B/PS bulges in DESI Legacy edge-on galaxies I: Sample building

TL;DR

This paper presents the largest sample of edge-on galaxies with B/PS bulges from DESI Legacy images, analyzing their properties and providing a resource for future studies on galaxy structure and evolution.

Contribution

The study introduces a new large sample of B/PS bulge galaxies identified via neural networks, with detailed analysis of their structural and statistical properties.

Findings

B/PS bulge galaxies have higher B/D ratios than non-B/PS galaxies.

Distribution of X-structure angles and ray lengths aligns with previous models.

B/PS bulge fraction increases sharply for stellar masses above 10^{10.4} solar masses.

Abstract

We present the biggest up-to-date sample of edge-on galaxies with B/PS bulges and X-structures. The sample was prepared using images from the DESI Legacy catalogue and contains about 2000 galaxies. To find suitable candidates in catalogue, we made the assumption that the residues (original images minus model) of galaxies with B/PS bulges should exhibit a characteristic X-shape. Galaxies with such features were selected by eye and then used as input data for a neural network training, which was applied to a bigger sample of edge-on galaxies. Using the available data and the photometric models from the literature, we investigated the observational and statistical properties of the sample created. Comparing the $B/D$ ratios for galaxies with and without B/PS bulges, we found that the $B/D$ ratio for galaxies from our sample is statistically higher, with typical values in the range $\approx 0.2-0.5$ depending on the decomposition procedure. We studied how the opening angles $\varphi$ of the X-structure and the length of its rays are distributed in the formed sample and found them to be consistent with previous measurements and predictions from $N$-body models, e.g. $\varphi \gtrsim 25~\deg$, but measured here for a much larger number of galaxies. We found a sharp increase in the B/PS bulge fraction for stellar masses $\log M_{\star} \gtrsim 10.4$, but for edge-on galaxies, which complements the results of previous works. The sample can be used in future work to test various bar models and their relationship with B/PS bulges, as well as to study their stability and evolution.