The Nature of a Galaxy along the Sight Line to PKS 0454+039

Abstract

We report on the properties of a faint blue galaxy (G1) along the line of sight to the QSO PKS 0454+039 from spectroscopic and imaging data. We measured emission lines of Hα, [S II] λλ6716, 6732, and [N II] λ6584 in the spectrum of G1 obtained with the Gemini/GMOS instrument. The spectroscopic redshift of G1 is z = 0.0715 ± 0.0002. From the extinction-corrected Hα flux, we determine a modest star formation rate of SFR = 0.07 M _⊙ yr^-1 and a specific SFR of log (sSFR) = -8.4. Using three different abundance indicators, we determine a nebular abundance 12 + log (O/H) ranging from 7.6 to 8.2. Based on the velocity dispersion inferred from the emission line widths and the observed surface brightness profile, we estimate the virial mass of G1 to be M _vir ~ 6.7 × 10⁹ M _⊙ with an effective radius of 2.0 kpc. We estimate the stellar mass of G1 using spectral energy distribution fitting to be M _sstarf ≈ 1.2 × 10⁷ M _⊙ and an r'-luminosity of L_{{{r^\prime }}}=1.5\times 10^8 L_\odot. Overall, G1 is a faint, low-mass, low-metallicity Im/H II galaxy. We also report on the line flux limits of another source (G3) which is the most likely candidate for the absorber system at z = 0.8596. From the spectrum of the QSO itself, we report a previously undetected Mg II λλ2796, 2803 absorption line system at z = 1.245.