[Paper Review] Radio-loud AGN in the first LoTSS data release: The lifetimes and environmental impact of jet-driven sources

M. J. Hardcastle, W. L. Williams+21 more|UvA-DARE (University of Amsterdam)|Nov 19, 2018

Galaxies: Formation, Evolution, Phenomena119 references49 citations

TL;DR

The paper builds a large RLAGN sample from LoTSS DR1 to study RLAGN lifetimes, jet powers, and their impact on environments, finding that local RLAGN can offset X-ray cooling in groups/clusters and that giant/LERG-like sources represent an old tail of the population.

ABSTRACT

We constructed a sample of 23,344 radio-loud active galactic nuclei (RLAGN) from the catalogue derived from the LOFAR Two-Metre Sky Survey (LoTSS) survey of the HETDEX Spring field. Although separating AGN from star-forming galaxies remains challenging, the combination of spectroscopic and photometric techniques we used gives us one of the largest available samples of candidate RLAGN. We used the sample, combined with recently developed analytical models, to investigate the lifetime distribution of RLAGN. We show that large or giant powerful RLAGN are probably the old tail of the general RLAGN population, but that the low-luminosity RLAGN candidates in our sample, many of which have sizes $<100$ kpc, either require a very different lifetime distribution or have different jet physics from the more powerful objects. We then used analytical models to develop a method of estimating jet kinetic powers for our candidate objects and constructed a jet kinetic luminosity function based on these estimates. These values can be compared to observational quantities, such as the integrated radiative luminosity of groups and clusters, and to the predictions from models of RLAGN feedback in galaxy formation and evolution. In particular, we show that RLAGN in the local Universe are able to supply all the energy required per comoving unit volume to counterbalance X-ray radiative losses from groups and clusters and thus prevent the hot gas from cooling. Our computation of the kinetic luminosity density of local RLAGN is in good agreement with other recent observational estimates and with models of galaxy formation.

Motivation & Objective

• Motivate the study of radio-loud AGN (RLAGN) as regulators of hot gas in groups and clusters.
• Construct a large RLAGN sample from LoTSS DR1 with optical/IR identifications and redshifts.
• Model RLAGN lifetimes to interpret observed size distributions.
• Estimate jet kinetic powers for RLAGN and build a local jet kinetic luminosity function.
• Assess the role of RLAGN feedback in balancing X-ray radiative losses in the local universe.

Proposed method

• Assemble a sample of 23,344 RLAGN from the LoTSS DR1 HETDEX field, using spectroscopic and photometric redshifts with WISE/PanSTARRS optical IDs.
• Define simple and composite radio sources with sizes based on PyBDSF fits and convex-hull extents for composites.
• Apply an optical/IR cross-match and redshift filtering to obtain the FCOZG and related samples.
• Use analytical dynamical models of radio source evolution to infer jet powers from observed radio properties.
• Construct the jet kinetic luminosity function in the local universe and compare to radiative outputs of groups/clusters and to galaxy formation models.
• Discuss RLAGN selection challenges, notably separating AGN from star-forming galaxies, using Sabater et al. diagnostic schemes.

Experimental results

Research questions

• RQ1 What is the lifetime distribution of RLAGN, and how does it relate to source size and luminosity?
• RQ2 Can a dynamical model of radio source evolution recover jet kinetic powers from LOFAR observations for a large RLAGN sample?
• RQ3 What is the local jet kinetic luminosity function and how does it compare to the radiative energy output of groups and clusters?
• RQ4 Do large or giant powerful RLAGN represent a distinct population with different lifetimes or jet physics compared to low-luminosity RLAGN?
• RQ5 Do RLAGN in the local universe provide sufficient energy to offset X-ray radiative losses in groups and clusters?

Key findings

• Large LoTSS DR1 RLAGN sample enables lifetime and jet-power inference for a wide population.
• Large/giant powerful RLAGN are likely the old tail of the RLAGN population, while many low-luminosity RLAGN may require different lifetimes or jet physics.
• A dynamical model can infer jet kinetic powers from radio data, enabling a local jet kinetic luminosity function.
• RLAGN in the local universe can supply the energy per comoving volume needed to counterbalance X-ray cooling in groups/clusters.
• The computed local jet kinetic luminosity density agrees with other observational estimates and with galaxy formation models.