On the Formation of Spiral Arms in Dwarf Galaxies

Spiral structure (both flocculent and Grand Design types) is very rarely observed in dwarf galaxies because the formation of spiral arms requires special conditions. In this work we analyze sample about 40 dS-galaxies found by scanning eye images late-type with $${{m}_{B}} < {{15}^{m}}$$ $${{M}_{B}} > - {{18}^{m}}$$ photometric diameter $${{D}_{{25}}} 12$$ kpc. We that apart from lower average gas (HI) fraction other properties including presence a bar isolation index do not differ much those for Irr or Sm-types similar luminosity rotation velocity (or specific angular momentum).There are practically no below 50–60 km s–1. To check conditions carried out series N-body/hydrodynamic simulations low-mass stellar-gaseous discy varying model kinematic parameters discs, their initial thickness, relative masses scale lengths stellar gaseous disc components, stellar-to-dark halo masses. came to conclusion gravitational mechanism effective only thin which non-typical galaxies, too slowly rotating galaxies. Therefore, small stellar/gaseous discs have ring structures. The thicker disc, more required form. reduced content many compared non-spiral ones may be result efficient star due higher volume density thank thinner discs.