim{}90\%$ for SNe-II is preferred. We find that massive disc galaxies have slightly flatter $Z_{\rm g}$ profiles than their lower-mass counterparts in L-GALAXIES 2020, due to more efficient enrichment of their outskirts via inside-out growth and metal-rich accretion. Such a weak, positive correlation between stellar mass and $Z_{\rm g}$ profile slope is also seen in our MaNGA-DR15 sample of 571 star-forming disc galaxies. Although, below ${\rm log}(M_{*}/{\rm M}_{\odot})\sim{}10.0$ this observational result is strongly dependent on the metallicity diagnostic and morphological selection chosen. In addition, a lowered maximum SN-II progenitor mass of $25{\rm M}_{\odot}$, reflecting recent theoretical and observational estimates, can also provide a good match to observed metallicity profiles at $z=0$ in L-GALAXIES 2020. However, this model version fails to reproduce an evolution in $Z_{\rm g}$ at fixed mass over cosmic time, or the magnesium abundances observed in the intracluster medium (ICM)., Comment: 22 pages, 19 figures. Accepted by MNRAS. (Missing citation hyperlinks corrected)

We present a photometric analysis of star and star cluster (SC) formation in a high-resolution simulation of a dwarf galaxy starburst that allows the formation of individual stars to be followed. Previous work demonstrated that the properties of the SCs formed in the simulation are in good agreement with observations. In this paper, we create mock spectral energy distributions and broad-band photometric images using the radiative transfer code SKIRT 9. We test several observational star formation rate (SFR) tracers and find that $24$ $\mu$m, total infrared and H$\alpha$ trace the underlying SFR during the (post)starburst phase, while UV tracers yield a more accurate picture of star formation during quiescent phases prior to and after the merger. We then place the simulated galaxy at distances of $10$ and $50$ Mpc and use aperture photometry at Hubble Space Telescope resolution to analyse the simulated SC population. During the starburst phase, a hierarchically forming set of SCs leads inaccurate source separation because of crowding. This results in estimated SC mass function slopes that are up to $\sim0.3$ shallower than the true slope of $\sim-1.9$ to $-2$ found for the bound clusters identified from the particle data in the simulation. The masses of the largest clusters are overestimated by a factor of up to $2.9$ due to unresolved clusters within the apertures. The aperture-based analysis also produces a relation between cluster formation efficiency and SFR surface density that is slightly flatter than that recovered from bound clusters. The differences are strongest in quiescent SF environments., Comment: 21 pages, accepted for publication in MNRAS

We present a variation of the recently updated Munich semi-analytical galaxy formation model, L-Galaxies, with a new gas stripping method. Extending earlier work, we directly measure the local environmental properties of galaxies to formulate a more accurate treatment of ram-pressure stripping for all galaxies. We fully re-calibrate the modified L-Galaxies model using a Markov Chain Monte Carlo (MCMC) method with the stellar mass function and quenched fraction of galaxies at $0\leq z\leq2$ as constraints. Due to this re-calibration, global galaxy population relations, including the stellar mass function, quenched fractions versus galaxy mass and HI mass function are all largely unchanged and remain consistent with observations. By comparing to data on galaxy properties in different environments from the SDSS and HSC surveys, we demonstrate that our modified model improves the agreement with the quenched fractions and star formation rates of galaxies as a function of environment, stellar mass, and redshift. Overall, in the vicinity of haloes with total mass $10^{12}$ to $10^{15}\rm M_{\odot}$ at $z=0$, our new model produces higher quenched fractions and stronger environmental dependencies, better recovering observed trends with halocentric distance up to several virial radii. By analysing the actual amount of gas stripped from galaxies in our model, we show that those in the vicinity of massive haloes lose a large fraction of their hot halo gas before they become satellites. We demonstrate that this affects galaxy quenching both within and beyond the halo boundary. This is likely to influence the correlations between galaxies up to tens of megaparsecs., Submitted to MNRAS. The full model output and model description are publicly available at https://lgalaxiespublicrelease.github.io

Due to the fact that HI mass measurements are not available for large galaxy samples at high redshifts, we apply a photometric estimator of the HI-to-stellar mass ratio (M_HI/M_*) calibrated using a local Universe sample of galaxies to a sample of galaxies at z ~ 1 in the DEEP2 survey. We use these HI mass estimates to calculate HI mass functions (HIMFs) and cosmic HI mass densities (Omega_HI), and to examine the correlation between star formation rate and HI gas content, for galaxies at z ~ 1. We have estimated HI gas masses for ~ 7,000 galaxies in the DEEP2 survey with redshifts in the range 0.75 < z < 1.4 and stellar masses M_* > 10^{10} M_solar, using a combination of the rest-frame ultraviolet-optical colour (NUV - r) and stellar mass density (mu_*) as a way to estimate M_HI/M_*. It is found that the high mass end of high-z HI mass function (HIMF) is quite similar to that of the local HIMF. The lower limit of Omega_HI,limit = 2.1 * 10^{-4} h_70^{-1}, obtained by directly integrating the HI mass of galaxies with M_* > 10^{10} M_solar, confirms that massive star-forming galaxies do not dominate the neutral gas at z ~ 1. We study the evolution of the HI mass to stellar mass ratio from z ~ 1 to today and find a steeper relation between HI gas mass fraction and stellar mass at higher redshifts. Specifically, galaxies with M_* = 10^{11} M_solar at z ~ 1 are found to have 3 - 4 times higher neutral gas fractions than local galaxies, while the increase is as high as 4 - 12 times at M_* = 10^{10} M_solar. The quantity M_HI/SFR exhibits very large scatter, and the scatter increases from a factor of 5 - 7 at z = 0 to factors close to a hundred at z = 1. This implies that there is no relation between HI gas and star formation in high redshift galaxies. The HI gas must be linked to cosmological gas accretion processes at high redshifts., 10 pages, 13 figures, A&A accepted

We have updated the Munich galaxy formation model, L-Galaxies, to follow the radial distributions of stars and atomic and molecular gas in galaxy discs. We include an H2-based star-formation law, as well as a detailed chemical-enrichment model with explicit mass-dependent delay times for SN-II, SN-Ia and AGB stars. Information about the star formation, feedback and chemical-enrichment histories of discs is stored in 12 concentric rings. The new model retains the success of its predecessor in reproducing the observed evolution of the galaxy population, in particular, stellar mass functions and passive fractions over the redshift range 0, published in MNRAS. A full description of the model is available as MNRAS online supplementary material and at https://lgalaxiespublicrelease.github.io/. Data from the model are publicly released in SQL-queryable form and in flat files at http://www.mpa-garching.mpg.de/millennium

We explore the abundance, spatial distribution, and physical properties of the OVI, OVII, and OVIII ions of oxygen in circumgalactic and intergalactic media (the CGM, IGM, and WHIM). We use the TNG100 and TNG300 large volume cosmological magneto-hydrodynamical simulations. Modeling the ionization states of simulated oxygen, we find good agreement with observations of the low-redshift OVI column density distribution function (CDDF), and present its evolution for all three ions from z=0 to z=4. Producing mock quasar absorption line spectral surveys, we show that the IllustrisTNG simulations are fully consistent with constraints on the OVI content of the CGM from COS-Halos and other low redshift observations, producing columns as high as observed. We measure the total amount of mass and average column densities of each ion using hundreds of thousands of simulated galaxies spanning 10^11 < Mhalo/Msun < 10^15 corresponding to 10^9 < M*/Msun < 10^12 in stellar mass. Stacked radial profiles of OVI are computed in 3D number density and 2D projected column, decomposing into the 1-halo and 2-halo terms. Relating halo OVI to properties of the central galaxy, we find a correlation between the (g-r) color of a galaxy and the total amount of OVI in its CGM. In comparison to the COS-Halos finding, this leads to a dichotomy of columns around star-forming versus passive galaxies at fixed stellar (or halo) mass. We demonstrate that this correlation is a direct result of blackhole feedback associated with quenching and represents a causal consequence of galactic-scale baryonic feedback impacting the physical state of the circumgalactic medium., MNRAS. For an interactive OVI/OVIII visualization, see the 2D explorer at http://www.tng-project.org (fig 5 updated in v2)

We introduce the first two simulations of the IllustrisTNG project, a next generation of cosmological magnetohydrodynamical simulations, focusing on the optical colors of galaxies. We explore TNG100, a rerun of the original Illustris box, and TNG300, which includes 2x2500^3 resolution elements in a volume twenty times larger. Here we present first results on the galaxy color bimodality at low redshift. Accounting for the attenuation of stellar light by dust, we compare the simulated (g-r) colors of 10^9 < M*/Msun < 10^12.5 galaxies to the observed distribution from the Sloan Digital Sky Survey (SDSS). We find a striking improvement with respect to the original Illustris simulation, as well as excellent quantitative agreement in comparison to the observations, with a sharp transition in median color from blue to red at a characteristic M* ~ 10^10.5 Msun. Investigating the build-up of the color-mass plane and the formation of the red sequence, we demonstrate that the primary driver of galaxy color transition in the TNG model is supermassive blackhole feedback in its low-accretion state. Across the entire population we measure a median color transition timescale dt_green of ~1.6 Gyr, a value which drops for increasingly massive galaxies. We find signatures of the physical process of quenching: at fixed stellar mass, redder galaxies have lower SFRs, gas fractions, and gas metallicities; their stellar populations are also older and their large-scale interstellar magnetic fields weaker than in bluer galaxies. Finally, we measure the amount of stellar mass growth on the red sequence. Galaxies with M* > 10^11 Msun which redden at z, The IllustrisTNG project website is http://www.tng-project.org

We have analyzed the emission line properties of 6019 Type II AGN at redshifts between 0.4-0.8 with [OIII] luminosities greater than 3x10^8 Lsun, characteristic of the Type II quasars first identified in population studies by Zakamska et al (2003). The AGN are drawn from the CMASS sample of galaxies with stellar masses greater than 10^11 Msun that were studied as part of the Baryon Oscillation Spectroscopic Survey (BOSS) and comprise 0.5% of the total population of these galaxies. Individual spectra have low S/N, so the analysis is carried out on stacked spectra in bins of [OIII] luminosity and estimated stellar age. The emission line ratios of the stacks are well fit with simple uniform-density photoionization models with metallicities between solar and twice solar. In the stacks, a number of emission lines are found to have distinct broad components requiring a double Gaussian rather than a single Gaussian fit, indicative of outflowing ionized gas. These are: [OIII]4959, [OIII]5007, [OII]3727,3729 and Halpha$. Higher ionization lines such as [NeIII]3869 and [NeV]3345 are detected in the stacks, but are well fit by single Gaussians. The broad components typically contain a third of the total line flux and have widths of 600 km/s for the oxygen lines and 900 km/s for Halpha. The fraction of the flux in the broad component and its width are independent of [OIII] luminosity, stellar age, radio and mid-IR luminosity. The stellar mass of the galaxy is the only parameter we could identify that influences the width of the broad line component., 14 pages, 13 figures, accepted for publication in MNRAS

Using a set of 15 high-resolution magnetohydrodynamic cosmological simulations of Milky Way formation, we investigate the origin of the baryonic material found in stars at redshift zero. We find that roughly half of this material originates from subhalo/satellite systems and half is smoothly accreted from the Inter-Galactic Medium (IGM). About $90 \%$ of all material has been ejected and re-accreted in galactic winds at least once. The vast majority of smoothly accreted gas enters into a galactic fountain that extends to a median galactocentric distance of $\sim 20$ kpc with a median recycling timescale of $\sim 500$ Myr. We demonstrate that, in most cases, galactic fountains acquire angular momentum via mixing of low-angular momentum, wind-recycled gas with high-angular momentum gas in the Circum-Galactic Medium (CGM). Prograde mergers boost this activity by helping to align the disc and CGM rotation axes, whereas retrograde mergers cause the fountain to lose angular momentum. Fountain flows that promote angular momentum growth are conducive to smooth evolution on tracks quasi-parallel to the disc sequence of the stellar mass-specific angular momentum plane, whereas retrograde minor mergers, major mergers and bar-driven secular evolution move galaxies towards the bulge-sequence. Finally, we demonstrate that fountain flows act to flatten and narrow the radial metallicity gradient and metallicity dispersion of disc stars, respectively. Thus, the evolution of galactic fountains depends strongly on the cosmological merger history and is crucial for the chemo-dynamical evolution of Milky Way-sized disc galaxies., Comment: MNRAS; accepted. Changes include: clarifications and additional discussion, particularly of the fountain flow statistics shown in Fig. 7; and a resolution study that shows the results are converged for two resolution levels (~10^5 and ~10^4 Msun per baryonic element)

The quenching of star formation in satellite galaxies is observed over a wide range of dark matter halo masses and galaxy environments. In the recent Guo et al (2011) and Fu et al (2013) semi-analytic + N-body models, the gaseous environment of the satellite galaxy is governed by the properties of the dark matter subhalo in which it resides. This quantity depends of the resolution of the N-body simulation, leading to a divergent fraction of quenched satellites in high- and low-resolution simulations. Here, we incorporate an analytic model to trace the subhaloes below the resolution limit. We demonstrate that we then obtain better converged results between the Millennium I and II simulations, especially for the satellites in the massive haloes ($\rm log M_{halo}=[14,15]$). We also include a new physical model for the ram-pressure stripping of cold gas in satellite galaxies. However, we find very clear discrepancies with observed trends in quenched satellite galaxy fractions as a function of stellar mass at fixed halo mass. At fixed halo mass, the quenched fraction of satellites does not depend on stellar mass in the models, but increases strongly with mass in the data. In addition to the over-prediction of low-mass passive satellites, the models also predict too few quenched central galaxies with low stellar masses, so the problems in reproducing quenched fractions are not purely of environmental origin. Further improvements to the treatment of the gas-physical processes regulating the star formation histories of galaxies are clearly necessary to resolve these problems., 15 papes, 11 figures, accepted for publication in MNRAS

We study the narrow emission line properties and stellar populations of a sample of 1385 AGN selected to have strong excess emission at mid-infrared wavelengths based on comparing Wide-field Infrared Survey Explorer W1-W2 band colours with optical stellar absorption line indicators. Our goal is to understand whether the physical conditions in the interstellar medium of these objects differ from those of local AGN selected by their optical emission line ratios. To enable this comparison, we construct a control sample of 50,000 optically-selected AGN with the same redshifts that do not have strong mid-IR excess emission. The mid-IR excess and control samples differ strongly in [OIII] line luminosity, ionized gas excitation mechanism, ionization state and electron density. We show that the radio-detected, mid-IR excess AGN constitute the most luminous and highly ionized AGN in the local Universe and they contribute primarily to the growth of black holes in the most massive galaxies. At least half of this black hole growth is occurring in galaxies with recent starbursts. The morphologies of these systems indicate that the starbursts have probably been triggered by galaxy-galaxy mergers and interactions. The most luminous AGN in our mid-IR excess sample have properties that are similar to the Type II quasars studied at higher redshifts. In contrast, the control sample constitute a class of lower ionization, less luminous AGN in more quiescent galaxies that contribute primarily to the growth of low mass black holes., Comment: 15 pages, 17 figures, accepted for publication in MNRAS

We use a data set of nearby galaxies drawn from the HERACLES, ATLAS3D, and COLD GASS surveys to study variations in molecular gas depletion time (Tdep) in galaxy structures such as bulges, grand-design spiral arms, bars and rings. Molecular gas is traced by CO line emission and star formation rate (SFR) is derived using the combination of far-ultraviolet and mid-infrared (MIR) data. The contribution of old stars to MIR emission for the ATLAS3D sample is corrected using 2MASS K-band images. We apply a two-dimensional image decomposition algorithm to decompose galaxies into bulges and discs. Spiral arms, bars and rings are identified in the residual maps, and molecular gas depletion times are derived on a square grid of 1 kpc^2 size. In previous work, we showed that Tdep correlates strongly with specific star formation rate (sSFR). We now find that at a given sSFR, the bulge has shorter Tdep than the disc. The shift to shorter depletion times is most pronounced in the inner bulge (R < 0.1Re). Grids from galaxies with bars and rings are similar to those from galactic bulges in that they have reduced Tdep at a given sSFR. In contrast, the Tdep versus sSFR relation in the discs of galaxies with spiral arms is displaced to longer Tdep at fixed sSFR. We then show that the differences in the Tdep-sSFR relation for bulges, discs, arms, bars and rings can be linked to variations in "stellar", rather than gas surface density between different structures. Our best current predictor for Tdep, both globally and for 1 kpc grids, is given by Tdep= -0.36log(Sigma_SFR)-0.5log(Sigma_*)+5.87., 14 pages, 13 figures, revised to version accepted in MNRAS

We examine the HI kinematics of the ``Bluedisk" ensemble of 48 galaxies selected from the Sloan Digital Sky Survey and observed in HI with the Westerbork Synthesis Radio Telescope. The sample consists of 25 galaxies with a high HI mass fraction and a comparatively large control sample comprising 23 galaxies of comparable stellar mass, stellar mass surface density, redshift, and inclination. By studying the HI velocity fields of these galaxies, we investigate whether there are signatures of ongoing gas accretion: i.e. global asymmetries and indications for warping and kinematical lopsidedness. We find no enhanced kinematical asymmetries between the HI-rich sample and the control sample galaxies, indicating no significant difference in kinematical signatures such as warping and lopsidedness. Furthermore, we find no difference in position angle and systemic velocity offset with respect to the optical between both sub-samples. We therefore do not find compelling evidence for enhanced global asymmetry of the HI-excess galaxies ensemble properties in comparison to the control sample galaxies.

Based on large optical and mid-infrared (IR) surveys, we investigate the relation between nuclear activity in local Seyfert 2 galaxies and galaxy interactions using a statistical neighbour counting technique. At the same level of host galaxy star formation (SF), we find that active galactic nuclei (AGNs) with stronger [OIII] emission lines do not show an excess of near neighbours, while AGNs with stronger mid-IR emission do have more near neighbours within a projected distance of 100 kpc. The excess neighbour count increases with decreasing projected radius. These results suggest a phase of torus formation during galaxy interactions., Comment: 5 pages, 2 figures, accepted to MNRAS

We describe the sample design for the SDSS-IV MaNGA survey and present the final properties of the main samples along with important considerations for using these samples for science. Our target selection criteria were developed while simultaneously optimizing the size distribution of the MaNGA integral field units (IFUs), the IFU allocation strategy, and the target density to produce a survey defined in terms of maximizing S/N, spatial resolution, and sample size. Our selection strategy makes use of redshift limits that only depend on i-band absolute magnitude ($M_i$), or, for a small subset of our sample, $M_i$ and color (NUV-i). Such a strategy ensures that all galaxies span the same range in angular size irrespective of luminosity and are therefore covered evenly by the adopted range of IFU sizes. We define three samples: the Primary and Secondary samples are selected to have a flat number density with respect to $M_i$ and are targeted to have spectroscopic coverage to 1.5 and 2.5 effective radii (Re), respectively. The Color-Enhanced supplement increases the number of galaxies in the low-density regions of color-magnitude space by extending the redshift limits of the Primary sample in the appropriate color bins. The samples cover the stellar mass range $5\times10^8 \leq M_* \leq 3\times10^{11} M_{\odot}$ and are sampled at median physical resolutions of 1.37 kpc and 2.5 kpc for the Primary and Secondary samples respectively. We provide weights that will statistically correct for our luminosity and color-dependent selection function and IFU allocation strategy, thus correcting the observed sample to a volume limited sample., Comment: Accepted for publication in AJ

Monthly Notices of the Royal Astronomical Society, 361 (4), ISSN:0035-8711, ISSN:1365-2966, ISSN:1365-8711

We use the latest version of the metal line absorption catalogue of Zhu & M��nard (2013) to study the clustering of MgII absorbers around massive galaxies (~10^11.5 M_sun), quasars and radio-loud AGN with redshifts between 0.4 and 0.75. Clustering is evaluated in two dimensions, by binning absorbers both in projected radius and in velocity separation. Excess MgII is detected around massive galaxies out to R_p=20 Mpc. At projected radii less than 800 kpc, the excess extends out to velocity separations of 10,000 km/s. The extent of the high velocity tail within this radius is independent of the mean stellar age of the galaxy and whether or not it harbours an active galactic nucleus. We interpret our results using the publicly available Illustris and Millennium simulations. Models where the MgII absorbers trace the dark matter particle or subhalo distributions do not fit the data. They overpredict the clustering on small scales and do not reproduce the excess high velocity separation MgII absorbers seen within the virial radius of the halo. The Illustris simulations which include thermal, but not mechanical feedback from AGN, also do not provide an adequate fit to the properties of the cool halo gas within the virial radius. We propose that the large velocity separation MgII absorbers trace gas that has been pushed out of the dark matter halos, possibly by multiple episodes of AGN-driven mechanical feedback acting over long timescales., 10 pages, 11 figures, accepted in MNRAS

The physical origin of the large-scale conformity in the colours and specific star formation rates of isolated low mass central galaxies and their neighbours on scales in excess of 1 Mpc is still under debate. One possible scenario is that gas is heated over large scales by feedback from active galactic nuclei (AGN), leading to coherent modulation of cooling and star formation between well-separated galaxies. In this Letter, the metal line absorption catalogue of Zhu & Menard (2013) is used to probe gas out to large projected radii around a sample of a million galaxies with stellar masses ~10^{10} M_{sun} and photometric redshifts in the range 0.4, Comment: 5 pages, accepted in MNRAS Letters

The goal of this paper is to investigate the physical nature of galaxies in the redshift range $0.02, Comment: 12 pages, 15 figures, accepted in MNRAS

We have used 4000 u break and HA indices in combination with SFR/M∗ derived from emission line flux measurements, to constrain the recent star formation histories of galaxies with stellar masses in the range 10 8 − 10 10 M⊙. The fraction of the total SFR density in galaxies with ongoing bursts is a strong function of stellar mass, de- clining from 0.85 at a stellar mass of 10 8 M⊙ to 0.25 for galaxies with M∗ ∼ 10 10 M⊙. Low mass galaxies are not all young. The distribution of half mass formation times for galaxies with stellar masses less than 10 9 M⊙ is broad, spanning the range 1-10 Gyr. The peak-to-trough variation in star formation rate among the bursting population ranges lies in the range 10-25. In low mass galaxies, the average duration of the burst bursts is comparable to the dynamical time of the galaxy. Galaxy structure is corre- lated with estimated burst mass fraction, but in different ways in low and high mass galaxies. High mass galaxies with large burst mass fractions are more centrally concen- trated, indicating that bulge formation is at work. In low mass galaxies, stellar surface densities µ∗ decrease as a function of Fburst. These results are in good agreement with the observational predictions of Teyssier et al (2013) and lend further credence to the idea that the cuspy halo problem can be solved by energy input from multiple star- bursts over the lifetime of the galaxy. We note that there is no compelling evidence for IMF variations in the population of star-forming galaxies in the local Universe.

We introduce the "Bluedisk" project, a large program at the Westerbork Synthesis Radio Telescope (WSRT) that has mapped the HI in a sample of 23 nearby galaxies with unusually high HI mass fractions, along with a similar-sized sample of control galaxies matched in stellar mass, size, inclination and redshift. This paper presents the sample selection, observational set-up, data reduction strategy, and a first analysis of the sizes and structural properties of the HI disks. We find that the HI-rich galaxies lie on the same HI mass versus HI size relation as normal spiral galaxies, extending it to total HI masses of $2 \times 10^{10} M_{\odot}$ and radii R1 of $\sim 100$ kpc (where R1 is defined as the radius where the HI column density reaches 1 $M_{\odot}$ pc$^{-2}$). HI-rich galaxies have significantly larger values of HI-to-optical size ratio at fixed stellar mass, concentration index, stellar and star formation rate surface density compared to the control sample. The disks of HI-rich galaxies are also significantly more clumpy (i.e. have higher HI Gini and $\Delta$Area coefficient) than those of normal spirals. There is no evidence that the disks of HI-rich galaxies are more disturbed: HI-rich galaxies exhibit no difference with respect to control samples in their distributions of HI asymmetry indices or optical/HI disk position angle differences. In fact, the center of the HI distribution corresponds more closely with the center of the optical light in the HI-rich galaxies than in the controls. All these results argue against a scenario in which new gas has been brought in by mergers. It is possible that they may be more consistent with cooling from a surrounding quasi-static halo of warm/hot gas., Comment: 26 pages, 14 figures. Submitted to MNRAS

We use long-slit spectroscopy from Moran et al. to study the radial dependence of the recent star formation histories of nearby galaxies with stellar masses greater than 10^10M_sun. We fit stellar population models to the combination of SSFR, D4000 and Hdelta_A and show that many galaxies have Balmer absorption line equivalent widths that require recent short-lived episodes or bursts of star formation. The fraction of galaxies that have experienced episodic rather than continuous star formation is highest for late-type galaxies with low stellar masses. In these systems, bursts occur both in the inner and outer regions of the galaxy. The fraction of stars formed in a single burst episode is typically around 15% of the total stellar mass in the inner regions of the galaxy and around 5% of the mass in the outer regions. When we average over the population, we find that such bursts contribute around a half of the total mass in stars formed in the last 2 Gyr. In massive galaxies, bursts occur predominantly in the outer disk. Around a third of all massive, bulge-dominated galaxies have experienced recent star formation episodes that are fully confined to their outer (R > 0.7R_90) regions. The fraction of stars formed in a single episode is only 2 - 3 % of the underlying stellar mass, but such bursts contribute nearly all the stellar mass formed in the last 2 Gyr. Recent star formation in outer disks is strongly correlated with the global atomic gas fraction of the galaxy, but not its global molecular gas fraction. We suggest that outer episodic star formation is triggered by gas accretion events., title modified, colors of bar plot changed, typos corrected, published in MNRAS

The observed correlation between star-formation in central galaxies and in their neighbours (a phenomenon dubbed galactic conformity) is in need of a convincing physical explanation. We use a volume-limited sample of galaxies with redshifts less than 0.03 drawn from the SDSS DR7 to investigate the scale dependence of the effect and how it changes as a function of the mass of the central galaxy. Conformity extends over a central galaxy stellar mass range spanning two orders of magnitude. In central galaxies with masses less than 10^10 M_sun, conformity extends out to scales in excess of 4 Mpc, well beyond the virial radii of their dark matter halos. For low mass central galaxies, large-scale conformity with neighbours is only seen when the centrals have low star formation rate or gas content. In contrast, at high stellar masses, conformity with neighbours applies in the gas-rich regime and is clearly confined to scales comparable to the virial radius of the dark matter halo of the central galaxy. Our analysis of a mock catalogue from the Guo et al (2011) models shows that conformity-like effects are much weaker than observed, and apply only to the low SFR/M* tail of neighbouring galaxies. In the models, the median and the upper percentiles of the SFR/M* distribution remain almost unchanged, which is in contradiction with the data. Conformity between low-mass, gas-poor central galaxies and their distant neighbours cannot be explained within the framework of halo occupation distribution (HOD) models. It is likely a signature of pre-heating of the intergalactic gas at an earlier epoch. The smaller-scale conformity between high-mass, gas-rich central galaxies and their close neighbours may be a signature of ongoing gas accretion onto central galaxies in a minority of massive dark matter halos., 12 pages, 12 figures, submitted to MNRAS

Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) is an optical fiber-bundle integral-field unit (IFU) spectroscopic survey that is one of three core programs in the fourth-generation Sloan Digital Sky Survey (SDSS-IV). With a spectral coverage of 3622 - 10,354 Angstroms and an average footprint of ~ 500 arcsec^2 per IFU the scientific data products derived from MaNGA will permit exploration of the internal structure of a statistically large sample of 10,000 low redshift galaxies in unprecedented detail. Comprising 174 individually pluggable science and calibration IFUs with a near-constant data stream, MaNGA is expected to obtain ~ 100 million raw-frame spectra and ~ 10 million reduced galaxy spectra over the six-year lifetime of the survey. In this contribution, we describe the MaNGA Data Reduction Pipeline (DRP) algorithms and centralized metadata framework that produces sky-subtracted, spectrophotometrically calibrated spectra and rectified 3-D data cubes that combine individual dithered observations. For the 1390 galaxy data cubes released in Summer 2016 as part of SDSS-IV Data Release 13 (DR13), we demonstrate that the MaNGA data have nearly Poisson-limited sky subtraction shortward of ~ 8500 Angstroms and reach a typical 10-sigma limiting continuum surface brightness mu = 23.5 AB/arcsec^2 in a five arcsec diameter aperture in the g band. The wavelength calibration of the MaNGA data is accurate to 5 km/s rms, with a median spatial resolution of 2.54 arcsec FWHM (1.8 kpc at the median redshift of 0.037) and a median spectral resolution of sigma = 72 km/s., Comment: 37 pages, 22 figures. Accepted for publication in AJ. v2 updates arXiv reference to Yan+16b, v3 fixes some embedded DR13 links. Version with full resolution figures is available at http://www.stsci.edu/~dlaw/Papers/MaNGA_Data.pdf

We analyze the properties of the circumgalactic gas (CGM) around 120 galaxies with stellar and dark matter halo masses similar to that of the Milky Way. We focus on the morphology and kinematics of the neutral hydrogen and how this depends on f_g, the ratio of gas-to-stellar mass within the optical radius. In gas-rich galaxies with f_g > 0.1, gas temperatures rise slowly from center of the halo out to the virial radius and average neutral gas column densities remain above 10^19 atoms cm^-2 out to radii of 50-70 kpc. In gas-poor galaxies with f_g < 0.1, gas temperatures rise quickly outside the edge of the disk to 10^6 K, and then remain fixed out to radii of 100 kpc. The column density of neutral gas quickly drops below 10^19 atoms cm^-2 at radii of 10 kpc. Neutral gas distributions are also more asymmetric in gas-poor galaxies. Most of the differences between gas-poor and gas-rich galaxies in the Illustris simulation can be attributed to the effects of "radio-mode" AGN feedback. In the Illustris simulation, the circumgalactic gas is found to rotate coherently about the center of the galaxy with a maximum rotational velocity of around 200 km/s. In gas-rich galaxies, the average coherence length of the rotating gas is 40 kpc, compared to 10 kpc in gas-poor galaxies. In the very most gas-rich systems, the CGM can rotate coherently over scales of 70-100 kpc. We discuss our results in the context of recent observations of the CGM in low mass galaxies via UV absorption-line spectroscopy and deep 21cm observations of edge-on spiral galaxies., 16 pages, 16 figures, accepted for publication in MNRAS

We have combined the semi-analytic galaxy formation model of Guo et al. (2011) with a novel particle-tagging technique to predict galaxy surface brightness profiles in a representative sample of ~1900 massive dark matter haloes (1012–1014 M⊙) from the Millennium II ΛCDM N body simulation. We focus on the outer regions of galaxies and stars accreted in mergers. Our simulations cover scales from the stellar haloes of Milky Way-like galaxies to the ‘cD envelopes’ of groups and clusters, and resolve low surface brightness substructure such as the tidal streams of dwarf galaxies. We find that the spatial distribution of stars in low surface brightness regions is tightly correlated with DM halo mass and that collisionless merging during the hierarchical assembly of galaxies largely determines the structure of spheroidal stellar components. Our ΛCDM model agrees well with the available data.

We study relationships between the stellar populations and interstellar medium in massive galaxies using the Galex Arecibo SDSS Survey (GASS). The sample consists of HI-observations (~1000 galaxies) and complementary H2-observations (330 galaxies) and long-slit spectroscopy (230 galaxies). Luminosity-weighted stellar population ages, metallicitites and element abundance ratios, are derived by fitting stellar population models of absorption line indices. We find that the ages correlate more strongly with molecular gas fraction (MH2/M*) than with neutral Hydrogen fraction (MHI/M*). This result strengthens the theory that H2 is a better tracer of star-formation than HI. The sample is dominated by negative metallicity-gradients and flat Mg/Fe-gradients. Galaxies with high MH2/M*-ratios show in general flat or weakly negative age-gradients. For low MH2/M*-ratios the age-gradients are overall negative. These results are in agreement with the inside-out galaxy formation scenario. For galaxies with high r90/r50-ratios, a sub-population show positive age-gradients indicating additional formation channels. Furthermore, for galaxies with high MH2/M*-ratios more massive systems have older stellar populations in their centers, suggesting downsizing within the inside-out formation scenario.

We examine how the atomic and molecular gas components of galaxies evolve to higher redshifts using the semi-analytic galaxy formation models of Fu et al. (2010) in which we track the surface density profiles of gas in disks. We adopt two different prescriptions based either on gas surface density and metallicity, or on interstellar pressure, to compute the molecular fraction as a function of radius in each disk. We demonstrate that the adopted star formation law determines how the {\em balance} between gas, stars and metals changes with time in the star-forming galaxy population, but does not influence the total mass in stars formed into galaxies at redshifts below $z\sim 2.5$. The redshift evolution of the mass-metallicity relation places strong constraints on the timescale over which cold gas is converted into stars in high redshift galaxies, and favours models where this remains constant at values around 1-2 Gyr. Future observations of the evolution of the average molecular-to-atomic gas ratio in galaxies as a function of stellar mass and redshift will constrain models of the atomic-to-molecular transition.

We introduce a new photometric estimator of the HI mass fraction (M_HI/M_*) in local galaxies, which is a linear combination of four parameters: stellar mass, stellar surface mass density, NUV-r colour, and g-i colour gradient. It is calibrated using samples of nearby galaxies (0.025

We analyze the role of bars in the build-up of central mass concentrations in massive, disk galaxies. Our parent sample consists of 3757 face-on disk galaxies with redshifts between 0.01 and 0.05, selected from the seventh Data Release of the Sloan Digital Sky Survey. 1555 galaxies with bars are identified using position angle and ellipticity profiles of the $i$-band light. We compare the ratio of the specific star formation rate measured in the 1-3 kpc central region of the galaxy to that measured for the whole galaxy. Galaxies with strong bars have centrally enhanced star formation; the degree of enhancement depends primarily on the ellipticity of the bar, and not on the size of the bar or on the mass or structure of the host galaxy. The fraction of galaxies with strong bars is highest at stellar masses greater than $3 \times 10^{10} M_{\odot}$, stellar surface densities less than $3 \times 10^8 M_{\odot}$ and concentration indices less than 2.5. In this region of parameter space, galaxies with strong bars either have enhanced central star formation rates, or star formation that is {\em suppressed} compared to the mean. This suggests that bars may play a role in the eventual quenching of star formation in galaxies. Only 50% of galaxies with strongly concentrated star formation have strong bars, indicating that other processes such as galaxy interactions also induce central star-bursts. We also find that the ratio of the size of the bar to that of the disk depends mainly on the colour of the galaxy, suggesting that the growth and destruction of bars are regulated by gas accretion, as suggested by simulations.

We compare the semi-analytic models of galaxy formation of Fu et al. (2010), which track the evolution of the radial profiles of atomic and molecular gas in galaxies, with gas fraction scaling relations derived from the COLD GASS survey (Saintonge et al 2011). The models provide a good description of how condensed baryons in galaxies with gas are partitioned into stars, atomic and molecular gas as a function of galaxy stellar mass and surface density. The models do not reproduce the tight observed relation between stellar surface density and bulge-to-disk ratio for this population. We then turn to an analysis of the"quenched" population of galaxies without detectable cold gas. The current implementation of radio-mode feedback in the models disagrees strongly with the data. In the models, gas cooling shuts down in nearly all galaxies in dark matter halos above a mass of 10**12 M_sun. As a result, stellar mass is the observable that best predicts whether a galaxy has little or no neutral gas. In contrast, our data show that quenching is largely independent of stellar mass. Instead, there are clear thresholds in bulge-to-disk ratio and in stellar surface density that demarcate the location of quenched galaxies. We propose that processes associated with bulge formation play a key role in depleting the neutral gas in galaxies and that further gas accretion is suppressed following the formation of the bulge, even in dark matter halos of low mass.

We study relations between stellar mass, star formation and gas-phase metallicity in a sample of 177,071 unique emission line galaxies from the SDSS-DR7, as well as in a sample of 43,767 star forming galaxies at z=0 from the cosmological semi-analytic model L-GALAXIES. We demonstrate that metallicity is dependent on star formation rate at fixed mass, but that the trend is opposite for low and for high mass galaxies. Low-mass galaxies that are actively forming stars are more metal-poor than quiescent low-mass galaxies. High-mass galaxies, on the other hand, have lower gas-phase metallicities if their star formation rates are small. Remarkably, the same trends are found for our sample of model galaxies. We find that massive model galaxies with low gas-phase metallicities have undergone a gas-rich merger in the past, inducing a starburst which exhausted their cold gas reservoirs and shut down star formation. This led to a gradual dilution in the gas-phase metallicities of these systems via accretion of gas. These model galaxies have lower-than-average gas-to-stellar mass ratios and higher-than-average central black hole masses. We confirm that massive galaxies with low gas-phase metallicities in our observational sample also have very massive black holes. We propose that accretion may therefore play a significant role in regulating the gas-phase metallicities of present-day massive galaxies.