1212.5270 (P. Cassata et al.)

HeII emitters in the VIMOS VLT Deep Survey: PopIII star formation or peculiar stellar populations in galaxies at 2    [PDF]

P. Cassata, O. Le Fevre, S. Charlot, T. Contini, O. Cucciati, B. Garilli, G. Zamorani, C. Adami, S. Bardelli, V. Le Brun, B. Lemaux, D. Maccagni, A. Pollo, L. Pozzetti, L. Tresse, D. Vergani, A. Zanichelli, E. Zucca

The aim of this work is to identify HeII emitters at 21200km/s), 3 AGN, and an additional 12 possible HeII emitters. The properties of the individual broad emitters are in agreement with expectations from a W-R model. On the contrary, the properties of the narrow emitters are not compatible with such model, neither with predictions of gravitational cooling radiation produced by gas accretion. Rather, we find that the EW of the narrow HeII line emitters are in agreement with expectations for a PopIII star formation, if the episode of star formation is continuous, and we calculate that a PopIII SFR of 0.1-10 Mo yr-1 only is enough to sustain the observed HeII flux. We conclude that narrow HeII emitters are either powered by the ionizing flux from a stellar population rare at z~0 but much more common at z~3, or by PopIII star formation. As proposed by Tornatore et al. (2007), incomplete ISM mixing may leave some small pockets of pristine gas at the periphery of galaxies from which PopIII may form, even down to z~2 or lower. If this interpretation is correct, we measure at z~3 a SFRD in PopIII stars of 10^6Mo yr^-1 Mpc^-3 qualitatively comparable to the value predicted by Tornatore et al. (2007).

View original: http://arxiv.org/abs/1212.5270