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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 (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: --------------------------------------------------- RA (2000) DE Designation(s) --------------------------------------------------- 19 10 15.7 +09 06 05 W49A = GAL 043.169+00.00 --------------------------------------------------- File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file tablea1.dat 118 255 The detected species toward the central position of the JCMT Spectral Legacy Survey (SLS) field
Byte-by-byte Description of file: tablea1.dat
Bytes Format Units Label Explanations
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 IntTmbdv ? Integrated line intensity 80- 83 F4.2 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
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.
History: From electronic version of the journal
(End) Patricia Vannier [CDS] 06-Aug-2015
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