Multifrequency study of a double–double radio galaxy J0028+0035

Marecki, A.; Jamrozy, M.; Machalski, J.; Pajdosz-Śmierciak, Urszula

doi:10.1093/mnras/staa3632

“…Restarted galaxies with three pairs of radio lobes have also been identified, the so-called 'triple-double' galaxies, for example B 0925+420 (Brocksopp et al 2007), 'Speca' (Hota et al 2011) and J 1216+0709 (Singh et al 2016). In the case of DDRGs, spectral age studies have provided estimates of the timescale of the quiescent phase to be between 10 5 yr and 10 7 yr and at most, ∼50% of the length of the previous active phase (Konar et al 2013;Orru et al 2015;Nandi et al 2019;Marecki et al 2020;Marecki 2021).…”

Section: Introductionmentioning

confidence: 99%

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

Kukreti

¹

,

Morganti

²

,

Shimwell

³

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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“…Restarted galaxies with three pairs of radio lobes have also been identified, the so-called 'triple-double' galaxies, for example B 0925+420 (Brocksopp et al 2007), 'Speca' (Hota et al 2011) and J 1216+0709 (Singh et al 2016). In the case of DDRGs, spectral age studies have provided estimates of the timescale of the quiescent phase to be between 10 5 yr and 10 7 yr and at most, ∼50% of the length of the previous active phase (Konar et al 2013;Orru et al 2015;Nandi et al 2019;Marecki et al 2020;Marecki 2021).…”

Section: Introductionmentioning

confidence: 99%

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

Kukreti,

Morganti,

Shimwell

et al. 2021

Preprint

2

1

0

View full text Add to dashboard Cite

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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“…A direct observable indication of the cessation and subsequent restart of activity in a radio-loud AGN takes the form of a double-double radio source (DDRS; Schoenmakers et al 2000) consisting of two co-linear pairs of radio lobes (see Saikia & Jamrozy 2009 for a review and e.g. Marecki et al 2021 for references to the latest papers on DDRSs). If the inner lobes resulting from the second active phase of a DDRS had been created only recently, their separation could have been too small to render them as a double in the image depicting the overall structure of the source.…”

Section: Introductionmentioning

confidence: 99%

Restarted activity in the 3C 328 radio galaxy

Marecki

¹

2021

A&A

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As a rule, both lobes of Fanaroff-Riley (FR) type-II radio sources are terminated with hotspots, but the 3C 328 radio galaxy is a specimen of an FR II-like object with a hotspot in only one lobe. A conceivable reason for such asymmetry is that the nucleus of 3C 328 was temporarily inactive. There was no energy transfer from it to the lobes during the period of quiescence, and so they began to fade out. However, under the assumption that the axis connecting the two lobes makes an appreciable angle with the sky plane, and hence one is considerably farther from the observer than the other, the lobes are observed at two distinct stages of evolution due to the light-travel lag. While the far-side lobe is still perceived as being of the FR II type with a hotspot, decay of the near-side lobe is already apparent. No jets are visible in the VLA images, but the VLBA observations of the inverted-spectrum core component of 3C 328 have revealed that it has a jet of a sub-arcsecond length pointing towards the lobe that shows evidence of decay. Since the jet always points to the near side, its observed orientation is in line with the scenario proposed here. The presence of the jet supports the inference that the nucleus of 3C 328 is currently active; however, given the fact that the jet is short (∼200 pc in projection), the activity must have restarted very recently. The lower and upper limits of the quiescent period length have been calculated.

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Multifrequency study of a double–double radio galaxy J0028+0035

Cited by 8 publications

References 68 publications

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

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

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

Restarted activity in the 3C 328 radio galaxy

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