2Mass Observation Of Infrared Quasars

The 2MASS observation of the infrared quasars (IR QSOs) known so far is presented in this paper. Compared with the optical selected quasars, infrared quasars are more dust-enshrouded and have redder colors and steeper spectral indices in the near infrared. In consequence, they are much younger than the optical selected quasars. The result may be helpful to the suggestion that the evolution links could be the ULIRGs - > the IR QSOs - > the optical selected quasars. This publication makes use of data products from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation of the United States.     

Incorporating photometric redshift probability density information into real-space clustering measurements

The use of photometric redshifts in cosmology is increasing. Often, however these photo- z are treated like spectroscopic observations, in that the peak of the photometric redshift, rather than the full probability density function (PDF), is used. This overlooks useful information inherent in the full PDF. We introduce a new real-space estimator for one of the most used cosmological statistics, the two-point correlation function, that weights by the PDF of individual photometric objects in a manner that is optimal when Poisson statistics dominate. As our estimator does not bin based on the PDF peak, it substantially enhances the clustering signal by usefully incorporating information from all photometric objects that overlap the redshift bin of interest. As a real-world application, we measure quasi-stellar object (QSO) clustering in the Sloan Digital Sky Survey (SDSS). We find that our simplest binned estimator improves the clustering signal by a factor equivalent to increasing the survey size by a factor of 2–3. We also introduce a new implementation that fully weights between pairs of objects in constructing the cross-correlation and find that this pair-weighted estimator improves clustering signal in a manner equivalent to increasing the survey size by a factor of 4–5. Our technique uses spectroscopic data to anchor the distance scale and it will be particularly useful where spectroscopic data (e.g. from BOSS) overlap deeper photometry (e.g. from Pan-STARRS, DES or the LSST). We additionally provide simple, informative expressions to determine when our estimator will be competitive with the autocorrelation of spectroscopic objects. Although we use QSOs as an example population, our estimator can and should be applied to any clustering estimate that uses photometric objects.     

New insights on the QSO radio-loud/radio-quiet dichotomy: SDSS spectra in the context of the 4D eigenvector1 parameter space

We search for a dichotomy/bimodality between radio-loud (RL) and radio-quiet (RQ) type 1 active galactic nuclei (AGN). We examine several samples of Slogan Digital Sky Survey (SDSS) quasi-stellar objects (QSOs) with high signal-to-noise ratio optical spectra and matching Faint Images of the Radio Sky at Twenty-cm/NRAO VLA Sky Survey (FIRST/NVSS) radio observations. We use the radio data to identify the weakest RL sources with a Fanaroff–Riley type II (FR II) structure to define a RL/RQ boundary which corresponds to log   L _1.4 GHz= 31.6  erg s⁻¹ Hz⁻¹. We measure the properties of broad-line Hβ and Fe  ii emission to define the optical plane of a 4DE1 spectroscopic diagnostic space. The RL quasars occupy a much more restricted domain in this optical plane compared to the RQ sources, which a 2D Kolmogorov–Smirnov test finds to be highly significant. This tells us that the range of broad-line region kinematics and structure for RL sources is more restricted than for the RQ QSOs, which supports the notion of dichotomy. FR II and CD RL sources also show significant 4DE1 domain differences that likely reflect differences in line-of-sight orientation (inclined versus face-on, respectively) for these two classes. The possibility of a distinct radio-intermediate (RI) population between RQ and RL source is disfavoured because a 4DE1 diagnostic space comparison shows no difference between RI and RQ sources. We show that searches for dichotomy in radio versus bolometric luminosity diagrams will yield ambiguous results mainly because in a reasonably complete sample, the radio brightest RQ sources will be numerous enough to blur the gap between RQ and RL sources. Within resolution constraints of NVSS and FIRST, we find no FR I sources among the broad-line quasar population.     

NoSOCS in SDSS – I. Sample definition and comparison of mass estimates

We use Sloan Digital Sky Survey (SDSS) data to investigate galaxy cluster properties of the systems first detected within Digitized Second Palomar Observatory Sky Survey. With the high-quality photometry of SDSS, we derived new photometric redshifts and estimated richness and optical luminosity. For a subset of low-redshift  ( z ≤ 0.1)  clusters, we have used SDSS spectroscopic data to identify groups in redshift space in the region of each cluster, complemented with massive systems from the literature to assure the continuous mass sampling. A method to remove interlopers is applied, and a virial analysis is performed resulting in the estimates of velocity dispersion, mass and a physical radius for each low- z system. We discuss the choice of maximum radius and luminosity range in the dynamical analysis, showing that a spectroscopic survey must be complete to at least   M *+ 1  if one wishes to obtain accurate and unbiased estimates of velocity dispersion and mass. We have measured X-ray luminosity for all clusters using archival data from ROSAT All Sky Survey. For a smaller subset (21 clusters), we selected temperature measures from the literature and estimated mass from the   M − T _X  relation, finding that they show good agreement with the virial estimate. However, these two mass estimates tend to disagree with the caustic results. We measured the presence of substructure in all clusters of the sample and found that clusters with substructure have virial masses higher than those derived from T _X. This trend is not seen when comparing the caustic and X-ray masses. That happens because the caustic mass is estimated directly from the mass profile, so it is less affected by substructure.     

Transformations between 2MASS, SDSS and BVRI photometric systems: bridging the near-infrared and optical

We present colour transformations for the conversion of the Two Micron All Sky Survey (2MASS) photometric system to the Johnson–Cousins UBVRI system and further into the Sloan Digital Sky Survey (SDSS) ugriz system. We have taken SDSS gri magnitudes of stars measured with the 2.5-m telescope from SDSS Data Release 5 (DR5), and BVRI and   JHK _s   magnitudes from Stetson's catalogue and Cutri et al., respectively. We matched thousands of stars in the three photometric systems by their coordinates and obtained a homogeneous sample of 825 stars by the following constraints, which are not used in previous transformations: (1) the data are dereddened, (2) giants are omitted and (3) the sample stars selected are of the highest quality. We give metallicity, population type and transformations dependent on two colours. The transformations provide absolute magnitude and distance determinations which can be used in space density evaluations at short distances where some or all of the SDSS ugriz magnitudes are saturated. The combination of these densities with those evaluated at larger distances using SDSS ugriz photometry will supply accurate Galactic model parameters, particularly the local space densities for each population.     

The Sloan Digital Sky Survey

The Sloan Digital Sky Survey (SDSS) is going to carry out a uniform survey of π steradians of the sky in the Northern Galactic cap and ∼ 225 deg² in the Southern Hemisphere. The survey consists of a photometric and a spectroscopic survey. The SDSS will generate accurate photometry in five bands of approximately tens of millions of galaxies, tens of millions of stars and roughly a million quasars. It will also take spectra and measure redshifts of approximately a million galaxies and ten thousand quasars. The main characteristics and components of the survey are a dedicated 2.5m telescope, wide field correctors for photometry and spectroscopy that will provide a field of view of ∼ 3 degrees, a photometric camera with 30 photometric and 22 astrometric CCDs, and two fibre-fed spectrographs of 320 fibres each. The survey will produce a publicly available science database of Terabytes dimensions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Color-Redshift Relations and Photometric Redshift Estimations of Quasars in Large Sky Surveys

With a recently constructed composite quasar spectrum and the X2 minimization technique, we describe a general method for estimating the photometric redshifts of a large sample of quasars by deriving theoretical color-redshift relations and comparing the theoretical colors with the observed ones. We estimated the photometric redshifts from the 5-band SDSS photometric data of 18678 quasars in the first major data release of SDSS and compared them with their spectroscopic redshifts. The difference is less than 0.1 for 47% of the quasars and less than 0.2 for 68%. Based on the calculation of the theoretical color-color diagrams of stars, galaxies and quasars both on the SDSS system and on the BATC system, we expect that we would be able to select candidates of high redshift quasars more efficaciously with the latter than with the former, provided the BATC survey can detect objects with magnitudes fainter than 21.     

基于NPSVM模型的超新星识别方法

巡天观测与高能物理、黑洞天文等领域均有密切的联系.基于星系-超新星二分类问题,研究光谱数据预处理,结合余弦相似度改善PCA(Principal Component Analysis)光谱分解特征提取方法,用SDSS(the Sloan Digital Sky Survey)、WISeREP(the Weizmann Interactive Supernova data REPository)组成的5620条光谱数据集训练支持向量机,可以得到0.498%泛化误差的识别模型和新样本分类概率.使用Neyman-Pearson决策方法建立NPSVM(Neyman-Pearson Support Vector Machine)模型可进一步降低超新星的漏判率.     

Downsizing of supermassive black holes from the SDSS quasar survey – II. Extension to z∼ 4

Starting from the quasar sample of the Sloan Digital Sky Survey (SDSS) for which the C  iv line is observed, we use an analysis scheme to derive the z -dependence of the maximum mass of active black holes, which overcomes the problems related to the Malmquist bias. The same procedure is applied to the low-redshift sample of SDSS quasars for which Hβ measurements are available. Combining with the results from the previously studied Mg  ii sample, we find that the maximum mass of the quasar population increases as  (1 + z )^1.64±0.04  in the redshift range  0.1 z 4  , which includes the epoch of maximum quasar activity.     

Estimating the redshift distribution of photometric galaxy samples – II. Applications and tests of a new method

In Lima et al. we presented a new method for estimating the redshift distribution,   N ( z )  , of a photometric galaxy sample, using photometric observables and weighted sampling from a spectroscopic subsample of the data. In this paper, we extend this method and explore various applications of it, using both simulations and real data from the Sloan Digital Sky Survey (SDSS). In addition to estimating the redshift distribution for an entire sample, the weighting method enables accurate estimates of the redshift probability distribution,   p ( z )  , for each galaxy in a photometric sample. Use of   p ( z )  in cosmological analyses can substantially reduce biases associated with traditional photometric redshifts, in which a single redshift estimate is associated with each galaxy. The weighting procedure also naturally indicates which galaxies in the photometric sample are expected to have accurate redshift estimates, namely those that lie in regions of photometric-observable space that are well sampled by the spectroscopic subsample. In addition to providing a method that has some advantages over standard photo- z estimates, the weights method can also be used in conjunction with photo- z estimates e.g. by providing improved estimation of   N ( z )  via deconvolution of   N ( z _phot)  and improved estimates of photo- z scatter and bias. We present a publicly available   p ( z )  catalogue for ∼78 million SDSS DR7 galaxies.     

Random forest algorithm for classification of multiwavelength data

We introduced a decision tree method called Random Forests for multiwavelength data classification. The data were adopted from different databases, including the Sloan Digital Sky Survey (SDSS) Data Release five, USNO, FIRST and ROSAT.We then studied the discrimination of quasars from stars and the classification of quasars,stars and galaxies with the sample from optical and radio bands and with that from optical and X-ray bands. Moreover, feature selection and feature weighting based on Random Forests were investigated. The performances based on different input patterns were compared. The experimental results show that the random forest method is an effective method for astronomical object classification and can be applied to other classification problems faced in astronomy. In addition, Random Forests will show its superiorities due to its own merits, e.g. classification, feature selection, feature weighting as well as outlier detection.     

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.     

Two Novel Approaches for Photometric Redshift Estimation based on SDSS and 2MASS

We investigate two training-set methods: support vector machines (SVMs) and Kernel Regression (KR) for photometric redshift estimation with the data from the databases of Sloan Digital Sky Survey Data Release 5 and Two Micron All Sky Survey. We probe the performances of SVMs and KR for different input patterns. Our experiments show that with more parameters considered, the accuracy does not always increase, and only when appropriate parameters are chosen, the accuracy can improve. 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. 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.     

Properties of radio-detected broad absorption line quasars from the Sloan Digital Sky Survey

We investigate the optical colors and radio morphologies of 214 broad absorption line (BAL) quasars with FIRST detections in the redshift range 1.68≤z≤4.93 drawn from the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5) quasar catalog. The radio-detected SDSS BAL quasars are found to have Δ(g?i) colors significantly redder than their non-BAL counterparts, with a mean color difference of 0.52 mag, in good agreement with the O–E (roughly B–R) color difference between radio-selected BAL and non-BAL quasars in the FIRST Bright Quasar Survey (FBQS). The vast majority (～90 %) of the radio-detected BAL quasars are found to be core-only sources, most of which show compact radio morphologies, consistent with the morphological results for the FBQS sample. Moreover, within the FIRST-detected SDSS sample, BAL quasars with GB6 detections are found to span a wide range in radio spectral indices, indistinguishable from that of non-BAL quasars, indicating no special line of sight for the presence of BALs. The properties of the present SDSS sample are more consistent with the evolutionary model, in which BALs are at an early evolutionary stage of quasars.     

A Study of Optical Light Variations of LINERs in SDSS

The Stripe82 has been repeatedly observed by SDSS (Sloan Digital Sky Survey) from 1998 to 2004, so as to provide us with opportunities to investigate the light variations of related objects. In this work, 29 broad-line LINERs (low-ionization nuclear emission line regions) in the Stripe82 are selected from the catalog LMCC (Light-Motion Curve Catalogue) to study their light variations. By comparing with the photometric measurements of the normal galaxies in LMCC, four candidates which possibly have light variations are picked up. Finally, after further veri?cations, it is found that there are two LINERs (SDSS J004828.80-001241.5 and SDSS J030203.53+005159.5) exhibiting relatively obvious light variations.     

The Sloan Digital Sky Survey monitor telescope pipeline

The photometric calibration of the Sloan Digital Sky Survey (SDSS) is a multi‐step process which involves data from three different telescopes: the 1.0‐m telescope at the US Naval Observatory (USNO), Flagstaff Station, Arizona (which was used to establish the SDSS standard star network); the SDSS 0.5‐m Photometric Telescope (PT) at the Apache Point Observatory (APO), NewMexico (which calculates nightly extinctions and calibrates secondary patch transfer fields); and the SDSS 2.5‐m telescope at APO (which obtains the imaging data for the SDSS proper). In this paper, we describe the Monitor Telescope Pipeline, MTPIPE, the software pipeline used in processing the data from the single‐CCD telescopes used in the photometric calibration of the SDSS (i.e., the USNO 1.0‐m and the PT). We also describe transformation equations that convert photometry on the USNO‐1.0m u ′g ′r ′i ′z ′ system to photometry the SDSS 2.5m ugriz system and the results of various validation tests of the MTPIPE software. Further, we discuss the semi‐automated PT factory, which runs MTPIPE in the day‐to‐day standard SDSS operations at Fermilab. Finally, we discuss the use of MTPIPE in current SDSS‐related projects, including the Southern u ′g ′r ′i ′z ′ Standard Star project, the u ′g ′r ′i ′z ′ Open Star Clusters project, and the SDSS extension (SDSS‐II). (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Recovering galaxy star formation and metallicity histories from spectra using VESPA

We introduce versatile spectral analysis (VESPA): a new method which aims to recover robust star formation and metallicity histories from galactic spectra. VESPA uses the full spectral range to construct a galaxy history from synthetic models. We investigate the use of an adaptative parametrization grid to recover reliable star formation histories on a galaxy-by-galaxy basis. Our goal is robustness as opposed to high-resolution histories, and the method is designed to return high time resolution only where the data demand it. In this paper we detail the method and we present our findings when we apply VESPA to synthetic and real Sloan Digital Sky Survey (SDSS) spectroscopic data. We show that the number of parameters that can be recovered from a spectrum depends strongly on the signal-to-noise ratio, wavelength coverage and presence or absence of a young population. For a typical SDSS sample of galaxies, we can normally recover between two and five stellar populations. We find very good agreement between VESPA and our previous analysis of the SDSS sample with MOPED.     

Constraining quasar host halo masses with the strength of nearby Lyα forest absorption

Using cosmological hydrodynamic simulations, we measure the mean transmitted flux in the Lyα forest for quasar sightlines that pass near a foreground quasar. We find that the trend of absorption with pixel quasar separation distance can be fitted using a simple power-law form including the usual correlation function parameters r ₀ and γ, so that     . From the simulations, we find the relation between r ₀ and quasar host mass, and formulate this as a way to estimate quasar host dark matter halo masses, quantifying uncertainties due to cosmological and IGM parameters, and redshift errors. With this method, we examine data for ∼9000 quasars from the Sloan Digital Sky Survey (SDSS) Data Release 5, assuming that the effect of ionizing radiation from quasars (the so-called transverse proximity effect) is unimportant (no evidence for it is seen in the data). We find that the best-fitting host halo mass for SDSS quasars with mean redshift z = 3 and absolute G -band magnitude −27.5 is  log  M /M_⊙= 12.68^+0.81_−0.67  . We also use the Lyman-Break Galaxy (LBG) and Lyα forest data of Adelberger et al. in a similar fashion to constrain the halo mass of LBGs to be  log₁₀  M /M_⊙= 11.41^+0.54_−0.59  , a factor of ∼20 lower than the bright quasars. In addition, we study the redshift distortions of the Lyα forest around quasars, using the simulations. We use the quadrupole to monopole ratio of the quasar Lyα forest correlation function as a measure of the squashing effect. We find its dependence on halo mass difficult to measure, but find that it may be useful for constraining cosmic geometry.