Hydrogen emission useful in measuring temperature of Dark Matter
20 August 2013
To more accurately constrain Dark Matter models, an international research team, led by our new CAASTRO member Danail Obreschkow (ICRAR-UWA), recently published a detailed analysis of galaxy rotation values as obtained by observational and simulated data. Obreschkow et al. compared data from HIPASS (HI Parkes All Sky Survey), a blind search for HI emission, with simulations from S3-SAX, the first semi-analytic cosmological model of resolved HI emission lines of galaxies based on the Millennium simulation.
Key to their comparison was to apply the same set of selection criteria to both data sets, such as limits of galaxy inclination angles, which reduced the number of samples available in each set but yielded a high level of confidence into the statistics of HI line profiles. They counted and binned the number of galaxies according to specific properties: HI linewidth, circular velocity, and HI mass.
All three properties were found to be reasonably consistent across the two data sets. Linewidth stood out as the best match where only the largest values in the observational data were identified as confused sources: galaxies in the same telescope beam with HI line profiles overlapping in frequency. HI mass counts were moderately consistent with a small bump at ~4 x 108 solar masses – which was found to be a feature of this particular semi-analytic model, absent in other models building on the Millennium simulation. Only velocity values differed more strongly, with sources at low velocities (<50km s-1) having been identified as optically faint or irregular with a wrongly identified inclination angle.
Source counts were generally in better agreement than space densities, due to the fact that, at the high end of the velocity function, HIPASS was dominated by gas-poor, fast-rotating, early-type galaxies, simply not detectable by HIPASS. The research team then compared their HI linewidth results with three different Dark Matter models (Cold Dark Matter and two Warm Dark Matter of different particle mass). If all free parameters were independently constrained, HI linewidth could be used to differentiate between models and was best aligned with the Cold Dark Matter model.