The main topic of my thesis (anticipated finish date Summer 2005) is a study of the velocity field of the local supercluster. I will be combining Tully-Fisher data (from the soon to be completed SFI++ sample) with published data on more local galaxies with primary distances (eg. Ceheids, TRGB, SBF). I will fit a 'Multiattractor Model' to this sample. The bulk of the velocity field in the local supercluster can be fit by assuming infall onto the Virgo Cluster (see the image on left), however there are still unexplained motions which can be fit by other more distance attractors - hence a multiattractor model offers the best simple solution to fit the velocity field.
This sample will represent an increase in the number of tracers in the local universe by several factors (the largest sample to date is the ~300 SBF galaxies in Tonry et al. 2000) and so should provide the best option for finding distances to local galaxies if they have not had their distance measured independent of their redshift.
|
| Shown is our estimated adjustement to the published HIMF from the HIPASS BGC if Hubble flow distances are not assumed (as they are for most of the galaxies in the published version). With this adjustment the HIPASS result becomes consistent with the earlier HIMF from Rosenberg & Schneider (who used distances corrected for local flows with a multiattractor model). |
Despite the fact that it is well known that local deviations from Hubble flow can be large, there is a tendency for authors to use Hubble flow distances (ie. VLG/H0) as the simplest estimator for the distance to a galaxy, when no measured distance is available. This can have serious consequences - as galactic parameters which depend on distance (like luminosity, HI mass, or linear size) can be systematically wrong. This work showed that a good understanding of the local velocity field is necessary to understand the properties of local galaxies, providing some of the justification for the topic of my thesis.
For this work we constructed mock catalogues of HI surveys to investigate the impact neglecting peculiar velocities can have on measurements of the HI mass function. We found that the low mass slope of the HI mass function can be in error by large amounts, depending on the survey volume and depth. This has an impact on the recent disagreements of the slope of the low mass end of the HIMF - which can be mostly explained away by this effect.