Scaling laws for dark matter halos of late-type and dwarf spheroidal galaxies

Speaker: 
John Kormendy (University of Texas at Austin)
Event Date and Time: 
Thu, 2017-03-23 12:30 - 13:45
Location: 
Hennings 301 - NOTE DIFFERENT LOCATION
Local Contact: 
Jaymie Matthews and Philip Stamp
Intended Audience: 
Graduate
Dark matter (DM) halos of Sc-Im and dwarf spheroidal (dSph) galaxies satisfy scaling laws: halos in lower-luminosity galaxies have smaller core radii, higher central densities, and smaller velocity dispersions. These results are based on maximum-disk rotation curve decompositions for giant galaxies and Jeans equation analysis for dwarfs. (1) We show that spiral, Im, and Sph galaxies with absolute magnitudes M_V > -18 form a sequence of decreasing baryon-to-DM surface density with decreasing luminosity. We suggest that this is a sequence of decreasing baryon retention vs. supernova-driven losses or decreasing baryon capture after cosmological reionization. (2) Structural differences between S+Im and Sph galaxies are small. Both are affected mostly by the physics that controls baryon depletion. (3) There is a linear correlation between the maximum rotation velocities of baryonic disks and the outer circular velocities V_circ of test particles in their DM halos. Baryons become unimportant at V_circ = 42 +- 4 km/s. Lower-mass galaxies are dim or dark. (4) We find that, absent baryon depletion and with all baryons converted into stars, dSph galaxies would be brighter by ~ 4.6 mag and dIm galaxies would be brighter by ~ 3.5 mag. Both have DM halos that are massive enough to help to solve the "Too Big To Fail" problem with DM galaxy formation. (5) We suggest that there exist many galaxies that are too dark to be discovered by current techniques, as implied by cold DM theory. (6) Central surface densities of DM halos are constant from M_B = -5 to -22. This implies a Faber-Jackson law with DM halo mass M proportional to (halo velocity dispersion)**4.
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