J/A+A/687/A26 SuperCAM CO(3-2) APEX survey in SMC (Saldano+, 2024)
SuperCAM CO(3-2) APEX survey at a 6 pc resolution in the
Small Magellanic Clouds.
Saldano H.P., Rubio M., Bolatto A.D., Sandstrom K, Swift B.J., Verdugo C.,
Jameson K., Walker C.K., Kulesa C., Spilker J., Bergman P., Salazar G.A.
<Astron. Astrophys. 687, A26 (2024)>
=2024A&A...687A..26S 2024A&A...687A..26S (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Carbon monoxide ; Radio lines ;
Interstellar medium
Keywords: ISM: abundances - ISM: clouds - ISM: molecules - galaxies: dwarf -
galaxies: individual: SMC - submillimeter: ISM
Abstract:
The Small Magellanic Cloud (SMC) is an ideal laboratory for studying
the properties of star-forming regions thanks to its low metallicity,
which has an impact on the molecular gas abundance. However, a small
number of molecular gas surveys of the entire galaxy have been carried
out in the last few years, limiting the measurements of interstellar
medium (ISM) properties in a homogeneous manner.
We present the CO(3-2) APEX survey at a 6pc resolution of the
bar of the SMC, observed with the SuperCAM receiver attached to the
APEX telescope. This high-resolution survey has allowed us to study
certain properties of the ISM and to identify CO clouds in the
innermost parts of the H2 envelopes.
We adopted the CO analysis in the SMC bar comparing the CO(3-2) survey
with that of the CO(2-1) of a similar resolution.We studied the
CO(3-2)-to-CO(2-1) ratio (R32), which is very sensitive to the
environment properties (e.g., star-forming regions). We analyzed the
correlation of this ratio with observational quantities that trace the
star formation such as the local CO emission, the Spitzer color
[70=160], and the total IR surface brightness measured from the
Spitzer and Herschel bands. For the identification of the CO(3-2)
clouds, we used the CPROPS algorithm, which allowed us to measure the
physical properties of the clouds. We analyzed the scaling
relationships of such physical properties.
We obtained R32=0.65±0.02 for the SW bar and a slightly higher
ratio, R32=0.7±0.1; for N66 in the SMC.We found that R32 varies
from region to region, depending on the star formation activity. In
regions dominated by HII and photo-dissociated regions (e.g., N22,
N66) R_32) tends to be higher than the median values. Meanwhile, lower
values were found toward quiescent clouds.We also found that R32 is
correlated with the IR color [70/160] and the total IR surface
brightness. This finding indicates that R32 increases with
environmental properties, such as the dust temperature, total gas
density, and radiation field. We identified 225 molecular clouds with
sizes of R>1.5pc and signal-to-noise ratios (S/N) of >3, of which only
17 are well resolved CO(3-2) clouds with S/N≳5. These 17 clouds
follow consistent scaling relationships to the inner Milky Way clouds
but with some departures. For instance, CO(3-2) tends to be less
turbulent and less luminous than the inner Milky Way clouds of similar
sizes. Finally, we estimated a median virial-based CO(3-2)-to-H2
conversion factor of 12.6+10-7M☉ (K.km/s/pc2)-1 for the
total sample.
Description:
We present a CO(3-2) survey at 6pc resolution in the Small Magellanic
Cloud (SMC) obtained with the SuperCAM instrument attached to the APEX
telescope. We perform a catalog of 225 molecular clouds in the whole
bar of the SMC. We use the CPROPS algorithm to identify the molecular
clouds and estimate their main CO parameters. We analyze the scaling
relations between the radius, velocity dispersion, luminosity, and
virial mass of the SMC clouds, and they are compared with those of
other low-metallicity galaxies and other surveys performed in the SMC
but using different J-transitions.
Parameters of CO clouds in the SMC are reported. All these parameters,
which were obtained by using CPROPS (Rosolowsky et al.,
2006PASP..118..590R 2006PASP..118..590R), are corrected for bias sensitivity and
resolution. We provide the APEX data cubes used in this article. Three
large regions were observed in the SMC, where the CO emission in the
transition J=3-2 was detected. All data cubes are in the antenna
temperature unit. We used a beam efficiency of 0.38 to convert the
antenna temperature to the main beam brightness temperature unit.
These cubes are those given by the automatic procedure developed by
the SORAL team, therefore, we recommend performing a new baseline fit
as we made for our article (see Sec. 2).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 96 225 Physical parameters of CO(3-2) clouds in the SMC
list.dat 104 3 List of fits files
fits/* . 3 Individual fits files
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 3 I3 --- ID Cloud number
5- 6 I2 h RAh Right ascension (J2000)
8- 9 I2 min RAm Right ascension (J2000)
11- 15 F5.2 s RAs Right ascension (J2000)
17 A1 --- DE- Declination sign (J2000)
18- 19 I2 deg DEd Declination (J2000)
21- 22 I2 arcmin DEm Declination (J2000)
24- 28 F5.2 arcsec DEs Declination (J2000)
31- 34 F4.1 pc R ?=0 Deconvolved radius
38- 40 F3.1 pc e_R ?=0 Deconvolved radius uncertainty
42- 46 F5.1 km/s Vc Peak Velocity
48- 50 F3.1 km/s e_Vc Peak Velocity uncertainty
52- 54 F3.1 km/s sigma Velocity dispersion
56- 58 F3.1 km/s e_sigma Velocity dispersion uncertainty
60- 62 F3.1 K Tp Peak temperature
64- 66 F3.1 K e_Tp Peak temperature uncertainty
68- 71 F4.1 10+2K.km/s ICO CO(3-2) intensity
73- 75 F3.1 10+2K.km/s e_ICO CO(3-2) intensity uncertainty
77- 80 F4.1 10+2K.km/s/pc2 LCO CO(3-2) luminosity
82- 84 F3.1 10+2K.km/s/pc2 e_LCO CO(3-2) luminosity uncertainty
86- 90 F5.1 10+3Msun Mvir ?=0 Virial Mass
93- 96 F4.1 10+3Msun e_Mvir ?=0 Virial Mass uncertainty
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Name of region
11- 12 I2 h RAh Right ascension (J2000)
14- 15 I2 min RAm Right ascension (J2000)
17- 20 F4.1 s RAs Right ascension (J2000)
22 A1 --- DE- Declination sign (J2000)
23- 24 I2 deg DEd Declination (J2000)
26- 27 I2 arcmin DEm Declination (J2000)
29- 32 F4.1 arcsec DEs Declination (J2000)
34- 36 I3 --- Nx Number of pixels along X-axis
38- 40 I3 --- Ny Number of pixels along Y-axis
42- 44 I3 --- Nz Number of slices
46 I1 arcsec px Pixel size
48- 49 I2 arcsec HPBW Final beam width
51- 55 F5.3 km/s dV Final spectral resolution
57- 60 F4.1 km/s lvel Lower value of velocity interval
62- 66 F5.1 km/s hvel Higher value of velocity interval
68- 99 A32 --- FileName Name of FITS file in subdirectory fits
101-104 I4 Mbyte Size Size of FITS file
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Acknowledgements:
Hugo Saldano, hpablohugo(at)gmail.com
(End) Patricia Vannier [CDS] 24-May-2024