Title:	Detection of H I 21 centimeter absorption by the warm neutral medium
Authors:	Carilli, C.L. Dwarakanath, K.S. Goss, W.M.
Keywords:	ISM: STRUCTURE ISM: ATOMS, GALAXY: FUNDAMENTAL PARAMETERS RADIO LINES: ISM
Issue Date:	20-Jul-1998
Publisher:	The University of Chicago Press for the American Astronomical Society
Citation:	Astrophysical Journal Letters, 1998, Vol.502, p.L79-L83
Abstract:	We have detected H I 21 cm line absorption by the warm neutral medium (WNM) using the Westerbork synthesis radio telescope. The absorption was detected toward Cygnus A at LSR velocities of -40 and -70 km s ^{-1} . These two velocity ranges were previously identified as being relatively free of cold absorbing clouds. The measured optical depth for the WNM along the line of sight to Cygnus A is (8.9+/-1.9)x10^{-4} at -70 km s ^{-1} and (8.5+/-2.0)x10^{-4} at -40 km s ^{-1} , with corresponding spin temperatures of 6000+/-1700 and 4800+/-1600 K, respectively. The volume filling factor for the WNM appears to be fairly high ( f~0.4 ).
URI:	http://hdl.handle.net/2289/1416
ISSN:	0004-637X 1538-4357 (online)
Alternative Location:	http://dx.doi.org/10.1086/311483
Copyright:	(1998) by the American Astronomical Society.
Appears in Collections:	Research Papers (A&A)

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