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Galaxy flybys, interactions where two independent halos inter-penetrate but detach at a later time and do not merge, occur frequently at lower redshifts. These interactions can significantly impact the evolution of individual galaxies - from the mass loss and shape transformation to the emergence of tidal features and formation of morphological disc structures. The main focus of this paper is on the dark matter mass loss of the secondary, intruder galaxy, with the goal of determining a functional relationship between the impact parameter and dark matter mass loss. Series of N-body simulations of typical galaxy flybys (10:1 mass ratio) with differing impact parameters show that the dark matter halo leftover mass of the intruder galaxy follows a logarithmic growth law with impact parameter, regardless of the way the total halo mass is estimated. The lost mass then, clearly, follows the exponential decay law. The stellar component stretches faster as the impact parameter decreases, following the exponential decay law with impact parameter. Functional dependence on impact parameter in all cases seems universal, but the fitting parameters are likely sensitive to the interaction parameters and initial conditions (e.g. the mass ratio of interacting galaxies, initial relative velocity of the intruder galaxy, interaction duration). While typical flybys, investigated here, could not be the sole culprit behind the formation of ultra-diffuse or dark matter deficient galaxies, they can still contribute significantly. Rare, atypical and stronger flybys are worth further exploring.

We investigate the response of self-interacting dark matter (SIDM) halos to the growth of galaxy potentials using idealized simulations, with each run in tandem with collisionless cold dark matter (CDM). We find that if the stellar potential strongly dominates in the central parts of a galaxy, then SIDM halos can be as dense as CDM halos on observable scales. For extreme cases, core collapse can occur, leading to SIDM halos that are denser and cuspier than their CDM counterparts. If the stellar potential is not dominant, then SIDM halos retain isothermal cores with densities far below CDM predictions. When a disk is present, the inner SIDM halo becomes more flattened in the disk plane than the CDM halo. These results are in excellent quantitative agreement with the predictions of Kaplinghat et al. We also simulated a cluster halo with a central stellar distribution similar to the brightest central galaxy of the cluster A2667. An SIDM halo simulated with the cross-section over mass provides a good match to the measured dark matter (DM) density profile, while an adiabatically contracted CDM halo is denser and cuspier. The profile of the same halo simulated with is not dense enough. Our findings are in agreement with previous results that is disfavored for DM collision velocities above about 1500 km s-1. More generally, the interaction between baryonic potentials and SIDM densities offers new directions for constraining SIDM cross-sections in galaxies where baryons are dynamically important.

We use a newly assembled sample of 3545 star-forming galaxies with secure spectroscopic, grism, and photometric redshifts at z = 1.5-2.5 to constrain the relationship between UV slope (β) and dust attenuation (L IR/L UV ≡ IRX). Our sample significantly extends the range of L UV and β probed in previous UV-selected samples, including those as faint as M 1600 = -17.4 () and -2.6 ≲ β ≲ 0.0. IRX is measured using stacks of deep Herschel data, and the results are compared with predictions of the IRX-β relation for different assumptions of the stellar population model and obscuration curve. We find that z = 1.5-2.5 galaxies have an IRX-β relation that is consistent with the predictions for an SMC curve if we invoke subsolar-metallicity models currently favored for high-redshift galaxies, while the commonly assumed starburst curve overpredicts the IRX at a given β by a factor of 3. IRX is roughly constant with L UV for L UV ≳ 3 109 L o. Thus, the commonly observed trend of fainter galaxies having bluer β may simply reflect bluer intrinsic slopes for such galaxies, rather than lower obscurations. The IRX-β relation for young/low-mass galaxies at z ≳; 2 implies a dust curve that is steeper than the SMC. The lower attenuations and higher ionizing photon output for low-metallicity stellar populations point to Lyman continuum production efficiencies, ξ ion, that may be elevated by a factor of ≈2 relative to the canonical value for L∗ galaxies, aiding in their ability to keep the universe ionized at z ∼ 2.

Hot, dust-obscured galaxies, or "Hot DOGs," are a rare, dusty, hyperluminous galaxy population discovered by the WISE mission. Predominantly at redshifts 2-3, they include the most luminous known galaxies in the universe. Their high luminosities likely come from accretion onto highly obscured supermassive black holes (SMBHs). We have conducted a pilot survey to measure the SMBH masses of five z ∼ 2 Hot DOGs via broad Hα emission lines, using Keck/MOSFIRE and Gemini/FLAMINGOS-2. We detect broad Hα emission in all five Hot DOGs. We find substantial corresponding SMBH masses for these Hot DOGs (∼ 109 M⊙), and their derived Eddington ratios are close to unity. These z ∼ 2 Hot DOGs are the most luminous active galactic nuclei for their BH masses, suggesting that they are accreting at the maximum rates for their BHs. A similar property is found for known z ∼ 6 quasars. Our results are consistent with scenarios in which Hot DOGs represent a transitional, high-accretion phase between obscured and unobscured quasars. Hot DOGs may mark a special evolutionary stage before the red quasar and optical quasar phases, and they may be present at other cosmic epochs.

We carry out a study of Sub-Millimeter Galaxies (SMGs) in the AKARI NEP-Deep field using the James Clerk Maxwell Telescope (JCMT) SCUBA-2 850 µm source catalog, released as part of the SCUBA-2 Cosmology Legacy Survey (S2CLS) program. The SCUBA-2 850 µm map has a root mean square (rms) noise of 1.2 mJy beam−1 and covers an area of 0.60 degree2. We find four SMGs which have counterparts to Herschel sources with spectroscopic redshifts in the literature. In addition, three dust obscured galaxies (DOGs) detected in Herschel bands are selected as a comparison sample. We derive IR luminosities of SMGs using the CIGALE code, which are similar to those of high redshift SMGs from previous studies. The contribution of AGN to the total IR luminosity in SMGs (2%–11%) is smaller than the lower limit for the one in DOGs (19%–35%), which is consistent with the expectation from the evolutionary scenario of massive galaxies. We search for SMGs in overdense regions as protocluster candidates and investigate four regions, including candidates around three DOGs. Finally, we argue that follow-up spectroscopic observation for the NEP-Deep field will provide crucial information to understand the role of SMGs in the evolution of massive galaxies.

We investigate the impact of local environment on the galaxy stellar mass function (SMF) spanning a wide range of galaxy densities from the field up to dense cores of massive galaxy clusters. Data are drawn from a sample of eight fields from the Observations of Redshift Evolution in Large-Scale Environments (ORELSE) survey. Deep photometry allow us to select mass-complete samples of galaxies down to 109M⊙. Taking advantage of > 4000 secure spectroscopic redshifts from ORELSE and precise photometric redshifts, we construct threedimensional density maps between 0.55 < z < 1.3 using a Voronoi tessellation approach. We find that the shape of the SMF depends strongly on local environment exhibited by a smooth, continual increase in the relative numbers of high- to low-mass galaxies towards denser environments. A straightforward implication is that local environment proportionally increases the efficiency of (a) destroying lower mass galaxies and/or (b) growth of higher mass galaxies. We also find a presence of this environmental dependence in the SMFs of starforming and quiescent galaxies, although not quite as strongly for the quiescent subsample. To characterize the connection between the SMFof field galaxies and that of denser environments, we devise a simple semi-empirical model. The model begins with a sample of ≈106 galaxies at zstart = 5 with stellar masses distributed according to the field. Simulated galaxies then evolve down to zfinal = 0.8 following empirical prescriptions for star-formation, quenching and galaxy-galaxy merging.We run the simulationmultiple times, testing a variety of scenarios with differing overall amounts of merging. Our model suggests that a large number of mergers are required to reproduce the SMF in dense environments. Additionally, a large majority of these mergers would have to occur in intermediate density environments (e.g. galaxy groups).

We test whether halo age and galaxy age are correlated at fixed halo and galaxy mass. The formation histories, and thus ages, of darkmatter haloes correlate with their large-scale density ρ, an effect known as assembly bias. We test whether this correlation extends to galaxies by measuring the dependence of galaxy stellar age on ρ. To clarify the comparison between theory and observation, and to remove the strong environmental effects on satellites, we use galaxy group catalogues to identify central galaxies and measure their quenched fraction, fQ, as a function of large-scale environment. Models that match halo age to central galaxy age predict a strong positive correlation between fQ and ρ. However, we show that the amplitude of this effect depends on the definition of halo age: assembly bias is significantly reduced when removing the effects of splashback haloes - those haloes that are central but have passed through a larger halo or experienced strong tidal encounters. Defining age using halo mass at its peak value rather than current mass removes these effects. In Sloan Digital Sky Survey data, at M* ≳ 1010 M⊙ h-2, there is a ~5 per cent increase in fQ from low-to-high densities, which is in agreement with predictions of dark matter haloes using peak halo mass. At lower stellar mass there is little to no correlation of fQ with ρ. For these galaxies, age matching is inconsistent with the data across the range of halo formation metrics that we tested. This implies that halo formation history has a small but statistically significant impact on quenching of star formation at high masses, while the quenching process in low-mass central galaxies is uncorrelated with halo formation history.

We introduce massive black holes (BHs) in the Feedback In Realistic Environments (FIRE) project and perform high-resolution cosmological hydrodynamic simulations of quasar-mass haloes [Mhalo(z = 2) ≈ 1012.5M⊙] down to z = 1. These simulations model stellar feedback by supernovae, stellar winds and radiation, and BH growth using a gravitational torque-based prescription tied to the resolved properties of galactic nuclei.We do not include BH feedback. We show that early BH growth occurs through short (≲1Myr) accretion episodes that can reach or even exceed the Eddington rate. In this regime, BH growth is limited by bursty stellar feedback continuously evacuating gas from galactic nuclei, and BHs remain undermassive in low-mass galaxies relative to the local MBH-Mbulgerelation. BH growth is more efficient at later times, when the nuclear stellar potential retains a significant gas reservoir, star formation becomes less bursty and galaxies settle into a more ordered state. BHs rapidly converge on to the observed scaling relations when the host reaches Mbulge ~1010M⊙. We show that resolving the effects of stellar feedback on the gas supply in the inner ~100 pc of galaxies is necessary to accurately capture the growth of central BHs. Our simulations imply that bursty stellar feedback has important implications for BH-galaxy relations, AGN demographics and time variability, the formation of early quasars and massive BH mergers.

We conduct a systematic study of galactic outflows in star-forming galaxies at z ∼ 0-2 based on the absorption lines of optical spectra taken from SDSS DR7, DEEP2 DR4, and Keck (Erb et al.). We carefully make stacked spectra of homogeneous galaxy samples with similar stellar mass distributions at z ∼ 0-2 and perform the multicomponent fitting of model absorption lines and stellar continua to the stacked spectra. We obtain the maximum (vmax) and central (vout) outflow velocities and estimate the mass loading factors (η), a ratio of the mass outflow rate to the star formation rate (SFR). Investigating the redshift evolution of the outflow velocities measured with the absorption lines whose depths and ionization energies are similar (Na I D and Mg I at z ∼ 0-1; Mg II and C II at z ∼ 1-2), we identify, for the first time, that the average value of vmax (vout) significantly increases by 0.05-0.3 dex from z ∼ 0 to 2 at a given SFR. Moreover, we find that the value of η increases from z ∼ 0 to 2 by η ∝ (1 + z)1.2±0.3 at a given halo circular velocity vcir, albeit with a potential systematics caused by model parameter choices. The redshift evolution of vmax (vout) and η is consistent with the galaxy-size evolution and the local velocity-SFR surface density relation and explained by high gas fractions in high-redshift massive galaxies, which is supported by recent radio observations. We obtain a scaling relation of η ∝ νcira for a = -0.2 ± 1.1 in our z ∼ 0 galaxies that agrees with the momentum-driven outflow model (a = -1) within the uncertainties.

We combined deep U-band and optical/near-infrared imaging, in order to select Lyman Break Galaxies (LBGs) at using U-V and colors in the Subaru Deep Field. The resulting sample of 5161 LBGs gives a UV luminosity function (LF) down to , with a steep faint-end slope of . We analyze UV-To-NIR energy distributions (SEDs) from optical photometry and photometry on IR median-stacked images. In the stacks, we find a systematic background depression centered on the LBGs. This results from the difficulty of finding faint galaxies in regions with higher-Than-Average surface densities of foreground galaxies, so we corrected for this deficit. Best-fit stellar population models for the LBG SEDs indicate stellar masses and star formation rates of and M o yr-1 at , down to and yr-1 at . The faint LBGs show a ∼1 mag excess over the stellar continuum in K-band. We interpret this excess flux as redshifted [O iii] lines. The observed excesses imply equivalent widths that increase with decreasing mass, reaching A (rest-frame). Such strong [O iii] emission is seen only in a miniscule fraction of local emission-line galaxies, but is probably universal in the faint galaxies that reionized the universe. Our halo occupation distribution analysis of the angular correlation function gives a halo mass of for the full sample of LBGs, and for the brightest half of the sample.

We conduct a systematic study of galactic outflows in star-forming galaxies at z ∼ 0-2 based on the absorption lines of optical spectra taken from SDSS DR7, DEEP2 DR4, and Keck (Erb et al.). We carefully make stacked spectra of homogeneous galaxy samples with similar stellar mass distributions at z ∼ 0-2 and perform the multicomponent fitting of model absorption lines and stellar continua to the stacked spectra. We obtain the maximum (vmax) and central (vout) outflow velocities and estimate the mass loading factors (η), a ratio of the mass outflow rate to the star formation rate (SFR). Investigating the redshift evolution of the outflow velocities measured with the absorption lines whose depths and ionization energies are similar (Na I D and Mg I at z ∼ 0-1; Mg II and C II at z ∼ 1-2), we identify, for the first time, that the average value of vmax (vout) significantly increases by 0.05-0.3 dex from z ∼ 0 to 2 at a given SFR. Moreover, we find that the value of η increases from z ∼ 0 to 2 by η ∝ (1 + z)1.2±0.3 at a given halo circular velocity vcir, albeit with a potential systematics caused by model parameter choices. The redshift evolution of vmax (vout) and η is consistent with the galaxy-size evolution and the local velocity-SFR surface density relation and explained by high gas fractions in high-redshift massive galaxies, which is supported by recent radio observations. We obtain a scaling relation of η ∝ νcira for a = -0.2 ± 1.1 in our z ∼ 0 galaxies that agrees with the momentum-driven outflow model (a = -1) within the uncertainties.

AbstractIR spectroscopy in the range 12–230 μm with the SPace IR telescope for Cosmology and Astrophysics (SPICA) will reveal the physical processes governing the formation and evolution of galaxies and black holes through cosmic time, bridging the gap between the James Webb Space Telescope and the upcoming Extremely Large Telescopes at shorter wavelengths and the Atacama Large Millimeter Array at longer wavelengths. The SPICA, with its 2.5-m telescope actively cooled to below 8 K, will obtain the first spectroscopic determination, in the mid-IR rest-frame, of both the star-formation rate and black hole accretion rate histories of galaxies, reaching lookback times of 12 Gyr, for large statistically significant samples. Densities, temperatures, radiation fields, and gas-phase metallicities will be measured in dust-obscured galaxies and active galactic nuclei, sampling a large range in mass and luminosity, from faint local dwarf galaxies to luminous quasars in the distant Universe. Active galactic nuclei and starburst feedback and feeding mechanisms in distant galaxies will be uncovered through detailed measurements of molecular and atomic line profiles. The SPICA’s large-area deep spectrophotometric surveys will provide mid-IR spectra and continuum fluxes for unbiased samples of tens of thousands of galaxies, out to redshifts of z ~ 6.

Winds arising from galaxies, star clusters, and active galactic nuclei are crucial players in star and galaxy formation, but it has proven remarkably difficult to use observations of them to determine physical properties of interest, particularly mass fluxes. Much of the difficulty stems from a lack of a theory that links a physically realistic model for winds' density, velocity and covering factors to calculations of light emission and absorption. In this paper we provide such a model. We consider a wind launched from a turbulent region with a range of column densities, derive the differential acceleration of gas as a function of column density, and use this result to compute winds' absorption profiles, emission profiles and emission intensity maps in both optically thin and optically thick species. The model is sufficiently simple that all required computations can be done analytically up to straightforward numerical integrals, rendering it suitable for the problem of deriving physical parameters by fitting models to observed data. We show that our model produces realistic absorption and emission profiles for some example cases, and argue that the most promising methods of deducing mass fluxes are based on combinations of absorption lines of different optical depths, or on combining absorption with measurements of molecular line emission. In the second paper in this series, we expand on these ideas by introducing a set of observational diagnostics that are significantly more robust than those commonly in use, and that can be used to obtain improved estimates of wind properties.

AbstractA far-infrared observatory such as the SPace Infrared telescope for Cosmology and Astrophysics, with its unprecedented spectroscopic sensitivity, would unveil the role of feedback in galaxy evolution during the last ~10 Gyr of the Universe (z = 1.5–2), through the use of far- and mid-infrared molecular and ionic fine structure lines that trace outflowing and infalling gas. Outflowing gas is identified in the far-infrared through P-Cygni line shapes and absorption blueshifted wings in molecular lines with high dipolar moments, and through emission line wings of fine-structure lines of ionised gas. We quantify the detectability of galaxy-scale massive molecular and ionised outflows as a function of redshift in AGN-dominated, starburst-dominated, and main-sequence galaxies, explore the detectability of metal-rich inflows in the local Universe, and describe the most significant synergies with other current and future observatories that will measure feedback in galaxies via complementary tracers at other wavelengths.

We present a suite of 15 cosmological zoom-in simulations of isolated dark matter haloes, all with masses of Mhalo ≈ 1010M⊙ at z = 0, in order to understand the relationship among halo assembly, galaxy formation and feedback's effects on the central density structure in dwarf galaxies. These simulations are part of the Feedback in Realistic Environments (FIRE) project and are performed at extremely high resolution (mbaryon = 500M⊙, mdm = 2500M⊙). The resultant galaxies have stellar masses that are consistent with rough abundance matching estimates, coinciding with the faintest galaxies that can be seen beyond the virial radius of the Milky Way (M*/M⊙ ≈ 105 - 107). This non-negligible spread in stellar mass at z = 0 in haloes within a narrow range of virial masses is strongly correlated with central halo density or maximum circular velocity Vmax, both of which are tightly linked to halo formation time. Much of this dependence of M* on a second parameter (beyond Mhalo) is a direct consequence of the Mhalo ~ 1010M⊙ mass scale coinciding with the threshold for strong reionization suppression: the densest, earliest-forming haloes remain above the UV-suppression scale throughout their histories while late-forming systems fall below the UV-suppression scale over longer periods and form fewer stars as a result. In fact, the latest-forming, lowest-concentration halo in our suite fails to form any stars. Haloes that form galaxies with M ≳ 2 × 106 M⊙ have reduced central densities relative to dark-matter-only simulations, and the radial extent of the density modifications is well-approximated by the galaxy half-mass radius r1/2. Lower-mass galaxies do not modify their host dark matter haloes at the mass scale studied here. This apparent stellar mass threshold of M ≈ 2 × 106-2 × 10-4 Mhalo is broadly consistent with previous work and provides a testable prediction of FIRE feedback models in Λcold dark matter.

Using observations from the first 2 yr of the MOSFIRE Deep Evolution Field (MOSDEF) survey, we study 13 active galactic nucleus (AGN) driven outflows detected from a sample of 67 X-ray, IR, and/or optically selected AGNs at. The AGNs have bolometric luminosities of, including both quasars and moderate-luminosity AGNs. We detect blueshifted, ionized gas outflows in the Hβ, [O iii], Hα, and/or [N ii] emission lines of 19% of the AGNs, while only 1.8% of the MOSDEF galaxies have similarly detected outflows. The outflow velocities span ∼300 to 1000 km s-1. Eight of the 13 outflows are spatially extended on similar scales to the host galaxies, with spatial extents of 2.5-11.0 kpc. Outflows are detected uniformly across the star-forming main sequence, showing little trend with the host galaxy star formation rate. Line ratio diagnostics indicate that the outflowing gas is photoionized by the AGNs. We do not find evidence for positive AGN feedback, in either our small MOSDEF sample or a much larger Sloan Digital Sky Survey sample, using the BPT diagram. Given that a galaxy with an AGN is 10 times more likely to have a detected outflow, the outflowing gas is photoionized by the AGNs, and estimates of the mass and energy outflow rates indicate that stellar feedback is insufficient to drive at least some of these outflows; they are very likely to be AGN driven. The outflows have mass-loading factors of the order of unity, suggesting that they help regulate star formation in their host galaxies, though they may be insufficient to fully quench it.

We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at 1 < z < 1.5, selected to span a factor >10 in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS, and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The newred-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over λ ~ 0.6-1.05 μm, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes z' < 24.25 and [3.6] μm < 22.5, and is therefore statistically complete for stellar masses M* ≳ 1010.3M⊙, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning u through K, in addition to deep IRAC imaging at 3.6 μm. The spectroscopy is ~50 per cent complete as of semester 17A, and we anticipate a final sample of ~500 new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT, and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius.

The latest measurements of cosmic microwave background electron-scattering optical depth reported by Planck significantly reduces the allowed space of reionization models, pointing toward a later ending and/or less extended phase transition than previously believed. Reionization impulsively heats the intergalactic medium (IGM) to , and owing to long cooling and dynamical times in the diffuse gas that are comparable to the Hubble time, memory of reionization heating is retained. Therefore, a late-ending reionization has significant implications for the structure of the Lyμ forest. Using state-of-the-art hydrodynamical simulations that allow us to vary the timing of reionization and its associated heat injection, we argue that extant thermal signatures from reionization can be detected via the Lyμ forest power spectrum at . This arises because the small-scale cutoff in the power depends not only the the IGM temperature at these epochs, but is also particularly sensitive to the pressure-smoothing scale set by the IGM full thermal history. Comparing our different reionization models with existing measurements of the Lyμ forest flux power spectrum at , we find that models satisfying Planck's constraint favor a moderate amount of heat injection consistent with galaxies driving reionization, but disfavoring quasar-driven scenarios. We study the feasibility of measuring the flux power spectrum at using mock quasar spectra and conclude that a sample of ∼10 high-resolution spectra with an attainable signal-to-noise ratio will allow distinguishing between different reionization scenarios.

We present the first spectroscopic measurement of multiple rest-frame optical emission lines at z > 4. During the MOSFIRE Deep Evolution Field survey, we observed the galaxy GOODSN-17940 with the Keck I/MOSFIRE spectrograph. The K-band spectrum of GOODSN-17940 includes significant detections of the [O ii]λλ3726,3729, [Ne iii]λ3869, and Hγ emission lines and a tentative detection of Hδ, indicating z spec = 4.4121. GOODSN-17940 is an actively star-forming z > 4 galaxy based on its K-band spectrum and broadband spectral energy distribution. A significant excess relative to the surrounding continuum is present in the Spitzer/IRAC channel 1 photometry of GOODSN-17940, due primarily to strong Hα emission with a rest-frame equivalent width of EW(Hα) = 1200. Based on the assumption of 0.5 Z o models and the Calzetti attenuation curve, GOODSN-17940 is characterized by . The Balmer decrement inferred from Hα/Hγ is used to dust correct the Hα emission, yielding . These M ∗ and star formation rate (SFR) values place GOODSN-17940 an order of magnitude in SFR above the z ∼ 4 star-forming "main sequence." Finally, we use the observed ratio of [Ne iii]/[O ii] to estimate the nebular oxygen abundance in GOODSN-17940, finding O/H ∼ 0.2 (O/H)o. Combining our new [Ne iii]/[O ii] measurement with those from stacked spectra at z ∼ 0, 2, and 3, we show that GOODSN-17940 represents an extension to z > 4 of the evolution toward higher [Ne iii]/[O ii] (i.e., lower O/H) at fixed stellar mass. It will be possible to perform the measurements presented here out to z ∼ 10 using the James Webb Space Telescope.

Dwarf galaxies are known to have remarkably low star formation efficiency due to strong feedback. Adopting the dwarf galaxies of the Milky Way (MW) as a laboratory, we explore a flexible semi-analytic galaxy formation model to understand how the feedback processes shape the satellite galaxies of the MW. Using Markov Chain Monte Carlo, we exhaustively search a large parameter space of the model and rigorously show that the general wisdom of strong outflows as the primary feedback mechanism cannot simultaneously explain the stellar mass function and the mass-metallicity relation of the MW satellites. An extended model that assumes that a fraction of baryons is prevented from collapsing into low-mass halos in the first place can be accurately constrained to simultaneously reproduce those observations. The inference suggests that two different physical mechanisms are needed to explain the two different data sets. In particular, moderate outflows with weak halo mass dependence are needed to explain the mass-metallicity relation, and prevention of baryons falling into shallow gravitational potentials of low-mass halos (e.g., "pre-heating") is needed to explain the low stellar mass fraction for a given subhalo mass.

We compile a sample of spectroscopically and photometrically selected cluster galaxies from four high-redshift galaxy clusters (1.59 < z < 1.71) from the Spitzer Adaptation of the Red-Sequence Cluster Survey (SpARCS), and a comparison field sample selected from the UKIDSS Deep Survey. Using near-infrared imaging from the Hubble Space Telescope, we classify potential mergers involving massive (M∗ ≥ 3 × 1010M⊙) cluster members by eye, based on morphological properties such as tidal distortions, double nuclei, and projected near neighbors within 20 kpc. With a catalog of 23 spectroscopic and 32 photometric massive cluster members across the four clusters and 65 spectroscopic and 26 photometric comparable field galaxies, we find that after taking into account contamination from interlopers, 11+7.0-5.6% of the cluster members are involved in potential mergers, compared to 24.7+5.3-4.6% of the field galaxies. We see no evidence of merger enhancement in the central cluster environment with respect to the field, suggesting that galaxy-galaxy merging is not a stronger source of galaxy evolution in cluster environments compared to the field at these redshifts.

We present ALMA CO (2-1) detections in 11 gas-rich cluster galaxies at z ∼ 1.6, constituting the largest sample of molecular gas measurements in z > 1.5 clusters to date. The observations span three galaxy clusters, derived from the Spitzer Adaptation of the Red-sequence Cluster Survey. We augment the >5σ detections of the CO (2-1) fluxes with multi-band photometry, yielding stellar masses and infrared-derived star formation rates, to place some of the first constraints on molecular gas properties in z ∼ 1.6 cluster environments. We measure sizable gas reservoirs of 0.5-2 × 1011 M in these objects, with high gas fractions (f gas) and long depletion timescales (τ), averaging 62% and 1.4 Gyr, respectively. We compare our cluster galaxies to the scaling relations of the coeval field, in the context of how gas fractions and depletion timescales vary with respect to the star-forming main sequence. We find that our cluster galaxies lie systematically off the field scaling relations at z = 1.6 toward enhanced gas fractions, at a level of ∼4σ, but have consistent depletion timescales. Exploiting CO detections in lower-redshift clusters from the literature, we investigate the evolution of the gas fraction in cluster galaxies, finding it to mimic the strong rise with redshift in the field. We emphasize the utility of detecting abundant gas-rich galaxies in high-redshift clusters, deeming them as crucial laboratories for future statistical studies.

We present an analysis of the relationship between the CO–H2 conversion factor (αCO) and total mass surface density (tot) in star-forming galaxies at z < 1.5. Our sample, which is drawn from the IRAM Plateau de Bure HIgh-z Blue Sequence Survey (PHIBSS) and the CO Legacy Database for GASS (COLD GASS), includes ‘normal’, massive star-forming galaxies that dominate the evolution of the cosmic star formation rate (SFR) at this epoch and probe the tot regime where the strongest variation in αCO is observed. We constrain αCO via existing CO observations, measurements of the SFR and an assumed molecular gas depletion time (tdep = Mgas/SFR) – the latter two of which establish the total molecular gas mass independent of the observed CO luminosity. For a broad range of adopted depletion times, we find that αCO is independent of total mass surface density, with little deviation from the canonical Milky Way value. This runs contrary to a scenario in which αCO decreases as surface density increases within the extended clouds of molecular gas that potentially fuel clumps of star formation in z ∼ 1 galaxies, similar to those observed in local ultra-luminous infrared galaxies. Instead, our results suggest that molecular gas, at both z ∼ 0 and z ∼ 1, is primarily in the form of self-gravitating molecular clouds. While CO observations suggest a factor of ∼3 reduction in the average molecular gas depletion time between z ∼ 0 and z ∼ 1, we find that, for typical galaxies, the structure of molecular gas and the process of star formation at z ∼ 1 is otherwise remarkably similar to that observed in local star-forming systems.

Central galaxies make up the majority of the galaxy population, including the majority of the quiescent population at M∗ > 1010M⊙. Thus, the mechanism(s) responsible for quenching central galaxies play a crucial role in galaxy evolution as whole. We combine a high-resolution cosmological N-body simulation with observed evolutionary trends of the "star formation main sequence," quiescent fraction, and stellar mass function at z < 1 to construct a model that statistically tracks the star formation histories and quenching of central galaxies. Comparing this model to the distribution of central galaxy star formation rates in a group catalog of the SDSS Data Release 7, we constrain the timescales over which physical processes cease star formation in central galaxies. Over the stellar mass range 109.5-1011M⊙ we infer quenching e-folding times that span 1.5-0.5 Gyr with more massive central galaxies quenching faster. For M∗ = 1010.5M⊙, this implies a total migration time of ∼4 Gyr from the star formation main sequence to quiescence. Compared to satellites, central galaxies take ∼2 Gyr longer to quench their star formation, suggesting that different mechanisms are responsible for quenching centrals versus satellites. Finally, the central galaxy quenching timescale we infer provides key constraints for proposed star formation quenching mechanisms. Our timescale is generally consistent with gas depletion timescales predicted by quenching through strangulation. However, the exact physical mechanism(s) responsible for this remain unclear.

We study the structure, age and metallicity gradients, and dynamical evolution using a cosmological zoom-in simulation of a Milky Way-mass galaxy from the Feedback in Realistic Environments project. In the simulation, stars older than 6 Gyr were formed in a chaotic, bursty mode and have the largest vertical scaleheights (1.5-2.5 kpc) by z = 0, while stars younger than 6 Gyr were formed in a relatively calm, stable disc. The vertical scaleheight increases with stellar age at all radii, because (1) stars that formed earlier were thicker 'at birth', and (2) stars were kinematically heated to an even thicker distribution after formation. Stars of the same age are thicker in the outer disc than in the inner disc (flaring). These lead to positive vertical age gradients and negative radial age gradients. The radial metallicity gradient is negative at the mid-plane, flattens at larger disc height |Z|, and turns positive above |Z| ~ 1.5 kpc. The vertical metallicity gradient is negative at all radii, but is steeper at smaller radii. These trends broadly agree with observations in the Milky Way and can be naturally understood from the age gradients. The vertical stellar density profile can be well described by two components, with scaleheights 200-500 pc and 1-1.5 kpc, respectively. The thick component is a mix of stars older than 4 Gyr, which formed through a combination of several mechanisms. Our results also demonstrate that it is possible to form a thin disc in cosmological simulations even with a strong stellar feedback.

We present ALMA [CI]($1-0$) (rest frequency 492 GHz) observations for asample of 13 strongly-lensed dusty star-forming galaxies originally discoveredat 1.4mm in a blank-field survey by the South Pole Telescope. We compare thesenew data with available [CI] observations from the literature, allowing a studyof the ISM properties of $\sim 30$ extreme dusty star-forming galaxies spanninga redshift range $2 < z < 5$. Using the [CI] line as a tracer of the molecularISM, we find a mean molecular gas mass for SPT-DSFGs of $6.6 \times 10^{10}$M$_{\odot}$. This is in tension with gas masses derived via low-$J$ $^{12}$COand dust masses; bringing the estimates into accordance requires either (a) anelevated CO-to-H$_2$ conversion factor for our sample of $\alpha_{\rm CO} \sim2.5$ and a gas-to-dust ratio $\sim200$, or (b) an high carbon abundance $X_{\rmCI} \sim 7\times10^{-5}$. Using observations of a range of additional atomicand molecular lines (including [CI], [CII], and multiple transitions of CO), weuse a modern Photodissociation Region code (3D-PDR) to assess the physicalconditions (including the density, UV radiation field strength, and gastemperature) within the ISM of the DSFGs in our sample. We find that the ISMwithin our DSFGs is characterised by dense gas permeated by strong UV fields.We note that previous efforts to characterise PDR regions in DSFGs may havesignificantly underestimated the density of the ISM. Combined, our analysissuggests that the ISM of extreme dusty starbursts at high redshift consists ofdense, carbon-rich gas not directly comparable to the ISM of starbursts in thelocal Universe.

The C iii] and C iv rest-frame UV emission lines are powerful probes of the ionization states of galaxies. They have furthermore been suggested as alternatives for spectroscopic redshift confirmation of objects at the epoch of reionization (), where the most frequently used redshift indicator, Lyα, is attenuated by the high fraction of neutral hydrogen in the intergalactic medium. However, currently only very few confirmations of carbon UV lines at these high redshifts exist, making it challenging to quantify these claims. Here, we present the detection of C iv λλ1548, 1551 Å in Hubble Space Telescope slitless grism spectroscopy obtained by GLASS of a Lyα emitter at z = 6.11 multiply imaged by the massive foreground galaxy cluster RXC J2248.7-4431. The C iv emission is detected at the 3σ-5σ level in two images of the source, with marginal detection in two other images. We do not detect significant C iii]λλ1907, 1909 Å emission implying an equivalent width Å (1σ) and (2σ). Combined with limits on the rest-frame UV flux from the He ii λ1640 Å emission line and the O iii]λλ1661, 1666 Å doublet, we put constraints on the metallicity and the ionization state of the galaxy. The estimated line ratios and equivalent widths do not support a scenario where an AGN is responsible for ionizing the carbon atoms. SED fits, including nebular emission lines, imply a source with a mass of log(M/M o) ∼ 9, SFR of around 10 M o yr-1, and a young stellar population old. The source shows a stronger ionizing radiation field than objects with detected C iv emission at and adds to the growing sample of low-mass (log(M/M o) ≲ 9) galaxies at the epoch of reionization with strong radiation fields from star formation.

We present a 0.4-8 μm multi-wavelength photometric catalog in the Extended Groth Strip (EGS) field. This catalog is built on the Hubble Space Telescope (HST) WFC3 and ACS data from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS), and it incorporates the existing HST data from the All-wavelength Extended Groth strip International Survey (AEGIS) and the 3D-HST program. The catalog is based on detections in the F160W band reaching a depth of F160W = 26.62 AB (90% completeness, point sources). It includes the photometry for 41,457 objects over an area of ≈ 206 arcmin2 in the following bands: HST/ACS F606W and F814W; HST WFC3 F125W, F140W, and F160W; Canada-France-Hawaii Telescope (CFHT)/Megacam u∗, g′, r′, i′ and z′; CFHT/WIRCAM J, H, and K S; Mayall/NEWFIRM J1, J2, J3, H1, H2, and K; Spitzer IRAC 3.6, 4.5, 5.8, and 8.0 μm. We are also releasing value-added catalogs that provide robust photometric redshifts and stellar mass measurements. The catalogs are publicly available through the CANDELS repository.

We present ALMA [CI]($1-0$) (rest frequency 492 GHz) observations for asample of 13 strongly-lensed dusty star-forming galaxies originally discoveredat 1.4mm in a blank-field survey by the South Pole Telescope. We compare thesenew data with available [CI] observations from the literature, allowing a studyof the ISM properties of $\sim 30$ extreme dusty star-forming galaxies spanninga redshift range $2 < z < 5$. Using the [CI] line as a tracer of the molecularISM, we find a mean molecular gas mass for SPT-DSFGs of $6.6 \times 10^{10}$M$_{\odot}$. This is in tension with gas masses derived via low-$J$ $^{12}$COand dust masses; bringing the estimates into accordance requires either (a) anelevated CO-to-H$_2$ conversion factor for our sample of $\alpha_{\rm CO} \sim2.5$ and a gas-to-dust ratio $\sim200$, or (b) an high carbon abundance $X_{\rmCI} \sim 7\times10^{-5}$. Using observations of a range of additional atomicand molecular lines (including [CI], [CII], and multiple transitions of CO), weuse a modern Photodissociation Region code (3D-PDR) to assess the physicalconditions (including the density, UV radiation field strength, and gastemperature) within the ISM of the DSFGs in our sample. We find that the ISMwithin our DSFGs is characterised by dense gas permeated by strong UV fields.We note that previous efforts to characterise PDR regions in DSFGs may havesignificantly underestimated the density of the ISM. Combined, our analysissuggests that the ISM of extreme dusty starbursts at high redshift consists ofdense, carbon-rich gas not directly comparable to the ISM of starbursts in thelocal Universe.

The C iii]λλ1907, 1909 rest-frame UV emission doublet has recently been detected in galaxies during the epoch of reionization (z > 6), with a high equivalent width (EW; 10 Å, rest frame). Currently, it is possible to obtain much more detailed information for star-forming galaxies at significantly lower redshift. Accordingly, studies of their far-UV spectra are useful for understanding the factors modulating the strength of C iii] emission. We present the first statistical sample of C iii] emission measurements in star-forming galaxies at z ∼ 1. Our sample is drawn from the DEEP2 survey and spans the redshifts 0.64 z 1.35 ((z) = 1.08). We find that the median EW of individual C iii] detections in our sample (1.30 Å) is much smaller than the typical value observed thus far at z > 6. Furthermore, out of 184 galaxies with coverage of C iii], only 40 have significant detections. Galaxies with individual C iii] detections have bluer colors and lower luminosities on average than those without, implying that strong C iii] emitters are in general young and low-mass galaxies without significant dust extinction. Using stacked spectra, we further investigate how C iii] strength correlates with multiple galaxy properties (M B, U - B, M ∗, star formation rate, specific star formation rate) and rest-frame near-UV (Fe ii∗ and Mg ii) and optical ([O iii] and Hβ) emission line strengths. These results provide a detailed picture of the physical environment in star-forming galaxies at z ∼ 1, and motivate future observations of strong C iii] emitters at similar redshifts.

We present the first results of the K-band Multi-Object Spectrometer (KMOS) Lens-Amplified Spectroscopic Survey, a new ESO Very Large Telescope large program, doing multi-object integral field spectroscopy of galaxies gravitationally lensed behind seven galaxy clusters selected from the Hubble Space Telescope (HST) Grism Lens-Amplified Survey from Space. Using the power of the cluster magnification, we are able to reveal the kinematic structure of 25 galaxies at 0.7 z 2.3, in four cluster fields, with stellar masses 7.8log;(M∗/Mo) 10.5. This sample includes five sources at Z > 1 with lower stellar masses than in any previous kinematic integral field unit (IFU) surveys. Our sample displays a diversity in kinematic structure over this mass and redshift range. The majority of our kinematically resolved sample is rotationally supported, but with a lower ratio of rotational velocity to velocity dispersion than in the local universe, indicating the fraction of dynamically hot disks changes with cosmic time. We find that no galaxies with stellar mass

Exploiting the data of the Grism Lens-Amplified Survey from Space (GLASS), we characterize the spatial distribution of star formation in 76 highly active star-forming galaxies in 10 clusters at 0.3 < z < 0.7. All of these galaxies are likely restricted to first infall. In a companion paper, we contrast the properties of field and cluster galaxies, whereas here we correlate the properties of H? emitters to a number of tracers of the cluster environment to investigate its role in driving galaxy transformations. H? emitters are found in the clusters out to 0.5 virial radii, the maximum radius covered by GLASS. The peak of the H? emission is offset with respect to the peak of the UV continuum. We decompose these offsets into a radial and a tangential component. The radial component points away from the cluster center in 60% of the cases, with 95% confidence. The decompositions agree with cosmological simulations; that is, the H? emission offset correlates with galaxy velocity and ram-pressure stripping signatures. Trends between H? emitter properties and surface mass density distributions and X-ray emissions emerge only for unrelaxed clusters. The lack of strong correlations with the global environment does not allow us to identify a unique environmental effect originating from the cluster center. In contrast, correlations between H? morphology and local number density emerge. We conclude that local effects, uncorrelated to the cluster-centric radius, play a more important role in shaping galaxy properties.

The ultraviolet background (UVB) emitted by quasars and galaxies governs the ionization and thermal state of the intergalactic medium (IGM), regulates the formation of high-redshift galaxies, and is thus a key quantity for modeling cosmic reionization. The vast majority of cosmological hydrodynamical simulations implement the UVB via a set of spatially uniform photoionization and photoheating rates derived from UVB synthesis models. We show that simulations using canonical UVB rates reionize and, perhaps more importantly, spuriously heat the IGM, much earlier (z ∼15) than they should. This problem arises because at z > 6, where observational constraints are nonexistent, the UVB amplitude is far too high. We introduce a new methodology to remedy this issue, and we generate self-consistent photoionization and photoheating rates to model any chosen reionization history. Following this approach, we run a suite of hydrodynamical simulations of different reionization scenarios and explore the impact of the timing of reionization and its concomitant heat injection on the thermal state of the IGM. We present a comprehensive study of the pressure smoothing scale of IGM gas, illustrating its dependence on the details of both hydrogen and helium reionization, and argue that it plays a fundamental role in interpreting Ly α forest statistics and the thermal evolution of the IGM. The premature IGM heating we have uncovered implies that previous work has likely dramatically overestimated the impact of photoionization feedback on galaxy formation, which sets the minimum halo mass able to form stars at high redshifts. We make our new UVB photoionization and photoheating rates publicly available for use in future simulations.

We combine deep Hubble Space Telescope grism spectroscopy with a new Bayesian method to derive maps of gas-phase metallicity for 10 star-forming galaxies at high redshift (). Exploiting lensing magnification by the foreground cluster MACS1149.6+2223, we reach sub-kiloparsec spatial resolution and push the limit of stellar mass associated with such high-z spatially resolved measurements below for the first time. Our maps exhibit diverse morphologies, indicative of various effects such as efficient radial mixing from tidal torques, rapid accretion of low-metallicity gas, and other physical processes that can affect the gas and metallicity distributions in individual galaxies. Based upon an exhaustive sample of all existing sub-kiloparesec resolution metallicity gradient measurements at high z, we find that predictions given by analytical chemical evolution models assuming a relatively extended star-formation profile in the early disk-formation phase can explain the majority of observed metallicity gradients, without involving galactic feedback or radial outflows. We observe a tentative correlation between stellar mass and metallicity gradients, consistent with the "downsizing" galaxy formation picture that more massive galaxies are more evolved into a later phase of disk growth, where they experience more coherent mass assembly at all radii and thus show shallower metallicity gradients. In addition to the spatially resolved analysis, we compile a sample of homogeneously cross-calibrated integrated metallicity measurements spanning three orders of magnitude in stellar mass at z ∼ 1.8. We use this sample to study the mass-metallicity relation (MZR) and find that the slope of the observed MZR can rule out the momentum-driven wind model at a 3σ confidence level.