ALBERT

Description: We present a two-dimensional analysis of the gaseous excitation and kinematics of the inner 2.5 1.7 kpc 2 of the low-ionization nuclear emission-line region (LINER)/Seyfert 1 galaxy Arp 102B, from optical spectra obtained with the Gemini Multi-Object Spectrograph Integral Field Unit on the Gemini North telescope at a spatial resolution of 250 pc. Emission-line flux maps show the same two-armed nuclear spiral we have discovered in previous observations with the Hubble Space Telescope Advanced Camera for Surveys. One arm reaches 1 kpc to the east and the other 500 pc to the west, with an 8.4 GHz Very Large Array bent radio jet correlating with the former. Gas excitation along the arms is low, with line ratios typical of LINERs, and which rule out gas ionization by stars. The gas density is highest (500–900 cm –3 ) at the nucleus and in the northern border of the east arm, at a region where the radio jet seems to be deflected. Centroid velocity maps suggest that most gas is in rotation in an inclined disc with line of nodes along position angle 88°, redshifts to the west and blueshifts to the east, with lower blueshifts correlated with the eastern arm and radio jet. This correlation suggests that the jet is interacting with gas in the disc. This interaction is supported by the gas excitation as a function of distance from the nucleus, which requires the contribution from shocks. Channel maps show blueshifts but also some redshifts at the eastern arm and jet location which can be interpreted as originated in the front and back walls of an outflow pushed by the radio jet, suggesting also that the outflow is launched close to the plane of the sky. Principal Component Analysis applied to our data supports this interpretation. We estimate a mass outflow rate along the east arm of 0.26-0.32 M yr – 1 (depending on the assumed outflow geometry), which is between one and two orders of magnitude higher than the mass accretion rate to the active nucleus, implying that there is mass-loading of the nuclear outflow from circumnuclear gas. The power of this outflow is 0.06–0.3 per cent L bol . We propose a scenario in which gas has been recently captured by Arp 102B in an interaction with Arp 102A, settling in a disc rotating around the nucleus of Arp 102B and triggering its nuclear activity. A nuclear jet is pushing the circumnuclear gas, giving origin to the nuclear arms. A blueshifted emitting gas knot is observed at 300 pc southeast from the nucleus and can be interpreted as another (more compact) outflow, with a possible counterpart to the northwest.

Description: We present the results of high-resolution VLBI (very long baseline interferometry) observations at 1.6 and 4.9 GHz of the radio-loud Seyfert galaxy, Mrk 6. These observations are able to detect a compact radio core in this galaxy for the first time. The core has an inverted spectral index ($\alpha ^{1.6}_{4.9}$ = +1.0 ± 0.2) and a brightness temperature of 1 10 8  K. Three distinct radio components, which resemble jet elements and/or hotspots, are also detected. The position angles of these elongated jet elements point not only to a curved jet in Mrk 6, but also towards a connection between the AGN and the kpc-scale radio lobes/bubbles in this galaxy. Firmer constraints on the star formation rate provided by new Herschel observations (SFR 〈 0.8 M  yr –1 ) make the starburst-wind-powered bubble scenario implausible. From plasma speeds, obtained via prior Chandra X-ray observations, and ram pressure balance arguments for the interstellar medium and radio bubbles, the north–south bubbles are expected to take 7.5 10 6 yr to form, and the east–west bubbles 1.4 10 6  yr. We suggest that the jet axis has changed at least once in Mrk 6 within the last 10 7 yr. A comparison of the nuclear radio-loudness of Mrk 6 and a small sample of Seyfert galaxies with a subset of low-luminosity FR I radio galaxies reveals a continuum in radio properties.

Description: Seyfert and LINER galaxies are known to exhibit compact radio emission on ~10–100 pc scales, but larger Kiloparsec-Scale Radio structures (KSRs) often remain undetected in sub-arcsec high-resolution observations. We investigate the prevalence and nature of KSRs in Seyfert and LINER galaxies using the 1.4 GHz VLA FIRST and NVSS observations. Our sample consists of 2651 sources detected in FIRST and of these 1737 sources also have NVSS counterparts. Considering the ratio of total to peak flux density ( = ( S int / S peak ) 1/2 ) as a parameter to infer the presence of extended radio emission we show that ≥30 per cent of FIRST-detected sources possess extended radio structures on scales larger than 1.0 kpc. The use of low-resolution NVSS observations help us to recover faint extended KSRs that are resolved out in FIRST observations and results in ≥42.5 per cent KSR sources in FIRST–NVSS sub-sample. This fraction is only a lower limit owing to the combination of projection, resolution and sensitivity effects. Our study demonstrates that KSRs may be more common than previously thought and are found across all redshifts, luminosities and radio loudness. The extranuclear radio luminosity of KSR sources is found to be positively correlated with the core radio luminosity as well as the [O iii ] 5007 Å line luminosity and this can be interpreted as KSRs being powered by AGN rather than star formation. The distributions of the FIR-to-radio ratios and mid-IR colours of KSR sources are also consistent with their AGN origin. However, contribution from star formation cannot be ruled out particularly in sources with low radio luminosities.

Description: Low-frequency observations at 325 and 610 MHz have been carried out for two ‘radio-loud’ Seyfert galaxies, NGC 4235 and NGC 4594 (Sombrero galaxy), using the Giant Meterwave Radio Telescope (GMRT). The 610 MHz total intensity and 325–610 MHz spectral index images of NGC 4235 tentatively suggest the presence of a ‘relic’ radio lobe, most likely from a previous episode of active galactic nucleus (AGN) activity. This makes NGC 4235 only the second known Seyfert galaxy after Mrk 6 to show signatures of episodic activity. Spitzer and Herschel infrared spectral energy distribution (SED) modelling using the clumpydream code predicts star formation rates (SFRs) that are an order of magnitude lower than those required to power the radio lobes in these Seyferts (~0.13–0.23 M  yr –1 compared to the required SFR of ~2.0–2.7 M  yr –1 in NGC 4594 and NGC 4235, respectively). This finding along with the detection of parsec and sub-kpc radio jets in both Seyfert galaxies, that are roughly along the same position angles as the radio lobes, strongly support the suggestion that Seyfert lobes are AGN powered. SED modelling supports the ‘true’ type 2 classification of NGC 4594: this galaxy lacks significant dust obscuration as well as a prominent broad-line region. Between the two Seyfert galaxies, there is an inverse relation between their radio-loudness and Eddington ratio and a direct relation between their Eddington-scaled jet power and bolometric power.

Description: We present optical integral field spectroscopy of the inner 2.5 x 3.4 kpc 2 of the broad-line radio galaxy Pictor A, at a spatial resolution of 400 pc. Line emission is observed over the whole field of view, being strongest at the nucleus and in an elongated linear feature (ELF) crossing the nucleus from the south-west to the north-east along PA 70°. Although the broad double-peaked Hα line and the [O i ]6300/Hα and [S ii ]6717+31/Hα ratios are typical of active galactic nuclei (AGNs), the [N ii ]6584/Hα ratio (0.15–0.25) is unusually low. We suggest that this is due to the unusually low metallicity of the gas. Centroid velocity maps show mostly blueshifts to the south and redshifts to the north of the nucleus, but the velocity field is not well fitted by a rotation model. Velocity dispersions are low (〈100 km s – 1 ) along the ELF, ruling out a jet–cloud interaction as the origin of this structure. The ELF shows both blueshifts and redshifts in channel maps, suggesting that it is close to the plane of the sky. The ELF is evidently photoionized by the AGN, but its kinematics and inferred low metallicity suggest that this structure may have originated in a past merger event with another galaxy. We suggest that the gas acquired in this interaction may be feeding the ELF.

Description: We present high-resolution radio continuum observations with the Karl G. Jansky very large array at 6, 8.5, 11.5 and 15 GHz of the double-peaked emission-line galaxy 2MASXJ12032061+1319316. The radio emission has a prominent S-shaped morphology with highly symmetric radio jets that extend over a distance of ~1.5 arcsec (1.74 kpc) on either side of the core of size ~0.1 arcsec (116 pc). The radio jets have a helical structure resembling the precessing jets in the galaxy NGC 326 which has confirmed dual active galactic nuclei (AGN). The nuclear bulge velocity dispersion gives an upper limit of (1.56 ± 0.26) x 10 8 M for the total mass of nuclear black hole(s). We present a simple model of precessing jets in 2MASXJ1203 and find that the precession time-scale is around 10 5 yr: this matches the source lifetime estimate via spectral ageing. We find that the expected supermassive black hole (SMBH) separation corresponding to this time-scale is 0.02 pc. We used the double-peaked emission lines in 2MASXJ1203 to determine an orbital speed for a dual AGN system and the associated jet precession time-scale, which turns out to be more than the Hubble time, making it unfeasible. We conclude that the S-shaped radio jets are due to jet precession caused either by a binary/dual SMBH system, a single SMBH with a tilted accretion disc or a dual AGN system where a close pass of the secondary SMBH in the past has given rise to jet precession.

Description: The optical spectra of Seyfert galaxies are often dominated by emission lines excited by both star formation and active galactic nucleus (AGN) activity. Standard calibrations (such as for the star formation rate) are not applicable to such composite (mixed) spectra. In this paper, we describe how integral field data can be used to spectrally and spatially separate emission associated with star formation from emission associated with accretion on to an AGN. We demonstrate our method using integral field data for two AGN host galaxies (NGC 5728 and NGC 7679) from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). The spectra of NGC 5728 and NGC 7679 form clear sequences of AGN fraction on standard emission line ratio diagnostic diagrams. We show that the emission line luminosities of the majority (〉85 per cent) of spectra along each AGN fraction sequence can be reproduced by linear superpositions of the emission line luminosities of one AGN dominated spectrum and one star formation dominated spectrum. We separate the Hα, Hβ, [N ii ]6583, [S ii ]6716, 6731, [O iii ]5007 and [O ii ]3726, 3729 luminosities of every spaxel into contributions from star formation and AGN activity. The decomposed emission line images are used to derive the star formation rates and AGN bolometric luminosities for NGC 5728 and NGC 7679. Our calculated values are mostly consistent with independent estimates from data at other wavelengths. The recovered star-forming and AGN components also have distinct spatial distributions which trace structures seen in high-resolution imaging of the galaxies, providing independent confirmation that our decomposition has been successful.