The MOSDEF-LRIS Survey: Probing ISM/CGM Structure of Star-Forming Galaxies at z~2 Using Rest-UV Spectroscopy

Abstract

The complex structure of gas, metals, and dust in the interstellar and circumgalactic medium (ISM and CGM, respectively) in star-forming galaxies can be probed by Ly$\alpha$ emission and absorption, low-ionization interstellar (LIS) metal absorption, and dust reddening E(B-V). We present a statistical analysis of the mutual correlations among Ly$\alpha$ equivalent width (EW${}_{Ly\alpha }$), LIS equivalent width (EW${}_{LIS}$), and E(B-V) in a sample of 157 star-forming galaxies at $z\sim 2.3$. With measurements obtained from individual, deep rest-UV spectra and spectral-energy distribution (SED) modeling, we find that the tightest correlation exists between EW${}_{LIS}$ and E(B-V), although correlations among all three parameters are statistically significant. These results signal a direct connection between dust and metal-enriched HI gas, and that they are likely co-spatial. By comparing our results with the predictions of different ISM/CGM models, we favor a dusty ISM/CGM model where dust resides in HI gas clumps and Ly$\alpha$ photons escape through the low HI covering fraction/column density intra-clump medium. Finally, we investigate the factors that potentially contribute to the intrinsic scatter in the correlations studied in this work, including metallicity, outflow kinematics, Ly$\alpha$ production efficiency, and slit loss. Specifically, we find evidence that scatter in the relationship between EW${}_{Ly\alpha }$ and E(B-V) reflects the variation in metal-to-HI covering fraction ratio as a function of metallicity, and the effects of outflows on the porosity of the ISM/CGM. Future simulations incorporating star-formation feedback and the radiative transfer of Ly$\alpha$ photons will provide key constraints on the spatial distributions of neutral hydrogen gas and dust in the ISM/CGM structure.

19 pages, 6 figures, 3 tables, accepted for publication in ApJ

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• The Low-Redshift Lyman Continuum Survey. Unveiling the ISM properties of low-$z$ Lyman continuum emitters
• The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyman Alpha Emission of High-Redshift Galaxies
• Lyman-Alpha Escape from Low-Mass, Compact, High-Redshift Galaxies
• The MOSDEF-LRIS Survey: Connection between Galactic-scale Outflows and the Properties of $z$~2 star-forming Galaxies
• Metal content of the circumgalactic medium around star-forming galaxies at z $\sim$ 2.6 as revealed by the VIMOS Ultra-Deep Survey
• Interpreting the Si II and C II line spectra from the COS Legacy Spectroscopic SurveY using a virtual galaxy from a high-resolution radiation-hydrodynamic simulation
• CECILIA: Ultra-Deep Rest-Optical Spectra of Faint Galaxies at Cosmic Noon