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Supermassive Primordial Black Holes for Nano-Hertz Gravitational Waves and High-redshift JWST Galaxies
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作者 Hai-Long Huang Yong Cai +2 位作者 Jun-Qian Jiang Jun Zhang Yun-Song Piao 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2024年第9期1-6,共6页
Recently,observational hints for supermassive black holes have been accumulating,prompting the question:Can primordial black holes(PBHs)be supermassive,particularly with masses M■10^(9)M_(⊙)?A supercritical bubble,c... Recently,observational hints for supermassive black holes have been accumulating,prompting the question:Can primordial black holes(PBHs)be supermassive,particularly with masses M■10^(9)M_(⊙)?A supercritical bubble,containing an inflating baby universe,that nucleated during inflation can evolve into a PBH in our observable universe.We find that when the inflaton slowly transitions past a neighboring vacuum,the nucleation rate of supercritical bubbles inevitably peaks,leading to a mass distribution of multiverse PBHs with a peak mass up to M■10^(11)M_(⊙).Thus,our mechanism naturally provides a primordial origin for supermassive black holes. 展开更多
关键词 (cosmology:)early universe (cosmology:)inflation (galaxies:)quasars:supermassive black holes
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Similarity of jet radiation between flat spectrum radio quasars and GeV narrow-line Seyfert 1 galaxies: a universal δ-Lc correlation 被引量:2
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作者 Yong-Kai Zhu Jin Zhang +4 位作者 Hai-Ming Zhang En-Wei Liang Da-Hai Yan Wei Cui Shuang-Nan Zhang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2016年第11期43-52,共10页
By modeling the broadband spectral energy distributions (SEDs) of a typical flat spectrum radio quasar (FSRQ, 3C 279) and two GeV narrow-line Seyfert 1 galaxies (NLSls, PMN J0948+0022 and 1H 0323+342) in diffe... By modeling the broadband spectral energy distributions (SEDs) of a typical flat spectrum radio quasar (FSRQ, 3C 279) and two GeV narrow-line Seyfert 1 galaxies (NLSls, PMN J0948+0022 and 1H 0323+342) in different flux stages with one-zone leptonic models, we find a universal correlation between their Doppler factors (δ) and peak luminosities (Lc) of external Compton scattering bumps. Compiling a combined sample of FSRQs and GeV NLSls, it is found that both FSRQs and GeV NLSls in different stages and in different sources follow the same δ-Lc correlation well. This indicates that the variations of observed luminosities may be essentially due to the Doppler boosting effect. The universal δ-Lo relation between FSRQs and GeV NLS 1 s in different stages may be further evidence that the particle acceleration and radiation mechanisms for the two kinds of sources are similar. In addition, by replacing Lc with the observed luminosity in the Fermi/LAT band (LLAT), this correlation holds and it may serve as an empirical indicator of δ. We estimate the δ values with LLAT for 484 FSRQs in the Fermi/LAT Catalog and they range from 3 to 41, with a median of 16, which are statistically consistent with the values derived by other methods. 展开更多
关键词 galaxies active - galaxies jets - quasars general - galaxies Seyfert
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The Difference between the α-disks of Seyfert 1 Galaxies and Quasars
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作者 Wei-HaoBian HongDong Yong-HengZhao 《Chinese Journal of Astronomy and Astrophysics》 CSCD 北大核心 2004年第1期61-66,共6页
In a previous paper, it was suggested that contamination of the nuclear luminosity by the host galaxy plays an important role in determining the parameters of the standard a disk of AGNs. Using the nuclear absolute B ... In a previous paper, it was suggested that contamination of the nuclear luminosity by the host galaxy plays an important role in determining the parameters of the standard a disk of AGNs. Using the nuclear absolute B band magnitude instead of the total absolute B band magnitude, we have recalculated the central black hole masses, accretion rates and disk inclinations for 20 Seyfert 1 galaxies and 17 Palomar-Green (PG) quasars. It is found that a small value of a is needed for the Seyfert 1 galaxies than for the PG quasars. This difference in a possibly leads to the different properties of Seyfert 1 galaxies and quasars. Furthermore, we find most of the objects in this sample are not accreting at super-Eddington rates if we adopt the nuclear optical luminosity in our calculation. 展开更多
关键词 galaxies: active - galaxies: nuclei - quasars: Seyfert
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Formation and Evolution of Galaxies and Its Black Holes and Quasars
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作者 Cuixiang Zhong 《Journal of Physical Science and Application》 2021年第2期9-20,共12页
Galaxy formation and evolution is one of the most active research areas in astrophysics,so many people have studied this area.But since they didn’t understand thoroughly the evolution law from satellite to planet the... Galaxy formation and evolution is one of the most active research areas in astrophysics,so many people have studied this area.But since they didn’t understand thoroughly the evolution law from satellite to planet then to star,their theories are very weak.In their theories,they proposed that large gas clouds collapsing to form a galaxy or more recently that matter started out in smaller clumps merged to form galaxy,which is incredible.Hence,the author of this paper,through studying the formation and orbit-variation of satellites,planets and stars,has put forward a new theory of galaxy formation and evolution,therefore revealing the hierarchical structure of galaxies and the formation and evolution of black holes and quasars. 展开更多
关键词 galaxies:structure galaxies:formation galaxies:evolution stars:black holes stars:quasars
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Merging History of Massive Galaxies at 3
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作者 Kemeng Li Zhen Jiang +2 位作者 Ping He Qi Guo Jie Wang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2023年第1期100-107,共8页
The observational data of high redshift galaxies become increasingly abundant,especially since the operation of the James Webb Space Telescope,which allows us to verify and optimize the galaxy formation model at high ... The observational data of high redshift galaxies become increasingly abundant,especially since the operation of the James Webb Space Telescope,which allows us to verify and optimize the galaxy formation model at high redshifts.In this work,we investigate the merging history of massive galaxies at 3<z<6 using a well-developed semi-analytic galaxy formation catalog.We find that the major merger rate increases with redshift up to 3 and then flattens.The fraction of wet mergers,during which the sum of the cold gas mass is higher than the sum of the stellar mass in two merging galaxies,also increases from~34%at z=0 to 96%at z=3.Interestingly,almost all major mergers are wet at z>3.This can be attributed to the high fraction(>50%)of cold gas at z>3.In addition,we study some special systems of massive merging galaxies at 3<z<6,including the massive gas-rich major merging systems and extreme dense proto-clusters,and investigate the supermassive black hole-dark matter halo mass relation and dual active galactic nuclei.We find that the galaxy formation model reproduces the incidence of those observed massive galaxies,but fails to reproduce the relation between the supermassive black hole mass and the dark matter halo mass at z~6.The latter requires more careful estimates of the supermassive black hole masses observationally.Otherwise,it could suggest modifications of the modeling of the supermassive black hole growth at high redshifts. 展开更多
关键词 galaxies evolution-galaxies formation-galaxies high-redshift-(galaxies:)quasars supermassive black holes
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Study of Central Intensity Ratio of Seyfert Galaxies in Nearby Universe
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作者 K.T.Vinod C.Baheeja +1 位作者 S.Aswathy C.D.Ravikumar 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2023年第4期85-93,共9页
We use the recently discovered simple photometric parameter Central Intensity Ratio(CIR)determined for a sample of 57 nearby(z<0.02)Seyfert galaxies to explore the central features of galaxies and their possible co... We use the recently discovered simple photometric parameter Central Intensity Ratio(CIR)determined for a sample of 57 nearby(z<0.02)Seyfert galaxies to explore the central features of galaxies and their possible connection with galaxy evolution.The sample of galaxies shows strong anti-correlation between CIR and mass of their central supermassive black holes(SMBHs).The SMBH masses of ellipticals are systematically higher for a given CIR value than those for lenticulars and spirals in the sample.However,the correlation between CIR and central velocity dispersion is weak.CIR appears less influenced by the excess flux produced by the central engine in these galaxies,when compared to spectroscopic parameters like velocity dispersion and OⅣflux,and proves to be a fast and reliable tool for estimating central SMBH mass. 展开更多
关键词 Galaxy evolution-galaxies active-galaxies photometry-(galaxies:)quasars supermassive black holes-galaxies SEYFERT
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The AGN Feedback in Compact Galaxies:On the Impact of a More Massive Central Black Hole
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作者 Yihuan Di Feng Yuan Suoqing Ji 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2023年第10期299-307,共9页
We conduct high-resolution hydrodynamical simulations using the MACER framework to investigate the interplay between the interstellar medium,active galactic nuclei(AGN)feedback and black hole(BH)feeding in a massive c... We conduct high-resolution hydrodynamical simulations using the MACER framework to investigate the interplay between the interstellar medium,active galactic nuclei(AGN)feedback and black hole(BH)feeding in a massive compact galaxy,with an emphasis on the impact of different central BH masses.We find that with a more massive central BH,high-speed outflows are more prominent,and the gas fraction in the compact galaxy is reduced.Due to the lower gas density and higher gas temperature,the compact galaxy with a more massive BH(MAS galaxy)remains predominantly single-phase with the cooling time t_(cool)■100t_(ff).In contrast,the compact galaxy with the reference BH mass(REF galaxy)maintains a higher gas fraction with a shorter cooling time,slightly more multiphase gas and less prominent outflows.We further demonstrate that the difference in gas thermal states and kinematics is caused by the stronger AGN feedback in the compact galaxy with a more massive BH,where the AGN wind power is twice as much as that with the reference BH.Since the AGN feedback efficiently suppresses the inflow rate and the BH feeding rate,the BH mass growth is significant in neither the compact galaxy with the reference BH nor that with the more massive BH,only by 24%and 11%of the initial BH mass,respectively,over the entire evolution time of 10 Gyr.We thus posit that without ex situ mass supply from mergers,the massive BHs in compact galaxies cannot grow significantly via gas accretion during the late phase,but might have already formed by the end of the rapid early phase of galaxy formation. 展开更多
关键词 galaxies:active galaxies:evolution galaxies:nuclei (galaxies:)quasars:supermassive black holes
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First Neutral Atomic Hydrogen Images of Quasar Host Galaxies
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作者 Jeremy Lim (Academia Sinica Institute of Astronomy & Astrophysics PO Box 1 87, Nankang, Taipei 115, Taiwan) Paul T. P. Ho (Harvard Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA) 《天文研究与技术》 CSCD 1999年第S1期205-209,共5页
Violent galactic encounters or mergers are the leading contenders for triggering luminous quasar activity at low redshifts: such interactions can lead to the concentration of gas in the host galactic nucleus, thus fue... Violent galactic encounters or mergers are the leading contenders for triggering luminous quasar activity at low redshifts: such interactions can lead to the concentration of gas in the host galactic nucleus, thus fueling the suspected central superrmassive black hole. Although optical images show a number of violently interacting systems, in many cases the evidence for such interactions is only circumstantial (e.g., asymmetric optical morphologies, projected nearby companion galaxies) or not at all apparent. Here we image quasar host galaxies for the first time in the redshifted 21 cm line emission of neutral atomic hydrogen (HI) gas, which in nearby galaxies has proven to be a particularly sensitive as well as enduring tracer of tidal interactions. The three quasars studied have different optical environments normally seen around low reshift quasars, ranging from a perhaps mildly interacting system to a relatively undisturbed host with a projected neighbouring galaxy to an isolated and apparently serene host galaxy. By contrast with their optical appearences, all three quasar host galaxies exhibit ongoing or remnant tidal HI disruptions tracing galactic encounters or mergers. These observations provide a better understanding of the likely stage of their interaction. 展开更多
关键词 NATURE First Neutral Atomic Hydrogen Images of quasar Host galaxies
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Eight new quasars discovered by the Guoshoujing Telescope (LAMOST) in one extragalactic field 被引量:1
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作者 Xue-Bing Wu Zhen-Dong Jia +18 位作者 Zhao-Yu Chen Wen-Wen Zuo Yong-Heng Zhao A-li Luo Zhong-Rui Bai Jian-Jun Chen Hao-Tong Zhang Hong-Liang Yan Juan-Juan Ren Shi-Wei Sun Hong Wu Yong Zhang Ye-Ping Li Qi-Shuai Lu You Wang Ji-Jun Ni Hai Wang Xu Kong Shi-Yin Shen 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2010年第8期745-752,共8页
We report the discovery of eight new quasars in one extragalactic field (a five-degree field centered at RA=08^h58^m08.2^s, Dec=01°32′29.7″) with the Guoshoujing Telescope (LAMOST) commissioning observation... We report the discovery of eight new quasars in one extragalactic field (a five-degree field centered at RA=08^h58^m08.2^s, Dec=01°32′29.7″) with the Guoshoujing Telescope (LAMOST) commissioning observations made on 2009 December 18. These quasars, with i magnitudes from 16.44 to 19.34 and redshifts from 0.898 to 2.773, were not identified in the SDSS spectroscopic survey, though six of them with redshifts less than 2.5 were selected as quasar targets in SDSS. Except for one source without near-IR Y-band data, seven of these eight new quasars satisfy a newly proposed quasar selection criterion involving both near-IR and optical colors. Two of them were found in the 'redshift desert' for quasars (z from 2.2 to 3), indicating that the new criterion is efficient for uncovering missing quasars with similar optical colors to stars. Although LAMOST encountered some problems during the commissioning observations, we were still able to identify 38 other known SDSS quasars in this field, with i magnitudes from 16.24 to 19.10 and redshifts from 0.297 to 4.512. Our identifications imply that a substantial fraction of quasars may be miss- ing in previous quasar surveys. The implication of our results to the future LAMOST quasar survey is discussed. 展开更多
关键词 quasars general -- quasars emission lines -- galaxies active
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New background quasars in the vicinity of the Andromeda Galaxy discovered with the Guoshoujing Telescope (LAMOST) 被引量:1
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作者 Zhi-Ying Huo Xiao-Wei Liu +17 位作者 Hai-Bo Yuan Hui-Hua Zhang Yong-Heng Zhao Jian-Jun Chen Zhong-Rui Bai Hao-Tong Zhang Hua-Wei Zhang Ruben Garcia-Benito Mao-Sheng Xiang Hong-Liang Yan Juan-Juan Ren Shi-Wei Sun Yong Zhang Ye-Ping Li Qi-Shuai Lu You Wang Ji-Jun Ni Hai Wang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2010年第7期612-620,共9页
We present preliminary analyses of spectra of quasar candidates in two Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST) test fields near M 31 where ... We present preliminary analyses of spectra of quasar candidates in two Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST) test fields near M 31 where one is close to the optical center of the disk and the other is towards the northeastern outskirts of the halo, obtained during the early stage of the GSJT commissioning in the last season of 2009. Both fields contain background low-redshift quasar candidates selected from the SDSS photometry. In total, 14 new quasars with redshifts up to 2 and i magnitudes between 16.7 and 19.2, are discovered, including 7 within the 2.5° central region of M 31. We briefly discuss the potential applications of these newly discovered bright quasars. 展开更多
关键词 galaxies individual (M31) -- quasars general -- quasars emission lines
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GeneticKNN:a weighted KNN approach supported by genetic algorithm for photometric redshift estimation of quasars 被引量:2
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作者 Bo Han Li-Na Qiao +3 位作者 Jing-Lin Chen Xian-Da Zhang Yan-Xia Zhang Yong-Heng Zhao 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2021年第1期165-177,共13页
We combine K-nearest neighbors(KNN)with a genetic algorithm(GA)for photometric redshift estimation of quasars,short for GeneticKNN,which is a weighted KNN approach supported by a GA.This approach has two improvements ... We combine K-nearest neighbors(KNN)with a genetic algorithm(GA)for photometric redshift estimation of quasars,short for GeneticKNN,which is a weighted KNN approach supported by a GA.This approach has two improvements compared to KNN:one is the feature weighted by GA;the other is that the predicted redshift is not the redshift average of K neighbors but the weighted average of median and mean of redshifts for K neighbors,i.e.p×zmedian+(1-p)×zmean.Based on the SDSS and SDSS-WISE quasar samples,we explore the performance of GeneticKNN for photometric redshift estimation,comparing with the other six traditional machine learning methods,i.e.the least absolute shrinkage and selection operator(LASSO),support vector regression(SVR),multi-layer perceptrons(MLP),XGBoost,KNN and random forest.KNN and random forest show their superiority.Considering the easy implementation of KNN,we make improvement on KNN as GeneticKNN and apply GeneticKNN on photometric redshift estimation of quasars.Finally the performance of GeneticKNN is better than that of LASSO,SVR,MLP,XGBoost,KNN and random forest for all cases.Moreover the accuracy is better with the additional WISE magnitudes for the same method. 展开更多
关键词 astronomical databases:catalogs (galaxies:)quasars:general methods:statistical techniques:miscellaneous
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Radio Luminosity,Black Hole Mass and Eddington Ratio for Quasars from the Sloan Digital Sky Survey 被引量:1
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作者 Wei-Hao Bian Yan-Mei Chen +2 位作者 Chen Hu Kai Huang Yan Xu 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2008年第5期522-536,共15页
We investigate the MBH-σ* relation for radio-loud quasars with redshifl z 〈 0.83 in Data Release 3 of the Sloan Digital Sky Survey (SDSS). The sample consists of 3772 quasars with better models of the H/4 and [O ... We investigate the MBH-σ* relation for radio-loud quasars with redshifl z 〈 0.83 in Data Release 3 of the Sloan Digital Sky Survey (SDSS). The sample consists of 3772 quasars with better models of the H/4 and [O Ⅲ] lines and available radio luminosity, including 306 radio-loud quasars, 3466 radio-quiet quasars with measured radio luminosity or upper-limit of radio luminosity (181 radio-quiet quasars with measured radio luminosity). The virial supermassive black hole mass (MBH) is calculated from the broad Hβline, and the host stellar velocity dispersion (σ*) is traced by the core [O Ⅲ] gaseous velocity dispersion. The radio luminosity and radio loudness are derived from the FIRST catalog. Our results are as follows: (1) For radio-quiet quasars, we confirm that there is no obvious deviation from the MBH-σ* relation defined for inactive galaxies when the uncertainties in ~IBH and the luminosity bias are concerned. (2) We find that the radio-loud quasars deviate more from the MBH-σ* relation than do the radio-quiet quasars. This deviation is only partly due to a possible cosmological evolution of the MBH-σ* relation and the luminosity bias. (3) The radio luminosity is proportional to MBH1.28+0.23-0.16(LBol/LEdd) ^1.29+0.31-0.24 for radio-quiet quasars and to -MBH3.10+0.60-0.70(LBol/LEdd)^4.18+1.40-1.10 - for radio-loud quasars. The weaker dependence of the radio luminosity on the mass and the Eddington ratio for radio-loud quasars shows that other physical effects would account for their radio luminosities, such as the spin of the black hole. 展开更多
关键词 quasars emission lines - galaxies nuclei -galaxies bulges - black hole physics
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Hydrodynamical simulations of the triggering of nuclear activities by minor mergers of galaxies 被引量:1
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作者 Chao Yang Jun-Qiang Ge You-Jun Lu 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2019年第12期245-256,共12页
Major mergers of galaxies are considered to be an efficient way to trigger Active Galactic Nuclei and are thought to be responsible for the phenomenon of quasars. This has however recently been challenged by observati... Major mergers of galaxies are considered to be an efficient way to trigger Active Galactic Nuclei and are thought to be responsible for the phenomenon of quasars. This has however recently been challenged by observations of a large number of low luminosity Active Galactic Nuclei at low redshift(z■1) without obvious major merger signatures. Minor mergers are frequently proposed to explain the existence of these Active Galactic Nuclei. In this paper, we perform nine high resolution hydrodynamical simulations of minor galaxy mergers, and investigate whether nuclear activities can be efficiently triggered by minor mergers, by setting various properties for the progenitor galaxies of those mergers. We find that minor galaxy mergers can activate the massive black hole in the primary galaxy with an Eddington ratio of f Edd > 0.01 and> 0.05(or a bolometric luminosity > 10^43 and > 10^44 erg s^-1) with a duration of 2.71 and 0.49 Gyr(or 2.69 and 0.19 Gyr), respectively. The nuclear activity of the primary galaxy strongly depends on the nucleus separation, such that the nucleus is more active as the two nuclei approach each other. Dual Active Galactic Nuclei systems can still possibly be formed by minor mergers of galaxies, though the time duration for dual Active Galactic Nuclei is only ~ 0.011 Gyr and ~ 0.017 Gyr with Eddington ratio of f Edd > 0.05 and bolometric luminosity > 10^44 erg s^-1. This time period is typically shorter than that of dual Active Galactic Nuclei induced by major galaxy mergers. 展开更多
关键词 galaxies:binary quasars:general methods:n-body simulations
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Discovery of six high-redshift quasars with the Lijiang 2.4 m telescope and the Multiple Mirror Telescope 被引量:1
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作者 Xue-Bing Wu Wen-Wen Zuo +6 位作者 Qian Yang Wei-Min Yi Chen-Wei Yang Wen-Juan Liu Peng Jiang Xin-Wen Shu Hong-Yan Zhou 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2012年第9期1185-1190,共6页
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... 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. 展开更多
关键词 quasars: general quasars: emission lines galaxies: active galax- ies: high-redshift
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A new strategy for estimating photometric redshifts of quasars 被引量:1
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作者 Yan-Xia Zhang Jing-Yi Zhang +1 位作者 Xin Jin Yong-Heng Zhao 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2019年第12期223-234,共12页
Based on the SDSS and SDSS-WISE quasar datasets, we put forward two schemes to estimate the photometric redshifts of quasars. Our schemes are based on the idea that the samples are firstly classified into subsamples b... Based on the SDSS and SDSS-WISE quasar datasets, we put forward two schemes to estimate the photometric redshifts of quasars. Our schemes are based on the idea that the samples are firstly classified into subsamples by a classifier and then a photometric redshift estimation of different subsamples is performed by a regressor. Random Forest is adopted as the core algorithm of the classifiers, while Random Forest and k NN are applied as the key algorithms of regressors. The samples are divided into two subsamples and four subsamples, depending on the redshift distribution. The performances based on different samples, different algorithms and different schemes are compared. The experimental results indicate that the accuracy of photometric redshift estimation for the two schemes generally improves to some extent compared to the original scheme in terms of the percents in |△z|1+zi< 0.1 and |△z|1+zi<0.2 and mean absolute error. Only given the running speed, k NN shows its superiority to Random Forest. The performance of Random Forest is a little better than or comparable to that of k NN with the two datasets. The accuracy based on the SDSS-WISE sample outperforms that based on the SDSS sample no matter by k NN or by Random Rorest. More information from more bands is considered and helpful to improve the accuracy of photometric redshift estimation. Evidently, it can be found that our strategy to estimate photometric redshift is applicable and may be applied to other datasets or other kinds of objects. Only talking about the percent in |△z|1+zi<0.3, there is still large room for further improvement in the photometric redshift estimation. 展开更多
关键词 astronomical databases:catalogs (galaxies:)quasars:general methods:statistical techniques:miscellaneous
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Photometric redshift estimation for quasars by integration of KNN and SVM 被引量:1
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作者 Bo Han Hong-Peng Ding +1 位作者 Yan-Xia Zhang Yong-Heng Zhao 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2016年第5期31-40,共10页
The massive photometric data collected from multiple large-scale sky surveys offer significant opportunities for measuring distances of celestial objects by photometric redshifts. However, catastrophic failure is an u... The massive photometric data collected from multiple large-scale sky surveys offer significant opportunities for measuring distances of celestial objects by photometric redshifts. However, catastrophic failure is an unsolved problem with a long history and it still exists in the current photometric redshift estimation approaches (such as the k-nearest neighbor (KNN) algorithm). In this paper, we propose a novel two-stage approach by integration of KNN and support vector machine (SVM) methods together. In the first stage, we apply the KNN algorithm to photometric data and estimate their corresponding Zphot. Our analysis has found two dense regions with catastrophic failure, one in the range of Zphot E [0.3, 1.2] and the other in the range of Zphot E [1.2, 2.1]. In the second stage, we map the photometric input pattern of points falling into the two ranges from their original attribute space into a high dimensional feature space by using a Gaussian kernel function from an SVM. In the high dimensional feature space, many outliers resulting from catastrophic failure by simple Euclidean distance computation in KNN can be identified by a classification hyperplane of SVM and can be further corrected. Experimental results based on the Sloan Digital Sky Survey (SDSS) quasar data show that the two-stage fusion approach can significantly mitigate catastrophic failure and improve the estimation accuracy of photometric redshifts of quasars. The percents in different /△z/ ranges and root mean square (rms) error by the integrated method are 83.47%, 89.83%, 90.90% and 0.192, respectively, compared to the results by KNN (71.96%, 83.78%, 89.73% and 0.204). 展开更多
关键词 catalogs -- galaxies distances and redshifts -- methods: statistical -- quasars general --surveys -- techniques: photometric
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On the Correlation between Radio Properties and Black Hole Mass of Quasars
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作者 Xue-Guang Zhang, Ting-Gui Wang and You-Jun LuCenter for Astrophysics, and Department of Astronomy and Applied Physics, University of Science and Technology of China, Hefei 230026 zxg@mail.ustc.edu.cn 《Chinese Journal of Astronomy and Astrophysics》 CSCD 北大核心 2003年第3期212-224,共13页
The question whether the radio properties of quasars are related to the massof the central black hole or the accretion rate is important for our understanding of the formationof relativistic jets, but no consensus has... The question whether the radio properties of quasars are related to the massof the central black hole or the accretion rate is important for our understanding of the formationof relativistic jets, but no consensus has been reached from statistical analyses. Using two largequasar samples, one radio-selected, one optical-selected, we re-examined these relations and findthat previous differences between radio- and optical- selected samples can be ascribed, at leastpartly, to the effect of the narrow line component. All previous claimed correlations are muchweaker, if exist at all. 展开更多
关键词 galaxies: active galaxies: nuclei quasars black hole
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A search for double-peaked narrow emission line galaxies and AGNs in the LAMOST DR1
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作者 Zhi-Xin Shi A-Li Luo +15 位作者 Georges Comte Xiao-Yan Chen Peng Wei Yong-Heng Zhao Fu-Chao Wu Yan-Xia Zhang Shi-Yin Shen Ming Yang Hong Wu Xue-Bing Wu Hao-Tong Zhang Ya-Juan Lei Jian-Nan Zhang Ting-Gui Wang Ge Jin Yong Zhang 《Research in Astronomy and Astrophysics》 SCIE CAS CSCD 2014年第10期1234-1250,共17页
The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has released more than two million spectra, which provide the opportunity to search for double-peaked narrow emission line (NEL) galaxies and ... The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) has released more than two million spectra, which provide the opportunity to search for double-peaked narrow emission line (NEL) galaxies and active galactic nuclei (AGNs). The double-peaked narrow-line profiles can be well modeled by two velocity components, respectively blueshifted and redshifted with respect to the sys- temic recession velocity. This paper presents 20 double-peaked NEL galaxies and AGNs found from LAMOST DR1 using a search method based on a multi-Gaussian fit of the narrow emission lines. Among them, ten have already been published by other authors, either listed as genuine double-peaked NEL objects or as asymmetric NEL objects, and the remaining ten are original discoveries. We discuss some pos- sible origins for the double-peaked narrow-line features, such as interaction between jet and narrow line regions, interaction with companion galaxies, and black hole bina- ries. Spatially resolved optical imaging and/or follow-up observations in other spectral bands are needed to further discuss the physical mechanisms at work. 展开更多
关键词 galaxies emission lines -- quasars emission lines -- methods dataanalysis
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An X-Ray Study of Lobe-Dominated Radio-Loud Quasars with XMM-Newton
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作者 Li-Ming Dou Wei-Min Yuan 《Chinese Journal of Astronomy and Astrophysics》 CSCD 2008年第6期653-670,共18页
We report on our results of X-ray spectral analysis for a sample of radio-loud quasars covering a wide range of the radio core-dominance parameter, R, from core- dominated to lobe-dominated objects, using data obtaine... We report on our results of X-ray spectral analysis for a sample of radio-loud quasars covering a wide range of the radio core-dominance parameter, R, from core- dominated to lobe-dominated objects, using data obtained mostly with the XMM-Newton Observatory. We find that the spectral shape of the underlying power-law continuum is flat even for the lobe-dominated objects (average photon index ~ 1.5), indistinguishable from that of core-dominated quasars. For lobe-dominated objects, contribution of X-rays from the jets is expected to be very small based on previous unification schemes, more than one order of magnitude lower than the observed X-ray luminosities. Assuming that radio-loud quasars follow the same X-ray-UV/optical luminosity relation for the disk-corona emission as found for radio-quiet quasars, we estimate the X-ray flux contributed by the disk-corona component from the optical/UV continuum. We find that neither the luminosity, nor the spectral shape, of the disk-corona X-ray emission can account for the bulk of the observed X-ray properties. Thus in lobe-dominated quasars, either the disk-corona X-ray emission is much enhanced in strength and flatter in spectral shape (photon index - 1.5) compared to normal radio-quiet quasars, or their jet X-ray emission is much enhanced compared to their weak radio core-jet emission. If the latter is the case, our result may imply that the jet emission in X-rays is less Doppler beamed than that in the radio. As a demonstrating example, we test this hypothesis by using a specific model in which the X-ray jet has a larger opening angle than the radio jet. 展开更多
关键词 galaxies active quasars general galaxies X-ray galaxies radio continuum
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Color-Redshift Relations and Photometric Redshift Estimations of Quasars in Large Sky Surveys
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作者 Xue-BingWu WeiZhang XuZhou 《Chinese Journal of Astronomy and Astrophysics》 CSCD 北大核心 2004年第1期17-27,共11页
With a recently constructed composite quasar spectrum and the χ<SUP>2</SUP> minimization technique, we describe a general method for estimating the photometric redshifts of a large sample of quasars by de... With a recently constructed composite quasar spectrum and the χ<SUP>2</SUP> 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. 展开更多
关键词 galaxies: photometry quasars: general quasars: emission lines surveys
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