Bibcode
de Boer, T. J. L.; Wills, Drew; Christensen, Charlotte; Cole, Andrew A.; Battaglia, G.; Starkenburg, Else; Martig, Marie; Brooks, Alyson M.; Beasley, M. A.; Wisnioski, Emily; Mendel, J. Trevor; Leaman, R.
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 472, Issue 2, p.1879-1896
Advertised on:
12
2017
Citations
28
Refereed citations
27
Description
We analyse age-velocity dispersion relations (AVRs) from kinematics of
individual stars in eight Local Group galaxies ranging in mass from
Carina (M* ˜ 106 M⊙) to M31
(M* ˜ 1011 M⊙).
Observationally the σ versus stellar age trends can be interpreted
as dynamical heating of the stars by giant molecular clouds, bars/spiral
arms or merging subhaloes; alternatively the stars could have simply
been born out of a more turbulent interstellar medium (ISM) at high
redshift and retain that larger velocity dispersion till present day -
consistent with recent integral field unit kinematic studies. To
ascertain the dominant mechanism and better understand the impact of
instabilities and feedback, we develop models based on observed star
formation histories (SFHs) of these Local Group galaxies in order to
create an evolutionary formalism that describes the ISM velocity
dispersion due to a galaxy's evolving gas fraction. These empirical
models relax the common assumption that the stars are born from gas that
has constant velocity dispersion at all redshifts. Using only the
observed SFHs as input, the ISM velocity dispersion and a mid-plane
scattering model fits the observed AVRs of low-mass galaxies without
fine tuning. Higher mass galaxies above Mvir ≳
1011 M⊙ need a larger contribution from latent
dynamical heating processes (for example minor mergers), in excess of
the ISM model. Using the SFHs, we also find that supernovae feedback
does not appear to be a dominant driver of the gas velocity dispersion
compared to gravitational instabilities - at least for dispersions
σ ≳ 25 km s-1. Together our results point to stars
being born with a velocity dispersion close to that of the gas at the
time of their formation, with latent dynamical heating operating with a
galaxy mass-dependent efficiency. These semi-empirical relations may
help constrain the efficiency of feedback and its impact on the physics
of disc settling in galaxy formation simulations.
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