The extinction law at high redshift (z>4) and its implications

1. The extinction law at high redshift (z>4) and its implications Simona Gallerani Osservatorio Astronomico di Roma in collaboration with: R. Maiolino; Y. Juarez; T. Nagao; A. Marconi, S. Bianchi, R. Schneider; F. Mannucci; T. Oliva; C. Willott; L. Jiang; X. Fan.

2. EXTINCTION CURVE AT z<4 FROM QUASAR SPECTRA BAL are the most reddened sub-class of QSOs Reddening SMC-like extinction curve as for noBAL QSOs at z<4 Reichard et al. 2003; Richards et al. 2003; Hopkins et al. 2004

3. EXTINCTION CURVE AT z~6 FROM QUASAR SPECTRA (Todini & Ferrara 01) Bluer than any BAL at low z (Maiolino et al.04) (Maiolino et al. 04) Extinction curve consistent with properties of dust theoretically expected from SNe

4. EXTINCTION CURVE AT z~6 FROM GRB SPECTRA Galactic (A3000Å=1.49) SMC (A3000Å=0.8) K Z J H GRB050904 at z=6.3 (Tagliaferri et al. 2005) SN dust (A3000Å=2) =QSO J1148 z=6.2 Calzetti (A3000Å=2) Data from Haislip et al. 06 Stratta et al. 06 (see also Watson et al. 2010)

5. A SAMPLE of 33 OPTICAL/NIR SPECTRA OF QSOs AT 4<z<6.4 Ftempl template by Reichard et al. 2003, having α=-1.62 A3000 absolute extinction at 3000 Å Aextinction curve normalized at 3000 Å (Data from Juarez et al. 2009; Jiang et al. 2007; Willott et al. 2009; Mortlock et al. 2008)

6. GRID OF EXTINCTION CURVES Empirical extinction curves from the local Universe SNe type dust Todini & Ferrara 01 Bianchi & Schneider 07 20 M 170 M nH=1cm-3 Pair instability SNe type dust SNe type dust Hirashita et al. 08 Hirashita et al. 08

7. DUST REDDENING IN 4<z<6.4 QSOs Extinction curve at 0<z<4 Extinction curves at 4<z<6.4 Gallerani et al. 2010, submitted to A&A Evidence for different dust properties (chemical composition? grain size distribution? dust sources?...) in the early Universe

8. THE EXTINCTION LAW AT HIGH REDSHIFT: Implications on galaxy spectra at z>4 Gallerani et al. 2010, submitted to A&A

9. THE EXTINCTION LAW AT HIGH REDSHIFT: Implications on galaxy spectra at z>4 λRF=1600 Å λRF=2300 Å The amount of dust in a galaxy is measured from the spectral slope β. Gallerani et al. 2010, submitted to A&A

10. THE EXTINCTION LAW AT HIGH REDSHIFT: Implications on galaxy spectra at z>4 λRF=1600 Å λRF=2300 Å The amount of dust inferred from a galaxy spectrum depends on the extinction curve adopted. Gallerani et al. 2010, submitted to A&A

11. THE EXTINCTION LAW AT HIGH REDSHIFT: Implications on the star formation rate at z>4 ~20 ≤ 3 Data from Bouwens et al. 09 The extinction curve inferred at z>4 implies a star formation rate at these epochs higher than previously estimated. Gallerani et al. 2010, submitted to A&A

12. CONCLUSIONS • Dust extinction in quasars at z<4 is described through • the SMC extinction curve. • We infer a mean extinction curve (MEC) from 4<z<6.4 • quasar spectra finding that it deviates from the SMC one. • Evidence for different dust properties in the early Universe, • (dust sources? chemical composition? grain size?…) • The meanextinction curve (MEC) at z>4 implies a star formation rate at these epochs higher than previously estimated. Gallerani et al. 2010, submitted to A&A