The rest-UV spectral properties of dwarf galaxies at z ∼ 2

This is the authors' abstract. We don't add key points for this paper.

Rest-utraviolet (UV) spectroscopy can constrain properties of the stellar populations, outflows, covering fractions, and can indirectly constrain the Lyman continuum escape fraction of galaxies. Many works have studied the rest-UV spectra of more massive star-forming galaxies and low-mass galaxies selected via strong nebular line emission or via Ly α emission. However, studies of rest-UV spectroscopy have yet to be done on an unbiased sample at low mass during the epoch of peak star formation (z~ 2). We present a stacked rest-UV spectrum of a complete sample of 16 dwarf galaxies (log( M*/M₎ median = 8.2) at z~ 2. The rest-UV Keck Low Resolution Imaging Spectrometer (Keck/LRIS) spectroscopy is complemented by rest-optical Keck/MOSFIRE spectroscopy and Hubble photometry. We find generally larger Ly α equivalent widths (EWLyα = 11.2\,\, Å) when compared with higher mass (log( M*/M₎ median = 10.3) composites from Keck Baryonic Structure Survey (KBSS, EWLyα = -5\,\, Å). The average low- and high-ionization absorption line equivalent widths (EWs; EWLIS and EWHIS, respectively) are weaker (EWLIS = –1.18 Å, EWHIS= –0.99 Å) in dwarf galaxies than in higher mass galaxies (EWLIS = –2.04 Å, EWHIS= –1.42 Å). The low-ionizatioz absorption lines (LIS) are optically thick and is thus a good tracer of the neutral hydrogen covering fraction. Both higher EWLyα and lower EWLIS measurements imply that the escape fraction of ionizing radiation is larger in lower mass galaxies at z~ 2.