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|Circumnuclear star-forming activities along the Hubble sequence|
In order to study circumnuclear star-forming activity along the Hubblesequence, we cross-correlated the Sloan Digital Sky Survey Data Release2 (SDSS DR2) with the Third Reference Catalog of Bright Galaxies (RC3)to derive a large sample of 1015 galaxies with both morphological andspectral information. Among these, 385 sources are classified asstar-forming galaxies, and the SDSS fibre covered the circumnuclearregions (0.2-2.0 kpc). By using the spectral synthesis method to removethe contribution from the underlying old stellar population, we measuredthe emission lines fluxes accurately, which are then used to estimatethe star-formation rates(SFRs). Our main findings are: (1) early-typespirals show much higher Hα luminosities, and hence higher SFRs,and also suffer more extinctions than late-type ones. The equivalentwidths (EWs) of Hα emission lines show a similar trend; however,the very late types (Sdm ~ Irr) do have large fractions of high EWs; (2)we confirm that D_n(4000) shows a strong correlation with the strengthsof metallic absorption lines (such as CN band, G band, and Mg Ib). Boththese lines and the Balmer absorption lines show interesting variationsbetween Sbc and Sd type galaxies; (3) the bar structure tightly relatesto the enhanced star formation activity, an effect that is even moresignificant in the early-type spirals. But we should note that the barstructure is not a necessary or sufficient condition for galaxies toharbor circumnuclear star formations.
|Probing the dynamics of cluster-lenses|
We propose a new approach to study the dynamical implications of massmodels of clusters for the velocity structure of galaxies in the core.Strong and weak lensing data are used to construct the total massprofile of the cluster, which is used in conjunction with the opticalgalaxy data to solve in detail for the nature of galaxy orbits and thevelocity anisotropy in the central regions. We also examine otherobservationally and physically motivated mass models, specifically thoseobtained from X-ray observations and N-body simulations. The aim of thisanalysis is to understand qualitatively the structure of the core, andto test some of the key assumptions of the standard picture of clusterformation regarding relaxation, virialization and equilibrium. Thistechnique is applied to the cluster Abell 2218, where we find evidencefor an anisotropic core, which we interpret as indicating the existenceof a dynamically disturbed central region. We find that the requirementof physically meaningful solutions for the velocity anisotropy placesstringent bounds on the slope of cluster density profiles in the innerregions.
|An image database. II. Catalogue between δ=-30deg and δ=70deg.|
A preliminary list of 68.040 galaxies was built from extraction of35.841 digitized images of the Palomar Sky Survey (Paper I). For eachgalaxy, the basic parameters are obtained: coordinates, diameter, axisratio, total magnitude, position angle. On this preliminary list, weapply severe selection rules to get a catalog of 28.000 galaxies, wellidentified and well documented. For each parameter, a comparison is madewith standard measurements. The accuracy of the raw photometricparameters is quite good despite of the simplicity of the method.Without any local correction, the standard error on the total magnitudeis about 0.5 magnitude up to a total magnitude of B_T_=17. Significantsecondary effects are detected concerning the magnitudes: distance toplate center effect and air-mass effect.
|X-ray and infrared selected AGN. II - Optical spectroscopy|
In a search for obscured active galactic nuclei, 144 X-ray/IR emittinggalaxies were selected. Optical spectroscopy of this sample ispresented. A classification according to the nuclear activity shows that28 are AGN, 39 are transition-type objects, and 44 are H II region-likegalaxies. Three of the 28 AGN are Seyfert 1 galaxies and the others areof Type 2. It is suggested that the objects identified as narrow lineAGN are obscured Seyfert 1. Most of the observed galaxies are seenedge-on, indicating that dust may have a flattened distribution coplanarto the disk of the parent galaxy. With the inclusion of the newlyidentified AGN, the sample of the X-ray emitting Seyfert 2 galaxies isfairly complete above a flux limit of log F(Hx) = -10.8.
|Investigation of galaxies of high surface brightness at 3.95 GHz.|
|Observations of galaxies of high surface brightness at 102 MHz|
Forty-four of the galaxies of high surface brightness listed byArakelyan have been observed at 102-MHz frequency with the Pushchinocophased antenna array by the interplanetary-scintillation method. Tenof these objects have been detected at flux-density levels above 1-2 Jy.Seven of them have scintillating components not greater than 1 arcsecacross. The galaxy Ark 448 shows 100 percent scintillation; Ark 451,nearly 100 percent. Spectra are established for the scintillatingcomponents. Almost all the scintillators either are E or S0 galaxies, orappear highly compact at photographic wavelengths.
|Accurate Optical Positions of Arakelian Galaxies|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1981AJ.....86..820K&db_key=AST
|Galaxies of high surface brightness|
Two lists are presented which contain 621 galaxies whose surfacebrightness, as derived from their apparent magnitudes, is at least 22.0magnitudes from an area of 1 sq arcsec. The lists were compiled in anattempt to verify observationally a possible correlation between surfacebrightness and nuclear activity. Four percent of all the galaxies in anarea of 4.5 sr at declinations higher than -3 deg and galactic latitudesgreater than 20 deg are listed, including 30 Markarian, 29 Zwicky, and 7blue Haro galaxies. A morphological study of 130 of the galaxiesindicates that about half are elliptical or lenticular, 50 are compactor peculiar, and that there is an excess of elliptical and lenticularobjects in comparison with a random sample. Notes on the morphologicaltypes and colors of the galaxies are provided along with identificationcharts.
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