The clustering of QSOs and the dark matter halos that host them

The spatial clustering of QSOs is an important measurable quantity which can be used to infer the properties of dark matter halos that host them.We construct a simple QSO model to explain the linear bias of QSOs measured by recent observations and explore the properties of dark matter halos that host a QSO.We assume that major mergers of dark matter halos can lead to the triggering of QSO phenomena,and the evolution of luminosity for a QSO generally shows two accretion phases,i.e.,initially having a constant Eddington ratio due to the self-regulation of the accretion process when supply is sufcient,and then declining in rate with time as a power law due to either diminished supply or long term disk evolution.Using a Markov Chain Monte Carlo method,the model parameters are constrained by fitting the observationally determined QSO luminosity functions（LFs）in the hard X-ray and in the optical band simultaneously.Adopting the model parameters that best fit the QSO LFs,the linear bias of QSOs can be predicted and then compared with the observational measurements by accounting for various selection efects in diferent QSO surveys.We find that the latest measurements of the linear bias of QSOs from both the SDSS and BOSS QSO surveys can be well reproduced.The typical mass of SDSS QSOs at redshift 1.53 6×1012h 1M⊙and the typical mass of BOSS QSOs at z².4 is²×1012h 1M⊙.For relatively faint QSOs,the mass distribution of their host dark matter halos is wider than that of bright QSOs because faint QSOs can be hosted in both big halos and smaller halos,but bright QSOs are only hosted in big halos,which is part of the reason for the predicted weak dependence of the linear biases on the QSO luminosity.     

Extragalactic dispersion measures of fast radio bursts

Fast radio bursts show large dispersion measures,much larger than the Galactic dispersion measure foreground.Therefore,they evidently have an extragalactic origin.We investigate possible contributions to the dispersion measure from host galaxies.We simulate the spatial distribution of fast radio bursts and calculate the dispersion measures along the sightlines from fast radio bursts to the edge of host galaxies by using the scaled NE2001 model for thermal electron density distributions.We find that contributions to the dispersion measure of fast radio bursts from the host galaxy follow a skew Gaussian distribution.The peak and the width at half maximum of the dispersion measure distribution increase with the inclination angle of a spiral galaxy,to large values when the inclination angle is over 70°.The largest dispersion measure produced by an edge-on spiral galaxy can reach a few thousand pc cm~(-3),while the dispersion measures from dwarf galaxies and elliptical galaxies have a maximum of only a few tens of pc cm~(-3).Notice,however,that additional dispersion measures of tens to hundreds of pc cm~(-3) can be produced by high density clumps in host galaxies.Simulations that include dispersion measure contributions from the Large Magellanic Cloud and the Andromeda Galaxy are shown as examples to demonstrate how to extract the dispersion measure from the intergalactic medium.     

Pulsar Discovery Prospect of FASTA

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) has discovered more than 650 new pulsars,which account for 20% of our known Galactic pulsar population. In this paper, we estimate the prospect of a pulsar survey with a radio telescope array to be planned—the FAST Array(FASTA), consists of six “FAST-type”telescopes. Such a sensitive radio telescope array would be a powerful instrument in probing the pulsar population deep into our Galaxy as well as in nearby galaxies. We simulate t...     

Re-Identification of the ''''Enigmatic'''' X-ray Source 1RXS J114003.0+124112

The ROSAT X-ray source 1RXS J114003.0 124112 was identified as a starburst galaxy at redshift 0.177 by He et al. The authors also noted that the source is almost two orders of magnitude brighter in X-ray than the X-ray-brightest starburst galaxy and it seems to be in a merging system, making this source an enigmatic system demanding further observations. Here we report a re-identification of 1RXS J114003.0 124112 using observations on the 2.6m telescope at Byurakan Astrophysical Observatory, Armenia and the SDSS data. The results indicate that the starburst activity is associated with the brighter object of the system, while the fainter object is a typical Seyfert 1 galaxy at a different redshift (0.282). Therefore, the two objects are not in a merging system, and the Seyfert 1 galaxy naturally accounts for the high X-ray flux. Three more objects reside in the vicinity, but they are all too faint to be responsible for the high X-ray flux.     

Fermi/LAT observations of lobe-dominant radio galaxy 3C 207 and possible radiation region of γ-rays

3 C 207 is a lobe-dominant radio galaxy with a one sided jet and bright knots, spanning a kpcMpc scale, which have been resolved in the radio, optical and X-ray bands. This target was confirmed as a γ-ray emitter with Fermi/LAT, but it is uncertain whether the γ-ray emission region is the core or knots due to the low spatial resolution of Fermi/LAT. We present an analysis of its Fermi/LAT data acquired during the past 9 years. Different from the radio and optical emission from the core, it is found that theγ-ray emission is steady without detection of flux variation at over a 2σ confidence level. This likely implies that the γ-ray emission is from its knots. We collect the radio, optical and X-ray data of knot-A,the closest knot from the core at 1.4′′, and compile its spectral energy distribution(SED). Although the single-zone synchrotron+SSC+IC/CMB model that assumes knot-A is at rest can reproduce the SED in the radio-optical-X-ray band, the predicted γ-ray flux is lower than the LAT observations and the derived magnetic field strength deviates from the equipartition condition by 3 orders of magnitude. Assuming that knot-A is moving relativistically, its SED from radio to γ-ray bands would be represented well with the single-zone synchrotron+SSC+IC/CMB model under the equipartition condition. These results likely suggest that the γ-ray emission may be from knot-A via the IC/CMB process and the knot should have relativistical motion. The jet power derived from our model parameters is also roughly consistent with the kinetic power estimated with radio data.     

Low-mass and high-mass supermassive black holes in radio-loud AGNs are spun-up in different evolution paths

How supermassive black holes(SMBHs) are spun-up is a key issue in modern astrophysics. As an extension to the study in Wang et al., here we address the issue by comparing the host galaxy properties of nearby(z 0.05) radio-selected Seyfert 2 galaxies. With the two-dimensional bulge+disk decompositions for the SDSS r-band images, we identify a dichotomy in various host galaxy properties for radio-loud SMBHs. By assuming that radio emission from the jet reflects a high SMBH spin, which stems from the well-known Blandford-Znajek mechanism of jet production, high-mass SMBHs(i.e., MBH 107.9 M⊙)have a preference for being spun-up in classical bulges, and low-mass SMBHs(i.e., MBH = 106-107 M⊙)in pseudo-bulges. This dichotomy suggests and confirms that high-mass and low-mass SMBHs are spun-up in different ways, i.e., a major "dry" merger and a secular evolution respectively.     

Radio Identifications of Markarian Galaxies and the Correlation between Radio and Far-Infrared Properties

By checking DSS optical images and NVSS radio images, 782 Markarian galaxies were identified to be NVSS radio sources. A comparison of the radio luminosity at 1.4 GHz and the far-infrared (FIR) luminosity for 468 "normal" galaxies shows a tight correlation. Most of the Seyfert galaxies and quasars follow the radio-FIR relation deduced from the "normal" galaxy sample, but with a somewhat larger scatter. A total 167 Markarian galaxies, comprising 100 "normal" galaxies, 66 Seyfert galaxies and one quasar, have either excess radio emission or much lower FIR spectral index α(25μm,60μm). These galaxies may be classified as "AGN-powered". For "normal" galaxies, the average q value (defined as the log ratio between FIR and radio luminosities) is 2.3. There seems a trend for q to slightly decrease with increasing radio luminosity. This may imply that the ongoing active star formation in galaxies with higher radio luminosities is more efficient in heating the cosmic-ray electrons.     

Integrated HI emission in galaxy groups and clusters

The integrated HI emission from hierarchical structures such as groups and clusters of galaxies can be detected by FAST at intermediate redshifts. Here we propose to use FAST to study the evolution of the global HI content of clusters and groups over cosmic time by measuring their integrated HI emissions. We use the Virgo Cluster as an example to estimate the detection limit of FAST, and have estimated the integration time to detect a Virgo type cluster at different redshifts(from z = 0.1 to z = 1.5). We have also employed a semi-analytic model(SAM) to simulate the evolution of HI contents in galaxy clusters. Our simulations suggest that the HI mass of a Virgo-like cluster could be 2–3 times higher and the physical size could be more than 50% smaller when redshift increases from z = 0.3 to z = 1. Thus the integration time could be reduced significantly and gas rich clusters at intermediate redshifts can be detected by FAST in less than 2 hours of integration time. For the local Universe, we have also used SAM simulations to create mock catalogs of clusters to predict the outcomes from FAST all sky surveys. Comparing with the optically selected catalogs derived by cross matching the galaxy catalogs from the SDSS survey and the ALFALFA survey, we find that the HI mass distribution of the mock catalog with 20 s of integration time agrees well with that of observations. However, the mock catalog with 120 s of integration time predicts many more groups and clusters that contain a population of low mass HI galaxies not detected by the ALFALFA survey. A future deep HI blind sky survey with FAST would be able to test such prediction and set constraints on the numerical simulation models. The observational strategy and sample selections for future FAST observations of galaxy clusters at high redshifts are also discussed.     

A Peculiar Broad Line Radio Galaxy 1938-155： VLA Observation at 90 cm

We observed 1938-155, a broad line radio galaxy (BLRG), with the Very Large Array (VLA) at 90cm with an angular resolution of 6.8" × 4.0". The source consists of two components separated by 4 arcsec (- 20kpc, for H0 = 65km s-1 Mpc-1, q0 = 0.5) along the SE-NW direction. Both components show steep-spectra with a similar spectral index α - 0.83 ± 0.07 (Sv ∝ v-α). The bright double components are surrounded by a low-brightness cocoon. The radio properties of the two bright components are consistent with the hot spots produced by twin jets. An upper limit of - 0.0008 for the core dominance parameter (R) is inferred, suggesting there is no prominent radio core in the source. Assuming a modest viewing angle 30f77, a jet velocity is estimated - 0.07 c, based on the jet to counter-jet brightness ratio (J). The lower limit in jet speed inferred is consistent with no Doppler beaming effect on the jet. The radio galaxy 1938-155 could be an exceptional BLRG with no prominent radio core or jet.     

Stellar Population Analysis of Galaxies based on Genetic Algorithms

We present a new method for determining the age and relative contribution of different stellar populations in galaxies based on the genetic algorithm. We apply this method to the barred spiral galaxy NGC 3384, using CCD images in U, B, V, R and I bands. This analysis indicates that the galaxy NGC 3384 is mainly inhabited by old stellar population (age >109yr). Some problems were encountered when numerical simulations are used for determining the contribution of different stellar populations in the integrated color of a galaxy. The results show that the proposed genetic algorithm can search efficiently through the very large space of the possible ages.     

Manifestations of bright points observed in G-band and Ca Ⅱ H by Hinode/SOT

An algorithm was developed for identifying and tracking a magnetic bright point, or bright point(BP) for short, observed in both the photosphere(G-band) and chromosphere(Ca Ⅱ H), as well as for pairing a photospheric BP(PBP) with its conjugate chromospheric BP(CBP). Two sets of data observed by Hinode/SOT in the quiet Sun near the disk center were analyzed. About 278 PBP-CBP pairs were identified and tracked. Lifetimes of both the PBPs and CBPs follow an exponential distribution with average lifetimes of 174 s and 163 s, respectively. We found that the differences in appearance time,in disappearance time and in lifetime of the two kinds of BPs all follow Gaussian distributions,which may indicate that the mechanisms of PBP and CBP formation/disintegration are different. However, the lifetimes of PBPs and CBPs are positively correlated with one another, with a correlation coefficient of 0.8. Furthermore, we calculated the horizontal displacement between the PBP and its conjugate CBP,which follows a Gaussian function with an average and standard deviation of(67.7 ± 38.5) km. We also calculated the amplitude of the flux tube shape change which might be caused by MHD waves propagating along the flux tube, and found that it follows an exponential distribution very well.     

A Multiwavelength Study of the Jets in FR-I Radio Galaxies： I. Data and Analysis

We compile a sample of 11 Fanaroff-Riley type I Radio Galaxies(FR-I RGs)with multi-wavelength observations to address the dynamic behavior of jets in these objects.Optical images acquired by the Hubble Space Telescope(HST)are carefully analyzed.The method and reduction procedure are described in detail. Unresolved optical cores emerge after having properly removed starlight from the host galaxies in eight of the FR-I RGs,of which five are new identifications.Broad band spectral properties of these newly identified compact cores are compared with that previously found in FR-I RGs,as well as the low-energy-peaked BL Lac objects. The similarity between them argues for the same non-thermal synchrotron origin. Well-resolved optical jets with knotty morphologies are found in three FR-I RGs in our sample,namely 3C 15,3C 66B and B20755 37.The optical counterparts to the inner radio/X-ray jets are identified and a clear one-to-one correspondence between the optical,radio and X-ray knots is found.The structure and information on the optical jets are discussed.Physical parameters such as the knots position,flux and size are also presented.Detailed comparison between the multi-wavelength data and radiative and dynamic models of jet will be made in a forthcoming paper.     

Analyzing the capability of a radio telescope in a bistatic space debris observation system

A bistatic space debris observation system using a radio telescope as the receiving part is introduced. The detection capability of the system at different working frequencies is analyzed based on real instruments. The detection range of targets with a fixed radar cross section and the detection ability of small space debris at a fixed range are discussed. The simulations of this particular observation system at different transmitting powers are also implemented and the detection capability is discussed. The simulated results approximately match the actual experiments. The analysis in this paper provides a theoretical basis for developing a space debris observation system that can be built in China.     

Test area of the SAGE survey

Sky surveys represent one of the most important efforts to improve developments in astrophysics,especially when using new photometric bands. We are performing the Stellar Abundance and Galactic Evolution(SAGE) survey with a self-designed SAGE photometric system, which is composed of eight photometric bands. The project mainly aims to study the stellar atmospheric parameters of ～0.5 billion stars in ～12 000 deg2 of the northern sky, which mainly focuses on Galactic astronomy, as well as some aspects of extragalactic astronomy. This work introduces the detailed data reduction process of the test field NGC 6791, including the data reduction of single-exposure images and stacked multi-exposure images, and properties of the final catalog.     

Seven-frequency VLBI Observations of the GHz-Peaked-Spectrum Source OQ 208

We present quasi-simultaneous VLBI images of the GHz-Peaked-Spectrum radio source OQ 208 obtained with the Very Long Baseline Array at 1.4,1.7,2.3,5.0,8.4,15.4GHz and the European VLBI Network at 6.7 GHz.The low frequency(1.4,1.7 and 2.3GHz)ob- servations reveal a weak and extended steep-spectrum component at about 30mas away at position angle-110°,which may be a remnant emission.The radio structure of OQ 208 con- sists of two mini-lobes at 5.0,6.7,8.4 and 15.4 GHz.Our spectral analysis further confirms that the southwest lobe undergoes free-free absorption and finds that the free-free absorption is stronger in the inner region.By fitting the 8.4 GHz images from 1994 to 2005,we obtain a separation speed of 0.031±0.006 mas yr~(-1)between the two mini-lobes.This indicates a jet proper motion of 0.105±0.020 c and a kinematic age of 219±42 yr for the radio source.     

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_* 10~(11) M_⊙).Different from previous works,we focus on the ones just formed(e.g.just reach?10~(11) 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 M_(SMBH) 10~(7.5) 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.     

The Feasibility of Constraining Dark Energy Using LAMOST Redshift Survey

We consider using future redshift surveys with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) to constrain the equation of state of dark energy ω. We analyze the Alcock & Paczyriski (AP) effect imprinted on the two-point correlation function of galaxies in redshift space. The Fisher matrix analysis is applied to estimate the expected error bounds of ω0 and ωa from galaxy redshift surveys, ω0 and ωa being the two parameters in the equation of state parametrization ω(z) = ω0 + ωaz/(1 + z). Strong degeneracies between ω0 and ωa are found. The direction of the degeneracy in ω0 - ωa plane, however, rotates counter-clockwise as the redshift increases. LAMOST can potentially contribute in the redshift range up to 0.5. In combination with other high redshift surveys, such as the proposed Kilo-Aperture Optical Spectrograph project (KAOS), the joint constraint derived from galaxy surveys at different redshift ranges is likely to efficiently break the degeneracy of ω0 and ωa. We do not anticipate that the nature of dark energy can be well constrained with LAMOST alone, but it may help to reduce the error bounds expected from other observations, such as the Supernova/Acceleration Probe (SNAP).     

Foreground removal of 21 cm fluctuation with multifrequency fitting

The 21 centimeter （21 cm） line emission from neutral hydrogen in the intergalactic medium （IGM） at high redshifts is strongly contaminated by foreground sources such as the diffuse Galactic synchrotron emission and free-free emission from the Galaxy, as well as emission from extragalactic radio sources, thus making its observation very complicated. However, the 21 cm signal can be recovered through its structure in frequency space, as the power spectrum of the foreground contamination is expected to be smooth over a wide band in frequency space while the 21 cm fluctuations vary significantly. We use a simple polynomial fitting to reconstruct the 21 cm signal around four frequencies 50, 100, 150 and 200 MHz with an especially small channel width of 20 kHz. Our calculations show that this multifrequency fitting approach can effectively recover the 21 cm signal in the frequency range 100 - 200 MHz. However, this method doesn＇t work well around 50 MHz because of the low intensity of the 21 cm signal at this frequency. We also show that the fluctuation of detector noise can be suppressed to a very low level by taking long integration times, which means that we can reach a sensitivity of ≈ 10 mK at 150 MHz with 40 antennas in 120 hours of observations.     

Estimation of Solar Observations with the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)

We present the estimation of solar observation with the Five-hundred-meter Aperture Spherical radio Telescope(FAST). For both the quiet Sun and the Sun with radio bursts, when pointing directly to the Sun, the total power received by FAST would be out of the safe operational range of the signal chain, even resulting in damage to the receiver. As a conclusion, the Sun should be kept at least ～2° away from the main beam during observations at～1.25 GHz. The separation for lower frequency should be ...     

A multiwavelength view of the ISM in the merger remnant galaxy Fornax A

We present multi-wavelength imagery of the merger remnant galaxy NGC 1316 with an objective to study the dust content and its association with the other phases of the interstellar medium. Color-index maps as well as extinction maps derived for this galaxy reveal an intricate and complex dust morphology in NGC 1316, i.e. there is a prominent lane in the inner part, while at about 6-7 kpc it apparently takes the form of an arc-like pattern extending along the northeast direction. In addition to this, several other dust clumps and knots are also evident in this galaxy. The dust emission mapped using Spitzer data at 8 μm indicates even more complex morphological structures of the dust in NGC 1316. The extinction curve derived over the optical to near-IR bands closely follows the standard Galactic curve, suggesting similar properties of the dust grains. The dust content of NGC 1316, estimated from optical extinction, is ～ 2.13 105M⊙ . This is a lower limit compared to that estimated using the IRAS flux densities of ～5.17×106M⊙ and the flux densities at 24, 70 and 160 μm from MIPS ～3.2×107M⊙ . High resolution Chandra observations of this merger remnant system have provided an unprecedented view of the complex nature exhibited by the distribution of hot gas in NGC 1316, which closely matches the morphology of ionized gas and to some extent also the dust. X-ray color-color plots for the resolved sources within the optical D 25 extent of NGC 1316 have enabled us to separate them into different classes.