Home     Getting Started     To Survive in the Universe    
Inhabited Sky
    News@Sky     Astro Photo     The Collection     Forum     Blog New!     FAQ     Press     Login  

NGC 2823



Upload your image

DSS Images   Other Images

Related articles

The Radio Galaxy Populations of Nearby Northern Abell Clusters
We report on the use of the NRAO VLA Sky Survey (NVSS) to identify radiogalaxies in 18 nearby Abell clusters. The listings extend from the coresof the clusters out to radii of 3 h-175 Mpc, whichcorresponds to 1.5 Abell radii and approximately 4 orders of magnitudein galaxy density. To create a truly useful catalog, we have collectedoptical spectra for nearly all of the galaxies lacking public velocitymeasurements. Consequently, we are able to discriminate between thoseradio galaxies seen in projection on the cluster and those that are inactuality cluster members. The resulting catalog consists of 329 clusterradio galaxies plus 138 galaxies deemed foreground or backgroundobjects, and new velocity measurements are reported for 273 of theseradio galaxies. The motivation for the catalog is the study of galaxyevolution in the cluster environment. The radio luminosity function is apowerful tool in the identification of active galaxies, as it isdominated by star-forming galaxies at intermediate luminosities andactive galactic nuclei (AGNs) at higher luminosities. The flux limit ofthe NVSS allows us to identify AGNs and star-forming galaxies down tostar formation rates less than 1 Msolar yr-1. Thissensitivity, coupled with the all-sky nature of the NVSS, allows us toproduce a catalog of considerable depth and breadth. In addition tothese data, we report detected infrared fluxes and upper limits obtainedfrom IRAS data. It is hoped that this database will prove useful in anumber of potential studies of the effect of environment on galaxyevolution. Based in part on observations obtained with the Apache PointObservatory 3.5 m telescope, which is owned and operated by theAstrophysical Research Consortium (ARC).

An Hα survey of eight Abell clusters: the dependence of tidally induced star formation on cluster density
We have undertaken a survey of Hα emission in a substantiallycomplete sample of CGCG galaxies of types Sa and later within 1.5 Abellradii of the centres of eight low-redshift Abell clusters (Abell 262,347, 400, 426, 569, 779, 1367 and 1656). Some 320 galaxies weresurveyed, of which 116 were detected in emission (39 per cent ofspirals, 75 per cent of peculiars). Here we present previouslyunpublished data for 243 galaxies in seven clusters. Detected emissionis classified as `compact' or `diffuse'. From an analysis of the fullsurvey sample, we confirm our previous identification of compact anddiffuse emission with circumnuclear starburst and disc emissionrespectively. The circumnuclear emission is associated either with thepresence of a bar, or with a disturbed galaxy morphology indicative ofongoing tidal interactions (whether galaxy-galaxy, galaxy-group, orgalaxy-cluster). The frequency of such tidally induced (circumnuclear)starburst emission in spirals increases from regions of lower to higherlocal galaxy surface density, and from clusters with lower to highercentral galaxy space density. The percentages of spirals classed asdisturbed and of galaxies classified as peculiar show a similar trend.These results suggest that tidal interactions for spirals are morefrequent in regions of higher local density and for clusters with highercentral galaxy density. The prevalence of such tidal interactions inclusters is expected from recent theoretical modelling of clusters witha non-static potential undergoing collapse and infall. Furthermore, inaccord with this picture, we suggest that peculiar galaxies arepredominantly ongoing mergers. We conclude that tidal interactions arelikely to be the main mechanism for the transformation of spirals to S0sin clusters. This mechanism operates more efficiently in higher densityenvironments, as is required by the morphological type-local surfacedensity (T-Σ) relation for galaxies in clusters. For regions ofcomparable local density, the frequency of tidally induced starburstemission is greater in clusters with higher central galaxy density. Thisimplies that, for a given local density, morphological transformation ofdisc galaxies proceeds more rapidly in clusters of higher central galaxydensity. This effect is considered to be the result of subclustermerging, and could account for the previously considered anomalousabsence of a significant T-Σ relation for irregular clusters atintermediate redshift.

Arcsecond Positions of UGC Galaxies
We present accurate B1950 and J2000 positions for all confirmed galaxiesin the Uppsala General Catalog (UGC). The positions were measuredvisually from Digitized Sky Survey images with rms uncertaintiesσ<=[(1.2")2+(θ/100)2]1/2,where θ is the major-axis diameter. We compared each galaxymeasured with the original UGC description to ensure high reliability.The full position list is available in the electronic version only.

The Dynamics of Poor Systems of Galaxies
We assemble and observe a sample of poor galaxy systems that is suitablefor testing N-body simulations of hierarchical clustering and otherdynamical halo models. We (1) determine the parameters of the densityprofile rho(r) and the velocity dispersion profile sigma_p(R), (2)separate emission-line galaxies from absorption-line galaxies, examiningthe model parameters and as a function of spectroscopic type, and (3)for the best-behaved subsample, constrain the velocity anisotropyparameter, beta, which determines the shapes of the galaxy orbits. Oursample consists of 20 systems, 12 of which have extended X-ray emissionin the ROSAT All-Sky Survey. We measure the 877 optical spectra ofgalaxies brighter than m_R~15.4 within 1.5 h^-1 Mpc of the systemcenters (we take H_0=100 h km s^-1 Mpc^-1). Thus, we sample the systemmembership to a radius typically three times larger than other recentoptical group surveys. The average system population is 30 galaxies, andthe average line-of-sight velocity dispersion is ~300 km s^-1. TheNavarro, Frenk, & White universal profile and the Hernquist modelboth provide good descriptions of the spatial data. In most cases anisothermal sphere is ruled out. Systems with declining sigma_p(R) arewell-matched by theoretical profiles in which the star-forming galaxieshave predominantly radial orbits (beta>0) many of these galaxies areprobably falling in for the first time. There is significant evidencefor spatial segregation of the spectroscopic classes regardless ofsigma_p(R).

Dynamics of cD Clusters of Galaxies. III. Redshift Data for 11 Abell Clusters
We present the final observational data for a spectroscopic study of asample of cD galaxy clusters. The goal of this program has been to studythe dynamics of the clusters, with emphasis on determining the natureand frequency of peculiar-velocity cD galaxies. In this paper we presentredshifts for 762 galaxies in the fields of the rich Abell clustersA779, A1691, A1749, A1767, A1837, A1927, A2067, A2079, A2089, A2199, andA2666. We also present preliminary dynamical properties for theseclusters using our measured redshifts.

Properties of nearby clusters of galaxies. III. A 76, A 157, A 407, A 505, A 671, A 779, A 1700, A 2028, A 2040, A 2052 A 2063, A 2065, A 2593, A 2657, A 2670
We present F band photometry, from digitized 48-inch Palomar plates, of2818 galaxies brighter than m_3+3 in 15 Abell clusters. For each galaxy,absolute coordinates, magnitude, size, ellipticity and orientation aregiven. For each cluster we provide finding charts and contour maps ofthe galaxy surface density. The absolute coordinates of the galaxies ofother 8 clusters presented in the first paper of this series are alsoincluded.

HI observations of galaxies in nearby Zwicky clusters
The results of a long term project of H I observations of galaxieswithin the boundaries of nearby Zwicky clusters are presented. Thedetection rate is rather low (233 out of 618, i.e., 38 percent) ascompared to other surveys carried out recently. Most of the radialvelocities of the detected galaxies are new determinations. The largespread in radial velocities for many of these clusters is a strongindication for the presence of several foreground and/or backgroundgalaxies.

Radio-emission spectra and surface brightnesses of radio galaxies
It is shown that radio galaxies with flat radio-emission spectra have,on the average, significantly higher optical surface brightness thanradio galaxies with steep spectra. The results obtained also suggestthat radio galaxies with flat spectra are in a more active phase ofevolution than galaxies with steep spectra. Intense star-formationprocesses appear to be occurring in the galaxies with flat spectra.

Galaxy alignments
Large areas of the sky around the brightest apparent magnitude galaxieshave been examined. In almost every case where they are not crowded byother right galaxies, clearly marked lines of higher red shift galaxieshave been going through, or originating from, the positions of thesebright apparent magnitude galaxies. It is shown that galaxies of about3000 to 5000 km/s red shift define narrow filaments of from 10 to 50 degin length. It is found that galaxies of very bright apparent magnitudetend to occur at the center or ends of these alignments. The 20brightest galaxies in apparent magnitude north of delta = 0 deg areinvestigated here. Of the 14 which are uncrowded by nearby brightgalaxies, a total of 13 have well marked-lines and concentrations offainter, higher red shift galaxies.

Infrared studies of elliptical galaxies. II - A radio-selected sample
An IR survey of radio galaxies in the Bologna B2 catalog is reported. Itis found that 40 percent of the sample has IR luminosities of at leastone billion solar luminosities, as opposed to about 8 pecent of normalellipticals. The galaxies are inhomogeneous in their IR properties. Themost IR-luminous galaxies are those listed as peculiar by Zwicky.Statistically, these galaxies are strikingly different from Seyfertgalaxies in their IR properties in that they show much more radioemission in comparison with their IR emission than do Seyferts, evenwhen the emission from the extended radio lobes has been discounted.

A Deep Sky Survey at 3.9-GHZ 7.7-GHZ and 14.4-GHZ
Not Available

Observations of low-luminosity radio galaxies at 102 MHz
Observational results for 38 low-luminosity radio galaxies at 102 MHzfrom interplanetary scintillation are reported. The information givenincludes the designation of each galaxy, the total flux at 102 MHz, theflux of the scientillating component and its angular diameter, and thesolar elongation. A more detailed analysis is given of the observationaldata for objects for which scintillating components were found.

RATAN-600 observations of 15 Bologna radio galaxies
Fifteen radio galaxies selected from the Bologna radio-source surveyhave been observed with the RATAN-600 telescope at nu = 3.66 or 3.95 GHz(two of them also at nu = 0.97, 7.69 GHz). The giant radio galaxy B21141 + 37 is surrounded by a halo measuring approximately 6 arcmin (1Mpc) across.

Relative orientations of the axes of radio sources and the elliptical galaxies associated with them
A study is made of the relationship between the major axes of radiogalaxies and the elliptical galaxies associated with them. It is foundthat if the ratio of the major axes of the radio galaxies to thediameters of the radio components is greater than 2.5 there is a clearcorrelation between the directions of the major axes of the radiogalaxies and the minor axes of the optical galaxies. But if the ratio isless than 2.5, then the directions of the major axes of the radio andthe optical galaxies are well correlated. This result agrees well with amechanism of formation of radio galaxies in which it is assumed thatthey are formed from clouds of relativistic particles that are ejectedfrom the central regions of the elliptical galaxies and move in thedipole magnetic field of these galaxies.

Radio and optical observations of 9 nearby Abell clusters - A262, A347, A569, A576, A779, A1213, A1228, A2162, A2666
A survey is made of 61 Abell clusters included in the HEAO-2 satelliteobserving program at 1.4 GHz. Data are presented on the nine clusters ofdistance class 1 and 2. With a view to establishing galaxy morphologiesand extending the sample of the galaxies with known velocities, platesand spectra are obtained with a 152-cm telescope. The bivariate radioluminosity function of the cluster galaxies is determined for the threemorphological types, E, SO, and S plus Irr, dividing these into threedifferent classes of absolute optical magnitude. The radio luminosityfunctions of E and SO galaxies in present clusters do not differ fromthose of E and SO galaxies in clusters having higher richness. Someevidence exists that spiral galaxies in clusters have a lowerprobability of being radio sources than field ones. Also included is abrief discussion of the sizes of cluster radio sources and thecorrelation between radio emission and the presence of emission linesfrom a galaxy.

The radio source near NGC 2823.
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1978MNRAS.182P...1F&db_key=AST

Variability of extragalactic sources at 2.7 GHz. II - Flux densities of 550 sources and further evidence for variations
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977AJ.....82...21B&db_key=AST

Observations of 40 low luminosity radio galaxies with the Westerbork Synthesis Radio Telescope
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1977A&AS...29..279F&db_key=AST

Optical identification of radio-sources selected from the B2 catalogue
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1972A&AS....6....1G&db_key=AST

Submit a new article

Related links

  • - No Links Found -
Submit a new link

Member of following groups:

Observation and Astrometry data

Right ascension:09h19m17.40s
Aparent dimensions:1.023′ × 0.617′

Catalogs and designations:
Proper Names   (Edit)
NGC 2000.0NGC 2823

→ Request more catalogs and designations from VizieR