ASU Electronic Theses and Dissertations
This collection includes most of the ASU Theses and Dissertations from 2011 to present. ASU Theses and Dissertations are available in downloadable PDF format; however, a small percentage of items are under embargo. Information about the dissertations/theses includes degree information, committee members, an abstract, supporting data or media.
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Filtering by
- All Subjects: Astrophysics
- Creators: Jansen, Rolf
(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.
In the modern universe, nearby dwarf galaxies with less than 1/10th the Solar metal abundance provide an opportunity to recalibrate our star formation laws and study the astrophysics of extremely metal-deficient (XMD) environments in detail. I assemble a sample of nearby dwarf galaxies, all within 100 megaparsecs, with nebular oxygen abundances between 1/5th and 1/50th Solar. I identify the subsample of these galaxies with space-based mid- and far-infrared data, and investigate the effects of extreme metallicities on the infrared-radio relationship. For ten of these galaxies, I have acquired 40 hours of observations with the Jansky Very Large Array (JVLA). C-band (4-8 GHz) radio continuum emission is detected from all 10 of these galaxies. These represent the first radio continuum detections from seven galaxies in this sample: Leo A, UGC 4704, HS 0822+3542, SBS 0940+544, and SBS 1129+476. The radio continuum in these galaxies is strongly associated with the presence of optical H-alpha emission, with spectral slopes suggesting a mix of thermal and non-thermal sources. I use the ratio of the radio and far-infrared emission to investigate behavior of the C-band (4-8 GHz) radio/infrared relation at metallicities below 1/10th Solar.
I compare the low metallicity sample with the 4.8 GHz radio/infrared relationship from the KINGFISHER nearby galaxy sample Tabatabaei et al. 2017 and to the 1.4 GHz radio/infrared relationship from the blue compact dwarf galaxy sample of Wu et al. 2008. The infrared/radio ratio q of the low metallicity galaxies is below the average q of star forming galaxies in the modern universe. I compare these galaxies' infrared and radio luminosities to their corresponding Halpha luminosities, and find that both the infrared/Halpha and the radio/H-alpha ratios are reduced by nearly 1 dex in the low metallicity sample vs. higher metallicity galaxies; however the deficit is not straightforwardly interpreted as a metallicity effect.
mining large datasets for transient phenomena. The evolution of massive stars and
compact objects can be studied over cosmic time by identifying supernovae (SNe) and
gamma-ray bursts (GRBs) in other galaxies and determining their redshifts. Modeling
GRBs and their afterglows to probe the jets of GRBs can shed light on the emission
mechanism, rate, and energetics of these events.
In Chapter 1, I discuss the current state of astronomical transient study, including
sources of interest, instrumentation, and data reduction techniques, with a focus
on work in the infrared. In Chapter 2, I present original work published in the
Proceedings of the Astronomical Society of the Pacific, testing InGaAs infrared
detectors for astronomical use (Strausbaugh, Jackson, and Butler 2018); highlights of
this work include observing the exoplanet transit of HD189773B, and detecting the
nearby supernova SN2016adj with an InGaAs detector mounted on a small telescope
at ASU. In Chapter 3, I discuss my work on GRB jets published in the Astrophysical
Journal Letters, highlighting the interesting case of GRB 160625B (Strausbaugh et al.
2019), where I interpret a late-time bump in the GRB afterglow lightcurve as evidence
for a bright-edged jet. In Chapter 4, I present a look back at previous years of
RATIR (Re-ionization And Transient Infra-Red Camera) data, with an emphasis on
the efficiency of following up GRBs detected by the Fermi Space Telescope, before
some final remarks and brief discussion of future work in Chapter 5.
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.