118517819
Quasar candidate selection and photometric redshift estimation based on SDSS and UKIDSS data
We present a sample of 8498 quasars with both SDSS ugriz optical and UKIDSS Y JHK near-IR photometric data. With this sample, we obtain the median colour-z relations based on 7400 quasars with magnitude uncertainties less than 0.1mag in all bands. By analyzing the quasar colours, we propose an empirical criterion in the Y K vs. g z colour-colour diagram to separate stars and quasars with redshift z < 4, and two other criteria for selecting high redshift quasars. Using the SDSS-UKIDSS colourz relations, we estimate the photometric redshifts of 8498 SDSS-UKIDSS quasars, and find that 85.0% of them are consistent with the spectroscopic redshifts within |�z| < 0.2, which leads to a significant increase of the photometric redshift accuracy than that based on the SDSS colour-z relations only. As two tests, we compare our colour selection criterion with a small UKIDSS/EDR quasar/star sample and a sample of 4671 variable sources in the SDSS Stripe 82 region with both SDSS and UKIDSS data. We find that they can be clearly divided into two classes (quasars and stars) by our criterion in the Y K vs. g z plot. We select 3834 quasar candidates from the variable sources with g < 20.5 in Stripe 82, 826 of them being SDSS quasars and the rest without SDSS spectroscopy. We estimate the photometric redshifts for 3519 quasar candidates with all UKIDSS Y JHK data and find an accuracy of 87.5% within |�z| < 0.2 with the spectroscopic redshifts of 819 SDSS-UKIDSS identified quasars among them. We demonstrate that even at the same spectroscopy limit as SDSS, with our criterion we can at least partially recover the missing quasars with z � 2.7 in SDSS. The SDSS identified quasars only take a small fraction (21.5%) of our quasar candidates selected from the variable sources in Stripe 82, indicating that a deeper spectroscopy is very promising in producing a much larger sample of quasars than SDSS. The implications of our current results to the future Chinese LAMOST quasar survey are also discussed.
198177313
Weighing black holes in the universe
The determination of the mass of black holes in our universe is crucial to understand their physics nature but is a great challenge to scientists. In this paper I briefly review some methods that are currently used to estimate the mass of black holes, especially those in X-ray binary systems and in galactic nuclei. Our recent progress in improving the mass estimates of supermassive black holes in active galactic nuclei by involving some empirical relations is presented. Finally I point out the similarities and common physics in Galactic black hole X-ray binaries and active galactic nuclei, and demonstrate that the black hole mass estimation is very much helpful to understand the accretion physics around black holes.
199676816
Discovering the missing bright quasars at intermediate redshifts based on the optical/near-IR color selections
5433221
A feedback compression star formation model and the black hole-bulge relations
We present a feedback compression model to describe galactic spheroid formation and its relation with the central nuclear activity. We suggest that the star formation itself can serve as the positive feedback in some extremely dense region to trigger the starburst. The star formation rate, as well as the related stellar feedback-induced turbulence, will be maximized under the regulation of the background dark halo's gravity. There is also stellar feedback acting inward to confine and obscure the central black hole (BH) until the BH grows sufficiently large to satisfy a balance condition between the accretion disk wind and the inward stellar feedback. The extremely vigorous star formation activity, the BH-bulge relations, the maximum velocity dispersion, and the maximum BH mass are investigated on the basis of such a scenario and are found to be consistent with observations.
2377462
Galaxy bulge formation: Interplay with dark matter halo and central supermassive black hole
We present a simple scenario where the formation of galactic bulges was regulated by the dark halo gravity and regulates the growth of the central supermassive black hole. Assuming the angular momentum is low, we suggest that bulges form in a runaway collapse due to the "gravothermal" instability once the central gas density or pressure exceeds a certain threshold. We emphasize that the threshold is nearly universal, set by the background NFW dark matter gravity gDM ~ 1.2 × 10-8 cm s-2 in the central cusps of halos. Unlike known thresholds for gradual formation of galaxy disks, we show that the universal "halo-regulated" star formation threshold for spheroids matches the very high star formation rate and star formation efficiency seen in high-redshift observations of central starburst regions. The starburst feedback also builds up a pressure shortly after the collapse. This large pressure could act both outward to halt further infall of gas from larger scales and inward to counter the Compton-thick wind launched from the central black hole in an Eddington accretion. Assuming the feedback balances inward and outward forces, our scenario naturally gives rise to the black hole-bulge relationships observed in the local universe.
18818885
Toward Understanding the Spectral Energy Distribution of Microquasars
We report results from a systematic study of the spectral energy distribution (SED) of XTE J1550–564 and its evolution during outbursts. The work is part of an on-going effort to understand the SED of microquasars in general. The main objectives include: 1) assessing the roles of jets and accretion flows; 2) re-examining spectral states, state transitions, and spectral hysteresis; and 3) disentangling variabilities associated with the jets and accretion flows and quantifying the coupling between the two. XTE J1550–564 is the first microquasar to have its jets directly imaged at X-ray energies. We began by applying a synchrotron model to the broadband SED of the western “blob” (in the jets) that was seen in 2002, to constrain the spectral energy distribution of radiating electrons in the “blob”. Assuming that the electron distribution is the same for all “blobs” in the jets, we then applied the model to the overall radio spectrum of the source and extrapolated the best fits to higher frequencies. In spite of significant degeneracy in the fits, it seems clear that the synchrotron radiation from the jet contributes little to the observed X-ray emission, when the source is relatively bright. Assuming that the X-ray emission originated mostly from the accretion flows, we took an empirical approach to model the X-ray spectrum and study its evolution. From the compilation of the SEDs of XTE J1550–564 during various outbursts in 1998–2000, we found it straightforward to define spectral states based on the shape of SEDs and visualize transitions between various states thus defined. There is evidence for spectral hysteresis associated with the rise and fall of the 2000 outburst. Comparing outbursts of varying magnitude, we can also see that a specific state transition may occur at different fluxes. We also examined correlation between the X-ray and radio fluxes of the source. While a rough correlation seems to be present, it is a fairly loose one. The implication of the results is discussed. Email: xuey@physics.purdue.edu, cui@physics.purdue.edu On leave from the Department of Astronomy, Peking University, Beijing 100871, P. R. China; wuxb@vega.bac.pku.edu.cn
118480496
A Comparative Study of fB within QCD Sum Rules with Two Typical Correlators up to Next-to-Leading Order
The B-meson decay constant fB is an important component for studying the B-meson decays, which can be studied through QCD sum rules. We make a detailed discussion on fB from two sum rules up to next-to-leading order, i.e. sum rules I and II, which are derived from the conventional correlator and the correlator with chiral currents respectively. It is found that these two sum rules are consistent with each other. The sum rules II involves less non-perturbative condensates as that of sum rules I, and in principle, it can be more accurate if we know the dimension-four gluon condensate well. It is found that fB decreases with the increment of mb, and to compare with the Belle experimental data on fB, both sum rules I and II prefer smaller pole b-quark mass, mb = 4.68 ± 0.07 GeV. By varying all the input parameters within their reasonable regions and by adding all the uncertainties in quadrature, we obtain fB = 172+23−25 MeV for sum rules I and fB = 214+26−34 MeV for sum rules II.
118447242
Heavy and light meson wavefunctions
We present a short review on the properties of heavy and light mesons’ light-cone wavefunctions (LCWFs), and their distribution amplitudes (DAs). The $$B$$B meson LCWFs can be treated by taking the heavy quark limit ($$m_b\rightarrow \infty $$mb→∞) and by using the heavy quark effective theory. Furthermore, we propose a simple model for the $$B$$B meson wavefunctions with 3-particle Fock states’ contributions, whose behaviors are controlled by two parameters $$\bar{\varLambda }$$Λ¯ and $$\delta $$δ. Using such model, the form factors $$F^{B\rightarrow \pi }_{+,0,{\text{T}}}$$F+,0,TB→π and $$F^{B\rightarrow K}_{+,0,{\text{T}}}$$F+,0,TB→K in large recoil region are studied up to $$\mathcal{O}(1/m_b^2)$$O(1/mb2) within the $$k_{{\mathrm{T}}}$$kT factorization approach. On the other hand, we adopt Brodsky-Huang-Lepage (BHL) prescription for constructing the WFs of the lighter pseudoscalars as $$\eta _c, D$$ηc,D-meson, pion, kaon, $$\eta ^{(\prime )}$$η(′) and etc. Such BHL-like model can be conveniently extended to construct the LCWFs for light scalar or vector mesons. Within such model the longitudinal distributions of those WFs are basically determined by a parameter $$B$$B, whose value can be determined via a global fit of experimental data.
118468710
New results on Pionic Twist-3 Distribution Amplitudes within the QCD Sum Rules
Furthermore, with the help of these moments, we construct a model for the twist-3 wave functions � p,�(x,k?), which have better end-point behavior and are helpful for perturbative QCD approach. The obtained twist-3 distribution amplitudes are adopted to calculate the B ! � transition form factor f +
118830580
Dynamics of holographic vacuum energy in the DGP model
We consider the evolution of the vacuum energy in the Dvali-Gabadadze-Porrati (DGP) model according to the holographic principle under the assumption that the relation linking the IR and UV cutoffs still holds in this scenario. The model is studied when the IR cutoff is chosen to be the Hubble scale H(-1), the particle horizon R(ph), and the future event horizon R(eh), respectively. The two branches of the DGP model are also taken into account. Through numerical analysis, we find that in the cases of H(-1) in the (+) branch and R(eh) in both branches, the vacuum energy can play the role of dark energy. Moreover, when considering the combination of the vacuum energy and the 5D gravity effect in both branches, the equation of state of the effective dark energy may cross -1, which may lead to the big rip singularity. Besides, we constrain the model with the Type Ia supernovae and baryon oscillation data and find that our model is consistent with current data within 1 sigma, and that the observations prefer either a pure holographic dark energy or a pure DGP model.
119115796
Dominant spin-flip effects for the hadronic-produced J/{psi} polarization at the Tevatron
Dominant spin-flip effects for the direct and prompt J/{psi} polarizations at Tevatron run II with collision energy 1.96 TeV and rapidity cut |y{sup J/{psi}}|<0.6 are systematically studied. The spin-flip effect for the transition of (cc){sub 8}[{sup 3}S{sub 1}] into J/{psi} is especially discussed with care. It is found that the spin-flip effect shall always dilute the J/{psi} polarization, and with a suitable choice of the parameters a{sub 0,1} and c{sub 0,1,2}, the J/{psi} polarization puzzle can be solved to a certain degree. At large transverse momentum p{sub t}, {alpha} for the prompt J/{psi} is reduced by {approx}50% for f{sub 0}=v{sup 2} and by {approx}80% for f{sub 0}=1. We also study the indirect J/{psi} polarization from the b decays, which however is slightly affected by the same spin-flip effect and then shall provide a better platform to determine the color-octet matrix elements.