We present surface photometry and metallicity measurements for 104 nearby dwarf galaxies imaged with the Advanced Camera for Surveys and Wide Field and Planetary Camera 2 aboard the Hubble Space Telescope. In addition, we carried out photometry for 26 galaxies of the sample and for Sextans B on images of the Sloan Digital Sky Survey. Our sample comprises dwarf spheroidal, irregular and transition type galaxies located within ∼10 Mpc in the field and in nearby groups: M81, Centaurus A, Sculptor and Canes Venatici I cloud. It is found that the early‐type galaxies have on average higher metallicity at a given luminosity in comparison to the late‐type objects. Dwarf galaxies with MB≥−12 to −13 mag deviate towards larger scalelengths from the scalelength–luminosity relation common for spiral galaxies, h∝L0.5B. The following correlations between fundamental parameters of the galaxies are consistent with expectations if there is pronounced gas loss through galactic winds: (1) between the luminosity of early‐type dwarf galaxies and the mean metallicity of constituent red giant branch stars, Z∼L0.4, (2) between mean surface brightness within the 25 mag arcsec−2 isophote and the corresponding absolute magnitude in the V and I bands, SB 25∼ 0.3M25 and (3) between the central surface brightness (or effective surface brightness) and integrated absolute magnitude of galaxies in the V and I bands, SB0∼ 0.5ML, SB e∼ 0.5 Me. The knowledge of basic photometric parameters for a large sample of dwarf galaxies is essential for a better understanding of their evolution.
We present the results of stellar photometry of polar-ring galaxies NGC 2685 and NGC 4650A, using the archival data obtained with the Hubble Space Telescope's Wide Field Planetary Camera 2. Polar rings of these galaxies were resolved into ∼ 800 and ∼ 430 stellar objects in the B, V and I c bands, considerable part of which are blue supergiants located in the young stellar complexes. The stellar features in the CM-diagrams are best represented by isochrones with metallicity Z = 0.008. The process of star formation in the polar rings of both galaxies was continuous and the age of the youngest detected stars is about 9 Myr for NGC 2685 and 6.5 Myr for NGC 4650A.
This paper is devoted to the analysis of new observational data for the group of galaxies NGC 7465/64/63, which were obtained at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) with the multimode instrument SCORPIO and the Multi Pupil Fiber Spectrograph. For one of group members (NGC 7465) the presence of a polar ring was suspected. Large-scale brightness distributions, velocity and velocity dispersion fields of the ionized gas for all three galaxies as well as line-of-sight velocity curves on the basis of emission and absorption lines and a stellar velocity field in the central region for NGC 7465 were constructed. As a result of the analysis of the obtained information, we revealed an inner stellar disk (r ≈ 0.5 kpc) and a warped gaseous disk in addition to the main stellar disk, in NGC 7465. On the basis of the joint study of photometric and spectral data it was ascertained that NGC 7464 is the irregular galaxy of the IrrI type, whose structural and kinematic peculiarities resulted most likely from the gravitational interaction with NGC 7465. The velocity field of the ionized gas of NGC 7463 turned out typical for spiral galaxies with a bar, and the bending of outer parts of its disk could arise owing to the close encounter with one of galaxies of the environment.
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