XMM-Newton Observations of the Spiral Galaxy M74 (NGC 628)

Abstract

The face-on spiral galaxy M74 (NGC 628) was observed by XMM-Newton on 2002 February 2. In total, 21 sources are found in the inner 5' from the nucleus (after rejection of a few sources associated to foreground stars). Hardness ratios suggest that about half of them belong to the galaxy. The higher luminosity end of the luminosity function is fitted by a power law of slope -0.8. This can be interpreted as evidence of ongoing star formation, in analogy with the distributions found in disks of other late-type galaxies. A comparison with previous Chandra observations reveals a new ultraluminous X-ray transient (L_X~1.5×10³⁹ ergs s^-1 in the 0.3-8 keV band) about 4' north of the nucleus. We find another bright transient source (L_X~5×10³⁸ ergs s^-1) about 5' northwest of the nucleus. The UV and X-ray counterparts of SN 2002ap are also found in this XMM-Newton observation; the hardness ratio of the X-ray counterpart suggests that the emission comes from the shocked circumstellar matter.