Multicolor Photometry Of The Merged Galaxy Cluster A401/A399

It is well known that galaxy clusters are the largest gravitationally bound systems in the universe.The history of cluster formation and evolution may provide vital clues about large-scale structure formation.Abell 401 and Abell 399(A401 and A399,hereafter)have been appreciated as a merging pair of clusters,and they are approaching to each other.The projected separation between two central eD galaxies is about 3 Mpc.The observations in optical,X-ray.and radio bands suggest an undergoing interaction in the intermediate region between these two clusters.Further investigating these galaxy clusters not only may provide some useful information for understanding the formation and evolution of galaxies in dense environments,but also could learn more about the influence on star formation activities in galaxies triggered by the cluster merger.In this thesis,wo take use of the photometric data obtained from the BATC(Beijing-Arizona-Taiwan-Connectieut)multi-color survey and the South galactic Cap U-band Sky Survey(SCUSS),and achieve a deep(h ? 20m.0)sample of member galaxies based on the photometric redshift technique,which includes 211 galaxies with known spectroscopic redshifts and 546 new-selected faint member galaxies.Then,luminosity function(LF)and star formation(SF)properties of member galaxies in A401/A399 system are investigated.The main results of our research are summarized as follows:1.Luminosity functions(LFs)(i)Based on the ?2 miniimization method,the overall LF for A401/399 system is fitted with the Schechter function with M*=-19.80-0.05 +0.04 and ? =0.0-0.07 +0.08.Meanwhile,on the basis of the temperature structure revealed by the X-ray observation,all member galaxies are divided into two subsamples in low-temperature and the high-temperature regions.Their median absolute magni-tudes are-19m.41 and-19m.83,respectively.It is found that the galaxies in high-temperature region have a higher overall luminosities than those in low-temperature region.(ii)We fit the LFs of cluster galaxies for A401 and A399 respectively,and obtain the characteristic absolute magnitude,M*=-19.68-0.06 +0.05,and the slope at faint,end,? = 0.32-0.09 +0.10,for A401 as a whole.We have M*=-19.72-0.06 +0.07 and a?-0.08-0.12 +0.09 for A399.It is evident that two clusters have a.similar characteristic magnitude,but the LF of A401 has a clear decline at faint end,indicating a lower fraction of faint galaxies in A401.This suggests that the cluster A401 seems to be a well evolved system,while A399 is still dynamically young.Additionally.the luminosity distributions of the high-temperature core regions of A401(#C1)and A399(?C2)are given,and their median values of MR are-19m.93 and-19m.71 respectively.Obviously.the galaxies in high-temperature core region of A401 are systematically more luminous.(iii)We compare the LFs of cluster galaxies in low-temperature outer re-gions of A401(#01)and A399(#02)with those in the intermediate regions(#(O3+C3)),and the median absolute magnitudes are-19m.36,-19m.38,and-20m.00 for the regions#01,#02,and#(O3+C3),respectively.It shows that the galaxies in the intermediate regions are significantly brighter than those in outer low-temperature regions.Interactions between two clusters may have en-hanced overall luminosity for the galaxies within intermediate regions.It can be interpreted that there is a.prominent filament connected with two clusters,and some massive galaxies are formed at early time from the gas in the intermediate region.2.Star formation(SF)properties of the member galaxiesBased on the codes of evolutionary synthesis model,PEGASE(v2.0)and FAST,the spectral energy distributions(SEDs)of member galaxies,including SCUSS u,BATC b-p and WISE W1,W2 bands,are fitted.The SF properties such as dust extinction,stellar mass,mean stellar age,mean interstellar medium(ISM)metallicity,and SFR time scale can be derived.The results are as follows:(i)The stellar masses of galaxies tend to increase with local surface density.The member galaxies in outer regions are found to have severe dust content,and more intense star formation activities,and more scattered distribution of the SF properties.On the contrary,the galaxies in core regions seem to have shorter SFR time scales,older stellar ages,and higher ISM metallicities.(ii)By comparing the distributions of mean stellar age and SFR time scale in the high-temperature core regions(#C1 and#C2)of A401 and A399.we find that the galaxies in core regions of A401 have younger stellar ages and longer SFR time scales.(iii)The galaxies in the high-temperature regions(#(C1+C2+C3))are found to have older stellar ages and shorter SFR time scales,indicating that a larger fraction of stars are formed later for the galaxies in low-temperature regions(#(O1+O2+O3)).(iv)For the galaxies in outer intermediate regions(#(O3+C3)),their mean stellar ages and SFR time scales are something between those in the outer regions#01 and#02.The galaxies in outer regions of A399(#02)seem to have oldest stellar ages and shortest SFR time scales.Above results support,the scenario that,these two clusters just come to merge,and they are approaching to each other.The star formation activities of member galaxies have not been significantly affected by the cluster interaction.