Oral Presentation
SXDF-ALMA 2-arcmin^2 Deep Survey: Stacking of Rest-Frame Near-Infrared Selected Objects
Presenter: Wei-Hao Wang (ASIAA)
We present stacking analyses on our ALMA deep 1.1 mm imaging in the SXDF using a 3.6 um selected galaxy sample drawn from the CANDELS WFC3 catalog. We successfully detect a faint galaxy population of ~ 0.03-0.05 mJy, which corresponds to L_IR < 10^11 Lsun and a star formation rate (SFR) of < 15 Msun/yr at z=2. We find that galaxies brighter in the rest-frame near-infrared tend to be also brighter at 1.1 mm, and galaxies fainter than [3.6um] = 23 do not produce detectable 1.1 mm emission. This suggests a correlation between stellar mass and SFR in distant galaxies, but outliers to this correlation are also observed in our ALMA survey, suggesting strongly boosted star formation or extremely large extinction. We also find tendencies that redder galaxies and galaxies at higher redshifts are brighter at 1.1 mm. Our ALMA field contains a bright single-dish source. However, we do not find evidence of bias in our stacking results caused by this bright source. By combining the fluxes of bright sources directly detected by ALMA and fluxes from faint sources detected in our stacking analyses, we recover a 1.1 mm surface brightness of up to 20.3+/-1.2 Jy/deg^2, which is comparable to the extragalactic background light measured by COBE. We also find that approximately half of the cosmic star formation may be obscured by dust and missed by deep optical surveys, based on the fraction of optically faint sources in our and previous ALMA studies and the COBE extragalactic background measurements. Much deeper and wider ALMA imaging is therefore needed to better constrain the obscured cosmic star formation history.
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