Search arXiv⌕ Search
Home/Archive/arXiv

arXiv · 1711.05268

The Shape of the Cosmic X-ray Background: Nuclear Starburst Discs and the Redshift Evolution of AGN Obscuration

Raj Gohil·David R. Ballantyne
View original source ↗Read source document ↗Export metadata ↓

Abstract

A significant number of active galactic nuclei (AGNs) are observed to be hidden behind dust and gas. The distribution of material around AGNs plays an important role in modeling the cosmic X-ray background (CXB), especially the fraction of Type-2 AGNs ($f_2$). One of the possible explanations for the obscuration in Seyfert galaxies at intermediate redshift is dusty starburst discs. We compute the 2D hydrostatic structure of 768 nuclear starburst discs (NSDs) under various physical conditions and also the distribution of column density along the line of sight ($N_{\text{H}}$) associated with these discs. Then, the $N_{\text{H}}$ distribution is evolved with redshift by using the redshift dependent distribution function of input parameters. The $f_2$ shows a strong positive evolution up to $z=2$, but only a weak level of enhancement at higher $z$. The Compton-thin and Compton-thick AGN fractions associated with these starburst regions increase as $\propto (1+z)^δ$ where the $δ$ is estimated to be 1.12 and 1.45, respectively. The reflection parameter $R_f$ associated with column density $N_{\text{H}} \geq 10^{23.5}$ cm$^{-2}$ extends from 0.13 at $z=0$ to 0.58 at $z=4$. A CXB model employing this evolving $N_{\text{H}}$ distribution indicates more compact ($R_{\text{out}}<120$ pc) NSDs provide a better fit to the CXB. In addition to "Seyfert-like" AGNs obscured by nuclear starbursts, we predict that 40 to 60 per cent of quasars must be Compton-thick to produce the peak of the CXB spectrum within observational uncertainty. The predicted total number counts of AGNs in 8-24 keV band are in fair agreement with observations from NuSTAR.

Explore related subjects

astro-ph.HE

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Raj Gohil, David R. Ballantyne. 2018-01-08. The Shape of the Cosmic X-ray Background: Nuclear Starburst Discs and the Redshift Evolution of AGN Obscuration. https://doi.org/10.1093/mnras%2Fsty068

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related papers

arXiv2026

Deciphering the Physical Origin of GRB 240825A: A Long GRB Lacking a Bright Supernova

We present a comprehensive multiwavelength analysis of GRB 240825A, a bright gamma-ray burst (GRB) detected by Fermi and Swift, with a prompt duration ($T_{\rm 90}$ $\sim$ 4 sec in 50-300 keV in GBM) near the boundary separating short and long GRBs, prompting a detailed investigation into its classification and progenitor. We use classical prompt metrics (duration, minimum variability timescale (MVT), lag, and spectral hardness) and modern classification techniques (machine-learning (ML) based t-SNE, support vector machine, energy-hardness-duration, and $\varepsilon \equiv E_{γ,\mathrm{iso},52} / E_{p,z,2}^{5/3}$) and find most properties (prompt energetics, placement on the Amati relation, and spectral lag) of GRB 240825A consistent with a collapsar origin. However, extensive late-time optical and NIR follow-up with the 10.4m GTC and 8.4m binocular LBT telescopes reveals no bright supernova (like SN 1998bw) is detected down to stringent limits (e.g., $m_r > 25.0$ mag at 17.59 days), despite a redshift of $z = 0.659$ measured from GTC spectroscopy. Host galaxy SED modeling with Prospector indicates a massive, and star-forming galaxy-typical of collapsar GRB hosts, though with a large offset. We compare these findings with hybrid events like GRB 211211A, GRB 230307A, GRB 200826A, including SNe-GRBs, and conclude that GRB 240825A most likely originated from a massive star collapse, possibly with the associated SN heavily obscured or intrinsically faint. This study emphasizes the need for multiwavelength follow-up and a multi-layered classification to determine GRB progenitors.

astro-ph.HE↗
arXiv2026

The impact of flickering variability and magnetisation on the dynamics, stability and morphology of radio-loud AGN jets

The physics governing the morphology of radio-loud AGN jets is not fully understood. We investigate how magnetization, flickering jet power and their interplay affects the morphology of radio galaxies. We present a grid of relativistic magnetohydrodynamic simulations using the PLUTO code covering constant and variable jets with two levels of magnetisation. We find that the constant high magnetisation jets can lead to highly asymmetrical cocoon morphologies, whilst the variable high magnetisation jet can exhibit a broken morphology, caused by a discontinuous jet beam. Our work highlights the importance of magnetisation and variability on the stability and resulting morphology of radio-loud AGN jets, suggesting both are significant factors in addition to jet power or environment. Furthermore, we show that the interaction between magnetisation and variability can lead to the development of localised kink instabilities along the jet beam. Finally, we discuss the effects of hydrodynamic mixing in low magnetisation jets and the role of viewing angle dependence in comparisons between our simulations and observed sources. To facilitate this comparison we present a library of simulated radio images at different times in the simulations and from various viewing angles, which highlight a diverse set of complex morphologies.

astro-ph.HE↗
arXiv2026

Magnetic Eruption and Nucleosynthesis in GRνMHD Simulations of Spinning Neutron Star Mergers

We present three-dimensional general relativistic magnetohydrodynamics simulations of equal-mass binary neutron star mergers with varied neutron star spin configurations and second-moment neutrino transport, following the formation and early evolution of long-lived remnants. We compare a fiducial irrotational binary with binaries having spins that are aligned or antialigned with the orbital angular momentum, and examime how spin affects the merger dynamics, magnetic field evolution, outflows, and nucleosynthesis. Compared to the fiducial case, the aligned spin configuration releases more cold, neutron-rich tidal ejecta in the equatorial plane, which enables the development of a more tightly collimated polar outflow erupting from the remnant and inner accretion disk. Conversely, the case with spins antialigned with the orbit experiences a more violent collision at merger, disrupting magnetic amplification, loading the environment with debris, and impeding the propagation of magnetically driven winds. Strong neutrino reprocessing of the polar outflow in the irrotational and aligned spin cases produces $2.4\times 10^{-3}\,M_\odot$ of proton-rich ($Y_e \geq 0.49$) material, resulting in the synthesis of light r-process elements, whose subsequent decay potentially sends a unique electromagnetic signal from long-lived remnants. However, the outflows remain too dense and slow to be consistent with typical short gamma-ray bursts.

astro-ph.HE↗