We study for the first time the environment of massive black hole (BH) seeds (~10^4-5 Msun) formed via the direct collapse of pristine gas clouds in massive haloes (>10^7 Msun) at z>6. Our model is based on the evolution of dark matter haloes within a cosmological N-body simulation, combined with prescriptions for the formation of BH along with both Pop III and Pop II stars. We calculate the spatially-varying intensity of Lyman Werner (LW) radiation from stars and identify the massive pristine haloes in which it is high enough to shut down molecular hydrogen cooling. In contrast to previous BH seeding models with a spatially constant LW background, we find that the intensity of LW radiation due to local sources, J_local, can be up to 10^6 times the spatially averaged background in the simulated volume and exceeds the critical value, J_crit, for the complete suppression of molecular cooling, in some cases by 4 orders of magnitude. Even after accounting for possible metal pollution in a halo from previous episodes of star formation, we find a steady rise in the formation rate of direct collapse (DC) BHs with decreasing redshift from 10^{-3}/Mpc^3/z at z=12 to 10^{-2}/Mpc^3/z at z=6. The onset of Pop II star formation at z~16 simultaneously marks the onset of the epoch of DCBH formation, as the increased level of LW radiation from Pop II stars is able to elevate the local levels of the LW intensity to J_local > J_crit while Pop III stars fail to do so at any time. The number density of DCBHs is sensitive to the number of LW photons and can vary by an order of magnitude at z=6 after accounting for reionisation feedback. Haloes hosting DCBHs are more clustered than similar massive counterparts that do not host DCBHs, especially at redshifts z>10. We also show that planned surveys with JWST should be able to detect the supermassive stellar precursors of DCBHs.Comment: 19 pages, 17 figures, v2 accepted for publication in MNRAS, minor additions in text and updates in reference

Growing supermassive black holes (∼ 10 9 M ) that power the luminous z > 6 quasars from light seeds -the remnants of the first stars -within a Gyr of the Big Bang poses a timing challenge. The formation of massive black hole seeds via direct collapse with initial masses ∼ 10 4 − 10 5 M alleviates this problem. Viable direct collapse black hole (DCBH) formation sites, the satellite halos of star-forming galaxies, merge and acquire stars to produce a new, transient class of high redshift objects, Obese Black hole Galaxies (OBGs). The accretion luminosity outshines that of the stars in OBGs. We predict the multi-wavelength energy output of OBGs and growing Pop III remnants at (z = 9) for standard and slim disk accretion as well as high and low metallicities of the associated stellar population. We derive robust selection criteria for OBGs -a pre-selection to eliminate blue sources followed by color-color cuts (3) and the ratio of X-ray flux to rest-frame optical flux (F X /F 444W >> 1). Our cuts sift out OBGs from other infra-red bright, high and low redshift contaminants. OBGs with predicted M AB < 25 makes them unambiguously detectable by the Mid-Infra-Red Instrument (MIRI), on the upcoming James Webb Space Telescope (JWST). For parameters explored here, growing Pop III remnants with predicted M AB < 30 will likely be undetectable by JWST. We demonstrate that JWST has the power to discriminate initial seeding mechanisms.

We investigate the environment in which direct-collapse black holes may form by analysing a cosmological, hydrodynamical simulation that is part of the First Billion Years project. This simulation includes the most relevant physical processes leading to direct collapse of haloes, most importantly, molecular hydrogen depletion by dissociation of H 2 and H − from the evolving Lyman-Werner radiation field. We selected a sample of pristine atomic cooling haloes that have never formed stars in their past, have not been polluted with heavy elements and are cooling predominantly via atomic hydrogen lines. Amongst them we identified six haloes that could potentially harbour massive seed black holes formed via direct collapse (with masses in the range of 10 4−6 M ⊙ ). These potential hosts of direct-collapse black holes form as satellites are found within 15 physical kpc of proto-galaxies, with stellar masses in the range ≈ 10 5−7 M ⊙ and maximal star formation rates of ≈ 0.1 M ⊙ yr −1 over the past 5 Myr, and are exposed to the highest flux of Lyman-Werner radiation emitted from the neighbouring galaxies. It is the proximity to these proto-galaxies that differentiates these haloes from rest of the sample.

Using Chandra observations in the 2.15 deg 2 COSMOS legacy field, we present one of the most accurate measurements of the Cosmic X-ray Background (CXB) spectrum to date in the [0.3-7] keV energy band. The CXB has three distinct components: contributions from two Galactic collisional thermal plasmas at kT∼0.27 and 0.07 keV and an extragalactic power-law with photon spectral index Γ=1.45±0.02. The 1 keV normalization of the extragalactic component is 10.91±0.16 keV cmRemoving all X-ray detected sources, the remaining unresolved CXB is best-fit by a power-law with normalization 4.18±0.26 keV cm −2 s −1 sr −1 keV −1 and photon spectral index Γ=1.57±0.10. Removing faint galaxies down to i AB ∼27-28 leaves a hard spectrum with Γ ∼1.25 and a 1 keV normalization of ∼1.37 keV cm −2 s −1 sr −1 keV −1 . This means that ∼91% of the observed CXB is resolved into detected X-ray sources and undetected galaxies. Unresolved sources that contribute ∼ 8 − 9% of the total CXB show a marginal evidence of being harder and possibly more obscured than resolved sources. Another ∼1% of the CXB can be attributed to still undetected star forming galaxies and absorbed AGN. According to these limits, we investigate a scenario where early black holes totally account for non source CXB fraction and constrain some of their properties. In order to not exceed the remaining CXB and the z ∼6 accreted mass density, such a population of black holes must grow in Compton-thick envelopes with N H >1.6×10 25 cm −2 and form in extremely low metallicity environments (Z ⊙ ) ∼ 10 −3 .

Direct collapse black holes (DCBH) have been proposed as a solution to the challenge of assembling supermassive black holes by z > 6 to explain the bright quasars observed at this epoch. The formation of a DCBH seed with M BH ∼ 10 4−5 M ⊙ requires a pristine atomiccooling halo to be illuminated by an external radiation field that is sufficiently strong to entirely suppress H 2 cooling in the halo. Many previous studies have attempted to constrain the critical specific intensity that is likely required to suppress H 2 cooling, denoted as J crit . However, these studies have typically assumed that the incident external radiation field can be modeled with a black-body spectrum. Under this assumption, it is possible to derive a unique value for J crit that depends only on the temperature of the black-body. In this study we consider a more realistic spectral energy distribution (SED) for the external source of radiation that depends entirely on its star formation history and age. The rate of destruction of the species responsible for suppressing molecular hydrogen cooling depends on the detailed shape of the SED. Therefore the value of J crit is tied to the shape of the incident SED of the neighbouring galaxy. We fit a parametric form to the rates of destruction of H 2 and H − that permit direct collapse. Owing to this, we find that J crit is not a fixed threshold but can lie anywhere in the range J crit ∼ 0.5-10 3 , depending on the details of the source stellar population.