Using 21cm absorption in small impact parameter galaxy-quasar pairs to probe low-redshift damped and sub-damped lyα systems

Sanchayeeta Borthakur, Todd M. Tripp, Min S. Yun, Emmanuel Momjian, Joseph D. Meiring, David V. Bowen, Donald G. York

Research output: Contribution to journalArticle

26 Citations (Scopus)

Abstract

To search for low-redshift damped Lyα (DLA) and sub-DLA quasar absorbers, we have conducted a 21cm absorption survey of radio-loud quasars at small impact parameters to foreground galaxies selected from the Sloan Digital Sky Survey (SDSS). Here we present the first results from this survey based on observations of SDSS J104257.58+074850.5 (z QSO = 2.66521), a quasar at an angular separation from a foreground galaxy (z gal = 0.03321) of 25 (1.7kpc in projection). The foreground galaxy is a low-luminosity spiral with on-going star formation (0.004 M yr-1kpc -2) and a metallicity of -0.27 0.05 dex. We detect 21cm absorption from the galaxy with the Green Bank Telescope (GBT), the Very Large Array (VLA), and the Very Long Baseline Array (VLBA). The absorption appears to be quiescent disk gas co-rotating with the galaxy and we do not find any evidence for outflowing cold neutral gas. The width of the main absorption line indicates that the gas is cold, Tk < 283K, and the H I column is surprisingly low given the impact parameter of 1.7kpc; we find that N(H I) ≤9.6 × 1019cm-2 (GBT) and N(H I) ≤1.5 × 1020cm-2 (VLBA). VLBA marginally resolves the continuum source and the absorber, and a lower limit of 27.1 × 13.9 pc is derived for the size of the absorbing cloud. In turn, this indicates a low density for a cold cloud, n(H I) < 3.5cm-3. We hypothesize that this galaxy, which is relatively isolated, is becoming depleted in H I because it is converting its interstellar matter into stars without a replenishing source of gas, and we suggest future observations to probe this and similar galaxies.

Original languageEnglish (US)
Pages (from-to)131-145
Number of pages15
JournalAstrophysical Journal
Volume713
Issue number1
DOIs
StatePublished - Jan 1 2010
Externally publishedYes

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quasars
probe
galaxies
Very Long Baseline Array (VLBA)
probes
gas
cold gas
absorbers
telescopes
interstellar matter
radio
Very Large Array (VLA)
neutral gases
parameter
gases
metallicity
star formation
cold
projection
luminosity

Keywords

  • Galaxies: abundances
  • Galaxies: ISM
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Using 21cm absorption in small impact parameter galaxy-quasar pairs to probe low-redshift damped and sub-damped lyα systems. / Borthakur, Sanchayeeta; Tripp, Todd M.; Yun, Min S.; Momjian, Emmanuel; Meiring, Joseph D.; Bowen, David V.; York, Donald G.

In: Astrophysical Journal, Vol. 713, No. 1, 01.01.2010, p. 131-145.

Research output: Contribution to journalArticle

Borthakur, Sanchayeeta ; Tripp, Todd M. ; Yun, Min S. ; Momjian, Emmanuel ; Meiring, Joseph D. ; Bowen, David V. ; York, Donald G. / Using 21cm absorption in small impact parameter galaxy-quasar pairs to probe low-redshift damped and sub-damped lyα systems. In: Astrophysical Journal. 2010 ; Vol. 713, No. 1. pp. 131-145.
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AU - Yun, Min S.

AU - Momjian, Emmanuel

AU - Meiring, Joseph D.

AU - Bowen, David V.

AU - York, Donald G.

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AB - To search for low-redshift damped Lyα (DLA) and sub-DLA quasar absorbers, we have conducted a 21cm absorption survey of radio-loud quasars at small impact parameters to foreground galaxies selected from the Sloan Digital Sky Survey (SDSS). Here we present the first results from this survey based on observations of SDSS J104257.58+074850.5 (z QSO = 2.66521), a quasar at an angular separation from a foreground galaxy (z gal = 0.03321) of 25 (1.7kpc in projection). The foreground galaxy is a low-luminosity spiral with on-going star formation (0.004 M ⊙ yr-1kpc -2) and a metallicity of -0.27 0.05 dex. We detect 21cm absorption from the galaxy with the Green Bank Telescope (GBT), the Very Large Array (VLA), and the Very Long Baseline Array (VLBA). The absorption appears to be quiescent disk gas co-rotating with the galaxy and we do not find any evidence for outflowing cold neutral gas. The width of the main absorption line indicates that the gas is cold, Tk < 283K, and the H I column is surprisingly low given the impact parameter of 1.7kpc; we find that N(H I) ≤9.6 × 1019cm-2 (GBT) and N(H I) ≤1.5 × 1020cm-2 (VLBA). VLBA marginally resolves the continuum source and the absorber, and a lower limit of 27.1 × 13.9 pc is derived for the size of the absorbing cloud. In turn, this indicates a low density for a cold cloud, n(H I) < 3.5cm-3. We hypothesize that this galaxy, which is relatively isolated, is becoming depleted in H I because it is converting its interstellar matter into stars without a replenishing source of gas, and we suggest future observations to probe this and similar galaxies.

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