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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]

Galaxy cluster outskirts mark the transition region from the mildly non-linear cosmic web to the highly non-linear, virialized, cluster interior. It is in this transition region that the intracluster medium (ICM) begins to influence the properties of accreting galaxies and groups, as ram pressure impacts a galaxy's cold gas content and subsequent star formation rate. Conversely, the thermodynamical properties of the ICM in this transition region should also feel the influence of accreting substructure (i.e. galaxies and groups), whose passage can drive shocks. In this paper, we use a suite of cosmological hydrodynamical zoom simulations of a single galaxy cluster, drawn from the nIFTy comparison project, to study how the dynamics of substructure accreted from the cosmic web influence the thermodynamical properties of the ICM in the cluster's outskirts. We demonstrate how features evident in radial profiles of the ICM (e.g. gas density and temperature) can be linked to strong shocks, transient and short-lived in nature, driven by the passage of substructure. The range of astrophysical codes and galaxy formation models in our comparison are broadly consistent in their predictions (e.g. agreeing when and where shocks occur, but differing in how strong shocks will be); this is as we would expect of a process driven by large-scale gravitational dynamics and strong, inefficiently radiating, shocks. This suggests that mapping such shock structures in the ICM in a cluster's outskirts (via e.g. radio synchrotron emission) could provide a complementary measure of its recent merger and accretion history. [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 Bayesian Analysis of Galaxies for Physical Inference and Parameter EStimation, or bagpipes, a new python tool that can be used to rapidly generate complex model galaxy spectra and to fit these to arbitrary combinations of spectroscopic and photometric data using the multinest nested sampling algorithm. We extensively test our ability to recover realistic star formation histories (SFHs) by fitting mock observations of quiescent galaxies from the mufasa simulation. We then perform a detailed analysis of the SFHs of a sample of 9289 quiescent galaxies from UltraVISTA with stellar masses, M * > 1010 M⊙ and redshifts 0.25 < |$z$| < 3.75. The majority of our sample exhibit SFHs that rise gradually then quench relatively rapidly over 1−2 Gyr. This behaviour is consistent with recent cosmological hydrodynamic simulations, where AGN-driven feedback in the low-accretion (jet) mode is the dominant quenching mechanism. At |$z$| > 1, we also find a class of objects with SFHs that rise and fall very rapidly, with quenching time-scales of <1 Gyr, consistent with quasar-mode AGN feedback. Finally, at |$z$| < 1 we find a population with SFHs which quench more slowly than they rise, over >3 Gyr, which we speculate to be the result of diminishing overall cosmic gas supply. We confirm the mass-accelerated evolution (downsizing) trend, and a trend towards more rapid quenching at higher stellar masses. However, our results suggest that the latter is a natural consequence of mass-accelerated evolution, rather than a change in quenching physics with stellar mass. We find 61 ± 8 per cent of |$z$| > 1.5 massive-quenched galaxies undergo significant further evolution by |$z$|  = 0.5. bagpipes is available at bagpipes.readthedocs.io. [ABSTRACT FROM AUTHOR]

We measure new estimates for the galaxy stellar mass function and star formation rates for samples of galaxies at z ∼ 4, 5, 6 and 7 using data in the CANDELS GOODS South field. The deep near-infrared observations allow us to construct the stellar mass function at z ≥ 6 directly for the first time. We estimate stellar masses for our sample by fitting the observed spectral energy distributions with synthetic stellar populations, including nebular line and continuum emission. The observed UV luminosity functions for the samples are consistent with previous observations; however, we find that the observed MUV-M* relation has a shallow slope more consistent with a constant mass-to-light ratio and a normalization which evolves with redshift. Our stellar mass functions have steep low-mass slopes (α ≈ −1.9), steeper than previously observed at these redshifts and closer to that of the UV luminosity function. Integrating our new mass functions, we find the observed stellar mass density evolves from $\log _{10} \rho _{*} = 6.64^{+0.58}_{-0.89}$ at z ∼ 7 to 7.36 ± 0.06 M⊙ Mpc− 3 at z ∼ 4. Finally, combining the measured UV continuum slopes (β) with their rest-frame UV luminosities, we calculate dust-corrected star formation rates (SFR) for our sample. We find the specific SFR for a fixed stellar mass increases with redshift whilst the global SFR density falls rapidly over this period. Our new SFR density estimates are higher than previously observed at this redshift. [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]

We carry out a new suite of cosmological radiation hydrodynamic simulations that explores the relative impacts on reionization-epoch star formation of galactic outflows and photoionization heating from a self-consistently grown extragalactic ultraviolet ionizing background (EUVB). We compare the predictions with observational constraints from the cosmic microwave background, the ultraviolet continuum luminosity function of galaxies, and the Lyα forest. By itself, an EUVB suppresses the luminosity function by less than 50% at z = 6 even if it is orders of magnitude stronger than observed. This overproduces the observed galaxy abundance by a factor of 3-5, indicating the need for an additional feedback process. We confirm that outflows readily suppress both the EUVB and the luminosity function into improved agreement with observations. Population I-II star formation can reionize the universe by z = 6 even in the presence of strong feedback from photoheating and outflows. The resulting EUVB suppresses star formation in halos with virial temperatures below 105 K but has a weaker impact on more massive halos. Nonetheless, halos with virial temperatures below 10-5 K contribute up to ~50% of all ionizing photons owing to the EUVB's inhomogeneity. Overall, star formation rate scales with halo mass Due to image rights restrictions, multiple line equation(s) cannot be graphically displayed for halos with Mh = 108.2-1010.2 M⊙. This is a steeper dependence than is often assumed in reionization models, boosting the expected power spectrum of 21 centimeter fluctuations on large scales. The luminosity function rises steeply to at least M1600 = -13 even in models that treat both outflows and an EUVB. indicating that reionization was driven by faint galaxies (M1600 ≥ -15) that have not yet been observed. Outflows and an EUVB interfere with each other's feedback effects in two ways. Outflows weaken the EUVB, limiting Jeans suppression of low-mass halos: this leads to overall de-amplification of suppression at early times (z > 8). Meanwhile, they amplify each other's impact on more massive halos, leading to overall amplification of suppression at later times. Our models cannot simultaneously explain observations of galaxies, the cosmic microwave background, and the intergalactic medium. Correcting for dynamic range limitations and adjusting our physical treatments will alleviate discrepancies, but observations may still require additional physical scalings such as a mass-dependent ionizing escape traction. [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]

In this contribution, we present the first census of oxygen in star-forming galaxies in the local universe. We examine three samples of galaxies with metallicities and star formation rates (SFRs) at z = 0.07, 0.8, and 2.26, including the Sloan Digital Sky Survey (SDSS) and DEEP2 survey. We infer the total mass of oxygen produced and mass of oxygen found in the gas-phase from our local SDSS sample. The star formation history is determined by requiring that galaxies evolve along the relation between stellar mass and SFR observed in our three samples. We show that the observed relation between stellar mass and SFR for our three samples is consistent with other samples in the literature. The mass-metallicity relation is well established for our three samples, and from this we empirically determine the chemical evolution of star-forming galaxies. Thus, we are able to simultaneously constrain the SFRs and metallicities of galaxies over cosmic time, allowing us to estimate the mass of oxygen locked up in stars. Combining this work with independent measurements reported in the literature, we conclude that the loss of oxygen from the interstellar medium of local star-forming galaxies is likely to be a ubiquitous process with the oxygen mass loss scaling (almost) linearly with stellar mass. We estimate the total baryonic mass loss and argue that only a small fraction of the baryons inferred from cosmological observations accrete onto galaxies. [ABSTRACT FROM AUTHOR]