Galaxy evolution in different environments within redshift z ∼ 0.8 universe

Abstract

This research aims to study the galaxy evolution within the local Universe at redshift below z ~ 0.8 and the evolution of galaxies at different areas which have different matter density. By using a sample of 702,352 galaxies that was collected from the Sloan Digital Sky Survey (SDSS) Data Release 15 (DR15). The interested sky areas are two areas, which have centered Right Ascension (RA) at 10h00m00s and 14h00m00s. Both RAs cover in -0.5˚ to 23.5˚ Declination range. To study the evolution of galaxies, the number density of galaxy, the evolution in galaxy's colors, and star formation activities are examined to be main parameters in both areas. Under the limitation of the spectroscopic data, the appropriate photometric redshift was used to represent the spectroscopic redshift in the range of 0.0 ≤ z ≤ 0.8. In summary, the number density is not clearly different, although the Declination and RA of the sky areas are disparate. However, the number density still steeply declines along the redshift direction. Considering the number density together with galaxies' Hα emission line from spectroscopic data, we find that both EW(Hα) and Hα flux similarly tend to decrease like the number density trends. Furthermore, the galaxies' color trend is found to be redder as a function of the redshift in the magnitude bin from -19 ≤ Mg ≤ -17. It implies that the overview of the star formation activity of the fainter galaxies at the lower redshift tend to show higher than the ones at higher redshift.