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

Ishrat Singh, GSSM

School Name

Governor's School for Science and Mathematics

Grade Level

12th Grade

Presentation Topic

Physics

Presentation Type

Mentored

Written Paper Award

1st Place

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.

Location

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.