Unravelling lifecycles and physics of radio-loud AGN in the SKA Era

Kapińska, A. D.; Hardcastle, M. J.; Jackson, C. A.; An, Tao; Baan, Willem A.; Jarvis, Matt J.

doi:10.22323/1.215.0173

Cited by 23 publications

(15 citation statements)

References 107 publications

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“…In any case, within the stated errors, the injection index is in approximate agreement with studies of active radio galaxies (Harwood et al 2015(Harwood et al , 2016. Furthermore, simulations suggest (Kapinska et al 2015) that the observed integrated spectrum can steepen owing to mixing of electron populations.…”

Section: Discussionsupporting

confidence: 85%

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Shulevski

Morganti

Harwood

et al. 2017

A&A

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We have observed the steep spectrum radio source B2 0924+30 using the LOw Frequency ARray (LOFAR) telescope. Hosted by a z=0.026 elliptical galaxy, it has a relatively large angular size of 12 (corresponding to 360 kpc projected linear size) and a morphology reminiscent of a remnant Fanaroff-Riley type II (FRII) radio galaxy. Studying active galactic nuclei (AGN) radio remnants can give us insight into the time-scales involved into the episodic gas accretion by AGNs and their dependence on the AGN host environment. The proximity of the radio galaxy allows us to make detailed studies of its radio structure and map its spectral index and radiative age distribution. We combine LOFAR and archival images to study the spectral properties at a spatial resolution of 1 . We derive low frequency spectral index maps and use synchrotron ageing models to infer ages for different regions of the source. Thus, we are able to extend the spectral ageing studies into a hitherto unexplored frequency band, adding more robustness to our results. Our detailed spectral index mapping, while agreeing with earlier lower resolution studies, shows flattening of the spectral index towards the outer edges of the lobes. The spectral index of the lobes is α 609 140 ∼ −1 and gradually steepens to α 609 140 ∼ −1.8 moving towards the inner edges of the lobes. Using radiative ageing model fitting we show that the AGN activity ceased around 50 Myr ago. We note that the outer regions of the lobes are younger than the inner regions which is interpreted as a sign that those regions are remnant hotspots. We demonstrate the usefulness of maps of AGN radio remnants taken at low frequencies and suggest caution over the interpretation of spectral ages derived from integrated flux density measurements versus age mapping. The spectral index properties as well as the derived ages of B2 0924+30 are consistent with it being an FRII AGN radio remnant. LOFAR data are proving to be instrumental in extending our studies to the lowest radio frequencies and enabling analysis of the oldest source regions.

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Section: Discussionsupporting

confidence: 85%

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Shulevski

Morganti

Harwood

et al. 2017

A&A

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“…Rottgering et al 2006, Kapinska et al 2015 and LOFAR now gives us the opportunity to investigate whether this is the case. However, precise modelling of the evolution of remnants and predicting the number of remnants in the radio sky remains challenging.…”

Section: Simulating the Population Of Active And Remnant Fri Radio Gamentioning

confidence: 99%

“…Firstly, the modelling of the radio spectrum of remnant sources provides constraints on the timescales of activity and quiescence of the radio source, i.e. on its duty cycle, and on their dynamical evolution (Kardashev 1962;Murgia et al 2011;Kaiser 2009;Kapinska et al 2015;Turner & Shabala 2015). Secondly, a better knowledge of the energetics of these objects can help quantify the role of radio AGN feedback, as well as give new insights into the formation of radio sources in galaxy clusters such as relics, brienza@astron.nl halos, and phoenixes (Slee et al 2001;Enßlin & Brüggen 2002;van Weeren et al 2009;de Gasperin et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Search and modelling of remnant radio galaxies in the LOFAR Lockman Hole field

Brienza

Godfrey

Morganti

et al. 2017

A&A

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178

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Context. The phase of radio galaxy evolution after the jets have switched off, often referred to as the remnant phase, is poorly understood and very few sources in this phase are known. Aims. In this work we present an extensive search for remnant radio galaxies in the Lockman Hole, a well-studied extragalactic field. We create mock catalogues of low-power radio galaxies based on Monte Carlo simulations to derive first-order predictions of the fraction of remnants in radio flux limited samples for comparison with our Lockman-Hole sample. Methods. Our search for remnant radio galaxies is based on LOFAR observations at 150 MHz combined with public survey data at higher frequencies. To enhance the selection process, and obtain a more complete picture of the remnant population, we use spectral criteria such as ultra-steep spectral index and high spectral curvature, and morphological criteria such as low radio core prominence and relaxed shapes to identify candidate remnant radio galaxies. Mock catalogues of radio galaxies are created based on existing spectral and dynamical evolution models combined with observed source properties. Results. We have identified 23 candidate remnant radio galaxies which cover a variety of morphologies and spectral characteristics. We suggest that these different properties are related to different stages of the remnant evolution. We find that ultra-steep spectrum remnants represent only a fraction of our remnant sample suggesting a very rapid luminosity evolution of the radio plasma. Results from mock catalogues demonstrate the importance of dynamical evolution in the remnant phase of low-power radio galaxies to obtain fractions of remnant sources consistent with our observations. Moreover, these results confirm that ultra-steep spectrum remnants represent only a small subset of the entire population (∼50%) when frequencies higher than 1400 MHz are not included in the selection process, and that they are biased towards old ages.

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“…During its first stage of completion, the Square Kilometre Array (SKA; Dewdney et al 2009) will include two instruments: SKA1-LOW (50 -350 MHz) and SKA1-MID (350 -14 GHz) (see e.g. Kapinska et al 2015). Wide and deep radio continuum surveys with the SKA will increase the number of low redshift radio AGN by orders of magnitude and will allow us to detect radio quiet AGN of luminosities as low as log L 1 GHz ∼ 23 out to redshifts of z ∼ 6 (Smolcic et al 2015).…”

Section: Future Work and Surveysmentioning

confidence: 99%

AGNs and Their Host Galaxies in the Local Universe: Two Mass-independent Eddington Ratio Distribution Functions Characterize Black Hole Growth

Weigel

Schawinski

Čaplar

et al. 2017

ApJ

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We use a phenomenological model to show that black hole growth in the local Universe (z 0.1) can be described by two separate, mass independent Eddington ratio distribution functions (ERDFs). We assume that black holes can be divided into two independent groups: those with radiatively efficient accretion, primarily hosted by optically blue and green galaxies, and those with radiatively inefficient accretion, which are mainly found in red galaxies. With observed galaxy stellar mass functions as input, we show that the observed AGN luminosity functions can be reproduced by using mass independent, broken power law shaped ERDFs. We use the observed hard X-ray and 1.4 GHz radio luminosity functions to constrain the ERDF for radiatively efficient and inefficient AGN, respectively. We also test alternative ERDF shapes and mass dependent models. Our results are consistent with a mass independent AGN fraction and AGN hosts being randomly drawn from the galaxy population. We argue that the ERDF is not shaped by galaxy-scale effects, but by how efficiently material can be transported from the inner few parsecs to the accretion disc. Our results are incompatible with the simplest form of mass quenching where massive galaxies host higher accretion rate AGN. Furthermore, if reaching a certain Eddington ratio is a sufficient condition for maintenance mode, it can occur in all red galaxies, not just the most massive ones.

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Unravelling lifecycles and physics of radio-loud AGN in the SKA Era

Cited by 23 publications

References 107 publications

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Radiative age mapping of the remnant radio galaxy B2 0924+30: the LOFAR perspective

Search and modelling of remnant radio galaxies in the LOFAR Lockman Hole field

AGNs and Their Host Galaxies in the Local Universe: Two Mass-independent Eddington Ratio Distribution Functions Characterize Black Hole Growth

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