The growth of mass in star-forming galaxies at high redshift

This thesis presents an analysis of star-forming galaxies across the cosmic noon (z~1-4) spanning a wide range in physical properties, from strongly dust-obscured systems, to more typical 'main-sequence' galaxies. Consistent analysis and methodology, together with the large sample sizes, allow us to compare and contrast populations of different stellar, gas and dark matter masses to assess their evolutionary trends and probe the mass build up across the 'main-sequence'. For consistent analysis throughout the thesis, we test and check the reliability of using an SED fitting code MAGPHYS (da Cunha et al. 2015) to derive photometric redshifts as well as key physical properties (such as stellar mass, far-infrared luminosity, star-formation rate) for high redshift star-forming galaxies in Chapter 2. Knowing the capabilities and shortcomings of the modelling code, in Chapters 3, 4 and 5, we model multi-wavelength photometric data to derive physical properties of galaxies across the 'main-sequence'. In Chapter 3, we analyse the physical properties of a large, homogeneously selected sample of ALMA-located sub-millimetre galaxies (SMGs) from the AS2UDS survey (Stach et al. 2019), which identified 707 SMGs across the ~1deg^2 field. We determine a median redshift of z=2.61+-0.08, and the redshift distribution is well fit by a model combining evolution of the gas fraction in halos with the growth of halo mass past a critical threshold of M_h~6x10^12Mo, thus SMGs may represent the highly efficient collapse of gas-rich massive halos. We suggest that almost all galaxies with M_*>3x10^11Mo have passed through an SMG-like phase. SMGs are broadly consistent with simple homologous systems in the far-infrared, such as a centrally illuminated starburst. Overall, this study provides strong support for an evolutionary link between the active, gas-rich SMG population at z>1 and the formation of massive, bulge-dominated galaxies across the history of the Universe. We analyse the physical properties of 121 sub-millimetre galaxies (SMGs) from the STUDIES 450-um survey in Chapter 4, and compare the results to 850-um-selected SMGs from Chapter 3 to understand the fundamental physical differences between the two populations at the observed depths. The 450-um sample has a median redshift of z=1.85+-0.12. The fainter 450-um-selected sources have higher space density than the brighter 850-um sample at z3, suggesting LIRGs are the main obscured population at z~1-2, while ULIRGs dominate at higher redshifts. Using a uniform ~180um-selected sample at z=1-2 and z=3-4, we suggest that higher-redshift sources have higher dust densities due to smaller inferred dust continuum sizes at a given dust mass, leading to higher dust attenuation. We suggest that the dust content of galaxies is governed by a combination of both the variation of gas content and dust destruction timescale. Finally, in Chapter 5 we present an on-going analysis of a sample of star-forming galaxies at z~1.5 from the KMOS Ultra-deep Rotational Velocity Survey (KURVS). We construct spatially-resolved 2D stellar mass maps from deep HST observations and use them to constrain the baryonic mass profile of the sample galaxies. Using these, together with the dynamical mass profiles from the deep H_alpha observations, we derive the dark matter profiles, which reveal high dark matter fractions (~0.8), even at effective radius

Hidden giants in JWST's PEARLS: An ultra-massive z=4.26 sub-millimeter galaxy that is invisible to HST

We present a multi-wavelength analysis using SMA, JCMT, NOEMA, JWST, HST, and SST of two dusty strongly star-forming galaxies, 850.1 and 850.2, seen through the massive cluster lens A1489. These SMA-located sources both lie at z=4.26 and have bright dust continuum emission, but 850.2 is a UV-detected Lyman-break galaxy, while 850.1 is undetected at <2um, even with deep JWST/NIRCam observations. We investigate their stellar, ISM, and dynamical properties, including a pixel-level SED analysis to derive sub-kpc-resolution stellar-mass and Av maps. We find that 850.1 is one of the most massive and highly obscured, Av~5, galaxies known at z>4 with M*~10^11.8 Mo (likely forming at z>6), and 850.2 is one of the least massive and least obscured, Av~1, members of the z>4 dusty star-forming population. The diversity of these two dust-mass-selected galaxies illustrates the incompleteness of galaxy surveys at z>3-4 based on imaging at <2um, the longest wavelengths feasible from HST or the ground. The resolved mass map of 850.1 shows a compact stellar mass distribution, Re(mass)~1kpc, but its expected evolution to z~1.5 and then z~0 matches both the properties of massive, quiescent galaxies at z~1.5 and ultra-massive early-type galaxies at z~0. We suggest that 850.1 is the central galaxy of a group in which 850.2 is a satellite that will likely merge in the near future. The stellar morphology of 850.1 shows arms and a linear bar feature which we link to the active dynamical environment it resides within.Comment: Submitted to ApJ, comments welcome

The ALMA Spectroscopic Survey Large Program: The Infrared Excess of z = 1.5–10 UV-selected Galaxies and the Implied High-redshift Star Formation History

We make use of sensitive (9.3 μJy beam−1 rms) 1.2 mm continuum observations from the Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra-Deep Field (ASPECS) large program to probe dust-enshrouded star formation from 1362 Lyman-break galaxies spanning the redshift range z = 1.5–10 (to ~7–28 M ⊙ yr−1 at 4σ over the entire range). We find that the fraction of ALMA-detected galaxies in our z = 1.5–10 samples increases steeply with stellar mass, with the detection fraction rising from 0% at 109.0 M ⊙ to ${85}_{-18}^{+9}$% at >1010 M ⊙. Moreover, on stacking all 1253 low-mass (${10}^{9.5}\,{M}_{\odot }$ and an SMC-like relation at lower masses. Using stellar mass and β measurements for z ~ 2 galaxies over the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we derive a new empirical relation between β and stellar mass and then use this correlation to show that our IRX–β and IRX–stellar mass relations are consistent with each other. We then use these constraints to express the IRX as a bivariate function of β and stellar mass. Finally, we present updated estimates of star formation rate density determinations at z > 3, leveraging present improvements in the measured IRX and recent probes of ultraluminous far-IR galaxies at z > 2