ACA CI observations of the starburst galaxy NGC 253
Journal article, 2016
Context. Carbon monoxide (CO) is widely used as a tracer of the molecular gas in almost all types of environments. However, several shortcomings of CO complicate usaging it as H-2 tracer, such as its optical depth effects, the dependence of its abundance on metallicity, or its susceptibility to dissociation in highly irradiated regions. Neutral carbon emission has been proposed to overcome some of these shortcomings and hence to help revealing the limits of CO as a measure of the molecular gas. Aims. We aim to study the general characteristics of the spatially and spectrally resolved carbon line emission in a variety of extragalactic sources and evaluate its potential as complementary H-2 tracer to CO. Methods. We used the Atacama Compact Array to map the [CI](P-3(1)-P-3(0)) line emission in the nearby starburst galaxy NGC 253 at unprecedented angular resolution (similar to 3 ''). This is the first well-resolved interferometric [CI] map of an extragalactic source. Results. We have detected the [CI] line emission at high significance levels along the central disk of NGC 253 and its edges where expanding shells have previously been found in CO. Globally, the distribution of the [CI] line emission strongly resembles that of CO, confirming the results of previous Galactic surveys that [CI] traces the same molecular gas as CO. However, we also identify a significant increase of [CI] line emission with respect to CO in (some of) the outflow or shocked regions of NGC 253, namely the bipolar outflow emerging from the nucleus. A first-order estimate of the [CI] column densities indicates abundances of [CI] that are very similar to the abundance of CO in NGC 253. Interestingly, we find that the [CI] line is marginally optically thick within the disk. Conclusions. The enhancement of the [CI]/CO line ratios (similar to 0.4-0.6) with respect to Galactic values (<= 0.1), especially in the shocked regions of NGC 253, clearly indicates that mechanical perturbation such as shocks and the strong radiation fields in this starburst galaxy have a marked effect on the carbon excitation and/or abundance.
galaxies: individual: NGC 253
submillimeter: galaxies
galaxies: starburst
galaxies: ISM
galaxies: active
Author
M. Krips
IRAM Institut de RadioAstronomie Millimetrique
S. Martin
Atacama Large Millimeter-submillimeter Array
European Southern Observatory Santiago
K. Sakamoto
Institute of Astrophysics and Astronomy, Academia Sinica Taiwan
Susanne Aalto
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
T. G. Bisbas
Max Planck Institut fur extraterrestrische Physik
University of Florida
A. Bolatto
University of Maryland
D. Downes
IRAM Institut de RadioAstronomie Millimetrique
A. Eckart
Universitat zu Koln
C. Feruglio
Scuola Normale Superiore di Pisa
S. G. Burillo
Observatorio Astronamico Nacional (OAN-IGN)
J.E. Geach
University of Hertfordshire
T. R. Greve
UCL
Sabine König
Chalmers, Earth and Space Sciences, Radio Astronomy and Astrophysics
S. Matsushita
Institute of Astrophysics and Astronomy, Academia Sinica Taiwan
R. Neri
IRAM Institut de RadioAstronomie Millimetrique
S. Offner
University of Massachusetts
A. B. Peck
National Radio Astronomy Observatory
S. Viti
UCL
J. Wagg
SKA Organziation
Astronomy and Astrophysics
0004-6361 (ISSN) 1432-0746 (eISSN)
Vol. 592 L3 L3Subject Categories (SSIF 2011)
Astronomy, Astrophysics and Cosmology
Roots
Basic sciences
Infrastructure
Onsala Space Observatory
DOI
10.1051/0004-6361/201628882