Investigating variations in the dust emissivity index in the Andromeda galaxy

Abstract

Over the past decade, studies of dust in the Andromeda galaxy (M31) have shown radial variations in the dust emissivity index ($\beta$). 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 ${}^{12}$CO(J=1-0) observations taken by the Combined Array for Research in Millimeter Astronomy (CARMA) and dust maps derived from \textit{Herschel} images, both with an angular resolution of 8" and spatial resolution of 30 pc, to study variations in $\beta$ across an area of $\approx$ 18.6 kpc${}^2$ in M31. We extract sources, which we identify as molecular clouds, by applying the astrodendro algorithm to the ${}^{12}$CO 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 $\beta$ is different inside and outside molecular clouds. Our results confirm the radial variations of $\beta$ seen in previous studies. However, we find little difference between the average $\beta$ inside molecular clouds compared to outside molecular clouds, in disagreement with models which predict an increase of $\beta$ 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.

arXiv comment14 pages, 11 figures, accepted for publication in MNRAS

References in corpus (38)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• Interstellar Dust Grains
• Planck 2013 results. XI. All-sky model of thermal dust emission
• PHIBSS: Unified Scaling Relations of Gas Depletion Time and Molecular Gas Fractions
• Structural Analysis of Molecular Clouds: Dendrograms
• The Evolving Interstellar Medium of Star Forming Galaxies Since z=2 as Probed by Their Infrared Spectral Energy Distributions
• ISM masses and the star formation law at Z = 1 to 6 // ALMA observations of dust continuum in 145 galaxies in the COSMOS survey field
• Andromeda's Dust
• Planck Early Results: All sky temperature and dust optical depth from Planck and IRAS: Constraints on the "dark gas" in our galaxy
• The Panchromatic Hubble Andromeda Treasury
• A Herschel [CII] Galactic plane survey I: the global distribution of ISM gas components
• Evolution of Interstellar Medium, Star Formation, and Accretion at High Redshift
• Fermi observations of Cassiopeia and Cepheus: diffuse gamma-ray emission in the outer Galaxy
• A Uniform Catalog of Molecular Clouds in the Milky Way
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA) II: Dust and Gas in Andromeda
• Molecular gas in the Andromeda galaxy
• A Wide-field High Resolution HI Mosaic of Messier 31: I. Opaque Atomic Gas and Star Formation Rate Density
• Giant Molecular Cloud Catalogues for PHANGS-ALMA: Methods and Initial Results
• Temperature as a third dimension in column-density mapping of dusty astrophysical structures associated with star formation
• Panoramic GALEX FUV and NUV imaging of M31 and M33
• Dust continuum emission as a tracer of gas mass in galaxies
• Can dust emission be used to map the interstellar medium in high-redshift galaxies? Results from the Herschel Reference Survey
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA). I: Global far-infrared and sub-mm morphology
• Planck intermediate results. XIV. Dust emission at millimetre wavelengths in the Galactic plane
• Cool dust heating and temperature mixing in nearby star-forming galaxies
• Variation in the dust emissivity index across M33 with Herschel and Spitzer (HerM33es)
• Clumping and the Interpretation of kpc-Scale Maps of the Interstellar Medium: Smooth HI and Clumpy, Variable H2 Surface Density
• Planck intermediate results. XXV. The Andromeda Galaxy as seen by Planck
• Submillimeter flux as a probe of molecular ISM mass in high-$z$ galaxies
• Molecular Gas Velocity Dispersions in the Andromeda Galaxy
• Dust Abundance Variations in the Magellanic Clouds: Probing the Lifecycle of Metals with All-Sky Surveys
• The Herschel Exploitation of Local Galaxy Andromeda (HELGA). VI. The distribution and properties of molecular cloud associations in M31
• The Dust in M31
• JINGLE V: Dust properties of nearby galaxies derived from hierarchical Bayesian SED fitting
• A lack of constraints on the cold opaque HI mass: HI spectra in M31 and M33 prefer multi-component models over a single cold opaque component
• JINGLE, a JCMT legacy survey of dust and gas for galaxy evolution studies: II. SCUBA-2 850 μm data reduction and dust flux density catalogues
• Lurking systematics in predicting galaxy cold gas masses using dust luminosities and star formation rates

Cited by in corpus (1)

• The Quest for the Missing Dust: II -- Two Orders of Magnitude of Evolution in the Dust-to-Gas Ratio Resolved Within Local Group Galaxies