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Astronomy Colloquium: Narendranath Patra

Date: Thu. September 12th, 2019, 3:00 pm-4:00 pm
Location: Sears 552

The missing satellite problem and the dark galaxies

Narendranath Patra (Raman Research Institute)

Though the Lambda-CDM model of cosmology has been immensely successful in explaining the observable universe at large scales, several inconsistencies yet persist between its predictions and observations in smaller scales. The `missing satellite’ problem is one of the significant ones. The number of predicted small galaxies within the virial radii of massive galaxies is found to be an order of magnitudes higher than what is observed as luminous satellites of such galaxies. Out of many proposed solutions to this problem, the ‘HVC-minihalo’ hypothesis is one of the promising ones. In this hypothesis, it is proposed that many of the primordial mini-halos (satellite galaxies) are disguised as the Compact/Ultra-compact High Velocity Clouds (CHVCs/UCHVCs). I will describe a formalism based on the hydrostatic equilibrium condition in an HI cloud to identify the mini-halos/satellite galaxies from the pool of CHVCs/UCHVCs. I will further apply this formalism to a recently discovered dwarf galaxy Leo-T and show that it needs a dark matter halo of a mass of ~ 3×10^6 M_sun to be stable under hydrostatic equilibrium. Using a Monte-Carlo approach, I also estimate the dark matter halo parameters for Leo-T and show that the ‘mass’ of a dark matter halo rather than its ‘structure’ primarily dictates the hydrostatic structure.

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