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.

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

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

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)

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)

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

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

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

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

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

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

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 mean extinction 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