Z～1.3-1.8 Research On The Properties Of The Lyman Break Galaxy

Astronomers want to understand how the Universe evolved from a very primitive initial state into what we are observing around us tody-galaxies of different morphologies,the large-scale structure of their distribution,clusters of galaxies,and active galaxies.In recent years,with the rapid development of science and technology,the capability of the telescope has been improved.Since 1995,the deep and multi-wavelength images was observed with the Space Telescope like ACS/HST in the fields,such as HDF,GOODs,CDF-S,COSMOS,and so on,and galaxies at the very high redshifts could be detected.How do we find high-redshift galaxies?Since hydrogen is the most abundant element in the Universe,there would a lya emission in some galaxies.If a galaxy at z≈λ/(1216A)-1 have Lya emission,then the image taken with the narrow-band filter centered on a wavelength λ should be particularly brighter than the image taken with the broader-band filter centered roughly on λ.This is called "narrow-band photometry" method.The second method is color method which can identify the galaxies at higher redshifts in deep,multiwavelengh surveys by using color criteria(Elston&Lu 2001,Wilson et al.2004,Daddi et al.2004,McCracken et al.2010,Eisenhardt et al.2012,Fang et al.2015),such as Lyman-break dropouts,BzK objects,distant red galaxies(DRGs),extremely red objects(EROs),Spitzer-selected EROs,BX/BM galaxies,as well as flux-selected submillimetre galaxies.Elston&Lu(2001)identified z=0.8～2 EROs in LOCKMAN HOLE or COSMOS fields.Daddi(2004)and McCracken(2010)identified z=1.4～2.5 BzKs.Rieke et al.(Rieke&Low.1972,Sanders&Mirabel 1996,Hwang et al.2010,Yuan et al.2010)have studied z=1～3 ULIRGs.Adelberger(2004)identified z=1～3 BM/BX galaxies.For Lyman-break dropouts,the method gets to consider energy levels in atomic hydrogen.Since hydrogen is so abundant in the Universe and its ionization cross-section so large,so photons with λ<912A would be absorbed by neutral hydrogen in its ground state.The galaxy at z～1 containing young stars would not be invisible in FUV-band filter.This method was called UV-drop-outs.Burgarella(2006)and Oteo(2013)adopt this method and identified the sample of z～1 Lyman-break galaxies(LBGs).By variation of the filter set,drop-outs can also be discovered at larger wavelengths.This method has been routinely applied up to higher redshifts,yielding NUV-drop-outs(z～2),U-drop-outs(z～3),B-drop-outs(z～4.5),V-drop-outs(z～5)and z-drop-outs(z～7).Within last ten years,Lyman-break galaxies technique is the most effective method to identify the star forming galaxies at high redshifts.The Lyman break galaxies are easily detected at z=2～6 in deep pencil beam surveys from the ground and with the Hubble Space Telescope(HST)(Steidel&Hamilton 1993,Steidel et al.1999,Shapley et al.2001,Giavalisco et al.2004,Adelberger et al.2004,Bouwens et al.2006,Yoshida et al.2006,Overzier et al.2008).By using drop-outs method,Bowler(2012)identified z～7 LBGs.Many people have analyzed the characteristics of LBGs.Giavalisco&Steidel(1996)and Lowenthal(1997)et al.studied the structure and size of LBGs and found that the high redshift galaxies are compact and large low surface brightness galaxies are rare.Governato et al.(Gover-nato et al.2001,Giavalisco&Dickinson 2001,Moustakas&Somerville 2002,Ouchi et al.2004,Adelberger et al.2005)found that the correlation length of LBGs at z=1.5～3.5 is r0 ≈ 4.2h-1 Mpc.Therefore LBGs has a strong clustering,which means that the large scale distribution of Lyman-break galaxies already existed at high redshift.Iwata et al.(2007)found the correlation between the UV luminosity and the clustering of UV-bright LBGs,which also suggests that L-BGs should be associated with dark matter halos.Therefore,LBGs are the tracer of material distribution.The inferred hight star-formation rate of LBGs implies an correspondingly high rate of su-pernova explosion(SNe).These release part of their energy in the form of kinetic energy to the interstellar medium in these galaxies.This process will give rise to two consequences.The first is that the interstellar medium(ISM)would be heated locally,which prevents further star formation in these regions.Secondly,the large amount of energy transferred from the SNe to the interstellar medium would launch a galactic wind.The galactic wind would be found in nearby galaxies from neutral hydrogen observations of edge-on spirals which show an extended gas distribution outside the disk and from the X-ray corona of spirals.On the other hand,as we all have known the cosmic star formation rate reached a maximum at z～1-3 and decreased dramatically toward z=0(Lilly et al.1996,Schiminovich et al.2005).There is only a little decrease in the UV luminosity density from z～3 to z～6(Ouchi et al.2004,Bouwens et al.2006),indicating that LBGs represent a ma-jor phase in the early stages of galaxy formation and evolution.Reddy&Steidel(2009)thought the blue star forming galaxies(e.g.LBGs)contribute greatly to the energy of thermal radiation of z=2-3 galaxies and also emphasized the importance of the blue star forming galaxies for us to understand the history of the star formation in the universe.After combining the data of the GALEX Deep Imaging Survey(DIS)with the Multi wave-length Survey(MUSYC)data of the ECDF-S field,the paper obtain photometric redshifts of the sources of the MUSYC’ s catalog using EAZY,a fast public photometric redshift code.Then,considering the observed flux of galaxies detected in the observed UV and U by GALEX and MUSYC respectively,and using the method of NUV-dropout,the paper have selected 75 samples of z～1.3-1.8 LBGs.Then,the paper measured stellar masses and dust reddening of the samples of z～1.3-1.8 LBGs by using template BC03 models and fast code.Lastly,the paper constructed the star formation rate-stellar mass plane of z～1.3-1.8 LBGs,and analyzed properties of photometry and morphology of the samples.The paper found the median SFR of 75 z～1.3-1.8 LBGs is about～20M⊙yr-1,and the slope of the SFR-M*relations is 0.613,which are similar to those observed by Magnelli et al.(2014).Our result support that z～1.3-1.8 LBGs have high SFR and are star forming galaxies.The paper also investigated morphology of the samples by GALFIT,and got the effective radius Re and Sersic indices of 53 z～1.3-1.8 LBGs from V-band images.The peaks of effective radius and of z～1.3-1.8 LBGs are～3 kpc which like the result of z=1-2 SFGs(Shibuya et al.2015).The Sersic indices of 53 z～1.3-1.8 LBGs are mostly less than 2,which support that they are disc-dominated,and obey the evolution of galaxies in morphology from high redshifts to low redshifts.The paper has been arranged as follows:In Sect.l,introduced the basic cosmology and the formation of galaxies and the properties of galaxies’s distribution.In Sect.2,introduced how to find high redshift galaxies.In Sect.3,introduced the field of E-CDFS,observed in MUSYC and GALEX projects,and the cross-match the MUSYC catalog and GALEX catalog.In Sect.4,the paper have selected a photometric sample of z～1.3-1.8 Lyman break galaxies by combining MUSYC catalogue with deep GALEX in the ECDF-S and calculated SFRs and masses of the samples.In Sect.5,analyzed the morphology of the samples.Throughout this paper,we assume an Qo=0.3,QA=0.7 and Ho=70kms-1Mpc-1 cosmology.Magnitudes are in the AB system and colors are given in the rest-frame unless stated otherwise.We assume a Chabrier initial mass function(IMF;Chabrier 2003),and defined the circularized half-light radius as size of galaxies.