Xuelei Chen

Does the mass of a black hole decrease due to the accretion of phantom energy

According to Babichev et al., the accretion of a phantom test fluid onto a Schwarzschild black hole will induce the mass of the black hole to decrease, however the backreaction was ignored in their calculation. Using new exact solutions describing black holes in a background Friedmann-Robertson-Walker universe, we find that the physical black hole mass may instead increase due to the accretion of phantom energy. If this is the case, and the future universe is dominated by phantom dark energy, the black hole apparent horizon and the cosmic apparent horizon will eventually coincide and, after that, the black hole singularity will become naked in finite comoving time before the big rip occurs, violating the cosmic censorship conjecture.

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.

The contribution of high redshift galaxies to the Near-Infrared Background

Several independent measurements have confirmed the existence of fluctuations (δFobs ≈ 0.1 nW/m 2 /sr at 3.6 �m) up to degree angular scales in the source-subtracted Near InfraRed Background (NIRB) whose origin is unknown. By combining high resolution cosmological N-body/hydrodynamical simulations with an analytical model, and by matching galaxy Luminosity Functions (LFs) and the constraints on reionization simultaneously, we predict the NIRB absolute flux and fluctuation amplitude produced by high-z (z > 5) galaxies (some of which harboring Pop III stars, shown to provide a negligible contribution). This strategy also allows us to make an empirical determination of the evolution of ionizing photon escape fraction: we find fesc = 1 at z ≥ 11, decreasing to ≈ 0.05 at z = 5. In the wavelength range 1.0 − 4.5 �m, the predicted cumulative flux is F = 0.2−0.04 nW/m 2 /sr. However, we find that the radiation from high-z galaxies (including those undetected by current surveys) is insufficient to explain the amplitude of the observed fluctuations: at l = 2000, the fluctuation level due to z > 5 galaxies is δF = 0.01 −0.002 nW/m 2 /sr, with a relative wavelength-independent amplitude δF/F = 4%. The source of the missing power remains unknown. This might indicate that an unknown component/foreground, with a clustering signal very similar to that of high-z galaxies, dominates the source-subtracted NIRB fluctuation signal. osmology: diffuse radiation–galaxies: high redshift–methods: numerical.

DISTRIBUTION OF SATELLITE GALAXIES IN HIGH-REDSHIFT GROUPS

We use galaxy groups at redshifts between 0.4 and 1.0 selected from the Great Observatories Origins Deep Survey to study the color-morphological properties of satellite galaxies and investigate possible alignment between the distribution of the satellites and the orientation of their central galaxy. We confirm the bimodal color and morphological-type distribution for satellite galaxies at this redshift range: the red and blue classes correspond to the early and late morphological types, respectively, and the early-type satellites are on average brighter than the late-type ones. Furthermore, there is a morphological conformity between the central and satellite galaxies: the fraction of early-type satellites in groups with an early-type central is higher than those with a late-type central galaxy. This effect is stronger at smaller separations from the central galaxy. We find a marginally significant signal of alignment between the major axis of the early-type central galaxy and its satellite system, while for the late-type centrals no significant alignment signal is found. We discuss the alignment signal in the context of shape evolution of groups.

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

Constraints on the Brans-Dicke gravity theory with the Planck data

\sigma_{w_0} \sim 0.082

BRIGHTEST SATELLITE GALAXY ALIGNMENT OF SLOAN DIGITAL SKY SURVEY GALAXY GROUPS

and

PERTURBATION THEORY OF THE COSMOLOGICAL LOG-DENSITY FIELD

\sigma_{w_a} \sim 0.21

Cosmological models with Lagrange multiplier field

from the BAO and RSD measurements,

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

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