The Low-Mass Baryon Cycle in QUEST Dwarf Galaxies I: Sample definition and first results

Abstract

We introduce the QUEST Dwarfs program, which connects low-mass galaxies' stellar populations, interstellar medium, and circumgalactic medium in a large and coherently analyzed sample using a combination of optical spectroscopy, broadband imaging, and FUV absorption spectra of bright background sources .We present initial results from the first-release sample, comprising 14 galaxies with stellar mass $M_\mathrm{star} \leq 10^9 M_\odot$ at $z\approx0.001-0.017$, each with at least one CGM absorption probe at projected distances $d_\mathrm{proj}\lesssim 100$ kpc. This representative sample triples the number of available probes within 1/3 of the halo radius of dwarf galaxies outside of the Local Group. We find that the total silicon column density declines much more rapidly with projected distance than \textsc{Hi}, implying that chemically enriched cool gas is preferentially concentrated in the inner CGM, while the increasing ionization fraction of hydrogen with radius likely enhances this contrast. Accounting for unobserved silicon in higher ionization stages, we infer total metal masses of $\log M_Z/M_\odot\approx4.8$ and $6.5$ in the cool CGM within $0.3 R_\mathrm{vir}$ for dwarfs with median $\log M_\mathrm{star}/M_\odot=7.6$ and 8.6, respectively. These reservoirs correspond to $\approx3$% and $\approx16$% of the total metals produced over the galaxies' lifetimes. More massive galaxies also exhibit systematically stronger metal absorption, suggesting that projected distance governs the radial decline of metal absorption while stellar mass sets the normalization of the CGM metal profile. Individual ions reveal a multiphase structure, with low-ionization species concentrated in the inner halo and higher-ionization species extending farther. The full QUEST Dwarfs survey will provide the statistical power needed to isolate the dominant drivers of CGM enrichment in low-mass halos.