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Optically bright active galactic nuclei in the ROSAT-Faint source catalogue
To build a large, optically bright, X-ray selected AGN sample we havecorrelated the ROSAT-FSC catalogue of X-ray sources with the USNOcatalogue limited to objects brighter than O=16.5 and then with the APSdatabase. Each of the 3212 coincidences was classified using theslitless Hamburg spectra. 493 objects were found to be extended and 2719starlike. Using both the extended objects and the galaxies known frompublished catalogues we built up a sample of 185 galaxies withO_APS<17.0 mag, which are high-probability counterparts of RASS-FSCX-ray sources. 130 galaxies have a redshift from the literature and foranother 34 we obtained new spectra. The fraction of Seyfert galaxies inthis sample is 20%. To select a corresponding sample of 144high-probability counterparts among the starlike sources we searched forvery blue objects in an APS-based color-magnitude diagram. Forty-onewere already known AGN and for another 91 objects we obtained newspectra, yielding 42 new AGN, increasing their number in the sample to83. This confirms that surveys of bright QSOs are still significantlyincomplete. On the other hand we find that, at a flux limit of 0.02count s-1 and at this magnitude, only 40% of all QSOs aredetected by ROSAT.Tables 2, 3 and 4 are only available in electronic form athttp://www.edpsciences.org
| Galaxy coordinates. II. Accurate equatorial coordinates for 17298 galaxies
Using images of the Digitized Sky Survey we measured coodinates for17298 galaxies having poorly defined coordinates. As a control, wemeasured with the same method 1522 galaxies having accurate coordinates.The comparison with our own measurements shows that the accuracy of themethod is about 6 arcsec on each axis (RA and DEC).
| Catalogue of HI maps of galaxies. I.
A catalogue is presented of galaxies having large-scale observations inthe HI line. This catalogue collects from the literature the informationthat characterizes the observations in the 21-cm line and the way thatthese data were presented by means of maps, graphics and tables, forshowing the distribution and kinematics of the gas. It containsfurthermore a measure of the HI extension that is detected at the levelof the maximum sensitivity reached in the observations. This catalogueis intended as a guide for references on the HI maps published in theliterature from 1953 to 1995 and is the basis for the analysis of thedata presented in Paper II. The catalogue is only available inelectronic form at the CDS via anonymous ftp 130.79.128.5 orhttp://cdsweb.u-strasbg.fr/Abstract.html
| A redshift survey toward a proposed void of galaxies suggested by the distribution of Abell clusters
A program of redshift measurements was carried out in a region of thesky in which a relative under-density of Abell clusters had been used toinfer the presence of a large (diameter about 40/h Mpc) void in thegeneral galaxy distribution. The purpose of this study was toinvestigate whether the large-scale distribution of galaxies is tracedby the distribution of rich clusters. Redshifts are presented for 308galaxies in the Zwicky Catalog in a 234 square degree region centered onR.A. about 2h, Decl. about 12 deg of which 229 have been newly measured.These data reveal a pattern of filamentary structure alternating withvoids of characteristic diameter about 25-30/h Mpc, throughout thevolume sampled. While the redshift data reveal an underdensity in thedistribution of galaxies in the general region suggested by the Abellcluster distribution, they do not support the existence there of a 40/hMpc diameter void.
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