2019ApJ...877...45M

We present deep continuum observations at a wavelength of 2 mm centered on the COSMOS field using the Goddard IRAM Superconducting Millimeter Observer (GISMO) at the IRAM 30 m telescope. These data constitute the widest deep 2 mm survey to date, reaching a uniform σ ∼ 0.23 mJy beam^–1 sensitivity over ∼250 arcmin² at ∼24'' resolution. We detect four sources at high significance (S/N >= 4.4) with an expected number of false detections of 0.09 sources and five sources at 4.4 > S/N >= 3.7 with an expected number of false detections of 1.65 sources. Combined with deep GISMO observations in GOODS-N, we constrain the 2 mm number counts over one decade in flux density. These measurements agree with most galaxy evolution models tested here, except those with a 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 ∼ 3. These four high-redshift (z > 3) galaxies have 3.9, SFRs ∼ 400-1200 M_☉ yr^–1, and M_dust ∼ 10^9.5 M_☉. They provide a relatively complete selection (∼66%) of the most luminous (L_IR > 10^12.6 L_☉) and highest-redshift (z > 3) galaxies detected within our survey area by AzTEC at 1.1 mm. We thus conclude that 2 mm 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 (∼6.2%), for which the absence of a (sub)millimeter counterpart supports a high-redshift origin (z >= 3).