J/A+A/578/A29 Column density maps in 4 IRDCs (Schneider+, 2015)
Understanding star formation in molecular clouds.
II. Signatures of gravitational collapse of IRDCs.
Schneider N., Csengeri T., Klessen R.S., Tremblin P., Ossenkopf V.,
Peretto N., Simon R., Bontemps S., Fedrrath C.
<Astron. Astrophys. 578, A29 (2015)>
=2015A&A...578A..29S 2015A&A...578A..29S
ADC_Keywords: Molecular clouds ; Infrared sources
Keywords: ISM: clouds - dust, extinction
Abstract:
We analyse column density and temperature maps derived from Herschel
dust continuum observations of a sample of prominent, massive infrared
dark clouds (IRDCs) i.e. G11.11-0.12, G18.82-0.28, G28.37+0.07, and
G28.53-0.25. We disentangle the velocity structure of the clouds using
13CO 1->0 and 12CO 3->2 data, showing that these IRDCs are the
densest regions in massive giant molecular clouds (GMCs) and not
isolated features. The probability distribution function (PDF) of
column densities for all clouds have a power-law distribution over all
(high) column densities, regardless of the evolutionary stage of the
cloud: G11.11-0.12, G18.82-0.28, and G28.37+0.07 contain
(proto)-stars, while G28.53-0.25 shows no signs of star formation.
This is in contrast to the purely log-normal PDFs reported for near
and/or mid-IR extinction maps. We only find a log-normal distribution
for lower column densities, if we perform PDFs of the column density
maps of the whole GMC in which the IRDCs are embedded. By comparing
the PDF slope and the radial column density profile of three of our
clouds, we attribute the power law to the effect of large-scale
gravitational collapse and to local free-fall collapse of pre- and
protostellar cores for the highest column densities. A significant
impact on the cloud properties from radiative feedback is unlikely
because the clouds are mostly devoid of star formation. Independent
from the PDF analysis, we find infall signatures in the spectral
profiles of 12CO for G28.37+0.07 and G11.11-0.12, supporting the
scenario of gravitational collapse. Our results are in line with
earlier interpretations that see massive IRDCs as the densest regions
within GMCs, which may be the progenitors of massive stars or
clusters. At least some of the IRDCs are probably the same features as
ridges (high column density regions with N>1023cm-2 over small
areas), which were defined for nearby IR-bright GMCs. Because IRDCs
are only confined to the densest (gravity dominated) cloud regions,
the PDF constructed from this kind of a clipped image does not
represent the (turbulence dominated) low column density regime of the
cloud.
Description:
Dust column density maps obtained from Herschel observations at 160,
250, 350, and 500 micron by a pixel-to-pixel SED fit. The unit is
cm^-2 (regardless what is written in the header).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 71 4 List of fits maps
fits/* . 4 Individual fits maps
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1 A1 --- --- [G]
2- 10 F9.5 deg GLON Galactic longitude
11- 19 F9.5 deg GLAT Galactic latitude
21- 24 F4.1 arcsec/pix Scale [13/14] Scale of the image
26- 28 I3 --- Nx [56/161] Number of pixels along X-axis
30- 32 I3 --- Ny [39/124] Number of pixels along Y-axis
34- 35 I2 Kibyte size Size of the fits file
37- 54 A18 --- FileName Name of the FITS file in subdirectory fits
56- 71 A16 --- Title Title of the file
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Acknowledgements:
Nicola Schneider, nschneid(at)cea.fr
References:
Schneider et al., Paper I 2015A&A...575A..79S 2015A&A...575A..79S
(End) Patricia Vannier [CDS] 21-Apr-2015