Search

We report on our combined analysis of HST , VLT/MUSE, VLT/SINFONI, and ALMA observations of the local Seyfert 2 galaxy, NGC 5728 to investigate in detail the feeding and feedback of the active galactic nucleus (AGN). The data sets simultaneously probe the morphology, excitation, and kinematics of the stars, ionized gas, and molecular gas over a large range of spatial scales (10 pc to 10 kpc). NGC 5728 contains a large stellar bar that is driving gas along prominent dust lanes to the inner 1 kpc where the gas settles into a circumnuclear ring. The ring is strongly star forming and contains a substantial population of young stars as indicated by the lowered stellar velocity dispersion and gas excitation consistent with H  ii regions. We model the kinematics of the ring using the velocity field of the CO (2–1) emission and stars and find it is consistent with a rotating disc. The outer regions of the disc, where the dust lanes meet the ring, show signatures of inflow at a rate of 1 M |$\odot$|  yr−1. Inside the ring, we observe three molecular gas components corresponding to the circular rotation of the outer ring, a warped disc, and the nuclear stellar bar. The AGN is driving an ionized gas outflow that reaches a radius of 250 pc with a mass outflow rate of 0.08 M |$\odot$|  yr−1 consistent with its luminosity and scaling relations from previous studies. While we observe distinct holes in CO emission which could be signs of molecular gas removal, we find that largely the AGN is not disrupting the structure of the circumnuclear region. [ABSTRACT FROM AUTHOR]

High-resolution observations from the submm to the optical wavelength regime resolve the central few 100 pc region of nearby galaxies in great detail. They reveal a large diversity of features: thick gas and stellar discs, nuclear starbursts, inflows and outflows, central activity, jet interaction, etc. Concentrating on the role circumnuclear discs play in the life cycles of galactic nuclei, we employ 3D adaptive mesh refinement hydrodynamical simulations with the RAMSES code to self-consistently trace the evolution from a quasi-stable gas disc, undergoing gravitational (Toomre) instability, the formation of clumps and stars and the disc's subsequent, partial dispersal via stellar feedback. Our approach builds upon the observational finding that many nearby Seyfert galaxies have undergone intense nuclear starbursts in their recent past and in many nearby sources star formation is concentrated in a handful of clumps on a few 100 pc distant from the galactic centre. We show that such observations can be understood as the result of gravitational instabilities in dense circumnuclear discs. By comparing these simulations to available integral field unit observations of a sample of nearby galactic nuclei, we find consistent gas and stellar masses, kinematics, star formation and outflow properties. Important ingredients in the simulations are the self-consistent treatment of star formation and the dynamical evolution of the stellar distribution as well as the modelling of a delay time distribution for the supernova feedback. The knowledge of the resulting simulated density structure and kinematics on pc scale is vital for understanding inflow and feedback processes towards galactic scales. [ABSTRACT FROM AUTHOR]

The active galaxy MCG-C6-30-15 has a 400 pc diameter stellar kinematically distinct core, counter-rotating with respect to the main body of the galaxy. Our previous high spatial resolution (0.1 arcsec) H-band observations of this galaxy mapped the stellar kinematics and [Fe II] 1.64 μm gas dynamics though mainly restricted to the spatial region of the counter-rotating core. In this work, we probe the stellar kinematics on a larger field of view and determine the ionized and molecular gas dynamics to study the formation of the counter-rotating core and the implications for active galactic nucleus (AGN) fuelling. We present integral field spectroscopy observations with SINFONI in the H and K bands in the central 1.2 kpc and with VIMOS HR-blue in the central 4 kpc of the galaxy. Ionized gas outflows of vout ~ 100 km s.1 are traced by the [Ca VIII] 2.32 μm coronal line and extend out to at least a radius of r ~ 140 pc. The molecular gas, traced by the H2 2.12 μm emission, is also counter-rotating with respect to the main body of the galaxy, indicating that the formation of the distinct core was associated with inflow of external gas into the centre of MCG-C6-30-15. The molecular gas traces the available gas reservoir for AGN fuelling and is detected as close as r ~ 50-C100 pc. External gas accretion is able to significantly replenish the fuelling reservoir suggesting that the event which formed the counter-rotating core was also the main mechanism providing gas for AGN fuelling. [ABSTRACT FROM AUTHOR]

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 1011 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 AV ≤ 3 for Seyfert 1–1.5s, while Seyfert 1.8–1.9s have AV 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 NH and the extinction to the BLR are consistent with the Galactic gas-to-dust ratio if NH variations are considered. [ABSTRACT FROM AUTHOR]

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. H13CN 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 LHCN and Mdyn that can be explained by a gas fraction of 10 per cent and a conversion factor αHCN ~ 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. [ABSTRACT FROM AUTHOR]

We combine two approaches to isolate the AGN luminosity at near-IR wavelengths and relate the near-IR pure AGN luminosity to other tracers of the AGN. Using integral-field spectroscopic data of an archival sample of 51 local AGNs, we estimate the fraction of non-stellar light by comparing the nuclear equivalent width of the stellar 2.3 µm CO absorption feature with the intrinsic value for each galaxy. We compare this fraction to that derived from a spectral decomposition of the integrated light in the central arcsecond and find them to be consistent with each other. Using our estimates of the near-IR AGN light, we find a strong correlation with presumably isotropic AGN tracers. We show that a significant offset exists between type 1 and type 2 sources in the sense that type 1 sources are 7 (10) times brighter in the near-IR at log LAGNMIR = 42.5 (log LAGNX = 42.5). These offsets only become clear when treating infrared type 1 sources as type 1 AGNs. All AGNs have very red near- to mid-IR dust colors. This, as well as the range of observed near-IR temperatures, can be explained with a simple model with only two free parameters: the obscuration to the hot dust and the ratio between the warm and hot dust areas. We find obscurations of AVhot = 5...15 mag for infrared type 1 sources and AVhot = 15...35 mag for type 2 sources. The ratio of hot dust to warm dust areas of about 1000 is nicely consistent with the ratio of radii of the respective regions as found by infrared interferometry. [ABSTRACT FROM AUTHOR]

Galactic gas-gas collisions involving a turbulent multiphase interstellar medium (ISM) share common ISM properties: dense extraplanar gas visible in CO, large linewidths (≳50 km s-1), strong mid-infrared H2 line emission, low star formation activity, and strong radio continuum emission. Gas-gas collisions can occur in the form of ram pressure stripping caused by the rapid motion of a spiral galaxy within the intracluster medium, galaxy head-on collisions, compression of the intragroup gas and/or galaxy ISM by an intruder galaxy which flies through the galaxy group at a high velocity, or external gas accretion on an existing gas torus in a galactic center. We suggest that the common theme of all these gas-gas interactions is adiabatic compression of the ISM leading to an increase of the turbulent velocity dispersion of the gas. The turbulent gas clouds are then overpressured and star formation is quenched. Within this scenario we developed a model for turbulent clumpy gas disks where the energy to drive turbulence is supplied by external infall or the gain of potential energy by radial gas accretion within the disk. The cloud size is determined by the size of a continuous (C-type) shock propagating in dense molecular clouds with a low ionization fraction at a given velocity dispersion. We give expressions for the expected volume and area filling factors, mass, density, column density, and velocity dispersion of the clouds. The latter is based on scaling relations of intermittent turbulence whose open parameters are estimated for the circumnuclear disk in the Galactic center. The properties of the model gas clouds (∼0.1 pc, ∼100 M⊙, Δv ≳ 6 kms-1) and the external mass accretion rate necessary for the quenching of the star formation rate due to adiabatic compression (Ṁ ∼ 1-10 M⊙ yr-1) are consistent with those derived from high-resolution H2 2.12 μm line observations. Based on these findings, a scenario for the evolution of gas tori in galactic centers is proposed and the implications for star formation in the Galactic center are discussed. [ABSTRACT FROM AUTHOR]

We present the first near-IR integral field spectroscopy observations of the galaxy MCG–6-30-15. The H-band data studied in this paper cover the central 500 pc of the galaxy at the best resolution (0.1 arcsec) so far. The spectra of the innermost regions are dominated by broad Brackett series emission lines and non-stellar continuum, under which we are able to trace the distribution and kinematics of the stars and also the [Fe ii] line emission. We find that there is a counter-rotating stellar core extending out to 125 pc, which appears to be associated with the [Fe ii] emission. Based on the mass-to-light ratio, and the presence of this emission line, we estimate the age of the central stellar population to be of the order of 65 Myr. We show that the gas needed to fuel the black hole is, at most, only 1 per cent of that needed to form these stars. We derive independent constraints on the black hole mass using the dynamical information and determine an upper limit for the black hole mass, MBH < 6 × 107 M⊙, that is consistent with other estimates. [ABSTRACT FROM AUTHOR]

In a matched sample of Seyfert and quiescent galaxies we simultaneously probe the stellar and molecular gas kinematics from 1 kpc down to 50 pc with the aim of identifying the dynamical processes dictating black hole accretion rates. This first paper compares the global characteristics of a sample of 10 galaxies. We find several differences within a radius of 500 pc that are correlated with active galactic nucleus (AGN) activity. The Seyferts have (1) a more centrally concentrated nuclear stellar surface brightness with lower stellar luminosities beyond a radius of 100 pc, (2) a lower stellar velocity dispersion within a radius of 200 pc, (3) elevated H2 1-0 S(1) luminosity out to a radius of at least 250 pc, and (4) more centrally concentrated H2 surface brightness profiles. These observed differences can be interpreted as evidence for Seyfert galaxies having a dynamically cold (in comparison to the bulge) nuclear structure composed of a significant gas reservoir and a relatively young stellar population. This structure is undetected (and possibly does not exist) in quiescent galaxies. The presence of such a nuclear structure in Seyfert galaxies provides evidence for inflow of the surrounding interstellar medium since the nuclear stellar population requires a supply of gas from which to form. The fueling of a Seyfert AGN is thus associated with the formation of a dynamically cold component of gas and stars on scales of hundreds of parsecs. [ABSTRACT FROM AUTHOR]

As part of an extensive study of the physical properties of active galactic nuclei (AGNs) we report high spatial resolution near-IR integral-field spectroscopy of the narrow-line region (NLR) and coronal-line region (CLR) of seven Seyfert galaxies. These measurements elucidate for the first time the two-dimensional spatial distribution and kinematics of the recombination line Bry and high-ionization lines [Si VI], [Al IX], and [Ca VIII] on scales <300 pc from the AGN. The observations reveal kinematic signatures of rotation and outflow in the NLR and CLR. The spatially resolved kinematics can be modeled as a combination of an outflow bicone and a rotating disk coincident with the molecular gas. High-excitation emission is seen in both components, suggesting it is leaking out of a clumpy torus. While NGC 1068 (Seyfert 2) is viewed nearly edge-on, intermediate-type Seyferts are viewed at intermediate angles, consistent with unified schemes. A correlation between the outflow velocity and the molecular gas mass in r < 30 pc indicates that the accumulation of gas around the AGN increases the collimation and velocity of the outflow. The outflow rate is 2-3 orders of magnitude greater than the accretion rate, implying that the outflow is mass loaded by the surrounding interstellar medium (ISM). In half of the observed AGNs, the kinetic power of the outflow is of the order of the power required by two-stage feedback models to be thermally coupled to the ISM and to match the MBH-σ* relation. In these objects, the radio jet is clearly interacting with the ISM, indicative of a link between jet power and outflow power. [ABSTRACT FROM AUTHOR]

Recently, high-resolution observations with the help of the near-infrared adaptive optics integral field spectrograph Spectrograph for INtegral Field Observations in the Near Infrared (SINFONI) at the Very Large Telescope proved the existence of massive and young nuclear star clusters in the centres of a sample of Seyfert galaxies. With the help of three-dimensional high-resolution hydrodynamical simulations with the Pluto code, we follow the evolution of such clusters, especially focusing on stellar mass loss feeding gas into the ambient interstellar medium and driving turbulence. This leads to a vertically wide distributed clumpy or filamentary inflow of gas on large scales (tens of parsec), whereas a turbulent and very dense disc builds up on the parsec scale. In order to capture the relevant physics in the inner region, we treat this disc separately by viscously evolving the radial surface density distribution. This enables us to link the tens of parsec-scale region (accessible via SINFONI observations) to the (sub-)parsec-scale region (observable with the mid-infrared interferometer instrument and via water maser emission). Thereby, this procedure provides us with an ideal testbed for data comparison. In this work, we concentrate on the effects of a parametrized turbulent viscosity to generate angular momentum and mass transfer in the disc and additionally take star formation into account. Most of the input parameters are constrained by available observations of the nearby Seyfert 2 galaxy NGC 1068, and we discuss parameter studies for the free parameters. At the current age of its nuclear starburst of 250 Myr, our simulations yield disc sizes of the order of 0.8–0.9 pc, gas masses of and mass transfer rates of through the inner rim of the disc. This shows that our large-scale torus model is able to approximately account for the disc size as inferred from interferometric observations in the mid-infrared and compares well to the extent and mass of a rotating disc structure as inferred from water maser observations. Several other observational constraints are discussed as well. [ABSTRACT FROM AUTHOR]

Our adaptive optics observations of nearby AGN at spatial resolutions as small as 0.″085 show strong evidence for recent, but no longer active, nuclear star formation. We begin by describing observations that highlight two contrasting methods by which gas can flow into the central tens of parsecs. Gas accumulation in this region will inevitably lead to a starburst, and we discuss the evidence for such events. We then turn to the impact of stellar evolution on the further inflow of gas by combining a phenomenological approach with analytical modelling and hydrodynamic simulations. These complementary perspectives paint a picture in which all the processes are ultimately regulated by the mass accretion rate into the central hundred parsecs, and the ensuing starburst that occurs there. The resulting supernovae delay accretion by generating a starburst wind, which leaves behind a clumpy interstellar medium. This provides an ideal environment for slower stellar outflows to accrete inwards and form a dense turbulent disk on scales of a few parsecs. Such a scenario may resolve the discrepancy between the larger scale structure seen with adaptive optics and the small-scale structure seen with VLTI. [ABSTRACT FROM PUBLISHER]

Recently, high-resolution observations made with the help of the near-infrared adaptive optics integral field spectrograph SINFONI at the VLT proved the existence of massive and young nuclear star clusters in the centers of a sample of Seyfert galaxies. With the help of high-resolution hydrodynamical simulations with the pluto code, we follow the evolution of such clusters, especially focusing on mass and energy feedback from young stars. This leads to a filamentary inflow of gas on large scales (tens of parsecs), whereas a turbulent and very dense disk builds up on the parsec scale. Here we concentrate on the long-term evolution of the nuclear disk in NGC 1068 with the help of an effective viscous disk model, using the mass input from the large-scale simulations and accounting for star formation in the disk. This two-stage modeling enables us to connect the tens-of-parsecs scale region (observable with SINFONI) with the parsec-scale environment (MIDI observations). At the current age of the nuclear star cluster, our simulations predict disk sizes of the order 0.8 to 0.9 pc, gas masses of order 106M⊙, and mass transfer rates through the inner boundary of order 0.025 M⊙yr−1, in good agreement with values derived from observations. [ABSTRACT FROM PUBLISHER]

In a survey of 18 nearby Seyfert nuclei, we find evidence for geometrically thick gas disks on scales of tens of parsecs. Mapping the interstellar medium traced by H2 ν = 1–0 S(1) emission using the infrared integral field spectrometers OSIRIS and SINFONI reveals general disk rotation with an additional significant component of random bulk motion implied by the high local velocity dispersion. The size scale of the typical nuclear gas disk is ~30 pc in radius with a comparable vertical height, and the distribution and kinematics suggest the gas is spatially mixed with the nuclear stellar population. Based on the estimated characteristic gas mass fraction of 10%, the average gas mass within this region is ~107M⊙. This suggests column densities of NH ~ 5 × 1023 cm−2, but the significantly lower densities implied by the stellar continuum extinction indicate that the gas distribution on these scales is dominated by dense clumps. We discuss the feasibility of constraining the masses of the central black holes via modeling of the gas disk kinematics, highlighting the importance of properly accounting for the gas velocity dispersion, and the use of these direct mass estimates to calibrate masses derived from the method of reverberation mapping. [ABSTRACT FROM PUBLISHER]

We present results from a survey of nearby AGN using the adaptive optics assisted integral-field spectrometer SINFONI on the VLT. These data enable us to study at high angular resolution (~ 0.″08) the distribution and kinematics of the low-ionization gas traced by the BrΓλ2.17 μm recombination line and [Si vi] λ 1.96 μm, [Al ix] λ 2.04 μm, and [Ca viii] λ 2.32 μm, the most prominent coronal lines in the near-IR. Overall, our results show that the coronal lines extend to a radius similar to that of narrow Brγ emission, mimicking in most cases the narrow-line region (NLR). In addition, the kinematics of the highly ionized species, and most of the Brγ kinematics, is dominated by non-circular motions with higher dispersion along the ionization cones, indicating that material is being accelerated and outflowing from a region very close to the AGN. [ABSTRACT FROM PUBLISHER]