NGC 3627: a galaxy-dwarf collision?^⋆

¹ Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstrasse 150, 44780 Bochum, Germany
e-mail: mawez@astro.rub.de
² Obserwatorium Astronomiczne Uniwersytetu Jagiellońskiego, ul. Orla 171, 30-244 Kraków, Poland

Received: 10 November 2011
Accepted: 26 June 2012

Abstract

Context. Group galaxies very often show distinct signs of interaction with both companion galaxies and the intragroup medium. X-ray observations are particularly helpful because they provide information on the temperatures and the densities of the hot gas in galaxies and intergalactic space. This can put important constraints on the nature and timescales of these interactions.

Aims. We use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy group to explain peculiar features visible in the polarized radio maps.

Methods. We analyzed soft X-ray (0.2−1 keV) emission from NGC 3627 to study the distribution of the hot gas and its temperature in different areas of the galaxy. Any change throughout the disk can reflect distortions visible in the radio polarized emission. We also studied two bright point sources that are probably tightly linked to the evolution of the galaxy.

Results. We find an increase in the temperature of the hot gas in the area of the polarized radio ridge in the western arm of the galaxy. In the eastern part of the disk we find two ultra-luminous X-ray sources. We note a large hot gas temperature difference (by a factor of 2) between the two bar ends.

Conclusions. The polarized radio ridge in the western arm of NGC 3627 is most likely formed by ram-pressure effects caused by the movement of the galaxy through the intragroup medium. To explain the distortions visible in the eastern part of the disk in polarized radio maps, the asymmetry of the bar, and the distortion of the eastern arm, we propose a recent collision of NGC 3627 with a dwarf companion galaxy.