# A reference sample of face-on bulgeless galaxies

## TL;DR

This paper compiles a sample of 220 face-on, bulgeless galaxies, analyzing their morphological features, nuclear properties, and potential as hosts for moderate-mass black holes, providing a valuable resource for galaxy evolution studies.

## Contribution

It introduces a new, well-defined sample of face-on bulgeless galaxies with detailed morphological and nuclear characteristics, suitable for further astrophysical research.

## Key findings

- Approximately half have bar-like structures across various magnitudes.
- 27-50% exhibit distorted spiral patterns.
- 40-60% have unresolved nuclei, correlated with luminosity.

## Abstract

We present a list of 220 face-on, almost bulgeless galaxies assumed to be counterparts to the objects from the Reference Flat Galaxy Catalog (RFGC). We selected the Sc, Scd and Sd-type galaxies according to their apparent axial ratio $log(r_{25}) < 0.05$ and major standard angular diameter $log(d_{25}) > 0.90$ as defined in HyperLEDA. The sample objects are restricted by the radial velocity $V_{LG} < 10000$ km/s 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%) 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% of the galaxies have distinct unresolved nuclei, and their presence steeply depend on the luminosity of the host galaxy.