A CO emission line from the optical and near-IR undetected submillimeter galaxy GN10

TL;DR

This paper reports the first detection of a CO emission line from a highly obscured submillimeter galaxy at z~4, demonstrating the effectiveness of millimeter spectroscopy in studying optically invisible galaxies and revealing a potentially large population of such high-redshift, dust-obscured galaxies.

Contribution

The study presents the first CO emission line detection from an optically and near-IR invisible galaxy, highlighting a new method to identify and analyze highly obscured, high-redshift galaxies.

Findings

Detected CO[4-3] line at z=4.0424 in GN10

Supports existence of a substantial population of high-z SMGs missed by optical surveys

Demonstrates millimeter spectroscopy as a powerful tool for studying obscured galaxies

Abstract

We report the detection of a CO emission line from the submillimiter galaxy (SMG) GN10 in the GOODS-N field. GN10 lacks any counterpart in extremely deep optical and near-IR imaging obtained with the Hubble Space Telescope and ground-based facilities. This is a prototypical case of a source that is extremely obscured by dust, for which it is practically impossible to derive a spectroscopic redshift in the optical/near-IR. Under the hypothesis that GN10 is part of a proto-cluster structure previously identified at z~4.05 in the same field, we searched for CO[4-3] at 91.4 GHz with the IRAM Plateau de Bure Interferometer, and successfully detected a line. We find that the most likely redshift identification is z=4.0424+-0.0013, based on: 1) the very low chance that the CO line is actually serendipitous from a different redshift; 2) a radio-IR photometric redshift analysis; 3) the identical radio-IR SED, within a scaling factor, of two other SMGs at the same redshift. The faintness at optical/near-IR wavelengths requires an attenuation of A_V~5-7.5 mag. This result supports the case that a substantial population of very high-z SMGs exists that had been missed by previous spectroscopic surveys. This is the first time that a CO emission line has been detected for a galaxy that is invisible in the optical and near-IR. Our work demonstrates the power of existing and planned facilities for completing the census of star formation and stellar mass in the distant Universe by measuring redshifts of the most obscured galaxies through millimeter spectroscopy.