Evolving Starburst Modeling of Far-Infrared/Submillimeter/Millimeter Line Emission. Ii. Application to M 82

Abstract

We present starburst models for far-infrared/sub-millimeter/millimeter line emission of molecular and atomic gas in an evolving starburst region, which is treated as an ensemble of noninteracting hot bubbles that drive spherical shells of swept-up gas into a surrounding uniform gas medium. These bubbles and shells are driven by stellar winds and supernovae within massive star clusters formed during an instantaneous starburst. The underlying stellar radiation from the evolving clusters affects the properties and structure of photodissociation regions (PDRs) in the shells, and hence the spectral energy distributions (SEDs) of the molecular and atomic line emission from these swept-up shells and the associated parent giant molecular clouds contain a signature of the stage of evolution of the starburst. The physical and chemical properties of the shells and their structure are computed using a simple, well-known similarity solution for the shell expansion, a stellar population synthesis code, and a time-dependent PDR chemistry model. The SEDs for several molecular and atomic lines ( 12 CO and its isotope 13 CO, HCN, HCO + , C, O, and C + ) are computed using a nonlocal thermodynamic equilibrium line radiative transfer model. By comparing our models with the available observed data of nearby infrared bright galaxies, especially M 82, we constrain the models and in the case of M 82, we provide estimates for the ages (5-6 Myr, 10 Myr) of recent starburst activity. We also derive a total H 2 gas mass of ∼(2-3.4) × 10 8 M for the observed regions of the central 1 kpc starburst disk of M 82.

A Census of the High-Density Molecular Gas in M82

“…Our findings are largely consistent with the evolving starburst model of Yao et al (2006) and Yao (2009), in which the gas in the nucleus of M82 is a superposition of expanding spherical bubbles around stellar clusters. The bubble interiors are ionized gas ([H ii] regions), and the shells are swept-up molecular gas, so the inside edges are PDR fronts.…”

“…Their estimated gas mass of 2 × 10 8 M ⊙ from CO in the central 1 kpc along the major axis (nearly identical to our modeled 50 ′′ × 15 ′′ region) is comparable to our measured 2.2 × 10 8 M ⊙ , and the shell density at the putative 3-10 Myr age is modeled to be 1-3×10 4 cm −3 , similar to what we find. However, as Yao (2009) notes, there are some inconsistencies in the model. While all of the observed molecular and atomic line emission is reproduced, the stellar luminosity which is required is only ∼5% of the observed far-IR luminosity in the same region, potentially the result of assuming zero pressure for the ambient ISM which results in more mass swept up in the modeled shells than is physical.…”

Star formation towards the Scutum tangent region and the effects of Galactic environment

“…The W43 giant molecular complex is considered to be a ministarburst region. The IR luminosity and number of Lyman continuum photons are numbers representative of those found in starburst galaxies such as M82 (Yao 2009). W43 is also undergoing an intense episode of high-mass star formation, producing ∼15 high-mass protoclusters with a star formation rate (SFR) of ∼25 per cent per 10 6 years (Motte, Schilke & Lis 2003).…”

A Population of Ultraluminous X-Ray Sources With an Accreting Neutron Star

“…We consider two cases of star formation activities for star forming galaxies like M82 and late-type galaxies like the MW. We adopt a constant overall star formation rate of 10M yr −1 over the last 100 Myr (Förster Schreiber et al 2003;Yao 2009) in case (1) , and a constant star formation rate 3M yr −1 over the 13 Gyr period in case (2).…”