Qirong Yuan

Full Calculation of Clumpiness Boost factors for Antimatter Cosmic Rays in the light of Lambda-CDM N-body simulation results. Abandoning hope in clumpiness enhancement?

Anti-proton and positron Galactic cosmic ray spectra are among the key targets for indirect detection of dark matter. The boost factors, corresponding to an enhancement of the signal and linked to the clumpiness properties of the dark matter distribution, have been taken as high as thousands in the past. The dramatic impact of these boost factors for indirect detection of antiparticles, for instance with the PAMELA satellite or the coming AMS-02 experiment, asks for their detailed calculation. We take into account the results of high resolution N-body dark matter simulations to calculate the most likely energy dependent boost factors linked to the cosmic ray propagation properties, for anti-protons and positrons. Starting from the mass and space distributions of sub-halos, the anti-proton and positron propagators are used to calculate the mean value and the variance of the boost factor for the primary fluxes. We take advantage of the statistical method introduced in Lavalle et al. (2007) and cross-check the results with Monte Carlo computations. By spanning some extreme configurations of sub-halo and propagation properties, we find that the average contribution of the clumps is negligible compared to that of the smooth dark matter component. Sub-halos do not lead to enhancement of the signals, unless they are taken with some extreme (unexpected) properties. This result is independent of the nature of the self-annihilating dark matter candidate considered, and provides precise estimates of the theoretical and the statistical uncertainties of the antimatter flux from dark matter substructures. Spectral distortions can still be expected in antimatter flux measurements, but scenarios invoking large and even mild clumpiness boost factors are strongly disfavoured by our analysis.

The origin and evolution of C iv Baldwin effect in QSOs from the Sloan Digital Sky Survey

Using a large sample of 26 623 quasars with redshifts in the range 1.5 <= z <= 5.1 with C IV lambda 1549 angstrom emission line in Fifth Data Release of the Sloan Digital Sky Survey (SDSS), we investigate the cosmological evolution of the Baldwin effect, i.e. the relation between the equivalent width (EW) of the C IV emission line and continuum luminosity. We confirm the earlier result that there exists a strong correlation between the C IV EW and the continuum luminosity, and we find that, up to z approximate to 5, the slope of the Baldwin effect seems to have no effect of cosmological evolution. A subsample of 13 960 quasars with broad C IV lambda 1549 angstrom emission line from SDSS is used to explore the origin of the Baldwin effect. We find that C IV EW have a strong correlation with the mass of supermassive black hole (SMBH), and a weak correlation with the Eddington ratio, L(Bol)/L(Edd). This suggests that the SMBH mass is probably the primary drive for the Baldwin effect.

Orientation of spin vectors of bright field disk galaxies in the local supercluster and its implication

Using the database of Photometric Atlas of Northern Bright Galaxies, the spatial orientation of 220 bright isolated held disk galaxies (41 SO, 174 S, and 5 Irr) in the Local Supercluster (LSC) has been analyzed. The sample of field galaxies is constructed by selecting disk galaxies with cz less than or equal to 3000 km s(-1) and excluding all galaxies of the groups or clusters of at least three members. Emphasis is placed on exploring morphological dependence of orientation of field galaxies.

Orientation of galaxies in the local supercluster: A review

The progress of the studies on the orientation of galaxies in the Local Supercluster (LSC) is reviewed and a summary of recent results is given. Following a brief introduction of the LSC, we describe the results of early studies based on two-dimensional analysis, which were mostly not conclusive. We describe next the three-dimensional analysis, which is used widely today. Difficulties and systematic effects are explained and the importance of selection effects is described. Then, results based on the new method and modern databases are given, which are summarized as follows. When the LSC is seen as a whole, galaxy planes tend to align perpendicular to the LSC plane with lenticulars showing the most pronounced tendency. Projections onto the LSC plane of the spin vectors of Virgo cluster member galaxies, and to some extent, those of the total LSC galaxies, tend to point to the Virgo cluster center. This tendency is more pronounced for lenticulars than for spirals. It is suggested that ‘field’ galaxies, i.e., those which do not belong to groups with more than three members, may be better objects than other galaxies to probe the information at the early epoch of the LSC formation through the analysis of galaxy orientations. Field lenticulars show a pronounced anisotropic distribution of spin vectors in the sense that they lay their spin vectors parallel to the LSC plane while field spirals show an isotropic spin-vector distribution.

Seven-year Multi-color Optical Monitoring of BL Lacertae Object S5 0716+714

We have monitored the BL Lacertae object S5 0716+714 in five intermediate optical wavebands from 2004 September to 2011 April. Here, we present data that include 8661 measurements representing one of the largest databases obtained for an object in the optical domain. A simple analysis of the data indicates that the object was active most of the time, and intraday variability was frequently observed. In total, the object varied by 2.614 mag in the i band. Strong bluer-when-brighter chromatism was observed on long, intermediate, and short timescales.

THE VARIABILITY OF OPTICAL Fe II EMISSION IN PG QSO 1700+518

It is found that Fe II emission contributes significantly to the optical and ultraviolet spectra of most active galactic nuclei. The origin of the optical/UV Fe II emission is still open to debate. The variability of Fe II would give clues to this origin. Using 7.5 yr spectroscopic monitoring data of one Palomar-Green (PG) quasi-stellar object (QSO), PG 1700+518, with strong optical Fe II emission, we obtain the light curves of the continuum f λ(5100 A), Fe II, the broad component of Hβ, and the narrow component of Hβ by spectral decomposition. Through the interpolation cross-correlation method, we calculate the time lags for the light curves of Fe II, the total Hβ, the broad component of Hβ, and the narrow component of Hβ with respect to the continuum light curve. We find that the Fe II time lag in PG 1700+518 is 209+100 –147 days, while the Hβ time lag cannot be determined. Assuming that the Fe II and Hβ emission regions follow the virial relation between the time lag and the FWHM for the Hβ and Fe II emission lines, we can derive the Hβ time lag to be 148+72 –104 days. The Hβ time lag calculated from the empirical luminosity-size relation is 222 days, which is consistent with our measured Fe II time lag. Considering the optical Fe II contribution, PG 1700+518 shares the same spectral slope variability characteristic, i.e., harder spectrum during brighter phase, as the other 15 PG QSOs in our previous work.

Orientation of the field galaxies in the local supercluster

In this paper we studied the orientation of the spin vectors (SVs) for 302 field galaxies in the Local Supercluster (LSC). All galaxies in our sample are selected from the Photometric Atlas of Northern Bright Galaxies after an exclusion of the members of the clusters and groups of galaxies with at least five members within the LSC. The SV orientation of these field galaxies is found to be anistropic, which is well shown in chi(2) tests of the azimuthal angle and area distributions. The histograms of the polar angle distribution exhibit a weak tendency that the field galaxies in the LSC preferentially have their SVs parallel to the LSC plane. Comparison with the results for the Virgo cluster members shows that the post-formation epoch dynamics did perturb the galactic SV orientation. This is supported by two facts: (i) There is a significant hump at high polar angle for the Virgo members while no similar hump is found in our sample. (ii) The SV projections on the LSC plane for the field galaxies show their excess direction significantly deviated from the direction pointing towards the Virgo center, unlike the Virgo cluster members

Morphological Dependence of Star Formation Properties for the Galaxies in the Merging Galaxy Cluster A2255

The merging cluster of galaxies A2255 is covered by the Sloan Digital Sky Survey (SDSS) survey. The physical parameters of 184 bright member galaxies derived from the SDSS data analyses by Brinchmann et al. allow a detailed study of the star formation properties of galaxies within a merging cluster at intermediate redshift. In this paper we perform a morphological classification on the basis of the SDSS imaging and spectral data and investigate the morphological dependence of the star formation rates (SFRs) for these member galaxies. As we expect, a tight correlation between the SFR normalized by stellar mass (SFR/M*) and the Hα equivalent width is found for the late-type galaxies in A2255. The correlation of SFR/M* with the continuum break strength at 4000 A is also confirmed. A SFR/M*-M* correlation is found for both early- and late-type galaxies, indicating that the star formation activity tends to be suppressed when the assembled stellar mass (M*) increases, and this correlation is tighter and steeper for the late-type cluster galaxies. Compared with the mass range of field spiral galaxies, only two massive late-type galaxies with M* > 1011 M⊙ have survived in A2255, suggesting that the gas disks of massive spiral galaxies could have been tidally stripped during cluster formation. In addition, the SFR variation with the projected radial distance is found to be heavily dependent on galaxy morphology: the early-type galaxies have a very weak inner decrease in SFR/M*, while the inner late-type galaxies tend to have higher SFR/M* values than the outer late-type galaxies. This may suggest that the galaxy-scale turbulence stimulated by the merging of subclusters might have played different roles in early- and late-type galaxies, which leads to a suppression of the star formation activity for E/S0 galaxies and an SFR enhancement for spiral and irregular galaxies.

Swift Observations of SMC X-3 during Its 2016–2017 Super-Eddington Outburst

The Be X-ray pulsar, SMC X-3 underwent a giant outburst from 2016 August to 2017 March, which was monitored with the Swift satellite. During the outburst, its broadband flux increased dramatically, and the unabsorbed X-ray luminosity reached an extreme value of

A study of the intrinsic flatness of disk galaxies

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