Fiery Cores: Bursty and Smooth Star Formation Distributions across
  Galaxy Centers in Cosmological Zoom-in Simulations
  We present an analysis of the $R\lesssim 1.5$ kpc core regions of seven
simulated Milky Way mass galaxies, from the FIRE-2 (Feedback in Realistic
Environments) cosmological zoom-in simulation suite, for a finely sampled
period ($\Delta t = 2.2$ Myr) of 22 Myr at $z \approx 0$, and compare them with
star formation rate (SFR) and gas surface density observations of the Milky
Way's Central Molecular Zone (CMZ). Despite not being tuned to reproduce the
detailed structure of the CMZ, we find that four of these galaxies are
consistent with CMZ observations at some point during this 22 Myr period. The
galaxies presented here are not homogeneous in their central structures,
roughly dividing into two morphological classes; (a) several of the galaxies
have very asymmetric gas and SFR distributions, with intense (compact)
starbursts occurring over a period of roughly 10 Myr, and structures on highly
eccentric orbits through the CMZ, whereas (b) others have smoother gas and SFR
distributions, with only slowly varying SFRs over the period analyzed. In class
(a) centers, the orbital motion of gas and star-forming complexes across small
apertures ($R \lesssim 150$pc, analogously $|l|<1^\circ$ in the CMZ
observations) contributes as much to tracers of star formation/dense gas
appearing in those apertures, as the internal evolution of those structures
does. These asymmetric/bursty galactic centers can simultaneously match CMZ gas
and SFR observations, demonstrating that time-varying star formation can
explain the CMZ's low star formation efficiency.
