A Caltech Library Service

Investigating variations in the dust emissivity index in the Andromeda Galaxy

Athikkat-Eknath, G. and Eales, S. A. and Smith, M. W. L. and Schruba, A. and Marsh, K. A. and Whitworth, A. P. (2022) Investigating variations in the dust emissivity index in the Andromeda Galaxy. Monthly Notices of the Royal Astronomical Society, 511 (4). pp. 5287-5300. ISSN 0035-8711. doi:10.1093/mnras/stab3135.

[img] PDF - Published Version
See Usage Policy.

[img] PDF - Accepted Version
See Usage Policy.

[img] Archive (ZIP) (Supplementary data) - Supplemental Material
See Usage Policy.


Use this Persistent URL to link to this item:


Over the past decade, studies of dust in the Andromeda Galaxy (M31) have shown radial variations in the dust emissivity index (β). Understanding the astrophysical reasons behind these radial variations may give clues about the chemical composition of dust grains, their physical structure, and the evolution of dust. We use ¹²CO(J = 1⟶⟶0) observations taken by the Combined Array for Research in Millimeter-wave Astronomy and dust maps derived from Herschel images, both with an angular resolution of 8 arcsec and with spatial resolution of 30 pc, to study variations in β across an area of ≈18.6 kpc² in M31. We extract sources, which we identify as molecular clouds, by applying the ASTRODENDRO algorithm to the ¹²CO and dust maps, which as a byproduct allows us to compare continuum emission from dust and CO emission as alternative ways of finding molecular clouds. We then use these catalogues to investigate whether there is evidence that β is different inside and outside molecular clouds. Our results confirm the radial variations of β seen in previous studies. However, we find little difference between the average β inside molecular clouds compared with that outside molecular clouds, in disagreement with models that predict an increase of β in dense environments. Finally, we find some clouds traced by dust with very little CO, which may be either clouds dominated by atomic gas or clouds of molecular gas that contain little CO.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
http://archives.esac.esa.intRelated ItemHerschel Science Archive
Athikkat-Eknath, G.0000-0002-7301-3879
Eales, S. A.0000-0002-7394-426X
Smith, M. W. L.0000-0002-3532-6970
Marsh, K. A.0000-0003-0107-7803
Whitworth, A. P.0000-0002-1178-5486
Additional Information:© 2021 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model ( Accepted 2021 October 22. Received 2021 October 22; in original form 2021 March 26. Published: 30 October 2021. GAE acknowledges the support of a UK Science and Technology Facilities Council (STFC) postgraduate studentship. GAE personally thanks Michael Anderson for useful discussions about the dendrogram algorithm. SAE, MWLS, and APW acknowledge the support of an STFC Consolidated Grant (ST/K00926/1). MWLS acknowledges support from the European Research Council (ERC) in the form of the Consolidator Grant COSMICDUST (ERC-2014-CoG-647939, PI H L Gomez). We thank the anonymous referee for suggestions that helped improved the quality of the manuscript. This research made use of ASTROPY,4CMOCEAN,5MATPLOTLIB6 (Hunter 2007), MULTICOLORFITS,7NUMPY8 (Harris et al. 2020), and SCIPY9 (SciPy 1.0 Contributors et al. 2020) PYTHON packages and the IPYTHON10 (Perez & Granger 2007) interactive shell. This research has made use of SAOImageDS911 (Joye & Mandel 2003) astronomical imaging and data visualization software. Data Availability: The raw far-infrared data used for this work are available on the Herschel Science Archive. The raw ¹²CO(J = 1⟶0) data used for this work are available on the CARMA data archive. The raw H I data used for this work are available upon request from Robert Braun.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)ST/K00926/1
European Research Council (ERC)647939
Subject Keywords:ISM: clouds –galaxies: individual: M31 –galaxies: ISM –Local Group
Issue or Number:4
Record Number:CaltechAUTHORS:20220426-777487400
Persistent URL:
Official Citation:G Athikkat-Eknath, S A Eales, M W L Smith, A Schruba, K A Marsh, A P Whitworth, Investigating variations in the dust emissivity index in the Andromeda Galaxy, Monthly Notices of the Royal Astronomical Society, Volume 511, Issue 4, April 2022, Pages 5287–5300,
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:114463
Deposited By: Tony Diaz
Deposited On:26 Apr 2022 19:38
Last Modified:26 Apr 2022 19:38

Repository Staff Only: item control page