Ly α Halo Properties and Dust in the Circumgalactic Medium of z ∼ 2 Star-forming Galaxies

Abstract

We present Keck Cosmic Web Imager integral-field unit observations around extended Ly α halos of 27 typical star-forming galaxies with redshifts 2.0 < z < 3.2 drawn from the MOSFIRE Deep Evolution Field survey. We examine the average Ly α surface brightness profiles in bins of star formation rate (SFR), stellar mass ( M * ), age, stellar continuum reddening, SFR surface density (Σ SFR ), and Σ SFR normalized by stellar mass (Σ sSFR ). The scale lengths of the halos correlate with stellar mass, age, and stellar continuum reddening and anticorrelate with SFR, Σ SFR , and Σ sSFR . These results are consistent with a scenario in which the down-the-barrel fraction of Ly α emission is modulated by the low-column-density channels in the interstellar medium, and in which the neutral gas covering fraction is related to the physical properties of the galaxies. Specifically, we find that this covering fraction increases with stellar mass, age, and E ( B − V ) and decreases with SFR, Σ SFR , and Σ sSFR . We also find that the resonantly scattered Ly α emission suffers greater attenuation than the (nonresonant) stellar continuum emission, and that the difference in attenuation increases with stellar mass, age, and stellar continuum reddening, and decreases with Σ sSFR . These results imply that more reddened galaxies have more dust in their circumgalactic medium.