Based on the Sloan Digital Sky Survey DR6 （SDSS） and the ＇Millennium Simulation （MS）, we investigate the alignment between galaxies and large-scale structure. For this purpose, we develop two new statistical tools, namely the alignment correlation function and the cos（20）-statistic. The former is a two-dimensional extension of the traditional two-point correlation function and the latter is related to the ellipticity correlation function used for cosmic shear measurements. Both are based on the cross correlation between a sample of galaxies with orientations and a reference sample which represents the large-scale structure. We apply the new statistics to the SDSS galaxy catalog. The alignment correlation function reveals an overabundance of reference galaxies along the major axes of red, luminous （L 〉 ～L＊） galaxies out to projected separations of 60 h-lMpc. The signal increases with central galaxy luminosity. No alignment signal is detected for blue galaxies. The cos（2θ）-statistic yields very similar results. Starting from a MS semi-analytic galaxy catalog, we assign an orientation to each red, luminous and central galaxy, based on that of the central region of the host halo （with size similar to that of the stellar galaxy）. As an alternative, we use the orientation of the host halo itself. We find a mean projected misalignment between a halo and its central region of -25°. The misalignment decreases slightly with increasing luminosity of the central galaxy. Using the orientations and luminosities of the semi-analytic galaxies, we repeat our alignment analysis on mock surveys of the MS. Agreement with the SDSS results is good if the central orientations are used. Predictions using the halo orientations as proxies for cen- tral galaxy orientations overestimate the observed alignment by more than a factor of 2. Finally, the large volume of the MS allows us to generate a two-dimensional map of the alignment correlation function, which shows the reference galaxy distribution to be fl
A. FaltenbacherCheng LiSimon D. M. WhiteYi-Peng JingShu-De MaoJie Wang
From the literature, we construct a sample of 25 Seyfert 2 galaxies （S2s）with a broad line region （BLR） detected in near infrared （NIR） spectroscopy and 29with NIR BLRs which were not detected. We find no significant difference betweenthe nuclei luminosity （extinction-corrected [OIII] 5007） and infrared color f 60/f25between the two populations, suggesting that the non-detections of NIR BLRs couldnot be due to low AGN luminosity or contamination from the host galaxy. As ex-pected, we find significantly lower X-ray obscurations in Seyfert 2s with NIR BLRdetection, supporting the unification scheme. However, such a scheme was challengedby the detection of NIR BLRs in heavily X-ray obscured sources, especially in sixof them with Compton-thick X-ray obscuration. The discrepancy could be solved bythe clumpy torus model and we propose a toy model demonstrating that IR-thin X-ray-thick S2s could be viewed at intermediate inclinations and compared with thoseIR-thick X-ray-thick S2s. We note that two of the IR-thin X-ray-thick S2s （NGC 1386and NGC 7674） experienced X-ray transitions, i.e. from Compton-thin to Compton-thick appearance or vice versa based on previous X-ray observations, suggesting thatX-ray transitions could be common in this special class of objects.
Hong-Bing CaiXin-Wen ShuZhen-Ya ZhengJun-Xian Wang
