The redshift and nature of AzTEC/COSMOS 1: A starburst galaxy at z=4.6

TL;DR

This study identifies AzTEC/COSMOS 1 as a young, massive, compact starburst galaxy at redshift 4.6, with high star formation rate and low CO emission, indicating unique star formation conditions in the early universe.

Contribution

First detailed multi-wavelength analysis of AzTEC/COSMOS 1 revealing its properties as a young, massive starburst galaxy at z=4.6 with implications for early galaxy formation.

Findings

Redshift determined as z=4.64-0.08+0.06.

Galaxy is extremely young (<50 Myr) and massive (~10^11 M_Sol).

Star formation rate is approximately 1300 M_Sol/yr.

Abstract

Based on broad/narrow-band photometry and Keck DEIMOS spectroscopy we report a redshift of z=4.64-0.08+0.06 for AzTEC/COSMOS 1, the brightest sub-mm galaxy in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 micron), CSO/SHARC II (350 micron), CARMA and PdBI (3 mm). We do not detect CO(5-4) line emission in the covered redshift ranges, 4.56-4.76 (PdBI/CARMA) and 4.94-5.02 (CARMA). If the line is within this bandwidth, this sets 3sigma upper limits on the gas mass to <~8x10^9 M_Sol and <~5x10^10 M_Sol, respectively (assuming similar conditions as observed in z~2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV-IR spectral energy distribution of AzTEC 1 shows that it is an extremely young (<~50 Myr), massive (M*~10^11 M_Sol), but compact (<~2 kpc) galaxy forming stars at a rate of ~1300 M_Sol/yr. Our results imply that AzTEC 1 is forming stars in a 'gravitationally bound' regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.