| 摘 要： | 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 (KVega < 22.0) in an area of ～ 5.5 arcmin2 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 KVega < 22.0. Down to KVega < 22.0, the number counts of sBzKs increase linearly with the K 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⊙ yr-1 and a typical stellar mass of ～ 1010M⊙. 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.
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