We present a robust method, weighted von Mises kernel density estimation, along with boundary correction to reconstruct the underlying number density field of galaxies. We apply this method to galaxies brighter than HST/F160w ≤ 26 AB mag at the redshift range of 0.4 ≤ z ≤ 5 in the five CANDELS fields (GOODS-N, GOODS-S, EGS, UDS, and COSMOS). We then use these measurements to explore the environmental dependence of the star formation activity of galaxies. We find strong evidence of environmental quenching for massive galaxies (M 10 11 M ) out to z ∼ 3.5 such that an over-dense environment hosts 20% more massive quiescent galaxies compared to an under-dense region. We also find that environmental quenching efficiency grows with stellar mass and reaches ∼ 60% for massive galaxies at z ∼ 0.5. The environmental quenching is also more efficient in comparison to the stellar mass quenching for low mass galaxies (M 10 10 M ) at low and intermediate redshifts (z 1.2). Our findings concur thoroughly with the "over-consumption" quenching model where the termination of cool gas accretion (cosmological starvation) happens in an over-dense environment and the galaxy starts to consume its remaining gas reservoir in depletion time. The depletion time depends on the stellar mass and could explain the evolution of environmental quenching efficiency with the stellar mass.

Measuring the chemical composition of galaxies is crucial to our understanding of galaxy formation and evolution models. However, such measurements are extremely challenging for quiescent galaxies at high redshifts, which have faint stellar continua and compact sizes, making it difficult to detect absorption lines and nearly impossible to spatially resolve them. Gravitational lensing offers the opportunity to study these galaxies with detailed spectroscopy that can be spatially resolved. In this work, we analyze deep spectra of MRG-M0138, a lensed quiescent galaxy at z = 1.98 which is the brightest of its kind, with an H-band magnitude of 17.1. Taking advantage of full spectral fitting, we measure [Mg/Fe] = 0.51 ± 0.05, [Fe/H] = 0.26 ± 0.04, and, for the first time, the stellar abundances of 6 other elements in this galaxy. We further constrained, also for the first time in a z ∼ 2 galaxy, radial gradients in stellar age, [Fe/H], and [Mg/Fe]. We detect no gradient in age or [Mg/Fe] and a slightly negative gradient in [Fe/H], which has a slope comparable to that seen in local early-type galaxies. Our measurements show that not only is MRG-M0138 very Mg-enhanced compared to the centers of local massive early-type galaxies, it is also very iron rich. These dissimilar abundances suggest that even the inner regions of massive galaxies have experienced significant mixing of stars in mergers, in contrast to a purely inside-out growth model. The abundance pattern observed in MRG-M0138 challenges simple galactic chemical evolution models that vary only the star formation timescale and shows the need for more elaborate models.

We investigate the clustering and halo properties of ∼ 5000 Lyα-selected emission line galaxies (LAEs) from the Slicing COSMOS 4K (SC4K) and from archival NB497 imaging of SA22 split in 15 discrete redshift slices between z ∼ 2.5 − 6. We measure clustering lengths of r 0 ∼ 3 − 6 h −1 Mpc and typical halo masses of ∼ 10 11 M for our narrowband-selected LAEs with typical L Lyα ∼ 10 42−43 erg s −1 . The intermediate band-selected LAEs are observed to have r 0 ∼ 3.5 − 15 h −1 Mpc with typical halo masses of ∼ 10 11−12 M and typical L Lyα ∼ 10 43−43.6 erg s −1 . We find a strong, redshift-independent correlation between halo mass and Lyα luminosity normalized by the characteristic Lyα luminosity, L (z). The faintest LAEs (L ∼ 0.1 L (z)) typically identified by deep narrowband surveys are found in 10 10 M halos and the brightest LAEs (L ∼ 7 L (z)) are found in ∼ 5 × 10 12 M halos. A dependency on the rest-frame 1500Å UV luminosity, M UV , is also observed where the halo masses increase from 10 11 M to 10 13 M for M UV ∼ −19 mag to −23.5 mag. Halo mass is also observed to increase from 10 9.8 M to 10 12.3 M for dust-corrected UV star formation rates from ∼ 0.6 M yr −1 to 10 M yr −1 and continues to increase up to 10 13.5 M in halo mass, where the majority of those sources are AGN. All the trends we observe are found to be redshift-independent. Our results reveal that LAEs are the likely progenitors of a wide range of galaxies depending on their luminosity, from dwarf-like, to Milky Way-type, to bright cluster galaxies. LAEs therefore provide unique insight into the early formation and evolution of the galaxies we observe in the local Universe.