Clustering Properties of Far-Infrared Sources in Hi-GAL Science Demonstration Phase Fields

The Astrophysical Journal (Impact Factor: 6.73). 04/2011; 735. DOI:10.1088/0004-637X/735/1/28
Source: arXiv

ABSTRACT We use a Minimum Spanning Tree algorithm to characterize the spatial
distribution of Galactic Far-IR sources and derive their clustering properties.
We aim to reveal the spatial imprint of different types of star forming
processes, e.g. isolated spontaneous fragmentation of dense molecular clouds,
or events of triggered star formation around HII regions, and highlight global
properties of star formation in the Galaxy. We plan to exploit the entire
Hi-GAL survey of the inner Galactic plane to gather significant statistics on
the clustering properties of star forming regions, and to look for possible
correlations with source properties such as mass, temperature or evolutionary
stage. In this paper we present a pilot study based on the two 2x2 square
degree fields centered at longitudes l=30 and l=59 obtained during the Science
Demonstration Phase (SDP) of the Herschel mission. We find that over half of
the clustered sources are associated with HII regions and infrared dark clouds.
Our analysis also reveals a smooth chromatic evolution of the spatial
distribution where sources detected at short-wavelengths, likely proto-stars
surrounded by warm circumstellar material emitting in the far-infrared, tend to
be clustered in dense and compact groups around HII regions while sources
detected at long-wavelengths, presumably cold and dusty density enhancements of
the ISM emitting in the sub-millimeter, are distributed in larger and looser

0 0
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We summarize the first results from the Gould Belt Survey, obtained toward the Aquila rift and Polaris Flare regions during the science demonstration phase of Herschel. Our 70-500 μm images taken in parallel mode with the SPIRE and PACS cameras reveal a wealth of filamentary structure, as well as numerous dense cores embedded in the filaments. Between ~350 and 500 prestellar cores and ~45-60 Class 0 protostars can be identified in the Aquila field, while ~300 unbound starless cores and no protostars are observed in the Polaris field. The prestellar core mass function (CMF) derived for the Aquila region bears a strong resemblance to the stellar initial mass function (IMF), already confirming the close connection between the CMF and the IMF with much better statistics than earlier studies. Comparing and contrasting our Herschel results in Aquila and Polaris, we propose an observationally-driven scenario for core formation according to which complex networks of long, thin filaments form first within molecular clouds, and then the densest filaments fragment into a number of prestellar cores via gravitational instability. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.Appendix A and Figures 3, 4 are only available in electronic form at
    Astronomy and Astrophysics, v.518, id.L102 (2010). 01/2010;
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: The Vulpecula OB association, VulOB1, is a region of active star formation located in the Galactic plane at 2.3 kpc from the Sun. Previous studies suggest that sequential star formation is propagating along this 100 pc long molecular complex. In this paper, we use Spitzer MIPSGAL and GLIMPSE data to reconstruct the star formation history of VulOB1, and search for signatures of past triggering events. We make a census of Young Stellar Objects (YSO) in VulOB1 based on IR color and magnitude criteria, and we rely on the properties and nature of these YSOs to trace recent episodes of massive star formation. We find 856 YSO candidates, and show that the evolutionary stage of the YSO population in VulOB1 is rather homogeneous - ruling out the scenario of propagating star formation. We estimate the current star formation efficiency to be ~8 %. We also report the discovery of a dozen pillar-like structures, which are confirmed to be sites of small scale triggered star formation. Comment: 30 pages, 11 figures, accepted for publication in ApJ
    The Astrophysical Journal 03/2010; · 6.73 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: The observed properties of young star clusters, such as the core radius and luminosity profile, change rapidly during the early evolution of the clusters. Here we present observations of 6 young clusters in M51 where we derive their sizes using HST imaging and ages using deep Gemini-North spectroscopy. We find evidence for a rapid expansion of the cluster cores during the first 20 Myr of their evolution. We confirm this trend by including data from the literature of both Galactic and extra-galactic embedded and young clusters, and possible mechanisms (rapid gas removal, stellar evolutionary mass-loss, and internal dynamical heating) are discussed. We explore the implications of this result, focussing on the fact that clusters were more concentrated in the past, implying that their stellar densities were much higher and relaxation times correspondingly shorter. Thus, when estimating if a particular cluster is dynamically relaxed, (i.e. when determining if a cluster's mass segregation is due to primordial or dynamical processes), the current relaxation time is only an upper-limit, with the relaxation time likely being significantly shorter in the past. Comment: 9 pages, 5 figures, accepted MNRAS
    Monthly Notices of the Royal Astronomical Society 06/2008; · 5.52 Impact Factor

Full-text (2 Sources)

Available from
Oct 3, 2012