J/ApJ/953/164 ACA CO(J=2-1) mapping of M33. I. Molecular clouds (Muraoka+, 2023)
ACA CO(J=2-1) mapping of the nearest spiral galaxy M33.
I. Initial results and identification of molecular clouds.
Muraoka K., Konishi A., Tokuda K., Kondo H., Miura R.E., Tosaki T.,
Onodera S., Kuno N., Kobayashi M.I.N., Tsuge K., Sano H., Kitano N.,
Fujita S., Nishimura A., Onishi T., Saigo K., Yamada R.I., Demachi F.,
Tachihara K., Fukui Y., Kawamura A.
<Astrophys. J., 953, 164 (2023)>
=2023ApJ...953..164M 2023ApJ...953..164M
ADC_Keywords: Galaxies, nearby; Local group; Molecular clouds; Carbon monoxide;
Space velocities; Velocity dispersion
Keywords: Triangulum Galaxy ; Local Group ; Molecular clouds ;
Interstellar medium
Abstract:
We present the results of ALMA-ACA 7m array observations in
12CO(J=2-1), 13CO(J=2-1), and C18O(J=2-1) line emission toward
the molecular-gas disk in the Local Group spiral galaxy M33 at an
angular resolution of 7.31"x6.50" (30x26pc). We combined the ACA 7m
array 12CO(J=2-1) data with the IRAM 30m data to compensate for
emission from diffuse molecular-gas components. The ACA+IRAM combined
12CO(J=2-1) map clearly depicts the cloud-scale molecular-gas
structure over the M33 disk. Based on the ACA+IRAM 12CO(J=2-1) cube
data, we cataloged 848 molecular clouds with a mass range from
103-106M☉. We found that high-mass clouds (≥105M☉)
tend to associate with the 8µm bright sources in the spiral arm
region, while low-mass clouds (<105M☉) tend to be apart from
such 8µm bright sources and to exist in the inter-arm region. We
compared the cataloged clouds with GMCs observed by the IRAM 30m
telescope at 49pc resolution (IRAM GMC), and found that a small IRAM
GMC is likely to be identified as a single molecular cloud even in
ACA+IRAM CO data, while a large IRAM GMC can be resolved into multiple
ACA+IRAM clouds. The velocity dispersion of a large IRAM GMC is mainly
dominated by the line-of-sight velocity difference between small
clouds inside the GMC rather than the internal cloud velocity
broadening.
Description:
Observations toward M33 were carried out in Band 6 (211-275GHz) with
the Atacama Compact Array (ACA) 7m antennas between 2019 August and
2021 August (project code 2018.A.00058.S). The target molecular lines
were 12CO(J=2-1), 13CO(J=2-1), and C18O(J=2-1).
The target field was the rectangle with the size of 1100"x1180"
(4.5kpcx4.8kpc), covering most of the molecular-gas disk of M33. The
total number of mosaic fields is 3129.
In addition to this, we retrieved the ALMA archival data (project
code 2017.1.00901.S and 2019.1.01182.S), which also observed the
molecular-gas disk of M33 by ACA 7m antennas with almost the same
spectral settings as our observations.
To evaluate the missing flux of the ACA observations, we measured the
global 12CO(J=2-1) luminosities over the M33 disk obtained by the
ACA 7m antennas and by the IRAM 30m telescope
(Druard+ 2014A&A...567A.118D 2014A&A...567A.118D).
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------------
01 33 50.89 +30 39 36.6 M33 = NAME Triangulum Galaxy
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table3.dat 125 848 List of cataloged molecular clouds
fits/* . 4 CO(J=2-1) data cubes obtained with ACA
in FITS format
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Description of file:
(1) M33ACA7m+IRAM12CO21cubepbcor_kelvin.fits.tar.gz (661 MB):
12CO(J=2-1) data cube obtained with the ACA 7m array combined with
the IRAM 30m telescope, 7.31"x6.50" beam, 0.7km/s resolution
(2) M33ACA7m-only12CO21cubepbcor_kelvin.fits.tar.gz (660.6 MB):
12CO(J=2-1) data cube obtained with the ACA stand-alone mode
(7m array only), 7.31"x6.50" beam, 0.7km/s resolution
(3) M33ACA7m-only13CO21cubepbcor_kelvin.fits.tar.gz (331.5 MB):
13CO(J=2-1) data cube obtained with the ACA stand-alone mode
(7m array only), 7.72"x6.86" beam, 1.4km/s resolution
(4) M33ACA7m-onlyC18O21cubepbcor_kelvin.fits.tar.gz (289.9 MB):
C18O(J=2-1) data cube obtained with the ACA stand-alone mode
(7m array only), 7.82"x6.96" beam, 1.6km/s resolution
See also:
VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)
J/ApJS/149/343 : Giant molecular clouds in M33 (Engargiola+, 2003)
J/ApJ/633/871 : Positions and photometry of HII knots in M51 (Calzetti+, 2005)
J/AJ/131/2478 : M31 and M33 UBVRI photometry (Massey+, 2006)
J/AJ/134/2474 : Hα emission-line stars in 7 dwarfs gal. (Massey+, 2007)
J/ApJ/661/830 : Giant molecular clouds of M33 (Rosolowsky+, 2007)
J/ApJ/686/948 : CO in extragalactic giant molecular clouds (Bolatto+, 2008)
J/ApJS/178/56 : CO observations of LMC Giant Molecular clouds (Fukui+, 2008)
J/ApJ/703/517 : The Spitzer Local Volume Legacy: IR photometry (Dale+, 2009)
J/ApJS/184/1 : Molecular clouds in the LMC by NANTEN. II. (Kawamura+, 2009)
J/A+A/522/A3 : M33 CO(2-1) and HI integrated intensity maps (Gratier+, 2010)
J/A+A/542/A108 : Giant molecular clouds in M33 (Gratier+, 2012)
J/ApJ/761/37 : CO obs. in giant molecular clouds of M33 (Miura+, 2012)
J/ApJ/784/3 : The PAWS catalogs of GMCs and islands in M51 (Colombo+, 2014)
J/A+A/594/A28 : Planck Catalog of Galactic cold clumps (PGCC) (Planck+, 2016)
J/A+A/601/A146 : M33 molecular clouds & young clusters (Corbelli+, 2017)
J/ApJ/834/57 : MW molecular clouds from 12CO (Miville-Deschenes+, 2017)
J/ApJS/257/43 : PHANGS-ALMA: CO(2-1) imaging of galaxies (Leroy+, 2021)
J/ApJ/927/149 : Low-J CO line ratios for 152 CO map pairs (Leroy+, 2022)
J/ApJ/949/63 : CO survey toward SMC north with ACA. II. (Ohno+, 2023)
Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- Seq [1/848] Cloud identifier number
5- 12 F8.5 deg RAdeg [23.32/23.7] Right Ascension (J2000) (1)
14- 21 F8.5 deg DEdeg [30.49/31] Declination (J2000) (1)
23- 26 F4.2 kpc Rgal [0.07/5.6] Galactocentric radius (2)
28- 31 I4 km/s VLSR [-267/-101] Local Standard of Rest radial
velocity
33- 36 F4.1 pc Rad [6.8/71.6] Deconvolved radius
38- 41 F4.1 pc e_Rad [1.9/19] Uncertainty in Rad
43- 45 F3.1 km/s sigmav [1/6.1] Deconvolved velocity dispersion
47- 49 F3.1 km/s e_sigmav [0.2/2.5] Uncertainty in sigmav
51- 55 F5.1 10+4Msun MCO [0.7/264.3] Luminosity mass from
12CO(J=2-1) flux
57- 60 F4.1 10+4Msun e_MCO [0.1/13.3] Uncertainty in MCO
62- 66 F5.1 10+4Msun MVir [1/185.4] Mass inferred from virial theorem
68- 71 F4.1 10+4Msun e_MVir [1/53.1] Uncertainty in MVir
73- 77 F5.2 K.km/s I12CO [0.5/45.8] The 12CO(J=2-1) intensity (1)
79- 82 F4.2 K.km/s e_I12CO [0.04/0.3] Uncertainty in I12CO
84- 88 F5.1 --- S/N [6/139.5] Signal-to-Noise ratio of
12CO(J=2-1) brightness temperature (1)
90 A1 --- l_I13CO The 3σ limit flag on I13CO
91- 95 F5.2 K.km/s I13CO [0.14/7.4] The 13CO(J=2-1) intensity (1)
97- 100 F4.2 K.km/s e_I13CO [0.04/0.2]? Uncertainty in I13CO
102 A1 --- l_R13/12 The 3σ limit flag on R13/12
103- 107 F5.2 --- R13/12 [0.03/0.41] Intensity ratio of 13CO(J=2-1)
to 12CO (J=2-1) (1)
109- 112 F4.2 --- e_R13/12 [0/0.05]? Uncertainty in R13/12
114- 116 I3 deg PA [-90/90] Position angle of major axis,
φ (3)
118- 121 F4.1 --- b/a [1/15] Ratio between major and minor axes (4)
123- 125 I3 --- IRAM [23/550]? GMC counterpart identified with
IRAM 30m telescope (5)
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Note (1): At peak position of the cloud.
Note (2): From the IR center of M33 (1:33:50.9, 30:39:37).
Note (3): Measured counterclockwise from north to east.
Note (4): After the deconvolution by the observing beam (7.5").
Note (5): Corbelli et al. (2017, J/A+A/601/A146); <[CBB2017] NNN> in Simbad.
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History:
From electronic version of the journal for the table
* FITS 12CO(J=2-1) data cubes downloaded from Zenodo,
DOI:10.5281/zenodo.8157657
Licences: cc-by
* Zenodo: Creative Commons Attribution 4.0 International
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 25-Sep-2025