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We present a study of the irregular dwarf galaxy Holmberg II based on ROSAT PSPC observations (total exposure time: 22 ksec). Holmberg II is a nearby (3.2 Mpc), well-studied dwarf irregular galaxy. It is famous for its interstellar medium which is dominated by expanding structures such as HI holes and shells. We search for X-ray emission from point sources as well as for diffuse emission, down to the detection limit of the ROSAT data. Using X-ray hardness ratio diagrams we differentiate between thermal plasma and power-law X-ray spectra which helps to determine the nature of the individual sources. Correlating the X-ray data with complementary observations ranging from the far-ultraviolet to the radio regime we increase the probability of correctly identifying sources belonging to Holmberg II. We did not detect soft X-ray emission originating from hot gas within supergiant HI shells above our luminosity sensitivity limit of (L_limit(0.1 - 2.1 keV) ~ 10^{37}erg/s). This finding can probably be attributed to blow-out in the case of the largest holes and insufficient sensitivity (due to strong photoelectric absorption) in case of the smaller HI holes. However we find faint X-ray sources well beyond the stellar body but within the HI distribution of Holmberg II, which suggests the presence of X-ray binaries. This indicates that star formation has taken place across the entire gaseous disk of Holmberg II in the past, some of which may have created the structures seen in the ISM at large galactocentric radii.
We present ROSAT PSPC and HRI observations of the dwarf irregular galaxy Holmberg II (UGC4305). This is one of the most luminous dwarf galaxies (Lx~ 10^{40} erg s^{-1} cm^{-2}) detected in the ROSAT All-Sky Survey. The X-ray emission comes from a sin
A detailed photometric study of star-forming regions (SFRs) in the galaxy Holmberg II has been carried out using archival observational data from the far infrared to ultraviolet obtained with the GALEX, Spitzer, and Herschel telescopes. Spectroscopic
The nearly face-on SBc galaxy M83 (NGC 5236) was observed for 25 ksec with the ROSAT PSPC. We detected 13 point-like sources in this galaxy, 10 of which were previously unknown. We measured extended X-ray radiation from almost the whole optically vis
We present the first broadband 0.3-25.0 kev X-ray observations of the bright ultraluminous X-ray source (ULX) Holmberg II X-1, performed by NuSTAR, XMM-Newton and Suzaku in September 2013. The NuSTAR data provide the first observations of Holmberg II
The mass function of galaxy clusters is a sensitive tracer of the gravitational evolution of the cosmic large-scale structure and serves as an important census of the fraction of matter bound in large structures. We obtain the mass function by fittin