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Asymmetry in the spatially integrated, 1D H  i global profiles of galaxies can inform us on both internal (e.g. outflows) and external (e.g. mergers, tidal interactions, and ram pressure stripping) processes that shape galaxy evolution. Understanding which of these primarily drive H  i profile asymmetry is of particular interest. In the lead-up to SKA pathfinder and SKA H  i emission surveys, hydrodynamical simulations have proved to be a useful resource for such studies. Here, we present the methodology behind, as well as first results, of ASymba: Asymmetries in H  i of Simba galaxies, the first time this simulation suite has been used for this type of study. We generate mock observations of the H  i content of these galaxies and calculate the profile asymmetries using three different methods. We find that |$M_{\rm H\, {\small I}}$| has the strongest correlation with all asymmetry measures, with weaker correlations also found with the number of mergers a galaxy has undergone, and gas and galaxy rotation. We also find good agreement with the xGASS sample, in which galaxies with highly asymmetric profiles tend to have lower H  i gas fractions than galaxies with symmetric profiles, and additionally find the same holds in sSFR parameter space. For low H  i mass galaxies, it is difficult to distinguish between asymmetric and symmetric galaxies, but this becomes achievable in the high H  i mass population. These results showcase the potential of ASymba and provide the groundwork for further studies, including comparison to upcoming large H  i emission surveys. [ABSTRACT FROM AUTHOR]

Recent high-resolution interferometric images of submillimetre galaxies (SMGs) reveal fascinatingly complex morphologies. This raises a number of questions: how does the relative orientation of a galaxy affect its observed submillimetre emission, and does this result in an 'orientation bias' in the selection and analysis of such galaxies in flux-limited cosmological surveys? We investigated these questions using the simba cosmological simulation paired with the dust radiative transfer code powderday. We selected eight simulated SMGs (S 850 ≳ 2 mJy) at z  = 2, and measured the variance of their 'observed' emission over 50 random orientations. Each galaxy exhibits significant scatter in its emission close to the peak of the thermal dust emission, with variation in flux density of up to a factor of 2.7. This results in an appreciable dispersion in the inferred dust temperatures and infrared luminosities (16th–84th percentile ranges of 5 K and 0.1 dex, respectively) and therefore a fundamental uncertainty in derived parameters such as dust mass and star formation rate (∼30 per cent for the latter using simple calibrations). Using a Monte Carlo simulation we also assessed the impact of orientation on flux-limited surveys, finding a bias in the selection of SMGs towards those with face-on orientations, as well as those at lower redshifts. We predict that the orientation bias will affect flux-limited single-dish surveys, most significantly at THz frequencies, and this bias should be taken into account when placing the results of targeted follow-up studies in a statistical context. [ABSTRACT FROM AUTHOR]

We investigate the Baryonic Tully–Fisher relation (BTFR) in the |$(100\, h^{-1}{\rm Mpc})^3$| simba hydrodynamical galaxy formation simulation together with a higher resolution |$(25\, h^{-1}{\rm Mpc})^3$| simba run, for over 10 000 disc-dominated, H  i -rich galaxies. We generate simulated galaxy rotation curves from the mass distribution, which we show yields similar results to using the gas rotational velocities. From this, we measure the galaxy rotation velocity V circ using four metrics: |$V_{\rm max}, V_{\rm flat}, V_{2R_e},$| and V polyex. We compare the predicted BTFR to the SPARC observational sample and find broad agreement. In detail, however, simba is biased towards higher V circ by up to 0.1 dex. We find evidence for the flattening of the BTFR in V circ > 300  km s−1 galaxies, in agreement with recent observational findings. simba 's rotation curves are more peaked for lower mass galaxies, in contrast with observations, suggesting overly bulge-dominated dwarf galaxies in our sample. We investigate for residuals around the BTFR versus H  i mass, stellar mass, gas fraction, and specific star formation rate, which provide testable predictions for upcoming BTFR surveys. simba 's BTFR shows sub-optimal resolution mass convergence, with the higher resolution run lowering V in better agreement with data. [ABSTRACT FROM AUTHOR]

We present a Bayesian full-spectral-fitting analysis of 75 massive (⁠|$M_* \gt 10^{10.3} \, \mathrm{M_\odot }$|⁠) UVJ-selected galaxies at redshifts of 1.0 < z < 1.3, combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with multiwavelength photometry. By the use of a sophisticated physical plus systematic uncertainties model, constructed within the bagpipes code, we place strong constraints on the star-formation histories (SFHs) of individual objects. We first constrain the stellar mass versus stellar age relationship, finding a steep trend towards earlier average formation time with increasing stellar mass (downsizing) of |$1.48^{+0.34}_{-0.39}$| Gyr per decade in mass, although this shows signs of flattening at |$M_* \gt 10^{11} \, \mathrm{M_\odot }$|⁠. We show that this is consistent with other spectroscopic studies from 0 < z < 2. This relationship places strong constraints on the AGN-feedback models used in cosmological simulations. We demonstrate that, although the relationships predicted by simba and illustristng agree well with observations at z = 0.1, they are too shallow at z = 1, predicting an evolution of ≲0.5 Gyr per decade in mass. Secondly, we consider the connections between green-valley, post-starburst, and quiescent galaxies, using our inferred SFH shapes and the distributions of galaxy physical properties on the UVJ diagram. The majority of our lowest-mass galaxies (⁠|$M_* \sim 10^{10.5} \, \mathrm{M_\odot }$|⁠) are consistent with formation in recent (z < 2), intense starburst events, with time-scales of ≲500 Myr. A second class of objects experience extended star-formation epochs before rapidly quenching, passing through both green-valley and post-starburst phases. The most massive galaxies in our sample are extreme systems: already old by z = 1, they formed at z ∼ 5 and quenched by z = 3. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity. [ABSTRACT FROM AUTHOR]

We present the results of a study utilizing ultradeep, rest-frame UV, spectroscopy to quantify the relationship between stellar mass and stellar metallicity for 681 star-forming galaxies at 2.5 < z < 5.0 (〈 z 〉 = 3.5 ± 0.6) drawn from the VANDELS survey. Via a comparison with high-resolution stellar population synthesis models, we determine stellar metallicities (Z ∗, here a proxy for the iron abundance) for a set of high signal-to-noise ratio composite spectra formed from subsamples selected by mass and redshift. Across the stellar mass range |$8.5\,\, \lt\,\, \mathrm{log}(\langle M_{\ast } \rangle /\rm {M}_{\odot })\,\, \lt\,\, 10.2$|⁠ , we find a strong correlation between stellar metallicity (Z ∗/Z⊙) and stellar mass, with stellar metallicity monotonically increasing from Z ∗/Z⊙ < 0.09 at |$\langle M_{\ast } \rangle = 3.2 \times 10^{8}\, \rm {M}_{\odot }$| to Z ∗/Z⊙ = 0.27 at |$\langle M_{\ast } \rangle = 1.7 \times 10^{10}\, \rm {M}_{\odot }$|⁠. In contrast, at a given stellar mass, we find no evidence for significant metallicity evolution across the redshift range of our sample. However, comparing our results to the z  = 0 stellar mass–metallicity relation for star-forming galaxies, we find that the 〈 z 〉 = 3.5 relation is consistent with being shifted to lower metallicities by ≃0.6 dex at all stellar masses. Contrasting our derived stellar metallicities with estimates of the gas-phase metallicities of galaxies at similar redshifts and stellar masses, we find evidence for enhanced |$\rm {O}/\rm {Fe}$| ratios in z  ≳ 2.5 star-forming galaxies of the order (O/Fe) ≳ 1.8 × (O/Fe)⊙. Finally, by comparing our results to the predictions of three cosmological simulations, we find that the 〈 z 〉 = 3.5 stellar mass–metallicity relation is consistent with current predictions for how outflow strength scales with galaxy stellar mass. This conclusion is supported by an analysis of one-zone analytic chemical evolution models, and suggests that the mass-loading parameter (⁠|$\eta =\dot{M}_{\mathrm{outflow}}/M_{\ast }$|⁠) scales as |$\eta \propto M_{\ast }^{\beta }$| with β ≃ −0.4. [ABSTRACT FROM AUTHOR]

We present Herschel PACS observations of the [C II] 158 μm emission line in a sample of 24 intermediate mass (9 < logM*/M☉ < 10) and low metallicity (0.4 < Z/Z☉ < 1.0) galaxies from the xCOLD GASS survey. In combination with IRAM CO(1-0) measurements, we establish scaling relations between integrated and molecular region L[C II]/LCO(1-0) ratios as a function of integrated galaxy properties. A Bayesian analysis reveals that only two parameters, metallicity and offset from the main sequence, Δ(MS), are needed to quantify variations in the luminosity ratio; metallicity describes the total dust content available to shield CO from UV radiation, while Δ(MS) describes the strength of this radiation field. We connect the L[C II]/LCO(1-0) ratio to the CO-to-H2 conversion factor and find a multivariate conversion function, which can be used up to z ~ 2.5. This function depends primarily on metallicity, with a second-order dependence on Δ(MS). We apply this to the full xCOLD GASS and PHIBSS1 surveys and investigate molecular gas scaling relations. We find a flattening of the relation between gas mass fraction and stellar mass at logM* < 10.0. While the molecular gas depletion time varies with sSFR, it is mostly independent of mass, indicating that the low LCO/SFR ratios long observed in low-mass galaxies are entirely due to photodissociation of CO and not to an enhanced star formation efficiency. [ABSTRACT FROM AUTHOR]

The Spitzer Extended Deep Survey (SEDS) is a very deep infrared survey within five well-known extragalactic science fields: the UKIDSS Ultra-Deep Survey, the Extended Chandra Deep Field South, COSMOS, the Hubble Deep Field North, and the Extended Groth Strip. SEDS covers a total area of 1.46 deg2 to a depth of 26 AB mag (3σ) in both of the warm Infrared Array Camera (IRAC) bands at 3.6 and 4.5μm. Because of its uniform depth of coverage in so many widely-separated fields, SEDS is subject to roughly 25% smaller errors due to cosmic variance than a single-field survey of the same size. SEDS was designed to detect and characterize galaxies from intermediate to high redshifts (z = 2–7) with a built-in means of assessing the impact of cosmic variance on the individual fields. Because the full SEDS depth was accumulated in at least three separate visits to each field, typically with six-month intervals between visits, SEDS also furnishes an opportunity to assess the infrared variability of faint objects. This paper describes the SEDS survey design, processing, and publicly-available data products. Deep IRAC counts for the more than 300,000 galaxies detected by SEDS are consistent with models based on known galaxy populations. Discrete IRAC sources contribute 5.6 ± 1.0 and 4.4 ± 0.8 nW m−2 sr−1 at 3.6 and 4.5μm to the diffuse cosmic infrared background (CIB). IRAC sources cannot contribute more than half of the total CIB flux estimated from DIRBE data. Barring an unexpected error in the DIRBE flux estimates, half the CIB flux must therefore come from a diffuse component. [ABSTRACT FROM AUTHOR]

ABSTRACT We examine the cosmic growth of the red sequence in a cosmological hydrodynamic simulation that includes a heuristic prescription for quenching star formation that yields a realistic passive galaxy population today. In this prescription, haloes dominated by hot gas are continually heated to prevent their coronae from fuelling new star formation. Hot coronae primarily form in haloes above ∼1012 M⊙, so that galaxies with stellar masses ∼1010.5 M⊙ are the first to be quenched and move on to the red sequence at z > 2. The red sequence is concurrently populated at low masses by satellite galaxies in large haloes that are starved of new fuel, resulting in a dip in passive galaxy number densities around ∼1010 M⊙. Stellar mass growth continues for galaxies even after joining the red sequence, primarily through minor mergers with a typical mass ratio ∼1:5. For the most massive systems, the size growth implied by the distribution of merger mass ratios is typically approximately two times the corresponding mass growth, consistent with observations. This model reproduces mass-density and colour-density trends in the local Universe, with essentially no evolution to z = 1, with the hint that such relations may be washed out by z ∼ 2. Simulated galaxies are increasingly likely to be red at high masses or high local overdensities. In our model, the presence of surrounding hot gas drives the trends with both mass and environment. [ABSTRACT FROM AUTHOR]

ABSTRACT We present 2D, integral field spectroscopy covering the rest-frame wavelengths of strong optical emission lines in nine submillimetre luminous galaxies (SMGs) at 2.0 < z < 2.7. The Gemini-North/Near-Infrared Integral Field Spectrograph (NIFS) and Very Large Telescope (VLT) Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) imaging spectroscopy allow the mapping of the gas morphologies and dynamics within the sources, and we measure an average Hα velocity dispersion of 〈σ〉 = 220 ± 80 km s−1 and an average half-light radius of 〈 r1/2〉 = 3.7 ± 0.8 kpc. The dynamical measure, 〈 Vobs/2σ〉 = 0.9 ± 0.1, for the SMGs is higher than in more quiescent star-forming galaxies at the same redshift, highlighting a difference in the dynamics of the two populations. The far-infrared star formation rates (SFRs) of the SMGs, measured using Herschel-SPIRE† far-infrared photometry, are on average 370 ± 90 M⊙ yr−1, which is ∼2 times higher than the extinction-corrected SFRs of the more quiescent star-forming galaxies. Six of the SMGs in our sample show strong evidence for kinematically distinct multiple components with average velocity offsets of 200 ± 100 km s−1 and average projected spatial offsets of 8 ± 2 kpc, which we attribute to systems in the early stages of major mergers. Indeed, all SMGs are classified as mergers from a kinemetry analysis of the velocity and dispersion field asymmetry. We bring together our sample with the seven other SMGs with integral field unit observations to describe the ionized gas morphologies and kinematics in a sample of 16 SMGs. By comparing the velocity and spatial offsets of the SMG Hα components with subhalo offsets in the Millennium Simulation data base, we infer an average halo mass for SMGs in the range of 13 < log ( M[ h−1 M⊙]) < 14. Finally, we explore the relationship between the velocity dispersion and star formation intensity within the SMGs, finding that the gas motions are consistent with the Kennicutt-Schmidt law and a range of extinction corrections, although they might also be driven by the tidal torques from merging or even the star formation itself. [ABSTRACT FROM AUTHOR]

In this investigation, we quantify the metallicities of low-mass galaxies by constructing the most comprehensive census to date. We use galaxies from the Sloan Digital Sky Survey (SDSS) and DEEP2 survey and estimate metallicities from their optical emission lines. We also use two smaller samples from the literature tha have metallicities determined by the direct method using the temperature sensitive [O III]λ4363 line. We examine the scatter in the local mass--metallicity (MZ) relation determined from ~20,000 star-forming galaxies in the SDSS and show that it is larger at lower stellar masses, consistent with the theoretical scatter in the MZ relation determined from hydrodynamical simulations. We determine a lower limit for the scatter in metallicities of galaxies down to stellar masses of ~107Mʘ which is only slightly smaller than the expected scatter inferred from the SDSS MZ relation and significantly larger than what has been previously established in the literature. The average metallicity of star-forming galaxies increases with stellar mass. By examining the scatter in the SDSS MZ relation, we show that this is mostly due to the lowest metallicity galaxies. The population of low-mass, metal-rich galaxies have properties that are consistent with previously identified galaxies that may be transitional objects between gas-rich dwarf irregulars and gas-poor dwarf spheroidals and ellipticals. [ABSTRACT FROM AUTHOR]

ABSTRACT Massive galaxies today typically are not forming stars despite being surrounded by hot gaseous haloes with short central cooling times. This likely owes to some form of 'quenching feedback' such as merger-driven quasar activity or radio jets emerging from central black holes. Here we implement heuristic prescriptions for these phenomena on-the-fly within cosmological hydrodynamic simulations. We constrain them by comparing to observed luminosity functions and colour-magnitude diagrams from the SDSS. We find that quenching from mergers alone does not produce a realistic red sequence, because 1-2 Gyr after a merger the remnant accretes new fuel and star formation re-ignites. In contrast, quenching by continuously adding thermal energy to hot gaseous haloes quantitatively matches the red galaxy luminosity function and produces a reasonable red sequence. Small discrepancies remain - a shallow red-sequence slope suggests that our models underestimate metal production or retention in massive red galaxies, while a deficit of massive blue galaxies may reflect the fact that observed heating is intermittent rather than continuous. Overall, injection of energy into hot halo gas appears to be a necessary and sufficient condition to broadly produce red and dead massive galaxies as observed. [ABSTRACT FROM AUTHOR]

The bimodality in observed present-day galaxy colours has long been a challenge for hierarchical galaxy formation models, as it requires some physical process to quench (and keep quenched) star formation in massive galaxies. Here, we examine phenomenological models of quenching by post-processing the star formation histories of galaxies from cosmological hydrodynamic simulations that reproduce observations of star-forming galaxies reasonably well. We consider recipes for quenching based on major mergers, halo mass thresholds, gas temperature thresholds and variants thereof. We compare the resulting simulated star formation histories to observed colour–magnitude diagrams and red and blue luminosity functions from SDSS. The merger and halo mass quenching scenarios each yield a distinct red sequence and blue cloud of galaxies that are in broad agreement with data, albeit only under rather extreme assumptions. In detail, however, the simulated red sequence slope and amplitude in both scenarios are somewhat discrepant, perhaps traceable to low metallicities in simulated galaxies. Merger quenching produces more massive blue galaxies, earlier quenching and more frosting of young stars; comparing to relevant data tends to favour merger over halo mass quenching. Although physically motivated quenching models can produce a red sequence, interesting generic discrepancies remain that indicate that additional physics is required to reproduce the star formation and enrichment histories of red and dead galaxies. [ABSTRACT FROM AUTHOR]

We present measurements of the specific angular momentum content (j) of galaxies drawn from the Simba cosmological hydrodynamic simulations. For the stellar, H i and baryonic matter components we demonstrate the existence of extremely tight relations between j and the mass contained within the radius at which the H i mass surface density decreases to 1 M ⊙ pc−2. These relations are broadly consistent with a variety of empirical measurements. We confirm the observational result that the scatter in the stellar j – M relation is driven largely by H i content, and measure the dependence of its scatter on the deviations of galaxies from other important scaling relations. For a given stellar mass, H i -rich/poor galaxies have more/less-than-average stellar specific angular momentum. A similar, yet weaker, correlation exists for H i mass fraction. Overall, our results demonstrate the utility of the Simba simulations as a platform for understanding and contextualising the data and results from forthcoming large galaxy surveys. [ABSTRACT FROM AUTHOR]