Upload your image
DSS Images Other Images
Submit a new article
|The Local Lyα Forest. III. Relationship between Lyα Absorbers and Galaxies, Voids, and Superclusters|
In this paper we use large-angle, nearby galaxy redshift surveys toinvestigate the relationship between the 81 low-redshift Lyαabsorbers in our Hubble Space Telescope GHRS survey and galaxies,superclusters, and voids. In a subsample of 46 Lyα absorberslocated in regions where the 2000 February 8 CfA catalog is completedown to at least L* galaxies, the nearest galaxy neighbors range from100 h-170 kpc to greater than 10h-170 Mpc. Of these 46 absorbers, eight are foundin galaxy voids. After correcting for path length and sensitivity, wefind that 22%+/-8% of the Lyα absorbers lie in voids, whichrequires that at least some low column density absorbers are notextended halos of individual bright galaxies. The number density ofthese clouds yields a baryon fraction of 4.5%+/-1.5% in voids. Thestronger Lyα absorbers (1013.2-1015.4cm-2) cluster with galaxies more weakly than galaxies clusterwith each other, while the weaker absorbers(1012.4-1013.2 cm-2) are more randomlydistributed. The median distance from a low-z Lyα absorber in oursample to its nearest galaxy neighbor (~500 h-170kpc) is twice the median distance between bright galaxies in the samesurvey volume. This makes any purported ``association'' between theseLyα absorbers and individual galaxies problematic. The suggestedcorrelation between Lyα absorber equivalent width (W) andnearest galaxy impact parameter does not extend to W<=200mÅ or to impact parameters greater than 200h-170 kpc. Instead, we find statistical supportfor the contention that absorbers align with large-scale filaments ofgalaxies. The pair of sight lines, 3C 273 and Q1230+0115, separated by0.9d on the sky, provides an example of eight absorbers and sevengalaxies aligned along a possible filamentary structure at least 20h-170 Mpc long. While some strong (W>400mÅ) Lyα absorbers may be gas in the extended gaseous halosof individual galaxies, much of the local Lyα ``forest'' appearsto be associated with the large-scale structures of galaxies and somewith voids. Based on observations with the NASA/ESA Hubble SpaceTelescope, obtained at the Space Telescope Science Institute, which isoperated by the Association of Universities for Research in Astronomy,Inc., under NASA contract NAS 5-26555.
|Nearby Optical Galaxies: Selection of the Sample and Identification of Groups|
In this paper we describe the Nearby Optical Galaxy (NOG) sample, whichis a complete, distance-limited (cz<=6000 km s-1) andmagnitude-limited (B<=14) sample of ~7000 optical galaxies. Thesample covers 2/3 (8.27 sr) of the sky (|b|>20deg) andappears to have a good completeness in redshift (97%). We select thesample on the basis of homogenized corrected total blue magnitudes inorder to minimize systematic effects in galaxy sampling. We identify thegroups in this sample by means of both the hierarchical and thepercolation ``friends-of-friends'' methods. The resulting catalogs ofloose groups appear to be similar and are among the largest catalogs ofgroups currently available. Most of the NOG galaxies (~60%) are found tobe members of galaxy pairs (~580 pairs for a total of ~15% of objects)or groups with at least three members (~500 groups for a total of ~45%of objects). About 40% of galaxies are left ungrouped (field galaxies).We illustrate the main features of the NOG galaxy distribution. Comparedto previous optical and IRAS galaxy samples, the NOG provides a densersampling of the galaxy distribution in the nearby universe. Given itslarge sky coverage, the identification of groups, and its high-densitysampling, the NOG is suited to the analysis of the galaxy density fieldof the nearby universe, especially on small scales.
|Triaxial bulges in the NIR|
We studied a sample of 14 non-interacting spiral galaxies with the aimof searching triaxial bulges. From the existence of triaxiality we areable to put a lower and upper limits on the central black hole to bulgemass ratio, M_BH/M_bul, in the host galaxy.
|Very Wide Galaxy Pairs of the Northern and Southern Sky|
We present highly accurate observations of the 21 cm line of hydrogen ingalaxies made at the Arecibo and Parkes Observatories. The galaxiesobserved have been identified, through rigorous selection criteriaapplied to the CfA and SSRS catalogs, as being members of pairs withprojected separations of up to 1.5 Mpc (H0 = 75 km s-1 Mpc-1). Theseobservations form the completion of the Chengalur-Nordgren galaxy pairsample with data previously published by Chengalur, Nordgren andcolleagues. The new selection criteria used in this paper are anextension to larger projected separations of the criteria usedpreviously. Forty-nine new galaxies are observed, while H I is detectedin 41 of them. With the addition of these galaxies, the completed samplehas highly accurate H I velocities for a total of 219 galaxies.
|The Southern Sky Redshift Survey|
We report redshifts, magnitudes, and morphological classifications for5369 galaxies with m_B <= 15.5 and for 57 galaxies fainter than thislimit, in two regions covering a total of 1.70 sr in the southerncelestial hemisphere. The galaxy catalog is drawn primarily from thelist of nonstellar objects identified in the Hubble Space TelescopeGuide Star Catalog (GSC). The galaxies have positions accurate to ~1"and magnitudes with an rms scatter of ~0.3 mag. We compute magnitudes(m_SSRS2) from the relation between instrumental GSC magnitudes and thephotometry by Lauberts & Valentijn. From a comparison with CCDphotometry, we find that our system is homogeneous across the sky andcorresponds to magnitudes measured at the isophotal level ~26 magarcsec^-2. The precision of the radial velocities is ~40 km s^-1, andthe redshift survey is more than 99% complete to the m_SSRS2 = 15.5 maglimit. This sample is in the direction opposite that of the CfA2; incombination the two surveys provide an important database for studies ofthe properties of galaxies and their large-scale distribution in thenearby universe. Based on observations obtained at Cerro TololoInter-American Observatory, National Optical Astronomy Observatories,operated by the Association of Universities for Research in Astronomy,Inc., under cooperative agreement with the National Science Foundation;Complejo Astronomico El Leoncito, operated under agreement between theConsejo Nacional de Investigaciones Científicas de laRepública Argentina and the National Universities of La Plata,Córdoba, and San Juan; the European Southern Observatory, LaSilla, Chile, partially under the bilateral ESO-ObservatórioNacional agreement; Fred Lawrence Whipple Observatory;Laboratório Nacional de Astrofísica, Brazil; and the SouthAfrican Astronomical Observatory.
|The Stromlo-APM Redshift Survey. IV. The Redshift Catalog|
The Stromlo-APM Redshift Survey consists of 1797 galaxies with b_J_ <17.15 selected randomly at a rate of 1 in 20 from automated platemeasurement (APM) scans. The survey covers a solid angle of 1.3 sr (4300deg^2^) in the south Galactic cap. Redshifts have been measured for 1790(99.6%) of the galaxies. The median galaxy recession velocity is 15,300km s^-1^, and so the volume probed is V ~ 1.38 x 10^6^ h^-3^ Mpc^3^. Inthis paper we describe the construction of the redshift catalog andpresent the survey data.
|Metallicity Indices for Multi-Population Models.II.Bulges of Galaxies|
We report metallicity indices in the Lick system (Hβ, Fe52, Fe53,NaD, Mg_2_) for a sample of 45 spiral bulges in the southern hemisphere.The velocity dispersion σ was also derived for each object. Spiralbulges and elliptical galaxies show a continuity in diagrams like theplane Mg_2_- or σ-Mg_2_. Using calibrations derived fromchemical evolutionary models, we estimated metallicities and abundanceratios for those bulges. The sample mean metallicity is [Fe/H]= -0.19+/- 0.27(rmsd), and the mean abundance ratios are [Mg/Fe] = 0.46 +/-0.11 (rmsd) and [Na/Fe] = 0.45 +/- 0.19(rmsd). These abundances suggestthat spiral bulges (like E's) were chemically enriched by type IIsupernovae, and that the main star formation era occurred in a timescale of the order of 1-2 Gyr.
|Southern Sky Redshift Survey - The catalog|
The catalog of radial velocities for galaxies which comprise thediameter-limited sample of the Southern Sky Redshift Survey ispresented. It consolidates the data of observations carried out at theLas Campanas Observatory, Observatorio Nacional, and South AfricanAstronomical Observatory. The criteria used for the sample selection aredescribed, as well as the observational procedures and the techniqueutilized to obtain the final radial velocities. The intercomparisonbetween radial velocity measurements from different telescopes indicatesthat the final data base is fairly homogeneous with a typical error ofabout 40 km/s. The sample is at present 90 percent complete, and themissing galaxies are predominantly objects with very low surfacebrightness for which it is very difficult to obtain optical redshifts.
|The plane W(Na I) X W(Mg I) - Effects of interstellar Na I in a sample of southern galaxies|
Galaxy spectra from a subsample of the Southern Sky Redshift Survey databank were used to study the equivalent width plane for the lines Na Ilambda 5893 A vs Mg I lambda 5175 A. An estimate of how important thecontribution of the interstellar gas for the sodium line is compared tothat of the stellar population. The sample is made up of galaxies withmorphological types from E to Sc and are distributed up to radialvelocities of 25,000 km/s, most of them smaller than 15,000 km/s. Mostearly type galaxies with dust lanes, particularly nearly edge-on So's,present an enhancement of the Na I line. Inclined spiral galaxies tendto present enhanced Na I with respect to face-on spirals. This tendency,previously found in a smaller sample of galaxies limited to V equal toor less than 6000 km/s, is now confirmed for more distant ones. In thelarge velocity sample it shows the global bulge rather than the verynucleus; the persistence of the effect suggests that the scale height ofthe gas layer in the central disk can reach a considerable fraction ofthe bulge radius.
|A southern redshift survey. I - Accurate redshifts for 500 galaxies observed at SAAO|
Radial velocities are presented for about 500 galaxies observed with anintensified Reticon photon-counting detector attached to the 1.9 mtelescope at the Sutherland field station of SAAO. The velocities weredetermined by cross correlation with standard velocity templates, fromthe measured wavelengths of emission lines, or from both techniques,with spectra covering the wavelength range from 3700 to 5400 A. Thefinal velocities appear to have the same zero point as H I radiovelocities, and have standard deviations of the order of 35 km/s, thoughcross-correlation velocities on their own may have significantly largererrors.
|The ON-CfA redshift survey of the southern hemisphere|
A redshift survey of a diameter-limited sample of southern galaxies hasbeen performed by the Observatorio Nacional in collaboration with theHarvard-Smithsonian Center for Astrophysics. Redshift data are presentedfor 442 galaxies. A relatively small mean difference of -5.2 km/s wasfound between the present redshifts and previous radio data.
|Southern Galaxy Catalogue.|
|Two chains of interesting southern galaxies : NGC 7172-7173-7174-7176and NGC 7201-7203-7204.|
Abstract image available at:http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1974ApJ...191..645R&db_key=AST
Submit a new link
Member of following groups:
Observation and Astrometry data
Catalogs and designations: