Ultraluminous X-ray sources (ULXs) are end points of stellar evolution. They are mostly interpreted as binary systems with a massive donor. They are also the most probable progenitors for BH-BH, and even more, for BH-NS coalescence. Parameters of ULXs are not know and need to be better determined, in particular the link with the metallicity of the environment which has been invoked frequently but not proven strongly. We have tackled this problem by using a MUSE DEEP mosaic of the Cartwheel galaxy and applying a Monte Carlo code that jointly fits spectroscopy and photometry. We measure the metallicity of the emitting gas in the ring and at the positions of X-ray sources by constructing spatially resolved emission line ratio maps and BPT diagnostic maps. The Carthweel is the archetypal ring galaxy and the location and formation time of new stellar populations is easier to reconstruct than in more normal galaxies. It has the largest population of ULXs ever observed in a single galaxy (16 sources have been classified as ULXs in Chandra and XMM-Newton data). The Cartwheel galaxy is therefore the ideal laboratory to study the relation between Star Formation (SF Rates and SF History) and number of ULXs and also their final fate. We find that the age of the stellar population in the outer ring is consistent with being produced in the impact (≤300Myr) and that the metallicity is mostly sub-solar, even if solutions can be found with a solar metallicity that account for most observed properties. The findings for the Cartwheel will be a testbed for further modelisation of binary formation and evolution paths.

X-ray surveys of normal galaxies, i.e. those that do not host actively supermassive black holes, have revealed important information on the nature of accreting stellar-mass compact objects (neutron stars and black holes), constraints on populations of possible intermediate-mass black holes (102–5M⊙), and on the reservoir of materials in the hot interstellar medium of the most massive galaxies. Here we summarize briefly the results of Chandra and NuSTAR surveys of several samples of galaxies covered during the 2015 IAU General Assembly. This includes a comprehensive study of six nearby starburst galaxies by the NuSTAR mission, of high-redshift galaxies from the 6 Ms Chandra Deep Field South for which evolutionary trends in X-ray emission over cosmic time have been measured, of collisional ring galaxies which are excellent local environments for studying intermediate-mass black holes and of elliptical galaxies which are ideal for study of the hot gas reservoirs containing the effects of stellar and AGN feedback.

The main purpose of this panel discussion was to encourage conversation around potential collaborations between the IAU Office of Astronomy for Development (OAD) and IAU Divisions. The discussion was facilitated by the OAD and the conversation revolved mainly around two questions: (i) What should the OAD be doing to enhance the work of the Divisions? (ii) What could the Divisions (both members and respective scientific discipline in general) contribute towards the implementation of the IAU strategic plan?

The Cartwheel is one of the most outstanding examples of a dynamically perturbed galaxy where star formation is occurring inside the ring–like structure. In previous studies with Chandra, we detected 16 Ultra Luminous X-ray sources lying along the southern portion of the ring. Their Luminosity Function is consistent with them being in the high luminosity tail of the High Mass X-ray Binaries distribution, but with one exception: source N.10. This source, detected with Chandra at LX = 1 × 1041 erg s−1, is among the brightest non–nuclear sources ever seen in external galaxies. Recently, we have observed the Cartwheel with XMM-Newton in two epochs, six months apart. After having been at its brightest for at least 4 years, the source has dimmed by at least a factor of two between the two observations. This fact implies that the source is compact in nature. Given its extreme isotropic luminosity, there is the possibility that the source hosts an accreting intermediate–mass black hole. Other sources in the ring vary in flux between the different datasets. We discuss our findings in the context of ULX models.

The recent evidence of a peculiar distribution of X-ray sources in the elliptical galaxy NGC 4261 reported by Zezas et al. has prompted us to study this galaxy combining archive X-ray and optical observations, from Chandra, INT, and HST. We find that a sizable fraction of the X-ray sources has a globular cluster as optical counterpart. This together with the shape of the luminosity function of the X-ray sources suggest that they are accreting low-mass binaries. We further show a remarkable similarity in the anisotropy of the projected spatial distributions of the optical and X-ray sources, which leads us to conclude that the spatial anisotropy of the X-ray sources in NGC 4261 is due to the anisotropy of the globular cluster population.

ROSAT HRI observations of the Cartwheel galaxy indicate that there is X-ray emission from the outer ring in connection with the strongest HII regions in the southern portion of the ring. No significant emission is detected from the nucleus or from the inner ring. This implies a strong connection between star formation activity and X-ray emission in this ring galaxy.

In this paper we discuss the cluster of galaxies 1E0839.9+2938, serendipitously discovered at x-ray wavelengths. The collected data imply that this is an example of cooling flow cluster.

We present a progress report on a major extension of the Einstein Observatory Medium Sensitivity Survey (MSS). The basic properties of the extragalactic sources identified with Active Galactic Nuclei (AGN) and clusters of galaxies are discussed. Results from previous work are briefly summarized.