Affiliation: Instituto de Astrofísica de Canarias (IAC)

Contribution: Poster

Title: Revealing the outskirts of Milky Way analogs

Abstract: In a hierarchical Universe, where mergers are expected to dominate the early
evolution of galaxies, the high fraction of massive bulgeless galaxies (i.e., pure
discs and galaxies with small bulges) observed in the nearby Universe represents
one small-scale problem of ΛCDM. The closest example of a massive bulgeless galaxy is our own, the Milky Way.
Therefore, a deeper understanding of the merger history of galaxies like the MW
is of outmost importance. The BEARD (Bulgeless Evolution And the Rise of
Discs) project is an international effort to provide multi-facility observational
constraints to demonstrate the success or failure of the hierarchical ΛCDM scenario at forming MW analogs. Two observational keys to know if giant spirals have undergone a merger
during their lifetime are: (i) to look for the features of these mergers in their
outskirts. These can be tidal tails, shells, or tidal streams, where each characteristic may tell a different story about the nature of the past merger history
of a galaxy. (ii) to measure the fraction of accreted mass in their stellar haloes,
which also provides information about the history of mergers and their relationship with the environment. In this talk, I will present our preliminary results from the analysis of merger
signatures and accreted mass fraction carried out on the sample of MW-analogs
observed with deep photometry, as part of the BEARD survey. Our study includes 20 galaxies, observed with the Wide Field Camera (WFC) on the Isaac
Newton Telescope (INT), achieving surface brightness depths ranging from 28
mag/arcsec^2
to 31 mag/arcsec^2
. This depth allows us to explore faint features
that are crucial for understanding the merger history and mass assembly of
these galaxies. The analysis involves several detailed steps, including the construction of the
extended PSF of the INT, subtraction of scattered light from foreground stars,
deconvolution of the surface brightness profiles of the galaxies, analysis of the
colors of residuals resulting from subtracting galaxy models from the images,
and measurement of the accreted mass fraction. These analyses help to unveil
the faint structures and extended haloes that are otherwise challenging to detect. The BEARD project exemplifies the synergy between observational campaigns and theoretical efforts in advancing our understanding of galaxy formation. Through the comparison between these observational results with simulations, we aim to refine our understanding of the hierarchical assembly process
and its role in the formation of bulgeless galaxies. This work not only sheds
light on the merger history of the Milky Way analogs but also contributes to the
broader picture of galaxy formation and evolution in the early Universe, with
implications for the standard cosmological model.

This contribution can be found at the Poster Hall.