Issue |
A&A
Volume 427, Number 1, November III 2004
|
|
---|---|---|
Page(s) | 35 - 44 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20041128 | |
Published online | 25 October 2004 |
The composite starburst/AGN nature of the superwind galaxy NGC 4666
1
INAF - Osservatorio Astronomico di Trieste, via GB Tiepolo 11, 34131 Trieste, Italy e-mail: persic@ts.astro.it
2
IASF/CNR – Sezione di Bologna, via P. Gobetti 101, 40129 Bologna, Italy
3
School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
4
CASS, University of California, San Diego, La Jolla, CA 92093, USA
5
INAF/Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
6
Dipartimento di Astronomia, Università di Padova, vicolo Osservatorio 2, 35122 Padova, Italy
7
IASF/CNR – Sezione di Firenze, l.go E. Fermi 5, 50125 Firenze, Italy
Received:
25
April
2003
Accepted:
15
June
2004
We report the discovery of a Compton-thick
AGN and of intense star-formation activity in the nucleus and disk, respectively, of the
nearly edge-on superwind galaxy NGC 4666. Spatially unresolved emission is detected by
BeppoSAX only at energies <10 keV, whereas spatially resolved emission from the whole disk is detected by XMM-Newton. A prominent ( keV) emission line at ~6.4 keV is detected by both instruments. From the XMM-Newton data alone the line is spectrally localized
at
keV, and seems to be spatially concentrated in the nuclear
region of NGC 4666. This, together with the presence of a flat (
) continuum
in the nuclear region, suggests the existence of a strongly absorbed (i.e., Compton-thick)
AGN, whose intrinsic 2–10 keV luminosity is estimated to be
erg s-1.
At energies
1 keV the integrated (BeppoSAX) spectrum is dominated by a ~0.25 keV thermal gas component distributed throughout the disk (resolved by XMM-Newton). At energies
~2–10 keV, the integrated spectrum is dominated by a steep (
) power-law
(PL) component. The latter emission is likely due to unresolved sources with luminosity
erg s-1 that are most likely accreting binaries (with
BH masses ≤8
). Such binaries, which are known to dominate the X-ray
point-source luminosity in nearby star-forming galaxies, have
PL spectra in
the relevant energy range. A
PL contribution from Compton scattering of
(the radio-emitting) relativistic electrons by the ambient FIR photons may add a truly
diffuse component to the 2–10 keV emission.
Key words: X-rays: galaxies / galaxies: starburst / galaxies: Seyfert / galaxies: individual: NGC 4666
© ESO, 2004
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