J/ApJ/949/63 CO survey toward SMC north with ACA. II. CO clouds (Ohno+, 2023)
An unbiased CO survey toward the northern region of the Small Magellanic Cloud
with the Atacama Compact Array.
II. CO cloud catalog.
Ohno T., Tokuda K., Konishi A., Matsumoto T., Sewilo M., Kondo H.,
Sano H., Tsuge K., Zahorecz S., Goto N., Neelamkodan N., Wong T.,
Fukushima H., Takekoshi T., Muraoka K., Kawamura A., Tachihara K.,
Fukui Y., Onishi T.
<Astrophys. J., 949, 63 (2023)>
=2023ApJ...949...63O 2023ApJ...949...63O
ADC_Keywords: Carbon monoxide; Magellanic Clouds; Molecular clouds;
Interstellar medium; Infrared sources
Keywords: Local Group ; Small Magellanic Cloud ; Molecular clouds ;
Star formation ; Interstellar medium ; Young stellar objects
Abstract:
The nature of molecular clouds and their statistical behavior in
subsolar metallicity environments are not fully explored yet. We
analyzed data from an unbiased CO(J=2-1) survey at the spatial
resolution of ∼2pc in the northern region of the Small Magellanic
Cloud with the Atacama Compact Array to characterize the CO cloud
properties. A cloud-decomposition analysis identified
426 spatially/velocity-independent CO clouds and their substructures.
Based on the cross-matching with known infrared catalogs by Spitzer
and Herschel, more than 90% CO clouds show spatial correlations with
point sources. We investigated the basic properties of the CO clouds
and found that the radius-velocity linewidth (R-σv) relation
follows the Milky Way-like power-law exponent, but the intercept is
∼1.5 times lower than that in the Milky Way. The mass functions
(dN/dM) of the CO luminosity and virial mass are characterized by an
exponent of ∼1.7, which is consistent with previously reported values
in the Large Magellanic Cloud and in the Milky Way.
Description:
This study uses the ALMA archival CO data in the SMC northern region
(2017.A.00054.S). The available data set includes the CO(J=2-1) and
CO(J=1-0) lines, and 1.3/2.6 mm continuum data with a field coverage
of ∼0.26deg2. The angular resolution and sensitivity of CO(J=2-1)
are 6.9"x6.6" (∼2pc) and ∼0.06K, respectively. The Cube data with a
velocity-channel width of 0.5km/s were used throughout the analysis in
this paper. The resultant detection limit in the CO(J=2-1) luminosity
is ∼1.0K.km/s.pc2 (see Paper I, Tokuda+ 2021ApJ...922..171T 2021ApJ...922..171T).
Cross-matching analysis between CO and Spitzer + Herschel infrared
sources; see Section 3.3.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 107 426 Physical properties of CO trunks
table2.dat 102 257 Physical properties of CO leaves
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See also:
II/305 : SAGE LMC and SMC IRAC Source Catalog (IPAC 2009)
J/ApJ/428/693 : Rosette Nebula and Maddalena Cloud structures (Williams+ 1994)
J/ApJ/551/852 : FCRAO CO survey of the outer Galaxy (Heyer+, 2001)
J/ApJS/149/343 : Giant molecular clouds in M33 (Engargiola+, 2003)
J/ApJ/655/212 : S3MC IRAC and MIPS photometry (Bolatto+, 2007)
J/ApJ/669/327 : S3MC: YSOs in N66, in SMC (Simon+, 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/AJ/142/103 : Cool evolved stars in SAGE-SMC and SAGE-LMC (Boyer+, 2011)
J/ApJS/197/16 : CO observations of LMC molecular clouds (MAGMA). (Wong+, 2011)
J/AJ/146/62 : HERschel HERITAGE in Magellanic Clouds (Meixner+, 2013)
J/ApJ/778/15 : SAGE-SMC III. Young stellar objects (Sewilo+, 2013)
J/ApJ/784/3 : The PAWS catalogs of GMCs and islands in M51 (Colombo+, 2014)
J/AJ/148/124 : Herschel key program Heritage (Seale+, 2014)
J/ApJ/835/55 : AzTEC/ASTE survey at 1.1mm toward the SMC (Takekoshi+, 2017)
J/ApJ/853/175 : 12CO & 13CO cores & clumps in LHA 120-N 55 (Naslim+, 2018)
J/ApJ/854/154 : N159 12CO and 13CO (2-1) clumps (Nayak+, 2018)
J/ApJ/904/13 : RVel for 10 giant eclipsing binaries (Graczyk+, 2020)
J/A+A/641/A97 : ALMA Magellanic Bridge A mol. clouds (Valdivia-Mena+, 2020)
J/ApJ/938/82 : CO mol. clumps and YSOs in NGC 602 region (O'Neill+, 2022)
J/A+A/672/A153 : CO(2-1) survey at 9pc resolution in SMC (Saldano+, 2023)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [0/425] Sequential trunk identifier used
in this work
5- 10 F6.3 deg RAdeg [14.42/17.3] Right Ascension (J2000)
12- 18 F7.3 deg DEdeg [-72.4/-71.8] Declination (J2000)
20- 24 F5.1 km/s Vel [116.1/192.5] Centroid velocity
26- 29 F4.2 km/s dV [0.27/3.44] Linewidth, σv
31- 34 F4.2 km/s e_dV [0.02/0.6] Uncertainty in dV
36- 39 F4.1 arcsec amaj [1.9/43.1] rms size of the major axis,
σmaj
41- 44 F4.1 arcsec bmin [1.4/18.5] rms size of the minor axis,
σmin
46- 51 F6.1 deg PA [-179.1/179.1] Position angle of the
major axis
53- 56 F4.1 K Tpeak [0.4/10.4] Brightness temperature, peak
value in voxels
58- 63 F6.1 K.pc2.km/s LCO2-1 [1.8/2625.2] CO(J=2-1) luminosity
65- 67 F3.1 K.pc2.km/s e_LCO2-1 [0.1/1.8] Uncertainty in LCO2-1
69- 73 F5.2 pc Rdeconv [0.16/15.6] Beam deconvolution size,
parsecs at D=62kpc
75- 78 F4.2 pc e_Rdeconv [0.02/0.3] Uncertainty in Rdeconv
80- 85 I6 Msun Mvir [45/191255] Virial mass,
1040*dV^2*Rdeconv (G1)
87- 90 I4 Msun e_Mvir [108/3147] Uncertainty in Mvir
92- 95 F4.1 10+21cm-2 NH2 [0.4/30.1] Column density, H2 (G2)
97- 101 I5 Msun MCO [32/47329] Total gas mass (G2)
103- 105 I3 100cm-3 nH2 [1/780] Volume density, H2 (G2)
107 A1 --- IR [AB ] IR source (1)
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Note (1): Code as follows:
A = Spitzer+Herschel YSO source (94 occurrences)
B = Spitzer YSO source (303 occurrences)
Blanks indicate starless cloud candidates (29 occurrences).
See Section 3.3.
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Byte-by-byte Description of file: table2.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [0/256] Sequential leaf identifier used
in this work
5- 10 F6.3 deg RAdeg [14.46/17.12] Right Ascension (J2000)
12- 18 F7.3 deg DEdeg [-72.3/-71.86] Declination (J2000)
20- 24 F5.1 km/s Vel [140.5/190.5] Centroid velocity
26- 29 F4.2 km/s dV [0.24/1.7] Linewidth, σv
31- 34 F4.2 km/s e_dV [0.05/0.5] Uncertainty in dV
36- 39 F4.1 arcsec amaj [1.9/11] Rms size of the major axis,
σmaj
41- 43 F3.1 arcsec bmin [1.1/6.2] Rms size of the minor axis,
σmin
45- 50 F6.1 deg PA [-179.4/179.5] Position angle of the
major axis
52- 55 F4.1 K Tpeak [0.4/10.4] Brightness temperature, peak
value in voxels
57- 61 F5.1 K.pc2.km/s LCO2-1 [2.6/608.4] CO(J=2-1) luminosity
63- 65 F3.1 K.pc2.km/s e_LCO2-1 [0.2/1.0] Uncertainty in LCO2-1
67- 70 F4.2 pc Rdeconv [0.06/4.34] Beam deconvolution size,
parsecs at D=62kpc
72- 75 F4.2 pc e_Rdeconv [0.04/0.32] Uncertainty in Rdeconv
77- 81 I5 Msun Mvir [21/11513] Virial mass, 1040*dV^2*Rdeconv
(G1)
83- 85 I3 Msun e_Mvir [76/819] Uncertainty in Mvir
87- 90 F4.1 10+21cm-2 NH2 [0.5/28.4] Column density, H2 (G2)
92- 96 I5 Msun MCO [47/10969] Total gas mass (G2)
98- 102 I5 100cm-3 nH2 [1/84116] Volume density, H2 (G2)
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Global notes:
Note (G1): virial mass, Mvir=1040*dv2*Rdeconv (Solomon+ 1987ApJ...319..730S 1987ApJ...319..730S)
assuming the density profile of p∝r-1, ignoring the effect of
external pressure and magnetic field.
Note (G2): The peak integrated intensity was used to calculate the H2
column density (NH2) with the assumptions of CO-to-H2 conversion
factor, XCO=7.5*1020cm-2(K.km.s-1)-1 (Muraoka+ 2017ApJ...844...98M 2017ApJ...844...98M)
in the SMC and intensity ratio of CO(J=2-1)/CO(J=1-0), R2-1/1-0 of
0.9 (Bolatto+ 2003ApJ...595..167B 2003ApJ...595..167B; Paper I, Tokuda+ 2021ApJ...922..171T 2021ApJ...922..171T).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-Jul-2025