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)

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

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

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 , 3C 273, Mrk 421, H 1821)

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

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 –

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)

The Sight Lines 3C 273 (Sembach et al. 2001) HE (A. Fox talk) MRC Mrk 1513 PG (A. Fox talk) PG (R. Ganguly poster) PHL 1811 PKS Ton S180 UGC PKS 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

The Sight Lines L.G.B. M.W. motion 3C 273 PG PKS PG HE Ton S180 MRC PKS PHL 1811 Mrk 509 Mrk 1513 UGC 12163

PHL 1811 O VI Å N V Å C IV Å Si IV Å Si III Å C II Å Si II Å O I Å

Ton S180 O VI Å N V Å C III Å Si III Å C II Å Si II Å

PKS O VI Å N V Å C IV Å Si III Å C II Å Si II Å

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 )  go to ionization models

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

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

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

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)