Ultra-flat galaxies selected from RFGC catalog. II. Orbital estimates of halo masses

Abstract

We used the Revised Flat Galaxy Catalog (RFGC) to select 817 ultra-flat (UF) edge-on disk galaxies with blue and red apparent axial ratios of (a/b) B > 10.0 and (a/b) R > 8.5. The sample covering the whole sky, except the Milky Way zone, contains 490 UF galaxies with measured radial velocities. Our inspection of the neighboring galaxies around them revealed only 30 companions with radial velocity difference of | ∆V |< 500 km s −1 inside the projected separation of R p < 250 kpc. Wherein, the wider area around the UF galaxy within R p < 750 kpc contains no other neighbors brighter than the UF galaxy itself in the same velocity span. The resulting sample galaxies mostly belong to the morphological types Sc, Scd, Sd. They have a moderate rotation velocity curve amplitude of about 120 km s −1 and a moderate K-band luminosity of about 10 10 L ⊙ . The median difference of radial velocities of their companions is 87 km s −1 , yielding the median orbital mass estimate of about 5 × 10 11 M ⊙ . Excluding six probable non-isolated pairs, we obtained a typical halo-mass-to-stellar-mass of UF galaxies of about 30, what is almost the same one as in the principal spiral galaxies, like M 31 and M 81 in the nearest groups. We also note that ultra-flat galaxies look two times less "dusty" than other spirals of the same luminosity.

Ha Images of Ultra-Flat Edge-On Spiral Galaxies

“…(1) the number of the galaxy in the RFGC catalog; (2) the equatorial coordinates; (3,4) the "blue" angular diameter in arcmin and apparent "blue" axial ratio from RFGC; (5) the heliocentric radial velocity of the galaxy in km s −1 ; (6) the effective wavelength of the filter ( Å) in which the galaxy was exposed; (7)…”

Ultra-flat galaxies selected from RFGC catalog. III. Star formation rate

“…Firstly, they are distributed over the sky quite homogeneously, without any visible clumps in the areas occupied by clusters of galaxies [28]. A more detailed examination has shown that about 60% of ultra-flat edge-on galaxies are isolated, while about 30% belong to diffuse associations of galaxies, and only 10% have nearby, physically bound neighbors [30,31]. It can therefore be assumed that star formation in these objects is mainly due to the internal processes, not being affected by nearby neighbors.…”

Star Formation in thin Disks of Spiral Galaxies Seen Face-On

“…or sSFR(M*) relationships. The important feature of these galaxies is their localization in regions of low cosmic density [8], where there are no noticeable traces of interactions with nearby neighbors.…”