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Minutes of the talk on :
     
The Search for HVCs in Other Galaxies
Mary Putman (U. Colorado)
A more detailed version of this talk by the speaker is available in
HTML,
PDF or
PPT format.
The principal questions I want to ask are:
- Are HVCs a common feature of star forming galaxies?
- Are there intergalactic HI clouds in the Local Group?
HVCs as Local Group building blocks, at distances up to a Mpc
Consider the typical properties of the smallest HVCs (compact HVCs) found
in HIPASS:
Distance | HI Mass | HI diameter |
At 5 kpc | meager objects ~116 solar masses | 60 pc |
At 50 kpc | 1.15 x 104 solar masses | 600 pc |
At 1 Mpc | 5 x 106 solar masses | 6 kpc |
That makes them vastly different objects at the different distances. Establishing
reliable distances is critical to the understanding of HVCs.
What do we know about HVC distances?
- Direct distances (background stars) only in the
big complexes in range 5-10 kpc.
- H-alpha emission measurements
- Ionizing radiation from MW could be detected if HVC within 100 kpc of MW.
- Detection proves closer distances.
- Searches in nearby groups:
- Sculptor
- Putman et al. (2003) found none to 107 solar masses.
- 2% of Sculptor to 3 x 106 solar masses
by de Blok et al. (2001) found none.
- Centaurus: Zwaan et al. (2001) found none.
- Constraints by Lya absorbers
- Ionization constraints
HVC's do not fit into the likely Local Group model, but they do fit into a
paradigm where they are located in the halo of the Milky Way. They
could be infalling fuel for star formation.
- Bryan & Norman suggest that the HVC's represent the smooth
accretion of intergalactic gas
- Harding et al. suggest that they trace minor mergers and
satellite accretion.
- Some of the clouds may be galactic fountain material.
Known examples
High velocity gas around other galaxies can be identified from maps and dynamics:
- Certainly seen around MW (Putman et al. 2003)
- Accretion in M81 group: Yun et al
- Leo ring
- M101 (van der Hulst & Sancisi)
- M83 (Park et al.)
- FCC35 (Putman et al. 1998)
- NGC 2442 (Ryder et al. 2001)
- NGC 2403 (Fraternali et al. 2002); anomolous velocities
- Look at Halpha around galaxies
e.g. SINGG (Meurer et al.; Survey for Ionization in Neutral Gas Galaxies)
- NGC 1533: clearly HVC's around it (Ryan-Weber et al. 2003)
Questions to be answered:
- Is there a relation between the presence of HVCs and
the star formation rate in the galaxy?
- What type of environments are galaxies with HVCs found in?
- Do the galaxies with HVCs always have nearby companions?
- How are HVCs related to absorbers which are also commonly found
in galaxy halos
- How are HVCs related to the OVII and lower column density
Lyalpha absorbers which are often 100s of kpc from a galaxy?
- How do HVCs fit into the CDM galaxy formation paradigm?
What would an ALFA survey find?
We can use the northern part of HIPASS extensions (decl +2 to +25o).
Based on the number of sources in the southern HIPASS zone,
there should be about 900 sources. If we stick to the inner zone,
say cz < 2000 km/s, there should be about 300 sources.
Note that the ALFA resolution gives 10 kpc at 10 Mpc.
For a survey of high sensitivity mapping of the
sample assuming an expected 30 km/s linewidth, the resulting
sensitivity would be NH ~ 1019 cm-2.
Such a survey would provide information of the location and frequency
of HVCs.
Questions/Discussion:
Riccardo |
Have you calculated the required integration times? |
Mary |
I haven't worked it all out yet. |
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Up: Minutes of the 1st
Previous: Ionization
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Last modified: Thu Apr 17 11:43:50 EDT 2003