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F. Massaro,
G. R. Tremblay,
D. E. Harris,
P. Kharb,
D. Axon,
B. Balmaverde,
S. A. Baum,
A. Capetti,
M. Chiaberge,
R. Gilli,
G. Giovannini,
P. Grandi,
F. D. Macchetto,
C. P. O'Dea,
G. Risaliti, W. Sparks,
E. Torresi
[show abstract]
[hide abstract]
ABSTRACT: We report on the second round of Chandra observations of the 3C snapshot
survey developed to observe the complete sample of 3C radio sources with z<0.3
for 8 ksec each. In the first paper, we illustrated the basic data reduction
and analysis procedures performed for the 30 sources of the 3C sample observed
during the Chandra Cycle 9, while here, we present the data for the remaining
27 sources observed during Cycle 12. We measured the X-ray intensity of the
nuclei and of any radio hotspots and jet features with associated X-ray
emission. X-ray fluxes in three energy bands: soft, medium and hard for all the
sources analyzed are also reported. For the stronger nuclei, we also applied
the standard spectral analysis which provides the best fit values of X-ray
spectral index and absorbing column density. In addition, a detailed analysis
of bright X-ray nuclei that could be affected by pileup has been performed.
X-ray emission was detected for all the nuclei of the radio sources in our
sample except for 3C 319. Amongst the current sample, there are two compact
steep spectrum radio sources; two broad line radio galaxies; and one wide angle
tail radio galaxy, 3C 89, hosted in a cluster of galaxies clearly visible in
our Chandra snapshot observation. In addition, we also detected soft X-ray
emission arising from the galaxy cluster surrounding 3C 196.1. Finally, X-ray
emission from hotspots have been found in three FR II radio sources and, in the
case of 3C 459, we also report the detection of X-ray emission associated with
the eastern radio lobe and as well as that cospatial with radio jets in 3C 29
and 3C 402.
10/2012;
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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]
[hide abstract]
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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[show abstract]
[hide abstract]
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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F. Massaro,
D. E. Harris,
G. Tremblay,
D. Axon,
S. Baum,
A. Capetti,
M. Chiaberge,
R. Gilli,
G. Giovannini,
P. Grandi,
F. D. Macchetto,
C. O'Dea,
G. Risaliti, W. Sparks
[show abstract]
[hide abstract]
ABSTRACT: We report on our Chandra Cycle 9 program to observe half of the 60 (unobserved by Chandra) 3C radio sources at z<0.3 for 8 ksec each. Here we give the basic data: the X-ray intensity of the nuclei and any features associated with radio structures such as hot spots and knots in jets. We have measured fluxes in soft, medium and hard bands and are thus able to isolate sources with significant intrinsic column density. For the stronger nuclei, we have applied the standard spectral analysis which provides the best fit values of X-ray spectral index and column density. We find evidence for intrinsic absorption exceeding a column density of 10^{22} cm^{-2} for one third of our sources. Comment: 12 pages, 37 figures (the complete version of the paper with all figures is available on line, see appendix for details), ApJ accepted
03/2010;
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D. E. Harris,
F. Massaro,
D. Axon,
S. A. Baum,
A. Capetti,
M. Chiaberge,
R. Gilli,
G. Giovannini,
P. Grandi,
F. D. Macchetto,
C. P. O'Dea,
G. Risaliti, W. Sparks
[show abstract]
[hide abstract]
ABSTRACT: We report on our Chandra Cycle 9 program to observe half of the 60 (as
yet) unobserved 3C radio sources at z<0.3 for 8 ksec each. We compare
the Chandra observations with VLA radio maps and HST data to search for
extended emission from jets and hot spots. A comparison of X-ray flux
maps in different energy bands provides photometry, an estimate of
intrinsic absorption of nuclear emission and information on the emission
of extended regions: diffuse emission around the nucleus, jets, and hot
spots. We have found X-ray counterparts to 5radio hot spots; 2 knots in
the curved jet of 3C17; and X-ray nuclear emission from all the radio
galaxies in our sample with only one exception. Included in our sample
are 3 Compact Steep Spectrum (CSS) radio galaxies and in one of these we
studied the extended X-ray emission spatially associated with the
optical emission line region. The work at SAO is supported by NASA grant
GO8-9114A.
08/2009; -1:116.
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E. Pian,
A. S. Fruchter,
L. E. Bergeron,
S. E. Thorsett,
F. Frontera,
M. Tavani,
E. Costa,
M. Feroci,
J. Halpern,
R. A. Lucas,
L. Nicastro,
E. Palazzi,
L. Piro, W. Sparks,
A. J. Castro-Tirado,
T. Gull,
K. Hurley,
and H. Pedersen
[show abstract]
[hide abstract]
ABSTRACT: We report on Hubble Space Telescope observations of the optical transient (OT) discovered in the error box of the gamma-ray burst GRB 970508. The object was imaged on 1997 June 2 with the Space Telescope Imaging Spectrograph and Near-Infrared Camera and Multiobject Spectrometer. The observations reveal a pointlike source with R = 23.1±0.2 and H = 20.6±0.3, in agreement with the power-law temporal decay seen in ground-based monitoring. Unlike the case of GRB 970228, no nebulosity is detected surrounding the OT of GRB 970508. We set very conservative upper limits of R~24.5 and H~22.2 on the brightness of any underlying extended source. If this subtends a substantial fraction of an arcsecond, then the R-band limit is ~25.5. In combination with Keck spectra that show Mg I absorption and [O II] emission at a redshift of z=0.835, our observations suggest that the OT is located in a star-forming galaxy with total luminosity 1 order of magnitude lower than the knee of the galaxy luminosity function, L*. Such galaxies are now thought to harbor the majority of star formation at z~1; therefore, these observations may provide support for a link between GRBs and star formation.
The Astrophysical Journal 01/2009; 492(2):L103. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
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;
-
[show abstract]
[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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M. A. Hughes,
D. Axon,
J. Atkinson,
A. Alonso-Herrero,
C. Scarlata,
A. Marconi,
D. Batcheldor,
J. Binney,
A. Capetti,
C. M. Carollo,
L. Dressel,
J. Gerssen,
D. Macchetto,
W. Maciejewski,
M. Merrifield,
M. Ruiz, W. Sparks,
M. Stiavelli,
and Z. Tsvetanov
[show abstract]
[hide abstract]
ABSTRACT: We investigate the central regions of 23 spiral galaxies using Space Telescope Imaging Spectrograph (STIS) spectroscopy and archival Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) imaging. The sample is taken from our program to determine the masses of central massive black holes (MBHs) in 54 nearby spiral galaxies. Stars are likely to contribute significantly to any dynamical central mass concentration that we find in our MBH program, and this paper is part of a series to investigate the nuclear properties of these galaxies. We use the Nuker law to fit surface brightness profiles, derived from the NICMOS images, to look for nuclear star clusters and find possible extended sources in three of the 23 galaxies studied (13%). The fact that this fraction is lower than that inferred from optical Hubble Space Telescope studies is probably due to the greater spatial resolution of those studies. Using R - H and J - H colors and equivalent widths of Hα emission (from the STIS spectra), we investigate the nature of the stellar population with evolutionary models. Under the assumption of hot stars ionizing the gas, as opposed to a weak active galactic nucleus (AGN), we find that there are young stellar populations (~10–20 Myr); however, these data do not allow us to determine what percentage of the total nuclear stellar population they form. In addition, in an attempt to find any unknown AGN, we use [N II] and [S II] line flux ratios (relative to Hα) and find tentative evidence for weak AGNs in NGC 1300 and NGC 4536.
The Astronomical Journal 12/2007; 130(1):73. · 4.03 Impact Factor
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M. A. Hughes,
A. Alonso-Herrero,
D. Axon,
C. Scarlata,
J. Atkinson,
D. Batcheldor,
J. Binney,
A. Capetti,
C. M. Carollo,
L. Dressel,
J. Gerssen,
D. Macchetto,
W. Maciejewski,
A. Marconi,
M. Merrifield,
M. Ruiz, W. Sparks,
M. Stiavelli,
Z. Tsvetanov,
Marel
[show abstract]
[hide abstract]
ABSTRACT: We have observed 54 nearby spiral galaxies with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope to obtain optical long-slit spectra of nuclear gas disks and STIS optical (~R band) images of the central 5'' × 5'' of the galaxies. These spectra are being used to determine the velocity field of nuclear disks and hence to detect the presence of central massive black holes. Here we present the spectra for the successful observations. Dust obscuration can be significant at optical wavelengths, and so we also combine the STIS images with archival Near-Infrared Camera and Multi-Object Spectrometer H-band images to produce color maps to investigate the morphology of gas and dust in the central regions. We find a great variety in the different morphologies, from smooth distributions to well-defined nuclear spirals and dust lanes.
The Astronomical Journal 12/2007; 126(2):742. · 4.03 Impact Factor
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C. Scarlata,
M. Stiavelli,
M. A. Hughes,
D. Axon,
A. Alonso-Herrero,
J. Atkinson,
D. Batcheldor,
J. Binney,
A. Capetti,
C. M. Carollo,
L. Dressel,
J. Gerssen,
D. Macchetto,
W. Maciejewski,
A. Marconi,
M. Merrifield,
M. Ruiz, W. Sparks,
Z. Tsvetanov,
and R. P. van der Marel
[show abstract]
[hide abstract]
ABSTRACT: We present surface photometry for the central regions of a sample of 48 spiral galaxies (mostly unbarred and barred of type Sbc or Sc) observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Surface brightness profiles (SBPs) were derived and modeled with a Nuker law. We also analyzed archival Wide Field Planetary Camera 2 images with a larger field of view, which are available for 18 galaxies in our sample. We modeled the extracted bulge SBPs with an exponential, an r1/4, or an rn profile. In agreement with previous studies, we find that bulges of Sbc galaxies fall into two categories: bulges well described by an exponential profile and those well described by an r1/4 profile. Only one galaxy requires the use of a more general Sérsic profile to properly describe the bulge. Nuclear photometrically distinct components are found in ~55% of the galaxies. For those that we classify as star clusters on the basis of their resolved extent, we find absolute magnitudes that are brighter on average than those previously identified in spiral galaxies. This might be due to a bias in our sample toward star-forming galaxies, combined with a trend for star-forming galaxies to host brighter central clusters.
The Astronomical Journal 12/2007; 128(3):1124. · 4.03 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We present HST/WFPC2 Linear Ramp Filter images of high surface brightness emission lines (either [OII], [OIII], or H-alpha+[NII]) in 80 3CR radio sources. We overlay the emission line images on high resolution VLA radio images (eight of which are new reductions of archival data) in order to examine the spatial relationship between the optical and radio emission. We confirm that the radio and optical emission line structures are consistent with weak alignment at low redshift (z < 0.6) except in the Compact Steep Spectrum (CSS) radio galaxies where both the radio source and the emission line nebulae are on galactic scales and strong alignment is seen at all redshifts. There are weak trends for the aligned emission line nebulae to be more luminous, and for the emission line nebula size to increase with redshift and/or radio power. The combination of these results suggests that there is a limited but real capacity for the radio source to influence the properties of the emission line nebulae at these low redshifts (z < 0.6). Our results are consistent with previous suggestions that both mechanical and radiant energy are responsible for generating alignment between the radio source and emission line gas. Comment: 80 pages, 54 figures. Accepted for publication in ApJS
10/2007;
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J. T. Radomski,
C. Packham,
E. Perlman,
P. Roche,
R. K. Piña,
C. M. Telesco,
D. Aitken,
A. Alonso-Herrero,
J. Biretta,
J. M. De Buizer,
R. S. Fisher,
A. Robinson, W. Sparks,
C. Tadhunter
[show abstract]
[hide abstract]
ABSTRACT: This paper represents only a summary of mid-IR observations of four AGN
presented at the Spitzer Space Telescope: New Views of the Cosmos
conference. For more detail please refer to the corresponding
publications.
11/2006; 357:263.
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[show abstract]
[hide abstract]
ABSTRACT: The value of accurately knowing the absolute calibration of the polarizing elements in the Near Infrared Camera and Multi-Object Spectrometer (NICMOS) becomes especially important when conducting studies which require measuring degrees of polarization of close to 1% in the near infrared. We present a comprehensive study of all previously observed polarimetric standards using the NIC2 camera on NICMOS. Considering both pre- and post-NICMOS Cooling System observations we find variations in the polarimetry consistent with the effects of sub-pixel mis-alignments and the point spread function. We also measure non-zero results from unpolarized standards indicating an instrumental polarization of p ~ 1.2%, theta ~ 88degrees. The lack of polarized and unpolarized standard stars with which to perform a comprehensive calibration study means we cannot be confident that the current calibration will be effective for a number of recent large NICMOS GO programs. Further observations of polarimetric standards are needed in order to fully characterize the behavior of NICMOS at around p=1%. Comment: 9 pages, 4 figures, PASP accepted
01/2006;
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J. W. Atkinson,
J. L. Collett,
A. Marconi,
D. J. Axon,
A. Alonso-Herrero,
D. Batcheldor,
J. J. Binney,
A. Capetti,
C. M. Carollo,
L. Dressel, [......],
J. Gerssen,
M. A. Hughes,
D. Macchetto,
W. Maciejewski,
M. R. Merrifield,
C. Scarlata, W. Sparks,
M. Stiavelli,
Z. Tsvetanov,
R. P. Van Der Marel
[show abstract]
[hide abstract]
ABSTRACT: We present Space Telescope Imaging Spectrograph emission-line spectra of the central regions of the spiral galaxies NGC 1300 and 2748. From the derived kinematics of the nuclear gas we have found evidence for central supermassive black holes in both galaxies. The estimated masses of the black holes in NGC 1300 and 2748 are (6.6+6.3−3.2) × 107 and (4.4+3.5−3.6) × 107 M⊙, respectively (both at the 95 per cent confidence level). These two black hole mass estimates contribute to the poorly sampled low-mass end of the nuclear black hole mass spectrum.
Monthly Notices of the Royal Astronomical Society 03/2005; 359(2):504 - 520. · 4.90 Impact Factor
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C. Scarlata,
M. Stiavelli,
M. Hughes,
D. Axon,
A. Alonso-Herrero,
J. Atkinson,
D. Batcheldor,
J. Binney,
A. Capetti,
M. Carollo,
L. Dressel,
J. Gerssen,
D. Macchetto,
W. Maciejewski,
A. Marconi,
M. Merrifield,
M. Ruiz, W. Sparks,
Z. Tsvetanov,
R. van der Marel
[show abstract]
[hide abstract]
ABSTRACT: We present surface photometry for the central regions of a sample of 48 spiral galaxies (mostly unbarred and barred of types Sbc or Sc) observed with the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope. Surface brightness profiles were derived and modeled with a Nuker law. We also analyzed archival Wide Field Planetary Camera~2 images with a larger field of view, available for 18 galaxies in our sample. We modeled the extracted bulge surface brightness profiles with an exponential, a de Vaucouleurs or a Sersic profile. In agreement with previous studies, we find that bulges of Sbc galaxies fall into two categories: bulges well described by an exponential profile and those well described by an de Vaucouleurs profile. Only one galaxy requires the use of a more general Sersic profile to properly describe the bulge. Nuclear photometrically distinct components are found in ~55% of the galaxies. For those that we classify as star clusters based on their resolved extent we find absolute magnitudes that are brighter on average than those previously identified in spiral galaxies. This might be due to a bias in our sample toward star forming galaxies, combined with a trend for star forming galaxies to host brighter central clusters.
09/2004;
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A. Marconi,
D. J. Axon,
A. Capetti,
W. Maciejewski,
J. Atkinson,
D. Batcheldor,
J. Binney,
M. Carollo,
L. Dressel,
H Ford,
J. Gerssen,
M. A. Hughes,
D. Macchetto,
M. R. Merrifield,
C. Scarlata, W. Sparks,
M. Stiavelli,
Z. Tsvetanov,
R. P. van der Marel
[show abstract]
[hide abstract]
ABSTRACT: We present HST/STIS spectra of the Sbc spiral galaxy NGC 4041 which were used to map the velocity field of the gas in its nuclear region. We detect the presence of a compact (r~0.4" ~40 pc), high surface brightness, rotating nuclear disk co-spatial with a nuclear star cluster. The disk is characterized by a rotation curve with a peak to peak amplitude of ~40 km/s and is systematically blueshifted by 10 - 20 km/s with respect to the galaxy systemic velocity. With the standard assumption of constant mass-to-light ratio and with the nuclear disk inclination taken from the outer disk, we find that a dark point mass of 1(-0.7;+0.6) 10^7 Msun is needed to reproduce the observed rotation curve. However the observed blueshift suggests the possibility that the nuclear disk could be dynamically decoupled. Following this line of reasoning we relax the standard assumptions and find that the kinematical data can be accounted for by the stellar mass provided that either the central mass-to-light ratio is increased by a factor of ~2 or that the inclination is allowed to vary. This model results in a 3 sigma upper limit of 6 10^6 Msun on the mass of any nuclear black hole. Overall, our analysis only allows us to set an upper limit of 2 10^7 Msun on the mass of the nuclear black hole. If this upper limit is taken in conjunction with an estimated bulge B magnitude of -17.7 and with a central stellar velocity dispersion of 95 km/s, then these results are not inconsistent with both the MBH-Lsph and the MBH-sigma correlations. Constraints on black hole masses in spiral galaxies of types as late as Sbc are still very scarce and therefore the present result adds an important new datapoint to our understanding of black hole demography. Comment: Accepted for publication in the Astrophysical Journal
11/2002;
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A. Marconi,
D. Axon,
J. Atkinson,
J. Binney,
A. Capetti,
M. Carollo,
L. Dressel,
H Ford,
J. Gerssen,
M. Hughes,
D. Macchetto,
W. Maciejewski,
M. Merrifield,
C. Scarlata, W. Sparks,
M. Stiavelli,
Z. Tsvetanov,
R. van der Marel
[show abstract]
[hide abstract]
ABSTRACT: We describe an on-going HST program aimed at determining the relationship between the nuclear black hole mass and bulge mass in spiral galaxies. We have selected a volume limited sample of 54 nearby spiral galaxies for which we already have ground based emission line rotation curves, CCD surface photometry and radio maps. We are now obtaining HST/STIS longslit observations of each of the galaxies in the sample in order to determine the nuclear Halpha rotation curve at high (~0.1") spatial resolution. We will use these data to measure the unresolved dark mass concentration at the nucleus of each object. Here we show the first results from observations of objects in the sample.
01/2001;
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[show abstract]
[hide abstract]
ABSTRACT: We present near-infrared imaging polarimetry observations of the nucleus of Cygnus A (z= 0.0567), taken with the NICMOS camera of the Hubble Space Telescope (HST) at a wavelength of 2.0 μm. These maps reveal a highly collimated region of polarized emission straddling the nucleus and extending to a radius of 1.2 arcsec. Remarkably, this feature coincides with one, but only one, limb of the edge-brightened bicone structure seen in the total intensity image. The high degree (Pk∼25 per cent) and orientation of the extended polarization feature are consistent with a scattering origin. Most plausibly, the detection of polarization along only one limb of the bicone is a consequence of intrinsic anisotropy of the near-infrared continuum within the radiation cones, with the direction of maximum intensity of the near-infrared radiation field significantly displaced from the direction of the radio axis. The unresolved nuclear core source is also highly polarized (Pk>28 per cent), with a position angle close to perpendicular to the radio axis. Given that this high degree of nuclear polarization can only be explained in terms of dichroic extinction if the dichroic mechanism is unusually efficient in Cygnus A, it is more likely that the nuclear polarization is caused by the scattering of nuclear light in an unresolved scattering region close to the active galactic nucleus. In this case, the flux of the core source in the K band is dominated by scattered rather than transmitted quasar light, and previous extinction estimates based on K-band photometry of the core substantially underestimate the true nuclear extinction.
Monthly Notices of the Royal Astronomical Society 03/2000; 313(4):L52 - L56. · 4.90 Impact Factor
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A. S. Fruchter,
E. Pian,
S. E. Thorsett,
L. E. Bergeron,
R. A. Gonzalez,
M. Metzger,
P. Goudfrooij,
K. C. Sahu,
H. Ferguson,
M. Livio, [......],
T. Galama,
P. Groot,
R. Hook,
C. Kouveliotou,
D. Macchetto,
J. van Paradijs,
E. Palazzi,
H. Pedersen, W. Sparks,
M. Tavani
[show abstract]
[hide abstract]
ABSTRACT: We report on observations of the fading optical counterpart of the gamma-ray burst GRB 970228, made with the Hubble Space Telescope STIS CCD approximately six months after outburst and with the HST/NICMOS and Keck/NIRC approximately one year after outburst. The unresolved counterpart is detected by STIS at V=28.0 +/- 0.25, consistent with a continued power-law decline with exponent -1.14 +/- 0.05. The counterpart is located within, but near the edge of, a faint extended source with diameter ~0."8 and integrated magnitude V=25.8 +/- 0.25. A reanalysis of HST and NTT observations performed shortly after the burst shows no evidence of proper motion of the point source or fading of the extended emission. Only the extended source is visible in the NICMOS images with a magnitude of H=23.3 +/- 0.1. The Keck observations find K = 22.8 +/- 0.3. Several distinct and independent means of deriving the foreground extinction in the direction of GRB 970228 all agree with A_V = 0.75 +/- 0.2. After adjusting for Galactic extinction, we find that the size of the observed extended emission is consistent with that of galaxies of comparable magnitude found in the Hubble Deep Field (HDF) and other deep HST images. Only 2% of the sky is covered by galaxies of similar or greater surface brightness; therefore the extended source is almost certainly the host galaxy. Additionally, we find that the extinction-corrected V - H and V - K colors of the host are as blue as any galaxy of comparable or brighter magnitude in the HDF. Taken in concert with recent observations of GRB 970508, GRB 971214, and GRB 980703 our work suggests that all four GRBs with spectroscopic identification or deep multicolor broad-band imaging of the host lie in rapidly star-forming galaxies. Comment: 24 pages, Latex, 4 PostScript figures, to appear in the May 10 issue of The Astrophysical Journal (Note: displayed abstract is abridged)
07/1998;
