Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Deep Andromeda JCMT-SCUBA2 Observations. The Submillimeter Maps and Giant Molecular Clouds

Sihan Jiao, Jingwen Wu, Hauyu Baobab Liu, Chao-Wei Tsai, Yuxin Lin, Di Li, Zhi-Yu Zhang, Yu Cheng, Linjing Feng, Henrik Beuther, Junzhi Wang, Lihwai Lin, Jakob den Brok, Ludan Zhang, Fengwei Xu, Fanyi Meng, Zongnan Li, Ryan P. Keenan, Si-Yue Yu, Niankun Yu, Zheng Zheng, Junhao Liu, Yuxiang Liu, Hao Ruan, Fangyuan Deng, Yuanzhen Xiong

TL;DR

This study delivers a deep, dust-continuum census of GMCs in M31 by combining JCMT-SCUBA2 450/850 μm maps with archival Herschel and Planck data, achieving ~50 pc resolution at 850 μm and robust multi-wavelength SED fitting to map dust properties. Using dendrogram analysis and a diffusion-based decomposition, the authors identify 572 GMCs (including 189 inter-arm clouds) across the disk, characterizing their masses $2\times10^{4}$–$6\times10^{6}$ $M_{\odot}$, sizes 30–130 pc, and a mass–size relation $M \propto R_c^{2.5}$. They find inter-arm GMCs are systematically less massive, more diffuse, colder, and have lower star-formation efficiency than on-arm clouds, with global and local SFE comparisons suggesting quenching signatures in galactic environments. The radial dust-property analysis shows more uniform $\beta$ across the disk when longer wavelengths are included, and ~19% of M31’s dust resides in the inter-arm region within the 10 kpc ring, providing a key constraint for dust evolution and star-formation-quenching scenarios in spiral galaxies.

Abstract

We have carried out unprecedentedly deep, nearly confusion-limited JCMT-SCUBA2 mapping observations on the nearest spiral galaxy, M31 (Andromeda). The 850 $μ$m image with a $\sim$50 pc resolution yields a comprehensive catalog of 383 giant molecular clouds (GMCs) that are associated with the spiral arms. In addition, it unveiled a population of 189 compact inter-arm GMCs in M31, which are mostly unresolved or marginally resolved. The masses of all these GMCs are in the range of 2$\times$10$^4$ -- 6$\times$10$^6$ $M_{\odot}$; the sizes are in the range of 30--130 pc. They follow a mass-size correlation, $M$ $\propto$ $R_{c}$$^{2.5}$. The inter-arm GMCs are systematically less massive, more diffuse, colder, and have lower star-forming efficiency (SFE) than on-arm GMCs. Moreover, within individual spatially resolved on-arm and off-arm M31 GMCs, the SFE is considerably lower than the SFE in molecular clouds in main sequence and green valley galaxies. Follow-up investigations on M31 GMCs may provide clues for how star formation may be quenched in galactic environments. Finally, we reconstrained the dust opacity spectral index $β$ in the M31 galaxy by combining our new JCMT observations with archival Herschel and Planck data and found that the radial variation of $β$ may not be as large as was proposed by previous studies.

Deep Andromeda JCMT-SCUBA2 Observations. The Submillimeter Maps and Giant Molecular Clouds

TL;DR

This study delivers a deep, dust-continuum census of GMCs in M31 by combining JCMT-SCUBA2 450/850 μm maps with archival Herschel and Planck data, achieving ~50 pc resolution at 850 μm and robust multi-wavelength SED fitting to map dust properties. Using dendrogram analysis and a diffusion-based decomposition, the authors identify 572 GMCs (including 189 inter-arm clouds) across the disk, characterizing their masses – , sizes 30–130 pc, and a mass–size relation . They find inter-arm GMCs are systematically less massive, more diffuse, colder, and have lower star-formation efficiency than on-arm clouds, with global and local SFE comparisons suggesting quenching signatures in galactic environments. The radial dust-property analysis shows more uniform across the disk when longer wavelengths are included, and ~19% of M31’s dust resides in the inter-arm region within the 10 kpc ring, providing a key constraint for dust evolution and star-formation-quenching scenarios in spiral galaxies.

Abstract

We have carried out unprecedentedly deep, nearly confusion-limited JCMT-SCUBA2 mapping observations on the nearest spiral galaxy, M31 (Andromeda). The 850 m image with a 50 pc resolution yields a comprehensive catalog of 383 giant molecular clouds (GMCs) that are associated with the spiral arms. In addition, it unveiled a population of 189 compact inter-arm GMCs in M31, which are mostly unresolved or marginally resolved. The masses of all these GMCs are in the range of 210 -- 610 ; the sizes are in the range of 30--130 pc. They follow a mass-size correlation, . The inter-arm GMCs are systematically less massive, more diffuse, colder, and have lower star-forming efficiency (SFE) than on-arm GMCs. Moreover, within individual spatially resolved on-arm and off-arm M31 GMCs, the SFE is considerably lower than the SFE in molecular clouds in main sequence and green valley galaxies. Follow-up investigations on M31 GMCs may provide clues for how star formation may be quenched in galactic environments. Finally, we reconstrained the dust opacity spectral index in the M31 galaxy by combining our new JCMT observations with archival Herschel and Planck data and found that the radial variation of may not be as large as was proposed by previous studies.

Paper Structure

This paper contains 13 sections, 4 equations, 7 figures.

Table of Contents

  1. Introduction
  2. OBSERVATIONS and methods
  3. JCMT-SCUBA2 Observations
  4. Supplementary Data
  5. Combining JCMT-SCUBA2 Images with Herschel and Planck Observations
  6. SED fitting
  7. Spatial Distribution of Dust Properties
  8. Column Density, Temperature, and Dust Opacity Index Distribution Maps
  9. Dust Property Trends with Galactocentric Radius
  10. The Structure of Spiral Arms
  11. Gaint Molecular Clouds
  12. Cloud Identification
  13. Giant Molecular Cloud Properties from Dendrogram

Figures (7)

  • Figure 1: The background color map shows the Herschel 250 $\mu$m image Fritz2012AASmith2012ApJ. The field of view of the HASHTAG survey SmithApJS is outlined in blue dot–dashed lines, while those of the JCMT large PI project and JCMT pilot project are shown in green solid and orange dashed lines, respectively.
  • Figure 2: The central panel shows the 850 $\mu$m continuum image of M31 at 14$"$ resolution, produced by combining Planck and JCMT-SCUBA2 observations. Orange dashed rectangles highlight eight zoomed-in, selected regions (A-H), to reveal detailed substructures. Regions A-F focus on inter-arm areas, while G and H display features within the spiral arm.
  • Figure 3: The 8$"$ resolution, 450 $\mu$m continuum image of M31 produced by combining Herschel and JCMT-SCUBA2 observations.
  • Figure 4: SEDs for pixels in different regions, constructed using Herschel 70/100/160/250/350/500 $\mu$m and JCMT-SCUBA2 850 $\mu$m measurements. The central pixel coordinates (RA/Dec) for each region are: 00:42:40.02; +41:17:29.36 (bulge region), 00:42:38.87; +41:27:35.34 (inter-arm region), and 00:41:05.48; +40:38:19.38 (on-arm region). The 70 and 100 $\mu$m measurements (blue points) are used as upper limits in the SED fitting.
  • Figure 5: The distribution of dust surface density (18$"$ angular resolution), temperature (18$"$ angular resolution), and $\beta$ (37$"$ angular resolution) obtained from the iterative SED fits. The detailed procedures are described in Section \ref{['section:res_t_n']}.
  • ...and 2 more figures