HCN(1–0) enhancement in the bar of NGC 2903

Free access article

Issue		A&A Volume 491, Number 3, December I 2008


Page(s)		703 - 711
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:200810162
Published online		01 October 2008

A&A 491, 703-711 (2008)
DOI: 10.1051/0004-6361:200810162

HCN(1–0) enhancement in the bar of NGC 2903

S. Leon¹, S. Jeyakumar², D. Pérez-Ramírez³, L. Verdes-Montenegro⁴, S. W. Lee⁵, and B. Ocaña Flaquer¹

¹ Instituto de Radioastronomía Milimétrica (IRAM), Avenida Divina Pastora 7, Núcleo Central, 18012 Granada, Spain
e-mail: leon@iram.es
² Departamento de Astronoma, Universidad de Guanajuato, AP 144, Guanajuato CP 36000, Mexico
³ University of Jaén, Jaén, Spain
⁴ Instituto de Astrofísica de Andalucía-CSIC, Granada, Spain
⁵ University of Toronto, Astronomy Department, Toronto, Canada

Received 8 May 2008 / Accepted 2 September 2008

Abstract
We have mapped the HCN(1–0) emission from two spiral galaxies, NGC 2903 and NGC 3504 to study the gas properties in the bars. The HCN(1–0) emission is detected in the center and along the bar of NGC 2903. The line ratio HCN(1–0)/ ¹²CO(1–0) ranges from 0.07 to 0.12 with the lowest value in the center. The enhancement of HCN(1–0) emission along the bar indicates a higher fraction of dense molecular gas in the bar than at the center. The mass of dense molecular gas in the center (2.2 $\times$ 10⁷ $\mathcal{M}_{\odot}$ ) is about 6 times lower than that in the bar (1.2 $\times$ 10⁸ $\mathcal{M}_{\odot}$ ). The total star formation rate (SFR) is estimated to be 1.4 $\mathcal{M}_{\odot}$ yr^-1, where the SFR at the center is 1.9 times higher than that in the bar. The time scale of consumption of the dense molecular gas in the center is about ~ 3 $\times$ 10⁷ yr which is much shorter than that in the bar of about 2 to 10 $\times$ 10⁸ yr. The dynamical time scale of inflow of the gas from the bar to the center is shorter than the consumption time scale in the bar, which suggests that the star formation (SF) activity at the center is not deprived of fuel. In the bar, the fraction of dense molecular gas mass relative to the total molecular gas mass is twice as high along the leading edge than along the central axis of the bar. The HCN(1–0) emission has a large velocity dispersion in the bar, which can be attributed partially to the streaming motions indicative of shocks along the bar. In NGC 3504, the HCN(1–0) emission is detected only at the center. The fraction of dense molecular gas mass in the center is about 15%. Comparison of the SFR with the predictions from numerical simulations suggest that NGC 2903 harbors a young type B bar with a strong inflow of gas toward the center whereas NGC 3504 has an older bar and has already passed the phase of inflow of gas toward the center.

Key words: galaxies: spiral -- galaxies: ISM -- galaxies: evolution

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.