The Equilibrium State of Molecular Regions in the Outer Galaxy

By M. Heyer, J. Carpenter, R. Snell. 2001

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A summary of global properties and an evaluation of the equilibrium state of molecular regions in the outer Galaxy are presented from the decomposition of the FCRAO Outer Galaxy Survey and targeted 12CO and 13CO observations of four giant molecular cloud complexes. The ensemble of identified objects includes both small, isolated clouds and clumps within larger cloud complexes. The 12CO luminosity function and size distribution of a subsample of objects with well-defined distances are determined such that ΔN/ΔLCO = L and ΔN/Δre = r. 12CO velocity dispersions show little variation with cloud sizes for radii less than 10 pc. It is demonstrated that the internal motions of regions with MCO = XCOLCO > 104 M☉ are bound by self-gravity, yet the constituent clumps of cloud complexes and isolated molecular clouds with MCO < 103 M☉ are not in self-gravitational equilibrium. The required external pressures to maintain the equilibrium of this population are (1-2) × 104 cm-3 K.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/f39c37130b8aef20d69245a33cdbba080c6cd46a

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Citations in the corpus

Molecular Clouds in the Milky Way (2015, methodology): “Other outer Galaxy cloud studies have been confined either to particular spiral arms (see below) or to the area of the FCRAO Outer Galaxy survey (Heyer et al. 2001, Brunt et al. 2003).”
THE STAR FORMATION RATE AND GAS SURFACE DENSITY RELATION IN THE MILKY WAY: IMPLICATIONS FOR EXTRAGALACTIC STUDIES (2010, background): “…maps from optical star counts (Duvert et al. 1986; Bachiller & Cernicharo 1986; Langer et al. 1989) and 2MASS data (Lombardi et al. 2006; Pineda et al. 2008), and theoretically by the assumption that giant molecular clouds are in gravitational equilibrium (Dickman et al. 1986; Heyer et al. 2001).”
Global hierarchical collapse in molecular clouds. Towards a comprehensive scenario (2019, background): “Instead, they suggest that the clouds exhibit a plain turbulence-scaling relation L ≡ σv/R 1/2 = cst, where L is hereinafter referred to as the Larson ratio.2 Padoan et al. (2016) report the scaling L ≈ cst. for their simulations of the SN-driven ISM, and noted that this is the scaling observed for ”
PHYSICAL PROPERTIES OF MOLECULAR CLOUDS FOR THE ENTIRE MILKY WAY DISK (2016, methodology): “Clouds in the outer Galaxy are more likely to have αvir >> 1, something already noted by many studies (Sodroski 1991; Heyer et al. 2001).”
THE MAGELLANIC MOPRA ASSESSMENT (MAGMA). I. THE MOLECULAR CLOUD POPULATION OF THE LARGE MAGELLANIC CLOUD (2011, methodology): “CO “islands” show a steeper mass spectrum than inferred from previous studies of GMCs in the Galaxy (Solomon et al. 1987) and of GMCs in the LMC using the NANTEN survey.”
Star Formation from Galaxies to Globules (2001, background): “The threshold is at about 104 M for the FCRAO outer galaxy CO survey (Heyer et al. 2001).”
The structure of the interstellar medium of star‐forming galaxies (2011, background): “Not only is the median α similar, but the simulations reproduce the observed weak scaling of α with Mcl, approximately α ∝ M−0.3cl , such that more massive clumps tend to be more bound (see Heyer et al. 2001).”
Neutral Atomic Phases of the Interstellar Medium in the Galaxy (2003, background): “…et al. (1987) found no giant molecular clouds (GMCs) at R > 10 kpc (after correcting their distances to a Galactocentric distance of 8.5 kpc); Heyer et al. (2001) found no clouds more massive than 105 M at R > 11:6 kpc, whereas half the molecular gas inside the solar circle is in clouds with…”
The Formation and Destruction of Molecular Clouds and Galactic Star Formation (2015, result): “For example,Tf = T∗ = 10Myrs corresponds to α ≈ 1.7, which agrees well with observations (Solomon et al. 1987; Kramer et al. 1998; Heyer et al. 2001; Roman Duval et al. 2010).”
The spiral structure of our Milky Way Galaxy (2009, background): “Nakagawa et al. (2005) revealed 70 molecular clouds in the Galactic Warp with a kinematic distance greater than about 14.5 kpc. Heyer et al. (2001) summarized the properties of molecular regions in the outer galaxy from the Five College Radio Astronomy Observatory Outer Galaxy Survey.”
A General Theory of Turbulence-regulated Star Formation, from Spirals to Ultraluminous Infrared Galaxies (2005, background): “…the total SFR by integrating the SFR over the GMC mass distribution, Ṁ ;pred ¼ Z 6 ; 106 M 104 M SFRA Mclð Þ 1 tA Mclð Þ dN d lnMcl dMcl ð61Þ 5:3 M yr 1: ð62Þ We have imposed a lower cutoff of 104M because vir 31 for GMCs with smaller masses (Heyer et al. 2001), which greatly reduces their SFR.”
The Global Evolution of Giant Molecular Clouds. I. Model Formulation and Quasi-Equilibrium Behavior (2006, unknown): “Nonetheless, at a qualitative level the result that clouds equilibrate to virial parameters ∼ 1 is in good agreement with observations showing that massive clouds are approximately virialized (Heyer et al. 2001; Blitz et al. 2005).”
Modeling the Pan-Spectral Energy Distribution of Starburst Galaxies. IV. The Controlling Parameters of the Starburst SED (2007, methodology): “The observational data comes from measurements of individual molecular clouds both within our galaxy (Larson 1981; Solomon et al. 1987; Heyer et al. 2001) and in neighbouring galaxies such as M33 (Rosolowsky et al. 2003) which all give hydrogen column densities of ∼ 1022 cm−2 independent of cloud…”
LOW VIRIAL PARAMETERS IN MOLECULAR CLOUDS: IMPLICATIONS FOR HIGH-MASS STAR FORMATION AND MAGNETIC FIELDS (2013, background): “Virial parameters in large cloud complexes were studied by, e.g., Solomon et al. (1987), Scoville et al. (1987), and Heyer et al. (2001).”