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
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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.
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The X-ray side of the absorptionby 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
oGas phase: N, O, Fe, Ne, Mg, Sio Dust: O (0.54keV), Fe (0.7-7.1keV), Mg (1.3keV),
Si(1.87keV) all constituents of silicates!o Dust: prominent iron features (Fe L and K-edge), oElement depletion is straightforward to determineoSensitive to a large range of column densities.oX-ray binaries are used as background light
mapping all the galactic planeoBoth scattering and absorption can be
simultaneously studied
Galactic Center observed by ROSAT0.1-2 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
• 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
(Lee+
09)
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
(Cost
an
tin
i+1
2 )
Mapping the diffuse ISM
Analysis of the diffuse gas in different directionsMetallic iron is favorite over e.g. Olivine.
Depletion: 15-25% for O65-90% for Fe
(Pin
to,
Kaast
ra,
Cost
an
tin
i +
20
13)
NH=1-4x1021cm-2
Are we detecting GEMS?
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)
Mg silicateMetallic iron
FeS
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