The Milky Way as a Star Formation Engine

Abstract

The cycling of material from the interstellar medium (ISM) into stars and the return of stellar ejecta into the ISM is the engine that drives the galactic ecology in normal spirals. This ecology is a cornerstone in the formation and evolution of galaxies through cosmic time. There remain major observational and theoretical challenges in determining the processes responsible for converting the low-density, diffuse components of the ISM into dense molecular clouds, forming dense filaments and clumps, fragmenting them into stars, expanding OB associations, and bound clusters, and characterizing the feedback that limits the rate and efficiency of star formation. This formidable task can be attacked effectively for the first time thanks to the synergistic combination of new global-scale surveys of the Milky Way from infrared to radio wavelengths, offering the possibility of bridging the gap between local and extragalactic star formation studies.The Herschel Hi-GAL survey, with its five-band 70-500µm full Galactic Plane mapping at 6-36 resolution, is the keystone of a set of continuum surveys that include GLIMPSE(360)+MIPSGAL@Spitzer, WISE and MSX, ATLASGAL@APEX, BGPS@CSO, and CORNISH@VLA. This suite enables us to measure the Galactic distribution and physical properties of dust on all scales and in all components of the ISM from diffuse clouds to filamentary complexes and hundreds of thousands of dense clumps. A complementary suite of spectroscopic surveys in various atomic and molecular tracers is providing the chemical fingerprinting of dense clumps and filaments, as well as essential kinematic information to derive distances and thus transform panoramic data into a 3D representation.The latest results emerging from these Galaxy-scale surveys are reviewed. New insights into cloud formation and evolution, filaments and their relationship to channeling gas onto gravitationally-bound clumps, the properties of these clumps, density thresholds for gravitational collapse, and star and cluster formation rates are discussed.

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

“…The resolution of the Herschel data is   5 36 -. The Herschel column densities were derived based on a fit to the spectral energy distribution (SED) using five photometric bands (70,160,250,350, and 500 μm) from Herschel Hi-GAL (Molinari et al 2010(Molinari et al , 2011). The absolute column density level is thus better calibrated in the Herschel map than in the ALMA+Herschel map (see Section 7).…”

Nonthermal particles and photons in starburst regions and superbubbles

“…The evolution of an SF system is an integral part of the ISM ecology and it starts from molecular cloud formation and ends with the destruction of the cloud by radiation and winds of massive stars, supernova explosions, dispersion of open clusters of massive stars or massive globular cluster formation. Above we have briefly discussed some aspects of the first stages of the SF process and a more detailed discussion can be found in Bromm and Larson (2004), McKee and Ostriker (2007), Zinnecker and Yorke (2007), Elmegreen (2011a), Kennicutt and Evans (2012), Sanchez Almeida et al (2014), Krumholz (2014), Molinari et al (2014), and Tan et al (2014).…”

“…Observations compiled in Figure 4 of Krumholz (2014) suggested ff ≈ 0.01 as the universal value for galaxies in the local Universe. The complex process of matter cycling from the ISM gas into stars with the return of metal rich material with high energy stellar ejecta is the driver of galactic evolution through cosmic time (see for a recent review Draine 2011, Molinari et al 2014, Krumholz 2014, and references therein). Cosmic gas accretion by galaxies affects global SF.…”

Hi-GAL, theHerschelinfrared Galactic Plane Survey: photometric maps and compact source catalogues

“…Methanol maser emission is characteristic of the early formation stage of massive stars; its association with cool dense clumps is a signpost for ongoing formation of massive stars and associated protoclusters in such objects. A more complete compilation of GP Surveys from the near-IR to the radio is provided in the review of Molinari et al (2014).…”

“…Today, it is possible for the first time to engage with this ambitious challenge, thanks to a new suite of modern Milky Way surveys that provide homogenous coverage of the entire Galactic plane (hereafter GP) and that have already started to transform the view of our Galaxy as a global star-formation engine (see Molinari et al 2014 for a recent review).…”