A near infrared Tully-Fisher survey behind the Galactic plane

Williams, Wendy L

A near infrared Tully-Fisher survey behind the Galactic plane

Master Thesis

2011

Publisher

University of Cape Town

Department

Department of Astronomy

Faculty

Faculty of Science

Abstract

This thesis presents a first look at the directly measured peculiar velocity low field within the Southern Zone of Avoidance. Large peculiar velocity surveys are hampered by the low detection rates and poor data quality of galaxies in the Zone of Avoidance (ZoA) where the obscuring effects of dust and stars in the Milky Way prevent the detection of galaxies across 10 - 20% of the sky. Moreover, dynamically significant structures lie hidden behind the Galactic plane. Dedicated surveys have been conducted to unveil the mass distribution within the ZoA. The ZoA peculiar velocity survey presented here makes use of deep systematic Hi survey data, new high resolution Hi observations and new deep near infrared (NIR) observations to provide high fidelity measurements for use with the NIR Tully-Fisher relation. Hi observations reveal galaxies where both optical and NIR surveys fail. The HIZOA deep Hi survey conducted at the 64m Parkes telescope revealed ~ 1 000 galaxies in the southern ZoA (Henning et al. 2005, Donley et al. 2005, Shafi 2008) . Accurate Hi linewidths are required for the measurement of Tully-Fisher distances. The fidelity of the Hi linewidths depends both on the velocity resolution and signal-to-noise ratio of the spectrum. New Hi data were therefore acquired at Parkes for 82 galaxies, providing a mean factor ~ 3:4 improvement in the fractional uncertainties in the 50% linewidth. A deep NIR follow-up survey of HIZOA galaxies within 6000 kms -1 was conducted using the 1:4m IRSF telescope using the SIRIUS camera for simultaneous imaging in the near infrared J, H and Ks bands. These deep, high resolution NIR observations are able to penetrate the dust and deblend foreground stars making it possible to detect the NIR counterparts for the Hi-detected galaxies. The survey images have an exposure time of 10 min resulting in a limiting magnitude approximately 2m deeper than the 2MASS survey and the SIRIUS camera has a 00:045 pix -1 pixel scale and 7:07 _ 7:07 field of view. The three-colour images were searched by eye for possible NIR-Hi counterparts resulting in a galaxy catalogue containing 567 galaxies in 422 fields. Of these fields the NIR counterparts were confirmed for 356 Hi galaxies. Algorithms for the subtraction of foreground stars were developed and used to obtain accurate surface photometry of each source. The NIR galaxy colours were used to investigate the nature of extinction in the ZoA. The results show that on average across the southern ZoA, the true extinction is 82% of the DIRBE/IRAS values provided by Schlegel et al. (1998). There is no significant variation in A preliminary peculiar velocity flowfield within the southern ZoA is derived by combining the Hi and NIR data. A strong flow towards the Great Attractor (GA) is observed. This flow field also shows possible indications of backside infall onto the GA, showing that the GA does indeed play an important role in the motion of the Local Group. The success of this study demonstrates the feasibility of further TF peculiar velocity studies in the ZoA, notably the extension of this survey to greater distances and an improved calibration of the TF relation for use in the ZoA.

Keywords

Astronomy

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