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J. F. Gallimore,
A. Yzaguirre,
J. Jakoboski,
M. J. Stevenosky, D. J. Axon,
S. A. Baum,
C. L. Buchanan,
M. Elitzur,
M. Elvis,
C. P. O'Dea,
A. Robinson
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J. F. Gallimore,
A. Yzaguirre,
J. Jakoboski,
M. J. Stevenosky, D. J. Axon,
S. A. Baum,
C. L. Buchanan,
M. Elitzur,
M. Elvis,
C. P. O'Dea,
A. Robinson
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[show abstract]
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ABSTRACT: We present new CRIRES spectroscopic observations of the Brγ emission line in the nuclear region of the Circinus galaxy, obtained with the aim of measuring the black hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an ideal benchmark for the spectroastrometric technique given its proximity and secure BH measurement obtained with the observation of its nuclear H 2 O maser disk. The kinematical data have been analyzed both with the classical method based on the analysis of the rotation curves and with the new method developed by us and based on spectroastrometry. The classical method indicates that the gas disk rotates in a gravitational potential resulting from an extended stellar mass distribution and a spatially unresolved dynamical mass of (1.7 ± 0.2) × 10 7 M ⊙ , concentrated within r < 7 pc, corresponding to the seeing-limited resolution of the observations. The new method is capable of probing the gas rotation at scales which are a factor ∼ 3.5 smaller than those probed by the rotation curve analysis, highlighting the potential of spectroastrometry. The dynamical mass which is spatially unresolved with the spectroastrometric method is a factor ∼ 2 smaller, 7.9 +1.4 −1.1 ×10 6 M ⊙ indicating that spectroastrometry has been able to spatially resolve the nuclear mass distribution down to 2 pc scales. This unresolved mass is still a factor ∼ 4.5 larger than the BH mass measurement obtained with the H 2 O maser emission indicating that, even with spectroastrometry, it has not been possible to resolve the sphere of influence of the BH. Based on literature data, this spatially unresolved dynamical mass distribution is likely dominated by warm molecular gas and it has been tentatively identified with the circum-nuclear torus which prevents a direct view of the central BH in Circinus. This mass distribution, with a size of ∼ 2pc, is similar in shape to that of the star cluster of the Milky Way suggesting that a molecular torus, forming stars at a high rate, might be the earlier evolutionary stage of the nuclear star clusters which are common in late type spirals.
Astronomy and Astrophysics 01/2013; 549. · 4.59 Impact Factor
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[show abstract]
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ABSTRACT: We present new CRIRES spectroscopic observations of BrGamma in the nuclear
region of the Circinus galaxy, obtained with the aim of measuring the black
hole (BH) mass with the spectroastrometric technique. The Circinus galaxy is an
ideal benchmark for the spectroastrometric technique given its proximity and
secure BH measurement obtained with the observation of its nuclear H2O maser
disk. The kinematical data have been analyzed both with the classical method
based on the analysis of the rotation curves and with the new method developed
by us and based on spectroastrometry. The classical method indicates that the
gas disk rotates in the gravitational potential of an extended stellar mass
distribution and a spatially unresolved mass of (1.7 +- 0.2) 10^7 Msun,
concentrated within r < 7 pc. The new method is capable of probing gas rotation
at scales which are a factor ~3.5 smaller than those probed by the rotation
curve analysis. The dynamical mass spatially unresolved with the
spectroastrometric method is a factor ~2 smaller, 7.9 (+1.4 -1.1) 10^6 Msun
indicating that spectroastrometry has been able to spatially resolve the
nuclear mass distribution down to 2 pc scales. This unresolved mass is still a
factor ~4.5 larger than the BH mass measurement obtained with the H2O maser
emission indicating that it has not been possible to resolve the sphere of
influence of the BH. Based on literature data, this spatially unresolved
dynamical mass distribution is likely dominated by molecular gas and it has
been tentatively identified with the circum-nuclear torus which prevents a
direct view of the central BH in Circinus. This mass distribution, with a size
of ~2pc, is similar in shape to that of the star cluster of the Milky Way
suggesting that a molecular torus, forming stars at a high rate, might be the
earlier evolutionary stage of the nuclear star clusters which are common in
late type spirals.
http://dx.doi.org/10.1051/0004-6361/200912530. 11/2012;
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B. Balmaverde,
A. Capetti,
P. Grandi,
E. Torresi,
M. Chiaberge,
J. Rodriguez Zaurin,
G. R. Tremblay, D. J. Axon,
S. A. Baum,
G. Giovannini,
P. Kharb,
F. D. Macchetto,
C. P. O Dea,
W. Sparks
[show abstract]
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ABSTRACT: We analyze Chandra observations of diffuse soft X-ray emission associated
with a complete sample of 3CR radio galaxies at z < 0.3. In this paper we focus
on the properties of the spectroscopic sub-classes of high excitation galaxies
(HEGs) and broad line objects (BLOs). Among the 33 HEGs we detect extended (or
possibly extended) emission in about 40% of the sources; the fraction is even
higher (8/10) restricting the analysis to the objects with exposure times
larger than 10 ks. In the 18 BLOs, extended emission is seen only in 2 objects;
this lower detection rate can be ascribed to the presence of their bright X-ray
nuclei that easily outshine any genuine diffuse emission.
A very close correspondence between the soft X-ray and optical line
morphology emerges. We also find that the ratio between [O III] and extended
soft X-ray luminosity is confined within a factor of 2 around a median value of
5. Both results are similar to what is seen in Seyfert galaxies.
We discuss different processes that could explain the soft X-ray emission and
conclude that the photoionization of extended gas, coincident with the narrow
line region, is the favored mechanism.
08/2012;
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ABSTRACT: We present new Spitzer IRS spectroscopy of Cygnus A, one of the most luminous radio sources in the local universe. Data on the inner 20'' are combined with new reductions of MIPS and IRAC photometry as well as data from the literature to form a radio through mid-infrared spectral energy distribution (SED). This SED is then modeled as a combination of torus reprocessed active galactic nucleus (AGN) radiation, dust enshrouded starburst, and a synchrotron jet. This combination of physically motivated components successfully reproduces the observed emission over almost 5 dex in frequency. The bolometric AGN luminosity is found to be 1012 L ☉ (90% of L IR), with a clumpy AGN-heated dust medium extending to ~130 pc from the supermassive black hole. Evidence is seen for a break or cutoff in the core synchrotron emission. The associated population of relativistic electrons could in principle be responsible for some of the observed X-ray emission though the synchrotron self-Compton mechanism. The SED requires a cool dust component, consistent with dust-reprocessed radiation from ongoing star formation. Star formation contributes at least 6 × 1010 L ☉ to the bolometric output of Cygnus A, corresponding to a star formation rate of ~10 M ☉ yr–1.
The Astrophysical Journal 02/2012; 747(1):46. · 6.02 Impact Factor
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ABSTRACT: (Abridged) We present the results from new 15 ks Chandra-ACIS and 4.9 GHz
Very Large Array observations of 13 galaxies hosting low luminosity AGN. This
completes the multiwavelength study of a sample of 51 nearby early-type
galaxies described in Capetti & Balmaverde (2005, 2006); Balmaverde & Capetti
(2006). The aim of the three previous papers was to explore the connection
between the host galaxies and AGN activity in a radio-selected sample. We
detect nuclear X-ray emission in eight sources and radio emission in all but
one (viz., UGC6985). The new VLA observations improve the spatial resolution by
a factor of ten: the presence of nuclear radio sources in 12 of the 13 galaxies
confirms their AGN nature. As previously indicated, the behavior of the X-ray
and radio emission in these sources depends strongly on the form of their
optical surface brightness profiles derived from Hubble Space Telescope
imaging, i.e., on their classification as "core", "power-law" or "intermediate"
galaxies. With more than twice the number of "power-law" and "intermediate"
galaxies compared to previous work, we confirm with a much higher statistical
significance that these galaxies lie well above the radio-X-ray correlation
established in FRI radio galaxies and the low-luminosity "core" galaxies. This
result highlights the fact that the "radio-loud/radio-quiet" dichotomy is a
function of the host galaxy's optical surface brightness profile. We present
radio-optical-X-ray spectral indices for all 51 sample galaxies. Survival
statistics point to significant differences in the radio-to-optical and
radio-to-X-ray spectral indices between the "core" and "power-law" galaxies
(Gehan's Generalized Wilcoxon test probability "p" for the two classes being
statistically similar is <10^-5), but not in the optical-to-X-ray spectral
indices (p=0.25).
01/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We measure the black hole mass in the nearby active galaxy Centaurus A (NGC
5128) using a new method based on spectroastrometry of a rotating gas disk. The
spectroastrometric approach consists in measuring the photocenter position of
emission lines for different velocity channels. In a previous paper we focused
on the basic methodology and the advantages of the spectroastrometric approach
with a detailed set of simulations demonstrating the possibilities for black
hole mass measurements going below the conventional spatial resolution. In this
paper we apply the spectroastrometric method to multiple longslit and integral
field near infrared spectroscopic observations of Centaurus A. We find that the
application of the spectroastrometric method provides results perfectly
consistent with the more complex classical method based on rotation curves: the
measured BH mass is nearly independent of the observational setup and spatial
resolution and the spectroastrometric method allows the gas dynamics to be
probed down to spatial scales of ~0.02", i.e. 1/10 of the spatial resolution
and ~1/50 of BH sphere of influence radius. The best estimate for the BH mass
based on kinematics of the ionized gas is then log(MBH (sin i)^2/M\odot)=7.5
\pm 0.1 which corresponds to MBH = 9.6(+2.5-1.8) \times 10^7 M\odot for an
assumed disk inclination of i = 35deg. The complementarity of this method with
the classic rotation curve method will allow us to put constraints on the disk
inclination which cannot be otherwise derived from spectroastrometry. With the
application to Centaurus A, we have shown that spectroastrometry opens up the
possibility of probing spatial scales smaller than the spatial resolution,
extending the measured MBH range to new domains which are currently not
accessible: smaller BHs in the local universe and similar BHs in more distant
galaxies.
10/2011;
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[show abstract]
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ABSTRACT: The nuclei of Seyfert 1 galaxies exhibit a range of optical polarization
characteristics that can be understood in terms of two scattering regions
producing orthogonal polarizations: an extended polar scattering region (PSR)
and a compact equatorial scattering region (ESR), located within the
circum-nuclear torus. Here we present NICMOS 2.0 micron imaging polarimetry of
6 "polar scattered" Seyfert 1 (S1) galaxies, in which the PSR dominates the
optical polarization. The unresolved nucleus (<0.58 arcsec) is significantly
polarized in only three objects, but 5 of the 6 exhibit polarization in a 0.58
to 1.5 arcsec circum-nuclear annulus. In Fairall 51 and ESO 323-G077, the
polarization position angle at 2 microns (theta2m) is consistent with the
average for the optical spectrum (thetav), implying that the nuclear
polarization is dominated by polar scattering at both wavelengths. The same is
probably true for NGC 3227. In both NGC 4593 and Mrk 766, there is a large
difference between theta2m and thetav off nucleus, where polar scattering is
expected to dominate. This may be due to contamination by interstellar
polarization in NGC 4593, but there is no clear explanation in the case of the
strongly polarized Mrk 766. Lastly, in Mrk 1239, a large change (~ 60deg) in
theta2m between the nucleus and the annulus indicates that the unresolved
nucleus and its immediate surroundings have different polarization states at 2
microns, which we attribute to the ESR and PSR, respectively. A further
implication is that the source of the scattered 2 micron emission in the
unresolved nucleus is the accretion disk, rather than torus hot dust emission.
02/2011;
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ABSTRACT: Using HST NICMOS 2 observations we have measured 1.6-micron near infrared nuclear luminosities of 100 3CR radio galaxies with z<0.3, by modeling and subtracting the extended emission from the host galaxy. We performed a multi-wavelength statistical analysis (including optical and radio data) of the properties of the nuclei following classification of the objects into FRI and FRII, and LIG (low-ionization galaxies), HIG (high-ionization galaxies) and BLO (broad-lined objects) using the radio morphology and optical spectra, respectively. The correlations among near infrared, optical, and radio nuclear luminosity support the idea that the near infrared nuclear emission of FRIs has a non-thermal origin. Despite the difference in radio morphology, the multi-wavelength properties of FRII LIG nuclei are statistically indistinguishable from those of FRIs, an indication of a common structure of the central engine. All BLOs show an unresolved near infrared nucleus and a large near infrared excess with respect to FRII LIGs and FRIs of equal radio core luminosity. This requires the presence of an additional (and dominant) component other than the non-thermal light. Considering the shape of their spectral energy distribution, we ascribe the origin of their near infrared light to hot circumnuclear dust. A near infrared excess is also found in HIGs, but their nuclei are substantially fainter than those of BLO. This result indicates that substantial obscuration along the line-of-sight to the nuclei is still present at 1.6 micron. Nonetheless, HIGs nuclei cannot simply be explained in terms of dust obscuration: a significant contribution from light reflected in a circumnuclear scattering region is needed to account for their multiwavelength properties. Comment: 20 pages, 16 figures. Accepted for publication on ApJ
The Astrophysical Journal 10/2010; · 6.02 Impact Factor
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ABSTRACT: We have observed the composite AGN-starburst galaxy NGC 6764 with the Very Large Baseline Array at 1.6 and 4.9 GHz. These observations have detected a "core-jet" structure and a possible weak counterjet component at 1.6 GHz. The upper limits to the core and jet (1.6-4.9 GHz) spectral index are 0.6 and 0.3, respectively. Taken together with the high brightness temperature of ~10^7 K for the core region, the radio emission appears to be coming from a synchrotron jet. At a position angle of 25 degrees, the parsec-scale jet seems to be pointing closely towards the western edge of the southern kpc-scale bubble in NGC 6764. A real connection between the parsec and sub-kpc scale emission would not only suggest the presence of a curved jet, but also a close link between the AGN jet and the radio bubbles in NGC 6764. We demonstrate that a precessing jet model can explain the radio morphology from parsec- to sub-kpc scales, and the model best-fit parameters of jet speed and orientation are fully consistent with the observed jet-to-counterjet surface brightness ratio. The jet however appears to be disrupted on scales of 100s of parsecs, possibly due to interaction with, and entrainment of the interstellar medium gas, which subsequently leads to the formation of bubbles. The jet energetics in NGC 6764 suggest that it would take 12-21 Myr to inflate the (southern) bubble. This timescale corresponds roughly to the starburst episode that took place in NGC 6764 about 15-50 Myr ago, and could be indicative of a close connection between jet formation and the starburst activity in this galaxy. Comment: 19 pages, 2 figures, accepted for publication in The Astrophysical Journal
09/2010;
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[show abstract]
[hide abstract]
ABSTRACT: Isophotal analysis of M87, using data from the Advanced Camera for Surveys, reveals a projected displacement of 6.8 +/- 0.8 pc (~ 0.1 arcsec) between the nuclear point source (presumed to be the location of the supermassive black hole, SMBH) and the photo-center of the galaxy. The displacement is along a position angle of 307 +/- 17 degrees and is consistent with the jet axis. This suggests the active SMBH in M87 does not currently reside at the galaxy center of mass, but is displaced in the counter-jet direction. Possible explanations for the displacement include orbital motion of an SMBH binary, gravitational perturbations due to massive objects (e.g., globular clusters), acceleration by an asymmetric or intrinsically one-sided jet, and gravitational recoil resulting from the coalescence of an SMBH binary. The displacement direction favors the latter two mechanisms. However, jet asymmetry is only viable, at the observed accretion rate, for a jet age of >0.1 Gyr and if the galaxy restoring force is negligible. This could be the case in the low density core of M87. A moderate recoil ~1 Myr ago might explain the disturbed nature of the nuclear gas disk, could be aligned with the jet axis, and can produce the observed offset. Alternatively, the displacement could be due to residual oscillations resulting from a large recoil that occurred in the aftermath of a major merger any time in the last 1 Gyr. Comment: ApJ Letters accepted
05/2010;
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J. F. Gallimore,
A. Yzaguirre,
J. Jakoboski,
M. J. Stevenosky, D. J. Axon,
S. A. Baum,
C. L. Buchanan,
M. Elitzur,
M. Elvis,
C. P. O'Dea,
A. Robinson
[show abstract]
[hide abstract]
ABSTRACT: The mid-far-infrared spectral energy distributions (SEDs) of 83 active galaxies, mostly Seyfert galaxies, selected from the extended 12 micron sample are presented. The data were collected using all three instruments, IRAC, IRS, and MIPS, aboard the Spitzer Space Telescope. The IRS data were obtained in spectral mapping mode, and the photometric data from IRAC and IRS were extracted from matched, 20 arcsec diameter circular apertures. The MIPS data were obtained in SED mode, providing very low resolution spectroscopy (R ~ 20) between ~ 55 and 90 microns in a larger, 20 by 30 arcsec synthetic aperture. We further present the data from a spectral decomposition of the SEDs, including equivalent widths and fluxes of key emission lines; silicate 10 and 18 micron emission and absorption strengths; IRAC magnitudes; and mid-far infrared spectral indices. Finally, we examine the SEDs averaged within optical classifications of activity. We find that the infrared SEDs of Seyfert 1s and Seyfert 2s with hidden broad line regions (HBLR, as revealed by spectropolarimetry or other technique) are qualitatively similar, except that Seyfert 1s show silicate emission and HBLR Seyfert 2s show silicate absorption. The infrared SEDs of other classes with the 12 micron sample, including Seyfert 1.8-1.9, non-HBLR Seyfert 2 (not yet shown to hide a type 1 nucleus), LINER and HII galaxies, appear to be dominated by star-formation, as evidenced by blue IRAC colors, strong PAH emission, and strong far-infrared continuum emission, measured relative to mid-infrared continuum emission. Comment: 78 pages, 13 figures
01/2010;
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[show abstract]
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ABSTRACT: We present models representing the scattering of quasar radiation off free
electrons and dust grains in geometries that approximate the structure of
quasar host galaxies. We show that, for reasonable assumptions, scattering
alone can easily produce ratios of nuclear (point source) to extended fluxes
comparable to those determined in studies of quasar hosts. This result suggests
that scattered quasar light, as well as stellar emission from the host galaxy,
contributes significantly to the detected extended flux, leading to uncertainty
in the inferred properties of quasar host. A significant contribution from
scattered quasar light will lead to overestimates of the luminosity and hence
mass of the host galaxy, and may also distort its morphology. Scattering of
quasar light within the host galaxy may provide alternative explanations for
the apparent peak in host luminosity at z = 2-3; possibly the overall average
higher luminosity of radio-loud host galaxies relative to those of radio-quiet
quasars (RQQs), and the apparent preference of high-luminosity RQQs for
spheroidal rather than disk galaxies.
05/2009;
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[show abstract]
[hide abstract]
ABSTRACT: We present the results of further Hubble Space Telescope (HST) imaging polarimetry of the inner region of NGC 1068 taken with the COSTAR corrected Faint Object Camera (FOC) in the ultraviolet (2400-2700 Å). The centro-symmetric polarization pattern revealed by previous HST imaging polarimetry is shown to extend even closer to the illumination source (the hidden nucleus). Even in the inner region the ultraviolet light is dominated by scattered radiation, as the average polarization is approximately 20%, and it can be as high as 65%, figures which are similar to those obtained previously at larger radii. These new data allow a more accurate determination of the position of the source of scattered radiation that is displaced by 020 north and 006 west from the position recently obtained by Capetti et al. This new location of the nucleus rules out both cloud B and the "twin-crescent" as the nucleus of NGC 1068. In agreement with the unified model for Seyfert galaxies, there appears to be no visible counterpart at this location. The good agreement with previous polarimetric observations demonstrates the integrity of the polarization capabilities of the FOC obtained after the installation of COSTAR.
The Astrophysical Journal 01/2009; 452(2):L87. · 6.02 Impact Factor
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[show abstract]
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ABSTRACT: The findings of a nine orbit calibration plan carried out during HST Cycle 15, to fully determine the NICMOS camera 2 (2.0 micron) polarization calibration to high accuracy, are reported. Recently Ueta et al. and Batcheldor et al. have suggested that NICMOS possesses a residual instrumental polarization at a level of 1.2-1.5%. This would completely inhibit the data reduction in a number of GO programs, and hamper the ability of the instrument to perform high accuracy polarimetry. We obtained polarimetric calibration observations of three polarimetric standards at three spacecraft roll angles separated by ~60deg. Combined with archival data, these observations were used to characterize the residual instrumental polarization in order for NICMOS to reach its full potential of accurate imaging polarimetry at p~1%. Using these data, we place an 0.6% upper limit on the instrumental polarization and calculate values of the parallel transmission coefficients that reproduce the ground-based results for the polarimetric standards. The uncertainties associated with the parallel transmission coefficients, a result of the photometric repeatability of the observations, are seen to dominate the accuracy of p and theta. However, the updated coefficients do allow imaging polarimetry of targets with p~1.0% at an accuracy of +/-0.6% and +/-15deg. This work enables a new caliber of science with HST. Comment: 13 pages, 9 figures, PASP accepted
12/2008;
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[show abstract]
[hide abstract]
ABSTRACT: Infrared-imaging observations that span the wavelength range of 0.8-2.35 μm have been obtained for the archetypal powerful radio galaxy Cygnus A using the Near-Infrared Camera and Multiobject Spectrograph on board the Hubble Space Telescope. At 2.25 μm, the images are dominated by the presence of a nuclear point source (FWHM < 021), whose flux is a factor of ~4 times less than the limits deduced from previous ground-based studies. The observations also reveal an edge-brightened biconical structure centered on the point source, which is strikingly similar to those observed around young stellar objects. The high polarization and orientation of the bicone relative to the radio axis lead us to conclude that it is an illuminated structure, while the edge brightening provides evidence that the bicone is defined as much by outflows in the nuclear regions as by the polar diagram of the illuminating quasar radiation field. A further implication of our observations is that not all of the anisotropy in the nuclear radiation field is caused by extinction on a scale less than 100 pc in the torus; some of the anisotropy must be generated by absorption and scattering in the dust lane on a 1 kpc scale.
The Astrophysical Journal 12/2008; 512(2):L91. · 6.02 Impact Factor
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[hide abstract]
ABSTRACT: The ability of NICMOS to perform high accuracy polarimetry is currently hampered by an uncalibrated residual instrumental polarization at a level of 1.2-1.5%. To better quantify and characterize this residual we obtained observations of three polarimetric standard stars at three separate space-craft roll angles. Combined with archival data, these observations were used to characterize the residual instrumental polarization to enable NICMOS to reach its full polarimetric potential. Using these data, we calculate values of the parallel transmission coefficients that reproduce the ground-based results for the polarimetric standards. The uncertainties associated with the parallel transmission coefficients, a result of the photometric repeatability of the observations, dominate the accuracy of p and theta. However, the new coefficients now enable imaging polarimetry of targets with p~1.0% at an accuracy of +/-0.6% and +/-15 degrees.
12/2008;
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C. L. Buchanan,
J. F. Gallimore,
C. P. O'Dea,
S. A. Baum, D. J. Axon,
A. Robinson,
J. Noel-Storr,
A. Yzaguirre,
M. Elitzur,
M. Elvis,
C. Tadhunter
[show abstract]
[hide abstract]
ABSTRACT: The infrared is a key wavelength regime for probing the dusty, obscured nuclear regions of active galaxies. We present results from an infrared study of 87 nearby Seyfert galaxies using the Spitzer Space Telescope and ground-based telescopes. Combining detailed modelling of the 3 - 100 micron spectral energy distributions with mid-IR spectral diagnostics and near-infrared observations, we find broad support for the unified model of AGNs. The IR emission of Seyfert 1s and 2s is consistent with their having the same type of central engine viewed at a different orientation. The nature of the putative torus is becoming clearer; in particular we present evidence that it is likely a clumpy medium. Mid-infrared correlations between tracers of star formation and AGN ionizing luminosity reveal the starburst-AGN connection implied by the black hole/bulge mass relation, however it is not yet clear if this is due to feedback.
08/2008;
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12/2007: pages 364-368;
