We present a study of the relation between galaxy stellar age and mass for 14 members of the z = 1.62 protocluster IRC 0218, using multiband imaging and HST G102 and G141 grism spectroscopy. Using UVJ colors to separate galaxies into star-forming and quiescent populations, we find that, at stellar masses M*>= 10(10.85)M circle dot the quiescent fraction in the protocluster is f(Q) = 1.0(-0.37)(+0.00), consistent with a similar to 2x enhancement relative to the field value, f(Q) = 0.45(-0.03)(+0.03). At masses 10(10.2)M circle dot <= M* <= 10(10.85)M circle dot, f(Q) in the cluster is f(Q) = 0.40(-0.18)(+0.20), consistent with the field value of f(Q) = 0.28(-0.02)(+0.02). Using galaxy D-n(4000) values derived from the G102 spectroscopy, we find no relation between galaxy stellar age and mass. These results may reflect the impact of merger- driven mass redistribution-which is plausible, as this cluster is known to host many dry mergers. Alternately, they may imply that the trend in f(Q) in IRC 0218 was imprinted over a short timescale in the protocluster's assembly history. Comparing our results with those of other high- redshift studies and studies of clusters at z similar to 1, we determine that our observed relation between f(Q) and stellar mass only mildly evolves between z similar to 1.6 and z similar to 1, and only at stellar masses M* <= 10(10.85) M circle dot Both the z similar to 1 and z similar to 1.6 results are in agreement that the red sequence in dense environments was already populated at high redshift, z greater than or similar to 3, placing constraints on the mechanism(s) responsible for quenching in dense environments at z >= 1.5.

We combine state-of-the-art models for the production of stellar radiation and its transfer through the interstellar medium (ISM) to investigate ultraviolet-line diagnostics of stars, the ionized and the neutral ISM in star-forming galaxies. We start by assessing the reliability of our stellar population synthesis modelling by fitting absorption-line indices in the ISM-free ultraviolet spectra of 10 Large Magellanic Cloud clusters. In doing so, we find that neglecting stochastic sampling of the stellar initial mass function in these young (similar to 10-100 Myr), low-mass clusters affects negligibly ultraviolet-based age and metallicity estimates but can lead to significant overestimates of stellar mass. Then, we proceed and develop a simple approach, based on an idealized description of the main features of the ISM, to compute in a physically consistent way the combined influence of nebular emission and interstellar absorption on ultraviolet spectra of star-forming galaxies. Our model accounts for the transfer of radiation through the ionized interiors and outer neutral envelopes of short-lived stellar birth clouds, as well as for radiative transfer through a diffuse intercloud medium. We use this approach to explore the entangled signatures of stars, the ionized and the neutral ISM in ultraviolet spectra of star-forming galaxies. We find that, aside from a few notable exceptions, most standard ultraviolet indices defined in the spectra of ISM-free stellar populations are prone to significant contamination by the ISM, which increases with metallicity. We also identify several nebular-emission and interstellar-absorption features, which stand out as particularly clean tracers of the different phases of the ISM.

We present CI(2-1) and multi-transition (CO)-C-12 observations of a dusty star-forming galaxy, ACT J2029+0120, which we spectroscopically confirm to lie at z = 2.64. We detect CO(3-2), CO(5-4), CO(7-6), CO(8-7), and CI (2-1) at high significance, tentatively detect HCO+(4-3), and place strong upper limits on the integrated strength of dense gas tracers (HCN(4-3) and CS(7-6)). Multi-transition CO observations and dense gas tracers can provide valuable constraints on the molecular gas content and excitation conditions in high-redshift galaxies. We therefore use this unique data set to construct a CO spectral line energy distribution (SLED) of the source, which is most consistent with that of a ULIRG/Seyfert or QSO host object in the taxonomy of the Herschel Comprehensive ULIRG Emission Survey. We employ RADEX models to fit the peak of the CO SLED, inferring a temperature of T similar to 117 K and n(H2) similar to 10(5) cm(-3), most consistent with a ULIRG/QSO object and the presence of high-density tracers. We also find that the velocity width of the C I line is potentially larger than seen in all CO transitions for this object, and that the L'(Ci(2-1))/L'(CO(3-2)) ratio is also larger than seen in other lensed and unlensed submillimeter galaxies and QSO hosts; if confirmed, this anomaly could be an effect of differential lensing of a shocked molecular outflow.

Our sensitive (sigma(n) approximate to 572 nJy beam(-1)), high-resolution (FWHM theta(1/2) = 0"22 approximate to 2 kpc at z greater than or similar to 1), 10 GHz image covering a single Karl G.. Jansky Very Large Array (VLA) primary beam (FWHM circle minus(1/2) approximate to 4.'25) in the GOODS-N field contains 32 sources with S-p greater than or similar to 2 mu Jy beam(-1) and optical and/or near-infrared (OIR) counterparts. Most are about as large as the star-forming regions that power them. Their median FWHM major axis is <theta(M)>= 167 +/- 32 mas approximate to 1.2 +/- 0.28 kpc, with rms scatter approximate to 91 mas approximate to 0.79 kpc. In units of the effective radius re that encloses half their flux, these radio sizes are re approximate to 69 +/- 13 mas approximate to 509 +/- 114 pc, with rms scatter approximate to 38 mas approximate to 324 pc. These sizes are smaller than those measured at lower radio frequencies, but agree with dust emission sizes measured at mm/sub-mm wavelengths and extinction-corrected H alpha sizes. We made a lowresolution (theta(1/2) = 1."0) image with approximate to 10x better brightness sensitivity, in order to detect extended sources and measure matched-resolution spectral indices alpha(10 GHz)(1.4 GHz) 10 GHz. It contains six new sources with Sp. 3.9 mJy beam-1 and OIR counterparts. The median redshift of all 38 sources is similar to z similar to = 1.24 +/- 0.15. The 19 sources with 1.4 GHz counterparts have a median spectral index of <alpha(1.4 GHz) (10 GHz)> = -0.74 +/- 0.10 10 GHz, with rms scatter approximate to 0.35. Including upper limits on a for sources not detected at 1.4 GHz flattens the median to <alpha(1.4 GHz) (10 GHz)> greater than or similar to -0.61 10 GHz, suggesting that the mu Jy radio sources at higher redshifts-and hence those selected at higher rest-frame frequencies-may have flatter spectra. If the non-thermal spectral index is alpha(NT) approximate to -0.85, the median thermal fraction of sources selected at median rest-frame frequency approximate to 20 GHz is greater than or similar to 48%.

abstract: A key open problem within galaxy evolution is to understand the evolution of galaxies towards quiescence. This work investigates the suppression of star-formation through shocks and turbulence at low-redshift, and at higher-redshifts, this work investigates the use of features within quiescent galaxy spectra to redshift estimation, and passive evolution of aging stellar populations to understand their star-formation histories. At low-$z$, this work focuses on the analysis of optical integral field spectroscopy data of a nearby ($z\sim0.0145$) unusual merging system, called the Taffy system because of radio emission that stretches between the two galaxies. This system, although a recent major-merger of gas-rich spirals, exhibits an atypically low star-formation rate and infrared luminosity. Strong evidence of shock heating as a mechanism for these atypical properties is presented. This result (in conjunction with many others) from the nearby Universe provides evidence for shocks and turbulence, perhaps due to mergers, as an effective feedback mechanism for the suppression of star-formation. At intermediate and higher-$z$, this work focuses on the analysis of Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) G800L grism spectroscopy and photometry of galaxies with a discernible 4000\AA\ break. The usefulness of 4000\AA/Balmer breaks as redshift indicators by comparing photometric, grism, and spectrophotometric redshifts (SPZs) to ground-based spectroscopic redshifts, is quantified. A spectral energy distribution (SED) fitting pipeline that is optimized for combined HST grism and photometric data, developed for this project, is presented. This pipeline is a template-fitting based routine which accounts for correlated data between neighboring points within grism spectra via the covariance matrix formalism, and also accounts for galaxy morphology along the dispersion direction. Evidence is provided showing that SPZs typically improve the accuracy of photometric redshifts by $\sim$17--60\%. For future space-based observatories like the Nancy Grace Roman Space Telescope (formerly the Wide Field InfraRed Survey Telescope, i.e., WFIRST) and Euclid, this work predicts $\sim$700--4400 galaxies\,degree$^{-2}$, within $1.6 \lesssim z \lesssim 3.4$, for galaxies with 4000\AA\ breaks and continuum-based redshifts accurate to $\lesssim$2\%. This work also investigates the star-formation histories of massive galaxies ($\mathrm{M_s \geq 10^{10.5}\, M_\odot}$). This is done through the analysis of the strength of the Magnesium absorption feature, Mgb, at $\sim$5175\AA. This analysis is carried out on stacks of HST ACS G800L grism data, stacked for galaxies binned on a color vs stellar mass plane. / Dissertation/Thesis / Doctoral Dissertation Astrophysics and Astronomy 2020

To Understand how galaxies were assembled across the cosmic time remains one of the most outstanding questions in astronomy. The core of this question is how today's Hubble Sequence, namely the differentiation of galaxy morphology and its correlation to galaxy physical properties, is formed. In this thesis, we investigate the origin of the Hubble Sequence through galaxies at z~2, an epoch when the cosmic star formation activity reaches its peak and the properties of galaxies undergo dramatic transitions. Galaxies at z~2 have two important features that are distinct from nearby galaxies: much higher frequency of clumpy morphology in star-forming systems, and much compacter size. To understand the nature of the two features requires investigations on the sub-structure of galaxies in a multi-wavelength way. In this thesis, we study samples of galaxies that are selected from GOODS and HUDF, where ultra-deep and high-resolution optical and near-infrared images allow us to study the stellar populations of the sub-structures of galaxies at the rest-frame optical bands for the first time, to answer two questions: (1) the nature of kiloparsec-scale clumps in star-forming galaxies at z$\sim$2 and (2) the existence of color gradient and stellar population gradient in passively evolving galaxies at z~2, which may provide clues to the mechanisms of dramatic size evolution of this type of galaxies. We further design a set of color selection criteria to search for dusty star-forming galaxies and passively evolving galaxies at z~3 to explore the question: when today's Hubble Sequence has begun to appear.

Comprehensive and robust analysis of galaxies found throughout cosmic time provides the means to probe the underlying characteristics of our Universe. Coupling observations and theory, spectral energy distribution (SED) fitting provides a method to derive the intrinsic properties of distant galaxies which then aid in defining galaxy populations and constraining current galaxy formation and evolution scenarios. One such population are the sub-millimeter galaxies (SMGs) whose high infrared luminosities -- typically associated with dust-obscured star formation -- and redshift distribution places them as likely key components in galaxy evolution. To fully analyze these systems, however, requires a near complete sampling of the full SED, detailed models that encapsulate the variety of physical processes and sophisticated methods for comparing the data and models. In this dissertation, we present the general propose, Monte Carlo Markov Chain (MCMC) based SED fitting routine SED Analysis Through Markov Chains (SATMC) and the insight we have gained in modeling a sample of AzTEC 1.1mm-detected SMGs. The MCMC engine and Bayesian formalism used in the construction of SATMC offers a unique view at the constraints on model parameter space that are often grossly simplified in traditional SED fitting methods. We first present the motivation behind SATMC and its MCMC algorithm. We also highlight a series of test cases that verify not only its reliability but its versatility to various astrophysical applications, including the field of photometric redshift estimation. We then present the AzTEC SMG sample and preliminary results obtained through counterpart identification, X-ray spectral modeling and SED fitting with SATMC. Finally, we present the latest work in detailed SED analysis of SMGs and how these results influence our understanding of the SMG population.

We introduce a new suite of radiation- hydrodynamical simulations of galaxy formation and reionization called Aurora. The Aurora simulations make use of a spatially adaptive radiative transfer technique that lets us accurately capture the small- scale structure in the gas at the resolution of the hydrodynamics, in cosmological volumes. In addition to ionizing radiation, Aurora includes galactic winds driven by star formation and the enrichment of the universe with metals synthesized in the stars. Our reference simulation uses 2 x 512(3) dark matter and gas particles in a box of size 25 h(-1) comoving Mpc with a force softening scale of at most 0.28 h(-1) kpc. It is accompanied by simulations in larger and smaller boxes and at higher and lower resolution, employing up to 2 x 1024(3) particles, to investigate numerical convergence. All simulations are calibrated to yield simulated star formation rate functions in close agreement with observational constraints at redshift z = 7 and to achieve reionization at z approximate to 8.3, which is consistent with the observed optical depth to reionization. We focus on the design and calibration of the simulations and present some first results. The median stellar metallicities of low- mass galaxies at z = 6 are consistent with the metallicities of dwarf galaxies in the Local Group, which are believed to have formed most of their stars at high redshifts. After reionization, the mean photoionization rate decreases systematically with increasing resolution. This coincides with a systematic increase in the abundance of neutral hydrogen absorbers in the intergalactic medium.

Une fraction non négligeable de l'histoire de la formation stellaire a lieu dans des environnements très affectés par la poussière. Il est donc naturel de se demander si on arrive à bien contraindre cette activité de formation d'étoiles. En effet, une part importante de cette activité pourrait être manquée due à la présence de poussière. C'est dans ce contexte que s'inscrit le travail que je vais présenter.Dans la première partie de ma thèse, j'ai eu pour but de déterminer la fraction de galaxies lumineuses formant des étoiles à haut redshift (i.e. 1.5 1mJy) présentent des couleurs 100/24 et 160/24 plus faibles que les autres sources du champ COSMOS et leur luminosité semble donc provenir majoritairement d'un AGN. Les avancées technologiques et l'exploration des longueurs d'ondes en infra-rouge lointain et en submillimétrique, avec notamment Herschel, SCUBA-2, Alma, JWST, permettront de mieux comprendre la connexion AGN/ flambée de formation stellaire au sein des galaxies jusqu'à des hauts redshifts.

L’objectif de ma thèse porte sur les interactions entre les noyaux actifs de galaxies et le milieu interstellaire des galaxies. En particulier, je mets l’accent sur les deux mécanismes possibles responsables de la production des vents par les trous noirs : les jets et les vents produits par le rayonnement de ces trous noirs. Les simulations hydrodynamiques de haute résolution des galaxies comprenant la rétroac- tion d’un jet ont montré que l’activité des noyaux actifs peut conduire à une pression exces- sive sur les régions denses de formation stellaire dans les galaxies, et donc à augmenter la formation d’étoiles, conduisant à un effet positif de rétroaction. Je montre que ces noyaux actifs induits par pression régulée et formation d’étoiles peuvent aussi être une explica- tion possible des taux de formation stellaire élevés observés dans l’Univers à haut décalage spectral. De plus, j’ai également étudié en détails comment le rayonnement émis à partir d’un disque d’accrétion autour du trou noir agit efficacement avec le milieu interstellaire et entraîne un fort vent galactique, en simulant la propagation des photons à partir des équations hydrodynamiques du rayonnement. Les simulations montrent que la grande luminosité d’un quasar est en effet capable de conduire des vents à grande échelle et à grande vitesse. Le rayonnement infrarouge est nécessaire pour transérer efficacement le gaz par multi-diffusion sur la poussière dans les nuages denses. Le nombre typique de multi-diffusion diminue rapidement quand le nuage central de gaz central se dilate et se rompt, ce qui permet au rayonnement de s’échapper à travers les canaux à faible densité. / Supermassive black holes (SMBHs) are known to reside in the centres of most large galaxies. The masses of these SMBHs are known to correlate with large-scale properties of the host galaxy suggesting that the growth of the BHs and large-scale structures are tightly linked. A natural explanation for the observed correlation is to invoke a self-regulated mechanism involving feedback from Active Galactic Nuclei (AGN). The focus of this thesis is on the interactions between AGN outflows and the ISM and how the feedback impacts the host galaxy. In particular, it focuses on the two possible mechanism of outflows, namely, outflows related to AGN jets and outflows produced by AGN radiation. High resolution, galaxy scale hydrodynamical simulations of jet-driven feedback have shown that AGN activity can over-pressurise dense star-formation regions of galaxies and thus enhance star formation, leading to a positive feedback effect. I propose, that such AGN-induced pressure-regulated star formation may also be a possible explanation of the high star formation rates recently found in the high-redshift Universe. In order to study in more detail the effects of over-pressurisation of the galaxy, I have performed a large set of isolated disc simulations with varying gas-richness in the galaxy. I found that even moderate levels of over-pressurisation of the galaxy boosts the global star formation rate by an order of magnitude. Additionally, stable discs turn unstable which leads to significant fragmentation of the gas content of the galaxy, similar to what is observed in high-redshift galaxies. The observed increase in the star formation rate of the galaxy is in line with theoretical predictions. I have also studied in detail how radiation emitted from a thin accretion disc surrounding the BH effectively couples to the surrounding ISM and drives a large scale wind. Quasar activity is typically triggered by extreme episodes of gas accretion onto the SMBH, in particular in high-redshift galaxies. The photons emitted by a quasar eventually couple to the gas and drive large scale winds. In most hydrodynamical simulations, quasar feedback is approximated as a local thermal energy deposit within a few resolution elements, where the efficiency of the coupling between radiation of the gas is represented by a single parameter tuned to match global observations. In reality, this parameter conceals various physical processes that are not yet fully un- derstood as they rely on a number of assumptions about, for instance, the absorption of photons, mean free paths, optical depths, and shielding. To study the coupling between the photons and the gas I simulated the photon propagation using radiation-hydrodynamical equations (RHD), which describe the emission, absorption and propagation of photons with the gas and dust. Such an approach is critical for a better understanding of the coupling between the radiation and gas and how hydrodynamical sub-grid models can be improved in light of these results...