Research On The Observational Characteristics Of Massive Compact Galaxies At Z?2

In recent years,compact galaxies have gradually become a hotspot of re-search for astronomers in the field of galactic physics.A large number of studies have confirmed the evolutionary sequence from compact star-forming galaxies(cSFGs)to compact quiescent galaxies(cQGs)at z?2.Then,how do the relevant physical properties change during the evolution from cSFGs to cQGs?What factors lead to such evolution?All of these issues are worth of our further thinking and discussions.In this paper,we make use of multi-band photometric data in the five 3D-HST/CANDELS fields(AEGIS,COSMOS,GOODS-N,GOODS-S and UDS)to create a sample of massive(M*?1010 M?)compact galaxies at high redshift(z?2).The sample is divided into three galaxy populations according to the values of sSFR(specific star formation rates):(i)compact star-forming galaxies(cSFGs),(ii)compact transition galaxies(cTGs),and(iii)compact quiescent galaxies(cQGs).To verify the internal connection among the three population-s of compact galaxies,we present the distributions of stellar mass(M*),dust content(AV and IRX),morphological and structural parameters(Sersic index n,re,Gini,M20,C),AGN fraction,and environmental density to make an analysis and comparison.As a result of this study,in case of holding similar distributions of stellar mass,the median values of dust content indicator AV(or IRX=(LIR>/(LUV>)continuously decrease on the way of cSFGs evolving into cQGs.Meanwhile,cTGs act as a "transition" population during the evolution of cSFGs to cQGs,lying between cSFGs and cQGs in terms of median values of AV and IRX.On the basis of comparing distributions of morphological and structural parameters,we also find that cTGs hold intermediate median val-ues of Sersic index n,Gini,M20 and C.Moreover,Sersic index n,Gini and C gradually increase while M20 continuously decrease during the evolution,which indicates that compact galaxies become more and more bulge-dominated with the growing bulge.Additionally,we separately explore the AGN detection rates in extended star-forming galaxies(eSFGs),cSFGs,cTGs and cQGs,finding that cSFGs hold the highest ratio of AGN.And AGN detection rates decrease with star formation slowing down,suggesting that AGN may play an important role in quenching compact galaxies.Besides,cSFGs,cTGs and cQGs are found to live in undistinguishable physical environments.By comparing the three populations of compact galaxies in physical proper-ties,we find a possible evolution path from cSFGs to cQGs:cSFGs are formed at high redshift by violent dissipation,such as major merger or disk instabili-ties.There also exits a”transition" phase,called cTGs,during the evolution from cSFGs to cQGs.The growing bulge and AGN feedback can both affect the process of quenching compact galaxies.However,AGN feedback is more likely to promote star formation in the early stage of cSFGs,while the growing bulge may become more and more efficient in quenching compact galaxies with the dissipation of gas.Besides,the environment contributes little to the evolution of compact galaxies.