Sunyaev–Zeldovich Signals from L* Galaxies: Observations, Analytics, and Simulations

Abstract

We analyze measurements of the thermal Sunyaev–Zeldovich (tSZ) effect arising in the circumgalactic medium (CGM) of L * galaxies, reported by J. N. Bregman et al. (B+22) and S. Das et al. (D+23). In our analysis, we use the Y. Faerman et al. CGM models, a new power-law model (PLM), and the TNG100 simulation. For a given M _vir , our PLM has four parameters: the fraction, f _hCGM , of the halo baryon mass in hot CGM gas, the ratio, ϕ _T , of the actual gas temperature at the virial radius to the virial temperature, and the power-law indices, a _P _,th and a _n for the thermal electron pressure and the hydrogen nucleon density. The B+22 Compton- y profile implies steep electron pressure slopes ( a _P _,th ≃ 2). For isothermal conditions, the temperature is at least 1.1 × 10 ^6 K, with a hot CGM gas mass of up to 3.5 × 10 ^11 M _⊙ for a virial mass of 2.75 × 10 ^12 M _⊙ . However, if isothermal, the gas must be expanding out of the halos. An isentropic equation of state is favored for which hydrostatic equilibrium is possible. The B+22 and D+23 results are consistent with each other and with recent (0.5–2 keV) CGM X-ray observations of Milky Way mass systems. For M _vir ≃ 3 × 10 ^12 M _⊙ , the scaled Compton pressure integrals, $E{(z)}^{-2/3}{Y}_{500}/{M}_{\mathrm{vir},12}^{5/3}$ , lie in the narrow range, 2.5 × 10 ^−4 –5.0 × 10 ^−4 kpc ^2 , for all three sets of observations. TNG100 underpredicts the tSZ parameters by factors ∼0.5 dex for the L * galaxies, suggesting that the feedback strengths and CGM gas losses are overestimated in the simulated halos at these mass scales.

Keywords

• Sunyaev-Zeldovich effect
• Circumgalactic medium
• L galaxies
• Hydrodynamical simulations