Progenitors of type Ia supernovae in elliptical galaxies

Although there is a nearly universal agreement that type Ia supernovae are associated with the thermonuclear disruption of a CO white dwarf, the exact nature of their progenitors is still unknown. The single degenerate scenario envisages a white dwarf accreting matter from a non-degenerate companion in a binary system. Nuclear energy of the accreted matter is released in the form of electromagnetic radiation or gives rise to numerous classical nova explosions prior to the supernova event. We show that combined X-ray output of supernova progenitors and statistics of classical novae predicted in the single degenerate scenario are inconsistent with X-ray and optical observations of nearby early type galaxies and galaxy bulges. White dwarfs accreting from a donor star in a binary system and detonating at the Chandrasekhar mass limit can account for no more than ~5% of type Ia supernovae observed in old stellar populations.Comment: To be published in Proceedings of "Astrophysics of neutron stars", Cesme, 201

Constraints from dwarf galaxies on black hole seeding and growth models with current and future surveys

Dwarf galaxies are considered to be potential ideal test-beds for constraining models of the seeding and tracing of the growth of supermassive and intermediate mass black holes (MBH) via their black hole occupation fraction (BHOF). Disentangling seeding from the confounding effects of mass assembly is, however, challenging. In this work, we use semi-analytical models (SAMs) to probe how various surveys perform at teasing apart different seed and growth scenarios. We check for differences in the measured BHOF given various cuts to black hole mass and AGN luminosity and develop a scheme to robustly compare SAMs, with their intrinsic uncertainties, to X-ray observations. We demonstrate that to tell seeding models apart, we need to detect or model all AGN brighter than $10^{37}\ \rm{erg \ s^{-1}}$ in galaxies of $M_* \sim 10^{8-10} \ \rm{M_{\odot}}$ Shallower surveys, like eRASS, cannot distinguish between seed models even with the compensation of a much larger survey volume. We show that the AMUSE survey strongly favours heavy seed models, growing with empirically motivated growth models either a power-law Eddington Ratio Distribution Function (ERDF) or one in which black hole accretion is tagged to the star-formation rate (AGN-MS). These two growth channels in turn can then be distinguished by the AGN luminosity function at $< 10^{44}\ \rm{erg \ s^{-1}}$. The different models also predict different radio scaling relations, which we quantify using the fundamental plane of black hole activity. We close with recommendations for the design of upcoming multi-wavelength campaigns that can optimally detect MBHs in dwarf galaxies.Comment: Submitted to AAS Journal

Constraining the Dark-matter Halo Mass of Isolated Low-surface-brightness Galaxies

Recent advancements in the imaging of low-surface-brightness objects revealed numerous ultra-diffuse galaxies in the local universe. These peculiar objects are unusually extended and faint: their effective radii are comparable to the Milky Way, but their surface brightnesses are lower than that of dwarf galaxies. Their ambiguous properties motivate two potential formation scenarios: the "failed" Milky Way, and the dwarf galaxy scenario. In this Letter, for the first time, we employ X-ray observations to test these formation scenarios on a sample of isolated, low-surface-brightness galaxies (LSBGs). Because hot gas X-ray luminosities correlate with the dark-matter halo mass, "failed" Milky-Way-type galaxies, which reside in massive dark-matter halos, are expected to have significantly higher X-ray luminosities than dwarf galaxies, which reside in low-mass dark-matter halos. We perform X-ray photometry on a subset of LSBGs identified in the Hyper Suprime-Cam Subaru survey, utilizing the XMM-Newton XXL North survey. We find that none of the individual galaxies show significant X-ray emission. By co-adding the signal of individual galaxies, the stacked galaxies remain undetected and we set an X-ray luminosity upper limit of L0.3-1 (2 keV) <= 6.2 x 10(37) (d/65 Mpc)(2) erg s(-1) for an average isolated LSBG. This upper limit is about 40 times lower than that expected in a galaxy with massive dark-matter halo, implying that the majority of isolated LSBGs reside in dwarf-size dark-matter halos