The IRAM/GISMO two-millimeter survey in the COSMOS field

Abstract

We present deep continuum observations at a wavelength of 2mm centered on the COSMOS field using the Goddard IRAM Superconducting Millimeter Observer (GISMO) at the IRAM 30m-telescope. These data constitute the widest deep 2mm survey to-date, reaching a uniform $\ddot{I}ƒ\sim 0.23$mJy beam${}^{-1}$ sensitivity over $\sim 250$arcmin${}^2$ at $\sim 24^{\prime \prime }$ resolution. We detect four sources at high significance (S/N$\ge$4.4) with an expected number of false detection of 0.09 sources, and five sources at $4.4>$S/N$\ge 3.7$ with an expected number of false detection of 1.65 sources. Combined with deep GISMO observations in GOODS-N, we constrain the 2mm number counts over one decade in flux density. These measurements agree with most galaxy evolution models tested here, except those with large population of dusty star-forming galaxies at $z>7$. Five GISMO sources have counterparts in (sub-)millimeter catalogs available in COSMOS. Their redshifts suggest that all but one lie above $z\sim 3$. These four high-redshift ($z>3$) galaxies have $\tilde{z}=3.9$, SFRs $\sim$400 - 1200M${}_{\odot }$yr${}^{-1}$ and $M_{\mathrm{dust}}\sim 10^{9.5}$M${}_{\odot }$. They provide a relatively complete selection ($\sim 66\%$) of the most luminous ($L_{\mathrm{IR}}>10^{12.6}$L${}_{\odot }$) and highest redshift ($z>3$) galaxies detected within our survey area by AzTEC at 1.1mm. We thus conclude that 2mm surveys favor the selection of massive, vigorously star-forming, high-redshift galaxies. This is corroborated by GISMO-C4, a source with a low false detection probability ($\sim 6.2\%$), for which the absence of a (sub-)millimeter counterpart supports a high redshift origin ($z\gtrsim 3$).

27 pages, 14 figures, accepted for publication in ApJ