Characterizing precursors to stellar clusters with Herschel

By C. Battersby, J. Bally, A. Ginsburg, J. Bernard, C. Brunt, G. Fuller, P. Martin, Sergio Molinari, J. Mottram, Nicolas Peretto and 2 more. 2011

137 citations recorded by the source corpus.

Context. Despite their profound effect on the universe, the formation of massive stars and stellar clusters remains elusive. Recent advances in observing facilities and computing power have brought us closer to understanding this formation process. In the past decade, compelling evidence has emerged that suggests infrared dark clouds (IRDCs) may be precursors to stellar clusters. However, the usual method for identifying IRDCs is biased by the requirement that they are seen in absorption against background mid-IR emission, whereas dust continuum observations allow cold, dense pre-stellar-clusters to be identified anywhere. Aims. We aim to understand what dust temperatures and column densities characterize and distinguish IRDCs, to explore the population of dust continuum sources that are not IRDCs, and to roughly characterize the level of star formation activity in these dust continuum sources. Methods. We use Hi-GAL 70 to 500 μm data to identify dust continuum sources in the l = 30° and l = 59° Hi-GAL science demonstration phase (SDP) fields, to characterize and subtract the Galactic cirrus emission, and perform pixel-by-pixel modified blackbody fits on cirrus-subtracted Hi-GAL sources. We utilize archival Spitzer data to indicate the level of star-forming activity in each pixel, from mid-IR-dark to mid-IR-bright. Results. We present temperature and column density maps in the Hi-GAL l = 30° and l = 59° SDP fields, as well as a robust algorithm for cirrus subtraction and source identification using Hi-GAL data. We report on the fraction of Hi-GAL source pixels which are mid-IR-dark, mid-IR-neutral, or mid-IR-bright in both fields. We find significant trends in column density and temperature between mid-IR-dark and mid-IR-bright pixels; mid-IR-dark pixels are about 10 K colder and have a factor of 2 higher column density on average than mid-IR-bright pixels. We find that Hi-GAL dust continuum sources span a range of evolutionary states from pre- to star-forming, and that warmer sources are associated with more star formation tracers. Additionally, there is a trend of increasing temperature with tracer type from mid-IR-dark at the coldest, to outflow/maser sources in the middle, and finally to 8 and 24 μm bright sources at the warmest. Finally, we identify five candidate IRDC-like sources on the far-side of the Galaxy. These are cold (~20 K), high column density (N(H2) > 1022 cm-2) clouds identified with Hi-GAL which, despite bright surrounding mid-IR emission, show little to no absorption at 8 μm. These are the first inner Galaxy far-side candidate IRDCs of which the authors are aware.

Subfields: Astronomy and Astrophysics, Spectroscopy

View Paper: https://www.semanticscholar.org/paper/7eb9d208ec55a41fb5c687a143acb2fba7834bfc

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Citations in the corpus

Hi-GAL, the Herschel infrared Galactic Plane Survey: Photometric maps and compact source catalogues: First data release for the inner Milky Way: +68° ≥ l ≥ -70° (2016, background): “…regions (e.g. Paladini et al. 2012; Tibbs et al. 2012, clumps and massive star formation (e.g. Elia et al. 2010; Bally et al. 2010; Elia et al. 2013; Battersby et al. 2011; Mottram & Brunt 2012; Wilcock et al. 2012; Veneziani et al. 2013; Beltrán et al. 2013; Strafella et al. 2015; Traficante et…”
Variations in the Galactic star formation rate and density thresholds for star formation (2012, methodology): “We derive the column density maps forthe region−2.5◦ < l < 3.5◦, |b| 6 0.5◦ using well-tested methods (Battersby et al. 2011).”
Star formation rates and efficiencies in the Galactic Centre (2017, methodology): “This has been subtracted for the emission at wavelengths >70 µm using the method presented in Battersby et al. (2011), which causes an average decrease of ∼20 per cent in the measured bolometric luminosity at each pixel.”
Dense gas in the Galactic central molecular zone is warm and heated by turbulence (2015, methodology): “The SED fits were performed on backgroundsubtracted data using an approach originally described in Battersby et al. (2011), which includes details of the fitting process and specification of assumed physical parameters.”
LOW VIRIAL PARAMETERS IN MOLECULAR CLOUDS: IMPLICATIONS FOR HIGH-MASS STAR FORMATION AND MAGNETIC FIELDS (2013, methodology): “We have used a power–law slope of 1.75 (Battersby et al. 2011) when interpolating and extrapolating (for wavelengths λ > 1.3 mm) between tabulated values.”
Molecular gas kinematics within the central 250 pc of the Milky Way (2016, methodology): “The P2 and P3 locations correspond to local peaks in the molecular hydrogen column density maps derived from Hi-GAL (Herschel infrared Galactic plane survey; Molinari et al. 2010) data (Battersby et al. 2011, Battersby et al. in prep.).”
ATLASGAL — towards a complete sample of massive star forming clumps ⋆ (2014, result): “These values are similar to those reported by Battersby et al. (2011) from a Herschel study of IRDCs (0.2–5 g cm−2).”
Planck 2013 results. XI. All-sky model of thermal dust emission (2013, methodology): “This A11, page 24 of 37 was revealed by previous studies (Cambrésy et al. 2001; Stepnik et al. 2003; Planck Collaboration XXV 2011), in particular using higher resolution Herschel data (Battersby et al. 2011; Roy et al. 2013), and is now confirmed and reinforced by our Planck analysis.”