3D mapping of the neutral X-ray absorption in the local interstellar medium: the Gaia and XMM-Newton synergy
We present a three-dimensional map of the hydrogen density distribution in the Galactic interstellar medium. The hydrogen-equivalent column densities were obtained from the Exploring the X-ray Transient and variable Sky project (EXTRAS) which provides equivalent N_H values from X-ray spectral fits of observations within the XMM-Newton Data Release. EXTRAS include multiple fits for each source, allowing an accurate determination of the equivalent column densities, which depends on the continuum modelling of the spectra. A cross-correlation between the EXTRAS catalogue and the first Gaia Data Release was performed in order to obtain accurate parallax and distance measurements. We use a Bayesian method explained in Rezaei Kh. et al. (2017) in order to predict the most probable distribution of the density at any arbitrary point, even for lines of sight along which there are no initial observation. The resulting map shows small-scale density structures which could not have been modelled by using analytic density profiles. In this paper, we present a proof of concept of the kind of science possible with the synergy of these catalogues. However, given the systematic uncertainties connected to the source identification and to the dependence of N_H on the spectral model, the present maps should be considered qualitatively at this point.
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/about_us/legal/notices). Accepted 2018 June 28. Received 2018 June 26; in original form 2018 January 23. Published: 30 June 2018. EG acknowledge support by the DFG cluster of excellence 'Origin and Structure of the Universe'. AK, MO, and JW acknowledge partial funding from the European Union's Seventh Framework Programme under grant agreement number 607452. We thank Rosine Lallement for providing the opacity distribution data in the Galactic plane. SR acknowledge partial funding from the Sonderforschungsbereich SFB 881 "The Milky Way System" of the German Research Foundation (DFG).
Submitted - 1806.11133.pdf
Published - sty1738.pdf