Mining Circumgalactic Baryons in the Low-Redshift Universe

(Abridged) This paper presents an absorption-line study of the multiphase circumgalactic medium (CGM) based on observations of Lya, CII, CIV, SiII, SiIII, and SiIV absorption transitions in the vicinities of 195 galaxies at redshift z<0.176. The galaxy sample is established based on a cross-comparison between public galaxy and QSO survey data and is characterized by a median redshift of =0.041, a median projected distance of =362 kpc to the sightline of the background QSO, and a median stellar mass of log(M_star/M_sun) = 9.7 \pm 1.1. Comparing the absorber features identified in the QSO apectra with known galaxy properties has led to strong constraints for the CGM absorption properties at z<~0.176. First, abundant hydrogen gas is observed out to d~500 kpc, well beyond the dark matter halo radius Rh of individual galaxies, with a mean covering fraction of ~60%. In contrast, no heavy elements are detected at d>~0.7 Rh from either low-mass dwarfs or high-mass galaxies. The lack of detected heavy elements in low- and high-ionization states suggests that either there exists a chemical enrichment edge at d~0.7 Rh or gaseous clumps giving rise to the observed absorption lines cannot survive at these large distances. Considering all galaxies at d>Rh leads to a strict upper limit for the covering fraction of heavy elements of ~3% (at a 95% confidence level) over d=(1-9) Rh. At d<Rh, differential covering fraction between low- and high-ionization gas is observed, suggesting that the CGM becomes progressively more ionized from d<0.3 Rh to larger distances. Comparing CGM absorption observations at low and high redshifts shows that at a fixed-fraction of Rh the CGM exhibits stronger mean absorption at z=2.2 than at z~0. We discuss possible pseudo-evolution of the CGM as a result of misrepresentation of halo radius.Comment: 25 pages, 13 figures; accepted for publication in MNRA

First R and I Lights and Their Photometric Analyses of GSC 02393-00680

We obtained complete $R$ and $I$ light curves of GSC 02393-00680 in 2008 and analyzed them with the 2003 version of the W-D code. It is shown that GSC 02393-00680 is a W-type shallow contact binary system with a high mass ratio $q=1.600$ and a degree of contact factor $f=5.0$. It will be a good example to check up on the TRO theory. A period investigation based on all available data suggests that the system has a small-amplitude period oscillation ($A_3=0.^{d}0030$; $T_3=1.92$years). This may indicate it has a moderate mass close third body, which is similar to XY Leo

Semiparametric GEE analysis in partially linear single-index models for longitudinal data

In this article, we study a partially linear single-index model for longitudinal data under a general framework which includes both the sparse and dense longitudinal data cases. A semiparametric estimation method based on a combination of the local linear smoothing and generalized estimation equations (GEE) is introduced to estimate the two parameter vectors as well as the unknown link function. Under some mild conditions, we derive the asymptotic properties of the proposed parametric and nonparametric estimators in different scenarios, from which we find that the convergence rates and asymptotic variances of the proposed estimators for sparse longitudinal data would be substantially different from those for dense longitudinal data. We also discuss the estimation of the covariance (or weight) matrices involved in the semiparametric GEE method. Furthermore, we provide some numerical studies including Monte Carlo simulation and an empirical application to illustrate our methodology and theory.Comment: Published at http://dx.doi.org/10.1214/15-AOS1320 in the Annals of Statistics (http://www.imstat.org/aos/) by the Institute of Mathematical Statistics (http://www.imstat.org