SIMBAD references

We present new multifrequency observations (X-ray ROSAT HRI, optical r Gunn–Thuan and near-infrared J and K imaging, and optical spectroscopy) of the interacting galaxy pair UCM 1259 + 2934 (NGC 4922A + B). These data are used to study the origin of the extended soft X-ray emission and the star formation history of the northern component of the interacting system. The southern component (NGC 4922S) shows no signs of activity, with an optical spectrum consistent with that of an elliptical galaxy, which is also supported by its morphology. The northern component (NGC 4922N) shows evidence of composite activity; the nuclear optical line ratios are intermediate between those of a LINER and a Seyfert 2 galaxy. Its circumnuclear regions resemble a normal H ii region. NGC 4922N can be classified as a transition object, in the sense that its optical emission lines may be produced by both a non-stellar continuum and hot stars.

The ROSAT HRI observation shows extended soft X-ray emission which appears to peak close to the nucleus of NGC 4922N, with luminosity L_X(0.1–2.4 keV)=(2.6–4.3)x10⁴¹ erg.s^–1, depending on the parameters of the adopted model. The extended nature of the source rules out a situation in which most of the X-ray emission originates from an active nucleus. The most likely mechanism responsible for the extended soft X-ray emission is star formation activity via supernova remnants and/or massive X-ray binaries (MXRBs) formed in a burst of star formation that occurred about 7x10⁶ yr ago, plus a large-scale supernova-driven wind. Based on the far-infrared versus X-ray correlations for high-flux IRAS galaxies, we can conclude that the soft X-ray emission is arising from both galaxies in the system, though dominated by the northern component.

An evolutionary synthesis model is used to investigate the star formation history of NGC 4922N. From the extinction-corrected r-J and J-K colours we argue that between 0.1 and 1 per cent of the total stellar mass of the galaxy was formed during the last episode of star formation. The star formation rate (SFR) of the northern component, 6≤SFR≤35 M_☉.yr^–1 as inferred from the Hα and far-infrared luminosities, is higher than typical SFRs of isolated galaxies. Such a high SFR could result from an episode of star formation triggered by interaction with the southern component.