ИСТИНА

To understand the origin of formation of extended disks of low surface brightness (LSB) we present detailed studies of four galaxies with big edge-on LSB disks. The edge-on position of these systems is beneficial because it boosts surface brightness giving an opportunity to assess stellar population properties of the LSB disk spectroscopically. We observed these systems with the Russian 6-meter telescope and at the Keck observatory. We also performed deep photometric observations of one of the galaxies with the 1.4-m Milankovi\'c telescope which we combined with archival HSC and DECaLS data available for other systems. By analyzing spectroscopic data, we estimated the properties of the stellar populations in the HSB+LSB regions of these galaxies as well as the radial profiles of gas metallicity and kinematics. From the photometrical observations we obtained the structural parameters of the disks. We estimated the dark halo mass contribution both dynamically and by assessing the ratio of radial to vertical disc scalelenghts. The dark halo to disk mass fractions lie in the range of 1 to 4 for these galaxies according to these two different approaches, both of which rely on the assumption of marginal gravitational stability of the disks. The gas metallicity gradient in these galaxies is about -0.07...-0.13 dex per exponential disc scalelength, which is consistent with other disky galaxies. We propose the possible formation scenarios for these galaxies giving greater credibility to the scenario in which LSB disks were formed by minor wet-mergers which agrees better with both photometrical and spectral data.