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Galaxies with stellar masses as high as roughly 10 11 solar masses have been identified 1 – 3 out to redshifts z of roughly 6, around 1 billion years after the Big Bang. It has been difficult to find massive galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 μm. Here we make use of the 1–5 μm coverage of the James Webb Space Telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass more than 10 10 solar masses) at 7.4 ≤  z  ≤ 9.1, 500–700 Myr after the Big Bang, including one galaxy with a possible stellar mass of roughly 10 11 solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples. James Webb Space Telescope early release observations used to search for intrinsically red galaxies from the first 750 million years of cosmic history find six candidate massive galaxies, possibly including one of roughly 10 11 solar masses.

Star formation in half of massive galaxies was quenched by the time the Universe was 3 billion years old 1 . Very low amounts of molecular gas seem to be responsible for this, at least in some cases 2 – 7 , although morphological gas stabilization, shock heating or activity associated with accretion onto a central supermassive black hole are invoked in other cases 8 – 11 . Recent studies of quenching by gas depletion have been based on upper limits that are insufficiently sensitive to determine this robustly 2 – 7 , or stacked emission with its problems of averaging 8 , 9 . Here we report 1.3 mm observations of dust emission from 6 strongly lensed galaxies where star formation has been quenched, with magnifications of up to a factor of 30. Four of the six galaxies are undetected in dust emission, with an estimated upper limit on the dust mass of 0.0001 times the stellar mass, and by proxy (assuming a Milky Way molecular gas-to-dust ratio) 0.01 times the stellar mass in molecular gas. This is two orders of magnitude less molecular gas per unit stellar mass than seen in star forming galaxies at similar redshifts 12 – 14 . It remains difficult to extrapolate from these small samples, but these observations establish that gas depletion is responsible for a cessation of star formation in some fraction of high-redshift galaxies. The authors report 1.3 mm observations of dust emission from strongly lensed galaxies where star formation is quenched, demonstrating that gas depletion is responsible for the cessation of star formation in some high-redshift galaxies.

Hubble Space Telescope, Keck telescope and Spitzer satellite data reveal the formation of the dense stellar core of a massive galaxy occurring three billion years after the Big Bang. Core formation values for GOODS-N-774 The galaxy GOODS-N-774 is identified here as a rarity, providing a possible example of a massive galaxy in the process of stellar core formation. Seen at a redshift of z = 2.3, as it was 11 billion years ago, GOODS-N-774 has a stellar mass of 100 billion solar masses and is forming stars at a rate of around 90 solar masses per year. From the star formation rate and size of the galaxy, the authors infer that many star-forming cores may be heavily obscured and could be under-represented in optical and near-infrared surveys. This might account for the fact that this is the first object to have been found to have both the stellar structure and the gas dynamics of a forming core. Most massive galaxies are thought to have formed their dense stellar cores in early cosmic epochs 1 , 2 , 3 . Previous studies have found galaxies with high gas velocity dispersions 4 or small apparent sizes 5 , 6 , 7 , but so far no objects have been identified with both the stellar structure and the gas dynamics of a forming core. Here we report a candidate core in the process of formation 11 billion years ago, at redshift z = 2.3. This galaxy, GOODS-N-774, has a stellar mass of 100 billion solar masses, a half-light radius of 1.0 kiloparsecs and a star formation rate of  solar masses per year. The star-forming gas has a velocity dispersion of 317 ± 30 kilometres per second. This is similar to the stellar velocity dispersions of the putative descendants of GOODS-N-774, which are compact quiescent galaxies at z  ≈ 2 (refs 8 , 9 , 10 , 11 ) and giant elliptical galaxies in the nearby Universe. Galaxies such as GOODS-N-774 seem to be rare; however, from the star formation rate and size of this galaxy we infer that many star-forming cores may be heavily obscured, and could be missed in optical and near-infrared surveys.

The IRAC mapping of the NMBS-II fields program is an imaging survey at 3.6 and 4.5 m with the Spitzer Infrared Array Camera (IRAC). The observations cover three Canada-France-Hawaii Telescope Legacy Survey Deep (CFHTLS-D) fields, including one also imaged by AEGIS, and two MUSYC fields. These are then combined with archival data from all previous programs into deep mosaics. The resulting imaging covers a combined area of about 3 deg2, with at least ∼2 hr integration time for each field. In this work, we present our data reduction techniques and document the resulting coverage maps at 3.6 and 4.5 m. All of the images are W-registered to the reference image, which is either the z-band stack image of the 25% best-seeing images from the CFHTLS-D for CFHTLS-D1, CFHTLS-D3, and CFHTLS-D4, or the K-band images obtained at the Blanco 4-m telescope at CTIO for MUSYC1030 and MUSYC1255. We make all images and coverage maps described here publicly available via the Spitzer Science Center.

Today's massive elliptical galaxies are primarily red-and-dead, dispersion supported ellipticals. The physical process(es) driving the shutdown or ‘quenching’ of star formation in these galaxies remains one of the least understood aspects of galaxy formation and evolution. Although today's spiral and elliptical galaxies exhibit a clear bimodality in their structures, kinematics, and stellar populations, it may be that the quenching and structural transformation do no occur simultaneously. In this talk I will present evidence that early quiescent galaxies, observed much closer to their quenching epoch at z ∼ 1, retain significant rotational support (∼ twice as much as local ellipticals). This suggests that the mechanisms responsible for shutting down star formation do not also have to destroy ordered motion in massive galaxies; the increased dispersion support could occur subsequently via hierarchical growth and minor merging. I will discuss this evidence in conjunction with recent ALMA studies of the dramatic range in molecular gas reservoirs of recently quenched high redshift galaxies to constrain quenching models. Finally, I will discuss prospects for extending spatially resolved spectroscopic studies of galaxies immediately following quenching with JWST and eventually 30-m class telescopes.

Early JWST observations have uncovered a population of red sources that might represent a previously overlooked phase of supermassive black hole growth 1 – 3 . One of the most intriguing examples is an extremely red, point-like object that was found to be triply imaged by the strong lensing cluster Abell 2744 (ref.  4 ). Here we present deep JWST/NIRSpec observations of this object, Abell2744-QSO1. The spectroscopy confirms that the three images are of the same object, and that it is a highly reddened ( A V  ≃ 3) broad emission line active galactic nucleus at a redshift of z spec  = 7.0451 ± 0.0005. From the width of Hβ (full width at half-maximum = 2,800 ± 250 km s −1 ), we derive a black hole mass of M BH = 4 − 1 + 2 × 1 0 7 M ⊙ . We infer a very high ratio of black-hole-to-galaxy mass of at least 3%, an order of magnitude more than that seen in local galaxies 5 and possibly as high as 100%. The lack of strong metal lines in the spectrum together with the high bolometric luminosity ( L bol  = (1.1 ± 0.3) × 10 45  erg s −1 ) indicate that we are seeing the black hole in a phase of rapid growth, accreting at 30% of the Eddington limit. The rapid growth and high black-hole-to-galaxy mass ratio of Abell2744-QSO1 suggest that it may represent the missing link between black hole seeds 6 and one of the first luminous quasars 7 . JWST/NIRSpec observations of Abell2744-QSO1 show a high black-hole-to-host mass ratio in the early Universe, which indicates that we are seeing the black hole in a phase of rapid growth, accreting at 30% of the Eddington limit.

The identification of sources driving cosmic reionization, a major phase transition from neutral hydrogen to ionized plasma around 600–800 Myr after the Big Bang 1 – 3 , has been a matter of debate 4 . Some models suggest that high ionizing emissivity and escape fractions ( f esc ) from quasars support their role in driving cosmic reionization 5 , 6 . Others propose that the high f esc values from bright galaxies generate sufficient ionizing radiation to drive this process 7 . Finally, a few studies suggest that the number density of faint galaxies, when combined with a stellar-mass-dependent model of ionizing efficiency and f esc , can effectively dominate cosmic reionization 8 , 9 . However, so far, comprehensive spectroscopic studies of low-mass galaxies have not been done because of their extreme faintness. Here we report an analysis of eight ultra-faint galaxies (in a very small field) during the epoch of reionization with absolute magnitudes between M UV  ≈ −17 mag and −15 mag (down to 0.005 L ⋆ (refs.  10 , 11 )). We find that faint galaxies during the first thousand million years of the Universe produce ionizing photons with log[ ξ ion  (Hz erg −1 )] = 25.80 ± 0.14, a factor of 4 higher than commonly assumed values 12 . If this field is representative of the large-scale distribution of faint galaxies, the rate of ionizing photons exceeds that needed for reionization, even for escape fractions of the order of 5%. An analysis of eight ultra-faint galaxies during the epoch of reionization with absolute magnitudes between −17 mag and −15  mag shows that most of the photons that reionized the Universe come from dwarf galaxies.

Within the established framework of structure formation, galaxies start as systems of low stellar mass and gradually grow into far more massive galaxies. The existence of massive galaxies in the first billion years of the Universe, as suggested by recent observations, seems to challenge this model, as such galaxies would require highly efficient conversion of baryons into stars. An even greater challenge in this epoch is the existence of massive galaxies that have already ceased forming stars. However, robust detections of early massive quiescent galaxies have been challenging due to the coarse wavelength sampling of photometric surveys. Here we report the spectroscopic confirmation with the James Webb Space Telescope of the quiescent galaxy RUBIES-EGS-QG-1 at redshift z  = 4.90, 1.2 billion years after the Big Bang. Deep stellar absorption features in the spectrum reveal that the stellar mass of the galaxy of 10 11   M ⊙ formed in a short 200 Myr burst of star formation, after which star formation activity dropped rapidly and persistently. According to current galaxy formation models, systems with such rapid stellar mass growth and early quenching are too rare to plausibly occur in the small area probed spectroscopically with JWST. Instead, the discovery of RUBIES-EGS-QG-1 implies that early massive quiescent galaxies can be quenched earlier or exhaust gas available for star formation more efficiently than assumed at present. RUBIES-EGS-QG-1 is an exceptionally massive and mature galaxy discovered just 1.2 billion years after the Big Bang. Its stars formed in an extremely rapid burst, posing a major challenge to all current theoretical models.

Once thought to be relies of a much earlier epoch, the most massive local galaxies are red and dead ellipticals, with little ongoing star formation or organized rotation. In the last decade, observations of their assumed progenitors have demonstrated that billions of years ago, massive galaxies were more compact and morphologically different, possibly with more disklike structures. The details of this observed evolution can place constraints on the physical processes that have driven massive galaxy evolution through cosmic time. The work presented in this thesis provides observational constraints on the dynamical and structural evolution of massive galaxies since z ~ 1.5 – 2 using a variety of photometric and spectroscopic surveys, including OBEY, SDSS, NMBS, and UDS. First, we find that although overall densities of these galaxies have decreased with time, the central densities of massive galaxies at high and low redshifts, are quite similar. This suggests that massive galaxies grow \"inside-out\": compact cores form early and then gradually build a more diffuse envelope of stars in their outskirts. Balancing the need for efficient size growth and consistent number densities of progenitor and descendent galaxies, we conclude that minor-merging is the best physical explanation for the observed size evolution. The remainder of this dissertation focuses on the inferred and measured dynamical evolution of massive galaxies since z ~ 2. Using velocity dispersions inferred by galaxy stellar masses and morphologies, we find that the number density of galaxies at a given velocity dispersion, or velocity dispersion function, is quite stable with redshift since z ~ 1.5, with a weak evolution at the low dispersion end due to a growing population of quenched galaxies. The constancy provides evidence in favor of inside-out growth of galaxies and is consistent with theoretical predictions that the central potentials of massive galaxies are set early. We suggest a toy model that requires that galaxy quenching must be extremely efficient at high velocity dispersions and quenching must be combined with rapidly increasing dispersions. We present two large spectroscopic studies of high-redshift massive galaxies using the Keck Telescopes: directly measuring absorption line kinematics for eight galaxies at z ~ 1.5 and ~ 100 galaxies at z ~ 0.7. Using a collection of cutting edge photometric and spectroscopic data, we verify that the z ~ 1.5 galaxies are dynamically massive and compact, with high measured velocity dispersions. Surprisingly, the spectra of many of the galaxies in this sample have extremely strong Balmer absorption lines, in contrast with massive galaxies in the Universe. These observations can only be explained by recently quenched star-formation within ~ 1 Gyr. Finally, we collect all spectroscopic data from these two surveys and ~ 6000 galaxies from the literature and examine the structural and dynamical evolution of galaxies in the Fundamental Plane since z ~ 2. We find that although the zeropoint of the luminosity fundamental plane evolves dramatically in the last 10 billion years, the mass fundamental plane exhibits very little redshift evolution. We note that a stable mass fundamental plane was predicted by simulations of merging galaxies. Finally, these results imply that galaxies must undergo evolution in their velocity dispersions, in addition to growing in size in order to remain on the Fundamental Plane. Overall, these results provide strong evidence for inside-out growth, minimal, but non-negligible, dynamical evolution and efficient quenching of massive galaxies since z ~ 2.

We present a detailed study of the partial rest-optical (\\(\\lambda_{\\mathrm{obs}} \\approx 3600-5600\\,\\)Å) spectra of \\(N = 328\\) star-forming galaxies at \\(0.6 < z < 1.0\\) from the Large Early Galaxy Astrophysics Census (LEGA-C). We compare this sample with low-redshift (\\(z \\sim 0\\)) galaxies from the Sloan Digital Sky Survey (SDSS), intermediate-redshift (\\(z \\sim 1.6\\)) galaxies from the Fiber Multi-Object Spectrograph (FMOS)-COSMOS Survey, and high-redshift (\\(z \\sim 2\\)) galaxies from the Keck Baryonic Structure Survey (KBSS). At a lookback time of \\(6-8\\ \\mathrm{Gyr}\\), galaxies with stellar masses \\(\\mathrm{log}(\\mathrm{M_{\\ast}/M_{\\odot}}) > 10.25\\) appear remarkably similar to \\(z \\sim 0\\) galaxies in terms of their nebular excitation, as measured using \\(\\mathrm{[O\\,III]}\\lambda5008 / \\mathrm{H}\\beta\\). There is some evidence that \\(0.6 < z < 1.0\\) galaxies with lower \\(\\mathrm{M_{\\ast}}\\) have higher \\(\\mathrm{[O\\,III]}\\lambda5008 / \\mathrm{H}\\beta\\) than \\(z \\sim 0\\) galaxies and are more similar to less evolved \\(z \\sim 1.6\\) and \\(z \\sim 2\\) galaxies, which are offset from the \\(z \\sim 0\\) locus at all \\(\\mathrm{M_{\\ast}}\\). We explore the impact selection effects, contributions from active galactic nuclei, and variations in physical conditions (ionization parameter and gas-phase oxygen abundance) have on the apparent distribution of \\(\\mathrm{[O\\,III]}\\lambda5008 / \\mathrm{H}\\beta\\) and find somewhat higher ionization and lower enrichment in \\(0.6 < z < 1.0\\) galaxies with lower \\(\\mathrm{M_{\\ast}}\\) relative to \\(z \\sim 0\\) galaxies. We use new near-infrared spectroscopic observations of \\(N = 53\\) LEGA-C galaxies to investigate other probes of enrichment and excitation. Our analysis demonstrates the importance of obtaining complete rest-optical spectra of galaxies in order to disentangle these effects.