Evidence for CO Shock Excitation in NGC 6240 from Herschel SPIRE Spectroscopy
Artikel i vetenskaplig tidskrift, 2013
We present Herschel SPIRE FTS spectroscopy of the nearby luminous infrared galaxy NGC 6240. In total 20 lines
are detected, including CO J = 4−3 through J = 13−12, 6 H2O rotational lines, and [C i] and [N ii] fine-structure
lines. The CO to continuum luminosity ratio is 10 times higher in NGC 6240 than Mrk 231. Although the COladders
of NGC 6240 and Mrk 231 are very similar, UV and/or X-ray irradiation are unlikely to be responsible for the
excitation of the gas in NGC 6240.We applied both C and J shock models to the H2 v = 1–0 S(1) and v = 2–1 S(1)
lines and the CO rotational ladder. The CO ladder is best reproduced by amodel with shock velocity vs = 10 km s−1
and a pre-shock density nH = 5 × 104 cm−3. We find that the solution best fitting the H2 lines is degenerate. The shock velocities and number densities range between vs = 17–47 km s−1 and nH = 107–5×104 cm−3, respectively.
The H2 lines thus need a much more powerful shock than the CO lines.We deduce that most of the gas is currently moderately stirred up by slow (10 km s−1) shocks while only a small fraction (1%) of the interstellar medium
is exposed to the high-velocity shocks. This implies that the gas is rapidly losing its highly turbulent motions. We argue that a high CO line-to-continuum ratio is a key diagnostic for the presence of shocks.
galaxies: individual (NGC 6240)
galaxies: active
galaxies: starburst
infrared: galaxies
galaxies: nuclei
Författare
R. Meijerink
Rijksuniversiteit Groningen
Universiteit Leiden
L. Kristensen
Universiteit Leiden
A. Weiss
Max-Planck-Gesellschaft
P. van der Werf
Universiteit Leiden
F. Walter
Max-Planck-Gesellschaft
M. Spaans
Rijksuniversiteit Groningen
A.F. Loenen
Universiteit Leiden
J. Fischer
Naval Research Laboratory
F. P. Israel
Universiteit Leiden
K. Isaak
European Space Research and Technology Centre (ESA ESTEC)
P. P. Papadopoulos
Max-Planck-Gesellschaft
Susanne Aalto
Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik
L. Armus
Spitzer Science Center
V. Charmandaris
Panepistimio Kritis
K.M. Dasyra
LERMA - Laboratoire d'Etudes du Rayonnement et de la Matiere en Astrophysique et Atmospheres
T. Diaz-Santos
Spitzer Science Center
A. Evans
National Radio Astronomy Observatory
University of Virginia
Yu Gao
Chinese Academy of Sciences
E. Gonzalez-Alfonso
Universidad de Alcala
R. Güsten
Max-Planck-Gesellschaft
C. Henkel
King Abdulaziz University
Max-Planck-Gesellschaft
C. Kramer
Institut de Radioastronomie Millimétrique (IRAM)
S. Lord
California Institute of Technology (Caltech)
J. Martin-Pintado
CSIC - Instituto de Estructura de la Materia (IEM)
D. A. Naylor
University of Lethbridge
D. B. Sanders
University of Hawaii
H. Smith
Harvard-Smithsonian Center for Astrophysics
L. Spinoglio
Istituto nazionale di astrofisica (INAF)
G. Stacey
Cornell University
S. Veilleux
University of Maryland
M.C. Wiedner
Centre national de la recherche scientifique (CNRS)
Astrophysical Journal Letters
2041-8205 (ISSN) 2041-8213 (eISSN)
Vol. 762 2 L16-L20 L16Ämneskategorier
Astronomi, astrofysik och kosmologi
Fundament
Grundläggande vetenskaper
DOI
10.1088/2041-8205/762/2/L16