arXiv subjects

Vanesa Douna

Publications and source records attributed to Vanesa Douna.

2 recordsLinked to original sources

arXiv2022

X-ray emission from star cluster winds in starburst galaxies

Inspired by the excess soft X-ray emission recently detected in Green Pea galaxies, we model the soft X-ray emission (0.5 - 2.0 keV) of hot gas from star cluster winds. By combining individual star clusters, we estimate the soft X-ray emission expected from the typically unresolved diffuse hot gas in starburst galaxies, devoid of competing emission from e.g., AGN or other unresolved point sources. We use stellar models of sub-solar metallicities (0.02 $Z_{\odot}$ and 0.4 $Z_{\odot}$), and take into account supernova explosions for massive stars. For lower metallicities, we find that stellar winds do not contribute significantly ($\lesssim 3$ % of the mechanical energy) to the observed soft X-ray emission of normal star forming galaxies. For higher metallicities and possibly also for larger proportions of massive star clusters in the simulated starburst galaxies, we reproduce well the observed correlation between star formation rate and X-ray luminosity previously reported in the literature. However, we find that no combination of model assumptions is capable of reproducing the substantial soft X-ray emission observed from Green Pea galaxies, indicating that other emission mechanisms (i.e. unusually large quantities of High-/Low-Mass X-ray Binaries, Ultra-Luminous X-ray sources, a modified initial mass function, Intermediate-Mass Black Holes, or AGN) are more likely to be responsible for the X-ray excess.

astro-ph.GA↗

arXiv2019

Green Peas in X-rays

Green Peas represent a population of compact, highly star-forming dwarf galaxies at redshifts z ~ 0.2-0.3 that have recently been found to show signatures of ultraviolet ionizing radiation leakage. They are being considered as analogs to high-redshift star-forming galaxies, possibly responsible for the cosmic reionization. Despite the intensive studies of Green Peas in the ultraviolet and optical domains, their X-ray properties have only so far been probed by nearby analogs. In this paper, we present the first measurements of Green Peas in the X-ray domain to constrain their spectral properties and fluxes at high energies. We analyzed XMM-Newton observations of three Green Pea sources. For two of them, we found an X-ray luminosity exceeding by a half-order of magnitude its predicted value, derived from the star formation rate and metallicity. Only an upper limit of the X-ray luminosity was derived for the third studied galaxy. Our results thus indicate that at least some Green Peas produce copious amounts of highly energetic photons, larger than detected in other star-forming galaxies. We discuss possible physical scenarios for the measured X-ray excess, including the presence of a hidden active galactic nucleus, a larger population of X-ray binaries, or ultra-luminous X-ray sources. Future spatially resolved X-ray images will discriminate between the models. Larger Green Pea samples will provide a possible link between the X-ray properties and the leaking ultraviolet radiation.

astro-ph.GA↗