A new multi-wavelength analysis of 620 galaxies attempts to disentangle physical phenomena contributing to the galaxies brightness in radio waves.
To properly understand the evolution of galaxies since the first galaxies I the early universe, we need to observe galaxies in different wavelengths, including visible light (optical), infrared, x-ray and radio. Each window of light “sees” different contributions to the galaxies’ brightness in that light. Optical and infrared brightness typically shows how much star formation activity – how many new stars are being formed – in a galaxy. In radio, often the brightest things we see are active galactic nuclei, when supermassive black holes in the centre of galaxies create powerful jets of matter that shine bright in radio.
Understanding the different sources of light – and possible dimming by dust and other mediums – is a complex disentanglement exercise where physically-motivated models of the phenomena are compared to observations.
In this paper, the team found that in faint radio sources, galaxies that emit faintly in radio, they are able to find a relationship with star formation activity taking place in the galaxy. Those faint sources are just observable with the newest radio telescopes such as the GMRT in India (used for this study) and the MeerKAT in South Africa (used for upcoming studies). In so-called radio loud sources – those that shine bright in radio waves – that relationship was however contaminated, and the team suspects that this comes from radio jets.
While their findings are coherent with many multi-wavelength studies of galaxy evolution, they conclude that a better classification of galaxies between radio quiet, radio loud and star forming needs to be developed, that better depicts the physical phenomena, like the presence of jets from the nucleus.
This study shows just how complex it is to derive deep insights of the evolution of galaxies over cosmic time, but such knowledge is key to understanding the universe as we see it today.
The Evolution of the Low-Frequency Radio AGN Population to z≃1.5 in the ELAIS N1 Field
E. F. Ocran, A. R. Taylor, M. Vaccari, C.H. Ishwara-Chandra, I. Prandoni, M. Prescott, C. Mancuso
Accepted for publication in MNRAS
Image credit: ESA/NASA Star formation in dwarf galaxy NGC1140 captured by the Hubble Space Telescope.