J/A+A/615/A18 NIKA view of two star-forming IRDCs (Rigby+, 2018)
A NIKA view of two star-forming infrared dark clouds:
Dust emissivity variations and mass concentration.
Rigby A. J., Peretto N., Adam R., Ade P., Andre P., Aussel H., Beelen A.,
Benoit A., Bracco A., Bideaud A., Bourrion O., Calvo M., Catalano A.,
Clark C.J.R., Comis B., De Petris M., Desert F.-X., Doyle S.,
Driessen E.F.C., Goupy J., Kramer C., Lagache G., Leclercq S.,
Lestrade J.-F., Macias-Perez J.F., Mauskopf P., Mayet F., Monfardini A.,
Pascale E., Perotto L., Pisano G., Ponthieu N., Reveret V., Ritacco A.,
Romero C., Roussel H., Ruppin F., Schuster K., Sievers A., Triqueneaux S.,
Tucker C., Zylka R.
<Astron. Astrophys. 615, A18 (2018)>
=2018A&A...615A..18R 2018A&A...615A..18R (SIMBAD/NED BibCode)
ADC_Keywords: Interstellar medium ; Molecular clouds ; Millimetric/submm sources
Keywords: stars: formation - submillimetre: ISM - ISM: clouds -
dust, extinction - ISM: structure
Abstract:
The thermal emission of dust grains is a powerful tool for probing
cold, dense regions of molecular gas in the interstellar medium, and
so constraining dust properties is key to obtaining accurate
measurements of dust mass and temperature.
By placing constraints on the dust emissivity spectral index, β,
towards two star-forming infrared dark clouds - SDC18.888-0.476 and
SDC24.489-0.689 - we aim to evaluate the role of mass concentration
in the associated star-formation activity.
We exploited the simultaneous 1.2mm and 2.0mm imaging capability of
the NIKA camera on the IRAM 30m telescope to construct maps of
β for both clouds, and by incorporating Herschel observations,
we created H2 column density maps with 13" angular resolution.
While we find no significant systematic radial variations around the
most massive clumps in either cloud on 0.1 pc scales, their mean
β values are significantly different, with
{bar}β=2.07±0.09(random)±0.25(systematic) for SDC18.888-0.476
and {bar}β=1.71±0.09(random)±0.25(systematic) for
SDC24.489-0.689. These differences could be a consequence of the very
different environments in which both clouds lie, and we suggest that
the proximity of SDC18.888-0.476 to the W39 HII region may raise
β on scales of ∼1pc. We also find that the mass in
SDC24.489-0.689 is more centrally concentrated and circularly
symmetric than in SDC18.888-0.476, and is consistent with a scenario
in which spherical globally-collapsing clouds concentrate a higher
fraction of their mass into a single core than elongated clouds that
will more easily fragment, distributing their mass into many cores.
We demonstrate that β variations towards interstellar clouds can
be robustly constrained with high signal-to-noise ratio (S/N) NIKA
observations, providing more accurate estimates of their masses. The
methods presented here will be applied to the Galactic Star Formation
with NIKA2 (GASTON) guaranteed time large programme, extending our
analysis to a statistically significant sample of star-forming clouds.
Description:
The FITS files of the NIKA photometric maps in the 260.0GHz (1.15mm)
and 150.0GHz (2.00mm) continuum wavebands towards the two IRDC targets
SDC18.888-0.476 and SDC24.489-0.689 have intensity units of Jy/beam.
The PSF-matching convolution kernel used in the construction of the
NIKA ratio maps is also included. We also include the
combined-resolution H2 column density maps, created using the method
described in Section 4.1, which have units of cm-2, and were created
using dust beta values of 2.07 and 1.71, respectively.
Objects:
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RA (2000) DE Designation(s)
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18 27 08.31 -12 41 38.9 SDC18.888-0.476 = SDC G18.888-0.476
18 38 25.25 -07 49 28.9 SDC24.489-0.689 = SDC G24.489-0.689
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 104 7 List of fits files
fits/* . 7 Individual fits files
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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- 9 F9.5 deg RAdeg ? Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg ? Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 30 I3 Kibyte size Size of FITS file
32- 53 A22 --- FileName Name of FITS file, in subdirectory fits
55-104 A50 --- Title Title of the FITS file
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Acknowledgements:
Andrew J. Rigby, RigbyA(at)cardiff.ac.uk
(End) Andrew J. Rigby [Cardiff Univ., UK], Patricia Vannier [CDS] 05-Mar-2018