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Many quiescent galaxies discovered in the early Universe by JWST raise fundamental questions on when and how these galaxies became and stayed quenched. Making use of the latest version of the semianalytic model GAEA that provides good agreement with the observed quenched fractions up toz∼ 3, we make predictions for the expected fractions of quiescent galaxies up toz∼ 7 and analyze the main quenching mechanism. We find that in a simulated box of 685 Mpc on a side, the first quenched massive (M_⋆∼ 10¹¹M_⊙), Milky Way–mass, and low-mass (M_⋆∼ 10^9.5M_⊙) galaxies appear atz∼ 4.5,z∼ 6.2, and beforez= 7, respectively. Most quenched galaxies identified at early redshifts remain quenched for more than 1 Gyr. Independently of galaxy stellar mass, the dominant quenching mechanism at high redshift is accretion disk feedback (quasar winds) from a central massive black hole, which is triggered by mergers in massive and Milky Way–mass galaxies and by disk instabilities in low-mass galaxies. Environmental stripping becomes increasingly more important at lower redshift.

We have identified 189 candidate z > 1.3 protoclusters and clusters in the LSST Deep Drilling Fields. This sample will enable the measurement of the metal enrichment and star formation history of clusters during their early assembly period through the direct measurement of the rate of supernovae identified through the LSST. The protocluster sample was selected from galaxy overdensities in a Spitzer/IRAC colour-selected sample using criteria that were optimized for protocluster purity using a realistic light-cone. Our tests reveal that $60\!-\!80~{{\ \rm per\ cent}}$ of the identified candidates are likely to be genuine protoclusters or clusters, which is corroborated by a ∼4σ stacked X-ray signal from these structures. We provide photometric redshift estimates for 47 candidates which exhibit strong peaks in the photo-z distribution of their candidate members. However, the lack of a photo-z peak does not mean a candidate is not genuine, since we find a stacked X-ray signal of similar significance from both the candidates that exhibit photo-z peaks and those that do not. Tests on the light-cone reveal that our pursuit of a pure sample of protoclusters results in that sample being highly incomplete ($\sim 4~{{\ \rm per\ cent}}$) and heavily biased towards larger, richer, more massive, and more centrally concentrated protoclusters than the total protocluster population. Most ($\sim 75~{{\ \rm per\ cent}}$) of the selected protoclusters are likely to have a maximum collapsed halo mass of between 1013 and 1014 M⊙, with only $\sim 25~{{\ \rm per\ cent}}$ likely to be collapsed clusters above 1014 M⊙. However, the aforementioned bias ensures our sample is $\sim 50~{{\ \rm per\ cent}}$ complete for structures that have already collapsed into clusters more massive than 1014 M⊙.

Luminous red galaxies, or LRGs, are representative of the most massive galaxies and were originally selected in the Sloan Digital Sky Survey as good tracers of large-scale structure. They are dominated by by uniformly old stellar populations, have low star formation rates, early type morphologies, and little cold gas. Despite having old stellar populations and little in situ star formation, studies have shown that they have grown their stellar mass since z = 1, implying that they grow predominantly via the accretion of satellites. Tests of this picture have been limited because of the lack of deep imaging data sets that both covers a large enough area of the sky to contain substantial numbers of LRGs and that also is deep enough to detect faint satellites. We use the 25 deg2 Early Data Release (EDR) of the DESI Legacy Imaging Surveys to characterize the satellite galaxy population of LRGs out to z = 0.65. The DESI Legacy Imaging Surveys are comprised of grz imaging to 2–2.5 mag deeper than SDSS and with better image quality. We use a new statistical background technique to identify excess populations of putative satellite galaxies around 1823 LRGs at 0.2 < z < 0.65. In three redshift and luminosity bins we measure the numbers of satellite galaxies and their r−z colour distribution down to rest-frame g-band luminosity limits at least 3.6 times fainter than L*. In addition, we develop a forward modeling technique and apply it to constrain the mean number of satellites in each of our redshift and luminosity bins. Finally, we use these estimates to determine the amount of stellar mass growth in LRGs down to the local Universe.

We explore models of massive (>1010 M⊙) satellite quenching in massive clusters at z ≳ 1 using an MCMC framework, focusing on two primary parameters: Rquench (the host-centric radius at which quenching begins) and τquench (the time-scale upon which a satellite quenches after crossing Rquench). Our MCMC analysis shows two local maxima in the 1D posterior probability distribution of Rquench at approximately 0.25 and 1.0 R200. Analysing four distinct solutions in the τquench–Rquench parameter space, nearly all of which yield quiescent fractions consistent with observational data from the GOGREEN survey, we investigate whether these solutions represent distinct quenching pathways and find that they can be separated between ‘starvation’ and ‘core quenching’ scenarios. The starvation pathway is characterized by quenching time-scales that are roughly consistent with the total cold gas (H2 + H i) depletion time-scale at intermediate z, while core quenching is characterized by satellites with relatively high line-of-sight velocities that quench on short time-scales (∼0.25 Gyr) after reaching the inner region of the cluster (<0.30 R200). Lastly, we break the degeneracy between these solutions by comparing the observed properties of transition galaxies from the GOGREEN survey. We conclude that only the ‘starvation’ pathway is consistent with the projected phase-space distribution and relative abundance of transition galaxies at z ∼ 1. However, we acknowledge that ram pressure might contribute as a secondary quenching mechanism.

We present an analysis of the galaxy stellar mass function (SMF) of 14 known protoclusters between 2.0 < z < 2.5 in the COSMOS field, down to a mass limit of 109.5 M⊙. We use existing photometric redshifts with a statistical background subtraction, and consider star-forming and quiescent galaxies identified from (NUV − r) and (r − J) colours separately. Our fiducial sample includes galaxies within 1 Mpc of the cluster centres. The shape of the protocluster SMF of star-forming galaxies is indistinguishable from that of the general field at this redshift. Quiescent galaxies, however, show a flatter SMF than in the field, with an upturn at low mass, though this is only significant at ∼2σ. There is no strong evidence for a dominant population of quiescent galaxies at any mass, with a fraction <15 per cent at 1σ confidence for galaxies with log M*/M⊙ < 10.5. We compare our results with a sample of galaxy groups at 1 < z < 1.5, and demonstrate that a significant amount of environmental quenching must take place between these epochs, increasing the relative abundance of high-mass ($\rm M_{\ast } \gt 10^{10.5} {\rm M}_{\odot }$) quiescent galaxies by a factor ≳ 2. However, we find that at lower masses ($\rm M_{\ast } \lt 10^{10.5} {\rm M}_{\odot }$), no additional environmental quenching is required.

We investigate the role of dense environments in suppressing star formation by studying $\rm \log _{10}(M_\star /M_\odot) \gt 9.7$ star-forming galaxies in nine clusters from the Local Cluster Survey (0.0137 < z < 0.0433) and a large comparison field sample drawn from the Sloan Digital Sky Survey. We compare the star formation rate (SFR) with stellar mass relation as a function of environment and morphology. After carefully controlling for mass, we find that in all environments, the degree of SFR suppression increases with increasing bulge-to-total (B/T) ratio. In addition, the SFRs of cluster and infall galaxies at a fixed mass are more suppressed than their field counterparts at all values of B/T. These results suggest a quenching mechanism that is linked to bulge growth that operates in all environments and an additional mechanism that further reduces the SFRs of galaxies in dense environments. We limit the sample to B/T ≤ 0.3 galaxies to control for the trends with morphology and find that the excess population of cluster galaxies with suppressed SFRs persists. We model the time-scale associated with the decline of SFRs in dense environments and find that the observed SFRs of the cluster core galaxies are consistent with a range of models including a mechanism that acts slowly and continuously over a long (2–5 Gyr) time-scale, and a more rapid (<1 Gyr) quenching event that occurs after a delay period of 1–6 Gyr. Quenching may therefore start immediately after galaxies enter clusters.

The Makani galaxy hosts the poster child of a galactic wind on scales of the circumgalactic medium. It consists of a two-episode wind in which the slow, outer wind originated 400 Myr ago (Episode I;R_I= 20 − 50 kpc) and the fast, inner wind is 7 Myr old (Episode II;R_II= 0 − 20 kpc). While this wind contains ionized, neutral, and molecular gas, the physical state and mass of the most extended phase—the warm, ionized gas—are unknown. Here we present Keck optical spectra of the Makani outflow. These allow us to detect hydrogen lines out tor= 30–40 kpc and thus constrain the mass, momentum, and energy in the wind. Many collisionally excited lines are detected throughout the wind, and their line ratios are consistent with 200–400 km s⁻¹shocks that power the ionized gas, withv_shock=σ_wind. Combining shock models, density-sensitive line ratios, and mass and velocity measurements, we estimate that the ionized mass and outflow rate in the Episode II wind could be as high as those of the molecular gas:$M_{\mathrm{II}}^{\mathrm{H}\mathrm{II}}\sim M_{\mathrm{II}}^{{\mathrm{H}}_2}=(1-2)\times {10}^9{M}_{\odot }$and$\mathit{dM}/{\mathit{dt}}_{\mathrm{II}}^{\mathrm{H}\mathrm{II}}\sim \mathit{dM}/{\mathit{dt}}_{\mathrm{II}}^{{\mathrm{H}}_2}=170-250M_{\odot }$yr⁻¹. The outer wind has slowed, so that$\mathit{dM}/{\mathit{dt}}_{\mathrm{I}}^{\mathrm{H}\mathrm{II}}\sim 10M_{\odot }$yr⁻¹, but it contains more ionized gas,$M_{\mathrm{I}}^{\mathrm{H}\mathrm{II}}=5\times {10}^9$M_⊙. The momentum and energy in the recent Episode II wind imply a momentum-driven flow (p“boost” ∼7) driven by the hot ejecta and radiation pressure from the Eddington-limited, compact starburst. Much of the energy and momentum in the older Episode I wind may reside in a hotter phase, or lie further into the circumgalactic medium.

We investigate galactic winds in the HizEA galaxies, a collection of 46 late-stage galaxy mergers atz= 0.4–0.8, with stellar masses of$\log (M_{*}/M_{\odot })=10.4–11.5$, star formation rates (SFRs) of 20–500M_⊙yr⁻¹, and ultra-compact (a few 100 pc) central star-forming regions. We measure their gas kinematics using the Mgiiλλ2796,2803 absorption lines in optical spectra from MMT, Magellan, and Keck. We find evidence of outflows in 90% of targets, with maximum outflow velocities of 550–3200 km s⁻¹. We combine these data with ten samples from the literature to construct scaling relations for outflow velocity versus SFR, star formation surface density (Σ_SFR),M_*, and SFR/M_*. The HizEA galaxies extend the dynamic range of the scaling relations by a factor of ∼2–4 in outflow velocity and an order of magnitude in SFR and Σ_SFR. The ensemble scaling relations exhibit strong correlations between outflow velocity, SFR, SFR/R, and Σ_SFR, and weaker correlations withM_*and SFR/M_*. The HizEA galaxies are mild outliers on the SFR andM_*scaling relations, but they connect smoothly with more typical star-forming galaxies on plots of outflow velocity versus SFR/Rand Σ_SFR. These results provide further evidence that the HizEA galaxies’ exceptional outflow velocities are a consequence of their extreme star formation conditions rather than hidden black hole activity, and they strengthen previous claims that Σ_SFRis one of the most important properties governing the velocities of galactic winds.

We present results on the properties of extreme gas outflows in massive (M_*∼ 10¹¹M_⊙), compact, starburst (star formation rate, SFR∼ 200M_⊙yr⁻¹) galaxies atz= 0.4–0.7 with very high star formation surface densities (Σ_SFR∼ 2000M_⊙yr⁻¹kpc⁻²). Using optical Keck/HIRES spectroscopy of 14 HizEA starburst galaxies, we identify outflows with maximum velocities of 820–2860 km s⁻¹. High-resolution spectroscopy allows us to measure precise column densities and covering fractions as a function of outflow velocity and characterize the kinematics and structure of the cool gas outflow phase (T∼ 10⁴K). We find substantial variation in the absorption profiles, which likely reflects the complex morphology of inhomogeneously distributed, clumpy gas and the intricacy of the turbulent mixing layers between the cold and hot outflow phases. There is not a straightforward correlation between the bursts in the galaxies’ star formation histories and their wind absorption line profiles, as might naively be expected for starburst-driven winds. The lack of strong Mgiiabsorption at the systemic velocity is likely an orientation effect, where the observations are down the axis of a blowout. We infer high mass outflow rates of ∼50–2200M_⊙yr⁻¹, assuming a fiducial outflow size of 5 kpc, and mass loading factors ofη∼ 5 for most of the sample. While these values have high uncertainties, they suggest that starburst galaxies are capable of ejecting very large amounts of cool gas that will substantially impact their future evolution.