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A comparison of 24μm and 6cm star-formation tracers in the spiral galaxy M83

Peters, Josephine

[Thesis]. Manchester, UK: The University of Manchester; 2015.

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Abstract

24μm and 6cm emission are both regarded as star formation tracers, but relate to different epochs in the lifetimes of massive stars (greater than or equal to 8 M_solar). 24 μm emission traces their birth and 6cm synchrotron emission traces the supernova explosions that occur 2-15 Myr later. The maintenance of the structure of spiral galaxies is widely explained by rotating gravitational potential wells called spiral density waves (SDWs) which predict older stars to appear downstream from younger stars. By comparing these two emissions in a galaxy with a strong spiral structure at sub-kpc scales insight into the movement of stars and thus influence of SDWs can be obtained. Comparing 24μm and 6cm emission also investigates the limits of the far infrared-radio correlation which has been seen to hold for a diverse range of galaxies at various redshifts.In this thesis, relative intensity profiles of regions sampling the spiral arms of grand design spiral galaxy M83 have been compared at 24 μm and 6cm wavelengths. The results show no offset between the two emission mechanisms at 37 pc scales in the spiral arms. Averaged profiles of the typical spiral arm regions show a broadening in the radio emission compared to the infrared which is consistent with but smaller than the average smearing of the radio emission recorded by previous studies (by 0.4 kpc). I conclude that the SDW in M83 is not strong enough to effect stars within star forming regions at 10 Myr timescales and that the far-infrared-radio correlation holds at smaller scales than previously recorded (37 pc). Better radio observations are required to investigate the behaviour of massive stars either side of the arms and the smearing of the radio relative to the infrared emission by including extended emission.