Related papers: Can nebular HeII emission be explained by ultra-lu…
Ultraluminous X-ray sources (ULXs) are enigmatic sources first discovered in the 1980s in external galaxies. They are characterized by their extraordinarily high X-ray luminosity, which often exceeds $10^{40}\, \rm{erg \; s^{-1}}$. Our…
We determined oxygen and iron abundances of the interstellar medium (ISM) using K-shell (O) and L-shell (Fe) X-ray photo-ionization edges towards Ultra luminous X-ray sources (ULXs). We determine the hydrogen column densities (n_H) towards…
We present results from Subaru/FMOS near-infrared (NIR) spectroscopy of 118 star-forming galaxies at $z\sim1.5$ in the Subaru Deep Field. These galaxies are selected as [OII]$\lambda$3727 emitters at $z\approx$ 1.47 and 1.62 from…
Aims: In light of recent discoveries of pulsating ULXs and recently introduced models, that propose neutron stars (NSs) as the central engines of ULXs, we revisit the (XMM-Newton and NuSTAR) spectra of eighteen well known ULXs, in search of…
We present a model for nebular emission in star forming galaxies, which takes into account the effects of dust reprocessing. The nebular emissions have been computed with CLOUDY and then included into GRASIL, our spectrophotometric code…
The nature of ultraluminous X-ray sources (ULXs) is still debated. Recent studies show that metal-poor massive stars can collapse into massive stellar black holes (MSBHs), that is black holes with mass > 25 Msun. Such MSBHs are sufficiently…
Some ultraluminous X-ray sources (ULXs) exhibit X-ray pulses, and their central sources are thought to be neutron stars. It has also been suggested that some are transient sources with Be-type donors. In this study, we use the mass…
X-ray Bright Optically Normal Galaxies (XBONGs) constitute a small but not negligible fraction of hard X-ray selected sources in recent Chandra and XMM-Newton surveys. Even though several possibilities were proposed to explain why a…
We present the results of optical panoramic and long-slit spectroscopy of the nebula MF16 associated with the Ultraluminous X-ray Source NGC6946 ULX-1. More than 20 new emission lines are identified in the spectra. Using characteristic line…
Classical Wolf-Rayet (WR) stars are hot, massive stars with depleted hydrogen. At low metallicities (Z), WN3-type WR stars have relatively thin winds and are major sources of ionizing flux. The detection of high-ionization emission lines in…
We have constructed a model to describe the optical emission from ultra-luminous X-ray sources (ULXs). We assume a binary model with a black hole accreting matter from a Roche lobe filling companion star. We consider the effects of…
Binary population synthesis combined with cosmological models suggest that X-ray emission from star-forming galaxies, consisting primarily of emission from X-ray binaries (XRBs) and the hot interstellar medium (ISM), could be an important,…
In this paper, we investigate the behaviour of the number of Lyman continuum ionizing photons as compared to the actual number of hydrogen recombinations in HII galaxies. We evaluate the number of ionizing photons from the population…
Emission-line regions are key to understanding the properties of galaxies, as they trace the exchange of matter and energy between stars and the interstellar medium (ISM). In nearby galaxies, individual nebulae can be identified as HII…
Observations of molecular clouds, prestellar cores, and protoplanetary disks have established that the HNC/HCN ratio may be a potent diagnostic of molecular gas physical conditions. The processes that govern the relative abundances of these…
We consider 400 H II galaxies in which the oxygen abundances were obtained by electron temperature based methods. We split the sample in three metallicity bins. In each bin, a narrow sequence is found not only in pure emission line ratio…
Non-resonant FeII* 2365, 2396, 2612, 2626 emission can potentially trace galactic winds in emission and provide useful constraints to wind models. From the 3'x3' mosaic of the Hubble Ultra Deep Field (UDF) obtained with the VLT/MUSE…
Spectrophotometry constitutes a unique way to obtain the whole diagnostics (density, temperature, ionic abundances) of ionized gas nebulae, thus providing invaluable information about the objects where they reside. If such nebulae are in…
It is well-known that photoionization is the major mechanism powering nebulae emission-lines. For about 30 years, numerical simulations using photoionization codes have been employed to analyze HII regions, planetary nebulae and active…
High mass X-ray binaries (HMXBs) may have had a significant impact on the heating of the intergalactic medium in the early universe. Study of HMXBs in nearby, low metallicity galaxies that are local analogues to early galaxies can help us…