| Description: | NGC 4203 is a nearby lenticular galaxy surrounded by an unusually large HI disc. In a paper now accepted for publication in MNRAS, a team lead by a PhD student Mustafa Yildiz (Kapteyn Astronomical Institute) used the WSRT to study this large gas reservoir. They find that the gas system (shown in blue in the above image) consists of two separate components: an inner star-forming ring and an outer HI disc. The inner ring contains metal-rich gas and a large amount of dust (red in the image). In contrast, the outer disc is likely to be poor in metals and dust. While the star-formation efficiency in the inner HI ring is comparable to that typical of the inner regions of spiral galaxies, it is much lower in the outer disc -- even in regions with high gas density. Nevertheless, the star formation efficiency in the outer HI disc is still consistent with that of the outer regions of spiral galaxies. These differences might be explained with different gas origins such as stellar mass loss for the inner regions and accretion from the intergalactic medium for the outer disc. The deep optical image also reveals a dwarf galaxy interacting with NGC 4203. Data for this study were collected with the WSRT and CFHT telescopes.
You can find more details in Star formation in the outer regions of the early type galaxy NGC 4203, Yildiz, M.K., Serra, P., Oosterloo, T.A., Peletier, R.F., Morganti, R., Duc, P.-A., Cuillandre, J.-C., Karabal, E. 2015, MNRAS, in press http://arxiv.org/abs/1505.02981
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