We present the first results of an analysis of the properties of the molecular gas in the nuclear regions (r 300 pc) of a sample of six nearby galaxies, based on new high-spatial-resolution ...observations obtained in the K-band with the near-infrared integral field spectrograph SINFONI at the Very Large Telescope. We derive 2D distributions of the warm molecular and ionized gas from the H2, Brγ and He i emission lines present in the spectra of the galaxies. We find a range of morphologies, including bar- and ring-like distributions and either centrally peaked or off-centre emission. The morphologies of the molecular and the ionized gas are not necessarily coincident. The observed emission-line ratios point towards thermal processes as the principal mechanism responsible for the H2 excitation in the nuclear and circumnuclear regions of the galaxies, independently of the presence of an active nucleus. We find that a rescaling of the H2 2.12 μm emission-line luminosity by a factor β 1200 gives a good estimate (within a factor of 2) of the total (cold) molecular gas mass. The galaxies of the sample contain large quantities of molecular gas in their centres, with total masses in the ∼105-108 M range. Nevertheless, these masses correspond to less than 3 per cent of the stellar masses derived for the galaxies in these regions, indicating that the presence of gas should not affect black hole mass estimates based on the dynamical modelling of the stars. The high spatial resolution provided by the SINFONI data allowed us to resolve a circumnuclear ring (with a radius of ∼270 pc) in the galaxy NGC 4536. The measured values of the Brγ equivalent width and the He i/Brγ emission-line ratio suggest that bursts of star formation occurred throughout this ring as recently as 6.5 Myr ago.
It is now well established that all galaxies with a massive bulge component harbour a central supermassive black hole (SMBH). The mass of the SMBH correlates with bulge properties such as the bulge ...mass and the velocity dispersion, which implies that the bulge and the central BH of a galaxy have grown together during the formation process. As part of an investigation of the dependence of the SMBH mass on bulge types and formation mechanisms, we present measurements of SMBH masses in two pseudo-bulge galaxies. The spiral galaxy NGC 3368 is double-barred and hosts a large pseudo-bulge with a tiny classical bulge component at the very centre. The S0 galaxy NGC 3489 has only a weak large-scale bar, a small pseudo-bulge and a small classical bulge. Both galaxies show weak nuclear activity in the optical, indicative of the presence of an SMBH. We present high-resolution, adaptive-optics-assisted, near-IR integral-field data of these two galaxies, taken with SINFONI at the Very Large Telescope, and use axisymmetric orbit models to determine the masses of the SMBHs. The SMBH mass of NGC 3368, averaged over the four quadrants, is 〈M•〉= 7.5 × 106 M⊙ with an error of 1.5 × 106 M⊙, which mostly comes from the non-axisymmetry in the data. For NGC 3489, a solution without a BH cannot be excluded when modelling the SINFONI data alone, but can be clearly ruled out when modelling a combination of SINFONI, OASIS and SAURON data, for which we obtain M•= (6.00+0.56−0.54∣stat± 0.64∣sys) × 106 M⊙. Although both galaxies seem to be consistent with the M•–σ relation, at face value they do not agree with the relation between bulge magnitude and BH mass when the total bulge magnitude (i.e. including both classical bulge and pseudo-bulge) is considered; the agreement is better when only the small classical bulge components are considered. However, taking into account the ageing of the stellar population could change this conclusion.
The masses of the most massive supermassive black holes (SMBHs) predicted by the M
BH-σ and M
BH-L relations appear to be in conflict. Which of the two relations is the more fundamental one remains ...an open question. NGC 1332 is an excellent example that represents the regime of conflict. It is a massive lenticular galaxy which has a bulge with a high velocity dispersion σ of ∼320 km s−1; bulge-disc decomposition suggests that only 44 per cent of the total light comes from the bulge. The M
BH-σ and the M
BH-L predictions for the central black hole mass of NGC 1332 differ by almost an order of magnitude. We present a stellar dynamical measurement of the SMBH mass using an axisymmetric orbit superposition method. Our SINFONI integral-field unit (IFU) observations of NGC 1332 resolve the SMBH's sphere of influence which has a diameter of ∼0.76 arcsec. The σ inside 0.2 arcsec reaches ∼400 km s−1. The IFU data allow us to increase the statistical significance of our results by modelling each of the four quadrants separately. We measure an SMBH mass of (1.45 ± 0.20) × 109 M⊙ with a bulge mass-to-light ratio of 7.08 ± 0.39 in the R band. With this mass, the SMBH of NGC 1332 is offset from the M
BH-L relation by a full order of magnitude but is consistent with the M
BH-σ relation.
Abstract
The formation and evolutionary history of M31 are closely related to its dynamical structures, which remain unclear due to its high inclination. Gas kinematics could provide crucial evidence ...for the existence of a rotating bar in M31. Using the position–velocity diagram of O
III
and H
i
, we are able to identify clear sharp velocity jump (shock) features with a typical amplitude over 100 km s
−1
in the central region of M31 (4.6 kpc × 2.3 kpc, or
20
′
×
10
′
). We also simulate gas morphology and kinematics in barred M31 potentials and find that the bar-induced shocks can produce velocity jumps similar to those in O
III
. The identified shock features in both O
III
and H
i
are broadly consistent, and they are found mainly on the leading sides of the bar/bulge, following a hallmark pattern expected from the bar-driven gas inflow. Shock features on the far side of the disk are clearer than those on the near side, possibly due to limited data coverage on the near side, as well as to obscuration by the warped gas and dust layers. Further hydrodynamical simulations with more sophisticated physics are desired to fully understand the observed gas features and to better constrain the parameters of the bar in M31.
ABSTRACT
This is the first of a series of papers dedicated to unveiling the mass composition and dynamical structure of a sample of flattened early‐type galaxies in the Coma cluster. We describe our ...modifications to the Schwarzschild code of Richstone et al. Applying a Voronoi tessellation in the surface of section, we are able to assign accurate phase‐space volumes to individual orbits and to reconstruct the full three‐integral phase‐space distribution function (DF) of any axisymmetric orbit library. Two types of tests have been performed to check the accuracy with which DFs can be represented by appropriate orbit libraries. First, by mapping DFs of spherical γ‐models and flattened Plummer models onto the library, we show that the resulting line‐of‐sight velocity distributions and internal velocity moments of the library match those derived directly from the DF to a precision better than that of present‐day observational errors. Secondly, by fitting libraries to the projected kinematics of the same DFs, we show that the DF reconstructed from the fitted library matches the input DF to a rms of about 15 per cent over a region in phase space covering 90 per cent of the mass of the library. The accuracy achieved allows us to implement effective entropy‐based regularization to fit real, noisy and spatially incomplete data.
We present high-dispersion spectra of two extremely massive star clusters in galactic merger remnants, obtained using the UVES spectrograph mounted on the ESO Very Large Telescope. One cluster, W30, ...is located in the ~500 Myr old merger remnant NGC 7252 and has a velocity dispersion and effective radius of $\sigma=27.5\pm2.5$ km s-1 and $R_{\rm eff}=9.3\pm1.7$ pc, respectively. The other cluster, G114, located in the ~3 Gyr old merger remnant NGC 1316, is much more compact, $R_{\rm eff}=4.08\pm0.55$ pc, and has a velocity dispersion of $\sigma=42.1\pm2.8$ km s-1. These measurements allow an estimate of the virial mass of the two clusters, yielding ${\cal{M}}_{\rm dyn}(W30)=1.59(\pm0.26)\times 10^7~{\cal{M}}_{\odot}$ and ${\cal{M}}_{\rm dyn}(G114)=1.64(\pm0.13)\times 10^7~{\cal{M}}_{\odot}$. Both clusters are extremely massive, being more than three times heavier than the most massive globular clusters in the Galaxy. For both clusters we measure light-to-mass ratios, which when compared to simple stellar population (SSP) models of the appropriate age, are consistent with a Kroupa-type stellar mass function. Using measurements from the literature we find a strong age dependence on how well SSP models (with underlying Kroupa or Salpeter-type stellar mass functions) fit the light-to-mass ratio of clusters. Based on this result we suggest that the large scatter in the light-to-mass ratio of the youngest clusters is not due to variations in the underlying stellar mass function, but instead to the rapidly changing internal dynamics of young clusters. Based on sampling statistics we argue that while W30 and G114 are extremely massive, they are consistent with being the most massive clusters formed in a continuous power-law cluster mass distribution. Finally, based on the positions of old globular clusters, young massive clusters (YMCs), ultra-compact dwarf galaxies (UCDs) and dwarf-globular transition objects (DGTOs) in κ-space we conclude that 1) UCDs and DGTOs are consistent with the high mass end of star clusters and 2) YMCs occupy a much larger parameter space than old globular clusters, consistent with the idea of preferential disruption of star clusters.
The supermassive black hole of Fornax A Nowak, N.; Saglia, R. P.; Thomas, J. ...
Monthly Notices of the Royal Astronomical Society,
12/2008, Volume:
391, Issue:
4
Journal Article
Peer reviewed
Open access
The radio galaxy Fornax A (NGC 1316) is a prominent merger remnant in the outskirts of the Fornax cluster. Its giant radio lobes suggest the presence of a powerful active galactic nuclei (AGN) and ...thus a central supermassive black hole (SMBH). Fornax A now seems to be in a transition state between active black hole growth and quiescence, as indicated by the strongly declined activity of the nucleus. Studying objects in this evolutionary phase is particularly important in order to understand the link between bulge formation and black hole growth, which is manifested in the M•–σ relation between black hole mass and bulge velocity dispersion. So far, a measurement of the SMBH mass has not been possible in Fornax A, as it is enshrouded in dust which makes optical measurements impossible. We present high-resolution adaptive optics assisted integral-field data of Fornax A, taken with SINFONI at the Very Large Telescope in the K band, where the influence of dust is negligible. The achieved spatial resolution is 0.085 arcsec, which is about a fifth of the diameter of the expected sphere of influence of the black hole. The stellar kinematics was measured using the region around the CO bandheads at 2.3 μm. Fornax A does not rotate inside the inner ∼3 arcsec. The velocity dispersion increases towards the centre. The weak AGN emission affects the stellar kinematics in the inner ∼0.06 arcsec only. Beyond this radius, the stellar kinematics appears relaxed in the central regions. We use axisymmetric orbit models to determine the mass of the SMBH in the centre of Fornax A. The three-dimensional nature of our data provides the possibility to directly test the consistency of the data with axisymmetry by modelling each of the four quadrants separately. According to our dynamical models, consistent SMBH masses M• and dynamical Ks-band mass-to-light ratios ϒ are obtained for all quadrants, with 〈M•〉= 1.3 × 108M⊙rms(M•) = 0.4 × 108M⊙ and 〈ϒ〉= 0.68rms(ϒ) = 0.03, confirming the assumption of axisymmetry. For the folded and averaged data, we find M•= 1.5+0.75−0.8× 108M⊙ and ϒ= 0.65+0.075−0.05 (3σ errors). Thus, the black hole mass of Fornax A is consistent within the error with the Tremaine et al. M•–σ relation, but is a factor of ∼4 smaller than expected from its bulge mass and the Marconi & Hunt relation.
We present an analysis of the H2 emission-line gas kinematics in the inner 4 arcsec radius of six nearby spiral galaxies, based on adaptive optics-assisted integral-field observations obtained in the ...K band with SINFONI/VLT. Four of the six galaxies in our sample display ordered H2 velocity fields, consistent with gas moving in the plane of the galaxy and rotating in the same direction as the stars. However, the gas kinematics is typically far from simple circular motion. We can classify the observed velocity fields into four different types of flows, ordered by increasing complexity: (1) circular motion in a disc (NGC 3351); (2) oval motion in the galaxy plane (NGC 3627 and NGC 4536); (3) streaming motion superimposed on circular rotation (NGC 4501); and (4) disordered streaming motions (NGC 4569 and NGC 4579). The H2 velocity dispersion in the galaxies is usually higher than 50 km s−1 in the inner 1-2 arcsec radii. The four galaxies with ordered kinematics have v/σ < 1 at radii less than 40-80 pc. The radius at which v/σ = 1 is independent of the type of nuclear activity. While the low values of v/σ could be taken as an indication of a thick disc in the innermost regions of the galaxies, other lines of evidence (e.g. H2 morphologies and velocity fields) argue for a thin disc interpretation in the case of NGC 3351 and NGC 4536. We discuss the implications of the high values of velocity dispersion for the dynamics of the gaseous disc and suggest caution when interpreting the velocity dispersion of ionized and warm tracers as being entirely dynamical. Understanding the nature and role of the velocity dispersion in the gas dynamics, together with the full 2D information of the gas, is essential for obtaining accurate black hole masses from gas kinematics.
Dynamical models for 17 early-type galaxies in the Coma cluster are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with ...luminosities between MB=−18.79 and −22.56. Kinematical long-slit observations cover at least the major-axis and minor-axis and extend to 1–4reff. Axisymmetric Schwarzschild models are used to derive stellar mass-to-light ratios and dark halo parameters. In every galaxy, the best fit with dark matter matches the data better than the best fit without. The statistical significance is over 95 per cent for eight galaxies, around 90 per cent for five galaxies and for four galaxies it is not significant. For the highly significant cases, systematic deviations between models without dark matter and the observed kinematics are clearly seen; for the remaining galaxies, differences are more statistical in nature. Best-fitting models contain 10–50 per cent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density, independent of the assumed dark matter density profile. The central phase-space density of dark matter is often orders of magnitude lower than that in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss–Hermite coefficient H4. Changing the balance between data-fit and regularization constraints does not change the reconstructed mass structure significantly: model anisotropies tend to strengthen if the weight on regularization is reduced, but the general property of a galaxy to be radially or tangentially anisotropic does not change. This paper is aimed to set the basis for a subsequent detailed analysis of luminous and dark matter scaling relations, orbital dynamics and stellar populations.
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