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.

ISM

IsM.

General-IsM

structure-local interstellar matter-radio lines

Author

J. B. R. Oonk

Netherlands Institute for Radio Astronomy (ASTRON)

R. J. van Weeren

Netherlands Institute for Radio Astronomy (ASTRON)

Harvard-Smithsonian Center for Astrophysics

Leiden University

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

University of Amsterdam

Space Telescope Science Institute (STScI)

J. Anderson

Max Planck Society

I. M. Avruch

Netherlands Institute for Space Research (SRON)

Fabien Batejat

Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics

R. Beck

Max Planck Society

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

Rhodes University

Square Kilometre Array, South Africa

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 Society

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

Radboud University

Netherlands Institute for Radio Astronomy (ASTRON)

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

Netherlands Institute for Radio Astronomy (ASTRON)

Leiden University

J. Griessmeier

University of Orléans

J. P. Hamaker

Netherlands Institute for Radio Astronomy (ASTRON)

T. E. Hassall

University of Southampton

The University of Sydney

University of Manchester

G. Heald

Netherlands Institute for Radio Astronomy (ASTRON)

J. W. T. Hessels

University of Amsterdam

Netherlands Institute for Radio Astronomy (ASTRON)

M. Hoeft

Thüringer Landessternwarte Tautenburg

A. Horneffer

Max Planck Society

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 Society

V. I. Kondratiev

Netherlands Institute for Radio Astronomy (ASTRON)

Astro Space Center of Lebedev Physical Institute

M. Kramer

Max Planck Society

University of Manchester

M. Kuniyoshi

Max Planck Society

G. Kuper

Netherlands Institute for Radio Astronomy (ASTRON)

J. van Leeuwen

Netherlands Institute for Radio Astronomy (ASTRON)

University of Southampton

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 Society

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 Society

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 Society

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

University of Bonn

Max Planck Society

S. Yatawatta

Netherlands Institute for Radio Astronomy (ASTRON)

P. Zarka

Open University

A. Zensus

Max Planck Society

Monthly Notices of the Royal Astronomical Society

0035-8711 (ISSN) 1365-2966 (eISSN)

Vol. 437 4 3506-3515

Subject Categories (SSIF 2011)

Astronomy, Astrophysics and Cosmology

Infrastructure

Onsala Space Observatory

DOI

10.1093/mnras/stt2158

More information

Latest update

3/17/2025