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We measure the bivariate luminosity function (BLF) of galaxy pairs and use it to probe and characterize the galaxy–galaxy interaction between pair members. The galaxy pair sample is selected from the main galaxy sample of Sloan Digital Sky Survey and supplied with a significant number of redshifts from the LAMOST spectral and GAMA surveys. We find the BLFs depend on the projected distance dp between pair members. At large separation dp > 150 h−1 kpc, the BLF degenerates into a luminosity function of single galaxies, indicating few interactions between pair members. At 100 h−1 kpc ≤ dp ≤ 150 h−1 kpc, the BLF starts to show a correlation between pair members, in the sense that the shape of the conditional luminosity function (CLF) of one member galaxy starts to depend on the luminosity of the other member galaxy. Specifically, the CLF with a brighter companion has a steeper faint-end slope, which becomes even more significant at 50 h−1 kpc ≤ dp ≤ 100 h−1 kpc. This behavior is consistent with the scenario—and also is the observational evidence—that dynamic friction drives massive major merger pairs to merge more quickly. At close distance dp ≤ 50 h−1 kpc, aside from the merging timescale effect, the BLF also shows an overall brightening of ΔMr ≥ 0.04 mag, which reveals the enhanced star formation of the close-pair phase. By combining this with the statistical conclusion that the star formation rate of late-type galaxies in close pairs is enhanced at a level of about 40%, we further conclude that the average starburst timescale of close pairs is as long as 0.4 Gyr. [ABSTRACT FROM AUTHOR]

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 . 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 Hα emitters to a number of tracers of the cluster environment to investigate its role in driving galaxy transformations. Hα emitters are found in the clusters out to 0.5 virial radii, the maximum radius covered by GLASS. The peak of the Hα 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 Hα emission offset correlates with galaxy velocity and ram-pressure stripping signatures. Trends between Hα 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 Hα 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. [ABSTRACT FROM AUTHOR]

Using deep Hubble Frontier Fields imaging and slitless spectroscopy from the Grism Survey from Space, we study 2200 cluster and 1748 field galaxies at to determine the impact of environment on galaxy size and structure at stellar masses , an unprecedented limit at these redshifts. Based on simple assumptions——we find no significant differences in half-light radii (re) between equal-mass cluster or field systems. More complex analyses——reveal local density (Σ) to induce only a 7% ± 3% (95% confidence) reduction in re beyond what can be accounted for by U − V color, Sérsic index (n), and redshift (z) effects. Almost any size difference between galaxies in high- and low-density regions is thus attributable to their different distributions in properties other than environment. Indeed, we find a clear color–re correlation in low-mass passive cluster galaxies () such that bluer systems have larger radii, with the bluest having sizes consistent with equal-mass star-forming galaxies. We take this as evidence that large-re low-mass passive cluster galaxies are recently acquired systems that have been environmentally quenched without significant structural transformation (e.g., by ram pressure stripping or starvation). Conversely, ∼20% of small-re low-mass passive cluster galaxies appear to have been in place since . Given the consistency of the small-re galaxies’ stellar surface densities (and even colors) with those of systems more than ten times as massive, our findings suggest that clusters mark places where galaxy evolution is accelerated for an ancient base population spanning most masses, with late-time additions quenched by environment-specific mechanisms mainly restricted to the lowest masses. [ABSTRACT FROM AUTHOR]