A diversity of dusty AGN tori - Data release for the VLTI/MIDI AGN Large Program and first results for 23 galaxies
TL;DR: In this paper, the authors used the MIDI interferometric instrument at the Very Large Telescope Interferometer (VLTI) to resolve the matter distribution on parsec scales and derived the flux and size estimates for 23 AGN tori.
Abstract: Context. The AGN-heated dust distribution (the “torus”) is increasingly recognized not only as the absorber required in unifying models, but as a tracer for the reservoir that feeds the nuclear super-massive black hole. Yet, even its most basic structural properties (such as its extent, geometry and elongation) are unknown for all but a few archetypal objects.Aims. In order to understand how the properties of AGN tori are related to feeding and obscuration, we need to resolve the matter distribution on parsec scales.Methods. Since most AGNs are unresolved in the mid-IR, even with the largest telescopes, we utilize the MID-infrared interferometric Instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) that is sensitive to structures as small as a few milli-arcseconds (mas). We present here an extensive amount of new interferometric observations from the MIDI AGN Large Program (2009–2011) and add data from the archive to give a complete view of the existing MIDI observations of AGNs. Additionally, we have obtained high-quality mid-IR spectra from VLT/VISIR to provide a precise total flux reference for the interferometric data.Results. We present correlated and total fluxes for 23 AGNs (16 of which with new data) and derive flux and size estimates at 12 μ m using simple axisymmetric geometrical models. Perhaps the most surprising result is the relatively high level of unresolved flux and its large scatter: The median “point source fraction” is 70% for type 1 and 47 % for type 2 AGNs meaning that a large part of the flux is concentrated on scales The half-light radii of the fainter sources are smaller than expected from the size ∝L 0.5 scaling of the bright sources and show a large scatter, especially when compared to the relatively tight size-luminosity relation in the near-infrared. It is likely that a common “size-luminosity” relation does not exist for AGN tori, but that they are dominated by intrinsic differences in their dust structures. Variations in the relative contribution of extended dust in the narrow line region or heated by star formation vs. compact AGN-heated dust and non-thermal emission also have to be taken into account.
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TL;DR: In this article, a Bayesian framework was developed for model comparison and parameter estimation of X-ray spectra of active galactic nuclei (AGN) in the 4 Ms Chandra Deep Field South.
Abstract: Context. Aims. Active galactic nuclei are known to have complex X-ray spectra that depend on both the properties of the accreting super-massive black hole (e.g. mass, accretion rate) and the distribution of obscuring material in its vicinity (i.e. the “torus”). Often however, simple and even unphysical models are adopted to represent the X-ray spectra of AGN, which do not capture the complexity and diversity of the observations. In the case of blank field surveys in particular, this should have an impact on e.g. the determination of the AGN luminosity function, the inferred accretion history of the Universe and also on our understanding of the relation between AGN and their host galaxies. Methods. We develop a Bayesian framework for model comparison and parameter estimation of X-ray spectra. We take into account uncertainties associated with both the Poisson nature of X-ray data and the determination of source redshift using photometric methods. We also demonstrate how Bayesian model comparison can be used to select among ten different physically motivated X-ray spectral models the one that provides a better representation of the observations. This methodology is applied to X-ray AGN in the 4 Ms Chandra Deep Field South.Results. For the ~350 AGN in that field, our analysis identifies four components needed to represent the diversity of the observed X-ray spectra: (1) an intrinsic power law; (2) a cold obscurer which reprocesses the radiation due to photo-electric absorption, Compton scattering and Fe-K fluorescence; (3) an unabsorbed power law associated with Thomson scattering off ionised clouds; and (4) Compton reflection, most noticeable from a stronger-than-expected Fe-K line. Simpler models, such as a photo-electrically absorbed power law with a Thomson scattering component, are ruled out with decisive evidence (B > 100). We also find that ignoring the Thomson scattering component results in underestimation of the inferred column density, N H , of the obscurer. Regarding the geometry of the obscurer, there is strong evidence against both a completely closed (e.g. sphere), or entirely open (e.g. blob of material along the line of sight), toroidal geometry in favour of an intermediate case. Conclusions. Despite the use of low-count spectra, our methodology is able to draw strong inferences on the geometry of the torus. Simpler models are ruled out in favour of a geometrically extended structure with significant Compton scattering. We confirm the presence of a soft component, possibly associated with Thomson scattering off ionised clouds in the opening angle of the torus. The additional Compton reflection required by data over that predicted by toroidal geometry models, may be a sign of a density gradient in the torus or reflection off the accretion disk. Finally, we release a catalogue of AGN in the CDFS with estimated parameters such as the accretion luminosity in the 2−10 keV band and the column density, N H , of the obscurer.
1,072 citations
Cites methods from "A diversity of dusty AGN tori - Dat..."
...This picture is further motivated by high-resolution optical space-based observations (Ferrarese et al. 1996; van der Marel & van den Bosch 1998), which show such a torus-like structures in ∼100−1000 pc scale, or more recently, mid-infrared interferometry (Burtscher et al. 2013)....
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TL;DR: A review of recent developments related to the unified model of active galactic nuclei (AGNs) can be found in this paper, where the authors focus on new ideas about the origin and properties of the central obscurer (torus) and the connection to its surroundings.
Abstract: This review describes recent developments related to the unified model of active galactic nuclei (AGNs). It focuses on new ideas about the origin and properties of the central obscurer (torus) and the connection to its surroundings. The review does not address radio unification. AGN tori must be clumpy but uncertainties about their properties persist. Today's most promising models involve disk winds of various types and hydrodynamic simulations that link the large-scale galactic disk to the inner accretion flow. Infrared (IR) studies greatly improved our understanding of the spectral energy distribution of AGNs, but they are hindered by various selection effects. X-ray samples are more complete. The dependence of the covering factor of the torus on luminosity is a basic relationship that remains unexplained. There is also much confusion regarding real type-II AGNs, which do not fit into a simple unification scheme. The most impressive recent results are due to IR interferometry, which is not in accord wit...
610 citations
Cites methods from "A diversity of dusty AGN tori - Dat..."
...(adopted from Burtscher et al. (2013), courtesy of Leonard Burtscher)....
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...MID-infrared interferometric Instrument (MIDI): The ESO interferometer working in the 8-13µm atmospheric window with projected baselines ranging from about 30 to 130m (e.g. Jaffe et al. 2004, Kishimoto et al. 2011b, Burtscher et al. 2013, Hönig et al. 2013)....
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...The MIDI latest results, summarized in Burtscher et al. (2013) and illustrated in Figure 4, include 23 sources with 8–13µm dimensions of 1-100 pc....
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Centre national de la recherche scientifique1, Chalmers University of Technology2, Spanish National Research Council3, INAF4, Max Planck Society5, Rutgers University6, University of Toulouse7, University of Cologne8, King Abdulaziz University9, ETH Zurich10, University of La Laguna11, Kapteyn Astronomical Institute12, Leiden University13
TL;DR: In this paper, the authors used the Atacama Large Millimeter Array (ALMA) to map the emission of a set of dense molecular gas (n(H2)'1056 cm3) tracers (CO(3-2), CO(6-5), HCN(4-3), HCO+CS(7-6)) and their underlying continuum emission in the central r ∼ 2 kpc of NGC 1068 with spatial resolutions ∼0:3000:500 (∼20-35 pc for the assumed distance of D = 14 Mpc
Abstract: Aims. We investigate the fueling and the feedback of star formation and nuclear activity in NGC 1068, a nearby (D = 14 Mpc) Seyfert 2 barred galaxy, by analyzing the distribution and kinematics of the molecular gas in the disk. We aim to understand if and how gas accretion can self-regulate.Methods. We have used the Atacama Large Millimeter Array (ALMA) to map the emission of a set of dense molecular gas (n(H2) ' 1056 cm3) tracers (CO(3-2), CO(6-5), HCN(4-3), HCO+(4-3), and CS(7-6)) and their underlying continuum emission in the central r ∼ 2 kpc of NGC 1068 with spatial resolutions ∼0:3000:500 (∼20-35 pc for the assumed distance of D = 14 Mpc). Results. The sensitivity and spatial resolution of ALMA give an unprecedented detailed view of the distribution and kinematics of the dense molecular gas (n(H2) ≈ 1056cm3) in NGC 1068. Molecular line and dust continuum emissions are detected from a r ∼ 200 pc off-centered circumnuclear disk (CND), from the 2.6 kpc-diameter bar region, and from the r ∼ 1:3 kpc starburst (SB) ring. Most of the emission in HCO+, HCN, and CS stems from the CND. Molecular line ratios show dramatic order-of-magnitude changes inside the CND that are correlated with the UV/X-ray illumination by the active galactic nucleus (AGN), betraying ongoing feedback. We used the dust continuum fluxes measured by ALMA together with NIR/MIR data to constrain the properties of the putative torus using CLUMPY models and found a torus radius of 20+6 10 pc. The Fourier decomposition of the gas velocity field indicates that rotation is perturbed by an inward radial flow in the SB ring and the bar region. However, the gas kinematics from r ∼ 50 pc out to r ∼ 400 pc reveal a massive (Mmol ∼ 2:7+0:9 1:2 × 107 M) outflow in all molecular tracers. The tight correlation between the ionized gas outflow, the radio jet, and the occurrence of outward motions in the disk suggests that the outflow is AGN driven. Conclusions. The molecular outflow is likely launched when the ionization cone of the narrow line region sweeps the nuclear disk. The outflow rate estimated in the CND, dM=dt ∼ 63+21 37 M yr1, is an order of magnitude higher than the star formation rate at these radii, confirming that the outflow is AGN driven. The power of the AGN is able to account for the estimated momentum and kinetic luminosity of the outflow. The CND mass load rate of the CND outflow implies a very short gas depletion timescale of ≤1 Myr. The CND gas reservoir is likely replenished on longer timescales by efficient gas inflow from the outer disk. © ESO 2014.
455 citations
Additional excerpts
...For comparison the modeled 12 µm interferometric half radius of the resolved and unresolved components of NGC 1068 is 1.6 pc (Burtscher et al. 2013)....
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TL;DR: In this article, the authors explore the evolution of stellar mass black hole binaries (BHBs) which are formed in the self-gravitating disks of active galactic nuclei (AGN).
Abstract: We explore the evolution of stellar mass black hole binaries (BHBs) which are formed in the self-gravitating disks of active galactic nuclei (AGN). Hardening due to three-body scattering and gaseous drag are effective mechanisms that reduce the semi-major axis of a BHB to radii where gravitational waves take over, on timescales shorter than the typical lifetime of the AGN disk. Taking observationally-motivated assumptions for the rate of star formation in AGN disks, we find a rate of disk-induced BHB mergers ($\mathcal{R} \sim 3~{\rm yr}^{-1}~{\rm Gpc}^{-3}$, but with large uncertainties) that is comparable with existing estimates of the field rate of BHB mergers, and the approximate BHB merger rate implied by the recent Advanced LIGO detection of GW150914. BHBs formed thorough this channel will frequently be associated with luminous AGN, which are relatively rare within the sky error regions of future gravitational wave detector arrays. This channel could also possess a (potentially transient) electromagnetic counterpart due to super-Eddington accretion onto the stellar mass black hole following the merger.
404 citations
Cites background from "A diversity of dusty AGN tori - Dat..."
...10 pc (Burtscher et al. 2013), motivating our fiducial choice of Rout = 10 pc: if the reader is curious about disks truncated at smaller radii, our results can be simply cut off beyond the desired radius (disk conditions in the T05 model do not depend on conditions exterior to the radius of…...
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TL;DR: In this paper, the authors review results from cosmic X-ray surveys of active galactic nuclei (AGNs) over the past 15 years that have dramatically improved our understanding of growing supermassive black holes in the distant universe.
Abstract: We review results from cosmic X-ray surveys of active galactic nuclei (AGNs) over the past $$\approx 15$$
years that have dramatically improved our understanding of growing supermassive black holes in the distant universe. First, we discuss the utility of such surveys for AGN investigations and the capabilities of the missions making these surveys, emphasizing Chandra, XMM-Newton, and NuSTAR. Second, we briefly describe the main cosmic X-ray surveys, the essential roles of complementary multiwavelength data, and how AGNs are selected from these surveys. We then review key results from these surveys on the AGN population and its evolution (“demographics”), the physical processes operating in AGNs (“physics”), and the interactions between AGNs and their environments (“ecology”). We conclude by describing some significant unresolved questions and prospects for advancing the field.
333 citations
References
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TL;DR: The straw person model (SPM) as mentioned in this paper has been proposed to explain the orientation effects of active galactic nuclei (AGN) and quasars in the line of sight (LOS) images.
Abstract: Because the critical central regions of Active Galactic Nuclei (AGN) and quasars are strongly nonspherical but spatially unresolved, orientation effects have been the source of much confusion. In fact, it now appears that much of the variety in AGN types is just the result of varying orientation relative to the line of sight. We can define an extreme hypothesis,, the straw person model (SPM), in which there are two basic types of AGN: the radio quiets and the radio louds. For each type there is a range in intrinsic luminosity, and the luminosity controls some properties such as the Fanaroff and Riley classes. However, at a given intrinsic luminosity, all other properties such as spectroscopic classification and VLBI component speeds are ascribed to orientation. This model is only a caricature of the unification idea, and is already ruled out on many grounds, but it will be useful for organizing the discussion. I’ll describe what I consider to be convincing evidence that orientation effects are important and widespread. The true situation may be in some sense half way between the SPM and the hypothesis that orientation doesn’t affect classification at aIl. To us optimists, the orienration cup is half full rather than half empty. Although it is too soon to say for sure, the hypothesis that most objects’ classifications would be different if seen from other directions is a tenable one today.
4,005 citations
"A diversity of dusty AGN tori - Dat..." refers background in this paper
...The parsec-scale dust distribution in Active Galactic Nuclei (AGNs), that is often referred to as the “torus”, is increasingly recognized not only as the absorber required for unification (Antonucci, 1993), but as a tracer for the reservoir that feeds the nuclear Super-Massive Black Hole (SMBH)....
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TL;DR: In this article, the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum are presented.
Abstract: We present an atlas of the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum. The primary (UVSX) sample includes 47 quasars for which the spectral energy distributions include X-ray spectral indices and UV data. Of these, 29 are radio quiet, and 18 are radio loud. The SEDs are presented both in figures and in tabular form, with additional tabular material published on CD-ROM. Previously unpublished observational data for a second set of quasars excluded from the primary sample are also tabulated. The effects of host galaxy starlight contamination and foreground extinction on the UVSX sample are considered and the sample is used to investigate the range of SED properties. Of course, the properties we derive are influenced strongly by the selection effects induced by quasar discovery techniques. We derive the mean energy distribution (MED) for radio-loud and radio-quiet objects and present the bolometric corrections derived from it. We note, however, that the dispersion about this mean is large (approximately one decade for both the infrared and ultraviolet components when the MED is normalized at the near-infrared inflection). At least part of the dispersion in the ultraviolet may be due to time variability, but this is unlikely to be important in the infrared. The existence of such a large dispersion indicates that the MED reflects only some of the properties of quasars and so should be used only with caution.
1,923 citations
"A diversity of dusty AGN tori - Dat..." refers methods in this paper
...This is the model 7 We assume Lbol ≈ 1.5LUV, from Elvis et al. (1994) and Runnoe et al. (2012), with the assumption of a flat powerlaw spectrum in the optical (e.g. Kishimoto et al., 2008)....
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TL;DR: In this paper, the authors quantify the importance of mass accretion during AGN phases in the growth of supermassive black holes (BH) by comparing the mass function of black holes in the local universe with that expected from AGN relics, which are black holes grown entirely with mass accumulation during AGNs phases.
Abstract: We quantify the importance of mass accretion during AGN phases in the growth of supermassive black holes (BH) by comparing the mass function of black holes in the local universe with that expected from AGN relics, which are black holes grown entirely with mass accretion during AGN phases. The local BH mass function (BHMF) is estimated by applying the well-known correlations between BH mass, bulge luminosity and stellar velocity dispersion to galaxy luminosity and velocity functions. We find that different correlations provide the same BHMF only if they have the same intrinsic dispersion. The density of supermassive black holes in the local universe which we estimate is ρBH = 4.6 +1.9 −1.4 h 2.7 × 10 5 M⊙ Mpc −3 . The relic BHMF is derived from the continuity equation with the only assumption that AGN activity is due to accretion onto massive BH’s and that merging is not important. We find that the relic BHMF at z = 0 is generated mainly at z 10 9 M⊙ but can become as large as ∼ 10 9 yr for the lowest acceptable ǫ and λ values.
1,586 citations
"A diversity of dusty AGN tori - Dat..." refers methods in this paper
...We use the prescription from Gandhi et al. (2009) that combines their midinfrared–X-ray relation and the X-ray bolometric correction factors from Marconi et al. (2004) and give the inferred bolometric luminosities for all targets as well as the expected inner radii in Table 6....
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TL;DR: This catalogue is a compilation of all known AGN in a compact and convenient form and includes position and redshift, as well as photometry (U, B,V) and 6 cm and 20 cm flux densities, when available.
Abstract: Aims. This catalogue is aimed at presenting a compilation of all known AGN in a compact and convenient form, and we hope that it will be useful to all workers in this field. Methods. Like the twelfth edition, it includes position and redshift, as well as photometry (U, B,V) and 6 cm and 20 cm flux densities, when available. Results. The present version contains 133 336 quasars, 1 374 BL Lac objects, and 34 231 active galaxies (including 16 517 Seyfert 1s), almost doubling the number listed in the 12th edition. We also give a list of all known lensed and double quasars.
714 citations