A Multi-wavelength Study of Early Star-forming Galaxies PDF Download

Author: Luke Jonathan Mark Davies
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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Author: Corentin Schreiber
Publisher: Springer
ISBN: 3319442937
Category : Science
Languages : en
Pages : 234

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Book Description
This thesis presents a pioneering method for gleaning the maximum information from the deepest images of the far-infrared universe obtained with the Herschel satellite, reaching galaxies fainter by an order of magnitude than in previous studies. Using these high-quality measurements, the author first demonstrates that the vast majority of galaxy star formation did not take place in merger-driven starbursts over 90% of the history of the universe, which suggests that galaxy growth is instead dominated by a steady infall of matter. The author further demonstrates that massive galaxies suffer a gradual decline in their star formation activity, providing an alternative path for galaxies to stop star formation. One of the key unsolved questions in astrophysics is how galaxies acquired their mass in the course of cosmic time. In the standard theory, the merging of galaxies plays a major role in forming new stars. Then, old galaxies abruptly stop forming stars through an unknown process. Investigating this theory requires an unbiased measure of the star formation intensity of galaxies, which has been unavailable due to the dust obscuration of stellar light.

Author: Irene Shivaei
Publisher:
ISBN: 9780355472042
Category : Cosmic dust
Languages : en
Pages : 20

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Redshift of z

Author: Brittany N. Vanderhoof
Publisher:
ISBN:
Category : Galaxies
Languages : en
Pages : 0

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Author: Drew Grinnell Brisbin
Publisher:
ISBN:
Category :
Languages : en
Pages : 167

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Book Description
Our recent studies in galaxy evolution have revealed a surprising new paradigm of star formation. Contrary to the notion that major mergers play an increasingly dominant role going backwards in cosmic history, we find that over the last ~10 Gyr, much of star formation has been fueled by accreting cold gas from the cosmic web. Accretion rates were presumably larger in the past, so star forming systems may have very different properties in the early Universe and today. Large scale astronomical surveys, such as the Herschel Multi-Tiered Extragalactic Survey (HerMES), and the Sloan Digital Sky Survey (SDSS) have provided a wealth of extragalactic data covering a statistically large number of sources. Targeted, niche surveys, like our fine structure line survey of star forming galaxies in the early Universe observed with the redshift (z) Early Universe Spectrometer (ZEUS) have provided detailed observations of high interest sources. We have made use of this diverse set of data to study galaxy evolution from the epoch of peak star formation at z=1-2 up to the present. Data from HerMES is a reliable probe of infrared emission, particularly useful for characterizing the far infrared dust peak, and therefore determining star formation rates out to redshifts of a few. Deep integrations with the Herschel SPIRE photometer rapidly reach the confusion limit, tempering its utility in studying faint high redshift galaxies. With appropriate care taken to identify blended sources, however, HerMES data is useful in identifying bright, red- shifted, star forming sources. We have compiled spectral energy distributions from HerMES and ancillary data and found that, even sources at high redshift are well fit by local star forming galaxy templates. In the local Universe, spectroscopic SDSS data has allowed us to estimate crucial galaxy properties on ~105 sources, providing an opportunity to observe general statistical trends, and constrain theories of galaxy evolution. A toy model of cold flow accretion powered star formation reproduces the observed fundamental plane of galaxy stellar mass, metallicity, and star formation for small and medium mass galaxies. Our fine structure line survey with ZEUS detected the [CII] 157.7 [MICRO SIGN]m line in eight galaxies from the epoch of peak star formation at z=1-2. We augmented this survey with observations of the [OI] 63 [MICRO SIGN]m line and far infrared photometry from Herschel, as well as Spitzer IRS spectra from the literature. Most of our sources have higher than average gas heating efficiency with L[CII] /LF IR 10[-]2 . We interpret the majority of them as being dominated by star formation powered PDRs, extending to kpc scales. In two sources there is evidence for enhanced [CII] emission due to heating by low velocity shocks. These findings are consistent with a picture of gas accretion fueling star formation on a near galaxy-wide scale. In synthesizing this data we find a remarkable consistency in the nature of star formation over the last 10 Gyr. In contrast with the model of sustained hierarchical merging, we find that star formation since z~2 is fueled largely by cold flow accretion of gas from the cosmic web, which presents itself as moderate density star formation with correspondingly moderate UV fields.

Author: Pietro M. Reviglio
Publisher:
ISBN:
Category :
Languages : en
Pages : 206

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Author: Madison V. Smith
Publisher:
ISBN:
Category : Astrophysics
Languages : en
Pages : 0

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I present the results of a multi-wavelength study of global, radial and local star formation histories (SFHs) in a statistical sample of 34 nearby galaxies. The SFHs are estimated using spectral energy distribution (SED) fitting, and are presented alongside classic indicators of changes in stellar population ages (optical colors, specific star formation rates, and H-alpha equivalent widths). I interpret the results of this methodology in the context of the literature for each galaxy. In addition to the global and radial measurements, ultraviolet-selected sources in each galaxy are detected and cataloged. I use two different methods (k-means clustering and two-point angular correlation functions) to describe the spatial distributions of these UV sources. I find that there is a connection between the clustering of UV sources in M63 and the presence of spiral arms. The less-clustered distributions of UV sources seen in galaxies without spiral arms suggests that the spiral arms help to cluster star formation in the stellar disk. Finally, I find that there is a detectable radial gradient in the age of the younger stellar population when looking at the full catalog of all UV sources. This result agrees with the leading theory for structure formation in the universe, the Lambda-CDM model, which theorizes that galaxies form and evolve "inside-out".

Author: Abraham Loeb
Publisher: Princeton University Press
ISBN: 1400834066
Category : Science
Languages : en
Pages : 210

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A concise introduction to cosmology and how light first emerged in the universe Though astrophysicists have developed a theoretical framework for understanding how the first stars and galaxies formed, only now are we able to begin testing those theories with actual observations of the very distant, early universe. We are entering a new and exciting era of discovery that will advance the frontiers of knowledge, and this book couldn't be more timely. It covers all the basic concepts in cosmology, drawing on insights from an astronomer who has pioneered much of this research over the past two decades. Abraham Loeb starts from first principles, tracing the theoretical foundations of cosmology and carefully explaining the physics behind them. Topics include the gravitational growth of perturbations in an expanding universe, the abundance and properties of dark matter halos and galaxies, reionization, the observational methods used to detect the earliest galaxies and probe the diffuse gas between them—and much more. Cosmology seeks to solve the fundamental mystery of our cosmic origins. This book offers a succinct and accessible primer at a time when breathtaking technological advances promise a wealth of new observational data on the first stars and galaxies. Provides a concise introduction to cosmology Covers all the basic concepts Gives an overview of the gravitational growth of perturbations in an expanding universe Explains the process of reionization Describes the observational methods used to detect the earliest galaxies

Author: Virginie Aline Montes
Publisher:
ISBN:
Category : Astrophysics
Languages : en
Pages : 240

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Author: Amanda Elaine Bauer
Publisher:
ISBN:
Category : Active galaxies
Languages : en
Pages : 336

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The work presented in this thesis investigates the evolution of starforming galaxies over the last ten billion years. This time period encompasses nearly three-fourths of the age of the Universe, when a substantial fraction of the total stellar mass forms, and the sites of active star formation shift to lower-mass galaxies. The first study presented here combines galaxies from the spectroscopic datasets of the FORS Deep Field and the MUNICS Survey and provides the first significant investigation of the specific star formation rate (SSFR; star formation rate [SFR] per unit stellar mass) over a wide range of stellar masses and redshifts (reaching redshift z = 1:5). From [OII]-derived SFRs, we find that low-mass galaxies have higher SSFRs all the way to z = 1:5, implying that star formation contributes progressively more to the growth of stellar mass in low-mass galaxies than in high-mass galaxies. In the follow-up to this study, we combine several near-infrared-selected samples to create one of the largest collections of galaxies with spectroscopic redshifts and morphologies from Hubble Space Telescope images, to characterize the stellar mass build up in galaxies since z = 1:6. The primary data comes from the FORS Deep Field, the MUNICS Survey, the GOODS-South field as observed by the K20 survey and ESO, and the Sloan Digital Sky Survey as a local comparison sample. After bringing together extensive photometric and spectroscopic data sets from several publicly available surveys, we use identical methods to derive physical properties and investigate how galaxy populations evolve with time. Galaxy properties include stellar masses derived from multiwavelength photometry, star formation rates calculated from [OII][lambda]3726Å emission lines, metallicity, color, and SSFRs. We find that the reddest, yet actively star-forming, disk-dominated galaxy population present at z ~ 1:3, decreases in number by z ~ 0:3 during the same timeframe when the bluest quiescent, disk-dominated galaxy population increases in number. We confirm the previously identified morphological separation in the SSFR versus M[subscript asterisk] plane found for local samples and for galaxies at z = 0:7: bulge-dominated galaxies are more massive and have lower SSFRs. We extend this relation for the first time to z = 1:6, showing that galaxies with high SSFRs and diskdominated structures tend to shift to lower masses as redshift decreases. We identify an observed upper envelop in SSFR that lies roughly parallel to lines of constant SFR, decreases with time, and is unaffected by incompleteness among the samples. We apply common star formation histories (constant, ex ponential, and power law) to understand the evolving populations we see, but cannot simultaneously reproduce low-mass galaxies with high SSFRs and highmass galaxies with low SSFRs at all redshifts and over our full mass range. Current semi-analytic models attempt to understand the mass at which galaxies stop forming stars through connections to Active Galactic Nuclei feedback, gas consumption, declining galaxy merger rates and/or changes in the incoming cold gas supply, but none can explain the gradual and constant decline of star formation consistent among all galaxies below this mass. We suggest a possible resolution where star formation histories of galaxies are dependent on morphology, in addition to the growing evidence for lower mass galaxies to begin forming stars at later times, and with lower initial SFRs than the initial SFRs experienced at earlier times by higher mass galaxies.