Kavli Affiliate: Mark Vogelsberger
| First 5 Authors: Sergey Khoperskov, Ivan Minchev, Noam Libeskind, Misha Haywood, Paola Di Matteo
| Summary:
Theory suggests that mergers play an important role in shaping galactic disks
and stellar haloes, which was observationally confirmed in the MW thanks to the
Gaia data. In this work, aiming to probe the contribution of mergers to the
in-situ stellar halo formation, we analyze six M31/MW analogues from the HESTIA
suite of cosmological hydrodynamical zoom-in simulations of the Local Group. We
found that all the HESTIA galaxies experience from 1 to 4 mergers with stellar
mass ratios between 0.2 and 1 relative to the host at the time of the merger.
These significant mergers, with a single exception, happened 7-11 Gyr ago. The
overall impact of the most massive mergers in HESTIA is clearly seen as a sharp
increase of the orbital eccentricity (and a corresponding decrease of the Vphi)
of preexisting disc stars of the main progenitor, thus reproducing well the
Splash/Plume-like feature discovered in the MW. We do find a correlation
between mergers/close pericentric passages of massive satellites and bursts of
the star formation in the in-situ component. Massive mergers sharply increase
the disc velocity dispersion of the in-situ stars, however, the latest
significant merger often heats up the disk up to the numbers when the
contribution of the previous ones is less prominent in the age-velocity
dispersion relation. In the HESTIA galaxies, the in-situ halo is an important
component of the inner stellar halo where its fraction is about 30-40%, while
in the outer parts it typically does not exceed ~5% beyond 15 kpc. The
simulations suggest that this component of the stellar haloes continues to grow
well after mergers conclude; however, the most significant contribution comes
from stars formed recently before the merger. The orbital analysis of the
HESTIA galaxies suggests that wedges in Rmax-Zmax space are mainly populated by
the stars born in between significant mergers.
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