Hot Gas in Nearby GalaxiesLi JiangtaoAstronomy Department of Nanjing UniversityDepartment of Astronomy, UMASS

Co-workersQ. Daniel Wang (UMASS)Yang Chen (NJU)Zhiyuan Li (UMASS)Shikui Tang (UMASS)Bing Jiang (NJU)Li Ji (MIT)Yangsen Yao (U Colorado)Judith A. Irwin (Queens University)Joern Rossa (U Florida)

OutlineX-ray emitting mechanismGalactic feedbackBasic problems in early-type galaxiesHot gas in normal galaxies (Milky Way, M 31, NGC 5866, NGC 5775)Summary

X-ray emitting mechanismMagnetic energyGravitational energyShock: In galaxies, since the specific energy of shock heating is highest, it is the dominate process.

Galactic feedbackAGNCentaurus ASombreroM82Star formation SNe Ia

In early type galaxiesOver cooling problem: Structure formation simulation predicted cooled gas is 2 or 3 times larger than observed in galaxies.Missing energy problem: The expected mechanical energy feedback is much larger than observed in X-ray emission.Missing gas problem: In S0 galaxies, observed gas mass only account for ~10% of the stellar evolution mass return.Tang et al.

Hot gas in normal galaxies: our GalaxyX-ray binaryROSAT all-sky survey in the -keV bandX-ray binaryAGNWang et al. 05, Yao & Wang 05/06, Yao et al. 06/07

Soft X-ray and UV absorption line: evidence for interaction between hot/cold gasYao & Wang 2006, Yao et al. 2006

M 310.5-1 keV1-2 keV2-8 keVMissing energy problem.Mass loss, evaporation plays an important role.Ionizing source for 10^4 K gas, evolved stars are the most important source. Li & Wang 2007Lx~2x1038 erg/sZh=0.6 kpc, but with flat tails at large z

Further evidence for interaction between cold/hot gas in S0 galaxies: (NGC 5866)Li, Wang & Li 2008

Feedback in disk-wide star forming galaxies: NGC 5775 Hot gas heating efficiency by SF is not much different from starburst galaxies.At least two components of diffuse hot gas:(1) Near disk with more mass-loading, heated by disk star forming regions, lower temperature.(2) In the bulge with little mass-loading, heated mainly by SNe Ia, higher temperature. Li et al. 2008

SummaryDiffuse hot gas in non-starburst, non-AGN galaxy halos:Temperature: ~0.3 keV, larger than gravitational energy, smaller than SNe specific energy. Sometimes there is a second component with higher temperature.Luminosity: 10^38-10^40 erg/s, much smaller compared with AGN.Mass: 10^7-10^9 M_solarOver cooling problem: Structure formation simulation predicted cooled gas is 2 or 3 times larger than observed in galaxies.Missing energy problem: The expected mechanical energy feedback is much larger than observed in X-ray emission.Missing gas problem: In S0 galaxies, observed gas mass only account for ~10% of the stellar evolution mass return.Solution of these problems: SNe heating and mass loss (in large galaxies, AGN feedback may be more important).

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