A spectroscopic study of NGC 6251 and its companion galaxies

Werner, PN; Worrall, D. M.; Birkinshaw, Mark

doi:10.1046/j.1365-8711.2000.03687.x

Cited by 5 publications

(5 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In addition, there are several candidates outside of our search area. UGC 10604 lies some 52 arcmin southeast of NGC 6251; with z = 0.0252, Werner et al (2000) consider it to be a member of the group. They similarly include UGC 10471a/b (a binary with z = 0.0239 for both members) which is nearly 1° south of the centre.…”

Section: Resultsmentioning

confidence: 99%

“…Birkinshaw & Worrall (1993) noted that there were four galaxies lying within 1° of NGC 6251 and it was not associated with a cluster capable of containing an intracluster medium as hot as 5 keV. In a subsequent study, Werner et al (2000) found eight galaxies to be members of the ‘poor group’. In order to search for more candidates and investigate the nature of the objects surrounding NGC 6251, we have obtained spectra of galaxies (brighter than m r ≃ 16) within a 45 arcmin radius using the 2.16‐m optical telescope in Hebei (Xinglong Station of the NAOC).…”

Section: Introductionmentioning

confidence: 97%

“…The radio components associated with NGC 6251 were discovered by Waggett, Warner & Baldwin (1977) who showed maps of the entire source and core region at frequencies of 151 and 1417 MHz. The large‐scale radio emission has an extent of , at a measured redshift of 0.0249 (Werner, Worrall & Birkinshaw 2000), which corresponds to a projected linear size of 1.8 Mpc. An impressive radio feature is the asymmetry of the jets and lobes [see Fig.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Group galaxies around giant radio galaxy NGC 6251

Chen

Peng

Strom

et al. 2011

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

We have investigated galaxies around NGC 6251 to search for an associated group. Our main goal is to study the environment around the giant radio galaxy to better understand the reasons for its size and structure. To this end, we have made spectroscopic observations with the 2.16-m optical telescope at Xinglong Station of the National Astronomical Observatories of China (NAOC) and obtained spectra of 45 objects (including four likely stars). The redshifts give us 10 new galaxies in a group, which are in addition to seven previously known members. The 17 galaxies' positions are compared with the radio emission. The optical velocity dispersion of group members within 0.7 Mpc of NGC 6251 is not consistent with that expected from correlation curves of X-ray luminosity L x versus velocity dispersion σ r . We briefly discuss this result, suggesting that in the NGC 6251 group, the density of X-ray emitting gas is unusually low, and this is the main reason for the size of the radio source.

show abstract

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Group galaxies around giant radio galaxy NGC 6251

Chen

Peng

Strom

et al. 2011

Monthly Notices of the Royal Astronomical Society

View full text Add to dashboard Cite

show abstract

“…The linear scale corresponding to 1 milliarcsec (mas) is 0.36 h −1 pc. The line-of-sight velocity dispersion of the sub-cluster is less than 300 km s −1 , implying that it is a poor cluster with an X-ray atmosphere temperature of 0.7 keV (Werner, et al 2000). Combined with plausible densities (consistent with the extended X-ray luminosity measured by Birkinshaw and Worrall (1993)), this gas temperature is far too low to confine any part of the spectacularly linear (e.g., see Figure 1 in Werner, et al (2001)) kpc-scale radio jet.…”

Section: Introductionmentioning

confidence: 99%

“…Spectroscopic observations with HST indicate the presence of a central black hole with a mass of (6 ± 2) × 10 8 M ⊙ (Ferrarese and Ford 1999). Although NGC 6251 is located near the edge of the cluster Zw 1609.0+8212, recent observations by Werner, et al (2000) show that this cluster contains at least three sub-clusters of galaxies that may not be physically related. NGC 6251 is associated with one of these sub-clusters.…”

Section: Introductionmentioning

confidence: 99%

What Happened to the NGC 6251 Counterjet?

Jones

Wehrle

2002

ApJ

View full text Add to dashboard Cite

We have used the Very Long Baseline Array to produce a high dynamic range image of the nucleus of NGC 6251 at 1.6 GHz and snapshot images at 5.0, 8.4, and 15.3 GHz to search for emission from a parsecscale counterjet. Previous VLBI images at 1.6 GHz have set a lower limit for the jet/counterjet brightness ratio near the core at about 80:1, which is larger than expected, given the evidence that the radio axis is fairly close to the plane of the sky. A possible explanation is that the inner few parsecs of the counterjet are hidden by free-free absorption by ionized gas associated with an accretion disk or torus. This would be consistent with the nearly edge-on appearance of the arcsecond-scale dust disk seen in the center of NGC 6251 by Hubble Space Telescope (HST). We detect counterjet emission close to the core at 1.6 GHz, but not at the higher frequencies. Given that the optical depth of free-free absorption falls off more rapidly with increasing frequency than the optically thin synchrotron emission from a typical radio jet, this result implies that the absence of a detectable parsec-scale counterjet at high frequencies is not due to free-free absorption unless the density of ionized gas is extremely high and we have misidentified the core at 1.6 GHz. The most likely alternative is a large jet/counterjet brightness ratio caused by relativistic beaming, which in turn requires the inner radio axis to be closer to our line of sight than the orientation of the HST dust disk would suggest.

show abstract

The gaseous environments of radio galaxies

Worrall

2002

New Astronomy Reviews

View full text Add to dashboard Cite

X-ray emission traces the gaseous environments of radio sources. The medium must be present for jet confinement, but what are its influence on jet fuelling, dynamics, propagation, and disruption? The observational situation is both complicated and enriched by radio sources being multi-component X-ray emitters, with several possible regions of non-thermal emission. Recent work, primarily based on sensitive ROSAT pointings, is used to contrast the X-ray emission and environments of radio sources with (a) low power, (b) high power at high redshift, (c) high power at lower redshift, and (d) GHz peaked spectrum emission. The trends in external gas density and pressure near extended radio structures are reviewed. Imminentlyavailable X-ray measurements with vastly improved resolution and sensitivity have great potential for resolving many open issues.

show abstract

A spectroscopic study of NGC 6251 and its companion galaxies

Cited by 5 publications

References 27 publications

Group galaxies around giant radio galaxy NGC 6251

Group galaxies around giant radio galaxy NGC 6251

What Happened to the NGC 6251 Counterjet?

The gaseous environments of radio galaxies

Contact Info

Product

Resources

About