Using a large sample of field and group galaxies drawn from the Pan-STARRS1 Medium-Deep Survey, we present the specific star formation rate (SSFR) - stellar mass (M*) relation, as well as the quiescent fraction versus M* relation in different environ
ments. We confirm that the fraction of quiescent galaxies is strongly dependent on environment at a fixed stellar mass, but that the amplitude and the slope of the star-forming sequence is similar between the field and groups: in other words, the SSFR-density relation at a fixed stellar mass is primarily driven by the change in the star-forming and quiescent fractions between different environments rather than a global suppression in the star formation rate for the star-forming population. However, when we restrict our sample to the cluster-scale environments ($M>10^{14}M_{solar}$), we find a global reduction in the SSFR of the star forming sequence of $17%$ at 4$sigma$ confidence as opposed to its field counterpart. After removing the stellar mass dependence of the quiescent fraction seen in field galaxies, the excess in the quiescent fraction due to the environment quenching in groups and clusters is found to increase with stellar mass. We argue that these results are in favor of galaxy mergers to be the primary environment quenching mechanism operating in galaxy groups whereas strangulation is able to reproduce the observed trend in the environment quenching efficiency and stellar mass relation seen in clusters. Our results also suggest that the relative importance between mass quenching and environment quenching depends on stellar mass -- the mass quenching plays a dominant role in producing quiescent galaxies for more massive galaxies, while less massive galaxies are quenched mostly through the environmental effect, with the transition mass around $1-2times10^{10}M_{solar}$ in the group/cluster environment. (abridged)
In order to understand the interactions between active galactic nuclei (AGN) and star formation during the evolution of galaxies, we investigate 142 galaxies detected in both X-ray and 70{mu}m observations in the COSMOS (Cosmic Evolution Survey) fiel
d. All of our data are obtained from the archive, X-ray point source catalogs from Chandra and XMM-Newton observations; far-infrared 70{mu}m point source catalog from Spitzer-MIPS observations. Although the IRAC [3.6{mu}m]-[4.5{mu}m] vs. [5.8{mu}m]-[8.0{mu}m] colours of our sample indicate that only ~63% of our sources would be classified as AGN, the ratio of the rest-frame 2-10 keV luminosity to the total infrared luminosity (8-1000{mu}m) shows that all of the sample has comparatively higher X-ray luminosity than that expected from pure star-forming galaxies, suggesting the presence of an AGN in all of our sources. From the analysis of the X-ray hardness ratio, we find that sources with both 70{mu}m and X-ray detection tend to have a higher hardness ratio relative to the whole X-ray selected source population, suggesting the presence of more X-ray absorption in the 70{mu}m detected sources. In addition, we find that the observed far-infrared colours of 70{mu}m detected sources with and without X-ray emission are similar, suggesting the far-infrared emission could be mainly powered by star formation.
Astronomy is entering in a new era of Extreme Intensive Data Computation and we have identified three major issues the new generation of projects have to face: Resource optimization, Heterogeneous Software Ecosystem and Data Transfer. We propose in t
his article a middleware solution offering a very modular and maintainable system for data analysis. As computations must be designed and described by specialists in astronomy, we aim at defining a friendly specific programming language to enable coding of astrophysical problems abstracted from any computer science specific issues. This way we expect substantial benefits in computing capabilities in data analysis. As a first development using our solution, we propose a cross-matching service for the Taiwan Extragalactic Astronomical Data Center.
Founded in 2010, the Taiwan Extragalactic Astronomical Data Center (TWEA-DC) has for goal to propose access to large amount of data for the Taiwanese and International community, focusing its efforts on Extragalactic science. In continuation with ind
ividual efforts in Taiwan over the past few years, this is the first steppingstone towards the building of a National Virtual Observatory. Taking advantage of our own fast indexing algorithm (BLINK), based on a octahedral meshing of the sky coupled with a very fast kd-tree and a clever parallelization amongst available resources, TWEA-DC will propose from spring 2013 a service of on-the-fly matching facility, between on-site and user-based catalogs. We will also offer access to public and private raw and reducible data available to the Taiwanese community. Finally, we are developing high-end on-line analysis tools, such as an automated photometric redshifts and SED fitting code (APz), and an automated groups and clusters finder (APFoF).
