EDP Sciences Journals List
Advanced Search
Subscriber Authentication Point
Home All issues Volume 442/3 Article
Free access article

Issue A&A
Volume 442, Number 3, November II 2005
Page(s) 861 - 877
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20053022



A&A 442, 861-877 (2005)
DOI: 10.1051/0004-6361:20053022

X-ray emission from NGC 1808: more than a complex starburst

E. Jiménez-Bailón1, M. Santos-Lleó1, M. Dahlem2, M. Ehle1, J. M. Mas-Hesse3, M. Guainazzi1, T. M. Heckman4 and K. A. Weaver5

1  XMM-Newton Science Operations Centre, ESAC, ESA, Apartado 50727, 28080 Madrid, Spain
    e-mail: Elena.Jimenez@sciops.esa.int
2  ATNF/CSIRO, Paul Wild Observatory, Locked Bag 194, Narrabri NSW 2390, Australia
3  Centro de Astrobiología (CSIC-INTA), 28850 Torrejón de Ardoz, Madrid, Spain
4  Dept. of Physics and Astronomy, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA
5  Laboratory for High Energy Astrophysics, NASA's Goddard Space Flight Center, Greenbelt, MD 20771, USA

(Received 8 March 2005 / Accepted 10 May 2005 )

Abstract
Earlier observations of NGC 1808 in various wavebands (X-ray, optical, near-infrared, radio) provided evidence for the existence of either a starburst or a Seyfert 2 nucleus. We here present the results of multiwavelength XMM-Newton and Chandra observations, which directly prove the co-existence of thermal diffuse plasma and non-nuclear unresolved point-like sources associated with the starburst activity, along with a Low Luminosity Active Galactic Nucleus (LLAGN) or an Ultra Luminous X-ray source (ULX). The broad bandwidth of XMM-Newton allows us to show that the unresolved nuclear source in NGC 1808 dominates the hard X-ray spectrum, while the emission in the soft regime, below 1 keV, is dominated by a thermal component associated to an extended starburst. Both EPIC and RGS data provide reliable detections of a number of emission lines from heavy elements, with abundances ranging from roughly 0.7 to 2.2 $Z_\odot$ for different elements. However, no 6.4 keV Fe K$\alpha$ fluorescence line emission was detected. The analysis of the nuclear region of NGC 1808 allows us to detect and disentangle the contribution of an unresolved nuclear X-ray source and the starburst region, but the exact nature of the nucleus remains unknown. The observed luminosity of NGC 1808 is $L_{2{-}10~\rm keV}=(1.61\pm0.06)\times10^{40}$ erg s-1. A comparison of our OM 212 nm image with a CTIO 4-m telescope H$\alpha$ frame shows a good general correspondence between the emission from massive stars and warm ionized gas, with minor deviations near the ends of the bar in NGC 1808. An aditional, very soft thermal spectral component with $kT\simeq 0.1$ keV has been discovered in the XMM-Newton spectral analysis, which most likely originates from the halo of NGC 1808.


Key words: galaxies: active -- galaxies: nuclei -- galaxies: general -- X-rays: general -- galaxies: evolution -- galaxies: halos -- galaxies: starburst -- individual: NGC 1808

SIMBAD Objects



© ESO 2005


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.