GRB 090423: high-z GRBs as a new tool to study the reionization epoch by Ruben Salvaterra Universita’ dell’Insubria - Como

most distant object ever observed ! GRB 090423: TNG spectrum Tanvir et al. 2009 Telescopio Nazionale Galileo ~14hrs after trigger obs=1216 A (1+z) z=8.1-0.3+0.1 most distant object ever observed !

GRB 090423: a typical long GRB Amati relation Typical long GRB with a canonical afterglow light-curve, likely the result of the collapse of a PopII star similar to low-z bursts

GRB 090423: a rare event? + evolution Basic assumptions: 1) GRBs follow the cosmic SFR 2) GRB LF is constant + evolution model free parameters are obtained by fitting the BATSE logN-logP BATSE Swift

GRB 090423: need of evolution No evolution models fail to reproduce the number of high-z (e.g. z>2.5) GRBs and to account for the detection of GRB 090423: luminosity or density evolution is needed GRB 090423 lum evo. dens evo. no evo.

High-z GRBs: expected numbers density evo. The high-z population: GRB 050904 @ z=6.3 GRB 080913 @ z=6.7 GRB 090423 @ z=8.2 z>6 1-7% of all Swift GRBs at z>6 assuming Plim=0.4 ph/s/cm2 Next generation of satellites (e.g. EXIST, XENIA, SVOM, JANUS) will rapidly increase the high-z sample. In particular EXIST will be able to detect tens of GRBs/yr at z>6 allowing a systematic study of the high-z GRB population

High-z GRBs: host galaxies Cosmological simulaton with GADGET: L=10 Mpc/h, Np=2563, Mp= 2x106Msun with chemical feedback  PopIII-PopII trans. radiative feedback mechanical feedback (SNyy and SNII) HST/WFC3 dropout LF simulated JWST H-band sky The simulation nicely reproduces the recent HST/WFC3 data without the need of any fine-tuning

High-z GRBs: host galaxies high SSFR bursty observed/low-z simulated/high-z low-Z environments

Mass-metallicity relation at high-z 050904 Berger et al. 2007 z=6 z=8 090423 Tanvir’s talk

High-z galaxies: reionization Only a small fraction (<20% at z>6) of the ionizing photons come from bright galaxies that we resolve in current deep field surveys. GRBs can be the signpost of those faint galaxies that provide the bulk of UV photons that reionized the Universe JWST will resolve the bulk of the sources of ionizing photons up to z=7.3

Constraining the reionization history zreion~ 7 zreion~ 6 GRB 050904 (Kawai et al. 2006) zreion~ 7 zreion~ 6 The dimension of the largest dark gap in the afterglow spectrum between Lya and Lyb can help to constrain the reionization history 60% 45% 30% 15% 40<Wmax<80 A 5 d 3 d 1 d 0.3 d 0.2 d 0.1 d GRB 050904 Wmax=63 A 80<Wmax<120 A

Conclusions The detection of GRB 090423 has shown that GRBs do form (and are detectable!!!) at very high-z. High-z GRBs represent a fundamental tool for the study of the reionization epoch, e.g.: signposts of faint galaxies that contributed mostly to the reionization process constrain the M-Z relation at very high-z constrain the reionization history ….