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Register a new userThe Impacts of Modeling Choices on the Inference of the Circumgalactic Medium Properties from Sunyaev-Zeldovich Observations
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As the signal-to-noise of Sunyaev-Zeldovich (SZ) cross-correlation measurements of galaxies improves our ability to infer properties about the circumgalactic medium (CGM), we will transition from being limited by statistical uncertainties to systematic uncertainties. Using thermodynamic profiles of the CGM created from the IllustrisTNG (The Next Generation) simulations we investigate the importance of specific choices in modeling the galaxy sample. These choices include different sample selections in the simulation (stellar vs. halo mass, color selections) and different fitting models (matching by the shape of the mass distribution, inclusion of a two-halo term). We forward model a mock galaxy sample into projected SZ observable profiles and fit these profiles to a generalized Navarro-Frenk-White profile using forecasted errors of the upcoming Simons Observatory experiment. We test the number of free parameters in the fits and show that this is another modeling choice that yields different results. Finally, we show how different fitting models can reproduce parameters of a fiducial profile, and show that the addition of a two-halo term and matching by the mass distribution of the sample are extremely important modeling choices to consider.
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We propose the use of the kinetic Sunyaev-Zeldovich (kSZ) effect to probe the circumgalactic medium (CGM), with the aid of a spectroscopic survey covering the same area of a SZ survey. One can design an optimal estimator of the kSZ effect of the CGM with a matched filter, and construct the cross correlation between the estimator and the peculiar velocity recovered from the galaxy survey, which can be measured by stacking a number of galaxies. We investigate two compelling profiles for the CGM, the MB profile (Maller & Bullock 2004) and the $beta$ profile, and estimate the detectability against the synergy of a fiducial galaxy survey with number density $10^{-3}h^3,$ Mpc$^{-3}$ and an ACT-like SZ survey. We show that the shape of the filter does not change much with redshift for the $beta$ profile, while there are significant side lobes at $z<0.1$ for the MB profile. By stacking $sim 10^4$ Milky Way-size halos around z $sim 0.5$, one can get $gtrsim$ 1 $sigma$ signal to noise (S/N) for the both profiles. The S/N increases with decreasing redshift before it reaches a maximum ($sim$ 7.5 at z $simeq$ 0.15 for the MB profile, $sim 19$ at $zsimeq 0.03$ for the $beta$ profile). Due to the large beam size, a Planck-like CMB survey can marginally detect the kSZ signal by stacking the same number of galaxies at $z<0.1$. The search for the CGM in realistic surveys will involve dividing the galaxies into subsamples with similar redshift and mass of host halos, and scaling the results presented here to obtain the S/N.
We study the effect of magnetic fields on a simulated galaxy and its surrounding gaseous halo, or circumgalactic medium (CGM), within cosmological zoom-in simulations of a Milky Way-mass galaxy as part of the Simulating the Universe with Refined Galaxy Environments (SURGE) project. We use three different galaxy formation models, each with and without magnetic fields, and include additional spatial refinement in the CGM to improve its resolution. The central galaxys star formation rate and stellar mass are not strongly affected by the presence of magnetic fields, but the galaxy is more disc-dominated and its central black hole is more massive when $B>0$. The physical properties of the CGM change significantly. With magnetic fields, the circumgalactic gas flows are slower, the atomic hydrogen-dominated extended discs around the galaxy are more massive and the densities in the inner CGM are therefore higher, the temperatures in the outer CGM are higher, and the pressure in the halo is higher and smoother. The total gas fraction and metal mass fraction in the halo are also higher when magnetic fields are included, because less gas escapes the halo. Additionally, we find that the CGM properties depend on azimuthal angle and that magnetic fields reduce the scatter in radial velocity, whilst enhancing the scatter in metallicity at fixed azimuthal angle. The metals are thus less well-mixed throughout the halo, resulting in more metal-poor halo gas. These results together show that magnetic fields in the CGM change the flow of gas in galaxy haloes, making it more difficult for metal-rich outflows to mix with the metal-poor CGM and to escape the halo, and therefore should be included in simulations of galaxy formation.
The circumgalactic medium (CGM) of nearby star-forming galaxies show clear indications of ion{O}{6} absorption accompanied by little to no ion{N}{5} absorption. This unusual spectral signature, accompanied by absorption from lower ionization state species whose columns vary by orders of magnitude along st{difference} textbf{different} sightlines, indicates that the CGM must be viewed as a dynamic, multiphase medium, such as occurs in the presence of turbulence. To explore this possibility, we carry out a series of chemodynamical simulations of a isotropic turbulent media, using the MAIHEM package. The simulations assume a metallicity of $0.3 Z_{odot}$ and a redshift zero metagalatic UV background, and they track ionizations, recombinations, and species-by-species radiative cooling for a wide range of elements. We find that turbulence with a one-dimensional velocity dispersion of $sigma_{1D} approx 60$ km/s replicates many of the observed features within the CGM, such as clumping of low ionization-state ions and the existence of ion{O}{6} at moderate ionization parameters. However, unlike observations, ion{N}{5} often arises in our simulations with derived column densities of a similar magnitude to those of ion{O}{6}. While higher values of $sigma_{1D}$ lead to a thermal runaway in our isotropic simulations, this would not be the case in stratified media, and thus we speculate that more complex models of the turbulence may well match the absence of ion{N}{5} in the CGM of star-forming galaxies.
We examine the thermal energy contents of the intergalactic medium (IGM) over three orders of magnitude in both mass density and gas temperature using thermal Sunyaev-Zeldovich effect (tSZE). The analysis is based on {it Planck} tSZE map and the cosmic density field, reconstructed for the SDSS DR7 volume and sampled on a grid of cubic cells of $(1h^{-1}{rm Mpc})^3$, together with a matched filter technique employed to maximize the signal-to-noise. Our results show that the pressure - density relation of the IGM is roughly a power law given by an adiabatic equation of state, with an indication of steepening at densities higher than about $10$ times the mean density of the universe. The implied average gas temperature is $sim 10^4,{rm K}$ in regions of mean density, $rho_{rm m} sim {overlinerho}_{rm m}$, increasing to about $10^5,{rm K}$ for $rho_{rm m} sim 10,{overlinerho}_{rm m}$, and to $>10^{6},{rm K}$ for $rho_{rm m} sim 100,{overlinerho}_{rm m}$. At a given density, the thermal energy content of the IGM is also found to be higher in regions of stronger tidal fields, likely due to shock heating by the formation of large scale structure and/or feedback from galaxies and AGNs. A comparison of the results with hydrodynamic simulations suggests that the current data can already provide interesting constraints on galaxy formation.
Single-phase photoionization equilibrium (PIE) models are often used to infer the underlying physical properties of galaxy halos probed in absorption with ions at different ionization potentials. To incorporate the effects of turbulence, we use the MAIHEM code to model an isotropic turbulent medium exposed to a redshift zero metagalactic UV background, while tracking the ionizations, recombinations, and species-by-species radiative cooling for a wide range of ions. By comparing observations and simulations over a wide range of turbulent velocities, densities, and metallicity with a Markov chain Monte Carlo technique, we find that MAIHEM models provide an equally good fit to the observed low-ionization species compared to PIE models, while reproducing at the same time high-ionization species such as ion{Si}{4} and ion{O}{6}. By including multiple phases, MAIHEM models favor a higher metallicity ($Z/Z_odot approx 40%$) for the circumgalactic medium compared to PIE models. Furthermore, all of the solutions require some amount of turbulence ($sigma_{rm 3D} geqslant 26 {rm km} {rm s}^{-1}$). Correlations between turbulence, metallicity, column density, and impact parameter are discussed alongside mechanisms that drive turbulence within the halo.
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