Clusters of galaxies have a huge mass which can act as gravitational lenses.Galaxies behind clusters can be distorted by the lenses to form arcs in images.Herein a search was done for giant lensed arcs using the SDSS ...Clusters of galaxies have a huge mass which can act as gravitational lenses.Galaxies behind clusters can be distorted by the lenses to form arcs in images.Herein a search was done for giant lensed arcs using the SDSS data.By visually inspecting SDSS images of newly identified clusters in the SDSS DR8 and Stripe 82 data,we discover 8 strong lensing clusters together with additional 3probable and 6 possible cases.The lensed arcs show bluer colors than the member galaxies of clusters.The masses and optical luminosities of galaxy clusters interior to the arcs are calculated.The mass-to-light ratios are found to be in the range of a few tens of M⊙/L⊙,consistent with the distribution of previously known lensing clusters.展开更多
Brightest Cluster Galaxies （BCGs） are mostly elliptical galaxies and very rarely have prominent star formations. We found that five out of 8,812 BCGs are E＋A （i.e., post-starburst） galaxies, having an Hd absorpti...Brightest Cluster Galaxies （BCGs） are mostly elliptical galaxies and very rarely have prominent star formations. We found that five out of 8,812 BCGs are E＋A （i.e., post-starburst） galaxies, having an Hd absorption line with an equivalent width 〉2.5 A and no distinct emission lines in [O II] and Ha-. The E＋A features we identified from the BCGs for the first time are not as significant as those in general galaxies, indicating that historically the star formations were not very violent.展开更多
Radio detection of pulsars in the Galactic disk is strongly affected by the dispersion and scattering effect of the interstellar medium and the Galactic background radio emission. In order to know the best conditions ...Radio detection of pulsars in the Galactic disk is strongly affected by the dispersion and scattering effect of the interstellar medium and the Galactic background radio emission. In order to know the best conditions for discovery of pulsars, we select and simulate pulsar samples in the Galactic disk, and calculate the detection probability with various observation conditions (such as observational frequency, telescope aperture, receiver bandwidth and integration time). We have found that the detection fraction increases with the telescope aperture, receiver bandwidth and integration time. To detect pulsars in the nearer half of the Galactic disk, the observation frequency should be in the range of 1-2 GHz, while for pulsars in the farther half of the disk, the frequency should be in the range of 3.5-4.5 GHz. Due to the strong influence of scattering, the short period pulsars are hard to be detected, especially for pulsars in the farther half of the Galactic disk.展开更多
Pulsar hulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar hulling pheno...Pulsar hulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar hulling phenomenon, by involving two key parameters, the nulling degree, X, which is defined as the angle in a rectangular coordinates for the numbers of nulling periods and bursting periods, and the nulling scale, N, which is defined as the effective length of the consecutive nulling periods and bursting periods. The nulling degree X can be calculated by tanX = Nnulling/Nbursting and the mean is related to the nulling fraction, while the nulling scale, N, is also a newly defined fundamental parameter which indicates how often the nulling occurs. We determined the distributions ofx and N for 10 pulsars by using the data in literature. We found that the nulling degree X indicates the relative length of nulling to that of bursting, and the nulling scale N is found to be related to the derivative of rotation frequency and hence the loss rate of rotational energy of pulsars. Their deviations reflect the randomness of the nulling process.展开更多
The survey data of Wide-field Infrared Survey Explorer(WISE)provide an opportunity for the identification of galaxy clusters.We present an efficient method for detecting galaxy clusters by combining the WISE data with...The survey data of Wide-field Infrared Survey Explorer(WISE)provide an opportunity for the identification of galaxy clusters.We present an efficient method for detecting galaxy clusters by combining the WISE data with SuperCOSMOS and 2MASS data.After performing star-galaxy separation,we calculate the number of companion galaxies around the galaxies with photometric redshifts previously estimated by the SuperCOSMOS,2MASS and WISE data.A scaled richness Rscal 30 is set as a criterion to identify clusters.From a sky area of 275 deg2of the Sloan Digital Sky Survey Stripe 82 region,we identify 302 clusters in the redshift range of 0.1<z<0.35,247(82%)of which are previously known SDSS clusters.The results suggest that our method is efficient for identifying galaxy clusters by using the all sky data of the SuperCOSMOS,2MASS and WISE.展开更多
Repeated scatterings of unpolarized photons by non-relativistic electrons in a static and uniform magnetic field are investigated by using the Boltzmann equation with quantum mechanical correction factors for the stim...Repeated scatterings of unpolarized photons by non-relativistic electrons in a static and uniform magnetic field are investigated by using the Boltzmann equation with quantum mechanical correction factors for the stimulated scattering effects.The resulting Kompaneets equation depends explicitly on the electron cyclotron frequency and the incidence angle of the incoming photons relative to the direction of the magnetic field.The evolutionary behavior of the photon spectrum and energy density is highly anisotropic with respect to the static external magnetic field.Possible applications of our results to the X-ray emission from compact and massive stellar objects are discussed in detail and those to the interaction of the microwave background radiation with the hot electrons in galactic clusters are discussed briefly.展开更多
基金supportedby the National Natural Science Foundation of China(Grant Nos.11103032and 11261140641)the China Ministry of Science and Technology(GrantNo.2013CB837900)the Young Researcher Grant of National Astronomical Observatories,Chinese Academy of Sciences
文摘Clusters of galaxies have a huge mass which can act as gravitational lenses.Galaxies behind clusters can be distorted by the lenses to form arcs in images.Herein a search was done for giant lensed arcs using the SDSS data.By visually inspecting SDSS images of newly identified clusters in the SDSS DR8 and Stripe 82 data,we discover 8 strong lensing clusters together with additional 3probable and 6 possible cases.The lensed arcs show bluer colors than the member galaxies of clusters.The masses and optical luminosities of galaxy clusters interior to the arcs are calculated.The mass-to-light ratios are found to be in the range of a few tens of M⊙/L⊙,consistent with the distribution of previously known lensing clusters.
基金supported by the Liaoning Educational Foundation of China (Grant No.2009A646)the National Natural Science Foundation of China (Grant Nos.10773016,10821061 and 1083303)+1 种基金the National Key Basic Research Science Foundation of China (Grant No.2007CB815403)Funding for the creation and distribution of the SDSS Archive has been provided by the Alfred P.Sloan Foundation
文摘Brightest Cluster Galaxies （BCGs） are mostly elliptical galaxies and very rarely have prominent star formations. We found that five out of 8,812 BCGs are E＋A （i.e., post-starburst） galaxies, having an Hd absorption line with an equivalent width 〉2.5 A and no distinct emission lines in [O II] and Ha-. The E＋A features we identified from the BCGs for the first time are not as significant as those in general galaxies, indicating that historically the star formations were not very violent.
基金supported by the National Natural Science Foundation of China (Grant Nos. 10773016, 10821001 and 10833003)the Initialization Fund for President Award Winner of Chinese Academy of Sciences
文摘Radio detection of pulsars in the Galactic disk is strongly affected by the dispersion and scattering effect of the interstellar medium and the Galactic background radio emission. In order to know the best conditions for discovery of pulsars, we select and simulate pulsar samples in the Galactic disk, and calculate the detection probability with various observation conditions (such as observational frequency, telescope aperture, receiver bandwidth and integration time). We have found that the detection fraction increases with the telescope aperture, receiver bandwidth and integration time. To detect pulsars in the nearer half of the Galactic disk, the observation frequency should be in the range of 1-2 GHz, while for pulsars in the farther half of the disk, the frequency should be in the range of 3.5-4.5 GHz. Due to the strong influence of scattering, the short period pulsars are hard to be detected, especially for pulsars in the farther half of the Galactic disk.
基金supported by China Ministry of Science and Technology(Grant No.2013CB837900)the National Natural Science Foundationof China(Grant Nos.10833003,11003023,11273029 and 11261140641)
文摘Pulsar hulling is a phenomenon of sudden cessation of pulse emission for a number of periods. The nulling fraction was often used to characterize the phenomenon. We propose a new method to analyse pulsar hulling phenomenon, by involving two key parameters, the nulling degree, X, which is defined as the angle in a rectangular coordinates for the numbers of nulling periods and bursting periods, and the nulling scale, N, which is defined as the effective length of the consecutive nulling periods and bursting periods. The nulling degree X can be calculated by tanX = Nnulling/Nbursting and the mean is related to the nulling fraction, while the nulling scale, N, is also a newly defined fundamental parameter which indicates how often the nulling occurs. We determined the distributions ofx and N for 10 pulsars by using the data in literature. We found that the nulling degree X indicates the relative length of nulling to that of bursting, and the nulling scale N is found to be related to the derivative of rotation frequency and hence the loss rate of rotational energy of pulsars. Their deviations reflect the randomness of the nulling process.
基金supported by the National Natural Science Foundation of China (Grant No.11103032)the Young Researcher Grant of National Astronomical Observatories,Chinese Academy of Sciences+3 种基金This publication makes use of data products from the Wide-field Infrared Survey Explorer,which is a joint project of the University of California,Los Angeles,and the Jet Propulsion Laboratory/California Institute of Technology,funded by the National Aeronautics and Space AdministrationFunding for the SDSS and SDSS-Ⅱ has been provided by the Alfred P.Sloan Foundation,the Participating Institutionsthe National Science Foundationthe U.S.Department of Energy,the National Aeronautics and Space Administration,the Japanese Monbukagakusho,the Max Planck Society,and the Higher Education Funding Council for England
文摘The survey data of Wide-field Infrared Survey Explorer(WISE)provide an opportunity for the identification of galaxy clusters.We present an efficient method for detecting galaxy clusters by combining the WISE data with SuperCOSMOS and 2MASS data.After performing star-galaxy separation,we calculate the number of companion galaxies around the galaxies with photometric redshifts previously estimated by the SuperCOSMOS,2MASS and WISE data.A scaled richness Rscal 30 is set as a criterion to identify clusters.From a sky area of 275 deg2of the Sloan Digital Sky Survey Stripe 82 region,we identify 302 clusters in the redshift range of 0.1<z<0.35,247(82%)of which are previously known SDSS clusters.The results suggest that our method is efficient for identifying galaxy clusters by using the all sky data of the SuperCOSMOS,2MASS and WISE.
基金supported by the National Natural Science Foundation of China (Grant Nos. Y011091001,11003023 and 10833003)
文摘Repeated scatterings of unpolarized photons by non-relativistic electrons in a static and uniform magnetic field are investigated by using the Boltzmann equation with quantum mechanical correction factors for the stimulated scattering effects.The resulting Kompaneets equation depends explicitly on the electron cyclotron frequency and the incidence angle of the incoming photons relative to the direction of the magnetic field.The evolutionary behavior of the photon spectrum and energy density is highly anisotropic with respect to the static external magnetic field.Possible applications of our results to the X-ray emission from compact and massive stellar objects are discussed in detail and those to the interaction of the microwave background radiation with the hot electrons in galactic clusters are discussed briefly.
