2015ApJ...811L...3T

We present the first results from the SXDF-Atacama Large Millimeter/submillimeter Array (ALMA) 1.5 arcmin² deep survey at 1.1 mm using ALMA. The map reaches a 1σ depth of 55 µJy/beam and covers 12 Hα-selected star-forming galaxies (SFGs) at z = 2.19 or z = 2.53. We have detected continuum emission from three of our Hα-selected sample, including one compact SFG with high stellar surface density, NB2315-07. They are all red in the rest-frame optical and have stellar masses of log (M_*/M_☉) > 10.9, whereas the other blue, main-sequence galaxies with = 10.0-10.8 are exceedingly faint, <290 µJy (2σ upper limit). We also find the 1.1 mm brightest galaxy, NB2315-02, to be associated with a compact (R_e= 0.7±0.1 kpc), dusty star-forming component. Given a high gas fraction (% or%) and high star formation rate surface density (/yr/kpc2), the concentrated starburst can build up within less than Myr a stellar surface density matching that of massive compact galaxies at z ∼ 2, provided at least 19±3% of the total gas is converted into stars in the galaxy center. On the other hand, NB2315-07, which already has such a high stellar surface density core, shows a gas fraction (%) and is located in the lower envelope of the star formation main sequence. This compact, less SFG is likely to be in an intermediate phase between compact, dusty star-forming and quiescent galaxies.