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We have measured the angular autocorrelation function of near-infrared galaxies in SERVS + DeepDrill, the Spitzer Extragalactic Representative Volume Survey and its follow-up survey of the Deep Drilling Fields, in three large fields totalling over 20 deg2 on the sky, observed in two bands centred on 3.6 and 4.5 μm. We performed this analysis on the full sample as well as on sources selected by [3.6]–[4.5] colour in order to probe clustering for different redshift regimes. We estimated the spatial correlation strength as well, using the redshift distribution from S-COSMOS with the same source selection. The strongest clustering was found for our bluest subsample, with 〈z〉 ∼ 0.7, which has the narrowest redshift distribution of all our subsamples. We compare these estimates to previous results from the literature, but also to estimates derived from mock samples, selected in the same way as the observational data, using deep light-cones generated from the SHARK semi-analytical model of galaxy formation. For all simulated (sub)samples, we find a slightly steeper slope than for the corresponding observed ones, but the spatial clustering length is comparable in most cases.

We explore the properties of central galaxies living in voids using the eagle cosmological hydrodynamic simulations. Based on the minimum void-centric distance, we define four galaxy samples: inner void, outer void, wall, and skeleton. We find that inner void galaxies with host halo masses $\lt 10^{12}\,\rm M_{\odot }$ have lower stellar mass and stellar mass fractions than those in denser environments, and the fraction of galaxies with star formation (SF) activity and atomic hydrogen (H i) gas decreases with increasing void-centric distance, in agreement with observations. To mitigate the influence of stellar (halo) mass, we compare inner void galaxies to subsamples of fixed stellar (halo) mass. Compared to denser environments, inner void galaxies with $M_{*}= 10^{[9.0-9.5]}\,\rm M_{\odot }$ have comparable SF activity and H i gas fractions, but the lowest quenched galaxy fraction. Inner void galaxies with $M_{*}= 10^{[9.5-10.5]}\,\rm M_{\odot }$ have the lowest H i gas fraction, the highest quenched fraction and the lowest gas metallicities. On the other hand, inner void galaxies with $M_{*}\gt 10^{10.5}\,\rm M_{\odot }$ have comparable SF activity and H i gas fractions to their analogues in denser environments. They retain the highest metallicity gas that might be linked to physical processes that act with lower efficiency in underdense regions such as AGN (active galaxy nucleus) feedback. Furthermore, inner void galaxies have the lowest fraction of positive gas-phase metallicity gradients, which are typically associated with external processes or feedback events, suggesting they have more quiet merger histories than galaxies in denser environments. Our findings shed light on how galaxies are influenced by their large-scale environment.

We present a pilot, untargeted extragalactic carbon monoxide (CO) emission-line survey using ALMACAL, a project utilizing ALMA calibration data for scientific purposes. In 33 deep (Texp > 40 min) ALMACAL fields, we report six CO emission-line detections above S/N > 4, one-third confirmed by MUSE observations. With this pilot survey, we probe a cosmologically significant volume of ∼105 cMpc3, widely distributed over many pointings in the southern sky, making the survey largely insusceptible to the effects of cosmic variance. We derive the redshift probability of the CO detections using probability functions from the Shark semi-analytical model of galaxy formation. By assuming typical CO excitations for the detections, we put constraints on the cosmic molecular gas mass density evolution over the redshift range 0 < z < 1.5. The results of our pilot survey are consistent with the findings of other untargeted emission-line surveys and the theoretical model predictions and currently cannot rule out a non-evolving molecular gas mass density. Our study demonstrates the potential of using ALMA calibrator fields as a multi-sightline untargeted CO emission-line survey. Applying this approach to the full ALMACAL database will provide an accurate, free of cosmic variance, measurement of the molecular luminosity function as a function of redshift.

Observations show that the surface brightness of disc galaxies can be well-described by a single exponential (TI), up-bending (TIII), or down-bending (TII) profiles in the outskirts. Here we characterize the mass surface densities of simulated late-type galaxies from the eagle project according to their distribution of mono-age stellar populations, the star formation activity, and angular momentum content. We find a clear correlation between the inner scale lengths and the stellar spin parameter, λ, for all three disc types with λ > 0.35. The outer scale lengths of TII and TIII discs show a positive trend with λ, albeit weaker for the latter. TII discs prefer fast rotating galaxies. With regards to the stellar age distribution, negative and U-shape age profiles are the most common for all disc types. Positive age profiles are determined by a more significant contribution of young stars in the central regions, which decrease rapidly in the outer parts. TII discs prefer relative higher contributions of old stars compared to other mono-age populations across the discs whereas TIII discs become progressively more dominated by intermediate age (2–6 Gyr) stars for increasing radius. The change in slope of the age profiles is located after the break of the mass surface density. We find evidence of larger flaring for the old stellar populations in TIII systems compared to TI and TII, which could indicate the action of other processes. Overall, the relative distributions of mono-age stellar populations and the dependence of the star formation activity on radius are found to shape the different disc types and age profiles.

We study the origin of misalignments between the stellar and star-forming gas components of simulated galaxies in the eagle simulations. We focus on galaxies with stellar masses ≥109 M⊙ at 0 ≤ z ≤ 1. We compare the frequency of misalignments with observational results from the SAMI survey and find that overall, eagle can reproduce the incidence of misalignments in the field and clusters, as well as the dependence on stellar mass and optical colour within the uncertainties. We study the dependence on kinematic misalignments with internal galaxy properties and different processes related to galaxy mergers and sudden changes in stellar and star-forming gas mass. We find that galaxy mergers happen in similar frequency in mis- and aligned galaxies, with the main difference being misaligned galaxies showing a higher tidal field strength and fraction of ex situ stars. We find that despite the environment being relevant in setting the conditions to misalign the star-forming gas, the properties internal to galaxies play a crucial role in determining whether the gas quickly aligns with the stellar component or not. Hence, galaxies that are more triaxial and more dispersion dominated display more misalignments because they are inefficient at realigning the star-forming gas towards the stellar angular momentum vector.

Using the eagle (Evolution and Assembly of GaLaxies and their Environments) suite of simulations, we demonstrate that both cold gas stripping and starvation of gas inflow play an important role in quenching satellite galaxies across a range of stellar and halo masses, M⋆ and M200. Quantifying the balance between gas inflows, outflows, and star formation rates, we show that even at z = 2, only $\approx 30{{\ \rm per\ cent}}$ of satellite galaxies are able to maintain equilibrium or grow their reservoir of cool gas – compared to $\approx 50{{\ \rm per\ cent}}$ of central galaxies at this redshift. We find that the number of orbits completed by a satellite on first-infall to a group environment is a very good predictor of its quenching, even more so than the time since infall. On average, we show that intermediate-mass satellites with M⋆ between will be quenched at $10^{9}\, {\rm M}_{\odot }\, {\rm and}\, 10^{10}\, {\rm M}_{\odot }$ first pericenter in massive group environments, $M_{200}\gt 10^{13.5}\, {\rm M}_{\odot }$; and will be quenched at second pericenter in less massive group environments, $M_{200}\lt 10^{13.5}\, {\rm M}_{\odot }$. On average, more massive satellites ($M_{\star }\gt 10^{10}\, {\rm M}_{\odot }$) experience longer depletion time-scales, being quenched between first and second pericenters in massive groups, while in smaller group environments, just $\approx 30{{\ \rm per\ cent}}$ will be quenched even after two orbits. Our results suggest that while starvation alone may be enough to slowly quench satellite galaxies, direct gas stripping, particularly at pericenters, is required to produce the short quenching time-scales exhibited in the simulation.

We study environmental quenching using the spatial distribution of current star formation and stellar population ages with the full SAMI Galaxy Survey. By using a star formation concentration index [C-index, defined as log10(r50, H α/r50, cont)], we separate our sample into regular galaxies (C-index ≥−0.2) and galaxies with centrally concentrated star formation (SF-concentrated; C-index <−0.2). Concentrated star formation is a potential indicator of galaxies currently undergoing ‘outside-in’ quenching. Our environments cover ungrouped galaxies, low-mass groups (M200 ≤ 1012.5M⊙), high-mass groups (M200 in the range 1012.5–14 M⊙) and clusters (M200 > 1014M⊙). We find the fraction of SF-concentrated galaxies increases as halo mass increases by 9 ± 2 per cent, 8 ± 3 per cent, 19 ± 4 per cent, and 29 ± 4 per cent for ungrouped galaxies, low-mass groups, high-mass groups, and clusters, respectively. We interpret these results as evidence for ‘outside-in’ quenching in groups and clusters. To investigate the quenching time-scale in SF-concentrated galaxies, we calculate light-weighted age (AgeL) and mass-weighted age (AgeM) using full spectral fitting, as well as the Dn4000 and HδA indices. We assume that the average galaxy age radial profile before entering a group or cluster is similar to ungrouped regular galaxies. At large radius (1–2 Re), SF-concentrated galaxies in high-mass groups have older ages than ungrouped regular galaxies with an age difference of 1.83 ± 0.38 Gyr for AgeL and 1.34 ± 0.56 Gyr for AgeM. This suggests that while ‘outside-in’ quenching can be effective in groups, the process will not quickly quench the entire galaxy. In contrast, the ages at 1–2 Re of cluster SF-concentrated galaxies and ungrouped regular galaxies are consistent (difference of 0.19 ± 0.21 Gyr for AgeL, 0.40 ± 0.61 Gyr for AgeM), suggesting the quenching process must be rapid.