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Impact of ultraviolet radiation from giant spirals on the evolution of dwarf galaxies
We show that ultraviolet (UV) radiation, with wavelengths shorter than2000 Å, escaping from the discs of giant spirals could be one ofthe principal factors affecting the evolution of low-mass satellitegalaxies. We demonstrate, using an analytical approach, that the Lymancontinuum part of the radiation field can lead to the ionization of theinterstellar medium (ISM) of dwarf galaxies through the process ofphotoevaporation, making the ISM virtually unobservable. Thefar-ultraviolet part (912 < λ < 2000 Å) is shown todominate over the internal sources of radiation for most of the Galacticdwarf spheroidals. The proposed environmental factor could be at leastpartially responsible for the bifurcation of the low-mass protogalaxiesinto two sequences: dwarf irregulars and dwarf spheroidals. We discussmany peculiarities of the Local Group early-type dwarfs, which can beaccounted for by the impact of the UV radiation from the host spiralgalaxy (Milky Way or M31).
| 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.
| 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.
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