The nature ofz  ~ 2.3 Lyman-αemitters

Abstract

We study the multi-wavelength properties of a set of 171 Lyα emitting candidates at redshift z = 2.25 found in the COSMOS field, with the aim of understanding the underlying stellar populations in the galaxies. We especially seek to understand what the dust contents, ages and stellar masses of the galaxies are, and how they relate to similar properties of Lyα emitters at other redshifts. The candidates here are shown to have different properties from those of Lyα emitters found at higher redshift, by fitting the spectral energy distributions (SEDs) using a Monte-Carlo Markov-Chain technique and including nebular emission in the spectra. The stellar masses, and possibly the dust contents, are higher, with stellar masses in the range log M * = 8.5−11.0 M and A V = 0.0−2.5 mag. Young population ages are well constrained, but the ages of older populations are typically unconstrained. In 15% of the galaxies only a single, young population of stars is observed. We show that the Lyα fluxes of the best fit galaxies are correlated with their dust properties, with higher dust extinction in Lyα faint galaxies. Testing for whether results derived from a light-weighted stack of objects correlate to those found when fitting individual objects we see that stellar masses are robust to stacking, but ages and especially dust extinctions are derived incorrectly from stacks. We conclude that the stellar properties of Lyα emitters at z = 2.25 are different from those at higher redshift and that they are diverse. Lyα selection appears to be tracing systematically different galaxies at different redshifts.

Stellar properties ofz ~ 1 Lyman-break galaxies from ACS slitless grism spectra

“…The parameters that are well determined are stellar mass, dust A V and age, although the age fits in the 2 SSP fits suffer from a degeneracy at the older age when the young population age is very young. In other words, when the young population age is very young, the light of these stars will outshine any older population, unless the mass fraction in the young population is very small (see Nilsson et al 2010, for a longer discussion on this). The ages and mass fractions for all the 2 SSP fits (the only runs with more than one age fitted) indicate that we are not able to identify an older population in any of the objects, and only upper limits on the mass fraction in a potential old population may be inferred.…”

Lyman-αemitters as tracers of the transitioning Universe

“…With the further Chandra detections presented in Nilsson et al (2011), this surplus of AGN is even larger. However, since comparing AGN fractions from different surveys has a bias due to the Lyα luminosity reached, a more careful investigation requires analysis that is independent of this bias.…”

“…AGN were selected among the LAEs by use of X-ray data from XMM (Hasinger et al 2007), Chandra (Elvis et al 2009), and the VLA (Schinnerer et al 2007). For details, see Nilsson et al ( , 2011. In total, 24 LAEs have been selected as AGN.…”

Extreme emission-line galaxies out toz~ 1 in zCOSMOS

“…Although Lyα selection may systematically trace different galaxies at different redshifts (Nilsson et al 2011) and a small fraction of Lyα emitters (LAEs) may be evolved galaxies (Pentericci et al 2009), most of them typically show low metallicity, blue colors, small sizes, and low dust attenuation, indicating an early stage of galaxy formation (e.g., Pirzkal et al 2007;Cassata et al 2011;Cowie et al 2011;Finkelstein et al 2011). A significant fraction of their low redshift (z ∼ 0.3) analogues are also found to be EELGs (e.g., Cowie et al 2011).…”