EDP Sciences
Free Access
Volume 427, Number 1, November III 2004
Page(s) 35 - 44
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361:20041128

A&A 427, 35-44 (2004)
DOI: 10.1051/0004-6361:20041128

The composite starburst/AGN nature of the superwind galaxy NGC 4666

M. Persic1, M. Cappi2, Y. Rephaeli3, 4, L. Bassani2, R. Della Ceca5, A. Franceschini6, L. Hunt7, G. Malaguti2 and E. Palazzi2

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 ( $EW \sim 1{-}2$ keV) emission line at ~6.4 keV is detected by both instruments. From the XMM-Newton data alone the line is spectrally localized at $E \simeq 6.42 \pm 0.03$ keV, and seems to be spatially concentrated in the nuclear region of NGC 4666. This, together with the presence of a flat ( $\Gamma\sim 1.3$) 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 $L_{2{-}10} \ga2 \times
10^{41}$ erg s -1. At energies $\la$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 ( $\Gamma\ga2$) power-law (PL) component. The latter emission is likely due to unresolved sources with luminosity $L \sim 10^{38}{-}10^{39}$ erg s -1 that are most likely accreting binaries (with BH masses $\leq$$M_\odot$). Such binaries, which are known to dominate the X-ray point-source luminosity in nearby star-forming galaxies, have $\Gamma\sim 2$ PL spectra in the relevant energy range. A $\Gamma\sim 1.8$ 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

SIMBAD Objects

© ESO 2004

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.