Super-Eddington accreting massive black holes as long-lived cosmological standards

TL;DR

This paper proposes using super-Eddington accreting massive black holes as long-lived cosmological distance indicators, based on their X-ray spectral properties, potentially providing a new cosmological ruler.

Contribution

The study introduces a novel method to estimate cosmological distances using SEAMBHs identified by their X-ray continuum slope, validated with a sample of narrow line Seyfert 1 galaxies.

Findings

Distances from the new method align better with standard distances for steeper X-ray spectra.

The method shows promise as a new cosmological ruler with large sample sizes.

X-ray spectral slope correlates with the accuracy of distance estimation.

Abstract

Super-Eddington accreting massive black holes (SEAMBHs) reach saturated luminosities above a certain accretion rate due to photon trapping and advection in slim accretion disks. We show that these SEAMBHs could provide a new tool for estimating cosmological distances if they are properly identified by hard X-ray observations, in particular by the slope of their 2-10 keV continuum. To verify this idea we obtained black hole mass estimates and X-ray data for a sample of 60 narrow line Seyfert 1 galaxies that we consider to be the most promising SEAMBH candidates. We demonstrate that the distances derived by the new method for the objects in the sample get closer to the standard luminosity distances as the hard X-ray continuum gets steeper. The results allow us to analyze the requirements for using the method in future samples of active black holes and to demonstrate that the expected uncertainty, given large enough samples, can make them into a useful, new cosmological ruler.