Browsing by Subject "High-redshift galaxies"
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Item Bridging star-forming galaxy and AGN ultraviolet luminosity functions at z = 4 with the SHELA wide-field survey(2018-12-06) Stevans, Matthew Louis, Jr.; Finkelstein, Steven L.This thesis presents a joint analysis of the rest-frame ultraviolet (UV) luminosity functions of continuum-selected star-forming galaxies and galaxies dominated by active galactic nuclei (AGNs) at z ~ 4. These 3,740 z ~ 4 galaxies are selected from broad-band imaging in nine photometric bands over 18 deg² in the Spitzer/HETDEX Exploratory Large Area Survey (SHELA) field. The large area and moderate depth of our survey provide a unique view of the intersection between the bright end of the galaxy UV luminosity function (M [subscript AB] < -22) and the faint end of the AGN UV luminosity function. We do not separate AGN-dominated galaxies from star-formation-dominated galaxies, but rather fit both luminosity functions simultaneously. These functions are best fit with a double power-law (DPL) for both the galaxy and AGN components, where the galaxy bright-end slope has a power-law index of -3:80 ± 0.10, and the corresponding AGN faint-end slope is α [subscript AGN] = -1.49 +0.30/-0.21. We cannot rule out a Schechter-like exponential decline for the galaxy UV luminosity function, and in this scenario the AGN luminosity function has a steeper faint-end slope of -2.08 +0.18/-0.11. Comparison of our galaxy luminosity function results with a representative cosmological model of galaxy formation suggests that the molecular gas depletion time must be shorter, implying that star formation is more efficient in bright galaxies at z = 4 than at the present day. If the galaxy luminosity function does indeed have a power-law shape at the bright end, the implied ionizing emissivity from AGNs is not inconsistent with previous observations. However, if the underlying galaxy distribution is Schechter, it implies a significantly higher ionizing emissivity from AGNs at this epoch.Item The imprint of the ionized intergalactic medium on the temperature anisotropy of the cosmic microwave background and the mutual-impact of reionization and small-scale structure(2015-08) Park, Hyunbae; Shapiro, Paul R.; Komatsu, Eiichiro; Finkelstein, Steven; Milosavljevic, Milos; Kumar, PawanIonized intergalactic medium (IGM) is an important component in cosmic history. After recombination, the universe went though a dark age until the first stars formed. Since the formation of the first stars, the ionized gas, on one hand, played an important role in the history of the universe and, on the other hand, left its imprints on observables that current and future experiments can measure. In this dissertation, we discuss both of each aspects about ionized gas. First, we discuss the mutual-impact of reionization and the IGM in small-scale structures. While reionization took place preferentially from densest regions of the universe, IGM in average density regions is expected to have been ionized externally by galaxies formed in denser regions. Until ionized by external radiation, the IGM is expected to have grown numerous small-scale structures. We simulate how the hydrodynamic feedback on the small-scale structures and its impact on recombination. Then, we also discuss our result on how recombination can impact on the global progress of the reionization. Compared to previous works, we improve on the resolution of simulation. Previous studies took into account only the structures that can form in photoionized gas down to 10⁸ M [sun symbol] in mass. Here, we present a study that resolves halos down to 10⁴ M [sun symbol] to account for structures that were able to form before the reionization heats the gas. Second, we discuss the kinetic Sunyaev-Zel'dovich effect on the Cosmic Microwave Background (CMB) : temperature fluctuations via the Doppler shift induced by the line-of-sight (LOS) component of the momentum of electrons in the ionized IGM. For the EoR contribution to the signal, we calculate the expected signal from simulations of cosmic reionization that, for the first time, includes the effect of "self-regulation" of reionization: star formation in low-mass galaxies (10⁸ M [sun symbol] [less than or equal to] M [subscript halo] [less than or equal to] 10⁹ M [sun symbol]) and minihalos (10⁵ M [sun symbol] [less than or equal to] M [subscript halo] [less than or equal to] 10⁸ M [sun symbol]) is suppressed if these halos form in regions that are already ionized or Lyman-Werner dissociated. For the post-reionization signal, we revisit the currently used model for non-linear transverse momentum power spectrum with a particular emphasis on the connected term that has been neglected in the literature.Item Investigating the stellar mass growth and quiescence of massive galaxies In the early universe using wide-field imaging(2019-09-24) Stevans, Matthew Louis, Jr.; Finkelstein, Steven L; Jogee, Shardha; Gebhardt, Karl; Evans, Neal; Gawiser, EricWhile galaxies formed stars most actively around z=2, or ~3 Gyr after the Big Bang, when the universal star formation density in the universe peaked. By this time a population of massive galaxies had already formed 10¹¹ - 10¹² [solar mass] of stars and some had their star-formation shut off in a process known as quenching. Understanding how these massive galaxies build up their stellar mass and then quench so early in the universe is a fundamental observational test of galaxy evolution. If not obscured by dust, massive galaxies are very bright, and can be observed in the optical and infrared (IR) to probe their redshifted ultraviolet (UV) and optical emission, respectively. The UV emission is produced by newly formed O and B type stars within 100 Myrs of forming, while the rest-frame optical light is produced by stars of all type and traces the stellar mass in the galaxy. By measuring the UV and optical output of galaxies, astronomers can derive star-formation rates and stellar masses. Measuring these properties for large samples of galaxies across a wide dynamic range provides benchmarks for simulations of galaxy formation and evolution physics. The work in this dissertation focuses on completing a wide field imaging survey of galaxies with high UV star-formation rates and high stellar masses at high redshift to perform the most statistically robust census to date. In Chapter 1 we motivate measuring the UV output and the quiescent fraction of high-redshift galaxies. To measure the UV output of massive star-forming galaxies at high redshift we utilize an extensive multi-wavelength dataset assembled in the Spitzer HETDEX Exploratory Large Area Survey (SHELA) Field. The data set includes five bands of deep optical imaging from the Dark Energy Camera (DECam), deep 3.6 micron and 4.5 micron imaging for Spitzer, and J and K [subscript s] imaging for the VISTA-CFHT Stripe 82 (VICS82) Near-infrared Survey. Our extensive dataset compiled from both ground and space-based observatories is uniquely capable of studying the most actively star-forming galaxies which are often very massive galaxies residing in the rarest high-sigma density peaks of the cosmic web. In Chapter 2 we study the bright end of the z=4 galaxy UV luminosity distribution or luminosity function by fitting the spectral energy distributions (SEDs) of the galaxies in our photometric data with Stellar Population Synthesis (SPS) models to measure the galaxies' redshifts and UV luminosity. In addition to measuring the bright end of the galaxy luminosity function, we had the unanticipated result of measuring the faint end of the z=4 active galactic nuclei (AGN) UV luminosity function, which has implications on the contribution of AGNs during the end of the reionization era. We compare our observed galaxy luminosity function to luminosity functions predicted by semi-analytical models (SAMs) with different prescriptions for star formation physics, such as the density of neutral hydrogen. We find our observations are consistent with predictions that galaxies at z=3-4 form stars more efficiently than at lower redshifts due to shorter neutral hydrogen depletion times. In Chapter 3, we measure the fraction of massive (M [subscript *] > 10¹¹ [solar mass] galaxies at z=3-5 in the largest volume to date. To do this we produce a K [subscript s] -selected catalog by combining deep K [subscript s] -band imaging from the NEWFIRM HETDEX survey (NHS), which we obtain, reduce, and catalog. We select quiescent galaxies by performing SED-fitting with SPS models to measure their redshifts, SFRs, and stellar masses. We define quiescent galaxies as having a specific SFR (sSFR; sSFR = SFR / stellar mass) < 10⁻¹¹ yr⁻¹. We measure a quiescent fraction of 10+/-4% among these massive galaxies with reduced errors due to cosmic variance and Poisson noise, which is consistent with the next largest sample of this galaxy population. We find that while the population of massive galaxies at z=3-5 is dominated by star-forming galaxies, a significant fraction have quenched, which suggests there exists a population of massive galaxies at even higher redshifts that have rapidly formed their stars and quenched in less than ~1.5 Gyr since the Big Bang. In Chapter 4 we present the outlook for studying the formation and evolution of massive quiescent galaxies in the early universe using current and future observatoriesItem The kinetic Sunyaev-Zel’dovich effect as a probe of the physics of cosmic reionization : the effect of self-regulated reionization(2014-12) Park, Hyunbae; Shapiro, Paul R.We calculate the angular power spectrum of the cosmic microwave background temperature fluctuations induced by the kinetic Sunyaev-Zel'dovich (kSZ) effect from the epoch of reionization (EOR). We use detailed N-body+radiative-transfer simulations to follow inhomogeneous reionization of the intergalactic medium. For the first time, we take into account the "self-regulation" of reionization: star formation in low-mass dwarf galaxies or minihalos is suppressed if these halos form in the regions that were already ionized or Lyman-Werner dissociated. Some previous work suggested that the amplitude of the kSZ power spectrum from the EOR can be described by a two-parameter family: the epoch of half-ionization and the duration of reionization. However, we argue that this picture applies only to simple forms of the reionization history which are roughly symmetric about the half-ionization epoch. In self-regulated reionization, the universe begins to be ionized early, maintains a low level of ionization for an extended period, and then finishes reionization as soon as high-mass atomically cooling halos dominate. While inclusion of self-regulation affects the amplitude of the kSZ power spectrum only modestly (~10%), it can change the duration of reionization by a factor of more than two. We conclude that the simple two-parameter family does not capture the effect of a physical, yet complex, reionization history caused by self-regulation. When added to the post-reionization kSZ contribution, our prediction for the total kSZ power spectrum is below the current upper bound from the South Pole Telescope. Therefore, the current upper bound on the kSZ effect from the EOR is consistent with our understanding of the physics of reionization.