Modelling optically dark clouds in clusters of galaxies
Advisor: Richard Wünsch (AI CAS) Co-advisor: Rhys Taylor (AI CAS) Funding: base scholarship supplemented from a national grant until the end of 2021. The net income will be at least 20 000 CZK/month until the end of 2021. Extension of the supplement beyond 2021 depends on availability of funds. Website: http://galaxy.asu.cas.cz/page/projects
Surveys of the Virgo cluster of galaxies in the neutral hydrogen 21cm line carried out with the 300 meter single-dish Arecibo radiotelescope have discovered a new class of objects. They are spatially unresolved clouds with masses of order 10^7 Solar masses and velocity dispersions more than hundred km/s (see the attached spectrum). Such high velocity dispersions suggest that dynamical masses of these objects are much higher (by factor 100-1000), in the range typical for galaxies. However, deep optical observations show no signs of galaxies (i.e stars) at those positions at all. One hypothesis of the origin of these objects suggests that they are in fact so called dark galaxies, i.e. dark matter halos that did not accrete enough baryons to form stars, predicted to exist by cosmological simulations. This hypothesis is supported by a recent discovery of the ultra diffuse galaxies consisting of a stellar population of the very low surface density embedded in a dark matter halo ~1000 times more massive that the stellar component. The optically dark clouds of the neutral hydrogen would be their natural extension - more extreme objects with even lower fraction of baryons leading to star formation below the detectable limit.
The aim of this project is to perform hydrodynamic simulations of the neutral hydrogen clouds embedded in dark matter halos. They will interact with the hot rarefied gas filling the galaxy clusters leading to an important question: under which conditions the neutral hydrogen clouds can survive. Another interesting question is what are the conditions necessary to prevent star formation inside those clouds. The numerical model will be based on the hydrodynamic code Flash which is widely used within our research group. Most of the physical modules needed for the given problem are ready as they were implemented to test another hypothesis of the origin of these clouds - a turbulent sphere in equilibrium with the hot ambient gas (see the attached figure). The comparison with the Arecibo data will be done with the help of R. Taylor who has an extensive experience with analysing the Arecibo data. A new neutral hydrogen survey has just been finished (WAVES) and discoveries of more such objects are expected.