Three regimes of CO emission in galaxy mergers

Abstract

The conversion factor ${\alpha }_{\mathrm{CO}}$ 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 ${\alpha }_{\mathrm{CO}}$ to be adopted remain highly uncertain. To provide better constraints, we apply the large velocity gradient method to a series of hydrodynamical simulations of galaxies and derive the evolution of ${\alpha }_{\mathrm{CO}}$. We report significant variations of ${\alpha }_{\mathrm{CO}}$, and identify three distinct regimes: disk galaxies, starbursts and post-burst phases. We show that estimating the star formation rate over 20 Myr smooths out some of these differences, but still maintains a distinction between disks and starbursts. We find a tighter correlation of ${\alpha }_{\mathrm{CO}}$ with the gas depletion time than with star formation rate, yet with deviations induced by the transitions to and from the starburst episodes. We conclude that ${\alpha }_{\mathrm{CO}}$ fluctuates because of both the feedback energy and the velocity dispersion. Identifying the phase of an interaction by classical means (e.g. morphology, luminosity) could then help selecting the relevant conversion factor to be used and get more accurate estimates of the molecular masses of galaxies.

arXiv commentA&A accepted, 6 pages, 5 figures

References in corpus (35)

• The CO-to-H2 Conversion Factor
• Very High Gas Fractions and Extended Gas Reservoirs in z=1.5 Disk Galaxies
• Different star formation laws for disks versus starbursts at low and high redshifts
• Combined CO & Dust Scaling Relations of Depletion Time and Molecular Gas Fractions with Cosmic Time, Specific Star Formation Rate and Stellar Mass
• The CO-to-H2 Conversion Factor and Dust-to-Gas Ratio on Kiloparsec Scales in Nearby Galaxies
• HCN Survey of Normal Spiral, IR-luminous and Ultraluminous Galaxies
• A General Model for the CO-H2 Conversion Factor in Galaxies with Applications to the Star Formation Law
• Regularity underlying complexity: a redshift-independent description of the continuous variation of galaxy-scale molecular gas properties in the mass-star formation rate plane
• The driving mechanism of starbursts in galaxy mergers
• On the Relationship Between Molecular Hydrogen and Carbon Monoxide Abundances in Molecular Clouds
• Modeling CO Emission: I. CO as a Column Density Tracer and the X-Factor in Molecular Clouds
• Starbursts triggered by inter-galactic tides and interstellar compressive turbulence
• Evidence of enhanced star formation efficiency in luminous and ultraluminous infrared galaxies
• The CO-H2 Conversion Factor in Disc Galaxies and Mergers
• A parsec-resolution simulation of the Antennae galaxies: Formation of star clusters during the merger
• The Spectral Energy Distribution of CO lines in M82
• A Theory for the Excitation of CO in Star Forming Galaxies
• Is HCN a True Tracer of Dense Molecular Gas in LIRGs and ULIRGs?
• SILCC-Zoom: The dynamical and chemical evolution of molecular clouds
• Discovery of Large Molecular Gas Reservoirs in Post-Starburst Galaxies
• A Multi-Transistion CO Study of the "Antennae" Galaxies NGC4038/9
• Modelling CO emission from hydrodynamic simulations of nearby spirals, starbursting mergers, and high-redshift galaxies
• One moment in time - modeling star formation in the Antennae
• Radio Continuum Observations of the Galactic Center: Photoevaporative Proplyd-like Objects near Sgr A*
• The X_CO conversion factor from galactic multiphase ISM simulations
• Star formation laws and thresholds from ISM structure and turbulence
• Unveiling the physical properties and kinematics of molecular gas in the Antennae Galaxies (NGC 4038/9) through high resolution CO (J = 3-2) observations
• The X-factor in Galaxies: II. The molecular hydrogen -- star formation relation
• Does the CO-to-H2 conversion factor depend on the star formation rate?
• Morphology and enhanced star formation in a Cartwheel-like ring galaxy
• Luminous Infrared Galaxies With the Submillimeter Array. III. The Dense Kiloparsec Molecular Concentrations of Arp 299
• Why Post-Starburst Galaxies are Now Quiescent
• Predicting HCN, HCO+, multi-transition CO, and dust emission of star-forming galaxies From local spiral and ultraluminous infrared galaxies to high-z star-forming and submillimeter galaxies
• Recovering the Physical Properties of Molecular Gas in Galaxies from CO SLED Modeling
• After the interaction: an efficiently star-forming molecular disk in NGC5195

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• The Physical Drivers and Observational Tracers of CO-to-H2 Conversion Factor Variations in Nearby Barred Galaxy Centers
• CO excitation, molecular gas density and interstellar radiation field in local and high-redshift galaxies
• A diversity of starburst-triggering mechanisms in interacting galaxies and their signatures in CO emission
• VINTERGATAN IV: Cosmic phases of star formation in Milky Way-like galaxies
• Some Die Filthy Rich: The Diverse Molecular Gas Contents of Post-starburst Galaxies Probed by Dust Absorption
• Molecular gas and star formation in nearby starburst galaxy mergers
• From giant clumps to clouds IV: extreme star-forming clumps on top of universal cloud scaling relations in gas-rich galaxies
• The interstellar medium of high-redshift galaxies: Gathering clues from C III] and [C II] lines
• Is this an Early Stage Merger? A Case Study on Molecular Gas and Star Formation Properties of Arp 240
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