X-ray study of WHIM

h1. X-ray study of WHIM

h2. Motivation


 * Warm-hot intergalactic medium (WHIM) are predicted to account for most of the missing baryons at the local Universe (REF?)
 * The best method to direct WHIM are the SZ effect and X-ray observations:
 * With SZ we can probe the electron gas pressure P_e
 * With X-ray we can probe the electron gas density n_e from the X-ray flux F_x and the electron gas temperature T_e from the energy spectrum
 * Since the SZ intensity depends on the gas density as n_e^1 and for the X-ray intensity it is $n_e^2, it follows that SZ observations are the better tracer for the low density WHIM.  However, an X-ray detection (and even a non-detection) of WHIM can give us more insides on the physical properties of WHIM because it is a highly non-virialized medium.


 * WHIM are best detected via SZ and X-rays in environments, where it has its highest pressure and density/temperature. Such environments can be found in filaments and nodes of the cosmic web.
 * In terms of SZ effect, this has already been shown by a pioneering work, where he stacked SZ observation from Planck of filaments and nodes and found in both cases a significant detection of WHIM. He used filaments between galaxies and as nodes he used "super-clusters":http://adsabs.harvard.edu/abs/2018arXiv180504555T.
 * In terms of X-rays, there are so far no significant defections in emission due to lack of sufficiently deep and sensitive all-sky data. There are however 3sigma defections in absorptions for a few filaments (REF?).


 * Alternative approaches: fluctuation study and study of individual objects

h2. Fluctuation study


 * Method: see my talk attachment:"Talk_Review_X-ray_fluctuations.pdf" [8MB]


 * *Status*: pending

h2. Individual objects


 * The filaments connecting towards a clusters ("Spiderlegs) or between nearby clusters ("cluster pairs") are ideal environment for direct X-ray study of WHIM and they are typically found in superclusters (hereafter: SC)

h3. Our approach


 * 1. Step: Supercluster X-ray survey (SXS):* find objects with great coverage of public X-ray data


 * two catalog used:
 * Superclusters detected with SDSS DR7 galaxies created by "Liivamägi+2012":http://adsabs.harvard.edu/abs/2012A%26A...539A..80L
 * Cluster pairs detected with Planck SZ data


 * *Status*: list of candidates made


 * 2. Step: Supercluster X-ray analysis*

!2011_PlanckEarlyResultsIX_Fig12.png! Ref: Crop of Fig.12 of "Planck early results. IX. XMM-Newton follow-up for validation of Planck cluster candidates":https://www.aanda.org/index.php?option=com_article&access=standard&Itemid=129&url=/articles/aa/abs/2011/12/aa16460-11/aa16460-11.html
 * Objects: Planck One and two


 * X-Ray Emission Analysis of Planck Two


 * *Status*: Analysis started