KAT-7 Science Verification: Hi Observations of NGC 3109 - Understanding its Kinematics and Mass Distribution

Location: 
Auditorium on the 2nd floor of the SKA South Africa office
Date: 
Thu, 02/05/2013 - 13:00 - 14:00
Speaker: 
Claude Carignan

Hi observations of the Magellanic-type spiral NGC 3109, obtained with the seven dish Karoo Array Telescope (KAT–7), are used to analyse its mass distribution. Our results are compared to what is obtained using VLA data. KAT–7 is the precursor of the SKA pathfinder MeerKAT, which is under construction. The short baselines and low system temperature of the telescope make it sensitive to large scale low surface brightness emission. The new observations with KAT–7 allow the measurement of the rotation curve of NGC 3109 out to 32′, doubling the angular extent of existing measurements. A total HI mass of 4.6 ×108 M⊙ is derived, 40% more than what was detected by VLA observations.

The observationally motivated pseudo-isothermal dark matter (DM) halo model can reproduce very well the observed rotation curve while the cosmologically motivated NFW DM model gives a much poorer fit to the data. While having a more accurate gas distribution has reduced the discrepancy between the observed RC and the MOdified Newtonian Dynamics (MOND) models, this is done at the expense of having to use unrealistic mass–to–light ratios and/or very large values for the universal constant a0. Different distances or HI content cannot reconcile MOND with the observed kinematics, in view of the small errors on those two quantities. This result for NGC 3109 continues to pose a serious challenge to the MOND theory.