Ultra-Flat Galaxies Selected from RFGC Catalog. III. Star Formation Rate
  We examine the star formation properties of galaxies with very thin disks
selected from the Revised Flat Galaxy Catalog (RFGC). The sample contains 333
ultra-flat galaxies (UFG) at high Galactic latitudes, $|b|>10^{\circ}$, with a
blue major angular diameter of $a\geq 1.2^{\prime}$, blue and red apparent
axial ratios of $(a/b)_b > 10$, $(a/b)_r > 8.5$ and radial velocities within
10000~km s$^{-1}$. As a control sample for them we use a population of 722 more
thick RFGC galaxies with $(a/b)_b > 7$, situated in the same volume. The UFG
distribution over the sky indicates them as a population of quite isolated
galaxies. We found that the specific star formation rate, sSFR FUV, determined
via the FUV GALEX flux, increases steadily from the early type to late type
disks for both the UFG and RFGC-UFG samples, showing no significant mutual
difference within each morphological type T. The population of UFG disks has
the average H,I-mass-to-stellar-mass ratio by $(0.25\pm0.03)$ dex higher than
that of RFGC--UFG galaxies. Being compared with arbitrary orientated disks of
the same type, the ultra-flat edge-on galaxies reveal that their total H,I mass
is hidden by self-absorption on the average by approximately 0.20 dex. We
demonstrate that using the robust stellar mass estimate via $\langle B-K
\rangle$-color and galaxy type T for the thin disks, together with a nowaday
accounting for internal extinction, yields their sSFR quantities definitely
lying below the limit of $-9.4$ dex,(yr$^{-1}$). The collected observational
data on UFG disks imply that their average star formation rate in the past has
been approximately three times the current SFR. The UFG galaxies have also
sufficient amount of gas to support their observed SFR over the following
nearly 9 Gyrs.
