arXiv subjects

R. Davé

Publications and source records attributed to R. Davé.

At least 37 records · Page 2Linked to original sources

arXiv2019

The VANDELS survey: the star-formation histories of massive quiescent galaxies at 1.0 < z < 1.3

We present a Bayesian full-spectral-fitting analysis of 75 massive ($M_* > 10^{10.3} M_\odot$) UVJ-selected galaxies at redshifts of $1.0 < z < 1.3$, combining extremely deep rest-frame ultraviolet spectroscopy from VANDELS with multi-wavelength 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 firstly constrain the stellar mass vs stellar age relationship, finding a steep trend towards earlier average formation with increasing stellar mass of $1.48^{+0.34}_{-0.39}$ Gyr per decade in mass, although this shows signs of flattening at $M_* > 10^{11} M_\odot$. 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 ($M_* \sim 10^{10.5} M_\odot$) are consistent with formation in recent ($z<2$), intense starburst events, with timescales of $\lesssim500$ 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 $z\sim5$ and quenched by $z=3$. However, we find evidence for their continued evolution through both AGN and rejuvenated star-formation activity.

astro-ph.GA↗

arXiv2019

The VANDELS survey: the stellar metallicities of star-forming galaxies at 2.5 < z < 5.0

We present the results of a study utilising ultra-deep, rest-frame UV, spectroscopy to quantify the relationship between stellar mass and stellar metallicity for 681 star-forming galaxies at $2.5<z<5.0$ ($\langle z \rangle = 3.5 \pm 0.6$) drawn from the VANDELS survey. Via a comparison with high-resolution stellar population models, we determine stellar metallicities for a set of composite spectra formed from subsamples selected by mass and redshift. Across the stellar mass range $8.5 < \mathrm{log}(\langle M_{\ast} \rangle/\rm{M}_{\odot}) < 10.2$ we find a strong correlation between stellar metallicity and stellar mass, with stellar metallicity monotonically increasing from $Z_{\ast}/\mathrm{Z}_{\odot} < 0.09$ at $\langle M_{\ast} \rangle = 3.2 \times 10^{8} \rm{M}_{\odot}$ to $Z_{\ast}/Z_{\odot} = 0.27$ 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, we find that the $\langle z \rangle = 3.5$ relation is consistent with being shifted to lower metallicities by $\simeq 0.6$ dex. Contrasting our derived stellar metallicities with estimates of gas-phase metallicities at similar redshifts, we find evidence for enhanced $\rm{O}/\rm{Fe}$ ratios of the order (O/Fe) $\gtrsim 1.8$ $\times$ (O/Fe)$_{\odot}$. Finally, by comparing our results to simulation predictions, we find that the $\langle z \rangle = 3.5$ stellar mass-metallicity relation is consistent with current predictions for how outflow strength scales with galaxy mass. This conclusion is supported by an analysis of analytic models, and suggests that the mass loading parameter ($η=\dot{M}_{\mathrm{outflow}}/M_{\ast}$) scales as $η\propto M_{\ast}^β$ with $β\simeq -0.4$.

astro-ph.GA↗

arXiv2018

On the Interpretation of Far-infrared Spectral Energy Distributions. I: The 850 $μ$m Molecular Mass Estimator

We use a suite of cosmological zoom galaxy formation simulations and dust radiative transfer calculations to explore the use of the monochromatic $850~μm$ luminosity (L$_{\rm ν,850}$) as a molecular gas mass (M$_{\rm mol}$) estimator in galaxies between $0 < z < 9.5$ for a broad range of masses. For our fiducial simulations, where we assume the dust mass is linearly related to the metal mass, we find that empirical L$_{\rm ν,850}$-M$_{\rm mol}$ calibrations accurately recover the molecular gas mass of our model galaxies, and that the L$_{\rm ν,850}$-dependent calibration is preferred. We argue the major driver of scatter in the L$_{\rm ν,850}$-M$_{\rm mol}$ relation arises from variations in the molecular gas to dust mass ratio, rather than variations in the dust temperature, in agreement with the previous study of Liang et al. Emulating a realistic measurement strategy with ALMA observing bands that are dependent on the source redshift, we find that estimating S$_{\rm ν,850}$ from continuum emission at a different frequency contributes $10-20\%$ scatter to the L$_{\rm ν,850}$-M$_{\rm mol}$ relation. This additional scatter arises from a combination of mismatches in assumed T$_{dust}$ and $β$ values, as well as the fact that the SEDs are not single-temperature blackbodies.Finally we explore the impact of a dust prescription in which the dust-to-metals ratio varies with metallicity. Though the resulting mean dust temperatures are $\sim50\%$ higher, the dust mass is significantly decreased for low-metallicity halos. As a result, the observationally calibrated L$_{\rm ν,850}$-M$_{\rm mol}$ relation holds for massive galaxies, independent of the dust model, but below L$_{\rm ν,850}\lesssim10^{28}$ erg s$^{-1}$ (metallicities $\log_{10}({\rm Z}/{\rm Z}_{\odot})\lesssim -0.8$) we expect galaxies may deviate from literature observational calibrations by $\gtrsim0.5$ dex.

astro-ph.GA↗

arXiv2017

SIGAME simulations of the [CII], [OI] and [OIII] line emission from star forming galaxies at z ~ 6

Of the almost 40 star forming galaxies at z>~5 (not counting QSOs) observed in [CII] to date, nearly half are either very faint in [CII], or not detected at all, and fall well below expectations based on locally derived relations between star formation rate (SFR) and [CII] luminosity. Combining cosmological zoom simulations of galaxies with SIGAME (SImulator of GAlaxy Millimeter/submillimeter Emission) we have modeled the multi-phased interstellar medium (ISM) and its emission in [CII], [OI] and [OIII], from 30 main sequence galaxies at z~6 with star formation rates ~3-23Msun/yr, stellar masses ~(0.7-8)x10^9Msun, and metallicities ~(0.1-0.4)xZsun. The simulations are able to reproduce the aforementioned [CII]-faintness at z>5, match two of the three existing z>~5 detections of [OIII], and are furthermore roughly consistent with the [OI] and [OIII] luminosity relations with SFR observed for local starburst galaxies. We find that the [CII] emission is dominated by the diffuse ionized gas phase and molecular clouds, which on average contribute ~66% and ~27%, respectively. The molecular gas, which constitutes only ~10% of the total gas mass is thus a more efficient emitter of [CII] than the ionized gas making up ~85% of the total gas mass. A principal component analysis shows that the [CII] luminosity correlates with the star formation activity as well as average metallicity. The low metallicities of our simulations together with their low molecular gas mass fractions can account for their [CII]-faintness, and we suggest these factors may also be responsible for the [CII]-faint normal galaxies observed at these early epochs.

astro-ph.GA↗

arXiv2016

The Minimum Halo Mass for Star Formation at z = 6 - 8

Recent analysis of strongly-lensed sources in the Hubble Frontier Fields indicates that the rest-frame UV luminosity function of galaxies at $z=$6--8 rises as a power law down to $M_\mathrm{UV}=-15$, and possibly as faint as -12.5. We use predictions from a cosmological radiation hydrodynamic simulation to map these luminosities onto physical space, constraining the minimum dark matter halo mass and stellar mass that the Frontier Fields probe. While previously-published theoretical studies have suggested or assumed that early star formation was suppressed in halos less massive than $10^9$--$10^{11} M_\odot$, we find that recent observations demand vigorous star formation in halos at least as massive as (3.1, 5.6, 10.5)$\times10^9 M_\odot$ at $z=(6,7,8)$. Likewise, we find that Frontier Fields observations probe down to stellar masses of (8.1, 18, 32)$\times10^6 M_\odot$; that is, they are observing the likely progenitors of analogues to Local Group dwarfs such as Pegasus and M32. Our simulations yield somewhat different constraints than two complementary models that have been invoked in similar analyses, emphasizing the need for further observational constraints on the galaxy-halo connection.

astro-ph.GA↗

arXiv2016

The Soft, Fluctuating UVB at $z\sim6$ as Traced by C IV, SiIV, and CII

The sources that drove cosmological reionization left clues regarding their identity in the slope and inhomogeneity of the ultraviolet ionizing background (UVB): Bright quasars (QSOs) generate a hard UVB with predominantly large-scale fluctuations while Population II stars generate a softer one with smaller-scale fluctuations. Metal absorbers probe the UVB's slope because different ions are sensitive to different energies. Likewise, they probe spatial fluctuations because they originate in regions where a galaxy-driven UVB is harder and more intense. We take a first step towards studying the reionization-epoch UVB's slope and inhomogeneity by comparing observations of 12 metal absorbers at $z\sim6$ versus predictions from a cosmological hydrodynamic simulation using three different UVBs: a soft, spatially-inhomogeneous "galaxies+QSOs" UVB; a homogeneous "galaxies+QSOs" UVB (Haardt & Madau 2012); and a QSOs-only model. All UVBs reproduce the observed column density distributions of CII, SiIV, and CIV reasonably well although high-column, high-ionization absorbers are underproduced, reflecting numerical limitations. With upper limits treated as detections, only a soft, fluctuating UVB reproduces both the observed SiIV/CIV and CII/CIV distributions. The QSOs-only UVB overpredicts both CIV/CII and CIV/SiIV, indicating that it is too hard. The Haardt & Madau (2012) UVB underpredicts CIV/SiIV, suggesting that it lacks amplifications near galaxies. Hence current observations prefer a soft, fluctuating UVB as expected from a predominantly Population II background although they cannot rule out a harder one. Future observations probing a factor of two deeper in metal column density will distinguish between the soft, fluctuating and QSOs-only UVBs.

astro-ph.CO↗

arXiv2015

The Reionization of Carbon

Observations suggest that CII was more abundant than CIV in the intergalactic medium towards the end of the hydrogen reionization epoch. This transition provides a unique opportunity to study the enrichment history of intergalactic gas and the growth of the ionizing background (UVB) at early times. We study how carbon absorption evolves from z=10-5 using a cosmological hydrodynamic simulation that includes a self-consistent multifrequency UVB as well as a well-constrained model for galactic outflows to disperse metals. Our predicted UVB is within 2-4 times that of Haardt & Madau (2012), which is fair agreement given the uncertainties. Nonetheless, we use a calibration in post-processing to account for Lyman-alpha forest measurements while preserving the predicted spectral slope and inhomogeneity. The UVB fluctuates spatially in such a way that it always exceeds the volume average in regions where metals are found. This implies both that a spatially-uniform UVB is a poor approximation and that metal absorption is not sensitive to the epoch when HII regions overlap globally even at column densites of 10^{12} cm^{-2}. We find, consistent with observations, that the CII mass fraction drops to low redshift while CIV rises owing the combined effects of a growing UVB and continued addition of carbon in low-density regions. This is mimicked in absorption statistics, which broadly agree with observations at z=6-3 while predicting that the absorber column density distributions rise steeply to the lowest observable columns. Our model reproduces the large observed scatter in the number of low-ionization absorbers per sightline, implying that the scatter does not indicate a partially-neutral Universe at z=6.

astro-ph.CO↗

arXiv2014

ZFOURGE/CANDELS: On the Evolution of M* Galaxy Progenitors from z=3 to 0.5

Galaxies with stellar masses near M* contain the majority of stellar mass in the universe, and are therefore of special interest in the study of galaxy evolution. The Milky Way (MW) and Andromeda (M31) have present day stellar masses near M*, at 5x10^10 Msol (MW-mass) and 10^11 Msol (M31-mass). We study the typical progenitors of these galaxies using ZFOURGE, a deep medium-band near-IR imaging survey, which is sensitive to the progenitors of these galaxies out to z~3. We use abundance-matching techniques to identify the main progenitors of these galaxies at higher redshifts. We measure the evolution in the stellar mass, rest-frame colors, morphologies, far-IR luminosities, and star-formation rates combining our deep multiwavelength imaging with near-IR HST imaging from CANDELS, and far-IR imaging from GOODS-H and CANDELS-H. The typical MW-mass and M31-mass progenitors passed through the same evolution stages, evolving from blue, star-forming disk galaxies at the earliest stages, to redder dust-obscured IR-luminous galaxies in intermediate stages, and to red, more quiescent galaxies at their latest stages. The progenitors of the MW-mass galaxies reached each evolutionary stage at later times (lower redshifts) and with stellar masses that are a factor of 2-3 lower than the progenitors of the M31-mass galaxies. The process driving this evolution, including the suppression of star-formation in present-day M* galaxies requires an evolving stellar-mass/halo-mass ratio and/or evolving halo-mass threshold for quiescent galaxies. The effective size and star-formation rates imply that the baryonic cold-gas fractions drop as galaxies evolve from high redshift to z~0 and are strongly anticorrelated with an increase in the Sérsic index. Therefore, the growth of galaxy bulges in M* galaxies corresponds to a rapid decline in the galaxy gas fractions and/or a decrease in the star-formation efficiency.

astro-ph.GA↗

arXiv2013

The Host Halos of OI Absorbers in the Reionization Epoch

We use a radiation hydrodynamic simulation of the hydrogen reionization epoch to study OI absorbers at z~6. The intergalactic medium (IGM) is reionized before it is enriched, hence OI absorption originates within dark matter halos. The predicted abundance of OI absorbers is in reasonable agreement with observations. At z=10, roughly 70% of sightlines through atomically-cooled halos encounter a visible (N_OI > 10^14 cm^-2) column. Reionization ionizes and removes gas from halos less massive than 10^8.4 M_0, but 20% of sightlines through more massive halos encounter visible columns even at z=5. The mass scale of absorber host halos is 10-100 times smaller than the halos of Lyman break galaxies and Lyman-alpha emitters, hence absorption probes the dominant ionizing sources more directly. OI absorbers have neutral hydrogen columns of 10^19-10^21 cm^-2, suggesting a close resemblance between objects selected in OI and HI absorption. Finally, the absorption in the foreground of the z=7.085 quasar ULASJ1120+0641 cannot originate in a dark matter halo because halo gas at the observed HI column density is enriched enough to violate the upper limits on the OI column. By contrast, gas at less than one third the cosmic mean density satisfies the constraints. Hence the foreground absorption likely originates in the IGM.

astro-ph.CO↗

arXiv2013

Evidence of Increased UV FeII Emission in Quasars in Candidate Overdense Regions

We present evidence for a skewed distribution of UV FeII emission in quasars within candidate overdense regions spanning spatial scales of ~ 50 Mpc at 1.11 < z < 1.67, compared to quasars in field environments at comparable redshifts. The overdense regions have an excess of high equivalent width sources (W2400 > 42 Å), and a dearth of low equivalent width sources. There are various possible explanations for this effect, including dust, Lyαfluorescence, microturbulence, and iron abundance. We find that the most plausible of these is enhanced iron abundance in the overdense regions, consistent with an enhanced star formation rate in the overdense regions compared to the field.

astro-ph.CO↗

arXiv2013

The properties of (sub)millimetre-selected galaxies as revealed by CANDELS HST WFC3/IR imaging in GOODS-South

We have exploited the HST CANDELS WFC3/IR imaging to study the properties of (sub-)mm galaxies in GOODS-South. After using the deep radio and Spitzer imaging to identify galaxy counterparts for the (sub-)mm sources, we have used the new CANDELS data in two ways. First, we have derived improved photometric redshifts and stellar masses, confirming that the (sub-)mm galaxies are massive ( =2.2x10^11 M_solar) galaxies at z=1-3. Second, we have exploited the depth and resolution of the WFC3/IR imaging to determine the sizes and morphologies of the galaxies at rest-frame optical wavelengths, fitting two-dimensional axi-symmetric Sersic models. Crucially, the WFC3/IR H-band imaging enables modelling of the mass-dominant galaxy, rather than the blue high-surface brightness features which often dominate optical (rest-frame UV) images of (sub-)mm galaxies, and can confuse visual morphological classification. As a result of this analysis we find that >95% of the rest-frame optical light in almost all of the (sub-)mm galaxies is well-described by either a single exponential disk, or a multiple-component system in which the dominant constituent is disk-like. We demonstrate that this conclusion is consistent with the results of high-quality ground-based K-band imaging, and explain why. The massive disk galaxies which host luminous (sub-)mm emission are reasonably extended (r_e=4 kpc), consistent with the sizes of other massive star-forming disks at z~2. In many cases we find evidence of blue clumps within the sources, with the mass-dominant disk becoming more significant at longer wavelengths. Finally, only a minority of the sources show evidence for a major galaxy-galaxy interaction. Taken together, these results support the view that most (sub-)mm galaxies at z~2 are simply the most extreme examples of normal star-forming galaxies at that era.

astro-ph.CO↗

arXiv2013

Chandra View of the Warm-Hot IGM toward 1ES 1553+113: Absorption Line Detections and Identifications (Paper I)

We present the first results from our pilot 500 ks Chandra-LETG Large Program observation of the soft X-ray brightest source in the z>=0.4 sky, the blazar 1ES 1553+113, aimed to secure the first uncontroversial detections of the missing baryons in the X-rays. We identify a total of 11 possible absorption lines, with single-line statistical significances between 2.2-4.1σ. Six of these lines are detected at high single-line statistical significance (3.6 <= sigma <= 4.1), while the remaining five are regarded as marginal detections in association with either other X-ray lines detected at higher significance and/or Far-Ultraviolet (FUV) signposts. In particular, five of these possible intervening absorption lines, are identified as CV and CVI Kαabsorbers belonging to three WHIM systems at z_X = 0.312, z_X = 0.237 and = 0.133, which also produce broad HI (and OVI for the z_X = 0.312 system) absorption in the FUV. For two of these systems (z_X = 0.312 and 0.237), the Chandra X-ray data led the a-posteriori discovery of physically consistent broad HI associations in the FUV, so confirming the power of the X-ray-FUV synergy for WHIM studies. The true statistical significances of these three X-ray absorption systems, after properly accounting for the number of redshift trials, are 5.8 sigma (z_X = 0.312; 6.3 sigma if the low-significance OV and CV K-beta associations are considered), 3.9 sigma (z_X = 0.237), and 3.8 sigma (\langle z_X \rangle = 0.133), respectively.

astro-ph.CO↗

arXiv2012

Gas Clumping in Self-Consistent Reionisation Models

We use a suite of cosmological hydrodynamic simulations including a self-consistent treatment for inhomogeneous reionisation to study the impact of galactic outflows and photoionisation heating on the volume-averaged recombination rate of the intergalactic medium (IGM). By incorporating an evolving ionising escape fraction and a treatment for self-shielding within Lyman limit systems, we have run the first simulations of "photon-starved" reionisation scenarios that simultaneously reproduce observations of the abundance of galaxies, the optical depth to electron scattering of cosmic microwave background photons τ, and the effective optical depth to Lymanαabsorption at z=5. We confirm that an ionising background reduces the clumping factor C by more than 50% by smoothing moderately-overdense (Δ=1--100) regions. Meanwhile, outflows increase clumping only modestly. The clumping factor of ionised gas is much lower than the overall baryonic clumping factor because the most overdense gas is self-shielded. Photoionisation heating further suppresses recombinations if reionisation heats gas above the canonical 10,000 K. Accounting for both effects within our most realistic simulation, C rises from <1 at z>10 to 3.3 at z=6. We show that incorporating temperature- and ionisation-corrected clumping factors into an analytical reionisation model reproduces the numerical simulation's τto within 10%. Finally, we explore how many ionising photons are absorbed during the process of heating filaments by considering the overall photon cost of reionisation in analytical models that assume that the IGM is heated at different redshifts. For reionisation redshifts of 9--10, cold filaments boost the reionisation photon budget by ~1 photon per hydrogen atom.

astro-ph.CO↗

arXiv2012

The Growth of Red Sequence Galaxies in a Cosmological Hydrodynamic Simulation

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, halos dominated by hot gas are continually heated to prevent their coronae from fueling new star formation. Hot coronae primarily form in halos above \sim10^12 M\odot, so that galaxies with stellar masses \sim10^10.5 M\odot are the first to be quenched and move onto the red sequence at z > 2. The red sequence is concurrently populated at low masses by satellite galaxies in large halos that are starved of new fuel, resulting in a dip in passive galaxy number densities around \sim10^10 M\odot. Stellar mass growth continues for galaxies even after joining the red sequence, primarily through minor mergers with a typical mass ratio \sim1:5. For the most massive systems, the size growth implied by the distribution of merger mass ratios is typically \sim2\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 \sim 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.

astro-ph.CO↗

arXiv2012

The Metallicities of Low Stellar Mass Galaxies and the Scatter in the Mass-Metallicity Relation

In this investigation we quantify the metallicities of low mass galaxies by constructing the most comprehensive census to date. We use galaxies from the SDSS and DEEP2 survey and estimate metallicities from their optical emission lines. We also use two smaller samples from the literature which have metallicities determined by the direct method using the temperature sensitive [OIII]4363 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 ~10^7 M_solar that is only slightly smaller than the expected scatter inferred from the SDSS MZ relation and significantly larger than what is 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 which are consistent with previously identified galaxies that may be transitional objects between gas-rich dwarf irregulars and gas-poor dwarf spheroidals and ellipticals.

astro-ph.CO↗

arXiv2011

Galactic Outflows and Photoionization Heating in the Reionization Epoch

We carry out a new suite of cosmological radiation hydrodynamic simulations and explore the relative impacts on reionization-epoch star formation of galactic outflows and photoionization heating. By itself, an extragalactic ultraviolet background (EUVB) suppresses the luminosity function by less than 50% at z=6, overproducing the observed galaxy abundance by a factor of 3-5. Galactic outflows restore agreement with observations without preventing Population II star formation from reionizing the Universe by z=6. The resulting EUVB suppresses star formation in halos with virial temperatures below 10^5K but has a weaker impact in more massive halos. Nonetheless, the low-mass halos contribute up to 50% of all ionizing photons owing to the EUVB's inhomogeneity. Overall, star formation rate scales as halo mass M_h to the 1.3-1.4 in halos with $M_h=10^{8.2--10.2}\msun$. 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 M_1600=-13, indicating that reionization was driven by faint galaxies (M_1600 >= -15) that have not yet been observed. Our models cannot simultaneously explain observations of galaxies, the cosmic microwave background, and the intergalactic medium. Increased dynamic range will alleviate the existing discrepancies, but observations may still require additional physics such as a variable ionizing escape fraction (abridged).

astro-ph.CO↗

arXiv2010

How is Star Formation Quenched in Massive Galaxies?

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 g-r 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 each scenario is 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 favor 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.

astro-ph.CO↗

arXiv2010

The Low-Redshift Lyman Alpha Forest toward 3C 273

We present an analysis of the Ly-a forest toward 3C 273 from the Space Telescope Imaging Spectrograph at ~7 km/s resolution, along with re-processed data from the Far Ultraviolet Spectroscopic Explorer. The high UV flux of 3C 273 allows us to probe the weak, low z absorbers. The main sample consists of 21 HI absorbers that we could discriminate to a sensitivity of log NHI~ 12.5. The redshift density for absorbers with 13.1 = 12.5, it is consistent with numerical model predictions. The Doppler parameter distribution is consistent with other low z samples. We find no evidence for a break in the column density power-law distribution to log NHI=12.3. A broad Ly-a absorber (BLA) is within Delta v =< 50 km/s and 1.3 local frame Mpc of two ~0.5L* galaxies, with an OVI absorber ~700 km/s away, similarly close to three galaxies and indicating overdense environments. We detect clustering on the Delta v<1000 km/s scale at 3.4 sigma significance for log NHI >= 12.6, consistent with the level predicted from hydrodynamical simulations, and indication for a Ly-a forest void at 0.09<z<0.12. We find at least two components for the z=0.0053 Virgo absorber, but the total NHI column is not significantly changed.

astro-ph.CO↗