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|A wide-field HI study of the NGC 1566 group|
We report on neutral hydrogen observations of a ~ 5.5 × 5.5deg2 field around the NGC 1566 galaxy group with themultibeam narrow-band system on the 64-m Parkes Telescope. We detected13 HI sources in the field, including two galaxies not previously knownto be members of the group, bringing the total number of confirmedgalaxies in this group to 26. Each of the HI galaxies can be associatedwith an optically catalogued galaxy. No `intergalactic HI clouds' werefound to an HI mass limit of ~3.5 ×108Msolar. We have estimated the expected HIcontent of the late-type galaxies in this group and find that the totaldetected HI is consistent with our expectations. However, while noglobal HI deficiency is inferred for this group, two galaxies exhibitindividual HI deficiencies. Further observations are needed to determinethe gas removal mechanisms in these galaxies.
|Intergalactic H II Regions Discovered in SINGG|
A number of very small isolated H II regions have been discovered atprojected distances up to 30 kpc from their nearest galaxy. These H IIregions appear as tiny emission-line objects in narrowband imagesobtained by the NOAO Survey for Ionization in Neutral Gas Galaxies(SINGG). We present spectroscopic confirmation of four isolated H IIregions in two systems; both systems have tidal H I features. Theresults are consistent with stars forming in interactive debris as aresult of cloud-cloud collisions. The Hα luminosities of theisolated H II regions are equivalent to the ionizing flux of only a fewO stars each. They are most likely ionized by stars formed in situ andrepresent atypical star formation in the low-density environment of theouter parts of galaxies. A small but finite intergalactic star formationrate will enrich and ionize the surrounding medium. In one system, NGC1533, we calculate a star formation rate of 1.5×10-3Msolar yr-1, resulting in a metal enrichment of~1×10-3 solar for the continuous formation of stars.Such systems may have been more common in the past and a similarenrichment level is measured for the ``metallicity floor'' in dampedLyα absorption systems.
|Structure and stellar content of dwarf galaxies. VII. B and R photometry of 25 southern field dwarfs and a disk parameter analysis of the complete sample of nearby irregulars|
We present B and R band surface photometry of 25 Southern field dwarfgalaxies within a distance of 10 Mpc. For each galaxy we give theessential model-free photometric parameters and, by fitting exponentialsto the surface brightness profiles, the central extrapolated surfacebrightness and the exponential scale length, in both colour bands.Surface brightness and colour profiles are shown. One of the objects, avery faint dwarf elliptical in the vicinity of NGC 2784, has beendiscovered in the course of this work. Drawing on the data from this andall previous papers of this series, we construct a complete sample of 72late-type (``irregular'') dwarf galaxies in nearby groups and the fieldwithin the 10 Mpc volume, to study the exponential-disk parameterrelations of these galaxies with respect to galaxy environment. Weconfirm our previous finding of statistically lower scale lengths/highercentral surface brightnesses for field and group galaxies as compared tocluster galaxies. However, using a clear-cut definition of ``group''versus ``field'' environment, we find no significant difference in thephotometric structure of group and field irregulars. A difference in thestar formation history may partly account for this structure-environmentrelation: for a given luminosity cluster dwarfs are on average redderthan field and group galaxies. We also report evidence for the colourgradients of dwarf irregulars being roughly inversely proportional tothe disk scale lengths. Supplementing our photometric data withkinematic data from the literature, we study possible relations withkinematic properties of the inner disk. Applying the dark matter scalingrelations for a Burkert halo we show that for field and group galaxiesof a given luminosity faster-than-mean disk rotational velocities at aradius of about two scale lengths are correlated with larger-than-meandisk scale lengths. Based on observations collected at the EuropeanSouthern Observatory, La Silla, Chile. Table 3 containing ``BRphotometry and kinematic data for the 72 irregular dwarf galaxies of ourcomplete sample'' is only available in electronic form at the CDS viaanonymous ftp to cdsarc.u-strasbg.fr (126.96.36.199) or viahttp://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/388/29
|The Dwarf Galaxy Population of the Dorado Group Down to MV~-11|
We present V and I CCD photometry of suspected low surface brightnessdwarf galaxies detected in a survey covering ~2.4 deg2 aroundthe central region of the Dorado group of galaxies. The low surfacebrightness galaxies were chosen based on their sizes and magnitudes atthe limiting isophote of 26 Vμ. The selected galaxies have magnitudesbrighter than V~20 (MV~-11 for an assumed distance to thegroup of 17.2 Mpc), with central surface brightnessesμ0>22.5 V mag arcsec-2, scale lengths h>2", anddiameters >=14" at the limiting isophote. Using these criteria, weidentified 69 dwarf galaxy candidates. Four of them are large very lowsurface brightness galaxies that were detected on a smoothed image,after masking high surface brightness objects. Monte Carlo simulationsperformed to estimate completeness, photometric uncertainties and toevaluate our ability to detect extended low surface brightness galaxiesshow that the completeness fraction is, on average, >80% for dwarfgalaxies with -17=14"). The V-I colors of the dwarfcandidates vary from -0.3 to 2.3 with a peak on V-I=0.98, suggesting arange of different stellar populations in these galaxies. The projectedsurface density of the dwarf galaxies shows a concentration toward thegroup center similar in extent to that found around five X-ray groupsand the elliptical galaxy NGC 1132 studied by Mulchaey & Zabludoff,suggesting that the dwarf galaxies in Dorado are probably physicallyassociated with the overall potential well of the group. Based on thedata collected at the Cerro Tololo Inter-American Observatory (CTIO) andLas Campanas Observatory, Chile.
|Total magnitude, radius, colour indices, colour gradients and photometric type of galaxies|
We present a catalogue of aperture photometry of galaxies, in UBVRI,assembled from three different origins: (i) an update of the catalogueof Buta et al. (1995) (ii) published photometric profiles and (iii)aperture photometry performed on CCD images. We explored different setsof growth curves to fit these data: (i) The Sersic law, (ii) The net ofgrowth curves used for the preparation of the RC3 and (iii) A linearinterpolation between the de Vaucouleurs (r(1/4) ) and exponential laws.Finally we adopted the latter solution. Fitting these growth curves, wederive (1) the total magnitude, (2) the effective radius, (3) the colourindices and (4) gradients and (5) the photometric type of 5169 galaxies.The photometric type is defined to statistically match the revisedmorphologic type and parametrizes the shape of the growth curve. It iscoded from -9, for very concentrated galaxies, to +10, for diffusegalaxies. Based in part on observations collected at the Haute-ProvenceObservatory.
|An Einstein X-Ray Survey of Optically Selected Galaxies. I. Data|
We present the results of a complete Einstein imaging proportionalcounter X-ray survey of optically selected galaxies from theShapley-Ames Catalog, the Uppsala General Catalogue, and the EuropeanSouthern Observatory Catalog. Well-defined optical criteria are used toselect the galaxies, and X-ray fluxes are measured at the opticallydefined positions. The result is a comprehensive list of X-ray detectionand upper limit measurements for 1018 galaxies. Of these, 827 haveeither independent distance estimates or radial velocities. Associatedoptical, redshift, and distance data have been assembled for thesegalaxies, and their distances come from a combination of directlypredicted distances and those predicted from the Faber-Burstein GreatAttractor/Virgocentric infall model. The accuracy of the X-ray fluxeshas been checked in three different ways; all are consistent with thederived X-ray fluxes being of <=0.1 dex accuracy. In particular,there is agreement with previously published X-ray fluxes for galaxiesin common with a 1991 study by Roberts et al. and a 1992 study byFabbiano et al. The data presented here will be used in further studiesto characterize the X-ray output of galaxies of various morphologicaltypes and thus to enable the determination of the major sourcescontributing to the X-ray emission from galaxies.
|Population studies in groups and clusters of galaxies. III - A catalog of galaxies in five nearby groups|
Five nearby groups of galaxies have been surveyed using large-scaleplates from the 2.5 m duPont Telescope at Las Campanas Observatory.Catalogs of galaxies brighter than B(T) = 20 are presented for the Leo,Dorado, NGC 1400, NGC 5044, and Antlia groups. A total of 1044 galaxiesare included, from visual inspection of 14 plates, covering 31 degsquare. Galaxies have been classified in the extended Hubble system, andgroup memberships have been assigned based on velocity (where available)and morphology. About half the galaxies listed are likely members of oneof the nearby groups. The catalogs are complete to B(T) = 18, althoughthe completeness limits vary slightly from group to group. Based on Kingmodel fits to the surface density profiles, the core radii of the groupsrange from 0.3 to 1 Mpc, and central densities range from 120 to 1900galaxies Mpc exp-3 brighter than M(BT) = -12.5. Dynamical analysisindicates that all of the groups are likely to be gravitationally bound.
|Southern Galaxy Catalogue.|
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