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Colloquia

The Astronomy department organises regular research colloquia. Visiting academics, staff, postdocs and postgraduate students who have recently completed their dissertation present colloquia in the department. 


Thursday 24 January 2019 [14:00 - 15:00]

Speaker: Dr Jack Radcliffe (University of Groningen, the Netherlands)

Title: Finding AGN in the faint radio sky - a high resolution perspective

Abstract: It is now widely accepted that the evolution of galaxies and the growth of the central supermassive black hole (SMBH) are intimately connected. Those SMBH which are active (hence Active Galactic Nuclei/AGN) have been shown to influence the host galaxy and such feedback mechanisms are also required by simulations. This makes understanding the abundances and influence of AGN in distant galaxies one of the hottest research topics around. While other multi-wavelength studies are invariantly affected by dust; radio, fuelled by the burgeoning capabilities of modern arrays, can provide a dust-free window into star-formation and AGN activity. However, many radio surveys are often have resolutions in excess of arcsecond which are insufficient to separate AGN and star-formation activity. To infer the existence of an AGN relies multi-wavelength diagnostics (e.g. X-rays, infra-red, radio-excess) which are often unreliable and incomplete. 

There is one key weapon missing from the AGN identification arsenal namely high resolution radio observations. Here, we can isolate high brightness temperature objects (>1E5 K) which can only be attributed to AGN in distant galaxies. In this talk, I will dispel the myth that high resolution radio surveys are constrained to small fields of view and I'll outline the developments that have made surveying degrees of the sky at milliarcsecond resolutions easy and routine (VLBI astronomers are not the black-belt radio astronomers anymore!). Using the GOODS-N field as an example, I will outline the pros and cons of AGN selection via high resolution radio observations followed by some results from the upcoming first data release from the e-MERLIN Galaxy Evolution (e-MERGE) survey. This survey provides a multi-wavelength, but crucially multi-resolution insight into the faint microJy radio source population. I'll conclude with a look to the future and the planned high resolution efforts in MeerKAT’s own deep field legacy survey, MIGHTEE. 


Tuesday 22 January 2019 [14:00 - 15:00]

Speaker: Brenda Namumba (UCT Astronomy)

Title: HI observations of Local Group dwarf  galaxies: HI distribution, kinematics, and star formation thresholds

Abstract: We investigate the HI properties of 3 dwarf irregular galaxies and one blue compact dwarf galaxy of the Local Group. The data set of each dwarf irregular galaxy was obtained with the Karoo Array Telescope (KAT-7) while the blue compact dwarf was observed with the Dominion Radio Astrophysical Observatory (DRAO) synthesis telescope. The KAT-7 observations has revealed 23% more neutral hydrogen (HI) gas mass in the outer disk of NGC 6822 than previous studies. An overestimate of the HI extent previously reported for Sextans A has been verified.  For IC 10, the complex HI features detected with DRAO are by a factor of  2 more extended than previous interferometric HI studies. The KAT-7 observations allow the measurement of the rotation curve of NGC 6822 out to 5.8 kpc, ~1 kpc further than existing measurements. The rotation curves of Sextans A and B are seen to decline in the outer parts. In the inner disk, the rotation curve of IC 10 rises steeply, then flattens until the last point where it rises again, with a maximum velocity of 30 km/s. The dark matter distribution in dwarf irregular galaxies is better described by the ISO model when a mass to light ratio of 0.2 is used. The galaxies are dark matter dominated at all radii. In the case of IC 10, the kinematics of the inner disk can be described without the need of a dark matter halo. This result does not exclude the possible presence of dark matter on larger scales.  The critical densities for gravitational instabilities are calculated using the Toomre-Q and cloud-growth based on shear criterion. In all cases, we find that in regions of star formation, the cloud growth criterion based on shear explains better the star formation.


Venue: AST seminar room (RW James building, room 5.40) - UCT upper campus

Co-ordinator: Dr Nathan Deg

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