The Holmberg Effect Of Galaxy Pairs In SDSS

The statistical study of pair of galaxies is an important means to explore the interaction and merger process of galaxies.It has been more than 80 years since Holmberg(1937)started to study galaxy pairs.More than 60 years ago,Holmberg(1958)discovered that the colors of paired galaxies are closely correlated.This result has been interpreted as reflecting a tendency for similar types of galaxies to form and evolve together.Late studies tended to confirm this result.So far,in the statistical study of galaxy pairs,the largest sample of low redshift galaxy pairs was identified from the main galaxy sample(MGS)of the Sloan Digital Sky Survey(SDSS).Although the spectroscopic completeness of the MGS is very high(about 90%),the completeness of the galaxy pairs identified from the spectroscopic MGS is only about 35 percent due to the “fiber collision” effect.Based on the work of Allam et al.(2004)and Tang Chao(2013),We obtained 8311 pairs of merging galaxies from the SDSS DR15 database,of which 3560 galaxies have redshifts.In order to increase the redshifts observation of the sample,we obtained the redshifts of 53 galaxies from LAMOST DR5.Among the 3613 galaxies with known spectroscopic redshift,there are 455 galaxy pairs with both member galaxies having redshift,which are the main sample used to study the Holmberg effect of paired galaxies in this paper.In addition,according to the distribution of concentration index,luminosity and redshift of the galaxy pair sample,the control galaxy sample was constructed by randomly selecting 1000 control galaxies from SDSS DR15 database for each merging galaxy.Based on these data,we compared the color index correlation between the merging galaxy pair sample and the control galaxy sample,verified the existence of the Holmberg effect,compared the correlation difference between model color and fiber color,and explored the influence of galaxy morphology type and separation between two components of pairs on the Holmberg effect.The main conclusions of this paper are as follows:Firstly,compared with the control galaxy sample,the color indices between the two components of paired galaxies clearly have significantly larger correlation coefficients,which further confirms the Holmberg effect.The correlation coefficients of fiber color are larger than that of model color,indicating that star formation triggered by intergalactic interactions tends to be centrally concentrated.Secondly,the Holmberg effect is influenced by morphological types of galaxy.We found that Late+Late pairs clearly have statistical correlation coefficients between the two components of pairs,while Early+Early pairs,Early+Late pairs and Late+Early pairs do not exhibit statistically significant Holmberg effect.This indicates that the Holmberg effect of paired galaxies not only depends on the color indices but also on the morphological type for two components of pairs.Finally,the separation between member galaxies has an impact on the Holmberg effect.Comparing the color indices correlation of subsamples of paired galaxies with different separations,we found that the smaller the separation of member galaxies in the subsample,the stronger the correlation is.The closer the member galaxies are,the more intense the star formation activity caused by the interaction well be.