Roy Goldner | Searcharxiv

arXiv2025

Accretion-Driven Turbulence in the Circumgalactic Medium

Simulations suggest that turbulence is ubiquitous in the circumgalactic medium (CGM), though the source and properties of CGM turbulence is uncertain. Using analytic considerations and hydrodynamic simulations we study how CGM turbulence is driven by gas accretion, thus providing a baseline for additional turbulence driving processes such as galaxy feedback. We demonstrate that in halos with mass $\sim 10^{10}-10^{12} M_{\odot}$ at $0 < z < 2$, accretion amplifies mild turbulent velocities near the virial radius of $\sigma_t(R_{\rm vir}) \sim 10 \, {\rm km \, s^{-1}}$ to virial velocities at inner CGM radii, $\sigma_t(0.1 R_{\rm vir}) \approx v_{\rm vir} \sim 100 \, {\rm km \, s^{-1}}$. Rapid cooling at these inner radii further implies that thermal pressure support is small, and the gas is dominated by the cool and warm ($\sim 10^4-10^5 \, {\rm K}$) phases. Inner CGM energetics in these halos is thus dominated by turbulence, with gas density distributions and velocity structure functions similar to those seen in simulations of isothermal supersonic turbulence, rather than those seen in subsonically turbulent stratified media such as the ICM. The accretion rate in these systems is regulated by the turbulence dissipation rate, in contrast with being regulated by the cooling rate as in more massive halos. We argue that galaxy feedback is unlikely to qualitatively change our conclusions unless it significantly depletes the CGM or continuously injects high specific energy material ($\gg v^2_{\rm vir}$). Such `turbulence-dominated' CGM can be identified in observations via the predicted wide lognormal ionization distributions and large velocity dispersions in UV absorption spectra.

astro-ph.GA↗

arXiv2025

Turbulence-dominated CGM: the origin of UV absorbers with equivalent widths of $\sim1$\AA

Theoretical arguments and observations suggest that in massive halos ($>10^{12}\,M_\odot$), the circumgalactic medium (CGM) is dominated by a 'hot' phase with gas temperature near the virial temperature ($T \approx T_{\rm vir}$) and a quasi-hydrostatic pressure profile. Lower-mass halos are however unlikely to be filled with a similar quasi-static hot phase, due to rapid radiative cooling. Using the FIRE cosmological zoom simulations, we demonstrate that the hot phase is indeed sub-dominant at inner radii ($\lesssim 0.3\,R_{\rm vir}$) of $\lesssim 10^{12}\,M_\odot$ halos, and the inner CGM is instead filled with $T \ll T_{\rm vir}$ gas originating in outflows and inflows, with a turbulent velocity comparable to the halo virial velocity. The turbulent velocity thus exceeds the mass-weighted sound speed in the inner CGM, and the turbulence is supersonic. UV absorption features from such CGM trace the wide lognormal density distributions of the predominantly cool and turbulent volume-filling phase, in contrast with tracing localized cool 'clouds' embedded in a hot medium. We predict equivalent widths of $W_\lambda \sim 2\lambda v_c/c \sim 1A$ for a broad range of strong UV and EUV transitions (Mg II, C II, C IV, Si II-IV, O III-V) in sightlines through inner CGM dominated by turbulent pressure of $\lesssim L^*$ galaxies at redshifts $0 \leq z \lesssim 2$, where $\lambda$ is the transition wavelength, $v_{\rm c}$ is the halo circular velocity and $c$ is the speed of light. Comparison of our predictions with observational constraints suggests that star-forming dwarf and $\lesssim L^*$ galaxies are generally dominated by turbulent pressure in their inner CGM, rather than by thermal pressure. The inner CGM surrounding these galaxies is thus qualitatively distinct from that around quenched galaxies and massive disks such as the Milky-Way and M31, in which thermal pressure likely dominates.

astro-ph.GA↗