Speaker
Description
The Λ Cold Dark Matter (ΛCDM) cosmological model predicts that galaxies grow through frequent hierarchical mergers. While this framework competently explains many observed large structures, it undergoes challenges when accounting for bulgeless galaxies. These systems are dominated by their disk component and show no, or only negligible, bulges. In the ΛCDM picture, hierarchical mergers are expected to trigger central mass growth, producing massive bulges and often disrupting disks. Nevertheless, large samples of bulgeless galaxies are observed. Locally, observations of the Milky Way (MW), particularly from large spectroscopic surveys and the Gaia mission, indicate that it consists of a thin disk with four spiral arms, a thick disk, and a central boxy/peanut-shaped bar. Any classical bulge, if present, accounts for at most ~8% of the total Galaxy mass, suggesting the MW as our closest example of a bulgeless galaxy. The BEARD (Bulgeless Evolution And the Rise of Discs) program intends to explore the nature of bulgeless galaxies through systematically characterising their morphology, kinematics, and stellar populations. BEARD is designed as a multi-facility project combining broadband and narrowband Hα imaging with long-slit and integral-field-unit spectroscopy, providing an unprecedentedly detailed and homogeneous view of the formation and evolution of these systems. The program focuses on a volume-limited sample of 66 nearby MW analogues: bulgeless galaxies with stellar masses greater than 10^10 M⊙ and bulge-to-total ratios lower than 0.1.
In P3, we aimed to follow up 18 southern and equatorial BEARD galaxies with the VST. By exploiting OmegaCAM's large field of view (~1 deg²) and excellent image quality, we extend deep photometry well beyond the target galaxies. Observations for six of the eighteen targets have been completed, while three additional systems have been partially covered. All observations follow a common strategy: five dithered Obs of 300 s each in the g and r bands. Through these observations, we will investigate the following goals. First, we aim to trace low-surface-brightness features—such as tidal tails, shells, and stellar streams—which constrain the merger history of the host galaxies. Second, we will detect and measure stellar halos and connect their mass fraction to the formation history of the hosts. Third, we map the distribution of satellite galaxies, offering insight into the large-scale environments and revealing the structural properties and formation mechanisms of the targets. In particular, we will pay special attention to the faintest satellites, for which deep imaging and the large VST field of view are particularly useful. Having observed a subsample, we are now able to develop and test the data analysis pipeline in preparation for a future completion run. During this meeting, I will present the current status of data reduction and discuss the resulting image quality. The reduced images reach surface brightness depths of ~28.7 mag arcsec⁻² in the g band and ~28.1 mag arcsec⁻² in the r band, at 3σ within a one-arcsecond aperture. Even deeper limits can be achieved using isophotal averaging.