Three regimes of CO emission in galaxy mergers

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Three regimes of CO emission in galaxy mergers. / Renaud, Florent; Bournaud, Frédéric; Daddi, Emanuele; Weiß, Axel.

I: Astronomy and Astrophysics, Vol. 621, 201834397, 2019.

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Renaud, Florent ; Bournaud, Frédéric ; Daddi, Emanuele ; Weiß, Axel. / Three regimes of CO emission in galaxy mergers. I: Astronomy and Astrophysics. 2019 ; Vol. 621.

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TY - JOUR

T1 - Three regimes of CO emission in galaxy mergers

AU - Renaud, Florent

AU - Bournaud, Frédéric

AU - Daddi, Emanuele

AU - Weiß, Axel

PY - 2019

Y1 - 2019

N2 - The conversion factor αCO from the observable CO(1-0) luminosity to the mass of molecular gas is known to vary between isolated galaxies and some mergers, but the underlying reasons are not clearly understood. Thus, the value(s) of αCO that are to be adopted remain highly uncertain. To provide better constraints, we applied the large velocity gradient method to a series of hydrodynamical simulations of galaxies and derived the evolution of αCO. We report significant variations of αCO, and identify three distinct regimes: Disk galaxies, starbursts, and post-burst phases. We show that estimating the star formation rate over 20Myr smoothes out some of these differences, but still maintains a distinction between disks and starbursts. We find a tighter correlation of αCO with the gas depletion time than with star formation rate, but deviations are induced by the transitions to and from the starburst episodes. We conclude that αCO fluctuates because of both feedback energy and velocity dispersion. Identifying the phase of an interaction by classical means (e.g., morphology or luminosity) could then help to select the relevant conversion factor that is to be used and to obtain more accurate estimates of the molecular masses of galaxies.

AB - The conversion factor αCO from the observable CO(1-0) luminosity to the mass of molecular gas is known to vary between isolated galaxies and some mergers, but the underlying reasons are not clearly understood. Thus, the value(s) of αCO that are to be adopted remain highly uncertain. To provide better constraints, we applied the large velocity gradient method to a series of hydrodynamical simulations of galaxies and derived the evolution of αCO. We report significant variations of αCO, and identify three distinct regimes: Disk galaxies, starbursts, and post-burst phases. We show that estimating the star formation rate over 20Myr smoothes out some of these differences, but still maintains a distinction between disks and starbursts. We find a tighter correlation of αCO with the gas depletion time than with star formation rate, but deviations are induced by the transitions to and from the starburst episodes. We conclude that αCO fluctuates because of both feedback energy and velocity dispersion. Identifying the phase of an interaction by classical means (e.g., morphology or luminosity) could then help to select the relevant conversion factor that is to be used and to obtain more accurate estimates of the molecular masses of galaxies.

KW - Galaxies: Star formation

KW - Intergalactic medium

U2 - 10.1051/0004-6361/201834397

DO - 10.1051/0004-6361/201834397

M3 - Article

VL - 621

JO - Astronomy & Astrophysics

T2 - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 1432-0746

M1 - 201834397

ER -