Evidence for 1000 km/s Molecular Outflows in the Local ULIRG Population

TL;DR

This study provides evidence for massive molecular outflows in local ULIRGs, revealing broad CO line wings indicative of high-velocity winds driven by intense starburst activity, impacting galaxy evolution models.

Contribution

First detection of broad CO line wings in a stacked spectrum of local ULIRGs, indicating widespread massive molecular outflows and insights into their chemical conditions.

Findings

Broad CO wings with delta_V~2000 km/s detected in stacked spectra.

Outflows account for up to 25% of CO luminosity, driven by starbursts with SFR ≥ 100 M_sun/yr.

Chemical analysis suggests variation in molecular gas abundance depending on nuclear conditions.

Abstract

The feedback from galactic outflows is thought to play an important role in shaping the gas content, star formation history, and ultimately the stellar mass function of galaxies. Here we present evidence for massive molecular outflows associated with ultra-luminous infrared galaxies (ULIRGs) in the coadded Redshift Search Receiver 12CO(1-0) spectrum. Our stacked spectrum of 27 ULIRGs at z = 0.043-0.11 (freq_rest = 110-120 GHz) shows broad wings around the CO line with delta_V(FWZI)~2000 km/s. Its integrated line flux accounts for up to 25+/-5% of the total CO line luminosity. When interpreted as a massive molecular outflow wind, the associated mechanical energy can be explained by a concentrated starburst with SFR \geq 100 M_sun/yr, which agrees well with their SFR derived from the FIR luminosity. Using the high signal-to-noise stacked composite spectrum, we also probe 13CO and 12CN emission in the sample and discuss how the chemical abundance of molecular gas may vary depending on the physical conditions of the nuclear region.