Master thesis project (~ 6 months):

The duty cycle of radio AGN across the galaxy population

Layout of the COSMOS field (2 sq deg) as compared to the full Moon and to other deep extragalactic fields.

Scientific Background

Understanding what drives the interplay between supermassive black holes (SMBHs) and their host galaxies is among the most debated topics in extragalactic astrophysics. The Cosmic Evolution Survey (COSMOS, Scoville et al. 2007) provide an excellent asset for tackling this question from a statistical and multi-wavelength perspective, owing to its exquisite baseline of ancillary photometry and redshifts.


Active Galactic Nuclei (AGN) represent the brightest phase of the SMBH duty cycle, although they are very rare (~1% of all SMBHs, according to simulations; e.g. Novak et al. 2011). This is because AGN might flicker on and off by several orders of magnitude over relatively short timescales (~10^5 yr; e.g. Shawinski et al. 2015) as compared to galaxy star formation (~10^8 yr). 


Radio emitting AGN manifest themselves by means of jets and/or lobe structures that can reach out to Mpc scales. Studying the incidence and evolution of radio AGN across the galaxy population can therefore help us understand the role of mechanical AGN feedback in quenching (and/or triggering) star formation in the most massive galaxies, as well as to elucidate the role of the host galaxy in triggering radio AGN activity.

Duty cycle of radio AGN (y-axis) as a function of galaxy stellar mass (x-axis) and colour-coded by redshift. See Delvecchio et al. (2022) for details.

However, radio AGN are not uniformly seen across all galaxies. In other words, the fraction of galaxies containing an AGN (i.e. AGN duty cycle) is likely dependent by a number of factors, such as redshift and galaxy stellar mass (Delvecchio et al. 2022). Specifically, more massive galaxies display, on average, a higher AGN duty cycle, raising from <1% at  M*~10^10 Msun up to 10% at M*~10^11 Msun, and slightly increasing with redshift (see Figure on the left). 

Why? These relations might hold important clues on the triggering mechanisms of AGN activity. 

Goal of this project: 

Building on previous studies which have looked at the incidence of radio AGN across specific sub-samples of galaxies (e.g. Delvecchio et al. 2022), the proposed thesis project will be aimed at mapping radio AGN activity across a full M*-selected galaxy sample, including passive, main sequence and starburst galaxies, at different stellar masses and across a wide redshift range (0.1<z<4.0). 

Method

Deliverables: