Extended Radio Emission and Star Formation in Cluster Spiral Galaxies

Internship made during my first year as an engineering student at Télécom Physique Strasbourg. Study of radio halos and star formation in Virgo Cluster galaxies using VLA data.

Abstract :

Radio waves emitted by galaxies give us precious informations on their shape, gaz diffusion method… Thanks to theVLA (Very Large Array), radio data from 6 galaxies in the Virgo Cluster have been collected at 6 and 20cm. After several modifications on the radio map (deprojections, convolutions…), it is possible to find a function (exponential or gaussian, modified or not) that fits the shape of the galaxy’s radio halo.
To do that, the difference between the model and observations is calculated, functions that have the least difference are more thoroughly studied throughout different graphs. First, a graph that shows the height of the galaxy in kpc indicates right away if this height is physically plausible or not. Then, a “slice by slice” graph of the galaxy offers a precise way of determining which of the functions studied is the best. Finally, a graph of residuals gives a very visual way of comparing functions.

After finding the best function for each of the 6 galaxies, we can note the heights and radio flux inside the thin disk and radio halo to make a more general study. CHANG-ES showed the linear link between height and radio halo height, the galaxies studied here seem to also follow this link. Moreover, another relation found here show the linear decrease of SFR and radio flux, the higher the SFR, the lower the radio flux. This last result needs to be confirmed by a larger study.

Keywords : Virgo Cluster, radio halo, star formation rate (SFR), morphological fitting, observational modeling.