The X-ray side of the absorption by interstellar dust Elisa Costantini (SRON) C. De Vries, S. Zeegers (SRON), C. Pinto (IoA), H. Mutschke (Jena U.), F. de Groot (Utrecht U.) , R. Waters (SRON), A. Tielens (Leiden U.) The life cycle of dust in the Universe, Nov. 18-22 2013, Taipei

Why X-rays? The X-ray band offers complementary information with respect to longer wavelengths. This opens up a new science window for ID investigation.

Uniqueness of X-rays Gas phase: N, O, Fe, Ne, Mg, Si Dust: O (0.54keV), Fe (0.7-7.1keV), Mg (1.3keV), Si(1.87keV) all constituents of silicates! Dust: prominent iron features (Fe L and K-edge), Element depletion is straightforward to determine Sensitive to a large range of column densities. X-ray binaries are used as background light  mapping all the galactic plane Both scattering and absorption can be simultaneously studied

Scattering produces a halo of diffuse emission around the source. Galactic Center observed by ROSAT 0.1-2 keV Scattering produces a halo of diffuse emission around the source. The intensity/shape of the halo depends on energy, dust size distribution, dust spatial distribution (Overbeck 71; Mauche & Gorenstein 91; Predehl & Schmitt 95 Predehl & Klose 96; Costantini+05; Smith, Dame, Costantini+06) Absorption is seen in spectra of X-ray sources behind dust. Dust distorts the photoelectric edges depending on the dust chemical composition (Lee+2005, 2009; Pinto, Kaastra, Costantini+2010,2013; Costantini+2005, 2012)

Absorption The light of the background source is absorbed by the intervening dust and gas  dozens of neutral and ionized absorption features. X-rays have lower resolution (R=400- 1000), but many more transitions than UV  better determination of multi-temperature components

Dust spectral effects (Lee+09) As NH increases we are sampling denser and denser environments up to the Galactic Center region. Most edges are modified by measurable dust absorption (shift +smearing) Depending on the dust environments we can access different edges

Absorption by diffuse ISM optimal view of O and Fe (NH~2x1021cm-2)  Fe is 90% and O 20% in dust Mg-rich silicates (rather than Fe-rich)  Metallic iron + traces of oxides (Costantini+12 )

Mapping the diffuse ISM Analysis of the diffuse gas in different directions Metallic iron is favorite over e.g. Olivine. Depletion: 15-25% for O 65-90% for Fe (Pinto, Kaastra, Costantini + 2013) NH=1-4x1021cm-2

Are we detecting GEMS? FeS Results from X-rays, using different instruments and techniques : evidence of Mg2SiO3 + Fe + oxides Is there any compound with such composition? GEMS= glass with embedded metal and sulfides (e.g. Bradley+04) They have an interplanetary origin, but some of them may have ISM origin (e.g. Keller&Messenger 08, Ishii+08) Metallic iron Mg silicate

Shortcoming: relatively few (and sparse) lab X-ray measurements of compounds interesting for astronomy are available for comparison with the data  Possible bias in the results

The DUSTLAB project Collect relevant dust samples of astronomical interest: e.g. silicates, sulfates 11 samples (courtesy of H. Mutschke) Crystalline & amorphous silicates Measurements of all relevant edges (O, Fe, Mg, Si, S) comprehensive modeling of observed edges Simultaneous fitting, reduced degeneracy Implemetation into fitting X-ray codes addition to existing measurements dust+gas+source modeling Complementary data: X-ray scattering halos, Spitzer (10µm feature), HST (oxygen depletion), CO maps

Measurements: Electron Microscope Utrecht (EMU) LUCIA O K at 0.543 keV Fe L at 0,.7 keV LUCIA Mg K at 1.3 keV Si K at 1.84 keV PHOENIX (test) DUBBLE Fe K edge at 7.1 keV

Si K edge measurements CHECK Poster by S. ZEEGERS! NH=3x1022cm-2 (Zeegers, Costantini+ in prep) Tested on the Si K edge of GX5-1, in the Galactic Center region: Depletion: 0.74 Abundance :1.5 Dust: amorphous pyroxene! Soleil-Paris LUCIA beamline: Mg and Si edges Measurable differences among silicates. 1 CHECK Poster by S. ZEEGERS!

The X-ray future of dust 1999 1999 XMM-Newton CHANDRA Astro-H Athena+ XIFU 2015 Astro-H SXS Athena+….2028? Dense environements can be investigated!

Future missions: Athena+ Investigation of dense environments NH=1x1023cm-2 SiK and FeK edges Galactic center densest regions (dust composition, depletion) will be only accessed with Athena+

Conclusions X-rays are a powerful tool to study interstellar dust Current and future instrumentations + new lab measurements will help in solving the still open (and important) issues about dust.

Preliminary results Fe K edge Amorphous and Crystals show DUBBLE Measurable differences DUBBLE O K edge @ EMU Striking differences do not show up in every edge  Need for multiple edge fitting