Rest frame optical properties of Lyman-alpha emitters from the HETDEX survey

HETDEX is a blind spectroscopic survey that is using use 78 fiber based integral field units to search for Lyman Alpha Emitting galaxies (LAEs) in the high redshift universe. HETDEX will discover about half a million LAEs to measure cosmological parameters of the young universe. An important ingredient to this is the precise quantification of the velocity offsets of the Lyα emission form their corresponding host systems. The latter can be measured from other optical emission lines. Here we present the results from VLT/KMOS near-infrared spectroscopic follow-ups of 8 Lyman-alpha emitters (LAEs) at z = 2.1 - 2.5 in the COSMOS field discovered by HETDEX. Observations are performed in the HK band. For these eight LEAs we detect rest-frame optical nebular lines Hα, [OIII]λλ4960,5008, for three of them we detect Hβ and for one [NII]λ6585. For non detected lines we measure a 1σ upper limit. We derive LAEs physical properties, including the Lyα velocity offset, star formation rate (SFR), gas-phase metallicity. Seven LAEs show a velocity shifts of Lyα relative to the systemic redshift ranging between +126 and +367 km/s with an average of +281 km/s. By matching KMOS3D and HETDEX catalogs we measure velocity offsets for 2 more LAEs finding a mean velocity shift of +247 km/s. The velocity offsets we measure from these two independent samples are compatible to Song et al. (2014). The Lyα velocity offsets show a moderate correlation with the measured SFR. We show that Lyα radiative transfer effects influence the correlation function measurements at s < 10 Mpc/h.