Rise and fall of molecular clouds across the M33 disk

Abstract

We carried out deep searches for CO line emission in the outer disk of M33, at R>7 kpc, and examined the dynamical conditions that can explain variations in the mass distribution of the molecular cloud throughout the disk of M33. We used the IRAM-30~m telescope to search for CO lines in the outer disk toward 12 faint mid-infrared (MIR) selected sources and in an area of the southern outer disk hosting MA1, a bright HII region. We detect narrow CO lines at the location of two MIR sources at galactocentric distances of about 8 kpc that are associated with low-mass young stellar clusters, and at four locations in the proximity of MA1. The paucity of CO lines at the location of weak MIR-selected sources probably arises because most of them are not star-forming sites in M33, but background sources. Although very uncertain, the total molecular mass of the detected clouds around MA1 is lower than expected given the stellar mass of the cluster, because dispersal of the molecular gas is taking place as the HII region expands. The mean mass of the giant molecular clouds (GMCs) in M33 decreases radially by a factor 2 from the center out to 4 kpc, then it stays constant until it drops at R>7 kpc. We suggest that GMCs become more massive toward the center because of the fast rotation of the disk, which drives mass growth by coalescence of smaller condensations as they cross the arms. The analysis of both HI and CO spectral data gives the consistent result that corotation of the two main arms in this galaxy is at a radius of 4.7+-0.3 kpc, and spiral shock waves become subsonic beyond 3.9 kpc. Perturbations are quenched beyond 6.5 kpc, where CO lines have been detected only around sporadic condensations associated with UV and MIR emission.

arXiv comment15 pages, 12 figures, Accepted for publication in A&A

References in corpus (51)

• The GALEX Ultraviolet Atlas of Nearby Galaxies
• Galaxies in a simulated $\Lambda$CDM Universe I: cold mode and hot cores
• The 24 Micron Source Counts in Deep Spitzer Surveys
• Toy Models for Galaxy Formation versus Simulations
• The Second Survey of the Molecular Clouds in the Large Magellanic Cloud by NANTEN I: Catalog of Molecular Clouds
• The PdBI Arcsecond Whirlpool Survey (PAWS): Environmental Dependence of Giant Molecular Cloud Properties in M51
• Dark matter and visible baryons in M33
• The Mass Spectra of Giant Molecular Clouds in the Local Group
• Spitzer Mid-to-Far-Infrared Flux Densities of Distant Galaxies
• Stellar kinematics across the Hubble sequence in the CALIFA survey: General properties and aperture corrections
• The effective stability parameter for two-component galactic discs: Is 1/Q ~ 1/Q_stars + 1/Q_gas ?
• Panoramic GALEX FUV and NUV imaging of M31 and M33
• The Detection of Inside-out Disk Growth in M33
• Giant Molecular Clouds in the Local Group Galaxy M33
• Orbits of Massive Satellite Galaxies: I. A Close Look at the Large Magellanic Cloud and a New Orbital History for M33
• Star formation in M33: multiwavelength signatures across the disk
• Gravitational Instabilities in Two-Component Galaxy Disks with Gas Dissipation
• The Contribution of Field OB Stars to the Ionization of the Diffuse Ionized Gas in M33
• The Nature of Faint 24 micron Sources Seen in Spitzer Observations of ELAIS-N1
• First Gaia Dynamics of the Andromeda System: DR2 Proper Motions, Orbits, and Rotation of M31 and M33
• From molecules to Young Stellar Clusters: the star formation cycle across the M33 disk
• Metal production in M33: space and time variations
• Molecular gas in low-metallicity starburst galaxies: Scaling relations and the CO-to-H${}_2$ conversion factor
• Dynamical signatures of a LCDM-halo and the distribution of the baryons in M33
• The Pattern Speeds of M51, M83 and NGC 6946 Using CO and the Tremaine-Weinberg Method
• The Varying Mass Distribution of Molecular Clouds Across M83
• Star formation efficiency as a function of metallicity: from star clusters to galaxies
• The building up of the disk galaxy M33 and the evolution of the metallicity gradient
• Star formation in M33: Spitzer photometry of discrete sources
• No Assembly Required: Mergers are Mostly Irrelevant for the Growth of Low-mass Dwarf Galaxies
• The Lifetime of Grand Design
• The Araucaria Project. A Distance Determination to the Local Group Spiral M33 from Near-Infrared Photometry of Cepheid Variables
• The Molecular Interstellar Medium of the Local Group Dwarf NGC6822
• Metallicity gradients in Local Universe galaxies: time evolution and effects of radial migration
• Properties and rotation of molecular clouds in M 33
• Evolutionary Description of Giant Molecular Cloud Mass Functions on Galactic Disks
• HI clouds in the proximity of M33
• Simulations of the flocculent spiral M33: what drives the spiral structure?
• Bar imprints on the inner gas kinematics of M33
• The cluster birthline in M33
• The population of Young Stellar Clusters throughout the disk of M33
• The molecular gas mass of M33
• The Detection of Molecular Gas in the Outskirts of NGC 6946
• Stellar structures in the outer regions of M33
• Unusually Luminous Giant Molecular Clouds in the Outer Disk of M33
• Spectral Energy Distributions of HII regions in M33 (HerM33es)
• The Probability Distribution Function of Gas Surface Density in M33
• Young star clusters in the outer disks of LITTLE THINGS dwarf irregular galaxies
• CLUES about M33: the reversed radial stellar age gradient in the outskirts of Triangulum galaxy
• A detailed view of a Molecular Cloud in the far outer disk of M33
• On the nature of faint mid-infrared sources in M33

Cited by in corpus (8)

• The global stability of M33 in MOND
• Comparing the Properties of GMCs in M33 from Simulations and Observations
• Gibbs Point Process Model for Young Star Clusters in M33
• Star formation drivers across the M33 disk
• Exploring extreme conditions for star formation: a deep search for molecular gas in the Leo ring
• Gaseous nebulae and massive stars in the giant HI ring in Leo
• Radio emission during the formation of stellar clusters in M33
• Molecular cloud matching in CO and dust in M33 II. Physical properties of giant molecular clouds