Are HighVelocity Clouds a Common Feature of Star

Are High-Velocity Clouds a Common Feature of Star Forming Galaxies? Wakker et al. (2000)

HVCs as Local Group Building Blocks? Grebel 1998

Compact HVC Typical HI Masses and Sizes • • • At 5 kpc MHI = 115 Mo d. HI = 60 pc n. HI = 5 x 10 -2 cm-3 MHI ~ 4. 5 D 2 (kpc) Size ~ 0. 4 deg 2 NHI ~ 1019 cm-2 At 50 kpc At 1 Mpc At 500 kpc 6 MHI=1. 15 x 104 Mo MHI=1. 15 x 106 Mo MHI=4. 6 x 10 Mo d. HI=600 pc n. HI=5 x 10 -3 d. HI=12 kpc d. HI=6 kpc cm-3 n. HI=5 x 10 -4 cm-3 n. HI=2. 5 x 10 -4 cm-3

HVC Distances • Direct methods

Direct Distance Determinations • Large complexes using halo stars • • • Complex A: 4 - 10 kpc Complex M: < 4 kpc Complex WE: < 13 kpc HVC 279 -33+120: < 50 kpc Complex C: > 6 kpc ~5 other HVCs: > 0. 3 kpc

HVC Distances • Direct methods • Ha emission measurements

Compact HVC Ha Detections Ha

HVC Distances • Direct methods • Ha emission measurements • Deep HI observations of groups

Deep Surveys of Groups Sculptor Group None to ~107 Mo (Putman et al. 2003) 2% of group, None to 3 x 106 Mo (de Blok et al. 2001) Same for Centaurus A n Small area in Local Group-like groups, 0 starfree HI objects to 7 x 106 Mo (Zwaan 2001) n Many other surveys of groups down to a few x 107 Mo have also found 0 (e. g. Lo et al. 1979, Dahlem et al. 2001)

HVC Distances • Direct methods • Ha emission measurements • Deep HI observations of groups and spiral galaxies • Lya absorbers

HVC Distances • Direct methods • Ha emission measurements • Deep HI observations of groups and spiral galaxies • Lya absorbers • Ionization constraints

Moore et al. (1999)

Incoming Star Formation Fuel? Wakker et al. (2000)

Smooth Accretion of Intergalactic Gas Bryan & Norman Bowen, Pettini & Blades (2002)

Mergers and Satellite Accretion Harding et al.

Galactic Fountain Material

Our Galaxy Putman et al. (2003)

M 81 Group (Yun, Ho & Lo 1994)

Leo Ring (Schneider et al. 1981)

Anomalous HI around galaxies • M 101 (van der Hulst & Sancisi 1988) • M 83 (O. K. Park et al. ) • FCC 35 (Putman et al. 1998) • NGC 2442 (Ryder et al. 2001)

NGC 2403 (lowest contour ~ 2 x 1019 cm-2; Fraternali et al. 2002)

Questions to be answered • Is there a relation between the presence of HVCs and a galaxy’s star formation rate?

SINGG = Survey for Ionization in Neutral Gas Galaxies (Meurer et al. )

NGC 1533 Ryan-Weber et al. (2003)

Questions to be answered • Is there a relation between the presence of HVCs • • • and a galaxy’s star formation rate? What type of environment are galaxies with HVCs found in? Are there near-by companions? How are HVCs related to the Ly-limit absorbers which also are commonly found in galaxy halos? And the O VI and lower column Lya absorbers which are often 100 s of kpc from a galaxy? How do HVCs fit into the CDM model of galaxy formation?

Target Selection • Northern extension of HIPASS (d = 2 – 25 o ) • Based on number of sources found in southern HIPASS, there should be ~900 sources • Stick to v < 2000 km/s, should be ~300 • ALFA resolution ~10 kpc at 10 Mpc • High-sensitivity mapping of the sample (to NHI~1019 cm-2, r~100 kpc) should provide information on the frequency and location of HVCs