THE LOCAL ENVIRONMENT OF ULTRALUMINOUS X-RAY SOURCES VIEWED BYXMM-NEWTON's OPTICAL MONITOR

Abstract

We have used XMM-Newton's Optical Monitor (OM) images to study the local environment of a sample of 27 Ultraluminous X-ray Sources (ULXs) in nearby galaxies. UVW1 fluxes were extracted from 100 pc regions centered on the ULX positions. We find that at least 4 ULXs (out of 10 published) have spectral types that are consistent with previous literature values. In addition the colors are similar to those of young stars. For the highest-luminosity ULXs, the UVW1 fluxes may have an important contribution from the accretion disk. We find that the majority of ULXs are associated with recent star-formation. Many of the ULXs in our sample are located inside young OB associations or starforming regions (SFRs). Based on their colors, we estimated ages and masses for star-forming regions located within 1 kpc from the ULXs in our sample. The resolution of the OM was insufficient to detect young dense super-clusters, but some of these star-forming regions are massive enough to contain such clusters. Only three ULXs have no associated SFRs younger than ∼50 Myr. The age and mass estimates for clusters were used to test runaway scenarios. The data are in general compatible with stellar-mass binaries accreting at super-Eddington rates and ejected by natal kicks. We also tested the hypothesis that ULXs are sub-Eddington accreting IMBHs ejected by three-body interactions, however this is not supported well by the data.

Roche-Lobe Overflow Systems Powered by Black Holes in Young Star Clusters: The Importance of Dynamical Exchanges

“…We chose the ULXs because they are mostly associated with star forming regions and/or young SCs (e.g. Zezas et al 2002;Kaaret et al 2004;Berghea 2009;Mapelli et al 2010;Poutanen et al 2013;Berghea et al 2013), because they ) and because they have an estimated luminosity (assuming isotropy) higher than the Eddington luminosity of a 10 M ⊙ BH. For the high luminosity and for the anti-correlation with metallicity, Mapelli et al (2009) proposed that (a fraction of) ULXs are associated with MSBHs (see also Zampieri & Roberts 2009;Mapelli et al 2010;Mapelli et al 2011a).…”

“…This may indicate that the dynamics of the parent SC enhances the formation of bright X-ray binaries. In addition, a significant fraction of these bright X-ray sources are found to be slightly displaced (by few tens to hundreds of parsecs) from the closest young SC (Zezas et al 2002;Kaaret et al 2004;Berghea 2009;Rangelov et al 2012;Poutanen et al 2013;Berghea et al 2013). This has been interpreted as a consequence of natal kicks (e.g.…”

“…We chose the ULXs because they are mostly associated with star forming regions and/or young SCs (e.g. Zezas et al 2002;Kaaret et al 2004;Berghea 2009;Mapelli et al 2010;Poutanen et al 2013;Berghea et al 2013), because they seem to anti-correlate with the local metallicity (e.g. Pakull & Mirioni 2002;Zampieri et al 2004;Soria et al 2005;Swartz, Tennant & Soria 2009;Mapelli et al 2009;Mapelli et al 2010;Mapelli et al 2011a;Kaaret & Feng 2013;Prestwich et al 2013) and because they have an estimated luminosity (assuming isotropy) higher than the Eddington luminosity of a 10 M ⊙ BH.…”

X-Ray Emission From the Taffy (Vv254) Galaxies and Bridge

“…If this "extragalactic H II region" was formed by a compression of gas in the bridge, it would only have had 10-20 Myr to form. However, this is feasible, since Berghea et al (2013) have shown that the ages of typical massive star clusters associated with ULXs are typically 10 Myr old. A more detailed study of the correlation between the position of Taffy B1 and the host molecular cloud and associated star-formation would be worthwhile.…”

Do open star clusters evolve towards energy equipartition?

“…Since mergers of BH binaries are among the most important sources of gravitational waves, the dynamical fate of BHs in star clusters strongly affects the predictions of the detection-rate by ground-based gravitational waves detectors (O'Leary et al 2006;Sadowski et al 2008;Downing et al 2010Downing et al , 2011Ziosi et al 2014;Morscher et al 2015;Rodriguez et al 2015;Chatterjee et al 2016;O'Leary et al 2016). Similarly, the dynamics of stellar remnants affects the demographics of X-ray binaries (Mapelli et al 2011;Downing et al 2011;Berghea et al 2013;Mapelli & Zampieri 2014;Goswami et al 2014). If equipartition is not reached, there might be relevant implications for the current local mass function of star clusters (e.g.…”