Unveiling the 100 pc scale nuclear radio structure of NGC 6217 with e-MERLIN and the VLA

Monthly Notices of the Royal Astronomical Society

Beswick

et al. 2021

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What determines the nuclear radio emission in local galaxies? To address this question, we combine optical [O iii] line emission, robust black hole (BH) mass estimates, and high-resolution e-MERLIN 1.5-GHz data, from the LeMMINGs survey, of a statistically complete sample of 280 nearby optically active (LINER and Seyfert) and inactive [H ii and absorption line galaxies (ALGs)] galaxies. Using [O iii] luminosity ($L_{\rm [O\, \small {III}]}$) as a proxy for the accretion power, local galaxies follow distinct sequences in the optical–radio planes of BH activity, which suggest different origins of the nuclear radio emission for the optical classes. The 1.5-GHz radio luminosity of their parsec-scale cores (Lcore) is found to scale with BH mass (MBH) and [O iii] luminosity. Below MBH ∼ 106.5 M⊙, stellar processes from non-jetted H ii galaxies dominate with $L_{\rm core} \propto M_{\rm BH}^{0.61\pm 0.33}$ and $L_{\rm core} \propto L_{\rm [O\, \small {III}]}^{0.79\pm 0.30}$. Above MBH ∼ 106.5 M⊙, accretion-driven processes dominate with $L_{\rm core} \propto M_{\rm BH}^{1.5-1.65}$ and $L_{\rm core} \propto L_{\rm [O\, \small {III}]}^{0.99-1.31}$ for active galaxies: radio-quiet/loud LINERs, Seyferts, and jetted H ii galaxies always display (although low) signatures of radio-emitting BH activity, with $L_{\rm 1.5\, GHz}\gtrsim 10^{19.8}$ W Hz−1 and MBH ≳ 107 M⊙, on a broad range of Eddington-scaled accretion rates ($\dot{m}$). Radio-quiet and radio-loud LINERs are powered by low-$\dot{m}$ discs launching sub-relativistic and relativistic jets, respectively. Low-power slow jets and disc/corona winds from moderately high to high-$\dot{m}$ discs account for the compact and edge-brightened jets of Seyferts, respectively. Jetted H ii galaxies may host weakly active BHs. Fuel-starved BHs and recurrent activity account for ALG properties. In conclusion, specific accretion–ejection states of active BHs determine the radio production and the optical classification of local active galaxies.

Section: Low-luminosity Agn and Disc-jet Couplingmentioning

confidence: 99%

LeMMINGs III. The e-MERLIN legacy survey of the Palomar sample: exploring the origin of nuclear radio emission in active and inactive galaxies through the [O iii] – radio connection

Monthly Notices of the Royal Astronomical Society

Beswick

et al. 2021

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“…The survey was designed to carry out shallow observations at 1.5 and 5 GHz without the largest e-MERLIN antenna, the Lovell telescope. In addition, several galaxies were observed to greater depth as part of LeMMINGs (i.e., with the Lovell telescope included): M 82 (Muxlow et al 2010), IC 10 (Westcott et al 2017, NGC 4151 (Williams et al 2017), NGC 5322 (Dullo et al 2018), M 51b (NGC 5195, Rampadarath et al 2018, and NGC 6217 (Williams et al 2019).…”

Section: The Palomar Sample and The Lemmings Survey 21 Sample Selectionmentioning

confidence: 99%

LeMMINGs – II. The e-MERLIN legacy survey of nearby galaxies. The deepest radio view of the Palomar sample on parsec scale

Monthly Notices of the Royal Astronomical Society

McHardy

et al. 2020

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We present the second data release of high-resolution (≤0.2 arcsec) 1.5-GHz radio images of 177 nearby galaxies from the Palomar sample, observed with the e-MERLIN array, as part of the LeMMINGs (Legacy e-MERLIN Multi-band Imaging of Nearby Galaxy Sample) survey. Together with the 103 targets of the first LeMMINGs data release, this represents a complete sample of 280 local active (LINER and Seyfert) and inactive galaxies (H ii galaxies and Absorption Line Galaxies, ALG). This large program is the deepest radio survey of the local Universe, ≳ 1017.6 W Hz−1, regardless of the host and nuclear type: we detect radio emission ≳0.25 mJy beam−1 for 125/280 galaxies (44.6 per cent) with sizes of typically ≲100 pc. Of those 125, 106 targets show a core which coincides within 1.2 arcsec with the optical nucleus. Although we observed mostly cores, around one third of the detected galaxies features jetted morphologies. The detected radio core luminosities of the sample range between ∼1034 and 1040 erg s−1. LINERs and Seyferts are the most luminous sources, whereas H ii galaxies are the least. LINERs show FR I-like core-brightened radio structures while Seyferts reveal the highest fraction of symmetric morphologies. The majority of H ii galaxies have single radio core or complex extended structures, which probably conceal a nuclear starburst and/or a weak active nucleus (seven of them show clear jets). ALGs, which are typically found in evolved ellipticals, although the least numerous, exhibit on average the most luminous radio structures, similar to LINERs.

“…The data were calibrated with version 0.7.9 of the CASA e-MERLIN pipeline. 1 The CASA e-MERLIN pipeline is similar to the previous AIPS data reduction procedure outlined in Williams et al (2017) (see also Westcott et al 2017;Baldi et al 2018;Williams et al 2019) for e-MERLIN continuum data: the pipeline performs standard calibration of e-MERLIN data by flagging radio frequency interference using AOFLAGGER (Offringa, van de Gronde & Roerdink 2012), solving the delays of the antennas, performing phase and amplitude calibration, bootstrapping the flux density scaling, fitting and applying a band pass, and making preliminary images and diagnostic plots, ready for further imaging and self-calibration of the target fields.…”

Section: O B S E Rvat I O N S a N D Data R E D U C T I O Nmentioning

confidence: 99%

“…In some cases, the radio variability is found to be related to activity in the jet, rather than in the self-absorbed synchrotron emitting core component attributed to the AGN (e.g. in NGC 1052, Baczko et al 2016, 2019. However, due to their intrinsic radioweakness, variability studies of LLAGNs have been limited to small samples of the best known sources, predominantly Seyfert galaxies (Wrobel 2000;Nagar et al 2002;Mundell et al 2009;Bell et al 2011).…”

mentioning

confidence: 99%

The curious activity in the nucleus of NGC 4151: jet interaction causing variability?

Monthly Notices of the Royal Astronomical Society

McHardy

et al. 2020

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A key characteristic of many active galactic nuclei (AGNs) is their variability, but its origin is poorly understood, especially in the radio domain. Williams et al. (2017) reported a ∼50 per cent increase in peak flux density of the AGN in the Seyfert galaxy NGC 4151 at 1.5 GHz with the e-MERLIN array. We present new high-resolution e-MERLIN observations at 5 GHz and compare these to archival MERLIN observations to investigate the reported variability. Our new observations allow us to probe the nuclear region at a factor three times higher resolution than the previous e-MERLIN study. We separate the core component, C4, into three separate components: C4W, C4E, and X. The AGN is thought to reside in component C4W, but this component has remained constant between epochs within uncertainties. However, we find that the Eastern-most component, C4E, has increased in peak flux density from 19.35 ± 1.10 to 37.09 ± 1.86 mJy beam−1, representing an 8.2σ increase on the MERLIN observations. We attribute this peak flux density increase to continue interaction between the jet and the emission line region (ELR), observed for the first time in a low-luminosity AGNs such as NGC 4151. We identify discrete resolved components at 5 GHz along the jet axis, which we interpret as areas of jet–ELR interaction.