GRBs as cosmological

probesThomas Krühler (DARK)

Thanks to J. Fynbo, D. Malesani, J. Hjorth,J. Greiner, D. A. Kann, D. Perley, N. Tanvir,

S. Klose and many othersVery High Energy Phenomena in the Universe 2013 @

La Thuile 13/03/2013

GRB as probes

Image Credit Nature 2008

Afterglows and redshifts

Afterglows

Kann+ 10

10 cm

60 cm

2 m

8 m

Bright, well studiedbut only ~20 % of Swift afterglows

With 2m telescopes:Observationally accessiblebut only ~50%

Afterglows, that we typically miss:

Intrinsically faint ?dust extinguished ?high-z ?

GRB studies in the sample Era- P60 (Cenko+ 09, Perley+ 09)- UVOT (Roming+ 09, Oates+ 09)- GROND (Greiner+ 10, TK+ 11)- Liverpool & FTS/N (Melandri+ 08)- VLT (Fynbo+ 10, Zafar+ 11)- ROTSE (Rykoff+ 09)- Dark hosts (Perley+ 09, 13) - VLT hosts (Hjorth+ 12, Malesani+ 12,

Jakobsson+12, Milvang-Jensen+ 12, TK+ 12) - VLT dark hosts (Rossi+ 12) - Bright Swift events (Salvaterra+ 12, Melandri+

12, Campana+ 12, Nava+ 12, D’Avanzo+12, Covino+ 13)

GRB redshifts

Afterglows and redshifts

Fynbo+ 09

From afterglow spectroscopy

Afterglows and redshifts

TK+ 11

- Very good and robustphoto-z’s up to z ~ 10- Simple spectrum- Unique identification

From afterglow photometry

Afterglows and redshiftsFrom host spectroscopy

- Requires good position (Swift/XRT or better < 3”)

- Is not time critical- Can easily be performed

for ‘old’ GRB

GRBs at the highest redshifts

GRBs at redshift z > 8GRBs as probes of high-redshift SF

GRB 090423: Spectroscopic redshift of z = 8.2(Tanvir+ 2009, Salvaterra+ 2009)

GRB 090429B: Photometric redshift of z ~ 9.4(Cucchiara+ 2011)

GRBs as probes of high-redshift SF

No detection of GRB hosts at z > 5 in ultra-deep HST pointings-> A lot of high-z star-formation is undetected in current surveys

Probing the galaxy luminosity function below sensitivity limits of even the deepest surveys

Tanvir+ 2012

GRBs as probes of star-formation

The fraction of high-z GRBs

- 5.5 +/- 2.8 % z > 5 (Greiner+ 10)- < 14 %, < 7 % z > 5, z > 7 (Perley+ 09)- 3-5 %, 0.2-0.7 % z > 5, z > 8 (Salvaterra+ 12)- < 14 %, < 5 % z > 6, z > 7 (Jakobsson+ 12)

- cp. SDSS/CFHT QSO: (~0.05 %) z > 5.7 (Willott+ 10)

(Greiner+ 10)

(Hjorth+ 12,Malesani+ 12,Jakobsson+ 12)

GRBs as probes of high-redshift SF

- Connect SFR w. GRB rate:

None to strong evolution:-> a ~ 0 … 2

(Virgili+11, Wang & Dai 11, Elliott+ 11, Jakobsson+12, Robertson & Ellis 12, Salvaterra+ 12, Coward+ 12)

(Robertson & Ellis 12)

GRBs as probes of high-redshift SF

GRBs hosts as probes of galaxies

GRBs as probes of high-redshift galaxies

Fruchter+ 06

The TOUGH sampleHjorth+12, Jakobsson+ 12, Milvang-Jensen+12, TK+ 12, Michalowski+12:Large (69 -> 200), uniform, X-ray-selected, well-defined (no physical biases), deep (observed with the most sensitive instrumentation)

The TOUGH sample

GRBs as probes of high-redshift galaxiesTK+ 2011 Perley+ 2013

Large columns of dust regularly detected. Dominant cause of ‘dark’ bursts-> Physical selection effect in redshift determination-> Biases in redshift distribution, physical properties inferred from optical follow-up (and any quantity that requires a redshift)

3. The hosts of long GRBs

The hosts of dark, dust-extinguished GRBs have hosts that are redder, more luminous, higher mass, star-formation higher metallicity hosts than the hosts of optically bright GRBs

TK+ 11

GRBs as probes of high-redshift galaxies

Dark burst samples

GRB hosts missing from previous sample studies are: -> Redder -> More luminous, more massive -> More star-forming

Perley+ 12

Optically unbiased samples

Hjorth+ 12

GRBs as probes of high-redshift galaxies

3. The hosts of long GRBs

(Perley+ 13)

GRBs as probes of high-redshift galaxies

• GRBs appear in all star-forming environments

• No metallicity cut-off• They are clustered at

the low-mass end of the galaxy distribution at low redshift

• If metallicity is indeed the driver of this relation, the trend should soften/disappear at z ~ 2 / 3

GRBs as probes of cosmic chemical

enrichment

GRBs as probes of cosmic chemical enrichment

Savaglio+ 12

TK+ 13

GRBs as probes of cosmic chemical enrichment

TK+ 13 Vreeswijk+ 07

GRBs as probes of molecular gasGRB 120815A X-shooter spectrum

GRB 080607 LRIS spectrum• Direct probe of

molecular gas (H2 & CO) at high-redshift.

• Key quantity for star-formation, directly accessible through GRB and QSO-DLAs

TK+ 13

Prochaska+ 09

Take-home messages

- Efficient measurement of GRB redshifts based on host galaxies at z

< 4!= time critical

!= optical afterglowsrequires only

! good position (X-ray, optical, sub-mm, radio)

! Not a function of feasibility (only resources)

Take-home messages

- GRBs emerged as the class of objects with the highest spectroscopic redshifts (z = 8.2, stay tuned for updates)

- Afterglow photo-z’s (up to z ~ 9.4 and beyond) are accurate, robust and unique

- Studies of metals/dust/gas deep in the ‘dark’ ages

- Huge potential with ALMA synergies

Take-home messages- GRBs are efficient tools for probes

of galaxy evolution and star-formation up to z ~ 8

- GRBs are hosted by all types of galaxies, including very metal rich ones (> solar)

- There are evolutionary effects at low-z, likely due to metallicity

- Accurate quantification is ongoing- Likely not dominant at z > 2 - 3

Take-home messages

- GRBs are routinely used as probes of cosmic chemical enrichment (up to z ~ 5 for now)

- Provide accurate, direct metallicities (like QSOs)

- Couple with galaxy studies (unlike QSOs)- Probing the metals, gas and molecular

content of star-forming regions and galaxies in unprecedented detail