Daniel

Kelson

We present the initial sample of redshifts for 3839 galaxies in the MeerKAT DEEP2 field-the most sensitive similar to 1.4 GHz radio field yet observed with sigma(n) = 0.55 mu Jy beam(-1), reaching the confusion limit. Using a spectrophotometric technique combining coarse optical spectra with broadband photometry, we obtain redshifts with sigma(z )less than or similar to 0.01(1 + z), as determined from repeat observations. The resulting radio luminosity functions between 0.2 < z < 1.3 from our sample of 3839 individual galaxies are in remarkable agreement with those inferred from previous modeling of radio source counts, confirming a greater than or similar to 50% excess in radio-based star formation rate density (SFRD) (z) measurements at 0.2 < z < 1.3 compared to those from the UV-IR. Several sources of systematic error are discussed-totalling similar to 0.13 dex when added in quadrature. Even in the event that all systematic errors work to decrease the radio-based SFRD values, they are incapable of reconciling differences between the radio-based measurements with those from the UV-IR at 0.5 < z < 1.3. We conclude that significant work remains to have confidence in a full accounting of the star formation budget of the Universe.

The connection between galaxies and dark matter halos is often quantified using the stellar mass-halo mass (SMHM) relation. Optical and near-infrared imaging surveys have led to a broadly consistent picture of the evolving SMHM relation based on measurements of galaxy abundances and angular correlation functions. Spectroscopic surveys at z greater than or similar to 2 can also constrain the SMHM relation via the galaxy autocorrelation function and through the cross-correlation between galaxies and Ly alpha absorption measured in transverse sight lines; however, such studies are very few and have produced some unexpected or inconclusive results. We use similar to 3000 spectra of z similar to 2.5 galaxies from the Ly alpha Tomography IMACS Survey (LATIS) to measure the galaxy-galaxy and galaxy-Ly alpha correlation functions in four bins of stellar mass spanning 10(9.2) less than or similar to M-*/M-circle dot less than or similar to 10(10.5). Parallel analyses of the MultiDark N-body and ASTRID hydrodynamic cosmological simulations allow us to model the correlation functions, estimate covariance matrices, and infer halo masses. We find that results of the two methods are mutually consistent and broadly accord with standard SMHM relations. This consistency demonstrates that we are able to measure and model Ly alpha transmission fluctuations delta(F) in LATIS accurately. We also show that the galaxy-Ly alpha cross-correlation, a free by-product of optical spectroscopic galaxy surveys at these redshifts, can constrain halo masses with similar precision to galaxy-galaxy clustering.

We present the stellar mass-stellar metallicity relation for 3491 star-forming galaxies at 2 less than or similar to z less than or similar to 3 using rest-frame far-ultraviolet spectra from the Ly alpha Tomography IMACS Survey (LATIS). We fit stellar population synthesis models from the Binary Population And Spectral Synthesis code (v2.2.1) to medium-resolution (R similar to 1000) and high signal-to-noise (>30 per 100 km s(-1) over the wavelength range 1221-1800 & Aring;) composite spectra of galaxies in bins of stellar mass to determine their stellar metallicity, primarily tracing Fe/H. We find a strong correlation between stellar mass and stellar metallicity, with stellar metallicity monotonically increasing with stellar mass at low masses and flattening at high masses (M-* greater than or similar to 10(10.3)M(circle dot)). Additionally, we compare our stellar metallicity measurements with the gas-phase oxygen abundance of galaxies at similar redshift and estimate the average [alpha/Fe] similar to 0.6. Such high alpha-enhancement indicates that high-redshift galaxies have not yet undergone significant iron enrichment through Type Ia supernovae. Moreover, we utilize an analytic chemical evolution model to constrain the mass loading parameter of galactic winds as a function of stellar mass. We find that as the stellar mass increases, the mass loading parameter decreases. The parameter then flattens or reaches a turning point at around M-* similar to 10(10.5)M(circle dot). Our findings may signal the onset of black-hole-driven outflows at z similar to 2.5 for galaxies with M-* greater than or similar to 10(10.5) M-circle dot.

High-resolution imaging of galaxies in rest-frame UV has revealed the existence of giant star-forming clumps prevalent in high-redshift galaxies. Studying these substructures provides important information about their formation and evolution and informs theoretical galaxy evolution models. We present a new method to identify clumps in galaxies' high-resolution rest-frame UV images. Using imaging data from CANDELS and UVCANDELS, we identify star-forming clumps in an HST/F160W <= 25 AB mag sample of 6767 galaxies at 0.5 <= z <= 3 in four fields, GOODS-N, GOODS-S, EGS, and COSMOS. We use a low-passband filter in Fourier space to reconstruct the background image of a galaxy and detect small-scale features (clumps) on the background-subtracted image. Clumpy galaxies are defined as those having at least one off-center clump that contributes a minimum of 10% of the galaxy's total rest-frame UV flux. We measure the fraction of clumpy galaxies (f(clumpy)) as a function of stellar mass, redshift, and galaxy environment. Our results indicate that f(clumpy) increases with redshift, reaching similar to 65% at z similar to 1.5. We also find that fclumpy in low-mass galaxies (9.5 <= log (M*/M circle dot) <= 10) is 10% higher compared to that of their high-mass counterparts (log M*/M circle dot) > 10.5). Moreover, we find no evidence of significant environmental dependence of f(clumpy) for galaxies at the redshift range of this study. Our results suggest that the fragmentation of gas clouds under violent disk instability remains the primary driving mechanism for clump formation, and incidents common in dense environments, such as mergers, are not the dominant processes.

We study the recent star formation histories (SFHs) of 575 intermediate-mass galaxies (IMGs, 10(9) M/M(?)10(10)) in COSMOS at 0.3 < z < 0.4 by comparing their H alpha and UV luminosities. These two measurements trace star formation rates (SFRs) on different timescales and together reveal fluctuations in recent activity. We compute LH alpha from Magellan IMACS spectroscopy, while LUV is derived from rest-frame 2800.1 photometry. Dust corrections are applied to each band independently. We compare the deviation of L-H alpha and L-UV from their respective star-forming sequences (i.e., delta log L-Ha and delta log L-UV), and after accounting for observational uncertainties we find a small intrinsic scatter between the two quantities (sigma(delta) ? 0.03 dex). This crucial observational constraint precludes strong fluctuations in the recent SFHs of IMGs: simple linear SFH models indicate that a population of IMGs would be limited to only factors of ?2 change in SFR over 200 Myr and ?30% on shorter timescales of 20 Myr. No single characteristic SFH for IMGs, such as an exponentially rising/falling burst, can reproduce the individual and joint distribution of delta log L-Ha and delta log L-UV. Instead, an ensemble of SFHs is preferred. Finally, we find that IMG SFHs predicted by recent hydrodynamic simulations, in which feedback drives rapid and strong SFR fluctuations, are inconsistent with our observations.