Yidong Xu

The brief era of direct collapse black hole formation

It has been proposed that the first, intermediate-mass (≈ 10 5−6 M⊙) black holes might form through direct collapse of unpolluted gas in atomic-cooling halos exposed to a strong Lyman-Werner (LW) or near-infrared (NIR) radiation. As these systems are expected to be Compton-thick, photons above 13.6 eV are largely absorbed and reprocessed into lower energy bands. It follows that direct collapse black holes (DCBHs) are very bright in the LW/NIR bands, typically outshining small high-redshift galaxies by more than 10 times. Once the first DCBHs form, they then trigger a runaway process of further DCBH formation, producing a sudden rise in their cosmic mass density. The universe enters the “DCBH era” at z ≈ 20 when a large fraction of atomic-cooling halos are experiencing DCBH formation. By combining the clustering properties of the radiation sources with Monte Carlo simulations we show that in this scenario the DCBH mass density rises from ∼ 5 M⊙ Mpc −3 at z ∼ 30 to the peak value ∼ 5×10 5 M⊙ Mpc −3 at z ∼ 14 in our fiducial model. However, the abundance of active (accreting) DCBHs drops after z ∼ 14, as gas in the potential formation sites (unpolluted halos with virial temperature slightly above 10 4 K) is photoevaporated. This effect almost completely suppresses DCBH formation after z ∼ 13. The DCBH formation era lasts only ≈ 150 Myr, but it might crucially provide the seeds of the supermassive black holes (SMBHs) powering z ∼ 6 quasars.

FORECASTS ON THE DARK ENERGY AND PRIMORDIAL NON-GAUSSIANITY OBSERVATIONS WITH THE TIANLAI CYLINDER ARRAY

The Tianlai experiment is dedicated to the observation of large scale structures (LSS) by the 21 cm intensity mapping technique. In this paper we make forecasts on its capability at observing or constraining the dark energy parameters and the primordial non-Gaussianity. From the LSS data one can use the baryon acoustic oscillation (BAO) and the growth rate derived from the redshift space distortion (RSD) to measure the dark energy density and equation of state. The primordial non-Gaussianity can be constrained either by looking for scale-dependent bias in the power spectrum, or by using the bispectrum. Here we consider three cases: the Tianlai cylinder array pathfinder which is currently being built, an upgrade of the pathfinder array with more receiver units, and the full-scale Tianlai cylinder array. Using the full-scale Tianlai experiment, we expect

THE 21 cm FOREST AS A PROBE OF THE REIONIZATION AND THE TEMPERATURE OF THE INTERGALACTIC MEDIUM

\sigma_{w_0} \sim 0.082

On the faint-end of the high-z galaxy luminosity function

and

The earliest galaxies seen in 21 cm line absorption

\sigma_{w_a} \sim 0.21

The radio structure of 3C 316, a galaxy with double-peaked narrow optical emission lines

from the BAO and RSD measurements,

The asymmetric structure of the Galactic halo

\sigma_{\rm f_{NL}}^{\rm local} \sim 14

The structure of the Galactic halo: SDSS versus SuperCOSMOS

from the power spectrum measurements with scale-dependent bias, and

TWO-DIMENSIONAL TOPOLOGY OF COSMOLOGICAL REIONIZATION

\sigma_{\rm f_{NL}}^{\rm local} \sim 22

Semi-numerical simulation of reionization with semi-analytical modeling of galaxy formation

and