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

• Complementary data: X-ray scattering halos, Spitzer (10µm feature), HST (oxygen depletion), CO maps

Measurements:

DUBBLEFe K edge at 7.1 keV

LUCIAMg K at 1.3 keVSi K at 1.84 keV

PHOENIX (test)

Electron Microscope Utrecht (EMU)O K at 0.543 keVFe L at 0,.7 keV

Si K edge measurements

Soleil-Paris LUCIA beamline: Mg and Si edgesMeasurable differences among silicates.

Tested on the Si K edge of GX5-1, in the Galactic Center region:Depletion: 0.74Abundance :1.5 Dust: amorphous pyroxene!

CHECK Poster by S. ZEEGERS!

(Zeeg

ers

, C

ost

an

tin

i+ i

n p

rep

)

NH=3x1022cm-2

The X-ray future of dust

CHANDRAXMM-Newton

Astro-H

1999 1999

2015

Athena+….2028?

Dense environements can be investigated!

Athena+ XIFU

Astro-H SXS

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.