Abstract
We present a study of 7 star-forming galaxies from the Cosmic Evolution Survey (COSMOS) observed with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST). The galaxies are located at relatively low redshifts, $z\sim$0.3, with morphologies ranging from extended and disturbed to compact and smooth. To complement the HST observations we also analyze observations taken with the VIMOS spectrograph on the Very Large Telescope (VLT). In our galaxy sample we identify three objects with double peak Lyman-$\alpha$ profiles similar to those seen in Green Pea compact galaxies and measure peak separations of 655, 374, and 275 km s$^{-1}$. We measure Lyman-$\alpha$ escape fractions with values ranging between 5-13\%. Given the low flux levels in the individual COS exposures we apply a weighted stacking approach to obtain a single spectrum. From this COS combined spectrum we infer upper limits for the absolute and relative Lyman continuum escape fractions of $f_{\rm abs}(\rm LyC)$ = 0.4$^{+10.1}_{-0.4}$\% and $f_{\rm res}(\rm LyC)$ = 1.7$^{+15.2}_{-1.7}$\%, respectively. Finally, we find that most of these galaxies have moderate UV and optical SFRs (SFRs $\lesssim$ 10 M$_{\odot}$ yr$^{-1}$).
Highlights
Star formation is the fundamental process transforming baryonic matter in the Universe, converting the hydrogen reservoir into heavy elements
We present a study of 7 star-forming galaxies from the Cosmic Evolution Survey (COSMOS) observed with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST)
Turning to the SFRs inferred from the UV/COS observations and those obtained from the optical/VIMOS data we find that the individual SFRs are marginally consistent within the errors, there is an offset for most of the targets with the optical SFRs being slightly higher than the UV rates with the exception of 1535411 and 1365128
Summary
Star formation is the fundamental process transforming baryonic matter in the Universe, converting the hydrogen reservoir into heavy elements. The presence of ionizing stars in star-forming galaxies has been inferred at z 7 using a variety of proxies such as dust emission, stellar absorption lines, nebular emission lines, and blue galaxy colors (Bouwens et al 2012; Barger et al 2012; Stark et al 2013; Finkelstein 2016) With these confirmed sources of ionizing photons at relatively highz, measurements of the Lyman continuum escape fraction, fesc(LyC), are critical for identifying the conditions and environments that benefit their escape onto the intergalactic medium (IGM). Efforts to observe escaping Lyman continuum radiation at relatively high redshifts (z > 1) are challenging because of possible contamination from low-redshift interlopers (Vanzella et al 2010; Mostardi et al 2015), but at redshifts z > 3 these star-forming galaxies are significantly affected by attenuation by the Lyα forest along the line of sight (Inoue et al 2014).
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