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Astron. Astrophys. 343, 373-384 (1999)

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ROSAT X-ray observations of the interacting pair of galaxies NGC 4410: evidence for a central starburst

D. Tschöke 1, G. Hensler 1 and N. Junkes 2

1 Institut für Theoretische Physik und Astrophysik, Universität Kiel, D-24098 Kiel, Germany (tschoeke@astrophysik.uni-kiel.de)
2 Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Received 21 July 1998 / Accepted 6 November 1998


We present X-ray observations of the interacting pair of galaxies NGC 4410a/b with the ROSAT HRI and PSPC. The ROSAT HRI images reveal a point-like source corresponding to NGC 4410a and an X-ray halo, extending [FORMULA] from the nucleus toward the southeast. The halo emission accounts for [FORMULA]1/3 ([FORMULA] = 1.3[FORMULA]10[FORMULA] erg s-1 in the 0.1-2.4 keV ROSAT band) of the total X-ray emission detected from NGC 4410a. The spectrum of the total X-ray emission from NGC 4410a can be fitted at best with a two-component emission model, combining a Raymond-Smith spectrum with T = 107 K and a power-law spectrum ([FORMULA] = 2.2). The fraction of the thermal component to the total flux within this model is 35%, supporting the results of the HRI observation. The total unresolved X-ray luminosity detected with the PSPC amounts to 4[FORMULA]10[FORMULA] erg s-1 in the ROSAT PSPC band (for D = 97 Mpc).

A preferable explanation might be the interaction between the two galaxies causing a circumnuclear starburst around the active nucleus in the peculiar late type Sab galaxy NGC 4410a. As a cumulative effect of exploding stars a superbubble forms a bipolar outflow from the galactic disk with an expansion time of [FORMULA]8 Myr. The central source injects mechanical energy at a constant rate of a few times 1042 erg s-1 into the superbubble.

A HST WFPC2 image decovers that NGC 4410a is seen almost face-on so that only the approaching outflow is visible. The HRI contours reveal an elongation of this outflow indicative for a faint X-ray ridge below the detection limit ([FORMULA] 1.4[FORMULA]10[FORMULA] erg s-1) toward the neighbouring galaxy NGC 4410b caused by its tidal interaction. NGC 4410b houses only a faint X-ray source ([FORMULA] 3.8[FORMULA]10[FORMULA] erg s-1).

Key words: X-rays: galaxies – galaxies: starbust – galaxies: interactions – galaxies: individual: NGC 4410 – galaxies: active

Send offprint requests to: D. Tschöke

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999