12809239
An Improved Cluster Richness Estimator
Minimizing the scatter between cluster mass and accessible observables is an important goal for cluster cosmology. In this work, we introduce a new matched filter richness estimator, and test its performance using the maxBCG cluster catalog. Our new estimator significantly reduces the variance in the L_X-richness relation, from \sigma_{\ln L_X}^2=(0.86\pm0.02)^2 to \sigma_{\ln L_X}^2=(0.69\pm0.02)^2. Relative to the maxBCG richness estimate, it also removes the strong redshift dependence of the richness scaling relations, and is significantly more robust to photometric and redshift errors. These improvements are largely due to our more sophisticated treatment of galaxy color data. We also demonstrate the scatter in the L_X-richness relation depends on the aperture used to estimate cluster richness, and introduce a novel approach for optimizing said aperture which can be easily generalized to other mass tracers.
121863790
A New Exactly Solvable Inflation Model and Its Power Spectrum
We present a new exactly solvable inflation model in which inflation can stop automatically, and in the approximately de Sitter limit, we give its power spectrum which can be tested in the future observations of cosmic microwave background anisotropy.
88518309
A GMBCG Galaxy Cluster Catalog of 55,424 Rich Clusters from SDSS DR7
We present a large catalog of optically selected galaxy clusters from the application of a new Gaussian Mixture Brightest Cluster Galaxy (GMBCG) algorithm to SDSS Data Release 7 data. The algorithm detects clusters by identifying the red sequence plus Brightest Cluster Galaxy (BCG) feature, which is unique for galaxy clusters and does not exist among field galaxies. Red sequence clustering in color space is detected using an Error Corrected Gaussian Mixture Model. We run GMBCG on 8240 square degrees of photometric data from SDSS DR7 to assemble the largest ever optical galaxy cluster catalog, consisting of over 55,000 rich clusters across the redshift range from 0.1 < z < 0.55. We present Monte Carlo tests of completeness and purity and perform cross-matching with X-ray clusters and with the maxBCG sample at low redshift. These tests indicate high completeness and purity across the full redshift range for clusters with 15 or more members.
119458029
O(N) Quintessence with a Cosine-Type Potential
We propose a quintessence model with a cosine-type potential, in which the scalar field Φa possesses an O(N) internal symmetry. The most prominent feature of this model is that it will not reduce to a cosmological constant even when |Φa| is spatially uniform and time-independent. Since different values of the potential parameter will lead to different cosmic microwave background anisotropies, which may be detectable in future satellite experiments, one can decide by observations whether the cosine-type quintessence consists of one scalar field or many fields with a symmetry constraint.
7857108
Cosmological dynamics of scalar fields with O(N) symmetry
In this paper, we study the cosmological dynamics of scalar fields with O(N) symmetry in general potentials. We compare the phase space of the dynamical systems of the quintessence and phantom and give the conditions for the existence of various attractors as well as their cosmological implications. We also show that the existence of a tracking attractor in O(N) phantom models requires the potential with Γ < 1/2, which makes the model with exponential potential possess no tracking attractor.
198140971
Charged D stars
We describe charged soliton stars with a solid angular deficit (charged boson D stars), and find the approximate solution in the external space. Besides, we discuss the stability of charged D stars and find when the number of bosons is less than certain value, charged D stars are quantum mechanically stable.
118439902
Jets and environment of microquasars
Two relativistic X-ray jets have been detected with the Chandra X-ray observatory from the black hole X-ray transient XTE J1550-564. We report a full analysis of the evolution of the two jets with a gamma-ray burst external shock model. A plausible scenario suggests a cavity outside the central source and the jets first travelled with constant velocity and then are slowed down by the interactions between the jets and the interstellar medium (ISM). The best fitted radius of the cavity is $\sim$0.36 pc on the eastern side and $\sim$0.46 pc on the western side, and the densities also show asymmetry, of $\sim$0.015 cm$^{-3}$ on the east to $\sim$0.21 cm$^{-3}$ on the west. A large scale low density region is also found in another microquasar system, H 1743-322. These results are consistent with previous suggestions that the environment of microquasars should be rather vacuous, compared to the normal Galactic environment. A generic scenario for microquasar jets is proposed, classifying the observed jets into three main categories, with different jet morphologies (and sizes) corresponding to different scales of vacuous environments surrounding them.