The Cosmic Evolution Survey (COSMOS) is an astronomical survey designed to probe the formation and evolution of galaxies as a function of both cosmic time (redshift) and the local galaxy environment. The survey covers a 2 square degree equatorial field with imaging by most of the major space-based telescopes and a number of large ground based telescopes, with many ongoing surveys. Over 2 million galaxies are detected, spanning 75% of the age of the Universe. The COSMOS survey involves more than 100 scientists in a dozen countries.
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This new study uses the COSMOS survey to measure the local environment (density) around galaxies at z < 3 and connects it to their star formation rates. The study suggests that the shutdown of star formation due to galaxies falling into dense environment (e.g., causing stripping and heating of gas) is dominant at z < 1. At higher redshifts, quenching of star formation is likely triggered by galaxy internal processes (feedback, etc).
The paper is accepted and ready to be checked out: http://arxiv.org/abs/
Image: An example of a jellyfish galaxy where 'tentacles' of gas are being stripped off the host galaxy due to its interaction with the hot gas in the cluster environment
A new paper by COSMOS member Andreas Faisst and team shows how to use Spitzer colors to derive emission line properties of 3 < z < 6 galaxies. Optical emission lines at z > 4 cannot be measured spectroscopically with current facilities. Since emission lines "contaminate" the Spitzer 3.6um and 4.5um channels, these can be used to estimate optical line emission without the need of spectra. The study of emission lines provides important information about galaxy formation in the early universe and also provides a sample of galaxies for future JWST follow-up. The ApJ paper is in print and can be retrieved here: http://stacks.iop.org/0004-637X/821/122
The COSMOS2015 catalogue combines the >30 band photometry and SED fits (photometric redshifts, stellar masses, SFRs, etc) of half a million sources up to z=6 spread over the 2 square-degrees of COSMOS.
In particular, it uses the new UltraVISTA images, as well as the Spitzer SPLASH photometry!
The paper by Laigle et al. (2016) explaining the catalog can be found on the arXiv now: http://arxiv.org/abs/1604.02350
The catalog can be downloaded via anonymous FTP.
Image: A comparison of spectroscopic and photometric redshifts of COSMOS2015 galaxies. The dashed and dashed-dot lines show zp=zs±0.05(1+zs) and zp=zs±0.15(1+zs), respectively. From Laigle et al (2016) Figure 12.