LOFAR view of NGC 3998, a sputtering AGN

Sridhar, S. S.; Morganti, Raffaella; Nyland, Kristina; Frank, B. S.; Harwood, J. J.; Oosterloo, Tom

doi:10.1051/0004-6361/201936796

Cited by 14 publications

(13 citation statements)

References 70 publications

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“…This is similar to what can be seen in a number of cases from the literature (e.g. Jamrozy et al 2007;Shulevski et al 2012;Frank et al 2016;Brienza et al 2018;Sridhar et al 2020), and is consistent with the rapid fading of remnants predicted by models (Kaiser & Cotter 2002;Hardcastle 2018;Turner et al 2018b and references therein). A similar criterion was also used by Saripalli et al (2012).…”

Section: Criteria For Selecting Candidate Restarted Radio Sourcessupporting

confidence: 91%

The life cycle of radio galaxies in the LOFAR Lockman Hole field

Jurlin

Morganti

Brienza

et al. 2020

A&A

116

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Radio galaxies are known to go through cycles of activity, where phases of apparent quiescence can be followed by repeated activity of the central supermassive black hole. A better understanding of this cycle is crucial for ascertaining the energetic impact that the jets have on the host galaxy, but little is known about it. We used deep LOFAR images at 150 MHz of the Lockman Hole extragalactic field to select a sample of 158 radio sources with sizes > 60″ in different phases of their jet life cycle. Using a variety of criteria (e.g. core prominence combined with low-surface brightness of the extended emission and steep spectrum of the central region) we selected a subsample of candidate restarted radio galaxies representing between 13% and 15% of the 158 sources of the main sample. We compare their properties to the rest of the sample, which consists of remnant candidates and active radio galaxies. Optical identifications and characterisations of the host galaxies indicate similar properties for candidate restarted, remnant, and active radio galaxies, suggesting that they all come from the same parent population. The fraction of restarted radio galaxies is slightly higher with respect to remnants, suggesting that the restarted phase can often follow after a relatively short remnant phase (the duration of the remnant phase being a few times 107 years). This confirms that the remnant and restarted phases are integral parts of the life cycle of massive elliptical galaxies. A preliminary investigation does not suggest a strong dependence of this cycle on the environment surrounding any given galaxy.

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Section: Criteria For Selecting Candidate Restarted Radio Sourcessupporting

confidence: 91%

The life cycle of radio galaxies in the LOFAR Lockman Hole field

Jurlin

Morganti

Brienza

et al. 2020

A&A

116

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“…The morphologies of the extended structures observed with LOFAR in the FR 0s recall what has been recently observed in other radio galaxies and in particular in the radio source associated with NGC 3998 (Sridhar et al, 2020). This galaxy produces a low-power and highly core dominated source with two elongated and distorted lobes of low-surface brightness with a total size of ∼ 30 kpc.…”

Section: Discussionsupporting

confidence: 81%

The LOFAR view of FR 0 radio galaxies

Capetti

Brienza

Baldi

et al. 2020

A&A

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We explore the low-frequency radio properties of the sources in the Fanaroff-Riley class 0 catalog (FR0CAT) as seen by the Low-Frequency ARray (LOFAR) observations at 150 MHz. This sample includes 104 compact radio active galactic nuclei (AGN) associated with nearby (z < 0.05) massive early-type galaxies. Sixty-six FR0CAT sources are in the sky regions observed by LOFAR and all of them are detected, usually showing point-like structures with sizes of ≲3–6 kpc. However, 12 FR 0s present resolved emission of low surface brightness, which contributes between 5% and 40% of the total radio power at 150 MHz, usually with a jetted morphology extending between 15 and 50 kpc. No extended emission is detected around the other FR 0s, with a typical luminosity limit of ≲5 × 1022 W Hz−1 over an area of 100 kpc × 100 kpc. The spectral slopes of FR 0s between 150 MHz and 1.4 GHz span a broad range (−0.7 ≲ α ≲ 0.8) with a median value of ᾱ ∼ 0.1; 20% of them have a steep spectrum (α ≳ 0.5), which is an indication of the presence of substantial extended emission confined within the spatial resolution limit. The fraction of FR 0s showing evidence for the presence of jets, by including both spectral and morphological information, is at least ∼40%. This study confirms that FR 0s and FR Is can be interpreted as two extremes of a continuous population of jetted sources, with the FR 0s representing the low end in size and radio power.

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“…Over the past few years, a new sub-group of candidate restarted radio galaxies has been found, which do not show spatially resolved spectral properties expected from old remnant plasma, for example an ultra steep spectrum (α > 1.2) and a steep curvature in the radio spectra (∆α ≥ 0.5). Instead, these sources show bright inner jets and very diffuse outer lobes with a homogeneous spatial distribution of spectral index, for example Centaurus A (McKinley et al 2018(McKinley et al , 2013Morganti et al 1999), B2 0258+35 (Brienza et al 2018), and more recently NGC 3998 (Sridhar et al 2020). Although the physical mechanism responsible for these properties is still under debate, some studies indicate that the older outer lobes could still be fuelled at low levels by the active inner jets (McKinley et al 2018).…”

Section: Introductionmentioning

confidence: 99%

Unmasking the history of 3C 293 with LOFAR sub-arcsecond imaging

Kukreti

Morganti

Shimwell

et al. 2022

A&A

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Active galactic nuclei (AGNs) show episodic activity, which can be evident in galaxies that exhibit restarted radio jets. These restarted jets can interact with their environment, leaving signatures on the radio spectral energy distribution. Tracing these signatures is a powerful way to explore the life of radio galaxies. This requires resolved spectral index measurements over a broad frequency range including low frequencies. We present such a study for the radio galaxy 3C 293, which has long been thought to be a restarted galaxy on the basis of its radio morphology. Using the International LOFAR telescope (ILT) we probed spatial scales as fine as ∼0.2 at 144 MHz, and to constrain the spectrum we combined these data with Multi-Element Radio Linked Interferometer Network (MERLIN) and Very Large Array (VLA) archival data at frequencies up to 8.4 GHz that have a comparable resolution. In the inner lobes (∼2 kpc), we detect the presence of a spectral turnover that peaks at ∼225 MHz and is most likely caused by free-free absorption from the rich surrounding medium. We confirm that these inner lobes are part of a jet-dominated young radio source (spectral age 0.17 Myr), which is strongly interacting with the rich interstellar medium (ISM) of the host galaxy. The diffuse emission surrounding these lobes on scales of up to ∼4.5 kpc shows steeper spectral indices (∆α ∼ 0.2-0.5, S ∝ ν −α ) and a spectral age of 0.27 Myr. The outer lobes (extending up to ∼100 kpc) have a spectral index of α ∼ 0.6-0.8 from 144-4850 MHz with a remarkably uniform spatial distribution and only mild spectral curvature (∆α 0.2). We propose that intermittent fuelling and jet flow disruptions are powering the mechanisms that keep the spectral index in the outer lobes from steepening and maintain the spatial uniformity of the spectral index. Overall, it appears that 3C 293 has gone through multiple (two to three) epochs of activity. This study adds 3C 293 to the new sub-group of restarted galaxies with short interruption time periods. This is the first time a spatially resolved study has been performed that simultaneously studies a young source as well as the older outer lobes at such low frequencies. This illustrates the potential of the International LOFAR telescope to expand such studies to a larger sample of radio galaxies.

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LOFAR view of NGC 3998, a sputtering AGN

Cited by 14 publications

References 70 publications

The life cycle of radio galaxies in the LOFAR Lockman Hole field

The life cycle of radio galaxies in the LOFAR Lockman Hole field

The LOFAR view of FR 0 radio galaxies

Unmasking the history of 3C 293 with LOFAR sub-arcsecond imaging

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