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IDM2008 - Identification of Dark Matter 2008
IDM2008 - Identification of Dark Matter 2008
18-22 August 2008 AlbaNova
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Red halos and dark baryons (15'+5')
On cosmological scales, somewhere between half and one third of the baryons 
in the low-redshift Universe are still unaccounted for, and the fraction of 
baryons missing from within the virial radii of galaxy-sized dark matter halos is 
of the same order. While the baryonic fraction of the overall dark matter is 
subdominant on large scales, the dark baryons may have a spatial distribution 
that is substantially different from that of the CDM and may therefore 
potentially interfere with attempts to test the clustering properties of CDM on 
subgalactic scales. Current models suggest that most of the dark baryons 
should be in the form of hot, tenuous gas, but a number of observations 
challenge this view, indicating that some of the missing baryons may be hiding 
in a cold, collapsed form. The red halos of galaxies represent one such piece 
that doesn't quite fit the puzzle.  Over the last 15 years, deep optical/near-IR 
images of galaxies have revealed faint and very red structures around galaxies 
of different types. The colours of these halos are too extreme to be reconciled 
with any type of previously detected stellar population, and non-stellar 
explanations like dust or ionized gas are also disfavoured. A stellar population 
containing an abnormally high fraction of low-mass stars is on the other hand 
consistent with all available data. Because of its high mass-to-light ratio, such a 
halo population could contribute substantially to the baryon budget of galaxies, 
despite adding as little as one percent to their overall light. Here, we review 
the current status of this field and report on ongoing searches for red halos 
around types of galaxies for which similar structures have not yet been 
detected. We also address the constraints that direct star counts in the halo of 
the Milky Way impose on any putative red halo of low-mass stars around our 
own galaxy, and discuss the implications for red halos around disk galaxies in 
Id: 381
Place: AlbaNova
Room: Oskar Klein auditorium
Starting date:
22-Aug-2008   10:45
Duration: 20'
Contribution type: Talk
Primary Authors: Dr. ZACKRISSON, Erik (Tuorla Observatory, Finland)
Co-Authors: Dr. FLYNN, Chris (Tuorla Observatory, Finland)
Dr. BERGVALL, Nils (Uppsala Observatory)
Ms. MICHEVA, Genoveva (Stockholm Observatory)
Dr. ÖSTLIN, Göran (Stockholm Observatory)
Mr. CALDWELL, Brady (Uppsala Observatory)
Presenters: Dr. ZACKRISSON, Erik
Material: slide Slides
Included in session: Dark matter cosmology / structure formation
Included in track: Dark matter cosmology / structure formation

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