전천후 측광 관측 데이터에서 별과 은하를 어떻게 구별할 것인가? (star-galaxy separation)
2017-08-25- Speaker : Minji Oh
- Date : 2017-08-23 14:30 ~ 15:30
- Place : L220
- Professor : Yong-Seon Song
star-galaxy separation은 전천후 측광 관측 데이터에서 좋은 galaxy (또는 star, quasar 등) catalogue를 만드는데 중요한 이슈이다.
기존에 주로 쓰이던 방법(& 이것의 문제점) 및 최근에 제안된 방법을 소개하고, 몇가지 데이터(SDSS, HSC, DECaLS)에 대해 진행된 star-galaxy separation을 담은 논문들의 일부를 소개한다.
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Star/galay separation - SDSS DR7
The SDSS photometric pipeline performs a morphological star/galaxy separation. The quality of this separation is therefore intimately related to the seeing and sky brightness. Photo's classifications have been tested against those of the COMBO survey (which effectively uses low-resolution spectroscopy for star/galaxy separation) in a region of the sky that both surveys have scanned. While the comparison was carried out for DR1 data, the DR2/DR3 data are not significantly different.
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How to separate stars from galaxies
The classificaiton_extendedness? parameter, which is based on the difference between the CModel and PSF magnitudes, is stored in the database and is a reasonable star/galaxy classifier. Using the star/galaxy separation from HST/ACS in COSMOS as the truth table, here we characterize the accuracy of our star/galaxy separation. The completeness is defined as a fraction of ACS stars properly classified as stars in HSC. The contamination is a fraction of ACS galaxies among objects classified as stars in HSC. Both the completeness and contamination rates are strong function of the seeing size and depth.
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First Data Release of the Hyper Suprime-Cam Subaru Strategic Program
The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a three-layered imaging survey aimed at addressing some of the most outstanding questions in astronomy today, including the nature of dark matter and dark energy. The survey has been awarded 300 nights of observing time at the Subaru Telescope and it started in March 2014. This paper presents the first public data release of HSC-SSP. This release includes data taken in the first 1.7 years of observations (61.5 nights) and each of the Wide, Deep, and UltraDeep layers covers about 108, 26, and 4 square degrees down to depths of i~26.4, ~26.5, and ~27.0 mag, respectively (5sigma for point sources). All the layers are observed in five broad bands (grizy), and the Deep and UltraDeep layers are observed in narrow bands as well. We achieve an impressive image quality of 0.6 arcsec in the i-band in the Wide layer. We show that we achieve 1-2 per cent PSF photometry (rms) both internally and externally (against Pan-STARRS1), and ~10 mas and 40 mas internal and external astrometric accuracy, respectively. Both the calibrated images and catalogs are made available to the community through dedicated user interfaces and database servers. In addition to the pipeline products, we also provide value-added products such as photometric redshifts and a collection of public spectroscopic redshifts. Detailed descriptions of all the data can be found online.