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GRBs as cosmological probes Thomas Krühler (DARK) Thanks to J. Fynbo, D. Malesani, J. Hjorth, J. Greiner, D. A. Kann, D. Perley, N. Tanvir, S. Klose and.

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Presentation on theme: "GRBs as cosmological probes Thomas Krühler (DARK) Thanks to J. Fynbo, D. Malesani, J. Hjorth, J. Greiner, D. A. Kann, D. Perley, N. Tanvir, S. Klose and."— Presentation transcript:

1 GRBs as cosmological probes Thomas Krühler (DARK) Thanks to J. Fynbo, D. Malesani, J. Hjorth, J. Greiner, D. A. Kann, D. Perley, N. Tanvir, S. Klose and many others Very High Energy Phenomena in the Universe La Thuile 13/03/2013

2 GRB as probes Image Credit Nature 2008

3 Afterglows and redshifts

4 Afterglows Kann cm 60 cm 2 m 8 m Bright, well studied but only ~20 % of Swift afterglows With 2m telescopes: Observationally accessible but only ~50% Afterglows, that we typically miss: Intrinsically faint ? dust extinguished ? high-z ?

5 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)

6 GRB redshifts

7 Afterglows and redshifts Fynbo+ 09 From afterglow spectroscopy

8 Afterglows and redshifts TK+ 11 -Very good and robust photo-z’s up to z ~ 10 -Simple spectrum -Unique identification From afterglow photometry

9 Afterglows and redshifts From host spectroscopy -Requires good position (Swift/XRT or better < 3”) -Is not time critical -Can easily be performed for ‘old’ GRB

10 GRBs at the highest redshifts

11 GRBs at redshift z > 8 GRBs as probes of high-redshift SF GRB : Spectroscopic redshift of z = 8.2 (Tanvir+ 2009, Salvaterra+ 2009) GRB B: Photometric redshift of z ~ 9.4 (Cucchiara+ 2011)

12 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

13 GRBs as probes of star-formation

14 The fraction of high-z GRBs /- 2.8 % z > 5 (Greiner+ 10) -< 14 %, < 7 % z > 5, z > 7 (Perley+ 09) -3-5 %, % 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

15 -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

16 GRBs hosts as probes of galaxies

17 GRBs as probes of high-redshift galaxies Fruchter+ 06

18 The TOUGH sample Hjorth+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)

19 The TOUGH sample

20 GRBs as probes of high-redshift galaxies TK+ 2011Perley 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)

21 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

22 Dark burst samples GRB hosts missing from previous sample studies are: -> Redder -> More luminous, more massive -> More star-forming Perley+ 12

23 Optically unbiased samples Hjorth+ 12

24 GRBs as probes of high-redshift galaxies

25 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

26 GRBs as probes of cosmic chemical enrichment

27 Savaglio+ 12 TK+ 13

28 GRBs as probes of cosmic chemical enrichment TK+ 13 Vreeswijk+ 07

29 GRBs as probes of molecular gas GRB A X-shooter spectrum GRB LRIS spectrum Direct probe of molecular gas (H 2 & CO) at high-redshift. Key quantity for star- formation, directly accessible through GRB and QSO-DLAs TK+ 13 Prochaska+ 09

30 Take-home messages -Efficient measurement of GRB redshifts based on host galaxies at z < 4 != time critical != optical afterglows requires only ! good position (X-ray, optical, sub-mm, radio) ! Not a function of feasibility (only resources)

31 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

32 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

33 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


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