THE SPECTRALLY RESOLVED Ly[alpha] EMISSION OF THREE Ly[alpha]-SELECTED FIELD GALAXIES AT z ~ 2.4 FROM THE HETDEX PILOT SURVEY

• Published in: The Astrophysical journal 2013-10, Vol.775 (2), p.1-20
• Main Authors: CHONIS, TAYLOR S, Blanc, Guillermo A, Hill, Gary J, Adams, Joshua J, Finkelstein, Steven L, Gebhardt, Karl, Kollmeier, Juna A, Ciardullo, Robin, Drory, Niv, Gronwall, Caryl, Hagen, Alex, OVERZIER, RODERIK A, Song, Mimi, ZEIMANN, GREGORY R
• Format: Article
• Language: English
• Subjects: Astronomical models; Emission; Emission spectroscopy; Galaxies; Mathematical models; Offsets; Spectral emissivity; Spectral resolution
• ISSN: 0004-637X; 1538-4357
• DOI: 10.1088/0004-637X/775/2/99

We present new results on the spectrally resolved Ly[alpha] emission of three Ly[alpha]-emitting field galaxies at z ~ 2.4 with high Ly[alpha] equivalent width (>100 [Angstrom]) and Ly[alpha] luminosity (~10 super(43) erg s super(-1)). At 120 km s super(-1) (FWHM) spectral resolution, the prominent double-peaked Ly[alpha] profile straddles the systemic velocity, where the velocity zero point is determined from spectroscopy of the galaxies' rest-frame optical nebular emission lines. The average velocity offset from systemic of the stronger redshifted emission component for our sample is 176 km s super(-1) while the average total separation between the redshifted and main blueshifted emission components is 380 km s super(-1). These measurements are a factor of ~2 smaller than for UV-continuum-selected galaxies that show Ly[alpha] in emission with lower Ly[alpha] equivalent widths. We compare our Ly[alpha] spectra to the predicted line profiles of a spherical "expanding shell" Ly[alpha] radiative transfer grid that models large-scale galaxy outflows. Specifically, blueward of the systemic velocity where two galaxies show a weak, highly blueshifted (by ~1000 km s super(-1)) tertiary emission peak, the model line profiles are a relatively poor representation of the observed spectra. Since the neutral gas column density has a dominant influence over the shape of the Ly[alpha] line profile, we caution against equating the observed Ly[alpha] velocity offset with a physical outflow velocity, especially at lower spectral resolution where the unresolved Ly[alpha] velocity offset is a convoluted function of several degenerate parameters. Referring to rest-frame ultraviolet and optical Hubble Space Telescope imaging, we find that galaxy-galaxy interactions may play an important role in inducing a starburst that results in copious Ly[alpha] emission as well as perturbing the gas distribution and velocity field, both of which have strong influence over the Ly[alpha] emission line profile.