X-RAY Study Of The Narrow Fe Kα Line Emission And Hot Gas Properties Of NGC 4388

The unified model of active galactic nuclei（AGN）proposes that different AGN optical spectral types are caused by different viewing angles with respect to an obscuring"torus".That is to say,these AGNs are intrinsically the same type of object.The majority of nearby active galactic nuclei are obscured by a large amount of circumnuclear cold gas and dust.There may be some problems for the structure of dusty torus under the framework of classical unified model.The torus may be clumpy,but not integrated.The primary emission from nucleus is reprocessed by these circumnuclear material,with a resulting compton reflection continuum and an associated fluorescent Fe Ka line at 6.4 keV.The Chandra data will allow us to further map the geometrical structure of Fe Kα emitting material and spectrally characterize these regions in detail.In Chapter 1,we summarized the related issues of unification model and Fe Ka line in AGN.In the first work,we mainly focuses on the study of the Fe Kα line and the detailed findings are as follows:In Chapter 2,we present imaging and spectral analysis of the Chandra observations of Seyfert 2 galaxy NGC 4388.Compared with previous studies,three prominent extended X-ray structures around the nucleus on kpc scale are well imaged,allowing an in-depth spatially resolved study.Both the extended hard continuum（4.0-6.0 keV）and the Fe Ka line（6.2-6.7 keV）show similar morphology.It is the same case with other Compton thick galaxies（e.g NGC 4945,NGC 1068,NGC 5643）with Fe Ka emission scale beyond torus.Indeed,most of our knowledge so far about the circumnuclear reprocessing matter,at least when their X-ray properties are concerned,is based on the brightest Compton thick sources due to their heavy obscuration,but NGC 4388 is one of the rare cases with a lower column density(NH<1.25×10²⁴,the inverse of the Thomson scattering cross-section)along the line of sight.Significant differences in equivalent width of the Fe Ka emission line（up to a factor of 3）are found for the nuclear and extended regions.Such a difference could be ascribed to different column densities or scattering angles with respect to the line of sight,rather than variations in iron abundances.The north-east and west extended structures appear to be aligned with the larger scale galactic disk and dust lane in the HST V-H color map,and are located at the peak of molecular gas（CO）distribution.The morphology of remaining extended features likely traces edges of a known radio jet,indicating that the outflow at kpc scale may have compressed the interstellar gas and produced clumps working as the reflector to enhance line emission.In addition,using[OIV]emission as a proxy of the AGN intrinsic luminosity,we find that both of the extended Fe Ka emission and reflection continuum are linearly correlated with the[OIV]luminosity,which indicates a connection between the central AGN and the extended emission.In Chapter 3,we mainly explore the ionization mechanism for the hot gas in the second work.Furthermore,the properties of galaxies are affected by the interaction between galaxy and intracluster medium（ICM）.NGC 4388 is often believed to be interacting strongly with the Virgo Cluster ICM at supersonic speeds.The cold ISM in the galactic disk are stripped from the galaxy disk.The extended stripped gas tail has been observed in Hα and HI 21 cm band.In this paper,the X-ray gas tail has been detected with Chandra and XMM-Newton data consistent with Hα and HI tail.Based on the numerical simulation results,a mach cone formed on the far side（leading edge）of the galaxy and some temperature rise in the bow-shocked region around the interaction point is expected.Unfortunately,deeper observation data are needed to find such a mach cone.