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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]

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]

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]

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]