X-ray detection of warm ionized matter in the Galactic halo. Issue 1 (23rd January 2016)

• Record Type: Journal Article
• Authors: Nicastro, F.; Senatore, F.; Gupta, A.; Guainazzi, M.; Mathur, S.; Krongold, Y.; Elvis, M.; Piro, L.
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 457:Issue 1(2016)
• Page Start: 676
• Page End: 694
• Publication Date: 2016-01-23
• Subjects: Galaxy: abundances -- Galaxy: disc -- Galaxy: halo -- local interstellar matter -- galaxies: ISM -- X-rays: ISM; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stv2923
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We report on a systematic investigation of the cold and mildly ionized gaseous baryonic metal components of our Galaxy, through the analysis of high-resolution Chandra and XMM–Newton spectra of two samples of Galactic and extragalactic sources. The comparison between lines of sight towards sources located in the disc of our Galaxy and extragalactic sources allows us for the first time to clearly distinguish between gaseous metal components in the disc and halo of our Galaxy. We find that a warm ionized metal medium (WIMM) permeates a large volume above and below the Galaxy's disc, perhaps up to the circum-galactic space. This halo WIMM imprints virtually the totality of the O i and O ii absorption seen in the spectra of our extragalactic targets, has a temperature of T $_{{\rm WIMM}}^{{\rm Halo}}=2900 \pm 900$ K, a density $\langle n_{\rm H}\rangle _{{\rm WIMM}}^{{\rm Halo}} = 0.023 \pm 0.009$ cm −3 and a metallicity $Z_{{\rm WIMM}}^{{\rm Halo}} = (0.4 \pm 0.1)$ Z⊙ . Consistently with previous works, we also confirm that the disc of the Galaxy contains at least two distinct gaseous metal components, one cold and neutral (the CNMM: cold neutral metal medium) and one warm and mildly ionized, with the same temperature of the halo WIMM, but higher density ($\langle n_{\rm H}\rangle _{{\rm WIMM}}^{{\rm Disc}} = 0.09 \pm 0.03$ cm −3 ) and metallicity ($Z_{{\rm WIMM}}^{{\rm Disc}} = 0.8 \pm 0.1$ Z⊙ ). By adopting a simple disc+sphere geometry for the Galaxy, we estimate masses of the CNMM and the total (disc + halo) WIMM of M CNMM ≲ 8 × 10 8 M⊙ and M WIMM ≃ 8.2 × 10 9 M⊙ .