X-ray Study of the Local Hot Gas

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 ~ 1016 cm-2.

4. R=1 Mpc Local Group 300 kpc

5. Target: 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

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 1015 cm-2 • H 1821+643 (Mathur et al. 2003) • 2-3  • Mkn 421 (Nicastro et al. 2004) • (0.7 - 1) x 1015 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. R R 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

17. ROSAT ALL SKY MAP

18. Soft X-ray Background • Three components: • Extragalactic X-ray background from point sources (and WHIM?), power law spectrum. • Local hot bubble, producing thermal emission around 106K, within a bubble with radius of ~ a few hundred pc around the Sun. • Halo component, producing thermal emission around 106.3 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 106 to 106.5 K.

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