Constraints on the galaxy `main sequence' at z > 5: the stellar mass of HDF850.1

Abstract

We present rest-frame optical and near-infrared detections of one of the highest redshift submm-selected galaxies to date, HDF850.1. We do not detect the previously proposed counterpart HDF850.1K in new deep J- and H-band Hubble Space Telescope Wide Field Camera 3 data, placing a strong limit of H - K > 3.8, concluding that the K-band source is spurious. However, we detect 5.8 and 8 μm emission co-located with the submm in deblended images. After modelling and removing the flux contributions from another foreground galaxy, we constrain the stellar mass of HDF850.1 to be (2.5 ± 1)μ^-1 × 10¹¹ M_⊙ for a lensing magnification μ = 1.9 ± 0.3, with a specific star formation rate of 8.5 Gyr^-1, faster than the 1-4 Gyr^-1 observed for UV-selected galaxies at this epoch.