J/A+A/677/A4ivo://CDS.VizieR/J/A+A/677/A4doi:10.26093/cds/vizier.36770004CDSCandini S.Brienza M.Bonafede A.Rajpurohit K.Biava N.Murgia M.,Loi F.van Weeren R.J.Vazza F.2024-11-06T20:05:59Z2023-08-25T10:06:09ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frradio-galaxiesradio-continuum-emissionRadio galaxies are a subclass of active galactic nuclei (AGN) in which accretion onto the supermassive black hole releases energy into the environment via relativistic jets. The jets are not constantly active throughout the life of the host galaxy and alternate between active and quiescent phases. Remnant radio galaxies are detected during a quiescent phase and define a class of unique sources that can be used to constrain the AGN duty cycle. We present, for the first time, a spatially resolved radio analysis of the radio galaxy associated with the galaxy NGC 6086 down to 144MHz and constraints on the spectral age of the diffuse emission to investigate the duty cycle and evolution of the source. We used three new low-frequency, high-sensitivity observations; the first was performed with the Low Frequency Array at 144MHz and the other two with the upgraded Giant Metrewave Radio Telescope at 400MHz and 675MHz, respectively. To these, we add two Very Large Array archival observations at higher frequencies (1400 and 4700MHz). In the new observations in the frequency range 144-675MHz, we detect a second pair of larger lobes and three regions within the remnant emission with a filamentary morphology. We analysed the spectral index trend in the inner remnant lobes and see systematically steeper values {alpha}_low_~1.1-1.3) at the lower frequencies compared to the gigahertz frequencies ({alpha}_high_~0.8-0.9). Steeper spectral indices are found in the newly detected outer lobes (up to {alpha}_outer_~2.1), as expected if they trace a previous phase of activity of the AGN. However, the differences between the spectra of the two outer lobes suggest different dynamical evolutions within the intra-group medium during their expansion and/or different magnetic field values. Using a single-injection radiative model and assuming equipartition conditions, we place constraints on the age of the inner and outer lobes and derive the duty cycle of the source. We estimate that the duration of the two active phases was 45Myr and 18Myr and the duration of the two inactive phases was 66Myr and 33Myr. This results in a total active time of t_on_~39%. The filamentary structures have a steep spectral index (~1) without any spectral index trend, and only one of them shows a steepening in the spectrum. Their origin is not yet clear, but they may have formed due to the compression of the plasma or due to magnetic field substructures.2023A&A...677A...4Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/677/A4CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/677/A4https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/677/A4http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/677/A4https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/677/A4https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/677/A4http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/677/A4GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/A+A/677/A4/list (List of fits images)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/A+A/677/A4/list?https://vizier.iucaa.in/viz-bin/conesearch/J/A+A/677/A4/list?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/A+A/677/A4/list?GETtext/xml+votable180.050000true243.1627129.473850.005555555555555556Associated datahttps://cdsarc.cds.unistra.fr/assocdata/?obs_collection=J/A+A/677/A46/9368https://cdsarc.cds.unistra.fr/viz-bin/moc/J/A+A/677/A4?format=asciiRadiodefaultJ/A+A/677/A4/listList of fits imagesrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintRAJ2000Right Ascension of center (J2000)degpos.eq.ra;meta.mainDEJ2000Declination of center (J2000)degpos.eq.dec;meta.mainNxNumber of pixels along X-axismeta.numberintNyNumber of pixels along Y-axismeta.numberintObs.dateObservation datestime.epoch;obsnullableFreq? Observed frequencyMHzem.freqfloatnullablesizeSize of FITS fileKibytephys.size;meta.fitsintFileNameName of FITS file, in subdirectory fitsmeta.id;meta.fitscharTitleTitle of the FITS filemeta.title;meta.fitschar