Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 4 of 4
Full-Text Articles in Physical Sciences and Mathematics
Spitzer Irs Observations Of Seyfert 1.8 And 1.9 Galaxies: A Comparison With Seyfert 1 And Seyfert 2, R. P. Deo, D. M. Crenshaw, S. B. Kraemer, M. Dietrich, Moshe Elitzur, H. Teplitz, T. J. Turner
Spitzer Irs Observations Of Seyfert 1.8 And 1.9 Galaxies: A Comparison With Seyfert 1 And Seyfert 2, R. P. Deo, D. M. Crenshaw, S. B. Kraemer, M. Dietrich, Moshe Elitzur, H. Teplitz, T. J. Turner
Physics and Astronomy Faculty Publications
We present Spitzer mid-infrared spectra of 12 Seyfert 1.8 and 1.9 galaxies over the 5-38 μm region. We compare the spectral characteristics of this sample to those of 58 Seyfert 1 and 2 galaxies from the Spitzer archives. An analysis of the spectral shapes, the silicate 10 μm feature and the emission-line fluxes have enabled us to characterize the mid-IR properties of Seyfert 1.8/1.9s. We find that the EWs of the 10 μm silicate feature are generally weak in all Seyfert galaxies, as previously reported by several studies. The few Seyfert galaxies in this sample that show …
Optically Thick [O I] And [C Ii] Emission Toward Ngc 6334a, N. P. Abel, A. P. Sarma, Thomas H. Troland, Gary J. Ferland
Optically Thick [O I] And [C Ii] Emission Toward Ngc 6334a, N. P. Abel, A. P. Sarma, Thomas H. Troland, Gary J. Ferland
Physics and Astronomy Faculty Publications
This work focuses on [O I] and [C II] emission toward NGC 6334A, an embedded H+ region/PDR only observable at infrared or longer wavelengths. A geometry in which nearly all the emission escapes out the side of the cloud facing the stars, such as Orion, is not applicable to this region. Instead, we find the geometry to be one in which the H+ region and associated PDR is embedded in the molecular cloud. Constant-density PDR calculations are presented which predict line intensities as a function of AV [or N(H)], hydrogen density (nH), and …
Dust And Pah Emission In The Star-Forming Active Nucleus Of Ngc 1097, R. E. Mason, N. A. Levenson, C. Packham, Moshe Elitzur, J. Radomski, A. O. Petric, G. S. Wright
Dust And Pah Emission In The Star-Forming Active Nucleus Of Ngc 1097, R. E. Mason, N. A. Levenson, C. Packham, Moshe Elitzur, J. Radomski, A. O. Petric, G. S. Wright
Physics and Astronomy Faculty Publications
The nucleus of the nearby galaxy NGC 1097 is known to host a young, compact (r < 9 pc) nuclear star cluster, as well as a low-luminosity active galactic nucleus (AGN). It has been suggested both that the nuclear stellar cluster is associated with a dusty torus and that low-luminosity AGNs like NGC 1097 do not have the torus predicted by the unified model of AGNs. To investigate these contradictory possibilities we have acquired Gemini/T-ReCS 11.7 and 18.3 μm images of the central few hundred parsecs of this galaxy at <45 pc angular resolution, in which the nucleus and spectacular, kiloparsec-scale star-forming ring are detected in both bands. The small-scale mid-IR luminosity implies thermal emission from warm dust close to the central engine. Fitting of torus models shows that the observed mid-IR emission cannot be accounted for by dust heated by the central engine. Rather, the principal source heating the dust in this object is the nuclear star cluster itself, suggesting that the detected dust is not the torus of AGN unified schemes (although it is also possible that the dusty starburst itself could provide the obscuration invoked by the unified model). Comparison of Spitzer IRS and Gemini GNIRS spectra shows that, although PAH bands are strong in the immediate circumnuclear region of the galaxy, PAH emission is weak or absent in the central 19 pc. The lack of PAH emission can probably be explained largely by destruction/ionization of PAH molecules by hard photons from the nuclear star cluster. If NGC 1097 is typical, PAH emission bands may not be a useful tool with which …
The Structure Of The Homunculus. Ii. Modeling The Physical Conditions In Η Carinae's Molecular Shell, Nathan Smith, Gary J. Ferland
The Structure Of The Homunculus. Ii. Modeling The Physical Conditions In Η Carinae's Molecular Shell, Nathan Smith, Gary J. Ferland
Physics and Astronomy Faculty Publications
We present models that reproduce the observed double-shell structure of the Homunculus Nebula around η Carinae, including the stratification of infrared H2 and [Fe II] emission seen in data obtained with the Phoenix spectrograph on Gemini South, as well as the corresponding stratified grain temperature seen in thermal-infrared data. Tuning the model to match the observed shell thickness allows us to determine the threshold density that permits survival of H2. An average density of nH~=(0.5-1)×107 cm-3 in the outer zone is required to allow H2 to exist at all latitudes in the …