Matching Items (4)
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- All Subjects: Galaxies
- Creators: Butler, Nathaniel
Description
Galaxies represent a fundamental catalyst in the ``lifecycle'' of matter in the Universe, and the study of galaxy assembly and evolution provides unique insight into the physical processes governing the transformation of matter from atoms to gas to stars. With the Hubble Space Telescope, the astrophysical community is able to study the formation and evolution of galaxies, at an unrivaled spatial resolution, over more than 90% of cosmic time. Here, I present results from two complementary studies of galaxy evolution in the local and intermediate redshift Universe which used new and archival HST images. First, I use archival broad-band HST WFPC2 optical images of local (d<63 Mpc) Seyfert-type galaxies to test the observed correlation between visually-classified host galaxy dust morphology and AGN class. Using quantitative parameters for classifying galaxy morphology, I do not measure a strong correlation between the galaxy morphology and AGN class. This result could imply that the Unified Model of AGN provides a sufficient model for the observed diversity of AGN, but this result could also indicate the quantitative techniques are insufficient for characterizing the dust morphology of local galaxies. To address the latter, I develop a new automated method using an inverse unsharp masking technique coupled to Source Extractor to detect and measure dust morphology. I measure no strong trends with dust-morphology and AGN class using this method, and conclude that the Unified Model remains sufficient to explain the diversity of AGN. Second, I use new UV-optical-near IR broad-band images obtained with the HST WFC3 in the Early Release Science (ERS) program to study the evolution of massive, early-type galaxies. These galaxies were once considered to be ``red and dead'', as a class uniformly devoid of recent star formation, but observations of these galaxies in the local Universe at UV wavelengths have revealed a significant fraction (30%) of ETGs to have recently formed a small fraction (5-10%) of their stellar mass in young stars. I extend the study of recent star formation in ETGs to intermediate-redshift 0.35<1.5 with the ERS data. Comparing the mass fraction and age of young stellar populations identified in these ETGs from two-component SED analysis with the morphology of the ETG and the frequency of companions, I find that at this redshift many ETGs are likely to have experienced a minor burst of recent star formation. The mechanisms driving this recent star formation are varied, and evidence for both minor merger driven recent star formation as well as the evolution of transitioning ETGs is identified.
ContributorsRutkowski, Michael (Author) / Windhorst, Rogier A. (Thesis advisor) / Bowman, Judd (Committee member) / Butler, Nathaniel (Committee member) / Desch, Steven (Committee member) / Young, Patrick (Committee member) / Arizona State University (Publisher)
Created2013
Description
Quasars, the visible phenomena associated with the active accretion phase of super- massive black holes found in the centers of galaxies, represent one of the most energetic processes in the Universe. As matter falls into the central black hole, it is accelerated and collisionally heated, and the radiation emitted can outshine the combined light of all the stars in the host galaxy. Studies of quasar host galaxies at ultraviolet to near-infrared wavelengths are fundamentally limited by the precision with which the light from the central quasar accretion can be disentangled from the light of stars in the surrounding host galaxy. In this Dissertation, I discuss direct imaging of quasar host galaxies at redshifts z ≃ 2 and z ≃ 6 using new data obtained with the Hubble Space Telescope. I describe a new method for removing the point source flux using Markov Chain Monte Carlo parameter estimation and simultaneous modeling of the point source and host galaxy. I then discuss applications of this method to understanding the physical properties of high-redshift quasar host galaxies including their structures, luminosities, sizes, and colors, and inferred stellar population properties such as age, mass, and dust content.
ContributorsMechtley, Matt R (Author) / Windhorst, Rogier A (Thesis advisor) / Butler, Nathaniel (Committee member) / Jansen, Rolf A (Committee member) / Rhoads, James (Committee member) / Scowen, Paul (Committee member) / Arizona State University (Publisher)
Created2014
Description
The field of exoplanet science has matured over the past two decades with over 3500 confirmed exoplanets. However, many fundamental questions regarding the composition, and formation mechanism remain unanswered. Atmospheres are a window into the properties of a planet, and spectroscopic studies can help resolve many of these questions. For the first part of my dissertation, I participated in two studies of the atmospheres of brown dwarfs to search for weather variations. To understand the evolution of weather on brown dwarfs we conducted a multi-epoch study monitoring four cool brown dwarfs to search for photometric variability. These cool brown dwarfs are predicted to have salt and sulfide clouds condensing in their upper atmosphere and we detected one high amplitude variable. Combining observations for all T5 and later brown dwarfs we note a possible correlation between variability and cloud opacity.
For the second half of my thesis, I focused on characterizing the atmospheres of directly imaged exoplanets. In the first study Hubble Space Telescope data on HR8799, in wavelengths unobservable from the ground, provide constraints on the presence of clouds in the outer planets. Next, I present research done in collaboration with the Gemini Planet Imager Exoplanet Survey (GPIES) team including an exploration of the instrument contrast against environmental parameters, and an examination of the environment of the planet in the HD 106906 system. By analyzing archival HST data and examining the near-infrared colors of HD 106906b, we conclude that the companion shows weak evidence of a circumplanetary dust disk or cloud. Finally, I measure the properties of the low mass directly imaged planet 51 Eridani b. We combined published J, H spectra with updated LP photometry, new K1, K2 spectra, and MS photometry. The new data confirms that the planet has redder than similar spectral type objects, which might be due to the planet still transitioning from to L-to-T. Model atmospheres indicate a cooler effective temperature best fit by a patchy cloud atmosphere making 51 Eri b an excellent candidate for future variability studies with the James Webb Space Telescope.
For the second half of my thesis, I focused on characterizing the atmospheres of directly imaged exoplanets. In the first study Hubble Space Telescope data on HR8799, in wavelengths unobservable from the ground, provide constraints on the presence of clouds in the outer planets. Next, I present research done in collaboration with the Gemini Planet Imager Exoplanet Survey (GPIES) team including an exploration of the instrument contrast against environmental parameters, and an examination of the environment of the planet in the HD 106906 system. By analyzing archival HST data and examining the near-infrared colors of HD 106906b, we conclude that the companion shows weak evidence of a circumplanetary dust disk or cloud. Finally, I measure the properties of the low mass directly imaged planet 51 Eridani b. We combined published J, H spectra with updated LP photometry, new K1, K2 spectra, and MS photometry. The new data confirms that the planet has redder than similar spectral type objects, which might be due to the planet still transitioning from to L-to-T. Model atmospheres indicate a cooler effective temperature best fit by a patchy cloud atmosphere making 51 Eri b an excellent candidate for future variability studies with the James Webb Space Telescope.
ContributorsRajan, Abhijith (Author) / Patience, Jennifer (Thesis advisor) / Young, Patrick (Thesis advisor) / Scowen, Paul (Committee member) / Butler, Nathaniel (Committee member) / Shkolnik, Evgenya (Committee member) / Arizona State University (Publisher)
Created2017
Description
New measurements of the Hα luminosity function (LF) and star formation rate
(SFR) volume density are presented for galaxies at z∼0.62 in the COSMOS field.
These results are part of the Deep And Wide Narrowband Survey (DAWN), a unique
infrared imaging program with large areal coverage (∼1.1 deg 2 over 5 fields) and
sensitivity (9.9 × 10 −18 erg/cm 2 /s at 5σ).
The present sample, based on a single DAWN field, contains 116 Hα emission-
line candidates at z∼0.62, 25% of which have spectroscopic confirmations. These
candidates have been selected through comparison of narrow and broad-band images
in the infrared and through matching with existing catalogs in the COSMOS field.
The dust-corrected LF is well described by a Schechter function with L* = 10 42.64±0.92
erg s −1 , Φ* = 10 −3.32±0.93 Mpc −3 (L* Φ* = 10 39.40±0.15 ), and α = −1.75 ± 0.09. From
this LF, a SFR density of ρ SF R =10 −1.37±0.08 M○ yr −1 Mpc −3 was calculated. An
additional cosmic variance uncertainty of ∼ 20% is also expected. Both the faint
end slope and luminosity density that are derived are consistent with prior results at
similar redshifts, with reduced uncertainties.
An analysis of these Hα emitters’ sizes is also presented, showing a direct corre-
lation between the galaxies’ sizes and their Hα emission.
(SFR) volume density are presented for galaxies at z∼0.62 in the COSMOS field.
These results are part of the Deep And Wide Narrowband Survey (DAWN), a unique
infrared imaging program with large areal coverage (∼1.1 deg 2 over 5 fields) and
sensitivity (9.9 × 10 −18 erg/cm 2 /s at 5σ).
The present sample, based on a single DAWN field, contains 116 Hα emission-
line candidates at z∼0.62, 25% of which have spectroscopic confirmations. These
candidates have been selected through comparison of narrow and broad-band images
in the infrared and through matching with existing catalogs in the COSMOS field.
The dust-corrected LF is well described by a Schechter function with L* = 10 42.64±0.92
erg s −1 , Φ* = 10 −3.32±0.93 Mpc −3 (L* Φ* = 10 39.40±0.15 ), and α = −1.75 ± 0.09. From
this LF, a SFR density of ρ SF R =10 −1.37±0.08 M○ yr −1 Mpc −3 was calculated. An
additional cosmic variance uncertainty of ∼ 20% is also expected. Both the faint
end slope and luminosity density that are derived are consistent with prior results at
similar redshifts, with reduced uncertainties.
An analysis of these Hα emitters’ sizes is also presented, showing a direct corre-
lation between the galaxies’ sizes and their Hα emission.
ContributorsGonzalez, Alicia (Author) / Rhoads, James E (Thesis advisor) / Malhotra, Sangeeta (Thesis advisor) / Butler, Nathaniel (Committee member) / Jansen, Rolf (Committee member) / Arizona State University (Publisher)
Created2017