The Central Parsecs of Centaurus A: High‐excitation Gas, a Molecular Disk, and the Mass of the Black Hole

Neumayer, Nadine; Cappellari, Michele; Reunanen, J.; Rix, H. W.; Werf, P. P. van der; Zeeuw, P. T. de; Davies, R. I.

doi:10.1086/523039

Cited by 145 publications

(265 citation statements)

References 47 publications

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“…11), our model naturally explains this as only due to the geometry of the disk. The presence of a small-scale bar is also ruled out by the near-IR data presented by Neumayer et al (2007).…”

Section: The H I Modelmentioning

confidence: 76%

Centaurus A: morphology and kinematics of the atomic hydrogen

Struve

Oosterloo

Morganti

et al. 2010

A&A

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We present new ATCA 21-cm line observations of the neutral hydrogen in the nearby radio galaxy Centaurus A. We image in detail (with a resolution down to 7 , ∼100 pc) the distribution of H i along the dust lane. Our data have better velocity resolution and better sensitivity than previous observations. The H i extends for a total of ∼15 kpc. The data, combined with a titled-ring model of the disk, allow to conclude that the kinematics of the H i is that of a regularly rotating, highly warped structure down to the nuclear scale.The parameters (in particular the inclination) of our model are somewhat different from some of the previously proposed models but consistent with what was recently derived from stellar light in a central ring. The model nicely describes also the morphology of the dust lane as observed with Spitzer. There are no indications that large-scale anomalies in the kinematics exist that could be related to supplying material for the AGN. Large-scale radial motions do exist, but these are only present at larger radii (r > 6 kpc). This unsettled gas is mainly part of a tail/arm like structure. The relatively regular kinematics of the gas in this structure suggests that it is in the process of settling down into the main disk. The presence of this structure further supports the merger/interaction origin of the H i in Cen A. From the structure and kinematics we estimate a timescale of 1.6−3.2 × 10 8 yr since the merging event. No bar structure is needed to describe the kinematics of the H i. The comparison of the timescale derived from the large-scale H i structure and those of the radio structure together with the relative regularity of the H i down to the sub-kpc regions does not suggest a oneto-one correspondence between the merger and the phase of radio activity. Interestingly, the radial motions of the outer regions are such that the projected velocities are redshifted compared to the regular orbits. This means that the blueshifted absorption discovered earlier and discussed in our previous paper cannot be caused by out-moving gas at large radius projected onto the centre. Therefore, the interpretation of the blueshifted absorption, together with at least a fraction of the redshifted nuclear absorption, as evidence for a regular inner disk, still holds. Finally, we also report the discovery of two unresolved clouds detected at 5.2 and 11 kpc away (in projection) from the H i disk. They are likely an other example of a left-over of the merger that brought the H i gas.

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“…11), our model naturally explains this as only due to the geometry of the disk. The presence of a small-scale bar is also ruled out by the near-IR data presented by Neumayer et al (2007).…”

Section: The H I Modelmentioning

confidence: 76%

Centaurus A: morphology and kinematics of the atomic hydrogen

Struve

Oosterloo

Morganti

et al. 2010

A&A

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“…Considering that there is also a non-thermal component, the value of the bolometric luminosity we give here has to be understood as an upper limit for the thermal accretion luminosity. With a central black hole mass of M BH 5 × 10 7 M (Neumayer et al 2007), this translates into an Eddington ratio around λ = 0.01, similar to NGC 4151 with λ 0.01−0.02 (Lubiński et al 2010). Based on long-term X-ray measurements by RXTE, Rothschild et al (2011) derived a lower average luminosity of L bol = 8 × 10 42 erg s −1 and thus an Eddington ratio of only λ 0.001.…”

Section: Cen a As A Seyfert Galaxymentioning

confidence: 86%

The hard X-ray emission of Centaurus A

Beckmann

Jean

Lubiński

et al. 2011

A&A

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Context. The radio galaxy Cen A has been detected all the way up to the TeV energy range. This raises the question about the dominant emission mechanisms in the high-energy domain. Aims. Spectral analysis allows us to put constraints on the possible emission processes. Here we study the hard X-ray emission, in order to distinguish between a thermal and a non-thermal inverse Compton process. Methods. Using hard X-ray data provided by INTEGRAL, we determined the cut-off of the power-law spectrum in the hard X-ray domain (3−1000 keV). In addition, INTEGRAL data are used to study the spectral variability. The extended emission detected in the gamma-rays by Fermi/LAT is investigated using the data of the spectrometre SPI in the 40−1000 keV range. Results. The hard X-ray spectrum of Cen A shows a significant cut-off at energies E C = 434 +106 −73 keV with an underlying power-law of photon index Γ = 1.73 ± 0.02. A more physical model of thermal Comptonisation (compPS) gives a plasma temperature of kT e = 206 ± 62 keV within the optically thin corona with Compton parameter y = 0.42 +0.09 −0.06 . The reflection component is significant at the 1.9σ level with R = 0.12 +0.09 −0.10 , and a reflection strength R > 0.3 can be excluded on a 3σ level. Time resolved spectral studies show that the flux, absorption, and spectral slope varied in the range f 3−30 keV = 1.2−9.2 × 10 −10 erg cm −2 s −1 , N H = 7−16 × 10 22 cm −2 , and Γ = 1.75−1.87. Extending the cut-off power-law or the Comptonisation model to the gamma-ray range shows that they cannot account for the high-energy emission. On the other hand, a broken or curved power-law model can also represent the data, therefore a non-thermal origin of the X-ray to GeV emission cannot be ruled out. The analysis of the SPI data provides no sign of significant emission from the radio lobes and gives a 3σ upper limit of f 40−1000 keV < ∼ 1.1 × 10 −3 ph cm −2 s −1 . Conclusions. While gamma-rays, as detected by CGRO and Fermi, are caused by non-thermal (jet) processes, the main process in the hard X-ray emission of Cen A is still not unambiguously determined, since it is either dominated by thermal inverse Compton emission or by non-thermal emission from the base of the jet.

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“…In fact, the presence of clouds of cold gas in unsettled/chaotic orbits, possibly triggering/fuelling the SMBH and maintaining a galaxy's nuclear activity, has been suggested for other (radio) AGN from, e.g., H i absorption features (e.g. Maccagni et al 2014, and references therein) and by the high velocity dispersion of the molecular gas in the central regions of some low-luminosity AGN (Mueller Sánchez 2006Neumayer et al 2007;Mezcua et al 2015;Maccagni et al 2016). …”

Section: Energetics and Triggeringmentioning

confidence: 99%

A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998

Frank

Morganti

Oosterloo

et al. 2016

A&A

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We study the nearby lenticular galaxy NGC 3998. This galaxy is known to host a low-power radio AGN with a kpc-size one-sided jet and a large, nearly polar H i disc. It is therefore a good system to study to understand the relation between the availability of cold-gas and the triggering of AGNs in galaxies. Our new WSRT data reveal two faint, S-shaped radio lobes extending out to ∼10 kpc from the galaxy centre. Remarkably, we find that the inner H i disc warps back towards the stellar mid-plane in a way that mirrors the warping of the radio lobes. We suggest that the polar H i disc was accreted through a minor merger, and that the torques causing it to warp in the inner regions are also responsible for feeding the AGN. The "S" shape of the radio lobes would then be due to the radio jets adapting to the changing angular momentum of the accreted gas. The extended radio jets are likely poorly collimated, which would explain their quick fading and, therefore, their rarity in galaxies similar to NGC 3998. The fuelling of the central super-massive black hole is likely occurring via "discrete events", suggested by the observed variability of the radio core and the extremely high core dominance, which we attribute to the formation and ejection of a new jet resulting from a recent fuelling event.

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The Central Parsecs of Centaurus A: High‐excitation Gas, a Molecular Disk, and the Mass of the Black Hole

Cited by 145 publications

References 47 publications

Centaurus A: morphology and kinematics of the atomic hydrogen

Centaurus A: morphology and kinematics of the atomic hydrogen

The hard X-ray emission of Centaurus A

A rare example of low surface-brightness radio lobes in a gas-rich early-type galaxy: the story of NGC 3998

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