Milky Way Star-Forming Complexes and the Turbulent Motion of the Galaxy's Molecular Gas

Abstract

We analyze Spitzer GLIMPSE, MSX, and WMAP images of the Milky Way to identify 8 micron and free-free sources in the Galaxy. Seventy-two of the eighty-eight WMAP sources have coverage in the GLIMPSE and MSX surveys suitable for identifying massive star forming complexes (SFC). We measure the ionizing luminosity functions of the SFCs and study their role in the turbulent motion of the Galaxy's molecular gas. We find a total Galactic free-free flux f ν = 46177.6 Jy; the 72 WMAP sources with full 8 micron coverage account for 34263.5 Jy (∼ 75%), with both measurements made at ν=94GHz (W band). We find a total of 280 SFCs, of which 168 have unique kinematic distances and free-free luminosities. We use a simple model for the radial distribution of star formation to estimate the free-free and ionizing luminosity for the sources lacking distance determinations. The total dust-corrected ionizing luminosity is Q = 2.9 ± 0.5 x 10 53 photons s −1 , which implies a galactic star formation rate oḟ M * = 1.2 ± 0.2 M ⊙ yr −1 . We present the (ionizing) luminosity function of the SFCs, and show that 24 sources emit half the ionizing luminosity of the Galaxy. The SFCs appear as bubbles in GLIMPSE or MSX images; the radial velocities associated with the bubble walls allow us to infer the expansion velocity of the bubbles. We calculate the kinetic luminosity of the bubble expansion and compare it to the turbulent luminosity of the inner molecular disk. SFCs emitting 80% of the total galactic free-free luminosity produce a kinetic luminosity equal to 65% of the turbulent luminosity in the inner molecular disk. This suggests that the expansion of the bubbles is a major driver of the turbulent motion of the inner Milky Way molecular gas.

The Link Between Turbulence, Magnetic Fields, Filaments, and Star Formation in the Central Molecular Zone Cloud G0.253+0.016

“…The fact that we see turbulence thus leads us to conclude that it must be driven by some physical stirring mechanism. In general, potential driving mechanisms include supernova explosions and expanding radiation fronts and shells induced by high-mass stellar feedback (McKee 1989;Balsara et al 2004;Krumholz et al 2006;Breitschwerdt et al 2009;Goldbaum et al 2011;Peters et al 2011;Lee et al 2012), winds , gravitational collapse and accretion of material (Vazquez-Semadeni et al 1998;Elmegreen & Burkert 2010;Klessen & Hennebelle 2010;Vázquez-Semadeni et al 2010;Federrath et al 2011b;Robertson & Goldreich 2012;Lee et al 2015), and Galactic spiral-arm compressions of H I clouds turning them into molecular clouds (Dobbs & Bonnell 2008;, as well as magnetorotational instability (MRI) and shear (Piontek & Ostriker 2007;Tamburro et al 2009). Jets and outflows from young stars and their accretion disks have also been suggested to drive turbulence (Norman & Silk 1980;Matzner & McKee 2000;Banerjee et al 2007;Nakamura & Li 2008;Cunningham et al 2009Cunningham et al , 2011Carroll et al 2010;Wang et al 2010;Plunkett et al 2013Plunkett et al , 2015Federrath et al 2014;Offner & Arce 2014).…”

The Milky Way Project and Atlasgal: The Distribution and Physical Properties of Cold Clumps Near Infrared Bubbles

“…The role of turbulence was studied in detail by McKee & Ostriker (2007); recently, Kruijssen et al (2014) identified it as a crucial regulator of a molecular cloudʼs star formation efficiency. The importance of bubbles was highlighted in recent work by and Lee et al (2012), who find that the feedback energy from expanding bubbles in star-forming complexes is a major driver of turbulence in the ISM of the inner Milky Way, possibly more important than that from supernovae. Both the triggering and quenching of star formation by massive stellar feedback are observed in smoothed particle hydrodynamics simulations by Dale et al (2005Dale et al ( , 2007 and Walch et al (2012).…”

The Galactic Center Molecular Cloud Survey

“…It forms stars at a rate of order 0.1 M yr −1 (Yusef-Zadeh et al 2009;Immer et al 2012b;Longmore et al 2013a;Koepferl et al 2015). The Milky Way contains (1.0 ± 0.3) × 10 9 M of molecular gas (Heyer & Dame 2015), while the star formation rate is 1 to 4 M yr −1 (Diehl et al 2006;Misiriotis et al 2006; Lee et al 2012). et al 2006, 2008), and collisionally-excited methanol masers (Mills et al 2015; also see Menten et al 2009, though) suggest that much of the gas in the CMZ is subject to violent gas motions, such as cloud-cloud collisions at high velocities.…”