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  • 1
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    Feeding and feedback in NGC 3081 (2016)
    Oxford University Press
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    Publication Date: 2016-01-29
    Description: We present two-dimensional gaseous kinematics of the inner 1.2  x  1.8 kpc 2 of the Seyfert 2 galaxy NGC 3081, from optical spectra (5600–7000 Å) obtained with the Gemini Multi Object Spectrograph integral field spectrograph on the Gemini North telescope at a spatial resolution of 100 pc. We have identified two components in the line emitting gas. A narrower component (full width at half-maximum, FWHM  60–100 km s –1 ), which appears to be gas in the galaxy disc, and which shows a distorted rotation pattern, is observed over the whole field of view. A broader component (FWHM 150–250 km s –1 ) is present in the inner 2 arcsec (200 pc) and shows blueshifts and redshifts in the near and far sides of the galaxy, respectively, consistent with a bipolar outflow. Assuming this to be the case, we estimate that the mass outflow rate in ionized gas ( $\dot{M}_{{\rm out}}$ ) is between 1.9  x 10 –3 and 6.9  x 10 –3  M  yr –1 . The subtraction of a rotation model from the narrower component velocity field reveals a pattern of excess blueshifts of 50 km s –1 in the far side of the galaxy and similar excess redshifts in the near side, which are cospatial with a previously known nuclear bar. We interpret these residuals as due to gas following non-circular orbits in the barred potential. Under the assumption that these motions may lead to gas inflows, we estimate an upper limit for the mass inflow rate in ionized gas of   1.3  x 10 –2  M  yr –1 .
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 2
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    Integral field spectroscopy of the circum-nuclear region of the radio Galaxy Pictor A (2016)
    Oxford University Press
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    Publication Date: 2016-03-11
    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.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 3
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    Thick discs, and an outflow, of dense gas in the nuclei of nearby Seyfert galaxies (2016)
    Oxford University Press
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    Publication Date: 2016-03-17
    Description: We discuss the dense molecular gas in central regions of nearby Seyfert galaxies, and report new arcsec resolution observations of HCN (1–0) and HCO + (1–0) for three objects. In NGC 3079, the lines show complex profiles as a result of self-absorption and saturated continuum absorption. H 13 CN reveals the continuum absorption profile, with a peak close to the galaxy's systemic velocity that traces disc rotation, and a second feature with a blue wing extending to –350 km s –1 that most likely traces a nuclear outflow. The morphological and spectral properties of the emission lines allow us to constrain the dense gas dynamics. We combine our kinematic analysis for these three objects, as well as another with archival data, with a previous comparable analysis of four other objects, to create a sample of eight Seyferts. In seven of these, the emission line kinematics imply thick disc structures on radial scales of ~100 pc, suggesting such structures are a common occurrence. We find a relation between the circum-nuclear L HCN and M dyn that can be explained by a gas fraction of 10 per cent and a conversion factor α HCN  ~ 10 between gas mass and HCN luminosity. Finally, adopting a different perspective to probe the physical properties of the gas around active galactic nuclei, we report on an analysis of molecular line ratios which indicates that the clouds in this region are not self-gravitating.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 4
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    Ionized gas kinematics within the inner kiloparsec of the Seyfert galaxy NGC 1365 (2016)
    Oxford University Press
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    Publication Date: 2016-05-25
    Description: We observed the nuclear region of the galaxy NGC 1365 with the integral field unit of the Gemini Multi Object Spectrograph mounted on the GEMINI-South telescope. The field of view covers 13 x 6 arcsec 2 (1173 x 541 pc 2 ) centred on the nucleus, at a spatial resolution of 52 pc. The spectral coverage extends from 5600 to 7000 Å, at a spectral resolution R = 1918. NGC 1365 hosts a Seyfert 1.8 nucleus, and exhibits a prominent bar extending out to 100 arcsec (9 kpc) from the nucleus. The field of view lies within the inner Lindblad resonance. Within this region, we found that the kinematics of the ionized gas (as traced by [O i ], [N ii ], Hα, and [S ii ]) is consistent with rotation in the large-scale plane of the galaxy. While rotation dominates the kinematics, there is also evidence for a fan-shaped outflow, as found in other studies based on the [O iii ] emission lines. Although evidence for gas inflowing along nuclear spirals has been found in a few barred galaxies, we find no obvious signs of such features in the inner kiloparsec of NGC 1365. However, the emission lines exhibit a puzzling asymmetry that could originate from gas which is slower than the gas responsible for the bulk of the narrow-line emission. We speculate that it could be tracing gas which lost angular momentum, and is slowly migrating from the inner Lindblad resonance towards the nucleus of the galaxy.
    Print ISSN: 0035-8711
    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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  • 5
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    Constraints on the broad-line region properties and extinction in local Seyferts (2016)
    Oxford University Press
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    Publication Date: 2016-09-02
    Description: We use high-spectral resolution ( R  〉 8000) data covering 3800–13 000 Å to study the physical conditions of the broad-line region (BLR) of nine nearby Seyfert 1 galaxies. Up to six broad H i lines are present in each spectrum. A comparison – for the first time using simultaneous optical to near-infrared observations – to photoionization calculations with our devised simple scheme yields the extinction to the BLR at the same time as determining the density and photon flux, and hence distance from the nucleus, of the emitting gas. This points to a typical density for the H i emitting gas of 10 11  cm –3 and shows that a significant amount of this gas lies at regions near the dust sublimation radius, consistent with theoretical predictions. We also confirm that in many objects, the line ratios are far from case B, the best-fitting intrinsic broad-line Hα/H β ratios being in the range 2.5–6.6 as derived with our photoionization modelling scheme. The extinction to the BLR, based on independent estimates from H i and He ii lines, is A V  ≤ 3 for Seyfert 1–1.5s, while Seyfert 1.8–1.9s have A V in the range 4–8. A comparison of the extinction towards the BLR and narrow-line region (NLR) indicates that the structure obscuring the BLR exists on scales smaller than the NLR. This could be the dusty torus, but dusty nuclear spirals or filaments could also be responsible. The ratios between the X-ray absorbing column N H and the extinction to the BLR are consistent with the Galactic gas-to-dust ratio if N H variations are considered.
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    Electronic ISSN: 1365-2966
    Topics: Physics
    Published by Oxford University Press
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