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A multibeam HI survey of the Virgo cluster - two isolated HI clouds?
We have carried out a fully sampled large area (4°× 8°)21-cm HI line survey of part of the Virgo cluster using the Jodrell Bankmultibeam instrument. The survey has a sensitivity some three timesbetter than the standard HIJASS (HI Jodrell All Sky Survey) and HIPASS(HI Parkes All Sky Survey) surveys. We detect 31 galaxies, 27 of whichare well-known cluster members. The four new detections have beenconfirmed in the HIPASS data and by follow-up Jodrell Bank pointedobservations. One object lies behind M86, but the other three have noobvious optical counterparts upon inspection of the digital sky surveyfields. These three objects were mapped at Arecibo with a smaller3.6-arcmin half power beam width (HPBW) and a four times bettersensitivity than the Jodrell Bank data, which allow an improveddetermination of the dimensions and location of two of the objects, butsurprisingly failed to detect the third. The two objects are resolved bythe Arecibo beam, giving them a size far larger than any optical imagesin the nearby field. To our mass limit of 5 ×107(Δv/50 km s-1) Msolar andcolumn density limit of 3 × 1018(Δv/50 kms-1) atom cm-2, these new detections representonly about 2 per cent of the cluster atomic hydrogen mass. Ourobservations indicate that the HI mass function of the cluster turnsdown at the low-mass end, making it very different to the field galaxyHI mass function. This is quite different to the Virgo cluster opticalluminosity function, which is much steeper than that in the generalfield. Many of the sample galaxies are relatively gas-poor compared withHI selected samples of field galaxies, confirming the `anaemic spirals'view of Virgo cluster late-type galaxies. The velocity distribution ofthe HI detected galaxies is also very different to that of the clusteras a whole. There are relatively more high-velocity galaxies in the HIsample, suggesting that they form part of a currently infallingpopulation. The HI sample with optical identifications has a minimum HIcolumn density cut-off more than an order of magnitude above thatexpected from the sensitivity of the survey. This observed columndensity is above the normally expected level for star formation tooccur. The two detections with no optical counterparts have very muchlower column densities than that of the rest of the sample, below thestar formation threshold.
| The UZC-SSRS2 Group Catalog
We apply a friends-of-friends algorithm to the combined Updated ZwickyCatalog and Southern Sky Redshift Survey to construct a catalog of 1168groups of galaxies; 411 of these groups have five or more members withinthe redshift survey. The group catalog covers 4.69 sr, and all groupsexceed the number density contrast threshold, δρ/ρ=80. Wedemonstrate that the groups catalog is homogeneous across the twounderlying redshift surveys; the catalog of groups and their membersthus provides a basis for other statistical studies of the large-scaledistribution of groups and their physical properties. The medianphysical properties of the groups are similar to those for groupsderived from independent surveys, including the ESO Key Programme andthe Las Campanas Redshift Survey. We include tables of groups and theirmembers.
| 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 Intrinsic Shapes of Low Surface Brightness Dwarf Irregular Galaxies and Comparison to Other Types of Dwarf Galaxies
In this paper, we measure the ellipticities of 30 low surface brightness(LSB) dwarf irregular (dI) galaxies and compare the ellipticitydistribution with that of 80 dwarf elliptical (dEs) and 62 blue-compactdwarfs (BCDs). We find that the ellipticity distribution of LSB dIs isvery similar to that of BCDs, and marginally different from that of dEs.We then determine the distribution of intrinsic shapes of dI galaxiesand compare this to the distributions of other types of dwarf galaxiesunder various assumptions. First, we assume that LSB dIs are either alloblate or all prolate, and use a nonparametric analysis to find thebest-fitting distribution of intrinsic shapes. With this assumption, wefind that the scarcity of nearly circular LSB dIs implies, at the 99%confidence level, that they cannot be a population of randomly orientedoblate or prolate objects, implying that LSB dIs are highly unlikely tobe disk-shaped systems. Next, we assume that dIs are triaxial, and use aparametric analysis to find permissible distributions of intrinsicshapes. We find that if the intrinsic axis ratios beta and gamma aredistributed according to a Gaussian with means beta_0 and gamma_0 and acommon standard deviation of sigma, the best-fitting set of parametersfor LSB dIs is (beta_0, gamma_0, sigma) = (0.66, 0.50, 0.15), and thebest fit for BCDs is (beta_0, gamma_0, sigma) = (0.66, 0.55, 0.16),while the best fit for dEs is (beta_0, gamma_0, sigma) = (0.78, 0.69,0.24). The dIs and BCDs thus have very similar shape distributions,given this triaxial hypothesis, while the dEs peak at a somewhat morespherical shape. Therefore, our results provide strong observationalevidence to support the evolutionary scenario in which the three typesof dwarf galaxy have a close relation with each other.
| Surface Photometry of Low Surface Brightness Dwarf Irregular Galaxies
We present CCD B and I surface brightness and color profiles for asample of 51 dwarf and low surface brightness (LSB) galaxies. Thegalaxies were drawn mainly from the sample of UGC dwarf and LSB galaxiesdetected in H I by Schneider et al. We focus our attention on extremedwarf irregulars (dIs) where turbulent motions are as important as ormore important than rotational motions, so that the majority of thedwarfs were chosen to have narrow H I line widths ({DELTA}V_20_ < 100km s^-1^), in addition to being nearby (v_0_ < 1500 km s^-1^).Foreach dI galaxy, we derive structural parameters for the underlying lowsurface brightness disk component on which are superimposed thestar-forming regions. We found that the central surface brightness ofthe underlying exponential component of dIs is similar to that of dwarfellipticals (dEs) but ~1.5 mag fainter than that of blue compact dwarfs(BCDs). As for the scale lengths, the dIs divide into two groups; onewhere, for a given B luminosity, the scale length of the underlyingexponential component is comparable to that of dEs and a factor of ~2larger than that of BCDs, and one group where the scale length of thedIs is comparable to that of BCDs but a factor of 2 smaller than that ofdEs. These differences in structural parameters put strong constraintson evolutionary scenarios among the three types of dwarfs. We use theCCD images to set up a tentative morphological classification scheme forLSB dIs based of the shape of the underlying low surface brightnesscomponent and the morphology and location of the star-forming regions ontop of it. The division of the dIs into two groups appears to becorrelated with morphology. There are a few dwarf spirals in our sample,which show fragments of low surface brightness spiral arms. We foundthat Nilson and Zwicky magnitudes are systematically too faint fordwarfs and LSB galaxies by 1-2 mag. The underlying disks in dIs have B-Icolors ~1.5, corresponding to a stellar population of G and Kmain-sequence or giant stars and are redder than those of BCDs. Thecolor profiles of the galaxies in the sample are generally flat, with nostrong gradient.
| KISO survey for ultraviolet-excess galaxies. XVII
Presented here are the 17th list and identification charts of theUV-excess galaxies which have been detected on the multicolor platestaken with the Kiso Schmidt telescope for 10 survey fields. In the skyarea of some 300 sq deg 379 objects are catalogued down to aphotographic magnitude of about 18.
| General study of group membership. II - Determination of nearby groups
We present a whole sky catalog of nearby groups of galaxies taken fromthe Lyon-Meudon Extragalactic Database. From the 78,000 objects in thedatabase, we extracted a sample of 6392 galaxies, complete up to thelimiting apparent magnitude B0 = 14.0. Moreover, in order to considersolely the galaxies of the local universe, all the selected galaxieshave a known recession velocity smaller than 5500 km/s. Two methods wereused in group construction: a Huchra-Geller (1982) derived percolationmethod and a Tully (1980) derived hierarchical method. Each method gaveus one catalog. These were then compared and synthesized to obtain asingle catalog containing the most reliable groups. There are 485 groupsof a least three members in the final catalog.
| A catalog of low-surface-brightness objects - Declination zone + 20 deg
Plates from the second Palomar Sky Survey are used to compile a list oflow-surface-brightness objects located along declination zone + 20 deg.Coordinates, descriptions, sizes, and ellipticities are presented usingthe same selection criteria of 1 arcmin limiting diameter as the UppsalaCatalog of Galaxies (Nilson 1973). Lists of previously known galaxieswith new low-surface-brightness features and interestinglow-surface-brightness objects with diameters between 0.5 and 1 arcminare also presented. As expected, the low-surface-brightness end of theluminosity function is dominated by late-type systems and dwarfs.Comparison with CCD surface photometry indicates an average limitingsurface brightness of 26.0 B mag/sq arcsec for this survey as comparedto 25.2 B mag/sq arcsec for the UGC. On the whole, too few newlow-surface-brightness galaxies have been found for the space density ofthese objects to be higher than that defined by conventional diskgalaxies.
| 21 centimeter study of spiral galaxies in the Coma supercluster
High-sensitivity, 21 cm line observations of 130 galaxies in theComa/A1367 Supercluster region are presented and used to study thelarge-scale distribution of galaxies in the direction of the ComaSupercluster and the H I content in spiral galaxies as a function of thelocal galaxy density. Groups of galaxies are found to form aquasi-continuous structure that connects the Local Supercluster to theComa Supercluster. This structure is composed of real filaments only inthe vicinity of the Coma Cluster. Spiral galaxies in the surveyed groupsand multiple systems have H I content not dissimilar from that ofisolated galaxies. Galaxies within about 1 Abell radius from the ComaCluster contain about three times less hydrogen on average than isolatedgalaxies. There is a strong tendency for galaxies that are more severelyH I-depleted to be redder and of earlier Hubble type. In the ComaCluster a considerable fraction of late-type, blue galaxies have largedeficiency parameters.
| Radio continuum survey of the Coma/A1367 supercluster. II - 1.5 GHz observations of 396 CGCG galaxies
1.5 GHz VLA radio continuum observations of 396 relatively isolated CGCGgalaxies in the Coma/A1367 supercluster yielded the detection of 95objects. These observations, added to the ones presented in previouspapers, form a complete sample of optically selected objects with m(p)equal to or less than 15.3. Two wide-angle-tailed sources have beenfound in smaller groups within the supercluster.
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