Giant Molecular Clouds in M33. I. BIMA All-Disk Survey

By G. Engargiola, R. Plambeck, Erik Rosolowsky, L. Blitz. 2003

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We present the first interferometric 12CO (J = 1 → 0) map of the entire Hα disk of M33. The 13″ diameter synthesized beam corresponds to a linear resolution of 50 pc, sufficient to distinguish individual giant molecular clouds (GMCs). From these data we generated a catalog of 148 GMCs with an expectation that no more than 15 of the sources are spurious. The catalog is complete down to GMC masses of 1.5 × 105 M⊙ and contains a total mass of 2.3 × 107 M⊙. Single-dish observations of CO in selected fields imply that our survey detects ∼50% of the CO flux, hence that the total molecular mass of M33 is 4.5 × 107 M⊙, approximately 2% of the H I mass. The GMCs in our catalog are confined largely to the central region (R < 4 kpc). They show a remarkable spatial and kinematic correlation with overdense H I filaments; the geometry suggests that the formation of GMCs follows that of the filaments. The GMCs exhibit a mass spectrum dN/dM ∝ M-2.6±0.3, considerably steeper than that found in the Milky Way and in the LMC. Combined with the total mass, this steep function implies that the GMCs in M33 form with a characteristic mass of ∼7 × 104 M⊙. More than 2/3 of the GMCs have associated H II regions, implying that the GMCs have a short quiescent period. Our results suggest the rapid assembly of molecular clouds from atomic gas, with prompt onset of massive star formation.

Subfields: Astronomy and Astrophysics, Instrumentation

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Citations in the corpus

The Molecular Gas Distribution and Schmidt Law in M33 (2003, background): “The spatial resolution of the observations (200 pc) is insufficient to detect individual GMCs if their typical size is 50 pc (Wilson & Scoville 1990; Engargiola et al. 2003; Rosolowsky et al. 2003).”
Before the first supernova: combined effects of H II regions and winds on molecular clouds (2014, unknown): “This in turn implies that, for any cloud mass function where there are more low–mass clouds than high–mass clouds, such as in M33 (Engargiola et al. 2003), most of the photons ionizing the ISM originate from low–mass clouds.”
The Role of Pressure in GMC Formation II: The H2-Pressure Relation (2006, background): “In nearby galaxies where the dominant state of the gas is atomic, the atomic gas occurs primarily in filaments (Kim et al. 1998; Engargiola et al. 2003; Leroy et al. 2006), and the formation of the filaments appears to precede the formation of the molecular gas (Blitz et al. 2006).”
The Resolved Properties of Extragalactic Giant Molecular Clouds (2008, unknown): “That study analyzed 20 fields in that galaxy with a resolution θ ∼ 6′′ ∼ 20 pc, targeting sources identified in the alldisk survey of Engargiola et al. (2003).”
The lifecycle of molecular clouds in nearby star-forming disc galaxies (2019, methodology): “Short cloud lifetimes (10−50 Myr) have been measured by classifying the clouds based on their star formation activity (Engargiola et al. 2003; Blitz et al. 2007; Kawamura et al. 2009; Murray 2011; Miura et al. 2012; Corbelli et al. 2017), or by quantifying the fraction of CO-bright versus Hα-bright…”
Modeling UV Radiation Feedback from Massive Stars. II. Dispersal of Star-forming Giant Molecular Clouds by Photoionization and Radiation Pressure (2018, background): “On the other hand, estimates based on the fraction of GMCs that are spatially coincident with H II regions and young star clusters in nearby galaxies favor lifetimes of a few tens of Myrs (Engargiola et al. 2003; Blitz et al. 2007; Kawamura et al. 2009; Miura et al. 2012; see also Murray 2011; Meidt”
Terahertz Spectroscopy for Astronomy: From Comets to Cosmology (2011, background): “The coincidence of molecular clouds with HI overdensity is evidence that clouds form out of the atomic gas. Caption andfigure from [ 35 ].”
THE CO-TO-H2 CONVERSION FACTOR FROM INFRARED DUST EMISSION ACROSS THE LOCAL GROUP (2011, methodology): “For M 33, we take CO data from Rosolowsky et al. (2007), which combines BIMA (Engargiola et al. 2003) and FCRAO data (Heyer et al. 2004).”
Scaling relations and the fundamental line of the local group dwarf galaxies (2008, unknown): “— (1) Alves & Nelson (2000); (2) Baggett et al. (1998); (3) Caldwell (1999); (4) Corbelli & Salucci (2000); (5) Côté et al. (1999); (6) Engargiola et al. (2003); (7) Grebel et al. (2003); (8) Grebel & Guhathakurta (1999); (9) Hopp et al. (1999); (10) Jacobsson (1970); (11) Larsen et al. (2000);…”
Molecular and atomic gas in the Local Group galaxy M 33 (2010, methodology): “Engargiola et al. (2003) observed the whole of the inner disk (up to about 5kpc along the major axis) with the BIMA array at 13′′ resolution; Heyer et al. (2004) ob- served the inner disk and a small major axis strip at 50” res- olution with FCRAO; Rosolowsky et al. (2007) combined…”
Cloud-scale Molecular Gas Properties in 15 Nearby Galaxies (2018, background): “Low-mass galaxies tend to show faint, isolated CO emission (Fukui et al. 1999; Engargiola et al. 2003; Schruba et al. 2017), distinct from the bright, spatially contiguous emission distributions observed in more massive galaxies (Hughes et al. 2013a).”
Implications for the formation of star clusters from extragalactic star formation rates (2004, background): “Just recently Engargiola et al. (2003) found that for M33 the typical lifetimes of giant molecular clouds (GMC) with masses ranging up to 7 × 105M⊙ are 10 to 20 × 106 yr, indicating a similar formation time for star clusters born form these clouds.”