The Two Body Problem in the Presence of Dark Energy and Modified Gravity: Application to the Local Group. (arXiv:1903.10849v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+McLeod_M/0/1/0/all/0/1">Michael McLeod</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lahav_O/0/1/0/all/0/1">Ofer Lahav</a>
We explore the mass of the Local Group via the use of the simple, dynamical
`timing argument’ in the context of a variety of theories of dark energy and
modified gravity: a cosmological constant, a perfect fluid with constant
equation of state $w$, quintessence (minimally coupled scalar field), MOND, and
symmetrons (coupled scalar field). We explore generic coupled scalar field
theories, with the symmetron model as an explicit example. We find that
theories which attempt to eliminate dark matter by using flat rotation curves
produce mass estimates in the timing argument which are not compatible with the
luminous mass of the galaxies alone. Assuming that the galaxies are on a first
pass, MOND gives of around $3times 10^{10} M_odot$, roughly 10% of the
luminous mass of the LG, although a higher mass can be obtained in the case of
a previous fly-by event between the MW and M31. The symmetron model suggests a
mass too high to be explained without additional dark matter
($mathcal{O}(10^{12}) M_odot$). We also demonstrate that tensions in
measurements of $H_0$ can produce an uncertainty in the Local Group mass
estimate comparable to observational uncertainties on the separation and
relative velocity of the galaxies, with values for the mass ranging from $4.55
– 5.43 times 10^{12} M_{odot}$ varying $h$ between 0.67 and 0.76.
We explore the mass of the Local Group via the use of the simple, dynamical
`timing argument’ in the context of a variety of theories of dark energy and
modified gravity: a cosmological constant, a perfect fluid with constant
equation of state $w$, quintessence (minimally coupled scalar field), MOND, and
symmetrons (coupled scalar field). We explore generic coupled scalar field
theories, with the symmetron model as an explicit example. We find that
theories which attempt to eliminate dark matter by using flat rotation curves
produce mass estimates in the timing argument which are not compatible with the
luminous mass of the galaxies alone. Assuming that the galaxies are on a first
pass, MOND gives of around $3times 10^{10} M_odot$, roughly 10% of the
luminous mass of the LG, although a higher mass can be obtained in the case of
a previous fly-by event between the MW and M31. The symmetron model suggests a
mass too high to be explained without additional dark matter
($mathcal{O}(10^{12}) M_odot$). We also demonstrate that tensions in
measurements of $H_0$ can produce an uncertainty in the Local Group mass
estimate comparable to observational uncertainties on the separation and
relative velocity of the galaxies, with values for the mass ranging from $4.55
– 5.43 times 10^{12} M_{odot}$ varying $h$ between 0.67 and 0.76.
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