1. Surveying the Highly Ionized HVCs with FUSE and HST Joe Collins (University of Colorado) Mike Shull (University of Colorado) Mark Giroux (East Tennessee State University) Sembach et al. (2003)

2. O VI: H I: (Sembach et al. 2003)

3. The Highly Ionized HVCs L.G.B. M.W. motion OVI HVCs not detected in HI 21-cm emission

4. Are these HVCs WHIM? Nicastro et al. (2002, 2003) propose that these objects trace Local Group WHIM The Evidence: 1) “Dipole” sky distribution of HVC velocities 2) Possible correlation with poorly-resolved z=0 OVII/VIII absorption (PKS 2155-304, 3C 273, Mrk 421, H 1821)

5. Kinematic sky distribution can be explained in several ways  Local Group WHIM  infall to L.G.B Galactic Infall R shell = 15 kpc V infall = 50 km/s standard Galactic rotation L.G.B. M.W. motion

6. Mass in Local Group WHIM (Cen & Ostriker 1999) N OVI = 10 cm T = 10 K Z = 0.1 Z solar R WHIM = 1 Mpc M hot ~ 10 M solar 14 –2 5.5 12

7. Survey of Highly Ionized HVCs FUSE data with S/N > 5 HST-STIS (public April 2004) –E140M –G140M  coverage of O I, C II/III/IV, Si II/III/IV, NV, and O VI Highly Ionized HVCs from Sembach et al. (2003)

8. The Sight Lines 3C 273 (Sembach et al. 2001) HE 0226-4110 (A. Fox talk) MRC 2251-178 Mrk 1513 PG 0953+414 (A. Fox talk) PG 1116+215 (R. Ganguly poster) PHL 1811 PKS 1302-102 Ton S180 UGC 12163 PKS 2155-304 Mrk 509 (Sembach et al. 1999; Collins, Shull, & Giroux 2004)  12 sight lines  Can consider whether these objects are more similar to Galactic halo HVCs or WHIM

9. The Sight Lines L.G.B. M.W. motion 3C 273 PG 1116+215 PKS 1302-102 PG 0953+414 HE 0226-4110 Ton S180 MRC 2251-178 PKS 2155-304 PHL 1811 Mrk 509 Mrk 1513 UGC 12163

10. PHL 1811 O VI 1031.93 Å N V 1238.82 Å C IV 1548.20 Å Si IV 1393.76 Å Si III 1206.50 Å C II 1334.53 Å Si II 1526.71 Å O I 1302.17 Å

11. Ton S180 O VI 1031.93 Å N V 1238.82 Å C III 977.02 Å Si III 1206.50 Å C II 1036.34 Å Si II 1260.42 Å

12. PKS 1302-102 O VI 1031.93 Å N V 1238.82 Å C IV 1548.20 Å Si III 1206.50 Å C II 1334.53 Å Si II 1260.42 Å

13. Survey Results 9 of 12 HVCs are detected in low ions (C II, Si II) 10 of 12 are detected in Si III or C III 2 in O VI only (3C 273, PKS 1302-102)  go to ionization models

14. CLOUDY Modeling AGN/QSO background –log Φ = 4.0 –power law, α = 1.8 Z = 0.1 Z solar 2σ errors on N ion Ton S180 log N(H I) = 16.6 log n H = –3.3

15. Ionization Modeling CLOUDY photoionization models C II, Si II detections imply n H > 10 cm O VI, C IV, Si IV are underpredicted  collisional ionization –3.5–3

16. Ionization Modeling Collisional Ionization Turbulent Mixing Layers (Slavin et al. 1993) Conductive Interfaces (Borkowski et al. 1990) can reproduce high ion ratios N(CIV) / N(OVI)=0.2–1.1 N(NV) / N(OVI) < 0.1–0.3 kinematic connection between low/high ions  both photo- and collisionally ionized components occur in the same cloud

17. Summary: Highly Ionized HVCs Low ion (CII, SiII) detections in 9 of 12 cases: –imply photoionization with log n H > –3.5 –are inconsistent with WHIM log n H = –5 to –6 High ions (CIV, SiIV, OVI) –share similar kinematics with the low ions –arise via collisional ionization at cloud interface Only 2 HVCs are detected solely in O VI –cannot rule out WHIM origin  multiphase objects similar to Galactic halo HI HVCs, albeit at low-N total (H)