arXiv subjects

A. Gurpide

Publications and source records attributed to A. Gurpide.

3 recordsLinked to original sources

arXiv2026

Investigating the ionization mechanisms powering the extreme emission lines in metal-poor galaxies

Extreme emission metal-poor galaxies (EEMPGs) are excellent local laboratories for understanding the extreme physical conditions and ionizing radiation fields in the early Universe. However, the exact source of high-ionization emission lines in them, whether from intermediate-mass black holes (IMBHs), ultra-luminous X-ray sources (ULXs), or radiative shocks, remains debated. We characterize the fundamental properties and ionizing radiation field on metal-poor EEMPGs, aiming to identify the dominant sources of the highly ionizing photons that drive these lines. We selected a sample of 11 EEMPGs, among the most metal-poor galaxies with JWST/MIRI observations known so far (12+log(O/H) < 8.0, or Z/Z$_\odot$ < 20%). Using optical and IR diagnostic diagrams for ions of both high and low ionization potential, we constrain the ionization source dominating their spectral features. We detect high-ionization lines, notably He II$λ$4686 in all galaxies and [Ne V] 14.3 $μ$m in 42% of a broader sample of local EEMPGs. The multi-wavelength diagnostic diagrams reveal that our EEMPGs are located in areas that normally are occupied by active galactic nuclei (AGNs) or between the star-formation and AGN sequences. Evaluating the energetics required to produce these lines, we find that radiative shocks and ULXs are not sufficient. Instead, our analysis suggests that a combination of sources with star-formation and a small contribution from an IMBH provide enough high-energy photon budget to explain the emission lines of ions with high-ionization potentials (> 54 eV). Our EEMPG sample, covering various properties, is ideal for studying the first galaxies. Their flux ratios of low- and high-ionization lines suggest stellar radiation as the likely ionization source, with a small contribution from an IMBH (4-8%). Pure shocks fail to explain the observed emission line ratios and ionizing photon budget.

astro-ph.GA↗

arXiv2025

QPEs as Lense-Thirring precession of super-Eddington flows

Quasi-periodic eruptions (QPEs) are a recently identified class of X-ray transient associated with tidal disruption events by supermassive black holes, and for which there are multiple possible explanations. In this paper we present a simple model which requires the black hole be spinning, be misaligned with the accretion flow (both conditions of which are almost certainly met) and that the accretion rate is a few times the Eddington limit. We speculate that the resulting Lense-Thirring torques force the disc and entrained outflows to precess, leading to increased X-ray flux when the wind-cone is oriented at lower inclinations to the observer. We test the range of parameters for which this model could explain the period and brightness of the QPE events discovered thus far, and make qualitative comparisons between the observed X-ray spectra and lightcurves to those extracted from GR-RMHD simulations. Overall, we find some areas of promising concordance, and identify challenges related to the details of current simulations.

astro-ph.HE↗

arXiv2022

Propeller states in locally super-critical ULXs

An expected signature of the presence of neutron stars in the population of ultraluminous X-ray sources (ULXs) are large scale changes in X-ray luminosity, as systems reach spin equilibrium and a propeller state ensues. We explore the predicted luminosity changes when the disc is locally super-critical, finding that a significant parameter space in dipole field strength and accretion rate (at large radius) can be accompanied by changes of less than an order of magnitude in luminosity. We discuss the spectral signature and locate three ULXs (IC 342 X-1, Cir ULX-5 and NGC 1313 X-1) which appear to show changes consistent with super-Eddington systems entering a propeller state, and place rough constraints on the dipole field strength of NGC 1313 X-1 of $<$ 10$^{10}$ G. This work implies that the most reliable means by which to search for putative propeller states will be to search for changes in hardness ratio and at high energies.

astro-ph.HE↗