Linear radio structures in selected Seyfert galaxies
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Abstract:
High-resolution Multi-Element Radio Linked Interferometer Network 5-GHz observations of seven Seyfert galaxies, selected as the ones previously showing evidence of collimated ejection, have been compared with high-resolution Hubble Space Telescope data. A radio and optical/near-ultraviolet emission correlation is apparent in all the sources. The radio maps reveal rich structures in the entire sample. NGC 2639 and TXFS 2226−184 have multiple-knot parsec-scale extended structures, Mrk 1034NED02, Mrk 1210, NGC 4922NED02 and NGC 5506 reveal one-sided jets, while IC 1481 exhibits jet features. Interaction between these very small (mostly mas) sub-kpc jets with dense material gives rise to symptoms of a disrupted medium, signatures of which are present in all the sources.Keywords:
Collimated light
Very-long-baseline interferometry
Hubble sequence
Surface brightness Ñuctuations (SBF) have been detected for three elliptical galaxiesÈNGC 3379 in the Leo group, NGC 4406 in the Virgo cluster, and NGC 4373 in the Hydra-Centaurus superclusterÈ using marginally sampled, deep images taken with the Planetary Camera of the WFPC2 instrument on the Hubble Space T elescope (HST ).The power spectrum of the Ñuctuations image is well Ðtted by an empirical model of the point-spread function constructed using point sources identiÐed in the Ðeld.Comparison with high-quality ground-based observations of all three galaxies show excellent agreement in the measurement of the distance modulus over a substantial range in distance.This demonstrates the capability of the Planetary Camera of WFPC2 to measure distances using the SBF technique despite the marginal sampling and small spatial coverage of the images.The residual variance due to unresolved sources in all three galaxies is only 2%È5% of the detected Ñuctuations signal, which conÐrms the advantage of HST imaging in minimizing the uncertainty of this SBF correction.Extensive consistency checks, including an independent SBF analysis using an alternate software package, suggest that our internal uncertainties are \0.02mag.The Ñuctuations magnitude for NGC 4373 is I F814W \ 31.310.05 mag, corresponding to a distance modulus of This implies a peculiar (m[M) 0 \ 32.99 ^0.11.velocity for this galaxy of 415 ^330 km s~1, which is smaller than derived from the relation.
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Cosmic distance ladder
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We present preliminary results from Hubble Space Telescope (HST)/WFPC2 observations of the central regions of the of the Galactic globular clusters M13 and M3. The clusters are almost identical in most respects, including chemical composition, but there are dramatic differences in both the horizontal-branch (HB) and blue straggler populations. The M13 HB has a long blue tail extending 4.5 mag in V, reaching well below the level of the main-sequence turnoff. M3 has no such feature. M3 and M13 are thus an extreme case of the "second-parameter problem" in HB morphology. Also present in the M13 HB are two gaps similar to those seen in the clusters NGC 6752 and NGC 2808. M3 has a specific frequency of blue stragglers 3 times larger than that of M13. Our results imply that neither age nor cluster density, two popular second-parameter candidates, are likely to be responsible for the observed differences.
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Horizontal branch
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We present a photometric study of the star-forming region NGC 346 and its surrounding field in the Small Magellanic Cloud, using data taken with the Advanced Camera for Surveys (ACS) on board the Hubble Space Telescope (HST). The data set contains both short and long exposures for increased dynamic range, and photometry was performed using the ACS module of the stellar photometry package DOLPHOT. We detected almost 100,000 stars over a magnitude range of V ~ 11 to V ~ 28 mag, including all stellar types from the most massive young stars to faint lower main-sequence and pre-main-sequence stars. We find that this region, which is characterized by a plethora of stellar systems and interesting objects, is an outstanding example of mixed stellar populations. We take into account different features of the color-magnitude diagram of all the detected stars to distinguish the two dominant stellar systems: The stellar association NGC 346 and the old spherical star cluster BS 90. These observations provide a complete stellar sample of a field about 5' × 5' around the most active star-forming region in this galaxy. Considering the importance of these data for various investigations in the area, we provide the full stellar catalog from our photometry. This paper is the first part of an ongoing study to investigate in detail the two dominant stellar systems in the area and their surrounding field.
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[Abridged] We present a first detailed analysis of resolved stellar populations in the dwarf galaxies NGC 185 and NGC 205 based on archival V- and I-band WFPC2 pointings. For NGC 185 we deduce that star formation was probably still active about 4 x 10^8 yr ago. Key abundance-related results are: (1) We identify ancient stars with [Fe/H] -1.11 +/- 0.08 dex for ancient stars. For NGC 205, we record (m-M)o = 24.76 +/- 0.1 mag, based on the RGB I-band tip magnitude method. We find that stars were probably still forming less than 3 x 10^8 yr ago, which is compatible with star formation triggered by an interaction with M31. Key abundance-related results are: (1) The RGB/ faint-AGB is significantly skewed to redder values than that of a control field in the outskirts of M31; it probably results from a relatively narrow metallicity and or age range for a significant fraction of the dwarf's stars. (2) For ancient stars we infer from colour information that the median [Fe/H] > -1.06+/-0.04 dex. We briefly compare the stellar populations of NGC 205, NGC 185 and NGC 147. Finally, we find an apparent blue excess in the outer region of the nuclear star cluster in NGC 205. It is as compact as a typical galactic globular cluster, but is quite bright (10^6 L_solar,R); and by matching its blue colour with models, its stellar population is young, up to a few times 10^8 yr old.
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We have studied Hubble Space Telescope archive imagery of the central region of the Seyfert 2 galaxy NGC 5427. The images were taken with F606W ( V -band) and F160W ( H -band) filters with the Wide Field and Planetary Camera 2 and the Near Infrared Camera and Multi-Object Spectrometer, respectively.
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Barred spiral galaxy
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Hubble Space Telescope First Observations of the Brightest Stars in the Virgo Galaxy M100 = NGC 4321
As part of both the Early Release Observations fromthe Hubble Space Telescope and the Key PRoject on the Extragalctic Distance Scale, we have obtained multi-wavelength BVR WFPC2 images for the face-on Virgo cluster spiral galaxy M11 = NGC 4321.
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