Pharos: distant beacons as cosmological probes. 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
distant beacons ascosmological probes
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
and V. D’Elia, S. Piranomonte, R. Perna, D. Lazzati, D. Guetta,L. Stella,
A. Antonelli, P. Ward and many others
early 21st Century astrophysics:
1997 1st GRB redshift (thank to BeppoSAX)
metal abundances, dynamics, gas ionization, dust
2000-200? Gunn-Peterson trough at z~6-?
(See Nicastro et al. poster)
1999 Warm IGM simulations
2001 1st Warm IGM detection (thank to Chandra)
1mCrab i.e. a bright AGN
GRBs also probe normal high z galaxies
peak of star formation
star formation rate
Mann et al. 2002 MNRAS, 332, 549
Prochaska et al. 2003
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 …
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.
30 Swift GRB with spectroscopic redshift
27 BeppoSAX and HETE2 GRB with spectroscopic redshift
118 Swift and 44 BeppoSAX+HETE2 GRBs localized in regions with NH(Gal)<41021
Due to the different Eband of localization? (BAT 15-150keV, WFC and WXC 2-20 keV)
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
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
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.
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; R18
GRB050922C: z=2.199 – 3.5hr after the GRB; R18
Complex, with many components spanning a velocity ranges from a few hundred to a few thousands km/s
Separating different components Piranomonte et al. 2006
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
Separating different components
D’Elia et al. 2006
Strong CII* for both components 2 and 3
3 2 1
Strong SiII*,OI* and OI** only for
4 3 2
Strong FeII and FeII* transitions only for component 2
Ne>a few 100
Assuming collisional excitation
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
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!
Nicastro et al.1999
Perna, Lazzati et al.
Lazzati et al. 2006
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
Savaglio et al. 2005,2006 Berger et al. 2006
Host em. lines