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: starburst

galaxies: nuclei

galaxies: individual (NGC 6240)

galaxies: active

infrared: galaxies

Författare

R. Meijerink

Leiden University

University of Groningen, Kapteyn Astronomical Institute

L. Kristensen

Leiden University

A. Weiss

Max Planck-institutet

P. van der Werf

Leiden University

F. Walter

Max Planck-institutet

M. Spaans

University of Groningen, Kapteyn Astronomical Institute

A.F. Loenen

Leiden University

J. Fischer

Naval Research Laboratory

F. P. Israel

Leiden University

K. Isaak

ESTEC

P. P. Papadopoulos

Max Planck-institutet

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

University of Virginia

National Radio Astronomy Observatory

Yu Gao

Purple Mountain Observatory Chinese Academy of Sciences

E. Gonzalez-Alfonso

Universidad de Alcala

R. Güsten

Max Planck-institutet

C. Henkel

King Abdulaziz University

Max Planck-institutet

C. Kramer

Instituto de Radioastronomia Milimetrica

S. Lord

CalTech

J. Martin-Pintado

CSIC - Instituto de Estructura de la Materia (IEM)

D. A. Naylor

University of Lethbridge

D. B. Sanders

University of Hawaii at Manoa

H. Smith

Harvard-Smithsonian Center for Astrophysics

L. Spinoglio

Istituto Nazionale Di Astrofisica, Rome

G. Stacey

Cornell University

S. Veilleux

University of Maryland

M.C. Wiedner

CNRS Centre National de la Recherche Scientifique

Astrophysical Journal Letters

2041-8205 (ISSN) 2041-8213 (eISSN)

Vol. 762 L16-L20 L16

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

DOI

10.1088/2041-8205/762/2/L16