SPICA

原始高柱密度ガスのガンマ線
バースト残光による探査法
平下博之 (H. Hirashita)
(筑波大学)
芝井広、竹内努
Contents:
1.
2.
3.
4.
High Column Density Clouds?
Absorption Intensity of H2
Infrared Extinction
Summary
Primeval (原始)
= not evolved (low metallicity/low dust content)
1. High Column Density Clouds?
これまでのQSO absorption line systemの研究
up to log N(H I) [cm–2] ~ 22
Possible bias due to dust extinction for log N(H I) > 22
(Fall et al. 1989; Vladilo & Péroux 2005).
より高い柱密度の系を観測する意義
Possibly related to star-forming places
Contribution to the total baryons in the Universe
Crucial to avoid dust extinction
→ Near-infrared H2 lines are useful (Shibai et al. 2001).
Why H2 lines?
Hirashita & Ferrara (2005)
Probability of 2N(H2)/N(H)
Dust-to-gas ratio ~ 1/100 of MW
log N(H2)/N(H)
large molecular fraction for log N(H) > 23
2. Absorption Intensity of H2
Absorption intensity
S Dn [1 – exp(–tline)] exp(–tdust)
Continuum flux
Competition between the line optical depth and
dust optical depth
Various Dust-to-Gas Ratio
Galactic extinction curve
0.001
0.01
0.1
Dust abundance
1
Various Source Fluxes
Typical flux of GRB afterglows
Dust-to-gas ratio ~ 1/100 of MW
3. Infrared Extinction
17 mm/2.12 mm line ratio
4. Summary
 Infrared H2 lines are useful for log N(H) > 22–23,
 because we can reduce the extinction effect.
 because a large fraction of H is in the form of H2.
 The H2 absorption in GRB is observable by SPICA.
 The extinction curves could be constrained by taking
line ratio.

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