@article{c343d0d2ee08486fb1f596820a505989,
title = "A NIKA view of two star-forming infrared dark clouds: Dust emissivity variations and mass concentration",
abstract = "Context. 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. Aims. 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. Methods. We exploited the simultaneous 1.2 and 2.0 mm imaging capability of the NIKA camera on the IRAM 30 m telescope to construct maps of β for both clouds, and by incorporating Herschel observations, we created H2 column density maps with 13″ angular resolution. Results. 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 β = 2.07 ± 0.09 (random) ± 0.25 (systematic) for SDC18.888-0.476 and 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 H II region may raise β on scales of ∼1 pc. 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. Conclusions. 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.",
keywords = "Dust extinction, ISM: clouds, ISM: structure, Stars: formation, Submillimeter: ISM",
author = "Rigby, {A. J.} and N. Peretto and R. Adam and P. Ade and P. Andr{\'e} and H. Aussel and A. Beelen and A. Beno{\^i}t and A. Bracco and A. Bideaud and O. Bourrion and M. Calvo and A. Catalano and Clark, {C. J.R.} and B. Comis and {De Petris}, M. and D{\'e}sert, {F. X.} and S. Doyle and Driessen, {E. F.C.} and J. Goupy and C. Kramer and G. Lagache and S. Leclercq and Lestrade, {J. F.} and Mac{\'i}as-P{\'e}rez, {J. F.} and Philip Mauskopf and F. Mayet and A. Monfardini and E. Pascale and L. Perotto and G. Pisano and N. Ponthieu and V. Rev{\'e}ret and A. Ritacco and C. Romero and H. Roussel and F. Ruppin and K. Schuster and A. Sievers and S. Triqueneaux and C. Tucker and R. Zylka",
note = "Funding Information: Acknowledgements. We thank the anonymous referee for helpful comments which have improved the quality and clarity of this paper. A. J. R. would like to thank the STFC for postdoctoral support under the consolidated grant number ST/N000706/1. N. P. also wishes to acknowledge support under the above STFC consolidated grant as well as further support from the STFC under grant number ST/M000893/1. We thank the Royal Society for providing computing resources under Research Grant number RG150741. We would like to thank the IRAM staff for their support during the campaigns. The NIKA dilution cryostat has been designed and built at the Institut N{\'e}el. In particular, we acknowledge the crucial contribution of the Cryogenics Group, and in particular Gregory Garde, Henri Rodenas, Jean Paul Leggeri, Philippe Camus. This work has been partially funded by the Foundation Nanoscience Grenoble, the LabEx FOCUS ANR-11-LABX-0013 and the ANR under the contracts “MKIDS”, “NIKA” and ANR-15-CE31-0017. This work has benefited from the support of the European Research Council Advanced Grant ORISTARS under the European Union{\textquoteright}s Seventh Framework Programme (Grant Agreement no. 291294). We acknowledge fundings from the ENIGMASS French LabEx (R. A. and F. R.), the CNES post-doctoral fellowship program (R. A.), the CNES doctoral fellowship program (A. R.) and the FOCUS French LabEx doctoral fellowship program (A. R.). This research made use of astrodendro, a Python package to compute dendrograms of Astronomical data (http://www.dendrograms.org/), as well as Astropy, a community-developed core Python package for astronomy (Astropy Collaboration et al. 2013), SciPy (Jones et al. 2001) and matplotlib (Hunter 2007). This research has also made use of the NASA Astrophysics Data System.",
year = "2018",
month = jul,
day = "1",
doi = "10.1051/0004-6361/201732258",
language = "English (US)",
volume = "615",
journal = "Astronomy and Astrophysics",
issn = "0004-6361",
publisher = "EDP Sciences",
}