Evidence for the kinematic Sunyaev-Zel’dovich effect with the Atacama Cosmology Telescope and velocity reconstruction from the Baryon Oscillation Spectroscopic Survey

Abstract

We use microwave temperature maps from two seasons of data from the Atacama Cosmology Telescope (ACTPol) at 146 GHz, together with the 'Constant Mass' CMASS galaxy sample from the Baryon Oscillation Spectroscopic Survey to measure the kinematic Sunyaev-Zel'dovich (kSZ) effect over the redshift range z = 0.4 − 0.7. We use galaxy positions and the continuity equation to obtain a reconstruction of the line-of-sight velocity field. We stack the cosmic microwave background temperature at the location of each halo, weighted by the corresponding reconstructed velocity. The resulting best fit kSZ model is preferred over the no-kSZ hypothesis at 3.3σ and 2.9σ for two independent velocity reconstruction methods, using 25, 537 galaxies over 660 square degrees. The effect of foregrounds that are uncorrelated with the galaxy velocities is expected to be well below our arXiv:1510.06442v1 [astro-ph.CO] 21 Oct 2015 2 signal, and residual thermal Sunyaev-Zel'dovich contamination is controlled by masking the most massive clusters. Finally, we discuss the systematics involved in converting our measurement of the kSZ amplitude into the mean free electron fraction of the halos in our sample. 98.70.Vc Introduction. Measurements of the anisotropy in the Cosmic Microwave Background radiation (CMB), together with constraints from Big Bang Nucleosynthesis and the Lyman-α forest, tightly constrain the total baryon abundance of the Universe at z 2 [1-3]. It is estimated that today, only about 10% of the baryons are found in stars or other neutral medium, while the majority of the rest are thought to occupy a warm, diffuse component [4]. A large fraction of this component is believed to be in the form of the Warm-Hot Intergalactic Medium (WHIM), at typical temperatures of 10 5 − 10 7 K, which is too cold and too diffuse to be visible with X-rays or through thermal Sunyaev-Zel'dovich (tSZ) observations, but at the same time too hot to collapse in dense cores and form stars [5]. Due to the difficulty in observing the WHIM using current methods, the spatial distribution and abundance of baryons in the outskirts of galaxies and clusters is still poorly constrained, especially for group-sized objects or smaller.The kinematic Sunyaev-Zel'dovich (kSZ) effect is the shift in CMB photon energy due to Thomson scattering off coherently moving electrons [6,7]. As we discuss below, the kSZ effect depends linearly on the local free electron density n e , is independent of temperature T e , and is therefore well-suited to probe the low density and low temperature outskirts of galaxies and clusters. This should be contrasted with the X-ray signal (∝ n 2

A one-dimensional hydrodynamic model for accretion, cooling, and heating of gas in dark matter haloes from z = 6 to z = 0

“…This enables us to compare the temporally varying state variables of the medium as well as the time-integrated quantities with those of existing models and observations and test the validity of the model which grows halos smoothly over cosmological times. The thermodynamics of the gas in clusters and groups is interesting to study, particularly with the advent of future galaxy redshift surveys and the measurement of the kinetic and thermal Sunyaev-Zel'dovich signal (Lim et al 2017, Park, Alvarez & Bond 2018, Schaan et al 2016) combined with the existing X-ray observations. In order to test a large number of ICM models and reasonable parametric profiles to compare with new observations, simple semi-analytical models (Flender, Nagai & McDonald 2017 ) are preferred over large scale hydrodynamic simulations.…”

“…Galaxy clusters, on the other hand, have been observed to contain the highest baryon content (Ettori 2003). Schaan et al 2016 discuss the baryon content of clusters and groups by combining data from Atacama Cosmology Telescope and "Constant Mass" CMASS galaxy sample from the Baryon Oscillation Spectroscopic survey to measure the kinetic SZ signal of the halos over the redshift range 0.4 − 0.7. They consider the kSZ signal obtained relative to the expected kSZ signal to be a proxy for the average baryon content.…”

“…We present comparisons of the radial gas density profiles of such SZ selected halos with that of the cluster in our model. Current observations also study the radial profiles of baryon fraction in clusters and groups by tracking the free electrons using kinetic SZ effect (e.g Schaan et al 2016) and may provide constraints on the simulations.…”

Detection of Missing Baryons in Galaxy Groups with Kinetic Sunyaev–Zel’dovich Effect

“…The detection of kSZE has so far been made only for a small number of systems (e.g Kashlinsky et al 2010) and from statistical measurements based on, e.g., the pair-wise and cross correlation methods (Hand et al 2012 Schaan et al (2016) found that a significant fraction of baryons may be associated with the large-scale structure traced by galaxies. A similar conclusion was reached by Hill et al (2016) by cross-correlating galaxies with CMB maps.…”

Pairwise Transverse Velocity Measurement with the Rees–Sciama Effect

“…We set σ to be the angular projection of the halo virial radius θ 200c . DGD3 can be thought of as a dipolar generalization of the aperture photometry filter used for kSZ detection (Li et al 2018;Soergel et al 2016;De Bernardis et al 2017;Schaan et al 2016). Evaluating Eq.…”