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Search Results: 1 - 10 of 378363 matches for " J. T. Radomski "
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Mid-ir emission from the nucleus of centaurus a
J. T. Radomski,C. Packham,N. A. Levenson,E. Perlman
Revista mexicana de astronomía y astrofísica , 2007,
Abstract: We present high spatial resolution mid-IR images of the nuclear region of Centaurus A. Images were obtained at 8.8 um, N-band (10.5uem), and 18.3um using the mid-IR in- strument T-ReCS on Gemini South, a pro- genitor to CanariCam on the Gran Telescopio Canarias (GTC).
Spatially-resolved mid-infrared spectroscopy of IC 5063
S. Young,C. Packham,C. M. Telesco,J. T. Radomski
Revista mexicana de astronomía y astrofísica , 2007,
Abstract: N-band spectroscopy of the radio strong Seyfert 2 active galaxy IC 5063 (z=0.0110) was obtained using Gemini South in conjunc- tion with the Thermal-Region Camera Spec- trograph (T-ReCS; Telesco et al. 1998). T- ReCS uses a Raytheon 320x240 pixel SiAs IBC array, at a plate scale of 0.08900 pixel-1. The observations were conducted on the nights of UT 2005 July 7 and 9 using the standard chop-nod technique to remove the time-variable sky background, telescope ther- mal emission, and the so-called 1/f detector noise. A 0.6700 wide slit was used aligned along the position angle of the radio axis at 305o(Morganti et al. 1998) and close to the extended narrow line emission region (ENLR) axis at 303_(Colina et al. 1991). The total on- source integration time was 1212 seconds.
Results of high-spatial resolution mid-ir imaging of NGC7172
J. J. Schaefer,C. Packham,J. T. Radomski,C. M. Telesco
Revista mexicana de astronomía y astrofísica , 2007,
Abstract: We present results from an analysis of high- spatial resolution images of the Seyfert 2 galaxy NGC 7172, as observed by T-ReCS on Gemini South at 10.4 microns. We model the IR SED of this AGN using our observations and archival data. We find that a best fit model describes the observed SED with a reddened stellar population and 2 thermal components.
Mid-Infrared Detection of a Hot Molecular Core in G29.96-0.02
J. M. De Buizer,A. Watson,J. T. Radomski,R. K. Pina,C. M. Telesco
Physics , 2001, DOI: 10.1086/338912
Abstract: We present high angular resolution (~0.5") 10 and 18 micron images of the region around G29.96-0.02 taken from the Gemini North 8-m telescope using the mid-infrared imager and spectrometer OSCIR. These observations were centered on the location of a group of water masers, which delineate the site of a hot molecular core believed to contain an extremely young, massive star. We report here the direct detection of a hot molecular core at mid-infrared wavelengths at this location. The size and extent of the core at 18 microns appears to be very similar to the morphology as seen in integrated NH3 maps. However, our observations indicate that the mid-infrared emission may not be exactly coincident with the NH3 emission.
NGC 1097 at high spatial resolution in the mid-infrared
R. E. Mason,N. A. Levenson,C. Packham,J. T. Radomski
Revista mexicana de astronomía y astrofísica , 2007,
Abstract: The possibility that the dusty torus of AGN unified schemes is connected with star forma- tion activity has been raised by many authors. Some or all of the nuclear obscuration might originate in clouds ejected from a starburst (e.g. Watabe & Umemura 2005), which could also provide the energy necessary to maintain the thickness of the torus. Star formation is quite commonly observed in AGN on few hun- dred pc scales, but the mid-IR emitting re- gions of the torus are much smaller, perhaps only a few pc across. The recent detection of a 106M, 106 yr-old stellar cluster < 9 pc from the nucleus of the nearby LINER/Sy1 galaxy, NGC1097 (Storchi-Bergmann et al. 2005) may therefore be a rare example of a starburst physically associated with an AGN torus.
Isotropic Mid-Infrared Emission from the Central 100 pc of Active Galaxies
N. A. Levenson,J. T. Radomski,C. Packham,R. E. Mason,J. J. Schaefer,C. M. Telesco
Physics , 2009, DOI: 10.1088/0004-637X/703/1/390
Abstract: Dust reprocesses the intrinsic radiation of active galactic nuclei (AGNs) to emerge at longer wavelengths. The observed mid-infrared (MIR) luminosity depends fundamentally on the luminosity of the central engine, but in detail it also depends on the geometric distribution of the surrounding dust. To quantify this relationship, we observe nearby normal AGNs in the MIR to achieve spatial resolution better than 100 pc, and we use absorption-corrected X-ray luminosity as a proxy for the intrinsic AGN emission. We find no significant difference between optically classified Seyfert 1 and 2 galaxies. Spectroscopic differences, both at optical and IR wavelengths, indicate that the immediate surroundings of AGNs is not spherically symmetric, as in standard unified AGN models. A quantitative analysis of clumpy torus radiative transfer models shows that a clumpy local environment can account for this dependence on viewing geometry while producing MIR continuum emission that remains nearly isotropic, as we observe, although the material is not optically thin at these wavelengths. We find some luminosity dependence on the X-ray/MIR correlation in the smallest scale measurements, which may indicate enhanced dust emission associated with star formation, even on these sub-100 pc scales.
Mid-Infrared Detection of a Hot Molecular Core in G29.96-0.02
A.M. Watson,J. M. De Buizer,J. T. Radomski,R. K. Piu00F1a
Revista mexicana de astronomía y astrofísica , 2003,
Abstract:
Subaru Spectroscopy and Spectral Modeling of Cygnus A
Matthew J. Merlo,Eric S. Perlman,Robert Nikutta,Christopher Packham,Moshe Elitzur,Masatoshi Imanishi,N. A. Levenson,James T. Radomski,Itziar Aretxaga
Physics , 2014, DOI: 10.1088/0004-637X/788/1/6
Abstract: We present high angular resolution ($\sim$0.5$^\prime$$^\prime$) MIR spectra of the powerful radio galaxy, Cygnus A, obtained with the Subaru telescope. The overall shape of the spectra agree with previous high angular resolution MIR observations, as well as previous Spitzer spectra. Our spectra, both on and off nucleus, show a deep silicate absorption feature. The absorption feature can be modeled with a blackbody obscured by cold dust or a clumpy torus. The deep silicate feature is best fit by a simple model of a screened blackbody, suggesting foreground absorption plays a significant, if not dominant role, in shaping the spectrum of Cygnus A. This foreground absorption prevents a clear view of the central engine and surrounding torus, making it difficult to quantify the extent the torus attributes to the obscuration of the central engine, but does not eliminate the need for a torus in Cygnus A.
Testing the AGN Unification Model in the Infrared
Cristina Ramos Almeida,N. A. Levenson,A. Alonso-Herrero,A. Asensio Ramos,J. M. Rodriguez Espinosa,A. M. Perez Garcia,C. Packham,R. Mason,J. T. Radomski,T. Diaz-Santos
Physics , 2012, DOI: 10.1088/1742-6596/372/1/012004
Abstract: We present near-to-mid-infrared spectral energy distributions (SEDs) for 21 Seyfert galaxies, using subarcsecond resolution imaging data. Our aim is to compare the properties Seyfert 1 (Sy1) and Seyfert 2 (Sy2) tori using clumpy torus models and a Bayesian approach to fit the infrared (IR) nuclear SEDs. These dusty tori have physical sizes smaller than 6 pc radius, as derived from our fits. Active galactic nuclei (AGN) unification schemes account for a variety of observational differences in terms of viewing geometry. However, we find evidence that strong unification may not hold, and that the immediate dusty surroundings of Sy1 and Sy2 nuclei are intrinsically different. The Type 2 tori studied here are broader, have more clumps, and these clumps have lower optical depths than those of Type 1 tori. The larger the covering factor of the torus, the smaller the probability of having direct view of the AGN, and vice-versa. In our sample, Sy2 tori have larger covering factors (C_T=0.95+/-0.02) and smaller escape probabilities than those of Sy1 (C_T=0.5+/-0.1). Thus, on the basis of the results presented here, the classification of a Seyfert galaxy may depend more on the intrinsic properties of the torus rather than on its mere inclination, in contradiction with the simplest unification model.
Testing the Unification Model for AGN in the Infrared: are the obscuring tori of Type 1 and 2 Seyferts different?
C. Ramos Almeida,N. A. Levenson,A. Alonso-Herrero,A. Asensio Ramos,J. M. Rodriguez Espinosa,A. M. Perez Garcia,C. Packham,R. Mason,J. T. Radomski,T. Diaz-Santos
Physics , 2011, DOI: 10.1088/0004-637X/731/2/92
Abstract: We present new mid-infrared (MIR) imaging data for three Type-1 Seyfert galaxies obtained with T-ReCS on the Gemini-South Telescope at subarcsecond resolution. Our aim is to enlarge the sample studied in a previous work to compare the properties of Type-1 and Type-2 Seyfert tori using clumpy torus models and a Bayesian approach to fit the infrared nuclear spectral energy distributions (SEDs). Thus, the sample considered here comprises 7 Type-1, 11 Type-2, and 3 intermediate-type Seyferts. The unresolved IR emission of the Seyfert 1 galaxies can be reproduced by a combination of dust heated by the central engine and direct AGN emission, while for the Seyfert 2 nuclei only dust emission is considered. These dusty tori have physical sizes smaller than 6 pc radius, as derived from our fits. Unification schemes of AGN account for a variety of observational differences in terms of viewing geometry. However, we find evidence that strong unification may not hold, and that the immediate dusty surroundings of Type-1 and Type-2 Seyfert nuclei are intrinsically different. The Type-2 tori studied here are broader, have more clumps, and these clumps have lower optical depths than those of Type-1 tori. The larger the covering factor of the torus, the smaller the probability of having direct view of the AGN, and vice-versa. In our sample, Seyfert 2 tori have larger covering factors and smaller escape probabilities than those of Seyfert 1. All the previous differences are significant according to the Kullback-Leibler divergence. Thus, on the basis of the results presented here, the classification of a Seyfert galaxy as a Type-1 or Type-2 depends more on the intrinsic properties of the torus rather than on its mere inclination towards us, in contradiction with the simplest unification model.
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