Keyer Thyme | Searcharxiv

arXiv2024

Gravitational Particle Production of Scalars: Analytic and Numerical Approaches Including Early Reheating

Cosmological gravitational particle production (GPP) is a generic mechanism by which particles are produced during the inflationary epoch. In this work we consider the GPP of massive scalars in an effort to fully understand the spectrum of the produced particles. We consider scalars which are conformally or minimally coupled to gravity, as well as models of both early and late reheating. We numerically calculate the particle production in each scenario and compare the results to analytic approximations from boundary matching, Stokes phenomenon, steepest descent, and inflaton scattering methods. For each method, we describe the regime of validity and show that there is good agreement between the analytic and numerical results.

hep-ph↗

arXiv2024

The physical origin of positive metallicity radial gradients in high-redshift galaxies: insights from the FIRE-2 cosmological hydrodynamic simulations

Using the FIRE-2 cosmological zoom-in simulations, we investigate the temporal evolution of gas-phase metallicity radial gradients of Milky Way-mass progenitors in the redshift range of $0.4<z<3$. We pay special attention to the occurrence of positive (i.e. inverted) metallicity gradients -- where metallicity increases with galactocentric radius. This trend, contrary to the more commonly observed negative radial gradients, has been frequently seen in recent spatially resolved grism observations. The rate of occurrence of positive gradients in FIRE-2 is about $\sim7\%$ for $0.4<z<3$ and $\sim13\%$ at higher redshifts ($1.5<z<3$), broadly consistent with observations. Moreover, we investigate the correlations among galaxy metallicity gradient, stellar mass, star formation rate (SFR), and degree of rotational support. Metallicity gradients show a strong correlation with both sSFR and the rotational-to-dispersion velocity ratio ($v_c/\sigma$), implying that starbursts and kinematic morphology of galaxies play significant roles in shaping these gradients. The FIRE-2 simulations indicate that galaxies with high sSFR (${\rm log(sSFR~[yr^{-1}])}\gtrsim-9.2$) and weak rotational support ($v_c/\sigma\lesssim 1$) are more likely -- by $\sim$15\% -- to develop positive metallicity gradients. This trend is attributed to galaxy-scale gas flows driven by stellar feedback, which effectively redistribute metals within the interstellar medium. Our results support the important role of stellar feedback in governing the chemo-structural evolution and disk formation of Milky Way-mass galaxies at the cosmic noon epoch.

astro-ph.GA↗