Measuring dynamical masses from gas kinematics in simulated high-redshift galaxies. (arXiv:1908.05274v1 [astro-ph.GA])

Measuring dynamical masses from gas kinematics in simulated high-redshift galaxies. (arXiv:1908.05274v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wellons_S/0/1/0/all/0/1">Sarah Wellons</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Faucher_Giguere_C/0/1/0/all/0/1">Claude-Andr&#xe9; Faucher-Gigu&#xe8;re</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Angles_Alcazar_D/0/1/0/all/0/1">Daniel Angl&#xe9;s-Alc&#xe1;zar</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hayward_C/0/1/0/all/0/1">Christopher C. Hayward</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Feldmann_R/0/1/0/all/0/1">Robert Feldmann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hopkins_P/0/1/0/all/0/1">Philip F. Hopkins</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Keres_D/0/1/0/all/0/1">Du&#x161;an Kere&#x161;</a>

Advances in instrumentation have recently extended detailed measurements of
gas kinematics to large samples of high-redshift galaxies. Relative to most
nearby, thin disk galaxies, in which gas rotation accurately traces the
gravitational potential, the interstellar medium (ISM) of z>1 galaxies is
typically more dynamic and exhibits elevated turbulence. If not properly
modeled, these effects can strongly bias dynamical mass measurements. We use
high-resolution FIRE-2 cosmological zoom-in simulations to analyze the physical
effects that must be considered to correctly infer dynamical masses from gas
kinematics. Our analysis covers a wide range of galaxy properties, from
low-redshift Milky-Way-mass galaxies to massive high-redshift galaxies (M_* >
10^11 M_sun at z=1). Selecting only snapshots where a well-ordered disk is
present, we calculate the rotational profile (r) of the cool (10^3.5 K < T < 10^4.5 K) gas and compare it to the circular velocity v_c=sqrt(GM_enc/r) assuming spherical symmetry. In the simulated massive high-redshift galaxies, the gas rotation traces the circular velocity reasonably well at intermediate radii r~1-3 kpc, but the two quantities diverge significantly outside that range. At larger radii, gradients in the turbulent pressure can bias dynamical mass measurements low by ~10-40%. In the interior, the assumption of a spherically-symmetric gravitational potential becomes increasingly poor owing to a massive disk component, reducing the gas rotational velocities by >~10%.
Finally, in the interior and exterior, the gas’ motion can be significantly
non-circular due to e.g. bars, satellites, and inflows/outflows. We discuss the
accuracy of commonly-used analytic models for pressure gradients (or
“asymmetric drift”) in the ISM of high-redshift galaxies.

Advances in instrumentation have recently extended detailed measurements of
gas kinematics to large samples of high-redshift galaxies. Relative to most
nearby, thin disk galaxies, in which gas rotation accurately traces the
gravitational potential, the interstellar medium (ISM) of z>1 galaxies is
typically more dynamic and exhibits elevated turbulence. If not properly
modeled, these effects can strongly bias dynamical mass measurements. We use
high-resolution FIRE-2 cosmological zoom-in simulations to analyze the physical
effects that must be considered to correctly infer dynamical masses from gas
kinematics. Our analysis covers a wide range of galaxy properties, from
low-redshift Milky-Way-mass galaxies to massive high-redshift galaxies (M_* >
10^11 M_sun at z=1). Selecting only snapshots where a well-ordered disk is
present, we calculate the rotational profile <v_phi>(r) of the cool (10^3.5 K <
T < 10^4.5 K) gas and compare it to the circular velocity v_c=sqrt(GM_enc/r)
assuming spherical symmetry. In the simulated massive high-redshift galaxies,
the gas rotation traces the circular velocity reasonably well at intermediate
radii r~1-3 kpc, but the two quantities diverge significantly outside that
range. At larger radii, gradients in the turbulent pressure can bias dynamical
mass measurements low by ~10-40%. In the interior, the assumption of a
spherically-symmetric gravitational potential becomes increasingly poor owing
to a massive disk component, reducing the gas rotational velocities by >~10%.
Finally, in the interior and exterior, the gas’ motion can be significantly
non-circular due to e.g. bars, satellites, and inflows/outflows. We discuss the
accuracy of commonly-used analytic models for pressure gradients (or
“asymmetric drift”) in the ISM of high-redshift galaxies.

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