#### Title

HIRES Analysis of Eight Candidate Dusty Absorbers: Implications for Chemical Evolution in Galaxies

#### School Name

Governor's School for Science and Mathematics

12th Grade

Physics

Mentored

#### Abstract

Quasar absorption systems (QASs) offer a way to spectroscopically study chemical evolution in galaxies, allowing one to better understand important astrophysical processes like stellar evolution, planet formation, and the development of life. Because their rich H I content can produce a substantial fraction of observable stars, classes of QASs including Lyman limit systems (LLSs) and damped Lyman-$\alpha$ absorbers (DLAs) provide a direct probe for analyzing the chemical evolution of metals in galaxies. QASs exhibiting dust absorption lines, known as dusty'' galaxies, are hypothesized to be more metallically enriched than similarly-redshifted QASs lacking dust-related absorption. Using the IRAF data reduction package and the apparent optical depth method, the quasar spectra of two candidate dusty QASs, a DLA at $z=0.692$ toward the quasar 3C 286 and an LLS at $z=1.795$ toward the quasar Ton 618, were analyzed. A search for rare elements led to a novel identification of Ga in the LLS. Relative to comparable dust-free QASs, at $-1.34\pm0.05$ dex, the DLA's metallicity was significantly lower than the mean metallicity at its redshift, whereas the LLS's metallicity, $0.86\pm0.12$ dex, was much higher than the mean metallicity at its redshift. However, due to the insufficient sample size of this study, more data is needed to determine a definite trend. Raw data for six additional QASs located along the sightline toward the quasar Q1246-057 ($z=2.247$) are provided as well, and will be analyzed in full in a future study.

Neville 306

#### Start Date

4-14-2018 12:15 PM

#### Presentation Format

Oral and Written

COinS

Apr 14th, 12:15 PM

HIRES Analysis of Eight Candidate Dusty Absorbers: Implications for Chemical Evolution in Galaxies

Neville 306

Quasar absorption systems (QASs) offer a way to spectroscopically study chemical evolution in galaxies, allowing one to better understand important astrophysical processes like stellar evolution, planet formation, and the development of life. Because their rich H I content can produce a substantial fraction of observable stars, classes of QASs including Lyman limit systems (LLSs) and damped Lyman-$\alpha$ absorbers (DLAs) provide a direct probe for analyzing the chemical evolution of metals in galaxies. QASs exhibiting dust absorption lines, known as dusty'' galaxies, are hypothesized to be more metallically enriched than similarly-redshifted QASs lacking dust-related absorption. Using the IRAF data reduction package and the apparent optical depth method, the quasar spectra of two candidate dusty QASs, a DLA at $z=0.692$ toward the quasar 3C 286 and an LLS at $z=1.795$ toward the quasar Ton 618, were analyzed. A search for rare elements led to a novel identification of Ga in the LLS. Relative to comparable dust-free QASs, at $-1.34\pm0.05$ dex, the DLA's metallicity was significantly lower than the mean metallicity at its redshift, whereas the LLS's metallicity, $0.86\pm0.12$ dex, was much higher than the mean metallicity at its redshift. However, due to the insufficient sample size of this study, more data is needed to determine a definite trend. Raw data for six additional QASs located along the sightline toward the quasar Q1246-057 ($z=2.247$) are provided as well, and will be analyzed in full in a future study.