31-05-2017 13:30 hs.
Hunting the dark galaxies / Cazando a las galaxias oscuras
Dr. Narendra Nath Patra – National Center for Radio Astrophysics (NCRA)
Assuming a hydrostatic equilibrium condition in an HI cloud we set up and solve the Poisson’s equation to calculate the observed HI structure. We construct an ‘iterative’ method to estimate the intrinsic velocity dispersion profile (which is not a directly observable quantity) and solve the hydrostatic equilibrium equation. We further use this method to identify if an HI cloud is hosted by a dark matter halo or not. Our simulation shows that the presence of a low mass dark matter halo in an HI cloud can alter the hydrostatic equilibrium significantly such as to introduce an easily detectable change in the surface density profile. We apply our method to Leo-T, a suspected dark galaxy and found that it is hosted by a dark matter halo of mass ~ 8.8 x 10^6 M_sun. We also estimated the dark matter halo parameters of Leo-T by solving HI structure in a large number of pseudo-isothermal halos and comparing the resulting HI surface density profiles to the observed one. The dark matter halo parameters found to be rho_0 ~ 0.25 M_sun/pc^3 and r_s ~ 141 parsec. Our analysis shows that, the `mass’ of the dark matter halo primarily determines the HI distribution of a cloud under hydrostatic equilibrium. Our method could be used to identify potential dark galaxies from a population of Compact or Ultra Compact High Velocity Clouds.