1. X-ray Study of the Local Hot Gas Taotao Fang UCB With Claude Canizares, Chris Mckee and Mark Wolfire

2. Z = 0 X-ray Absorber

3. Where are the local X-ray absorbers? Typically these lines are unresolved, which implies an upper limit of line width of ~ 0.025 Å, or ~ 350 km s -1 at 21.6 Å. This means a upper limit of distance of ~ 5 Mpc if the Hubble constant is 70 km s -1 Mpc -1. The typical column density of O VII absorbers is ~ 10 16 cm -2.

4. 300 kpc Local Group R=1 Mpc

5. MS 0737+7441 PG 1211+143 NGC 3227 Mkn 509 NGC 4258 Ton S180 MCG 6-30-15 NGC 7469 NGC 4593 Mkn 766 H 1426+428 Ton 1388 PKS 0558-504 Mkn 501 NGC 3783 1H 1219+301 H 1821+643 3C 273 NGC 5548 NGC 4051 PKS 2155-304 Mkn 421 Target:

11. ALL SKY MAP, O VI AND O VII O VI data from Sembach et al. (2003)

13. X-ray Absorption in the Intervening Systems: (z > 0) PKS 2155-304 (Fang et al. 2002) –4 x 10 15 cm -2 H 1821+643 (Mathur et al. 2003) –2-3  Mkn 421 (Nicastro et al. 2004) –(0.7 - 1) x 10 15 cm -2 3C 120 (Mckernan et al. 2004) –Based on very low counts (<10 counts per bin)

14. Why we see so many local (z = 0) absorbers with high column densities, but so little intervening absorbers with small column densities? One solution: these X-ray absorbers are associated with our Milky Way, in stead of the Local Group. –Expected number of absorber along LOS; –Soft X-ray background emission measurement; –Some diagnostic observations;

15. Expected Number of Absorbers: Basic assumption: X-ray absorbers are associated with halos, either MW type, or LG type. Model A: halo distribution (PS) + gas distribution (NFW) + metal distribution –TOO MANY UNCERTAINTIES, CAN FIT ANY DATA! Model B: start from observations –Covering factor: C –Uniformly distributed within the halo RR

17. ROSAT ALL SKY MAP

18. Three components: –Extragalactic X-ray background from point sources (and WHIM?), power law spectrum. –Local hot bubble, producing thermal emission around 10 6 K, within a bubble with radius of ~ a few hundred pc around the Sun. –Halo component, producing thermal emission around 10 6.3 K. X- ray data showed (Garmire et al. 1992) the emission measure from this component is: Combining with X-ray absorption measure, we found: CAUTION: the temperature of this hot halo component is extremely uncertain, varying from 10 6 to 10 6.5 K. Soft X-ray Background

19. Diagnostic Observations 4U 1820 (LMXB) D < 7.6 kpc Futamoto et al (2004) GX 339 (LMXB) D < 4.0 kpc Miller et al (2004) Caution: high column density of O VIII!

21. Total Baryon Mass and Fraction

22. Summary Observation: –In a total of 22 los, Chandra & XMM detected 9 los show z = 0 X-ray absorption lines with high column density; –All los with more than 60 counts per bin showed z = 0 lines; –Very few intervening absorption systems were reported, with very low ion column densities. We argue that these local X-ray absorbers are possibly associated with MW halo, instead of intragroup medium in LG –Expected number of the absorbers –Soft X-ray background emission measurement; –Diagnostic observations of nearby targets From SXB and X-ray absorption measurement, we constrain the the properties of the X-ray absorbers as

23. Total Baryon Mass and Fraction Given a covering factor C, total number of X-ray “cloud” with a radius of r and within a halo of radius R, are: Since the total mass within these X-ray “cloud” must be smaller than the total baryon mass of the halo, we have:

24. Ionization fraction for O VI, O VII, and O VIII

25. McCammon et al. (2002)

26. Chandra Moon Observation

27. Chandra Moon Spectrum Wergerlin et al.(2004)

28. X-ray Emission Line Measurement In most case, the line intensity of O VII triplet is: At the temperature where O VII ionization peaks, the collisional excitation rate We then have:

29. X-ray Study of the Local Hot Gas