A reference sample of face-on bulgeless galaxies

Abstract

We present a list of 220 face-on, almost bulgeless galaxies assumed to be counterparts to the objects from the Reference Flat Galaxy Catalogue (RFGC). We selected the Sc-, Scd-, and Sd-type galaxies according to their apparent axial ratio log(r25) < 0.05 and major standard angular diameter log(d25) > 0.90 as defined in HyperLEDA. The sample objects are restricted by the radial velocity VLG < 10, 000 km s-1 and a declination of above-30 deg. The morphological composition of our sample is quite similar to that of RFGC. We notice the following common properties of face-on bulgeless galaxies. About half of them have bar-like structures occurring in the whole range of the absolute magnitudes of galaxies: from-17 to-22 mag. An essential part of our sample (27-50 per cent) exhibit distorted spiral patterns. The galaxies do not show significant asymmetry in numbers of the 'S'-and 'Z'-like spin orientation. The mean (pseudo-)bulge-to-total mass ratio for the sample is estimated as 0.11. Due to a negligible internal extinction, low-light background, and small projection effect, the face-on Sc-Sd discs are suitable objects to recognize their central nuclei as moderate-mass BH candidates. About 40-60 per cent of the galaxies have distinct unresolved nuclei, and their presence steeply depends on the luminosity of the host galaxy.