A dwarf galaxy near the sight line to PKS 0454 + 0356: A fading "faint blue galaxy"?

Charles C. Steidel, Mark Dickinson, David V. Bowen

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We report the discovery of a dwarf galaxy (MB = -17.2 for H0 = 50 km s-1 Mpc-1) at z = 0.072 which is only 4″ (3.7 h-1100 kpc) in projection from the line of sight to the bright quasar PKS 0454 + 0356 (zem = 1.345). The dwarf has very blue optical and optical/infrared colors and exhibits line emission indicative of ongoing or recent star formation. However, there is no detection of Ca λλ3934, 3969 absorption at zabs = 0.072 to equivalent width limits (3 σ) of ∼40 mÅ, which would suggest an H I column density along the line of sight of less than 5 × 1019 cm-2, if the Ca II/H I ratio is similar to sight lines in the Galaxy. Based on the absence of Ca II absorption and the unusually weak line emission given the very blue color of the dwarf, we speculate that it may be close to exhausting its supply of gas. As its star formation rate declines, the galaxy's blue magnitude should fade substantially, eventually reaching a quiescent state in accord with its K luminosity of ∼0.005 L*. Future observations of the sight line to PKS 0454 + 0356 using HST in search of Mg II resonance lines, or a search for 21 cm absorption against the quasar radio continuum, could place even more stringent limits on the extent of the gas associated with an intrinsically faint, star-forming dwarf.

Original languageEnglish (US)
Pages (from-to)L77-L80
JournalAstrophysical Journal
Issue number2 PART 2
StatePublished - Aug 20 1993
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Galaxies: distances and redshifts
  • Galaxies: evolution
  • Quasars: absorption lines


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