The mildly active nuclear region in the galaxy M81 (henceforth, M81‹) is one of
the nearest low-luminosity active galactic nuclei (LLAGN) whose structure is marginally
resolved when probed with Very Long Baseline Interferometry (VLBI). Motivated by the
way resolved radio sources usually appear on the smallest scales, i.e., a core with a one-
sided jet structure, we developed a strictly one-sided, asymmetric triangular model, which
we call ASYM, with brightness distribution along a line segment on the sky, with maximum
brightness at one end of the segment fading linearly to zero at the other end. The ASYM
model is compared and contrasted with an elliptical Gaussian model (hereafter, GAUS), by
fitting existing VLBI data of M81‹ at 39 epochs between 1993 and 2003 at 8.4 and 5.0 GHz
with the two models. Contrary to what we envisioned, we find that for 77% of our epochs,
a simple GAUS model fits the visibility data of M81‹ at 8.4 GHz better (i.e., has a lower
reduced 2) than the ASYM model. We conclude that M81‹ is not strictly a one-sided,
asymmetric jetted source; as is thought to be the case for the majority of AGN observed
at VLBI scales. Our results imply that M81‹ is mostly symmetrical with a significant jet
counterpart which cannot be overlooked. / School of Interdisciplinary Research and Graduate Studies (SIRGS) / M. Sc. (Astronomy)
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:unisa/oai:uir.unisa.ac.za:10500/23817 |
| Date | 04 1900 |
| Creators | Ramessur, Arvind |
| Contributors | Leeuw, L. L., Bietenholtz, M. |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | 1 online resource (xiv, 91 leaves) : illustrations (some color), graphs (some color), map |
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