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We compare the properties of stellar populations for globular clusters (GCs) and field stars in two dwarf spheroidal galaxies (dSphs): ESO269-66, a close neighbour of NGC5128, and KKs3, one of the few isolated dSphs within 10 Mpc. We analyse the surface density profiles of low and high metallicity (blue and red) stars in two galaxies using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favour of the metallicity and age gradients in dSphs; 2) globular clusters in KKs3 and ESO 269-66 contain 4 and 40 percent of all stars with [Fe / H] ~ 1.6 dex and the age of 12 Gyr, correspondingly. Therefore, GCs are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO269-66, probably, thanks to its isolation.
Using high accuracy distance estimates, we study the three-dimensional distribution of galaxies in five galaxy groups at a distance less than 5 Mpc from the Milky Way. Due to proximity of these groups our sample of galaxies is nearly complete down to extremely small dwarf galaxies with absolute magnitudes MB = -12. We find that the average number-density profile of the groups shows a steep power-law decline dn/dV ∼ R-3 at distances R=(100–500) kpc consistent with predictions of the standard cosmological model. We also find that there is no indication of a truncation or a cutoff in the density at the expected virial radius: the density profile extends at least to 1.5 Mpc. Vast majority of galaxies within 1.5 Mpc radius around group centres are gas-rich star-forming galaxies. Early-type galaxies are found only in the central ∼ 300 kpc region. Lack of dwarf spheroidal and dwarf elliptical galaxies in the field and in the outskirts of large groups is a clear indication that these galaxies experienced morphological transformation when they came close to the central region of forming galaxy group.
We present a study of two dE/dSph members of the nearby M 81 group of galaxies, KDG 61 and KDG 64. Direct HST/ACS images and integrated-light spectra of 6 m telescope of Special Astrophysical Observatory (Russia) have been used for quantitative star formation history analysis. The spectroscopic and colour-magnitude diagrams analysis gives consistent results. These galaxies appear to be dominated by an old population (12–14 Gyr) of low metallicity ([Fe/H] ∼−1.5). Stars of ages about 1 to 4 Gyr have been detected in both galaxies. The later population shows marginal metal enrichment. Our radial velocity measurement suggests that the HII knot on the line-of-sight of KDG 61 is not gravitationally attached to the galaxy.
We consider the star formation properties of dwarf galaxies in the Cen A group observed within our HST/ACS projects number 9771 and 10235. We model color-magnitude diagrams of the galaxies under consideration and measure star formation rate and metallicity dependence on time. We study the environmental dependence of the galaxy evolution and probable origin of the dwarf galaxies in the group.
1. The data. We study detailed star formation histories (SFH) of 14 dwarf galaxies in the central parts (≤ 300 Kpc) of the two nearby galaxy groups: M 81 (D=3.6 Mpc) and Cen A (D = 3.8 Mpc). The images of 7 galaxies were selected from the sample of about 50 nearby dwarf galaxies observed with the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope within our prog. 9771 & 10235, (PI I.Karachentsev). The rest of the images (ACS and WFPC2) were taken from the Hubble Archive (prog. 9884, 5898 and 6964).
Over the last five years, enormous progress in accurate distance measurements for nearby galaxies has been attained. The Hubble Space Telescope allows us to estimate distances of about 7–10% accuracy using red giant branch (RGB) up to 8 Mpc. Now we have very accurate distances for more than 200 galaxies within ~6 Mpc.
We derive quantitative star formation histories (SFH) of the two dwarf spheroidal (KK 197 and ESO 269-066) and one dwarf irregular (ESO 381-018) galaxies in the nearby Centaurus A group. The data are part of our sample of about 50 nearby dwarf galaxies observed with the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope (prog. 9771 & 10235, PI I.Karachentsev). Deep color-magnitude diagram (CMD) of KK 197 is shown in Fig.1.
Until very recently, our knowledge of the local peculiar velocity field has been severely hampered by the lack of reliable distance measurements. HST has dramatically changed this situation, allowing astronomers to obtain accurate distances to more than 150 nearby galaxies. This number could easily reach 400 if enough observing time would be dedicated to snapshot observation of the objects in the catalog of Karachentsev et al (2004). Such a dense grid of objects correctly placed in their 3D position would provide key information on the amplitude of peculiar motions, the radial domain of bound groups, the clustering and morphological segregation properties of galaxies, and the incidence of extreme dwarfs galaxies. The key instrument to measure distances with HST is the Tip of the Red Giant Branch technique. The full exploitation of this powerful distance estimator requires a deeper understanding of the possible sources of errors and biases, such as the absolute calibration of the I-band magnitude of the tip and its dependency on age and metallicity of the underlying population, the possible contamination by AGB stars, the breakdown of the methodology in sparsely populated colour-magnitude diagrams and when the tip is close to the photometric limit.
Computer analysis using profiles generated by the
PSI-BLAST program identified a superfamily of proteins
homologous to eukaryotic transglutaminases. The members
of the new protein superfamily are found in all archaea,
show a sporadic distribution among bacteria, and were detected
also in eukaryotes, such as two yeast species and the nematode
Caenorhabditis elegans. Sequence conservation
in this superfamily primarily involves three motifs that
center around conserved cysteine, histidine, and aspartate
residues that form the catalytic triad in the structurally
characterized transglutaminase, the human blood clotting
factor XIIIa′. On the basis of the experimentally
demonstrated activity of the Methanobacterium
phage pseudomurein endoisopeptidase, it is proposed that
many, if not all, microbial homologs of the transglutaminases
are proteases and that the eukaryotic transglutaminases
have evolved from an ancestral protease.
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