The duty cycle of local radio galaxies

Shabala, Stanislav S.; Ash, Summer; Alexander, Paul; Riley, J. M.

doi:10.1111/j.1365-2966.2008.13459.x

Cited by 125 publications

(200 citation statements)

References 55 publications

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“…For the purposes of this work, we only use the GALEX near-ultraviolet (NUV) filter, which is centred at 2300 Å. Following Shabala et al (2008), we use a matching radius of 2 arcsec for the radio-optical matching, which yields high (96 per cent) completeness and low (0.3 per cent) contamination. GALEX observations are then matched to the SDSS objects with a matching radius of 4 arcsec (see e.g.…”

Section: Sdss and Galex Photometrymentioning

confidence: 99%

The triggering of local AGN and their role in regulating star formation

Kaviraj

Shabala

Deller

et al. 2015

Mon. Not. R. Astron. Soc.

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We explore the processes that trigger local AGN and the role of these AGN in regulating star formation, using ∼550 nearby galaxies observed by the mJy Imaging VLBA Exploration at 20 cm (mJIVE) survey. The 10 7 K brightness temperature required for an mJIVE detection cannot be achieved via star formation alone, allowing us to unambiguously detect nearby radio AGN and study their role in galaxy evolution. Radio AGN are an order of magnitude more common in early-type galaxies (ETGs) than in their late-type counterparts. The VLBI-detected ETGs in this study have a similar stellar mass distribution to their undetected counterparts, are typically not the central galaxies of clusters and exhibit merger fractions that are significantly higher than in the average ETG. This suggests that these radio AGN (which have VLBI luminosities >10 22 W Hz −1 ) are primarily fuelled by mergers, and not by internal stellar mass-loss or cooling flows. Our radio AGN are a factor of ∼3 times more likely to reside in the UV-optical red sequence than the average ETG. Furthermore, typical AGN lifetimes (a few 10 7 yr) are much shorter than the transit times from blue cloud to red sequence (∼1.5 Gyr). This indicates that nearby (merger-triggered) AGN appear several dynamical time-scales into the associated star formation episode. This implies that such AGN typically couple only to residual gas, at a point where star formation has already declined significantly, and are, therefore, unlikely to play a significant role in regulating the star formation episode.

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Section: Sdss and Galex Photometrymentioning

confidence: 99%

The triggering of local AGN and their role in regulating star formation

Kaviraj

Shabala

Deller

et al. 2015

Mon. Not. R. Astron. Soc.

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“…. The duty cycle likely has a dependence on galaxy mass and source power during the active phase, as suggested by statistical studies (Best et al 2005;Shabala et al 2008).…”

Section: Introductionmentioning

confidence: 99%

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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“…However, not all optical galaxies exhibit radio emission (at least at the depth of current surveys) and it is important to investigate the physical mechanism that triggers this emission. For AGN-induced activity, the difference between radio-quiet and radio-loud galaxies is naturally connected to the availability of fuel for the central engine, the black hole mass, and its emission efficiency (see e.g., Shabala et al 2008, and references therein), while for star-forming objects it is closely related to the strength of the star-formation episode.…”

Section: Introductionmentioning

confidence: 99%

Properties and environment of radio-emitting galaxies in the VLA-zCOSMOS survey

Bardelli¹,

Schinnerer

Smolčić

et al. 2010

A&A

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Aims. We investigate the properties and the environment of radio sources with optical counterparts from the combined VLA-COSMOS and zCOSMOS samples. The advantage of this sample is the availability of optical spectroscopic informations, high quality redshifts, and accurate density determination. Methods. By comparing the star formation rates estimated from the optical spectral energy distribution with those based on the radio luminosity, we divide the radio sources in to three families passive AGN, non-passive AGN, and star-forming galaxies. These families occupy specific regions of the 8.0−4.5 μm infrared color-specific star-formation plane, from which we extract the corresponding control samples. Results. Only the passive AGN have a significantly different environmental distribution from their control sample. The fraction of radio-loud passive AGN increases from ∼2% in underdense regions to ∼15% for overdensities (1 + δ) greater than 10. This trend is also present as a function of richness of the groups hosting the radio sources. Passive AGN in overdensities tend to have higher radio luminosities than those in lower density environments. Since the black hole mass distribution is similar in both environments, we speculate that, for low radio luminosities, the radio emission is controlled (by fuel availability or confinement of the radio jet by local gas pressure) by the interstellar medium of the host galaxy, while in other cases it is determined by the structure (group or cluster) in which the galaxy resides.

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The duty cycle of local radio galaxies

Cited by 125 publications

References 55 publications

The triggering of local AGN and their role in regulating star formation

The triggering of local AGN and their role in regulating star formation

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

Properties and environment of radio-emitting galaxies in the VLA-zCOSMOS survey

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