J/A+A/641/A97 ALMA Magellanic Bridge A molecular clouds (Valdivia-Mena+, 2020)
ALMA resolves molecular clouds in metal-poor Magellanic Bridge A.
Valdivia-Mena M.T., Rubio M., Bolatto A.D., Saldano H.P., Verdugo C.
<Astron. Astrophys. 641, A97 (2020)>
=2020A&A...641A..97V 2020A&A...641A..97V (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; Interstellar medium ; Radio sources
Keywords: ISM: clouds - Magellanic Clouds - ISM: molecules - submillimeter: ISM
Abstract:
The Magellanic Bridge is a tidal feature located between both
Magellanic Clouds, containing young stars formed in situ. Its
proximity allows high-resolution studies of molecular gas, dust and
star formation in a tidal, low metallicity environment. Our goal is to
characterize gas and dust emission in Magellanic Bridge A, the source
with the highest 870um excess of emission found in single dish
surveys. Using the ALMA telescope including the Morita Array, we
mapped with sub-parsec resolution a 3arcmin, field of view centered on
the Magellanic Bridge A molecular cloud, in 1.3mm continuum emission
and 12CO(2-1 line emission. This region was also mapped in continuum
at 870um and in 12CO(2-1) line emission at ∼6pc resolution with the
APEX telescope. To study its dust properties, we also use archival
Herschel and Spitzer data. We combine the ALMA and APEX 12CO(2-1)
line cubes to study the molecular gas emission. Magallanic Bridge A
breaks up into two distinct molecular clouds in dust and 12CO(2-1)
emission, which we call North and South. Dust emission in the North
source, according to our best parameters from fitting the far-infrared
fluxes, is ∼3K colder than in the South source in correspondence to
its less developed star formation. Both dust sources present large
submillimeter excesses in LABOCA data: according to our best fits the
excess over the modified blackbody (MBB) fit to the Spitzer/Herschel
continuum is E(870um)∼7 and E(870um)∼3 for the North and South sources
respectively. Nonetheless, we do not detect the corresponding 1.3mm
continuum with ALMA. Our limits are compatible with the extrapolation
of the MBB fits and therefore we cannot independently confirm the
excess at this longer wavelength. The 12CO(2-1) emission is
concentrated in two parsec-sized clouds with virial masses around 400
and 700M☉ each. Their bulk volume densities are
n(H2)∼0.7-2.6x103cm-3, larger than typical bulk densities of
Galactic molecular clouds. The 12CO luminosity to H2 mass
conversion factor αCO is 6.5 and 15.3M☉/(K.(km/s)pc2)
for the North and South clouds, calculated using their respective
virial masses and 12CO(2-1) luminosities. Gas mass estimates from
our MBB fits to dust emission yields masses M∼1.3x103M☉ and
2.9x103M☉ for North and South respectively, a factor of ∼4
larger than the virial masses we infer from 12CO.
Description:
Magellanic Bridge A was observed with ALMA, located at Llano de
Chajnantor in Atacama, Chile. We used Band 6 observations taken with
the 12m array and the 7m array (also known as the Morita Array), which
include continuum emission observations and the 12CO(2-1) line
emission data. In this paper we refer to the 12CO(2-1) line as
CO(2-1). Observations were performed in separate cycles: we used 7m
array data taken during Cycle 1 and 12m array observations taken in
Cycle 2. The datasets belong to project 2012.1.00683.S (PI M. Rubio).
Objects:
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RA (2000) DE Designation(s)
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03 11 -77.5 Magellanic Bridge = NAME Magellanic Bridge
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 180 2 List of fits images
fits/* . 2 Individual fits images
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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 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 53 A26 "datime" Obs.date Observation date
55- 61 F7.3 GHz Freq ? Observed frequency
63- 65 I3 Kibyte size Size of FITS file
67-119 A53 --- FileName Name of FITS file, in subdirectory fits
121-180 A60 --- Title Title of the FITS file
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Acknowledgements:
Maria Valdivia, maria.valdivia(at)ug.uchile.cl
(End) Patricia Vannier [CDS] 27-Aug-2020