Linking galaxies to dark matter haloes at $zsim1$ : dependence of galaxy clustering on stellar mass and specific star formation rate

We study the dependence of angular two-point correlation functions on stellar mass ($M_{*}$) and specific star formation rate (sSFR) of $M_{*}>10^{10}M_{odot}$ galaxies at $zsim1$. The data from UKIDSS DXS and CFHTLS covering 8.2 deg$^{2}$ sample scales larger than 100 $h^{-1}$Mpc at $zsim1$, allowing us to investigate the correlation between clustering, $M_{*}$, and star formation through halo modeling. Based on halo occupation distributions (HODs) of $M_{*}$ threshold samples, we derive HODs for $M_{*}$ binned galaxies, and then calculate the $M_{*}/M_{rm halo}$ ratio. The ratio for central galaxies shows a peak at $M_{rm halo}sim10^{12}h^{-1}M_{odot}$, and satellites predominantly contribute to the total stellar mass in cluster environments with $M_{*}/M_{rm halo}$ values of 0.01--0.02. Using star-forming galaxies split by sSFR, we find that main sequence galaxies ($rm log,sSFR/yr^{-1}sim-9$) are mainly central galaxies in $sim10^{12.5} h^{-1}M_{odot}$ haloes with the lowest clustering amplitude, while lower sSFR galaxies consist of a mixture of both central and satellite galaxies where those with the lowest $M_{*}$ are predominantly satellites influenced by their environment. Considering the lowest $M_{rm halo}$ samples in each $M_{*}$ bin, massive central galaxies reside in more massive haloes with lower sSFRs than low mass ones, indicating star-forming central galaxies evolve from a low $M_{*}$--high sSFR to a high $M_{*}$--low sSFR regime. We also find that the most rapidly star-forming galaxies ($rm log,sSFR/yr^{-1}>-8.5$) are in more massive haloes than main sequence ones, possibly implying galaxy mergers in dense environments are driving the active star formation. These results support the conclusion that the majority of star-forming galaxies follow secular evolution through the sustained but decreasing formation of stars.

Clustering of Extremely Red Objects in Elais-N1 from the UKIDSS DXS with optical photometry from Pan-STARRS1 and Subaru

We measure the angular clustering of 33 415 extremely red objects (EROs) in the Elais-N1 field covering 5.33 deg$^{2}$, which cover the redshift range $z=0.8$ to $2$. This sample was made by merging the UKIDSS Deep eXtragalactic Survey (DXS) with the optical Subaru and Pan-STARRS PS1 datasets. We confirm the existence of a clear break in the angular correlation function at $sim 0.02^{circ}$ corresponding to $1 h^{-1}$ Mpc at $zsim1$. We find that redder or brighter EROs are more clustered than bluer or fainter ones. Halo Occupation Distribution (HOD) model fits imply that the average mass of dark matter haloes which host EROs is over $10^{13} h^{-1} M_{odot}$ and that EROs have a bias ranging from 2.7 to 3.5. Compared to EROs at $zsim1.1$, at $zsim1.5$ EROs have a higher bias and fewer are expected to be satellite galaxies. Furthermore, EROs reside in similar dark matter haloes to those that host $10^{11.0} M_{odot}<M_{*}<10^{11.5} M_{odot}$ galaxies. We compare our new measurement and HOD fits with the predictions of the GALFORM semi-analytical galaxy formation model. Overall, the clustering predicted by GALFORM gives an encouraging match to our results. However, compared to our deductions from the measurements, GALFORM puts EROs into lower mass haloes and predicts that a larger fraction of EROs are satellite galaxies. This suggests that the treatment of gas cooling may need to be revised in the model. Our analysis illustrates the potential of clustering analyses to provide observational constraints on theoretical models of galaxy formation.

A wide-field photometric survey for extratidal tails around five metal-poor globular clusters in the Galactic halo

Wide-field deep gri images obtained with the Megacam of the Canada-France-Hawaii Telescope (CFHT) are used to investigate the spatial configuration of stars around five metal-poor globular cluster M15, M30, M53, NGC 5053, and NGC 5466, in a field-of-view ~3 degree. Applying a mask filtering algorithm to the color-magnitude diagrams of the observed stars, we sorted clusters member star candidates that are used to examine the characteristics of the spatial stellar distribution surrounding the target clusters. The smoothed surface density maps and the overlaid isodensity contours indicate that all of the five metal-poor globular clusters exhibit strong evidence of extratidal overdensity features over their tidal radii, in the form of extended tidal tails around the clusters. The orientations of the observed extratidal features show signatures of tidal tails tracing the clusters orbits, inferred from their proper motions, and effects of dynamical interactions with the Galaxy. Our findings include detections of a tidal bridge-like feature and an envelope structure around the pair of globular clusters M53 and NGC 5053. The observed radial surface density profiles of target clusters have a deviation from theoretical King models, for which the profiles show a break at 0.5~0.7r_t, extending the overdensity features out to 1.5~2r_t. Both radial surface density profiles for different angular sections and azimuthal number density profiles confirm the overdensity features of tidal tails around the five metal-poor globular clusters. Our results add further observational evidence that the observed metal-poor halo globular clusters originate from an accreted satellite system, indicative of the merging scenario of the formation of the Galactic halo.