EDP Sciences
Free Access
Issue
A&A
Volume 436, Number 2, June III 2005
Page(s) 397 - 409
Section Astrophysical processes
DOI https://doi.org/10.1051/0004-6361:20042398
Published online 30 May 2005


A&A 436, 397-409 (2005)
DOI: 10.1051/0004-6361:20042398

Diagnostics of irradiated gas in galaxy nuclei

I. A far-ultraviolet and X-ray dominated region code
R. Meijerink1 and M. Spaans2

1  Sterrewacht Leiden, PO Box 9513, 2300 RA Leiden, The Netherlands
    e-mail: meijerin@strw.leidenuniv.nl
2  Kapteyn Astronomical Institute, PO Box 800, 9700 AV Groningen, The Netherlands

(Received 19 November 2004 / Accepted 22 February 2005)

Abstract
We present a far-ultraviolet (PDR) and an X-ray dominated region (XDR) code. We include and discuss thermal and chemical processes that pertain to irradiated gas. An elaborate chemical network is used and a careful treatment of PAHs and H2 formation, destruction and excitation is included. For both codes we calculate four depth-dependent models for different densities and radiation fields, relevant to conditions in starburst galaxies and active galactic nuclei. A detailed comparison between PDR and XDR physics is made for total gas column densities between ~1020 and ~1025 cm-2. We show cumulative line intensities for a number of fine-structure lines (e.g., [CII], [OI], [CI], [SiII], [FeII]), as well as cumulative column densities and column density ratios for a number of species (e.g., CO/H2, CO/C, HCO+/HCN, HNC/HCN). The comparison between the results for the PDRs and XDRs shows that column density ratios are almost constant up to $N_{\rm H}=10^{22}\ {\rm
cm^{-2}}$ for XDRs, unlike those in PDRs. For example, CO/C in PDRs changes over four orders of magnitude from the edge to $N_{\rm H}=10^{22}\ {\rm
cm^{-2}}$. The CO/C and CO/H2 ratios are lower in XDRs at low column densities and rise at $N_{\rm H}>10^{23}\ {\rm
cm^{-2}}$. At most column densities $N_{\rm H} > 10^{21.5}\ {\rm
cm^{-2}}$, HNC/HCN ratios are lower in XDRs too, but they show a more moderate increase at higher $N_{\rm H}$.


Key words: astrochemistry -- galaxies: starburst -- galaxies: active

SIMBAD Objects



© ESO 2005

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.