Browsing by Author "Nikutta, Robert"

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    A tale of three galaxies: A "CLUMPY" view of the spectroscopically anomalous galaxies IRAS F10398+1455, IRAS F21013-0739 and SDSS J0808+3948
    (2016) Xie, Yanxia; Nikutta, Robert; Hao, Lei; Li, Aigen
    We investigate the dust properties in three spectroscopically anomalous galaxies (IRAS F10398+1455, IRAS F21013-0739 and SDSS J0808+3948). Their Spitzer/IRS spectra are characterized by a steep similar to 5-8 gm emission continuum, strong emission bands from polycyclic aromatic hydrocarbon (PAH) molecules, and prominent 10 mu m silicate emission. The steep similar to 5-8 mu m continuum and strong PAH emission features suggest the presence of starbursts, while the silicate emission is indicative of significant heating from AGNs. The simultaneous detection of these two observational properties has rarely been reported on galactic scale. We employ the PAHETT software to estimate their starlight contributions, and the CLUMPY model for the components contributed by the AGN tori. We find that the CLUMPY model is generally successful in explaining the overall dust infrared emission, although it appears to emit too flat at the similar to 5-8 mu m continuum to be consistent with that observed in IRAS F10398+1455 and IRAS F210130739. The flat similar to 5-8 mu m continuum calculated from the CLUMPY model could arise from the adopted specific silicate opacity of Ossenkopf et al. (1992) which exceeds that of the Draine and Lee (1984) "astronomical silicate" by a factor up to 2 in the similar to 5-8 mu m wavelength range. Future models with a variety of dust species incorporated in the CLUMPY radiation transfer regime are needed for a thorough understanding of the dust properties of these spectroscopically anomalous galaxies. (C) 2016 Elsevier Ltd. All rights reserved.
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    A TALE OF THREE GALAXIES: DECIPHERING THE INFRARED EMISSION OF THE SPECTROSCOPICALLY ANOMALOUS GALAXIES IRAS F10398+1455, IRAS F21013-0739, AND SDSS J0808+3948
    (IOP PUBLISHING LTD, 2015) Xie, Yanxia; Li, Aigen; Hao, Lei; Nikutta, Robert
    The Spitzer/Infrared Spectrograph spectra of three spectroscopically anomalous galaxies (IRAS F10398+ 1455, IRAS F21013-0739, and SDSS J0808+3948) are modeled in terms of a mixture of warm and cold silicate dust, and warm and cold carbon dust. Their unique infrared (IR) emission spectra are characterized by a steep similar to 5-8 mu m emission continuum, strong emission bands from polycyclic aromatic hydrocarbon (PAH) molecules, and prominent silicate emission. The steep similar to 5-8 mu m emission continuum and strong PAH emission features suggest the dominance of starbursts, while the silicate emission is indicative of significant heating from active galactic nuclei (AGNs). With warm and cold silicate dust of various compositions ("astronomical silicate," amorphous olivine, or amorphous pyroxene) combined with warm and cold carbon dust (amorphous carbon, or graphite), we are able to closely reproduce the observed IR emission of these galaxies. We find that the dust temperature is the primary cause in regulating the steep similar to 5-8 mu m continuum and silicate emission, insensitive to the exact silicate or carbon dust mineralogy and grain size a as long as a. 1 mm. More specifically, the temperature of the similar to 5-8 mu m continuum emitter (which is essentially carbon dust) of these galaxies is similar to 250-400 K, much lower than that of typical quasars, which is similar to 640 K. Moreover, it appears that larger dust grains are preferred in quasars. The lower dust temperature and smaller grain sizes inferred for these three galaxies compared with that of quasars could be due to the fact that they may harbor a young/weak AGNs that is not maturely developed yet.
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    HIGH-VELOCITY BIPOLAR MOLECULAR EMISSION FROM AN AGN TORUS
    (2016) Gallimore, Jack F.; Elitzur, Moshe; Maiolino, Roberto; Marconi, Alessandro; O'Dea, Christopher P.; Lutz, Dieter; Baum, Stefi A.; Nikutta, Robert; Impellizzeri, C. M. V.; Davies, Richard; Kimball, Amy E.; Sani, Eleonora
    We have detected in ALMA observations CO J = 6 -> 5 emission from the nucleus of the Seyfert galaxy NGC 1068. The low-velocity (up to +/- 70 km s(-1) relative to systemic) CO emission resolves into a 12 x 7 pc structure, roughly aligned with the nuclear radio source. Higher-velocity emission (up to +/- 400 km s(-1)) is consistent with a bipolar outflow in a direction nearly perpendicular (similar or equal to 80 degrees) to the nuclear disk. The position-velocity diagram shows that in addition to the outflow, the velocity field may also contain rotation about the disk axis. These observations provide compelling evidence in support of the disk-wind scenario for the active galactic nucleus obscuring torus.
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    INFRARED SPECTRAL ENERGY DISTRIBUTION DECOMPOSITION OF WISE-SELECTED, HYPERLUMINOUS HOT DUST-OBSCURED GALAXIES
    (2016) Fan, Lulu; Han, Yunkun; Nikutta, Robert; Drouart, Guillaume; Knudsen, Kirsten K.
    We utilize a Bayesian approach to fit the observed mid-IR-to-submillimeter/millimeter spectral energy distributions (SEDs) of 22 WISE-selected and submillimeter-detected, hyperluminous hot dust-obscured galaxies (Hot DOGs), with spectroscopic redshift ranging from 1.7 to 4.6. We compare the Bayesian evidence of a torus plusgraybody (Torus+GB) model with that of a torus-only (Torus) model and find that the Torus+GB model has higher Bayesian evidence for all 22 Hot DOGs than the torus-only model, which presents strong evidence in favor of the Torus+GB model. By adopting the Torus+GB model, we decompose the observed IR SEDs of Hot DOGs into torus and cold dust components. The main results are as follows. (1) Hot DOGs in our submillimeter-detected sample are hyperluminous (L-IR >= 10(13) L-circle dot), with torus emission dominating the IR energy output. However, cold dust emission is non-negligible, contributing on average similar to 24% of total IR luminosity. (2) Compared to QSO and starburst SED templates, the median SED of Hot DOGs shows the highest luminosity ratio between mid-IR and submillimeter at rest frame, while it is very similar to that of QSOs at similar to 10-50 mu m, suggesting that the heating sources of Hot DOGs should be buried AGNs. (3) Hot DOGs have high dust temperatures (T-dust similar to 72 K) and high IR luminosity of cold dust. The T-dust-L-IR relation of Hot DOGs suggests that the increase in IR luminosity for Hot DOGs is mostly due to the increase of the dust temperature, rather than dust mass. Hot DOGs have lower dust masses than submillimeter galaxies (SMGs) and QSOs within a similar redshift range. Both high IR luminosity of cold dust and relatively low dust mass in Hot DOGs can be expected by their relatively high dust temperatures. (4) Hot DOGs have high dust-covering factors (CFs), which deviate from the previously proposed trend of the dust CF decreasing with increasing bolometric luminosity. Finally, we can reproduce the observed properties in Hot DOGs by employing a physical model of galaxy evolution. This result suggests that Hot DOGs may lie at or close to peaks of both star formation and black hole growth histories, and represent a transit phase during the evolutions of massive galaxies, transforming them from the dusty starburst-dominated phase to the optically bright QSO phase.
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    Modeling the Infrared Reverberation Response of the Circumnuclear Dusty Torus in AGNs: The Effects of Cloud Orientation and Anisotropic Illumination
    (IOP PUBLISHING LTD, 2017) Almeyda, Triana; Robinson, Andrew; Richmond, Michael; Vazquez, Billy; Nikutta, Robert
    The obscuring circumnuclear torus of dusty molecular gas is one of the major components of active galactic nuclei (AGN). The torus can be studied by analyzing the time response of its infrared (IR) dust emission to variations in the AGN continuum luminosity, a technique known as reverberation mapping. The IR response is the convolution of the AGN ultraviolet/optical light curve with a transfer function that contains information about the size, geometry, and structure of the torus. Here, we describe a new computer model that simulates the reverberation response of a clumpy torus. Given an input optical light curve, the code computes the emission of a 3D ensemble of dust clouds as a function of time at selected IR wavelengths, taking into account light travel delays. We present simulated dust emission responses at 3.6, 4.5, and 30 mu m that explore the effects of various geometrical and structural properties, dust cloud orientation, and anisotropy of the illuminating radiation field. We also briefly explore the effects of cloud shadowing (clouds are shielded from the AGN continuum source). Example synthetic light curves have also been generated, using the observed optical light curve of the Seyfert 1 galaxy NGC 6418 as input. The torus response is strongly wavelength-dependent, due to the gradient in cloud surface temperature within the torus, and because the cloud emission is strongly anisotropic at shorter wavelengths. Anisotropic illumination of the torus also significantly modifies the torus response, reducing the lag between the IR and optical variations.
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    Near- to mid-infrared imaging and spectroscopy of two buried AGNs of the nearby merging galaxy NGC 6240 with Subaru/IRCS plus AO and GTC/CanariCam
    (2014) Mori, Tamami I.; Imanishi, Masatoshi; Alonso-Herrero, Almudena; Packham, Chris; Almeida, Cristina Ramos; Nikutta, Robert; Gonzalez-Martin, Omaira; Perlman, Eric; Saito, Yuriko; Levenson, Nancy A.
    We report near-infrared K', L', and M' band imaging observations of the nearby merging galaxy NGC 6240 with the Infrared Camera and Spectrograph on the Subaru telescope. The observations were performed with the assistance of the Subaru Adaptive Optics System, and the achieved spatial resolutions were around 0 ''.10-0 ''.20. We also obtained new mid-infrared imaging in the Si-2 filter band (8.7 mu m) and N-band (7.5-13 mu m) spectroscopy of this galaxy with the CanariCam on the Gran Telescopio Canarias with a spatial resolution of 0 ''.4-0 ''.5. In the K' band image the two nuclei of the galaxy each show a double peak suggesting the complex geometry of the source, while the L', M', and Si-2 band images show single compact structures in each of the two nuclei. Assuming that the center core observed at wavelengths longer than 3.8 mu m is associated with dust heated by the buried AGN, we re-evaluated the spectral energy distributions (SEDs) of the southern nucleus from 2 to 30 mu m with additional literature values, and performed the SED+spectroscopy fit using the clumpy torus models of Nenkova et al. (2008a, ApJ, 685, 145; 2008b, ApJ, 685, 160) and a Bayesian fitting approach. The model fit suggests that the high covering factor torus emission in the southern nucleus is also obscured by foreground dust in the host galaxy. The estimated AGN bolometric luminosity of the southern nucleus, L-bol(AGN) similar to 1 x 10(45) erg s(-1), accounts for approximately 40% of the whole luminosity of the system.
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    The Black Hole-Galaxy Connection: Interplay between Feedback, Obscuration, and Host Galaxy Substructure
    (2022) Juneau, Stephanie; Goulding, Andy D.; Banfield, Julie; Bianchi, Stefano; Duc, Pierre-Alain; Ho, I-Ting; Dopita, Michael A.; Scharwaechter, Julia; Bauer, Franz E.; Groves, Brent; Alexander, David M.; Davies, Rebecca L.; Elbaz, David; Freeland, Emily; Hampton, Elise; Kewley, Lisa J.; Nikutta, Robert; Shastri, Prajval; Shu, Xinwen; Vogt, Frederic P. A.; Wang, Tao; Wong, O. Ivy; Woo, Jong-Hak
    There is growing evidence for physical influence between supermassive black holes and their host galaxies. We present a case study of the nearby galaxy NGC 7582, for which we find evidence that galactic substructure plays an important role in affecting the collimation of ionized outflows as well as contributing to the heavy active galactic nucleus (AGN) obscuration. This result contrasts with a simple, small-scale AGN torus model, according to which AGN-wind collimation may take place inside the torus itself, at subparsec scales. Using 3D spectroscopy with the Multi Unit Spectroscopic Explorer instrument, we probe the kinematics of the stellar and ionized gas components as well as the ionization state of the gas from a combination of emission-line ratios. We report for the first time a kinematically distinct core (KDC) in NGC 7582, on a scale of similar to 600 pc. This KDC coincides spatially with dust lanes and starbursting complexes previously observed. We interpret it as a circumnuclear ring of stars and dusty, gas-rich material. We obtain a clear view of the outflowing cones over kiloparsec scales and demonstrate that they are predominantly photoionized by the central engine. We detect the back cone (behind the galaxy) and confirm previous results of a large nuclear obscuration of both the stellar continuum and H ii regions. While we tentatively associate the presence of the KDC with a large-scale bar and/or a minor galaxy merger, we stress the importance of gaining a better understanding of the role of galaxy substructure in controlling the fueling, feedback, and obscuration of AGNs.
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    X-ray spectral and eclipsing model of the clumpy obscurer in active galactic nuclei
    (2019) Buchner, Johannes; Brightman, Murray; Nandra, Kirpal; Nikutta, Robert; Bauer, Franz E.
    We present a unification model for a clumpy obscurer in active galactic nuclei (AGN) and investigate the properties of the resulting X-ray spectrum. Our model is constructed to reproduce the column density distribution of the AGN population and cloud eclipse events in terms of their angular sizes and frequency. We developed and released a generalised Monte Carlo X-ray radiative transfer code, XARS, to compute X-ray spectra of obscurer models. The geometry results in strong Compton scattering, causing soft photons to escape also along Compton-thick sight lines. This makes our model spectra very similar to our TORUS previous model or something similar However, only if we introduce an additional Compton-thick reflector near the corona, we achieve good fits to NuSTAR spectra. This additional component in our model can be interpreted as part of the dust-free broad-line region, an inner wall or rim, or a warped disk. It cannot be attributed to a simple disk because the reflector must simultaneously block the line of sight to the corona and reflect its radiation. We release our model as an Xspec table model and present corresponding CLUMPY infrared spectra, paving the way for self-consistent multi-wavelength analyses.