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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
· · ·
MHI ~ 4.5 D2 (kpc) Size ~ 0.4 deg2 NHI ~ 1019 cm-2 At 500 kpc dHI=6 kpc cm-3 nHI=5 x 10-4 cm-3 At 5 MHI dHI nHI kpc = 115 Mo = 60 pc = 5 x 10-2 cm-3

At 50 kpc dHI=600 pc nHI=5 x 10-3

At 1 Mpc dHI=12 kpc nHI=2.5 x 10-4 cm-3

MHI=1.15 x 104 Mo MHI=1.15 x 106 Mo MHI=4.6 x 106 Mo


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 HVC279-33+120: < 50 kpc Complex C: > 6 kpc ~5 other HVCs: > 0.3 kpc


HVC Distances
· Direct methods · H emission measurements


Compact HVC H Detections

H


HVC Distances
· Direct methods · H emission measurements · Deep HI observations of groups


Deep Surveys of Groups
! Small area in Local

Sculptor Group None to ~107 Mo
(Putman et al. 2003)

Group-like groups, 0 starfree HI objects to 7 x 106 Mo (Zwaan 2001)
! Many other surveys of

2% of group, None to 3 x 106 Mo (de
Blok et al. 2001) Same for Centaurus A

Lo et al. 1979, Dahlem et al. 2001)

groups down to a few x 107 Mo have also found 0 (e.g.


HVC Distances
· Direct methods · H emission measurements · Deep HI observations of groups and spiral galaxies · Ly absorbers


HVC Distances
· Direct methods · H emission measurements · Deep HI observations of groups and spiral galaxies · Ly 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)


M81 Group
(Yun, Ho & Lo 1994)


Leo Ring
(Schneider et al. 1981)


Anomalous HI around galaxies
· M101 · M83
al.) (van der Hulst & Sancisi 1988) (O. K. Park et (Putman et

· FCC35
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 Ly absorbers which are often 100s of kpc from a galaxy? · How do HVCs fit into the CDM model of galaxy formation?


Target Selection
· Northern extension of HIPASS ( = 2 ­ 25o )

· 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