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Early Dust Evolution in an Extreme Environment
FrИdИric Galliano (NRC / NASA GSFC); Eli Dwek (NASA GSFC); Ant Jones (IAS Orsay)

SDSS J1148+5251: a hyperluminous high metallicity galaxy, in the early universe
SDSS J1148+5251 (Fan et al. 2003) is the most distant quasar known to date (z=6.42). · Its high resolution CO(3-2) data suggests a disk that extends out to 2.5 kpc (right image; Walter et al. 2004). · Various metal tracers, like the [FeII], [MgII] and [CII] lines, as well as the large amount of CO and dust emission, indicate a nearly solar metallicity. · It has been extensively studied at many wavelengths (e.g. Bertoldi et al. 2003; Charmandaris et al. 2004; Robson et al. 2004; Beelen et al. 2006).

An exceptionally high star formation rate...
The rest frame IR SED of this quasar (right panel; Dwek et al. 2006) indicates that it is an HYLIRG (LIR>1013 L). A naive conversion of LIR into star formation rate (hereafter SFR) gives SFRIR=3500-5000 M/yr. This estimation is consistent with the value of 3000 M/yr usually quoted in the litterature.

Name SDSS J1148+5251

Redshift 6.42

Molecular gas mass 2в1010 M

Dynamical mass 5в1010 M

IR luminosity (2-3)в1013 L

Dust temperature 50-60 K

Dust mass (1-4)в108 M

When massive stars control dust evolution
· SDSS J1148+5251 is a very young system. Assuming that it began its star formation at the reionization (z10), its age at z=6.42 is 400 Myr, which is the average lifetime of an AGB star. we can neglect the contribution of AGB stars to the evolution of the galaxy. · Massive stars dominating the elemental evolution, we can simplify the gas and dust evolution equations, by considering instantaneous recycling:

Star formation or nuclear activity ?
The SED of SDSS J1148+5251 is remarkably flat (figure below; Dwek et al. 2006), especially the rest frame near-IR observations (Charmandaris et al. 2004; Spitzer/IRS). Several origins are possible for this excess: · Emission from low-mass stars: this explanation would require 10 to match the 2 µm flux.
12

M of stars, in order

· Emission from the AGN: this solution is shown on the figure below. The AGN spectrum is a taken as a power-law. The stellar component has been synthesized with PEGASE (Fioc & Rocca-Volmerange 1997), with a star formation scenario consistent with our dust evolution modelling.

A reasonably high star formation rate...
· The relation between the gas content and the star formation rate required to solve the equations above is given by the Kennicutt (1998) law (right panel). · Adopting a total gas mass of relation gives a star formation SFRK98=200-800 M/yr (Dwek is significantly lower than the the IR luminosity. (2-5)в1010 M, this rate of et al. 2006), which estimation from

A controversially moderate star formation rate...

A short-term memory dust content
· In SDSS J1148+5251, massive stars are responsible for dust production and destruction the dust lifetime is independent of the star formation history:

· The fit of the SED (figure above) indicates that the luminosity of the AGN is comparable to the luminosity of the starburst: LAGN (1-3)вLSB. · It explains the discrepancies between the star formation rates estimated from the IR luminosity, and from the gas surface density. A significant fraction of the IR luminosity originates into the AGN.

Mass of gas swept-up: 140-260 M/SN

The star formation rate of this quasar is probably close to SFR600-800 M/yr.

Summary and conclusion
· Consequently, the measure of the dust mass provides an estimation of the average dust yield per SNe: · SDSS J1148+5251 is a distant quasar at z=6.42. It is a nearly solar metallicity hyperluminous IR galaxy, in the early universe. It challenges our understanding of dust formation in extreme environments how could such a high mass of dust have formed in only a few 100 Myr ? · The dust production by low-mass stars can be neglected since the age of comparable to the mean lifetime of an AGB star. Therefore, massive stars principal source of dust. We modelled the dust formation by massive stars destruction by SNe shock waves. We showed that, in order to produce the amount, the dust yield per SN must be high (Yd>0.3 M/SN). J1148+5251 is should be the and its observed dust

·The two left figures (Dwek et al. 2006) show the evolution of the gas and dust masses, in SDSS J1148+5251. On each panel, two solutions are shown: 1) a closed-box model; and 2) a model with an infall of gas.

SNe must produce a lot of dust
· The solution of the dust evolution equations (left figures), in the case of SDSS J1148+5251, indicates that the dust yield per SNe must be high, in order to explain the amount of dust observed (Dwek et al. 2006): Y
dust SN

· Our detailed study of the SED, as well as the disagreement between two independent star formation tracers, indicate that the total energy budget of this galaxy is dominated by the central black hole the previous studies overestimated the star formation rate by a factor of 3-4.

References:
Beelen, Cox, Benford et al. 2006, ApJ, accept. Bertoldi, Carilli, Cox et al. 2003, A&A, 406, L55 Charmandaris et al. 2004, ApJS, 154, 142 Dwek, Galliano & Jones 2006, in prep. Fan, Strauss, Schneider et al. 2003, AJ, 125, 1649 Fioc & Rocca-Volmerange 1997, A&A, 326, 950 Kennicutt 1998, ApJ, 498, 541 Robson, Priddey, Isaak et al. 2004, MNRAS, 351, L29 Walter, Carilli, Bertoldi et al. 2004, ApJ, 615, L17

0.3-1 M/SN