arXiv subjects

Bin Yue

Publications and source records attributed to Bin Yue.

61 records · Page 4Linked to original sources

arXiv2013

Infrared background signatures of the first black holes

Angular fluctuations of the Near InfraRed Background (NIRB) intensity are observed up to scales $\simlt 1^{\ensuremath{^{\circ}}}$. Their interpretation is challenging as even after removing the contribution from detected sources, the residual signal is $>10$ times higher than expected from distant galaxies below the detection limit and first stars. We propose here a novel interpretation in which early, intermediate mass, accreting direct collapse black holes (DCBH), which are too faint to be detected individually in current surveys, could explain the observed fluctuations. We find that a population of highly obscured ($N_{\rm H}\simgt 10^{25} \rm cm^{-2}$) DCBHs formed in metal-free halos with virial temperature $10^4$ K at $z\simgt 12$, can explain the observed level $\approx 10^{-3}$ (nW m$^{-2}$ sr$^{-1})^2$ of the 3.6 and 4.5 $μ$m fluctuations on scales $>100''$. The signal on smaller scales is instead produced by undetected galaxies at low and intermediate redshifts. Albeit Compton-thick, at scales $θ> 100''$ DCBHs produce a CXB (0.5-2 keV)-NIRB ($4.5 \rm μm$) cross-correlation signal of $\simeq 10^{-11}$ erg s$^{-1}$ cm$^{-2}$ nW m$^{-2}$ sr$^{-1}$ slightly dependent on the specific value of the absorbing gas column ($N_{\rm H} \approx 10^{25} \rm cm^{-2}$) adopted and in agreement with the recent measurements by \cite{2012arXiv1210.5302C}. At smaller scales the cross-correlation is dominated by the emission of high-mass X-ray binaries (HMXB) hosted by the same low-$z$, undetected galaxies accounting for small scale NIRB fluctuations. These results outline the great potential of the NIRB as a tool to investigate the nature of the first galaxies and black holes.

astro-ph.CO↗

arXiv2013

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

Several independent measurements have confirmed the existence of fluctuations ($δF_{\rm obs}\approx 0.1 \rm nW/m^{2}/sr$ at $3.6 \rm μm$) 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 $f_{\rm esc} = 1$ at $z \ge 11$, decreasing to $\approx 0.05$ at $z = 5$. In the wavelength range $1.0-4.5 \rm μm$, the predicted cumulative flux is $F =0.2-0.04 \rm nW/m^2/sr$. 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 $δF = 0.01-0.002 \rm nW/m^2/sr$, 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.

astro-ph.CO↗

arXiv2012

Semi-Numerical Simulation of Reionization with Semi-Analytical Modeling of Galaxy Formation

In a semi-numerical model of reionization, the evolution of ionization fraction is simulated approximately by the ionizing photon to baryon ratio criterion. In this paper we incorporate a semi-analytical model of galaxy formation based on the Millennium II N-body simulation into the semi-numerical modeling of reionization. The semi-analytical model is used to predict the production of ionizing photons, then we use the semi-numerical method to model the reionization process. Such an approach allows more detailed modeling of the reionization, and also connects observations of galaxies at low and high redshifts to the reionization history. The galaxy formation model we use was designed to match the low-$z$ observations, and it also fits the high redshift luminosity function reasonably well, but its prediction on the star formation falls below the observed value, and we find that it also underpredicts the stellar ionizing photon production rate, hence the reionization can not be completed at $z \sim 6$ without taking into account some other potential sources of ionization photons. We also considered simple modifications of the model with more top heavy initial mass functions (IMF), with which the reionization can occur at earlier epochs. The incorporation of the semi-analytical model may also affect the topology of the HI regions during the EoR, and the neutral regions produced by our simulations with the semi-analytical model appeared less poriferous than the simple halo-based models.

astro-ph.CO↗

arXiv2012

Reionization in the Warm Dark Matter Model

Compared with the cold dark matter (CDM) model, in the warm dark matter (WDM) model formation of small scale structure is suppressed. It is often thought that this would delay the reionization of the intergalactic medium (IGM), as the star formation rate during the epoch of reionization (EOR) would be lowered. However, during the later stage of the EOR, a large portion of the ionizing photons are consumed by recombination inside the minihalos, where the gas has higher density and recombination rates than the gas in the IGM. The suppression of small scale structure would therefore reduce the recombination rate, and could potentially shorten the reionization process. This effect is investigated here by using the analytical "bubble model" of reionization. We find that in some cases, though the initiation of the EOR is delayed in the WDM model, its completion could be even earlier than the CDM case, but the effect is generally small. We obtain limits on the WDM particles mass for different reionization redshifts.

astro-ph.CO↗

arXiv2011

Constraint on dark matter annihilation with dark star formation using Fermi extragalactic diffuse gamma-ray background data

It has been proposed that during the formation of the first generation stars there might be a "dark star" phase in which the power of the star comes from dark matter annihilation. The adiabatic contraction process to form the dark star would result in a highly concentrated density profile of the host halo at the same time, which may give enhanced indirect detection signals of dark matter. In this work we investigate the extragalactic $γ$-ray background from dark matter annihilation with such a dark star formation scenario, and employ the isotropic $γ$-ray data from Fermi-LAT to constrain the model parameters of dark matter. The results suffer from large uncertainties of both the formation rate of the first generation stars and the subsequent evolution effects of the host halos of the dark stars. We find, in the most optimistic case for $γ$-ray production via dark matter annihilation, the expected extragalactic $γ$-ray flux will be enhanced by 1-2 orders of magnitude. In such a case, the annihilation cross section of the supersymmetric dark matter can be constrained to the thermal production level, and the leptonic dark matter model which is proposed to explain the positron/electron excesses can be well excluded. Conversely, if the positron/electron excesses are of a dark matter annihilation origin, then the early Universe environment is such that no dark star can form.

astro-ph.CO↗

arXiv2010

Leptonic dark matter annihilation in the evolving universe: constraints and implications

The cosmic electron and positron excesses have been explained as possible dark matter (DM) annihilation products. In this work we investigate the possible effects of such a DM annihilation scenario during the evolution history of the Universe. We first calculate the extragalactic $γ$-ray background (EGRB), which is produced through the final state radiation of DM annihilation to charged leptons and the inverse Compton scattering between electrons/positrons and the cosmic microwave background. The DM halo profile and the minimal halo mass, which are not yet well determined from the current N-body simulations, are constrained by the EGRB data from EGRET and Fermi telescopes. Then we discuss the impact of such leptonic DM models on cosmic evolution, such as the reionization and heating of intergalactic medium, neutral Hydrogen 21 cm signal and suppression of structure formation. We show that the impact on the Hydrogen 21 cm signal might show interesting signatures of DM annihilation, but the influence on star formation is not remarkable. Future observations of the 21 cm signals could be used to place new constraints on the properties of DM.

astro-ph.CO↗

arXiv2009

The contribution of the IGM and minihalos to the 21 cm signal of reionization

We study the statistical properties of the cosmological 21 cm signal from both the intergalactic medium (IGM) and minihalos, using a reionization simulation that includes a self--consistent treatment of minihalo photoevaporation. We consider two models for minihalo formation and three typical thermal states of the IGM -- heating purely by ionization, heating from both ionizing and $\rm Lyα$ photons, and a maximal "strong heating" model. We find that the signal from the IGM is almost always dominant over that from minihalos. In our calculation, the differential brightness temperature, $δT_b,$ of minihalos is never larger than 2 mK. Although there are indeed some differences in the signals from the minihalos and from the IGM, even with the planned generation of radio telescopes it will be unfeasible to detect them. However, minihalos significantly affect the ionization state of the IGM and the corresponding 21 cm flux.

astro-ph.CO↗