arXiv subjects

Yong-Heng Zhao

Publications and source records attributed to Yong-Heng Zhao.

47 records · Page 3Linked to original sources

arXiv2011

The Diagnostics and Possible Evolution in Active Galactic Nuclei Associated With Starburst Galaxies

We present a large sample which contains 45 Seyfert 1 galaxies (Sy1s), 46 hidden broad-line region (HBLR) Seyfert 2 galaxies (Sy2s), 57 non-HBLR Sy2s, and 22 starburst galaxies to distinguish their properties and to seek the possible evolution of active galactic nuclei (AGNs) and starburst galaxies. We show that (1) using a plot of [O III] ł5007/H/alpha versus [N II] ł6584/H/alpha of standard optical spectral diagnostic diagrams, we find that a equation can separate well non-HBLR Sy2s and HBLR Sy2s; (2) the emission-line ratios and both the combination of the ratios and polycyclic aromatic hydrocarbon (PAH) strength are utilized effectively to separate starburst galaxies and Seyfert galaxies; (3) we compare a number of quantities from the data and confirm well the separations with statistics; (4) on the basis of statistics, we suggest that HBLR Sy2s may be the counterparts of Sy1s at edge-on orientation. In addition, we discuss the possibility of starburst galaxies evolving to non-HBLR Sy2s and HBLR Sy2s and then evolving to Sy1s based on the statistical analysis.

astro-ph.HE↗

arXiv2011

The meaning inferred from the spin period distribution of normal pulsars

We make statistics about the number distribution of normal radio pulsars according to the pulsar spin period. And find the physical meaning of the traditional statistical method about this problem is very limited. According to the statistical method proposed by us, the distribution rule is exactly the exponentially decay with the spin period increasing, especially important, which can be interpreted as normal radio pulsar number decays as the radiative elements decay. It discloses that though belonging to two different extreme scales of the universe and having different inner active mechanisms, the normal radio pulsars and radiative elements accord with the same varying rule. And like the half decay period of the radiative elements we can also introduce the half decay spin period of the normal radio pulsars.

astro-ph.SR↗

arXiv2011

Ionization structure and Fe K$α$ energy for irradiated accretion disks

We study the radial ionization structure at the surface of an X-ray illuminated accretion disk. We plot the expected iron K$α$ line energy as a function of the Eddington ratio and of the distance of the emitting matter from the central source, for a non-rotating and a maximally-rotating black hole. We compare the predicted disk line energies with those measured in an archival sample of active galactic nuclei observed with {\it Chandra}, {\it XMM-Newton} and {\it Suzaku}, and discuss whether the line energies are consistent with the radial distances inferred from reverberation studies. We also suggest using rapidly-variable iron K$α$ lines to estimate the viscosity parameter of an accretion disk. There is a forbidden region in the line energy versus Eddington ratio plane, at low Eddington ratios, where an accretion disk cannot produce highly-ionized iron K$α$ lines. If such emission is observed in low-Eddington-ratio sources, it is either coming from a highly-ionized outflow, or is a blue-shifted component from fast-moving neutral matter.

astro-ph.HE↗

arXiv2011

The Different Nature in Seyfert 2 Galaxies With and Without Hidden Broad-Line Regions

We compile a large sample of 120 Seyfert 2 galaxies (Sy2s) which contains 49 hidden broad-line region (HBLR) Sy2s and 71 non-HBLR Sy2s. From the difference in the power sources between two groups, we test if HBLR Sy2s are dominated by active galactic nuclei (AGNs), and if non-HBLR Sy2s are dominated by starbursts. We show that: (1) HBLR Sy2s have larger accretion rates than non-HBLR Sy2s; (2) HBLR Sy2s have larger \Nev $λ14.32$/\Neii $λ12.81$ and \oiv $λ25.89$/\Neii $λ12.81$ line ratios than non-HBLR Sy2s; (3) HBLR Sy2s have smaller $IRAS$ $f_{60}/f_{25}$ flux ratio which shows the relative strength of the host galaxy and nuclear emission than non-HBLR Sy2s. So we suggest that HBLR Sy2s and non-HBLR Sy2s are AGN-dominated and starburst-dominated, respectively. In addition, non-HBLR Sy2s can be classified into the luminous ($L_{\rm [O III]}>10^{41} \rm ergs s^{-1}$) and less luminous ($L_{\rm [O III]}<10^{41} \rm ergs s^{-1}$) samples, when considering only their obscuration. We suggest that: (1) the invisibility of polarized broad lines (PBLs) in the luminous non-HBLR Sy2s depends on the obscuration; (2) the invisibility of PBLs in the less luminous non-HBLR Sy2s depends on the very low Eddington ratio rather than the obscuration.

astro-ph.HE↗

arXiv2010

Hard X-ray photon index as an indicator of bolometric correction in active galactic nuclei

We propose the rest-frame 2-10 keV photon index, \ga, acting as an indicator of the bolometric correction, \lb/$L_{\rm 2-10keV}$ (where \lb~ is the bolometric luminosity and $L_{\rm 2-10keV}$ is the rest-frame 2-10 keV luminosity), in radio-quiet active galactic nuclei (AGNs). Correlations between \ga~ and both bolometric correction and Eddington ratio are presented, based on simultaneous X-ray, UV, and optical observations of reverberation -mapped AGNs. These correlations can be compared with those for high-redshift AGNs to check for any evolutionary effect. Assuming no evolutionary effect in AGNs' spectral properties, together with the independent estimates of $L_{\rm 2-10keV}$, the bolometric correction, Eddington ratio, and black hole (BH) mass can all be estimated from these correlations for high-redshift AGNs, with the mean uncertainty of a factor of 2-3. If there are independent estimates of BH masses, \ga~ for high-redshift AGNs can be used to determine their true \lb~ and $L_{\rm 2-10keV}$, and in conjunction with the redshift, can be potentially used to place constraints on cosmology by comparison with the rest-frame 2-10 keV flux. We find that the true $L_{\rm 2-10keV}$ estimated from \ga~ for the brightest Type I AGNs with $z<1$ in the Lockman Hole is generally in agreement with the observed $L_{\rm 2-10keV}$. However, there are still many uncertainties, such as the accurate determination of the intrinsic \ga~ for distant AGNs and the large uncertainty in the luminosities obtained, which call for significant further study before ``AGN cosmology'' can be considered a viable technique.

astro-ph.CO↗

arXiv2010

Star formation histories and evolution of 35 brightest E+A galaxies from SDSS DR5

We pick out the 35 brightest galaxies from Goto's E+A galaxies catalogue which are selected from the Sloan Digital Sky Survey Data Release 5. The spectra of E+As are prominently characterized by the strong Balmer absorption lines but little [Oii] or H_alpha emission lines. In this work we study the stellar populations of the sample galaxies by fitting their spectra using ULySS, which is a robust full spectrum fitting method. We fit each of the sample with 1-population (a single stellar population-a SSP) and 3-population (3 SSPs) models, separately. By 1-population fits, we obtain SSP-equivalent ages and metallicities which correspond to the `luminosity-weighted' averages. By 3-population fits, we divide components into three groups in age (old stellar population-OSP, intermediate-age stellar population-ISP, and young stellar population-YSP), and then get the optimal age, metallicity and population fractions in both mass and light for OSP, ISP and YSP. During the fits, both Pegase.HR/Elodie3.1 and Vazdekis/Miles are used as two independent population models. The two models result in generally consistent conclusions as follows: for all the sample galaxies, YSPs (< 1Gyr) make important contributions to the light. However, the dominant contributors to mass are OSPs. We also reconstruct the smoothing star formation histories (SFHs) by giving star formation rate (SFR) versus evolutionary age. In addition, we fit the E+A sample and 34 randomly selected elliptical galaxies with 2-population (2 SSPs) model. We obtain the equivalent age of old components for each of the E+A sample and elliptical galaxies. By comparison, the old components of E+As are statistically much younger than those of ellipticals. From the standpoint of the stellar population age, this probably provides an evidence for the proposed evolutionary link from E+As to early-types (E/S0s).

astro-ph.CO↗

arXiv2007

Two novel approaches for photometric redshift estimation based on SDSS and 2MASS databases

We investigate two training-set methods: support vector machines (SVMs) and Kernel Regression (KR) for photometric redshift estimation with the data from the Sloan Digital Sky Survey Data Release 5 and Two Micron All Sky Survey databases. We probe the performances of SVMs and KR for different input patterns. Our experiments show that the more parameters considered, the accuracy doesn't always increase, and only when appropriate parameters chosen, the accuracy can improve. Moreover for different approaches, the best input pattern is different. With different parameters as input, the optimal bandwidth is dissimilar for KR. The rms errors of photometric redshifts based on SVM and KR methods are less than 0.03 and 0.02, respectively. Finally the strengths and weaknesses of the two approaches are summarized. Compared to other methods of estimating photometric redshifts, they show their superiorities, especially KR, in terms of accuracy.

astro-ph↗

arXiv2006

Possible Streams of the Globular Clusters in the Galaxy

This paper aims to retrieve the ghost streams under the pre-assumption that all the globular clusters in our Galaxy were formed in the very early merge events. The results are based on two speculations: that the specific energy and angular momentum of the globular clusters after merge are not changed in process of evolution and that the globular clusters with common origin would stay in the same orbit plane as parent galaxy. In addition, taking into account the apo-galacticum distance of the orbits, five possible streams were suggested with a significant confidence. The number of streams is consistent with previous results. Three of the four well established members of the Sagittarius stream were found to be in one of our streams. Several other globular clusters in our result were also thought to come from accretion by previous research. Furthermore, the orbital parameters of the streams are derived, which provide a way to testify whether these streams are true with the help of the accurate measurement of proper motions of the globular clusters.

astro-ph↗

arXiv2006

The DWT Power Spectrum of the two-degree Field Galaxy Redshift Survey

The power spectrum of the two-degree Field Galaxy Redshift Survey (2dFGRS) sample is estimated with the discrete wavelet transform (DWT) method. The DWT power spectra within $0.04 <k< 2.3 h$Mpc$^{-1}$ are measured for three volume-limited samples defined in connective absolute magnitude bins $-19 \sim -18$, $-20 \sim -19$ and $-21 \sim -20$. We show that the DWT power spectrum can effectively distinguish $Λ$CDM models of $σ_8=0.84$ and $σ_8=0.74$. We adopt maximum likelihood method to perform three-parameter fitting with bias parameter $b$, pairwise velocity dispersion $σ_{pv}$ and redshift distortion parameter $β=Ω_m^{0.6}/b$ to the measured DWT power spectrum. Fitting results denotes that in a $σ_8=0.84$ universe the best fitted $Ω_m$ given by the three samples are consistent in the range $0.28 \sim 0.36$, and the best fitted $σ_{pv}$ are $398^{+35}_{-27}$, $475^{+37}_{-29}$ and $550 \pm 20$km/s for the three samples, respectively. However in the model of $σ_8=0.74$, our three samples give very different values of $Ω_m$. We repeat the fitting by using empirical formula of redshift distortion. The result of the model of low $σ_8$ is still poor, especially, one of the best value $σ_{pv}$ is as large as $10^3$km/s. The power spectrum of 2dFGRS seems in disfavor of models with low amplitude of density fluctuations.

astro-ph↗

arXiv2006

A Comptonization Model for the Prompt Optical and Infrared Emission of GRB 041219A

Prompt optical emission from the $γ$-ray burst of GRB 041219A has been reported by Vestrand et al. There was a fast rise of optical emission simultaneous with the dominant $γ$-ray pulse, and a tight correlation with the prompt $γ$-ray emission has been displayed. These indicate that the prompt optical emission and $γ$-ray emission would naturally have a common origin. We propose that this optical component can be modeled by considering the Comptonization of $γ$-ray photons by an electron cloud. As a result of this mechanism, the arrival time of the optical photons is delayed compared with that of the $γ$-rays. We restrict that the lag time to be shorter than 10 s, within which the prompt optical emission is considered to vary simultaneously with the prompt $γ$-ray emission. Taking the observations of GRB 041219A into account, we derive the number density of the surrounding electron cloud required for Comptonization. The redshift of GRB 041219A is predicted to be $z\lesssim 0.073$ as well.

astro-ph↗

arXiv1997

EGRET gamma-ray source 2EG J0809+5117, a quasar with redshift of 1.14?

The low dispersion (400$Å$/mm) spectrum of the optical counterpart of a flat-spectrum radio source 87GB 080315.5+512613, which is one of two possible radio counterparts of 2EG J0809+5117, was obtained recently. The optical counterpart, which is $2.02''$ away from 87GB 080315.5+512613 and $19.3'$ away from 2EG J0809+5117, was identified as a quasar with redshift of 1.14. We noted that Mattox et al. (1997) suggested the other radio counterpart 87GB 080459.4+495915 (OJ 508), which is $87.1'$ away from 2EG J0809+5117, is the more potential identification, though it was previously suggested to be the identification (with low confidence) of another nearby EGRET source 2EG J0807+4849. Our observation suggests that it is quite possible that 87GB 080315.5+512613 is the identification of 2EG J0809+5117 rather than 87GB 080459.4+495915. But we still can not exclude the possibility of 87GB 080459.4+495915 at present. Moreover, in order to determine whether or not 87GB 080315.5+512613 is a blazar type quasar, the optical polarization and variability measures of its optical counterpart are strongly encouraged.

astro-ph↗