Search and Study of Dwarf and LSB Galaxies in the NGC3923 Group
Language: Italian This thesis is written in Italian
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Original Italian title:
Ricerca e studio di galassie nane e di bassa brillanza nel gruppo NGC3923
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Pamela Imperatore, Università degli Studi di Bologna, 2008-09
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Academic area
Mathematical and Physical Sciences
A key problem in understanding galaxy evolution is to single out the role of low-surface brightness objects. These galaxies are known to display a wide range of morphological and spectrophotometric properties such as to rise question whether they can be considered an individual class of objects, or rather sort "by products" of the formation of bright elliptical and spiral galaxies. The problem is not a secondary one as dwarf galaxies display continuous star formation activity leading to conclude that they might have operated in past epochs as efficient "engines" to enrich interstellar matter. While for some dwarfs ellipticals we might be dealing with an evolutionary scenario, resembling that of globular clusters, in other situations it has to be explained why star formation could have proceeded all over the entire galaxy life. An important feature resides in the spatial distribution of LSB galaxies that seem to fill the present-day Universe, contrary to the early-type galaxy distribution that better traces clusters. The role of these galaxies is more interesting in the framework of CDM theory, since they are seen as the basic building blocks to form more massive systems. A systematic observational work to map the LSB galaxies distribution in selected zones of the sky has been carried out by different teams, leading to complete survey and morphological catalogues of loose groups of galaxies. Accurate spectroscopic observations of LSB galaxies still remain a difficult task. A complementary view can be gained through the study of smaller groups. In addition these have the advantage that a moderate-sized sample would be representative of the whole galaxy population, while depth effects would be minimized.

My thesis project aimsat carrying out a search of the faint galaxy population in several loose groups at low redshift. As a first "pilot" experiment , we imaged the region around galaxy NGC3923 and its loose surrounding group in serach for the faintest population of dwarfs. The group characterizes for diffuse X-ray emission, with a morphology centered on the bright elliptical galaxy. Our proposed pointings include the elliptical NGC3904 which forms a non-interacting pair with NGC3923. At this stage of the program, we have obtained deep B and R mapping of 1x1 square degree field across the galaxy group in order to pick up the basic color and morphological information of its galaxy population. The entire field has been divided into 4 different sub-areas centered on NGC3923,each corresponding to one 30x30 pointing. The data consist of deep Wide Field Imager observations, requiring 5 different frames per WFI pointing per band.All frames of each sub-areas have been co-added together in a deep exposure. Ad hoc technical solutions have been developed for correcting illumination gradients by means of super-sky flat field, and to remove color effects and astrometric distortions. The reduction of data was performed within the IRAF environments, using the package MSCRED. Our survey has been led to the compilation of a deep and complete catalog of the sorrounding population close and/or around the dominant elliptical of the group. Using a sophisticated method based on the study of the apparent morphology, brightness and color, as provided by the SeXtractor analysis of the field, we have selected and located on the sky a sample of about 50 dE,dS0 and dI candidates.