Swirls of FIRE: Spatially Resolved Gas Velocity Dispersions and Star Formation Rates in FIRE-2 Disk Environments. (arXiv:1911.00020v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Orr_M/0/1/0/all/0/1">Matthew E. Orr</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:+Medling_A/0/1/0/all/0/1">Anne M. Medling</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:+Murray_N/0/1/0/all/0/1">Norman Murray</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pineda_J/0/1/0/all/0/1">Jorge L. Pineda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Faucher_Giguere_C/0/1/0/all/0/1">Claude-André Faucher-Giguère</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Keres_D/0/1/0/all/0/1">Dušan Kereš</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Su_K/0/1/0/all/0/1">Kung-Yi Su</a>
We study the spatially resolved (sub-kpc) gas velocity dispersion
($sigma$)–star formation rate (SFR) relation in the FIRE-2 (Feedback in
Realistic Environments) cosmological simulations. We specifically focus on
Milky Way mass disk galaxies at late times. In agreement with observations, we
find a relatively flat relationship, with $sigma approx 15-30$ km/s in
neutral gas across 3 dex in SFRs. We show that higher dense gas fractions
(ratios of dense gas to neutral gas) and SFRs are correlated at constant
$sigma$. Similarly, lower gas fractions (ratios of gas to stellar mass) are
correlated with higher $sigma$ at constant SFR. The limits of the
$sigma$-$Sigma_{rm SFR}$ relation correspond to the onset of strong
outflows. We see evidence of “on-off” cycles of star formation in the
simulations, corresponding to feedback injection timescales of 10-100 Myr,
where SFRs oscillate about equilibrium SFR predictions. Finally, SFRs and
velocity dispersions in the simulations agree well with feedback-regulated and
marginally stable gas disk (Toomre’s $Q =1$) model predictions, and the data
effectively rule out models assuming that gas turns into stars at (low)
constant efficiency (i.e., ${rm 1%}$ per free-fall time). And although the
simulation data do not entirely exclude gas accretion/gravitationally powered
turbulence as a driver of $sigma$, it appears to be strongly subdominant to
stellar feedback in the simulated galaxy disks.
We study the spatially resolved (sub-kpc) gas velocity dispersion
($sigma$)–star formation rate (SFR) relation in the FIRE-2 (Feedback in
Realistic Environments) cosmological simulations. We specifically focus on
Milky Way mass disk galaxies at late times. In agreement with observations, we
find a relatively flat relationship, with $sigma approx 15-30$ km/s in
neutral gas across 3 dex in SFRs. We show that higher dense gas fractions
(ratios of dense gas to neutral gas) and SFRs are correlated at constant
$sigma$. Similarly, lower gas fractions (ratios of gas to stellar mass) are
correlated with higher $sigma$ at constant SFR. The limits of the
$sigma$-$Sigma_{rm SFR}$ relation correspond to the onset of strong
outflows. We see evidence of “on-off” cycles of star formation in the
simulations, corresponding to feedback injection timescales of 10-100 Myr,
where SFRs oscillate about equilibrium SFR predictions. Finally, SFRs and
velocity dispersions in the simulations agree well with feedback-regulated and
marginally stable gas disk (Toomre’s $Q =1$) model predictions, and the data
effectively rule out models assuming that gas turns into stars at (low)
constant efficiency (i.e., ${rm 1%}$ per free-fall time). And although the
simulation data do not entirely exclude gas accretion/gravitationally powered
turbulence as a driver of $sigma$, it appears to be strongly subdominant to
stellar feedback in the simulated galaxy disks.
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