Physical Statistical Analysis Of High-redshift, Massive And Compact Galaxies

The formation and evolution of high-redshift massive(M*≥1010M☉)galax-ies are a hotspot in galaxy astronomy.By studying the redshift evolution of galaxy in size,astronomers find a special class of galaxies with high surface den-sity of stellar mass,that is,massive compact galaxies.These galaxies fall into two categories:compact star-forming galaxies(cSFGs)and compact quiescent galaxies(cQGs).It is found that massive compact galaxies are ubiquitous at high redshifts,but are quite rare in the local universe.Why the abundance of com-pact galaxies are discrepant at different redshifts and how those massive compact galaxies form and evolve.In this thesis,we utilise the multi-band photometric data from 3D-HST/CANDELS to study the physical properties of compact galax-ies,mainly including the following two aspects:(1)The abundance of compact galaxies at 1<z<3;(2)The physical properties of cSFGs with and without active galactic nucleus(AGNs)at 2<z<3.Based on the multi-band photometric data in five 3D-HST/CANDELS(i.e.,AEGIS,COSMOS,GOODS-N,GOODS-S and UDS)fields,we construct a large sample of massive（M*≥1010M☉),high-redshift(1<z<3)compact galaxies,and quantifly the fractional abundance and comoving number density of massive compact galaxies as a function of redshift.Firstly,high-redshift massive galaxies are divided into star-forming galaxies(SFGs)and quiescent galaxies(QGs)by using the rest-frame UVJ diagram,then the samples of cSFGs and cQGs are constructed by eight compactness criteria.The results manifest that the effect of compactness definition on abundance estimate of high-redshift compact galaxies is remarkable.Regardless of the compactness criteria adopted,the proportion of cSFGs(cQGs)in SFGs(QGs)and its number density with redshift are found to be rather similar.Large samples of the cQGs exhibit a sustaining increase in number density from z～J 3 to 2 and a plateau at 1<z<2.For massive cSFGs,a plateau in the number density at 2<z<3 can be found,as well as a continuous drop from z～2 to 1.The evolutionary trends of the cQG and cSFG abundances support the scenario that the cSFGs at z(?)2 may have been rapidly quenched into quiescent phase via violent dissipational processes such as major merger and disk instabilities.Rarity of the cSFGs at lower redshifts(z<1)can be interpreted by the decrease of gas reservoirs in dark matter halos and theconsequent low efficiency of gas-rich dissipation.To further investigate the physical properties of cSFGs with or without AGNs,we construct a sample of cSFGs with compactness criterion ∑1.5>10.45 M☉ kpc-1.5 at 2<z<3.In a sample of 221 massive cSFGs,66 AGNs are select-ed by X-ray detection,middle Infrared radiation criteria and SED fitting using CIGALE code,and the rest are non-AGNs.In terms of multiple AGN selection methods,the AGN fraction is～30±3.1%,which is higher than the result using a single AGN selection method.Then,we investigate the differences of physical properties between AGNs and non-AGNs,including stellar population parame-ters,structure and environment at 2<z<2.5 and 2.5≤z<3.We find that the AGNs possess the similar stellar mass,specific star formation rate(sSFR),the ratio of LIR to LUV(IRX≡LIR/LUV),Sersic index(n),the radius(r20),Gini coefficient(Gini)and concentration index(C)distributions to non-AGNs.The compact star-forming systems are formed by dissipative compaction events,such as major merger and violent disk instabilities.With the gradual consumption of available gas and dust,the structures of cSFGs have a tendency to be get-ting more concentrated with the cosmic time,and both AGNs and non-AGNs in cSFGs inhabit in similar environment.