Characterizing the Circumgalactic Medium of the Lowest-Mass Galaxies: A Case Study of IC 1613

Abstract

Using 10 sightlines observed with the Hubble Space Telescope/Cosmic Origins Spectrograph, we study the circumgalactic medium (CGM) and outflows of IC1613, which is a low-mass ($M_{\ast }\sim 10^8{M}_{\odot }$), dwarf irregular galaxy on the outskirts of the Local Group. Among the sightlines, 4 are pointed towards UV-bright stars in IC1613, and the other 6 sightlines are background QSOs at impact parameters from 6 kpc ($<0.1R_{200}$) to 61 kpc ($0.6R_{200}$). We detect a number of Si II, Si III, Si IV, C II, and C IV absorbers, most of which have velocities less than the escape velocity of IC1613 and thus are gravitationally bound. The line strengths of these ion absorbers are consistent with the CGM absorbers detected in dwarf galaxies at low redshifts. Assuming that Si II, Si III, and Si IV comprise nearly 100% of the total silicon, we find 3% ($\sim$8$\times$10${}^3{\mathrm{M}}_{\odot }$), 2% ($\sim$7$\times$10${}^3{\mathrm{M}}_{\odot }$), and 32--42% [$\sim$(1.0--1.3)$\times$10${}^5{\mathrm{M}}_{\odot }$] of the silicon mass in the stars, interstellar medium, and within $0.6R_{200}$ of the CGM of IC1613. We also estimate the metal outflow rate to be ${\dot{\mathrm{M}}}_{\mathrm{out},\mathrm{Z}}\ge 1.1\times 10^{-5}{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$ and the instantaneous metal mass loading factor to be ${\eta }_{\mathrm{Z}}\ge 0.004$, which are in broad agreement with available observation and simulation values. This work is the first time a dwarf galaxy of such low mass is probed by a number of both QSO and stellar sightlines, and it shows that the CGM of low-mass gas-rich galaxies can be a large reservoir enriched with metals from past and ongoing outflows.

Resubmitted to ApJ with the referee's comments addressed. Minor changes were made to the original draft

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