Non-sphericity of ultra-light axion dark matter halos in the Galactic dwarf spheroidal galaxies. (arXiv:1902.03054v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hayashi_K/0/1/0/all/0/1">Kohei Hayashi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Obata_I/0/1/0/all/0/1">Ippei Obata</a>
Ultra-light axion (ULA) dark matter is one of the possible solutions to
resolve small-scale problems, especially the core-cusp problem. This is because
ULA dark matter can create a central soliton core in all dark halos stemmed
from the quantum pressure against gravity below the de Broglie wavelength,
which becomes manifest on astrophysical scales with axion mass range
$sim10^{-22}$ eV. In this work, we apply our non-spherical dynamical models to
the kinematic data of eight classical dwarf spheroidals (dSphs) to obtain more
reliable and realistic limits on ULA particle mass. This is motivated by the
reasons that the light distributions of the dSphs is not spherical, nor are the
shapes of dark halos predicted by ULA dark matter simulations. Compared with
the previous studies on ULA dark matter assuming spherical mass models, our
result is less stringent than those constraints due to the uncertainties on
non-sphericity. On the other hand, remarkably, we find that the dSphs would
prefer to have a flattened dark halo rather than spherical one, especially
Draco favors a strongly elongated dark halo caused naively by the assumption of
a soliton-core profile. Moreover, our consequent non-spherical core profiles
are much more flattened than numerical predictions based on ULA dark matter,
even though there are still uncertainties on the estimation of dark halo
structure. To alleviate this discrepancy, further understanding of baryonic
and/or ULA dark matter physics on small mass scales might be needed.
Ultra-light axion (ULA) dark matter is one of the possible solutions to
resolve small-scale problems, especially the core-cusp problem. This is because
ULA dark matter can create a central soliton core in all dark halos stemmed
from the quantum pressure against gravity below the de Broglie wavelength,
which becomes manifest on astrophysical scales with axion mass range
$sim10^{-22}$ eV. In this work, we apply our non-spherical dynamical models to
the kinematic data of eight classical dwarf spheroidals (dSphs) to obtain more
reliable and realistic limits on ULA particle mass. This is motivated by the
reasons that the light distributions of the dSphs is not spherical, nor are the
shapes of dark halos predicted by ULA dark matter simulations. Compared with
the previous studies on ULA dark matter assuming spherical mass models, our
result is less stringent than those constraints due to the uncertainties on
non-sphericity. On the other hand, remarkably, we find that the dSphs would
prefer to have a flattened dark halo rather than spherical one, especially
Draco favors a strongly elongated dark halo caused naively by the assumption of
a soliton-core profile. Moreover, our consequent non-spherical core profiles
are much more flattened than numerical predictions based on ULA dark matter,
even though there are still uncertainties on the estimation of dark halo
structure. To alleviate this discrepancy, further understanding of baryonic
and/or ULA dark matter physics on small mass scales might be needed.
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