Stellar populations and Lyman-alpha emission from lensed z > 6 galaxies

Abstract

We present results from an SED analysis of two lensed high-z objects, the z=6.56 galaxy HCM6A behind the cluster Abell 370 discovered by Hu et al. (2002) and the triple arc at z~7 behind Abell 2218 found by Kneib et al. (2004). For HCM 6A we find indications for the presence of dust in this galaxy, and we estimate the properties of its stellar populations (SFR, age, etc.), and the intrinsic Lyman-alpha emission. From the "best fit" reddening (E(B-V)~0.25) its estimated luminosity is L~(1-4)e.+11 Lsun, in the range of luminous infrared galaxies. For the arc behind Abell 2218 we find a most likely redshift of z~6.0-7.2 taking into account both our photometric determination and lensing considerations. SED fits indicate generally a low extinction but do not strongly constrain the SF history. Best fits have typical ages of ~3 to 400 Myr. The apparent 4000 Ang break observed recently by Egami et al. (2004) from combination of IRAC/Spitzer and HST observations can also well be reproduced with templates of young populations (~15 Myr or even younger) and does not necessarily imply old ages. Finally, we briefly examine the detectability of dusty lensed high-z galaxies with Herschel and ALMA.