Constraining the baryon fraction in the Warm Hot Intergalactic Medium at low redshifts with PLANCK data

TL;DR

This study uses Planck CMB data cross-correlated with galaxy surveys to constrain the baryon content in the Warm-Hot Intergalactic Medium, providing limits consistent with previous detections and models.

Contribution

It introduces a novel cross-correlation method between Planck data and galaxy-based templates to constrain the WHIM baryon fraction at low redshifts.

Findings

Marginal detection of the WHIM signal compatible with the tSZ effect.

No significant contribution from bound gas in galaxy halos.

Constraints support that up to 45% of baryons are in filaments at specific densities and temperatures.

Abstract

We cross-correlate foreground cleaned Planck Nominal Cosmic Microwave Background (CMB) maps with two templates constructed from the Two-Micron All-Sky Redshift Survey of galaxies. The first template traces the large-scale filamentary distribution characteristic of the Warm-Hot Intergalactic Medium (WHIM) out to ~90 Mpc/h. The second traces preferentially the virialized gas in unresolved halos around galaxies. We find a marginal signal from the correlation of Planck data and the WHIM template with a signal-to-noise from 0.84 to 1.39 at the different Planck frequencies, and with a frequency dependence compatible with the thermal Sunyaev-Zel'dovich (tSZ) effect. When we restrict our analysis to the 60% of the sky outside the plane of the Galaxy and known point sources and galaxy clusters, the cross-correlation at zero lag is 0.064 +/- 0.051 muK. The correlation extends out to ~6 deg, which at the median depth of our template corresponds to a physical length of ~ 6-8 Mpc/h. On the same fraction of the sky, the cross-correlation of the CMB data with the second template is <0.17 muK (95% C.L.), providing no statistically significant evidence of a contribution from bound gas to the previous result. This limit translates into a physical constraint on the properties of the shock-heated WHIM of a log-normal model describing the weakly nonlinear density field. We find that our upper limit is compatible with a fraction of 45% of all baryons residing in filaments at overdensities ~1-100 and with temperatures in the range 10^4.5-10^7.5 K, in agreement with the detection at redshift z~0.5 of van Waerbeke et al. (2014).