J/A+A/577/A127 W49A JCMT Spectral Legacy Survey spectroscopy (Nagy+, 2015)
Physical and chemical differentiation of the luminous star-forming region W49A.
Results from the JCMT Spectral Legacy Survey.
Nagy Z., Van Der Tak F.F.S., Fuller G.A., Plume R.
<Astron. Astrophys., 577, A127-127 (2015)>
=2015A&A...577A.127N 2015A&A...577A.127N (SIMBAD/NED BibCode)
ADC_Keywords: Associations, stellar ; Spectroscopy
Keywords: stars: formation - ISM: molecules
Abstract:
The massive and luminous star-forming region W49A is a well-known
Galactic candidate to probe the physical conditions and chemistry
similar to those expected in external starburst galaxies. We aim to
probe the physical and chemical structure of W49A on a spatial scale
of ∼0.8pc based on the JCMT Spectral Legacy Survey, which covers the
frequency range between 330 and 373GHz. The wide 2x2-arcmin field and
the high spectral resolution of the HARP instrument on JCMT provides
information on the spatial structure and kinematics of the cloud
traced by the observed molecular lines. For species where multiple
transitions are available, we estimate excitation temperatures and
column densities using a population diagram method that takes beam
dilution and optical depth corrections into account. We detected 255
transitions corresponding to 63 species in the 330-373GHz range at the
center position of W49A. Excitation conditions can be probed for 14
molecules, including the complex organic molecules CH3CCH, CH3CN,
and CH3OH. The chemical composition suggests the importance of
shock, photon-dominated region (PDR), and hot core chemistry. Many
molecular lines show a significant spatial extent across the maps
including CO and its isotopologues, high density tracers (e.g., HCN,
HNC, CS, HCO+), and tracers of UV irradiation (e.g., CN and C2H).
The spatially extended species reveal a complex velocity-structure of
W49A with possible infall and outflow motions. Large variations are
seen between the subregions with mostly blue-shifted emission toward
the eastern tail, mostly red-shifted emission toward the northern
clump, and emission peaking around the expected source velocity toward
the southwest clump. A comparison of column density ratios of
characteristic species observed toward W49A to Galactic PDRs suggests
that while the chemistry toward the W49A center is driven by a
combination of UV irradiation and shocks, UV irradiation dominates for
the northern clump, eastern tail, and southwest clump regions. A
comparison to a starburst galaxy and an active galactic nucleus
suggests similar C2H, CN, and H2CO abundances (with respect to the
dense gas tracer 34CS) between the ∼0.8pc scale probed for W49A and
the >1kpc regions in external galaxies with global star formation.
Description:
We carried out the SLS observations using the 16-receptor (spatial
pixel) Heterodyne Array Receiver Programme B (HARP-B, 325-375GHz) and
the Auto-Correlation Spectral Imaging System (ACSIS) correlator
at the James Clerk Maxwell Telescope1 (JCMT) on Mauna Kea, Hawaii. We
carried out the observations in jiggle position switch mode, sampled
every 7.5" for a 2x2-arcmin field centered on
RA=19:10:13.4; DE=09:06:14 (J2000).
Objects:
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RA (2000) DE Designation(s)
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19 10 15.7 +09 06 05 W49A = GAL 043.169+00.00
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 118 255 The detected species toward the central position
of the JCMT Spectral Legacy Survey (SLS) field
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Mol Molecule
20- 21 A2 --- n_Mol [abc*C ] Note on Mol (1)
23- 46 A24 --- Trans Transition
47- 54 F8.1 MHz Freq Frequency
56- 62 F7.2 K Eup ?=- Upper level energy
64- 70 E7.3 s-1 Aij ?=- Einstein coefficient
72- 78 F7.2 K.km/s IntTmbdv ? Integrated line intensity
80- 83 F4.2 K.km/s e_IntTmbdv ? rms uncertainty on IntTmbdv
85- 89 F5.2 km/s VLSR ? LSR velocity
91- 95 F5.3 km/s e_VLSR ? rms uncertainty on VLSR
97-101 F5.2 km/s FWHM ? FWHM of the line
103-107 F5.2 km/s e_FWHM ? rms uncertainty on FWHM (2)
109-113 F5.2 K Tpeak ? Peak temperature
115-118 F4.2 K e_Tpeak ? rms uncertainty on Tpeak
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Note (1): Notes as follows:
* = transitions were detected toward AFGL 2591 in the SLS survey
(Van der Wiel, 2011, Ph.D. Thesis, Univ. Groningen)
C = transitions have a non-Gaussian line profile. The FWHM line widths of
these asymmetric lines are from a Gaussian fitting. Their intensity is
obtained by integrating over the whole line and their VLSR
is the velocity at Tpeak.
a = May be blended with SO17O.
b = Probably blended with 34SO2152,14-141,13 at 358988MHz.
c = HC3N 41-40 is probable, but the line intensity is not consistent with
its other three detected transitions.
Note (2): The parameters without error bars are fixed parameters in the fit.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 06-Aug-2015