ACA CI observations of the starburst galaxy NGC 253
Artikel i vetenskaplig tidskrift, 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.

submillimeter: galaxies

galaxies: starburst

galaxies: ISM

galaxies: active

galaxies: individual: NGC 253

Författare

M. Krips

Institut de RadioAstronomie Millimetrique (IRAM)

S. Martin

Atacama Large Millimeter-submillimeter Array (ALMA)

European Southern Observatory Santiago

K. Sakamoto

Academia Sinica

Susanne Aalto

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

T. G. Bisbas

Max Planck-institutet

University of Florida

A. Bolatto

University of Maryland

D. Downes

Institut de RadioAstronomie Millimetrique (IRAM)

A. Eckart

Universität zu Köln

C. Feruglio

Scuola Normale Superiore di Pisa

S. G. Burillo

Observatorio Astronamico Nacional (OAN-IGN)

J.E. Geach

University of Hertfordshire

T. R. Greve

University College London (UCL)

Sabine König

Chalmers, Rymd- och geovetenskap, Radioastronomi och astrofysik

S. Matsushita

Academia Sinica

R. Neri

Institut de RadioAstronomie Millimetrique (IRAM)

S. Offner

University of Massachusetts

A. B. Peck

National Radio Astronomy Observatory

S. Viti

University College London (UCL)

J. Wagg

SKA Organisation

Astronomy and Astrophysics

0004-6361 (ISSN) 1432-0746 (eISSN)

Vol. 592 L3 L3

Ämneskategorier

Astronomi, astrofysik och kosmologi

Fundament

Grundläggande vetenskaper

Infrastruktur

Onsala rymdobservatorium

DOI

10.1051/0004-6361/201628882

Mer information

Senast uppdaterat

2018-09-06