Speaker
Description
In galaxy clusters, we have observed that star-forming spiral galaxies can evolve into passive S0 galaxies. This process, known as 'environmental processing', is primarily driven by the ram pressure exerted by the intracluster medium (ICM) on the galaxies that enter the cluster. This pressure can strip a galaxy of its interstellar medium (ISM), which can stop its star formation. Recent observations of galaxy clusters using LOFAR have revealed that an increasing number of spiral galaxies host radio-continuum tails which can extend for tens of kpc outside of the stellar disk. These tails are caused by the large-scale ISM outflows that are induced by the ram pressure. The gradients in the synchrotron emission, produced by the relativistic electrons embedded in the stripped ISM clouds, can constrain the velocity of the ISM outflows from the stellar disk. To test this hypothesis, a semi-empirical model was developed based on the pure synchrotron cooling of a radio plasma moving along the stripping direction with a uniform velocity. This model can reproduce the multi-frequency radio continuum emission of the ram-pressure-induced outflows. In an exploratory study on seven galaxies in Abell 2255 (z=0.08012), deep LOFAR and uGMRT observations at 144 and 400 MHz were used to showcase the results. The model successfully reproduces the observed properties of the radio-continuum tails, with projected outflow velocities ranging from 160 to 430 km/s. This new piece of information can help us understand the poorly-known physics of the interplay between the stripped ISM and the surrounding ICM in the stripped tails of these galaxies.
Additionally, this semi-empirical model can expand the use of radio observations of ram-pressure-stripped galaxies in clusters and groups. With the advent of SKA, the availability of these observations is expected to grow over the coming years. By combining deep radio, X-ray, and optical observations, we will be able to quantitatively characterize the role of ram pressure stripping in quenching the galaxies in dense environments.
