J/ApJS/282/39 JCMT SCUBA-2 obs. of M31 with Herschel & Planck data (Jiao+, 2026)
Deep Andromeda JCMT SCUBA-2 Observations. The Submillimeter Maps and Giant
Molecular Clouds.
Jiao S., Wu J., Liu H.B., Tsai C.-W., Lin Y., Li Di, Zhang Z.-Y.,
Cheng Yu, Feng L., Beuther H., Wang J., Lin L., den Brok J., Zhang L.,
Xu F., Meng F., Li Z., Keenan R.P., Yu S.-Y., Yu N., Zheng Z., Liu J.,
Liu Y., Ruan H., Deng F., Xiong Y.
<Astrophys. J. Suppl. Ser., 282, 39 (2026)>
=2026ApJS..282...39J 2026ApJS..282...39J
ADC_Keywords: Millimetric/submm sources; Interstellar medium; Galaxies, nearby;
Molecular clouds; Carbon monoxide
Keywords: Andromeda Galaxy ; Interstellar medium ; Galaxy structure ;
Giant molecular clouds ; Interstellar dust
Abstract:
We have carried out unprecedentedly deep, nearly confusion-limited
JCMT SCUBA-2 mapping observations on the nearest spiral galaxy, M31
(Andromeda). The 850µm image with a ∼50pc 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 interarm GMCs in M31, which are mostly unresolved or
marginally resolved. The masses of all these GMCs are in the range of
2x104-6x106M☉; the sizes are in the range of 30-130pc. They
follow a mass-size correlation, M∝Rc2.5. The interarm GMCs
are systematically less massive, more diffuse, colder, and have lower
star formation 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 in β may not be as large as has been proposed by
previous studies.
Description:
Prior to the James Clerk Maxwell Telescope (JCMT) large PI project, we
conducted pilot SCUBA-2 observations of M31 (JCMT project codes
M17AP007 and M17BP040, PI: Sihan Jiao), which were carried out over
the period of 2017 February-October.
To characterize the interarm clouds in detail, we performed follow-up
observations by using the IRAM 30m telescope (project ID: 059-18,
PI: Sihan Jiao), Northern Extended Millimeter Array (Project ID:
W18BW, PI: Sihan Jiao), and ALMA (project code: 2019.1.01847.S,
PI: Sihan Jiao). A comprehensive analysis of the interarm clouds in
this pilot region will be presented in Paper II (Jiao+ 2026,
in preparation).
Aiming to establish a comprehensive and detailed survey toward
interarm GMCs in M31, we completed a JCMT large PI project (JCMT
project code S19BP002, PI: Jingwen Wu) to survey the M31 interarm
regions with ∼280hr SCUBA-2 observations reaching a similar
sensitivity, <1.5mJy/beam, at the 850um band as in the previous pilot
study. The observed region covers an area of ∼1.7°x0.6°, from
the Galactic center to the Galactocentric radius of R∼15kpc, with
SCUBA-2 at 450 and 850um simultaneously.
M31 has been mapped using the PACS instrument, the SPIRE instrument on
Herschel, and the High Frequency Instrument on Planck. The following
analysis uses 100/160/250/350/500um Herschel data from
Fritz+ 2012A&A...546A..34F 2012A&A...546A..34F and Groves+ (2012MNRAS.426..892G 2012MNRAS.426..892G). The
Herschel maps have an angular resolution of 12.5", 13.3", 18.2",
24.5", and 36.0" at 100, 160, 250, 350, and 500um, respectively. We
retrieved the Planck High Frequency Instrument 353GHz image, which
is presented in Planck Coll. (2015A&A...582A..28P 2015A&A...582A..28P).
To investigate the molecular hydrogen gas content in M31, we used
12CO J=1-0 observations taken by the IRAM 30m telescope. This was
taken during 1995-2001, covering an area of about 2.0°x0.5°
(extending to ∼18kpc) with a velocity resolution of 2.6km/s and an
angular resolution of 23" (see details in Section 4.7.1).
The data products used in this study, including the JCMT SCUBA-2 maps
as well as the spectral energy distribution (SED)-derived dust
property maps, are publicly available at
https://github.com/SihanJiao/Deep-Andromeda-JCMT-SCUBA2-Observations.
Objects:
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RA (ICRS) DE Designation(s)
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00 42 44.33 +41 16 07.5 M31 = NAME Andromeda Galaxy
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 97 572 Physical properties of selected regions
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See also:
VI/139 : Herschel Observation Log (Herschel Science Centre, 2013)
J/ApJ/654/240 : Giant molecular clouds in M31 (Rosolowsky+, 2007)
J/ApJS/173/293 : UV-Optical galaxy color-magnitude diagram I. (Wyder+, 2007)
J/A+A/487/993 : MAMBO Mapping of c2d Clouds and Cores (Kauffmann+, 2008)
J/AJ/136/2782 : Star formation efficiency in nearby galaxies (Leroy+, 2008)
J/ApJ/723/492 : Physical properties of GRS Mocs (Roman-Duval+, 2010)
J/A+A/542/A108 : Giant molecular clouds in M33 (Gratier+, 2012)
J/A+A/567/A71 : M31 Herschel images (Viaene+, 2014)
J/ApJ/784/3 : The PAWS cat. of GMCs and islands in M51 (Colombo+, 2014)
J/ApJ/798/58 : HELGA VI. Giant molecular cloud assoc. in M31 (Kirk+, 2015)
J/A+A/590/A131 : Giant molecular filaments in the MW (Abreu-Vicente+, 2016)
J/A+A/586/A50 : CMZ H2CO temperature maps (Ginsburg+, 2016)
J/MNRAS/465/1789 : SCUBA-2 Cosmology Legacy Survey (Geach+, 2017)
J/ApJ/834/57 : MW molecular clouds from 12CO (Miville-Deschenes+, 2017)
J/MNRAS/477/4116 : GAMA. galaxy structure across green valley (Kelvin+, 2018)
J/ApJ/862/13 : The Carnegie-Irvine Galaxy Survey. VI. Spirals (Yu+, 2018)
J/MNRAS/483/4291 : Properties of JCMT CO(3-2) molecular clouds (Colombo+, 2019)
J/MNRAS/493/351 : A large catalogue of molecular clouds (Chen+, 2020)
J/A+A/634/A83 : THOR DR2 source list (Wang+, 2020)
J/ApJS/257/43 : PHANGS-ALMA: CO(2-1) imaging of galaxies (Leroy+, 2021)
J/ApJ/945/L19 : SFR & molecular gas surface densities (Sun+, 2023)
J/A+A/692/A226 : Cloud matching in M33. II. (Keilmann+, 2024)
http://hashtag.astro.cf.ac.uk/DR1.html : HASHTAG DR1 homepage
http://www.esa.int/Science_Exploration/Space_Science/Planck : Planck homepage
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/572] Running sequence number
5- 9 A5 --- OnArm On-arm cloud?
11- 12 I2 h RAh [0] Hour of right ascension (J2000)
14- 15 I2 min RAm [40/45] Minute of right ascension (J2000)
17- 21 F5.2 s RAs Second of right ascension (J2000)
22 A1 --- DE- [+] Sign of declination (J2000)
23- 24 I2 deg DEd [40/41] Degree of declination (J2000)
26- 27 I2 arcmin DEm Arcminute of declination (J2000)
29- 32 F4.1 arcsec DEs Arcsecond of declination (J2000)
34- 38 I5 pc2 Area [2974/60175] Physical area
40- 46 F7.3 pc Rc [30.7/138.4] Effective radius
48- 53 F6.3 kpc R [0.4/14.6] Annular radius
55- 58 F4.1 K Tdust [11.1/31.1] Dust temperature
60- 63 F4.2 --- beta [0.93/2.43] Dust opacity index
65- 68 F4.2 Msun/pc2 SigDust [0.09/1.7] Dust surface density
70- 75 F6.2 Msun/pc2 SigGas [5.8/201.8] Gas surface density
77- 81 F5.2 10+5Msun Mass [0.17/59.9] Cloud mass
83- 87 F5.2 cm-3 nH [4/95.6] Gas mean volume density
89- 97 F9.6 Msun/yr/kpc2 SFR [-0.0003/0.05] Star Formation Rate
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History:
From electronic version of the journal
License: CC-BY-4.0
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 22-Jul-2026