Star-Forming Galaxies at z~2 in the Hubble Ultra Deep Field

Abstract

Using a simple color selection based on B-, z- and K-band photometry, BzK= (z-K)_AB-(B-z)_AB>-0.2, we picked out 52 star-forming galaxies at 1.4<z<2.5 (sBzKs) from a K-band selected sample (K_Vega<22.0) in an area of ~5.5 arcmin^2 of the Hubble Ultra Deep Field (UDF). We develop a new photometric redshift method, and the error in our photometric redshifts is less than 0.02(1+z). From the photometric redshift distribution, we find the BzK color criterion can be used to select star-forming galaxies at 1.4<z<2.5 with K_Vega<22.0. Down to K_Vega<22.0, the number counts of sBzKs increase linearly with the K-band magnitude; the sBzKs are strongly clustered, and most of them have irregular morphologies on the ACS images. They have a median reddening of E(B-V)~0.28, an average star formation rate of ~36 M_sun/yr and a typical stellar mass of 10^10 M_sun. The UV criterion for the galaxies at z~2 can select most of the faint sBzKs in the UDF, but it does not work well for bright, massive, highly-reddened, actively star-forming galaxies.

11 pages, 8 figures, Chin.J.Astron.Astrophys.8:1-11,2008