Discovery of carbon radio recombination lines in absorption towards Cygnus A
Journal article, 2014
We present the first detection of carbon radio recombination line absorption along the line of sight to Cygnus A. The observations were carried out with the Low Frequency Array in the 33-57 MHz range. These low-frequency radio observations provide us with a new line of sight to study the diffuse, neutral gas in our Galaxy. To our knowledge this is the first time that foreground Milky Way recombination line absorption has been observed against a bright extragalactic background source. By stacking 48 carbon alpha lines in the observed frequency range we detect carbon absorption with a signal-to-noise ratio of about 5. The average carbon absorption has a peak optical depth of 2 x 10(-4), a line width of 10 km s(-1) and a velocity of +4 km s(-1) with respect to the local standard of rest. The associated gas is found to have an electron temperature T-e similar to 110 K and density n(e) similar to 0.06 cm(-3). These properties imply that the observed carbon alpha absorption likely arises in the cold neutral medium of the Orion arm of the Milky Way. Hydrogen and helium lines were not detected to a 3 Sigma peak optical depth limit of 1.5 x 10(-4) for a 4 km s(-1) channel width. Radio recombination lines associated with Cygnus A itself were also searched for, but are not detected. We set a 3 Sigma upper limit of 1.5 x 10(-4) for the peak optical depth of these lines for a 4 km s(-1) channel width.
structure-local interstellar matter-radio lines
ISM
General-IsM
IsM.
Author
J. B. R. Oonk
Netherlands Institute for Radio Astronomy (ASTRON)
R. J. van Weeren
Harvard-Smithsonian Center for Astrophysics
Leiden University
Netherlands Institute for Radio Astronomy (ASTRON)
F. Salgado
Leiden University
L. K. Morabito
Leiden University
Aggm Tielens
Leiden University
H. Rottgering
Leiden University
A. Asgekar
Netherlands Institute for Radio Astronomy (ASTRON)
G. J. White
Open University
STFC Rutherford Appleton Laboratory
A. Alexov
Space Telescope Science Institute (STScI)
University of Amsterdam
J. Anderson
Max-Planck Institute for Radio Astronomy
I. M. Avruch
Netherlands Institute for Space Research (SRON)
Fabien Batejat
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
R. Beck
Max-Planck Institute for Radio Astronomy
M. E. Bell
The University of Sydney
I. van Bemmel
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Bentum
Netherlands Institute for Radio Astronomy (ASTRON)
G. Bernardi
Square Kilometre Array, South Africa
Rhodes University
P. Best
University of Edinburgh
A. Bonafede
University of Hamburg
F. Breitling
Leibniz Institute for Astrophysics Potsdam
M. Brentjens
Netherlands Institute for Radio Astronomy (ASTRON)
J. Broderick
University of Southampton
M. Brüggen
University of Hamburg
H. R. Butcher
Australian National University
B. Ciardi
Max Planck Institute for Astrophysics
John Conway
Chalmers, Earth and Space Sciences, Onsala Space Observatory
A. Corstanje
Radboud University
F. De Gasperin
University of Hamburg
E. de Geus
Netherlands Institute for Radio Astronomy (ASTRON)
M. de Vos
Netherlands Institute for Radio Astronomy (ASTRON)
S. Duscha
Netherlands Institute for Radio Astronomy (ASTRON)
J. Eisloffel
Thüringer Landessternwarte Tautenburg
D. Engels
Hamburg Observatory
J. van Enst
Netherlands Institute for Radio Astronomy (ASTRON)
H. Falcke
Netherlands Institute for Radio Astronomy (ASTRON)
Radboud University
R. A. Fallows
Netherlands Institute for Radio Astronomy (ASTRON)
R. Fender
University of Southampton
C. Ferrari
Université Nice Sophia Antipolis (UNS)
W. Frieswijk
Netherlands Institute for Radio Astronomy (ASTRON)
M. A. Garrett
Leiden University
Netherlands Institute for Radio Astronomy (ASTRON)
J. Griessmeier
University of Orléans
J. P. Hamaker
Netherlands Institute for Radio Astronomy (ASTRON)
T. E. Hassall
University of Manchester
University of Southampton
The University of Sydney
G. Heald
Netherlands Institute for Radio Astronomy (ASTRON)
J. W. T. Hessels
Netherlands Institute for Radio Astronomy (ASTRON)
University of Amsterdam
M. Hoeft
Thüringer Landessternwarte Tautenburg
A. Horneffer
Max-Planck Institute for Radio Astronomy
A. van der Horst
University of Amsterdam
M. Iacobelli
Leiden University
N. J. Jackson
University of Manchester
E. Juette
Ruhr-Universität Bochum
A. Karastergiou
University of Oxford
W. Klijn
Netherlands Institute for Radio Astronomy (ASTRON)
J. Kohler
Max-Planck Institute for Radio Astronomy
V. I. Kondratiev
Astro Space Center of Lebedev Physical Institute
Netherlands Institute for Radio Astronomy (ASTRON)
M. Kramer
University of Manchester
Max-Planck Institute for Radio Astronomy
M. Kuniyoshi
Max-Planck Institute for Radio Astronomy
G. Kuper
Netherlands Institute for Radio Astronomy (ASTRON)
J. van Leeuwen
University of Southampton
Netherlands Institute for Radio Astronomy (ASTRON)
P. Maat
Netherlands Institute for Radio Astronomy (ASTRON)
G. Macario
Université Nice Sophia Antipolis (UNS)
G. Mann
Leibniz Institute for Astrophysics Potsdam
S. Markoff
University of Amsterdam
J. P. McKean
Netherlands Institute for Radio Astronomy (ASTRON)
M. Mevius
Netherlands Institute for Radio Astronomy (ASTRON)
Kapteyn Astronomical Institute
J. C. A. Miller-Jones
University of Amsterdam
Curtin University
J. D. Mol
Netherlands Institute for Radio Astronomy (ASTRON)
D. D. Mulcahy
Max-Planck Institute for Radio Astronomy
H. Munk
Netherlands Institute for Radio Astronomy (ASTRON)
M. J. Norden
Netherlands Institute for Radio Astronomy (ASTRON)
E. Orru
Netherlands Institute for Radio Astronomy (ASTRON)
H. Paas
University of Groningen
M. Pandey-Pommier
Lyon Observatory
V. N. Pandey
Netherlands Institute for Radio Astronomy (ASTRON)
R. Pizzo
Netherlands Institute for Radio Astronomy (ASTRON)
A. G. Polatidis
Netherlands Institute for Radio Astronomy (ASTRON)
W. Reich
Max-Planck Institute for Radio Astronomy
A. M. M. Scaife
University of Southampton
A. Schoenmakers
Netherlands Institute for Radio Astronomy (ASTRON)
D. Schwarz
Bielefeld University
A. Shulevski
Kapteyn Astronomical Institute
J. Sluman
Netherlands Institute for Radio Astronomy (ASTRON)
O. Smirnov
Square Kilometre Array, South Africa
Rhodes University
C. Sobey
Max-Planck Institute for Radio Astronomy
B. W. Stappers
University of Manchester
M. Steinmetz
Leibniz Institute for Astrophysics Potsdam
J. Swinbank
University of Amsterdam
M. Tagger
University of Orléans
Y. Tang
Netherlands Institute for Radio Astronomy (ASTRON)
C. Tasse
Observatoire de Paris-Meudon
S. ter Veen
Radboud University
S. Thoudam
Radboud University
C. Toribio
Netherlands Institute for Radio Astronomy (ASTRON)
R. van Nieuwpoort
Netherlands Institute for Radio Astronomy (ASTRON)
Netherlands eScience Center
R. Vermeulen
Netherlands Institute for Radio Astronomy (ASTRON)
C. Vocks
Leibniz Institute for Astrophysics Potsdam
C. Vogt
Netherlands Institute for Radio Astronomy (ASTRON)
Ramj Wijers
University of Amsterdam
M. W. Wise
Netherlands Institute for Radio Astronomy (ASTRON)
O. Wucknitz
Max-Planck Institute for Radio Astronomy
University of Bonn
S. Yatawatta
Netherlands Institute for Radio Astronomy (ASTRON)
P. Zarka
Open University
A. Zensus
Max-Planck Institute for Radio Astronomy
Monthly Notices of the Royal Astronomical Society
0035-8711 (ISSN) 1365-2966 (eISSN)
Vol. 437 4 3506-3515Subject Categories
Astronomy, Astrophysics and Cosmology
Infrastructure
Onsala Space Observatory
DOI
10.1093/mnras/stt2158