Pharos: distant beacons as cosmological probes Fabrizio Fiore The “Pharos” of Alexandria, one of the Seven Wonders of the ancient world, was the tallest building on Earth (120m). Its mysterious mirror, which reflection could be seen more than 55 km off-shore fascinated scientists for centuries. Fabrizio Fiore and V. D’Elia, S. Piranomonte, R. Perna, D. Lazzati, D. Guetta,L. Stella, A. Antonelli, P. Ward and many others

Gamma ray bursts: one of the great wonders of the Universe GRBs combine 4 themes of early 21st Century astrophysics: Among the most energetic events in the Universe 1997 1st GRB redshift (thank to BeppoSAX) Galaxies in the age of star formation metal abundances, dynamics, gas ionization, dust The recombination epoch 2000-200? Gunn-Peterson trough at z~6-? The fate of the baryons & large scale structure (See Nicastro et al. poster) 1999 Warm IGM simulations 2001 1st Warm IGM detection (thank to Chandra)

Can we use GRB to track star-formation at high-z? through: Minutes after the GRB event their afterglows are the brightest sources in the sky at cosmological redshift. Afterglows can be used to probe the high redshift Universe : Can we use GRB to track star-formation at high-z? through: High resolution spectroscopy of UV lines Statistical studies GRB010222 10 Crab! Crab 1mCrab i.e. a bright AGN

Galaxies in the Age of Star Formation GRBs also probe normal high z galaxies peak of star formation Star formation in the Universe peaked at z~2 star formation rate GRB Hosts Studies of z=>1-2 galaxies are biased against dusty environments. redshift, (1+z) GRB hosts are normal galaxies Mann et al. 2002 MNRAS, 332, 549 GRB afterglows will reveal host Galaxy dynamics, abundances, & dust content at z>1

The history of the metal enrichment in the Universe Savaglio 2003 Prochaska et al. 2003

Spectroscopy of UV lines Star-formation regions (and the interstellar matter in general) are complex. Can we truly learn anything about star-forming regions from afterglow’s spectroscopy? Or, are we just doing meteorology? Just like to try to understand the physics of the atmosphere from the observation of one (a few) lightning …

Statistical studies Selection effects complex and Porciani & Madau 2001, Schmidt 2001, Guetta et al. 2004, Jakobsson et al. 2005 and many others. But…. Too few z, 30-50% only of well selected GRB samples. Selection effects complex and difficult to account for.

Redshift distributions 30 Swift GRB with spectroscopic redshift 27 BeppoSAX and HETE2 GRB with spectroscopic redshift

Peak flux distributions

NH distributions 118 Swift and 44 BeppoSAX+HETE2 GRBs localized in regions with NH(Gal)<41021 Due to the different Eband of localization? (BAT 15-150keV, WFC and WXC 2-20 keV)

Selection effect for different localization bands X-ray localization: biased against large z=0 obscuration ==> BSAX and HETE2 samples miss highly obscured, low-z GRB. ==> Swift localizes highly obscured, low-z GRB, but dust extinction makes their optical afterglow faint, and so more difficult z determinations Z=9 5.3 3 1 .5 0 NH=1024cm-2

Selection effects Redshift 1) Sensitivity: BSAX and HETE2 samples biased against X-ray faint GRB 2) Localization Eband: BSAX and HETE2 samples biased against highly obscured GRB (preferably at low z) 3) Spectroscopic identification: dust in the host galaxy plays a major role

Spectroscopy of UV lines 1- The GRB surrounding medium: its physical and dynamical state can be easily modified by the GRB and its afterglow. Geometry, density and physical state of the gas can be constrained by line variability and comparison of line ratios to expectation of time dependent photoionization codes. 2- The ISM of the host galaxy. Metal column densities, gas ionization and kinematics.These studies have so far relied upon either Lyman Break Galaxies or Damped Lyman Alpha systems, which may not truly be representative of the whole high-z galaxy population. GRB afterglows can provide new, independent tools to study high z galaxies.

DATA GRB050730: z=3.968 - 4hr after the GRB; R18 UVES spectra 3200-9400 A, slit 1”, resolution=42,000 FORS spectra 3800-9500 A, slit 1”, resolution=1000 GRB020813: z=1.245 - 24 hours after the GRB; R=20.4 GRB021004: z=2.328 - 12 hours after the GRB; R=18.6 GRB050730: z=3.968 - 4hr after the GRB; R18 GRB050922C: z=2.199 – 3.5hr after the GRB; R18

The ISM probed by GRB afterglow Complex, with many components spanning a velocity ranges from a few hundred to a few thousands km/s

Comparison with CLOUDY models: Ionization parameter assuming solar abundances Ionization parameter constrained in a relatively small range with no clear trend with the system velocity. This can be interpreted as density fluctuations on top of a regular R-2 wind density profile.

GRB0500922C UVES spectrum Separating different components Piranomonte et al. 2006

GRB050730 UVES spectrum Strong fine structure transition: CII*, SiII*, OI*, OI**, FeII*, FeII**, FeII***. Prochaska et al. 2006: Observed abundances of excited ions are well explained by UV pumping with the gas at r~a few hundred pc from the GRB

GRB050730: a slightly different approach: Separating different components D’Elia et al. 2006

GRB050730 Strong CII* for both components 2 and 3 3 2 1

GRB050730 Strong SiII*,OI* and OI** only for component 2 3 2 4 3 2

GRB050730 3 2 Strong FeII and FeII* transitions only for component 2

Fine structure lines Two main processes: Radiative excitation; 2) Collisional exitation

GRB050730 Fine structure lines component 2 T=2650+3000-1000 K Ne>a few 100 Assuming collisional excitation NCII/NCII*~0.5

GRB050730 fine structure lines Component 3 NCII/NCII*~1.8, higher than that of Component 2! Ne = a few 10 Assuming collisional excitation

and distance of the clouds from the GRB GRB050730 gas ionization and distance of the clouds from the GRB Huge (and variable) ionizing flux! CI<12.3 [CIV/CII] and [SiIV/SiII] of components 2 and 3 similar. If density is different by a factor 10 (100), the distance from the GRB of component 3 is 3 (10) times higher than that of component 2. Similar conclusion reached assuming UV pumping as dominant mechanism for excited transitions Need detailed time-dependent photoionization codes!

Time dependent photoionization Nicastro et al.1999 Perna, Lazzati et al. Strong variation with time of ion abundances A tool to constrain gas geometry and density through ion ratio variations Lazzati et al. 2006

Metallicities In case of multiple components it is truly difficult to estimate H columns for each, even with high quality spectroscopy. The spatial distribution of heavy elements can be very different from that of H. The star-forming regions hosting the GRB are likely to be much more enriched than the outer galaxy regions

GRB host galaxy metallicities 000926 050820 060206 050401 030323 050904 050730

GRB host galaxy metallicities However… metallicity depends on: Impact factor Galaxy mass Star-formation rate Etc….

1) Metallicity depend on impact factor GRB021004 galaxy DLA

2) Metallicity depends on galaxy mass: Savaglio et al. 2005,2006 Berger et al. 2006 Host em. lines 050904, abs.

Statistical population studies … should consider Complex selection effects, different localization bands and NH distributions should be taken into account SFR / metallicities / masses appropriate for the typical GRB hosts