Growth of Black Holes and Their Host Spheroids in (Sub)mm-loud High-Redshift QSOs

We study the growth of black holes and stellar population in spheroids at high redshift using several （sub）mm-loud QSO samples. Applying the same criteria established in an earlier work, we find that, similar to IR QSOs at low redshift, the far-infrared emission of these （sub）mm-loud QSOs mainly originates from dust heated by starbursts. By combining low-z IR QSOs and high-z （sub）mm-loud QSOs, we find a trend that the star formation rate （M＊） increases with the accretion rate （Mace）. We compare the values of M＊/Macc for submm emitting galaxies （SMGs）, far-infrared ultraluminous/hypeduminous QSOs and typical QSOs, and construct a likely evolution scenario for these objects. The （sub）mm-loud QSO transition phase has both high Macc and M＊ and hence is important for establishing the correlation between the masses of black holes and spheroids.

Discovery of six high-redshift quasars with the Lijiang 2.4 m telescope and the Multiple Mirror Telescope

Quasars with redshifts greater than 4 are rare, and can be used to probe the structure and evolution of the early universe. Here we report the discovery of six new quasars with i-band magnitudes brighter than 19.5 and redshifts between 2.4 and 4.6 from spectroscopy with the Yunnan Faint Object Spectrograph and Camera (YFOSC) at the Lijiang 2.4 m telescope in February, 2012. These quasars are in the list of z > 3.6 quasar candidates selected by using our proposed J K/i Y criterion and the photometric redshift estimations from the SDSS optical and UKIDSS near-IR photometric data. Nine candidates were observed by YFOSC, and five among six new quasars were identified as z > 3.6 quasars. One of the other three objects was identified as a star and the other two were unidentified due to the lower signal-to-noise ratio of their spectra. This is the first time that z > 4 quasars have been discovered using a telescope in China. Thanks to the Chinese Telescope Access Program (TAP), the redshift of 4.6 for one of these quasars was confirmed by the Multiple Mirror Telescope (MMT) Red Channel spectroscopy. The continuum and emission line properties of these six quasars, as well as their central black hole masses and Eddington ratios, were obtained.

Investigating the Evolution of Amati Parameters with Redshift

Gamma-ray bursts(GRBs) are among the brightest objects in the Universe and, hence, can be observed up to a very high redshift. Properly calibrated empirical correlations between intensity and spectral correlations of GRBs can be used to estimate the cosmological parameters. However, the possibility of the evolution of GRBs with redshift is a long-standing puzzle. In this work, we used 162 long-duration GRBs to determine whether GRBs below and above a certain redshift have different properties. The GRBs are split into two groups, and we fit the Amati relation for each group separately. Our findings demonstrate that estimations of the Amati parameters for the two groups are substantially dissimilar. We perform simulations to investigate whether the selection effects could cause the difference. Our analysis shows that the differences may be either intrinsic or due to systematic errors in the data, and the selection effects are not their true origin. However, in-depth analysis with a new data set comprised of 119 long GRBs shows that intrinsic scatter may partly be responsible for such effects.

Reionizing Islands with Inhomogeneous Recombinations

Observations are beginning to constrain the history of the epoch of reionization(EoR).Modeling the reionization process is indispensable to interpret the observations,to infer the properties of ionizing sources,and to probe the various astrophysical processes from the observational data.Here we present an improved version of the seminumerical simulation islandFAST,by incorporating inhomogeneous recombinations and a corresponding inhomogeneous ionizing background,and simulate the reionization process of neutral islands during the late EoR.We find that the islands are more fragmented in models with inhomogeneous recombinations than the case with a homogeneous recombination number.In order to investigate the effects of basic assumptions in the reionization modeling,we compare the results from islandFAST with those from 21cmFAST for the same assumptions on the ionizing photon sources and sinks,to find how the morphology of the ionization field and the reionization history depend on the different treatments of these two models.Such systematic bias should be noted when interpreting the upcoming observations.

Investigating the Hubble Tension Through Hubble Parameter Data

The Hubble constant(H_0),which represents the expansion rate of the universe,is one of the most important cosmological parameters.The recent measurements of H0using the distance ladder methods such as type Ia supernovae are significantly greater than the CMB measurements by Planck.The difference points to a crisis in the standard model of cosmology termed Hubble tension.In this work we compare different cosmological models,determine the Hubble constant and comment on the Hubble tension using the data from differential ages of galaxies.The data we use are free from systematic effects as the absolute age estimation of the galaxies is not needed.We apply the Bayesian approach along with the commonly used maximum likelihood method to estimate H_0 and calculate the AIC scores to compare the different cosmological models.The non-flat cosmological model provides a higher value for matter density as well as the Hubble constant compared to the flatΛCDM model.The AIC score is smaller for the flatΛCDM cosmology compared to the non-flat model indicating the flat model a better choice.The best-fit values of H_0 for both these models are 68.7±3.1 km s^(-1)Mpc^(-1)and 72.2±4km s^(-1)Mpc^(-1),respectively.Our results are consistent with the CCHP measurements.However,the flat model result does not agree with the SH0ES result,while the non-flat result is inconsistent with the Planck value.

Average Luminous Mass of Early Galaxies at z = 10 - 20 Predicted as ~109 Solar Masses

This paper predicts the average luminous mass of galaxies that will be detected by JWST space telescope at redshift z ≈ 10 - 20. The prediction, derived in the paper, is based on holographic analysis, developed from quantum mechanics, general relativity, thermodynamics, and Shannon information theory. Consistent with early JWST data, ~109 solar masses is the predicted average luminous mass of early galaxies at z ≈ 10 - 20 that will be detected by JWST.

(亚)毫米干涉阵观测的星系强引力透镜研究进展

近年来,强引力透镜的样本选择和研究从此前主要局限于光学-红外波段,拓展到毫米/亚毫米波段。目前大约有200个强引力透镜系统在毫米/亚毫米波段的广域河外观测中被发现。ALMA,NOEMA,SMA等射电干涉阵提供的高灵敏度、高分辨率的观测,结合强引力透镜放大作用,将高红移星系的研究带入一个新时代。主要从观测样本、建模方法、科学应用等方面介绍了当下(亚)毫米波段星系-星系强引力透镜的研究现状。

Effects of Redshift on the Classifying Criteria of BL Lacertae Objects

We have collected a sample of 70 BL Lacs （33 radio-selected BL Lacs and 37 X-ray selected BL Lacs） with multi-waveband data for investigating the classifying criteria of BL Lacertae Objects. For each source, we estimate its luminosities in radio, optical and X-ray, the broad-band spectral index from radio to X-ray and the peak frequency of the synchrotron emission, and make a statistical analysis of the data obtained. Our main results are as follows： （1） The broad-band spectral index and the peak frequency have no correlation with the redshift, while they are inversely correlated with each other and they could be regarded as equivalent classifying criteria of BL Lac objects. （2） There are significant effects of the luminosity/redshift relation on the observed luminosity distribution in our sample, hence, if the radio luminosity is to be used as a classifying criterion of BL Lac objects, it should not be regarded as equivalent to the broad-band spectral index or the peak frequency. （3） Our resuits supply a specific piece of evidence for the suggestion that the use of luminosities always introduces a redshift bias to the data and show that the location of the peak frequency is not always linked to the luminosity of any wave band.

Radio spectral index from NVSS and TGSS

I extract the radio spectral index,α,from 541 195 common sources observed in the 150 MHz TIFR GMRT Sky Survey(TGSS) and the 1.4 GHz NRAO VLA Sky Survey(NVSS).This large common source catalog covers about 80% of the sky.The flux density limits in these surveys are such that the observed galaxies are presumably hosts of active galactic nuclei(AGNs).I confirm the steepening of αwith increasing flux density for this large sample and provide a parametric fit between α and flux density.Next,I divide the data into low flux(LF) and high flux(HF) density samples with roughly equal numbers of galaxies.The LF sample contains all galaxies below 100 m Jy TGSS and 20 m Jy NVSS flux density and the HF sample is all galaxies above 100 m Jy TGSS and 20 m Jy NVSS.I observe an increase in α with source size(TGSS measured),saturating for large sizes to 0.89 ± 0.22 and 0.76 ± 0.21 for the LF and HF sources,respectively.I discuss the observed results and possible physical mechanisms to explain observedα dependence with source size for LF and HF samples.

Conditions for galaxy quenching at 0.5

We investigate two classes of conditions for galaxy quenching at 0.510^10 M⊙)have much higher stellar mass surface densities within the central 1 kpc(∑1)and smaller sizes than star-forming galaxies in the same stellar mass range.In addition,the quiescent fractions significantly increase with the increase of∑1 regardless of whether galaxies are centrals or satellites.In contrast,we find that the overall lower-mass quiescent galaxies(M*<~10^10M⊙)have slightly higher E1 and comparable sizes compared to starforming galaxies of the same mass and at the same redshift.At z<1.5,satellites have higher halo masses and larger quiescent fractions than those of centrals at a given∑1(stellar mass).Our findings indicate that the significant growth of the galaxy cores is closely related to the quenching of massive galaxies since z^2.5,while the environmental effect plays an important role in the quenching of low-mass galaxies at z≤1.5.

Estimating Black Hole Masses of AGNs using Ultraviolet Emission Line Properties

Based on measured broad line region sizes in the reverberation-mapping AGN sample, two new empirical relations are introduced to estimate the central black hole masses of radio-loud high-redshift （z 〉 0.5） AGNs. First, using the archival IUE/HST spectroscopy data at UV band for the reverberation-mapping objects, we obtained two new empirical relations between the BLR size and Mg Ⅱ/C Ⅳ emission line luminosity. Secondly, using the newly determined black hole masses of the reverberation-mapping sample as calibration, we found two new relationships for determining the black hole mass with the full width at half maximum and the luminosity of Mg Ⅱ/C Ⅳ line. We then apply the relations to estimate the black hole masses of the AGNs in the Large Bright Quasar Survey and a sample of radio-loud quasars. For the objects with small radio-loudness, the black hole mass estimated using the RBLR-LMg Ⅱ/C Ⅳ relation is consistent with that from the RBLR-L3000 A/1350 A relation. For radio-loud AGNs, however, the mass estimated from the RBLR-LMg Ⅱ/C Ⅳ relation is systematically lower than that from the continuum luminosity L3000 A/13S0 A Because jets could have significant contributions to the UV/optical continuum luminosity of radio-loud AGNs, we emphasize once again that for radio-loud AGNs, the emission line luminosity may be a better tracer of the ionizing luminosity than the continuum luminosity, so that the relations between the BLR size and UV emission line luminosities should be used to estimate the black hole masses of high redshift radio-loud AGNs.

Stellar Mass Function of Lyman Break Galaxies： Theoretical Perspective

Adopting the observational distributions of star formation rates and half-light radii of Lyman break galaxies （LBGs） in the rest frame UV, we investigate empirically the predicted stellar mass function for LBGs. It is found that a peak exists at mass around 1.5 × 10^10M⊙ for their stellar mass function and there have been significant amount of LBGs with stellar masses higher than 10^11M⊙ at z ～ 3. There should be two families for LBG population observed by the Infrared Array Camera （IRAC） （which is a key instrument in the infrared space telescope Spitzer）, one is red and the other is blue, which are consistent with recent works. Moreover, the predicted comoving correlation lengths for LBGs with different stellar masses, i.e., with different 8 μm magnitudes, are also discussed. The red LBGs should be clustered in space more strongly than the blue LBGs. These predictions can and will be tested by the observations of IRAC, and will provide strong constraints on the current hierarchical galaxy formation model.

Observational Constraints on the Unified Dark-Energy-Dark-Matter Model

We investigate the constraints on a generalized Chaplygin gas （GCG） model using the gold sample type-Ia supernovae （She Ia） data, the new Supernova Legacy Survey （SNLS） Sne Ia data and the size of baryonic acoustic oscillation peak found in Sloan Digital Sky Survey （SDSS）. In a spatially flat universe case we obtain, at a 95.4% confidence level, A8 = 0.76^＋0.07 -0.07 and α= 0.028^＋0.322 -0.2382 Our results are consistent with the ACDM model （α= 0）, but rule out the standard Chaplygin gas model （α= 1）.

Morphology and structure of BzK-selected galaxies at z ～ 2 in the CANDELS-COSMOS field

Utilizing a BzK-selecfion technique, we obtain 14 550 star-forming galaxies （sBzKs） and 1763 passive galaxies （pBzKs） at z - 2 from the K-selected （KAB 〈 22.5） catalog in the COSMOS/UltraVISTA field. The differential number counts of sBzKs and pBzKs are consistent with the results from the literature. Compared to the observed results, semi-analytic models of galaxy formation and evolution provide too few （many） galaxies at the high （low） mass end. Moreover, we find that the star formation rate and stellar mass of sBzKs follow the relation of the main sequence. Based on HST/Wide Field Camera 3 F160W imaging, we find a wide range of morphological diversities for sBzKs, from diffuse to early-type spiral structures, with relatively high M20, large size and low G, while pBzKs have elliptical-like compact morphologies with lower M20, smaller size and higher G, indicating a more concentrated and symmetric spatial extent of stellar population distribution in pBzKs than sBzKs. Furthermore, the sizes of pBzKs （sBzKs） at z - 2 are on average two to three （one to two） times smaller than those of local early-type （late-type） galaxies with similar stellar mass. Our findings imply that the two classes have different evolution models and mass assembly histories.

Morphology and structure of extremely red objects at z ～ 1 in the CANDELS-COSMOS field

Using high-resolution HST/Wide Field Camera 3 F125W imaging from the CANDELS-COSMOS field, we report the structural and morphological properties of extremely red objects （EROs） at -z 1. Based on the UVJ color criteria, we sepa- rate EROs into two types： old passive galaxies （OGs） and dusty star-forming galaxies （DGs）. For a given stellar mass, we find that the mean size of OGs （DGs） is smaller by a factor of - 2 （1.5） than that of present-day early-type （late-type） galaxies at a rest-frame optical wavelength. We derive the average effective radii of OGs and DGs, corresponding to 2.09 ± 1.13 kpc and 3.27± 1.14 kpc, respectively. Generally, the DGs are heterogeneous, with mixed features including bulges, disks and irregular structures, with relatively high M20, large size and low G. By contrast, OGs have elliptical-like compact morphologies with lower M20, smaller size and higher G, indicating a more concentrated and symmetric spatial extent of the stellar population distribution in OGs than DGs. These findings imply that OGs and DGs have different evolutionary processes, and that the minor merger scenario is the most likely mechanism for the structural properties of OGs. However, the size evolution of DGs is possibly due to the secular evolution of galaxies.

Star-Forming Galaxies at z～2 in the Hubble Ultra Deep Field

Using a simple color selection based on B-, z- and K-band photometry, BzK =（z - K）AB - （B - Z）AB 〉 -0.2, we picked out 52 star-forming galaxies at 1.4 ≤z ≤ 2.5 （sBzKs） from a K-band selected sample （Kvega 〈 22.0） in an area of - 5.5 arcmin^2 of the Hubble Ultra Deep Field （UDF）. We develop a new photometric redshift method, and the error in our photometric redshifts is less than 0.02（1 ＋ z）. From the photometric redshift distribution, we find the BzK color criterion can be used to select star-forming galaxies at 1.4≤ z ≤ 2.5 with Kvega 〈 22.0. Down to Kvega 〈 22.0, the number counts of sBzKs increase linearly with the K magnitude; the sBzKs are strongly clustered, and most of them have irregular morphologies on the ACS images. They have a median reddening of E（B - V） - 0.28, an average star formation rate of - 36 M⊙ yr^-1 and a typical stellar mass of - 10^10 M⊙. The UV criterion for the galaxies at z - 2 can select most of the faint sBzKs in the UDF, but it does not work well for bright, massive, highly-reddened, actively star-forming galaxies.

Spectral energy distribution similarity of the local galaxies and the 3.6μm selected galaxies from the Spitzer Extended Deep Survey

The Spitzer Extended Deep Survey(SEDS)as a deep and wide mid-infrared(MIR)survey project provides a sample of 500000+sources spreading 1.46 square degree and a depth of 26 AB mag(3σ).Combining with the previous available data,we build a PSF-matched multi-wavelength photometry catalog from u band to 8μm.We fit the SEDS galaxies spectral energy distributions by the local galaxy templates.The results show that the SEDS galaxy can be fitted well,indicating the high redshift galaxy(z~1)shares the same templates with the local galaxies.This study would facilitate the further study of the galaxy luminosity and high redshift mass function.

The formation and evolution of massive galaxies

The discovery of massive galaxies at high redshifts,especially the passive ones,poses a big challenge for the current standard galaxy formation models.Here we use the semi-analytic galaxy formation model developed by Henriques et al.to explore the formation and evolution of massive galaxies(MGs,stellar-mass M*>1011 M⊙).Different from previous works,we focus on the ones just formed(e.g.just reach?1011 M⊙).We find that most of the MGs are formed around z=0.6,with the earliest formation at z>4.Interestingly,although most of the MGs in the local Universe are passive,we find that only 13%of the MGs are quenched at the formation time.Most of the quenched MGs at formation already host a very massive supermassive black hole(SMBH)which could power the very effective AGN feedback.For the star-forming MGs,the ones with more massive SMBH prefer to quench in shorter timescales;in particular,those with MSMBH>107.5 M⊙have a quenching timescale of~0.5 Gyr and the characteristic MSMBH depends on the chosen stellar mass threshold in the definition of MGs as a result of their co-evolution.We also find that the"in-situ"star formation dominates the stellar mass growth of MGs until they are formed.Over the whole redshift range,we find the quiescent MGs prefer to stay in more massive dark matter halos,and have more massive SMBH and less cold gas masses.Our results provide a new angle on the whole life of the growth of MGs in the Universe.

Decomposing the host galaxy from high-z QSOs using principal component analysis

High resolution deep imaging from space and adaptive optics techniques with large ground-based facilities have enabled studies examining faint host galaxies of high redshift quasi-stellar objects (QSOs). However, the related image processing techniques, especially for a precise point-spread function (PSF) reconstruction and characterization of the host galaxy light profiles, have yet to be optimized. We present here the scientific performance of a principal component analysis (PCA) based PSF subtraction of the central bright point source of high redshift QSO images, as well as further characterization of the host galaxy profile by directly fitting a Sèrsic model to the residual image using the Markov Chain Monte Carlo (MCMC) algorithm. With a set of reference PSF star images which represent interleaving exposures between the QSO imaging, we can create an orthogonal basis of eigen-images and restore the PSF of QSO images by projecting the QSO images onto the basis. In this way, we can quantify the modes in which the PSF varies with time by a basis function that characterizes the temporal variations of the reference star as well as the QSO images. To verify the algorithm, we performed a simulation and applied this method to one of the high-z QSO targets from Mechtley et al. We demonstrate that the PCA-based PSF subtraction and further modeling of the galaxy’s light profile using MCMC fitting would sufficiently remove the effects from central dominating point sources, and improve characterization ability for the host galaxies of high-z QSOs to the background noise level which is much better than previous two-component fitting procedures.

AGN Lifetimes in UV-selected Galaxies: A Clue to Supermassive Black Hole-galaxy Coevolution

The coevolution between supermassive black holes(SMBHs) and their host galaxies has been proposed for more than a decade,albeit with little direct evidence about black hole accretion activities regulating galaxy star formation at z> 1.In this paper,we study the lifetimes of X-ray active galactic nuclei(AGNs) in UV-selected red sequence(RS),blue cloud(BC) and green valley(GV) galaxies,finding that AGN accretion activities are most prominent in GV galaxies at z ~1.5-2,compared with RS and BC galaxies.We also compare AGN accretion timescales with typical color transition timescales of UV-selected galaxies.We find that the lifetime of GV galaxies at z~1.5-2 is very close to the typical timescale when the AGNs residing in them stay in the high-accretion-rate mode at these redshifts;for BC galaxies,the consistency between the color transition timescale and the black hole strong accretion lifetime is more likely to happen at lower redshifts(z <1).Our results support the scenario where AGN accretion activities govern UV color transitions of host galaxies,making galaxies and their central SMBHs coevolve with each other.