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Title: Small-scale properties of atomic gas in extended disks of galaxies

We present high-resolution H I 21 cm observations with the Karl G. Jansky Very Large Array for three H I rich galaxies in absorption against radio quasars. Our sample contains six sightlines with impact parameters from 2.6 to 32.4 kpc. We detected a narrow H I absorber of FWHM 1.1 km s{sup –1} at 444.5 km s{sup –1} toward SDSS J122106.854+454852.16 probing the dwarf galaxy UCG 7408 at an impact parameter of 2.8 kpc. The absorption feature was barely resolved and its width corresponds to a maximum kinetic temperature, T{sub k} ≈ 26 K. We estimate a limiting peak optical depth of 1.37 and a column density of 6 × 10{sup 19} cm{sup –2}. The physical extent of the absorber is 0.04 kpc{sup 2} and covers ∼25%-30% of the background source. A comparison between the emission and absorption strengths suggests the cold-to-total H I column density in the absorber is ∼30%. Folding in the covering fraction, the cold-to-total H I mass is ∼10%. This suggest that condensation of warm H I (T{sub s} ∼ 1000 K) to cold phase (T{sub s} < 100 K) is suppressed in UGC 7408. The unusually low temperature of the H I absorber also indicatesmore » inefficiency in condensation of atomic gas into molecular gas. The suppression in condensation is likely to be the result of low metal content in this galaxy. The same process might explain the low efficiency of star formation in dwarf galaxies despite their huge gas reservoirs. We report the non-detection of H I in absorption in five other sightlines. This indicates that either the cold gas distribution is highly patchy or the gas is much warmer (T{sub s} > 1000 K) toward these sightlines.« less
Authors:
;  [1] ;  [2] ;  [3] ;  [4] ; ;  [5]
  1. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD 21218 (United States)
  2. National Radio Astronomy Observatory, Socorro, NM 87801 (United States)
  3. Department of Astronomy and Astrophysics, University of Chicago, Chicago, IL 60637 (United States)
  4. Princeton University Observatory, Peyton Hall, Ivy Lane, Princeton, NJ 08544 (United States)
  5. Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
Publication Date:
OSTI Identifier:
22370282
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 795; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION; COMPARATIVE EVALUATIONS; DENSITY; DETECTION; DISTRIBUTION; EFFICIENCY; ELEMENT ABUNDANCE; EMISSION; GALAXIES; MASS; METALS; QUASARS; STARS; ULTRAVIOLET RADIATION