Characterizing CO Emitters in the SSA22-AzTEC26 Field

TL;DR

This study characterizes four CO-emitting galaxies near SSA22-AzTEC26, revealing their physical properties, redshifts, and star formation activity, highlighting the diversity of gas-rich galaxies detectable through blind CO line searches.

Contribution

It provides the first detailed physical characterization of multiple CO emitters in the SSA22-AzTEC26 field using multi-band ALMA data, demonstrating the effectiveness of blind CO searches in identifying diverse galaxy populations.

Findings

Two galaxies are CO(2-1) at z≈1.12-1.15.

One galaxy is CO(3-2) at z=2.124.

All are massive with large gas reservoirs, some with low star formation rates.

Abstract

We report the physical characterization of four CO emitters detected near the bright submillimeter galaxy (SMG) SSA22-AzTEC26. We analyze the data from Atacama Large Millimeter/submillileter Array band 3, 4, and 7 observations of the SSA22-AzTEC26 field. In addition to the targeted SMG, we detect four line emitters with a signal-to-noise ratio $>5.2$ in the cube smoothed with 300 km s$^{-1}$ FWHM Gaussian filter. All four sources have NIR counterparts within 1$\arcsec$. We perform UV-to-FIR spectral energy distribution modeling to derive the photometric redshifts and physical properties. Based on the photometric redshifts, we reveal that two of them are CO(2-1) at redshifts of 1.113 and 1.146 and one is CO(3-2) at $z=2.124$. The three sources are massive galaxies with a stellar mass $\gtrsim10^{10.5}M_\odot$, but have different levels of star formation. Two lie within the scatter of the main sequence (MS) of star-forming galaxies at $z\sim1-2$, and the most massive galaxy lies significantly below the MS. However, all three sources have a gas fraction within the scatter of the MS scaling relation. This shows that a blind CO line search can detect massive galaxies with low specific star formation rates that still host large gas reservoirs and that it also complements targeted surveys, suggesting later gas acquisition and the need for other mechanisms in addition to gas consumption to suppress star formation.