  The problem of missing baryons in the local universe remains an open
question. One propose alternative is that at low redshift missing baryons are
in the form of the Warm Hot Intergalactic Medium (WHIM). In order to test this
idea, we present a detailed analysis of X-ray high-resolution spectra of six
extragalactic sources, Mrk 421, 1ES 1028+511, 1ES 1553+113, H2356-309, PKS
0558-504 and PG 1116+215, obtained with the XMM-Newton Reflection Grating
Spectrometer to search for signals of WHIM and/or circumgalactic medium (CGM)
X-ray absorbing gas. We fit the X-ray absorption with the IONeq model, allowing
us to take into account the presence of X-ray spectral features due to the
multiphase component of the local ISM. An additional IONeq component is
included to model the WHIM absorption, instead of the traditional Gaussian
absorption line modeling. We found no statistical improvement in the fits when
including such component in any of the sources, concluding that we can safely
reject a successful detection of WHIM absorbers towards these lines of sights.
Our simulation shows that the presence of the multiphase ISM absorption
features prevents detection of low-redshift WHIM absorption features in the 17
A spectral region for moderate exposures using high-resolution spectra.
