Eli Visbal

The observable signature of late heating of the Universe during cosmic reionization

Models and simulations of the epoch of reionization predict that spectra of the 21-centimetre transition of atomic hydrogen will show a clear fluctuation peak, at a redshift and scale, respectively, that mark the central stage of reionization and the characteristic size of ionized bubbles. This is based on the assumption that the cosmic gas was heated by stellar remnants—particularly X-ray binaries—to temperatures well above the cosmic microwave background at that time (about 30 kelvin). Here we show instead that the hard spectra (that is, spectra with more high-energy photons than low-energy photons) of X-ray binaries make such heating ineffective, resulting in a delayed and spatially uniform heating that modifies the 21-centimetre signature of reionization. Rather than looking for a simple rise and fall of the large-scale fluctuations (peaking at several millikelvin), we must expect a more complex signal also featuring a distinct minimum (at less than a millikelvin) that marks the rise of the cosmic mean gas temperature above the microwave background. Observing this signal, possibly with radio telescopes in operation today, will demonstrate the presence of a cosmic background of hard X-rays at that early time.

Direct collapse black hole formation from synchronized pairs of atomic cooling haloes

High-redshift quasar observations imply that supermassive black holes (SMBHs) larger than

The 21-cm signature of the first stars during the Lyman–Werner feedback era

\sim 10^9 ~ M_\odot

The signature of the first stars in atomic hydrogen at redshift 20

formed before

A No-Go Theorem for Direct Collapse Black Holes Without a Strong Ultraviolet Background

z=6

High-redshift star formation in a time-dependent Lyman–Werner background

. That such large SMBHs formed so early in the Universe remains an open theoretical problem. One possibility is that gas in atomic cooling halos exposed to strong Lyman-Werner (LW) radiation forms

Gravitational wave background from Population III binary black holes consistent with cosmic reionization

10^4-10^6 ~ M_\odot

Formation of massive Population III galaxies through photoionization feedback: a possible explanation for CR 7

supermassive stars which quickly collapse into black holes. We propose a scenario for direct collapse black hole (DCBH) formation based on synchronized pairs of pristine atomic cooling halos. We consider halos at very small separation with one halo being a subhalo of the other. The first halo to surpass the atomic cooling threshold forms stars. Soon after these stars are formed, the other halo reaches the cooling threshold and due to its small distance from the newly formed galaxy, is exposed to the critical LW intensity required to form a DCBH. The main advantage of this scenario is that synchronization can potentially prevent photoevaporation and metal pollution in DCBH-forming halos. Since the halos reach the atomic cooling threshold at nearly the same time, the DCBH-forming halo is only exposed to ionizing radiation for a brief period. Tight synchronization could allow the DCBH to form before stars in the nearby galaxy reach the end of their lives and generate supernovae winds. We use N-body simulations to estimate the abundance of DCBHs formed in this way. The largest source of uncertainty in our estimate is the initial mass function (IMF) of metal free stars formed in atomic cooling halos. We find that even for tight synchronization, the density of DCBHs formed in this scenario could explain the SMBHs implied by

Direct collapse black hole formation via high-velocity collisions of protogalaxies

z=6

Limits on Population III star formation in minihaloes implied by Planck

quasar observations. Metal pollution and photoevaporation could potentially reduce the abundance of DCBHs below that required to explain the observations in other models that rely on a high LW flux.