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Probing the high redshift (2-3) IGM through OVI absorption

Probing the high redshift (2-3) IGM through OVI absorption. Sowgat Muzahid (IUCAA, INDIA) Supervisor : R. Srianand (IUCAA, INDIA) Collaborator : P. Petitjean (IAP, FRANCE). Plan of the talk : Introduction Issues we want to address Data Sample and Search procedure

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Probing the high redshift (2-3) IGM through OVI absorption

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  1. Probing the high redshift (2-3) IGM through OVI absorption Sowgat Muzahid (IUCAA, INDIA) Supervisor : R. Srianand (IUCAA, INDIA) Collaborator : P. Petitjean (IAP, FRANCE)

  2. Plan of the talk : • Introduction • Issues we want to address • Data Sample and Search procedure • Statistical properties of OVI systems • Conclusions

  3. Introduction • OVI : fifth ionization state of Oxygen, I. P ~ 113.9 eV • Strongest transitions OVI λλ1032,1037 Å falls in the UV regime • Collisional ionization fraction of OVI peaks at T ~ 3 × 105 K • OVI is the best species to probe : • Photo-ionized gas subject to hard ionizing photon . • Gas with fairly high temperature where collisional ionization is important . Gnat & Sternberg 2007

  4. Introduction • Census of baryons at low redshift (z< 0.5) implies that ~ 50% of the baryonic mass (as predicted by BBN) is yet to be detected . (Fukugita et al. 1998) • Recent numerical simulations predict that a substantial fraction of this “missing baryons” could reside in a warm – hot phase of the IGM . • ( [WHIM ] , T ~ 105 – 107 K) (Cen & Ostriker 1999 ; Dave’ et al. 2001) • Relatively cooler phase of the WHIM can be probed by OVI absorption . • OVI lines with rest frame EW > 40 mÅ are primarily produced by collisionally ionized gas at : • T ~ few 105 Kand δ ~ 5 – 100 . (Fang & Bryan – 2001)

  5. Issues we are interested in .. • Spatial distribution of OVI absorbers hence the high temperature regions and/or regions affected by hard ionizing photons . • Physical properties of OVI absorbers at high redshift. Is there any fundamental difference in the properties of what is seen in the local universe ? • ( AnyEvolution ? ). • Estimating the contribution of OVI absorbers to the baryon inventory around redshift 2 - 3 . • Absorption study is indirect in nature . Big challenge is to relate the LOS properties to the global picture of the absorber. • Large homogeneous sample is needed !!

  6. Data Sample • We have ~ 100 high resolution QSO absorption spectra from VLT/UVES . • 18 best quality spectra have been picked up to analyze . • These data were obtained in the course of the large programme “The Cosmic Evolution of the IGM” . Typical resolution ~ 45,000 (6.6 km/s) and S/R ~ 70 /pixel, wave length coverage 3200 Å to 10,000 Å . • This provide a homogeneous sample of QSO sight lines in the redshift range 2.1 - 3.3 . • These sight lines allow us to study OVI systems for redshift ~ 1.9 - 3.0 where the Ly-alpha forest is not too severe .

  7. Data Sample • We search OVI systems mainly in two ways .. • Guided (by other metal lines) search : • Blind search : • We classify OVI systems mainly into three categories .. • Type I : OVI lines are accompanied by other metal lines . • Type II : OVI with only Lyman series lines . • Type III : OVI with consistent profiles without metal lines • and Lyman series lines . • This classification is motivated by the facts that .. • Type I >> representative of photoionized gas . • Type II >> representative of high temp. gas . • Type III >> representative of highly ionized and high temp. gas .

  8. Data Sample • Example of a type I (left) and a type II (right) system . • We use our own Voigt profile fitting code .

  9. Data Sample • We have identified more than 70 OVI systems ( Biggest OVI sample ever reported ! ). • We fit 51 OVI systems comprised of 188 components from 14 LOS. • Type I : 45 Type II : 06 Type III : 00 • Type II & III systems are always affected by possible Ly-series contaminations which leads to false detections !! • Highest redshift : 2.9075 • Lowest redshift : 1.9643 • Median redshift : 2.32 • Median N(HI) : 14.19 cm-2

  10. Statistical Properties of OVI absorbers • No redshift evolution of N(OVI) for 1.9 ≤ z ≤ 2.9 .

  11. Statistical Properties of OVI absorbers • With the same spirit of OVI system classification we divide total 188 OVI components into two main categories .. • OVI with CIV : 87(188) • OVI without CIV : 101(188) • This is just to see if there is any difference in properties in this two sub samples which are supposed to trace photoionized and collisionally ionized gas respectively . • We will use two indicators for further analysis • b-para = 14.4 km/s ( b ≥ 14.4 km/s is consistent with CIE) • NOVI =13.5 cm-2 ( which is the crossover column density according to the simulation of the low redshift OVI systems.)

  12. Statistical Properties of OVI absorbers • 107(188) i.e ~ 57% of total OVI • 53(87) i.e ~ 61% of OVI with CIV • 54(101) i.e ~ 53% of OVI without CIV • components show N(OVI) > 13.5 cm-2 • No significant difference between OVI components with and without CIV for N(OVI) > 13.5cm-2 is seen in a two sided KS test. • (only ~ 77% significance level)

  13. Statistical Properties of OVI absorbers • 88(188) i.e ~ 47 % of total OVI • 38(87) i.e ~ 44 % OVI with CIV • 50(101) i.e ~ 50 % OVI without CIV • components show b-parameter consistent with CIE i.e b > 14.4 km/s ( T > 2×105 K) • A two sided KS test does not show any significant difference between components with and without CIV for b > 14.4 km/s.

  14. Statistical Properties of OVI absorbers • 64(87) ~ 74% components show bOVI > bCIV • 22(93) ~ 24% components show bOVI > bHI • CIV and OVI are appear to be associated kinematically but originally trace different phases of the (multiphase!) IGM.

  15. Statistical Properties of OVI absorbers • NOVI almost constant for 7 decades variation in NHI . • If the HI and OVI phases were well mixed, we would expect multiphase ratio (NHI/NOVI) to be constant with NHI . • Green points are taken from Fox et al. 2007. They have studied hot halos in high redshift protogalaxies . • Its intriguing that nowhere (from low density Ly-alpha forests to high density DLAs) OVI is varying that much. • NHI /NOVI ~ NHI1.20± 0.01 • Danforth & Shull shown that such correlation exists at low redshift z < 0.15 . They found : • NHI /NOVI ~ NHI 0.9±0.1 Danforth & Shull-05

  16. Statistical Properties of OVI absorbers b – N correlation ?? OVI systems from wide varieties of astrophysical regions (LMC, SMC, HVCs, Halo, Disk, Starburst, IGM) in low redshift show b – N correlation . Heckman et al. -02 • Radiatively cooling hot gas passing through coronal regime gives rise to such correlation. • For log (b) > 1.6 , NOVI increases linearly with temp.

  17. Statistical Properties of OVI absorbers b – N correlation ?? • b – N correlation is well known in case of HI (eqn. of state) • Here we find mild b-N correlation. • rs = 0.5 is good enough to rule out the null hypothesis . • Bias ??? • Low column with large ‘b’ will be affected by S/N .

  18. Statistical Properties of OVI absorbers b – N correlation ?? • Spearman Rank coefficient: 0.500 • Slope = 2.00 ± 0.24 • Intercept = 11.20 ± 0.27 • Spearman Rank coefficient: 0.537 • Slope = 2.02 ± 0.20 • Intercept = 11.29 ± 0.23

  19. Statistical Properties of OVI absorbers A simple model • We run CLOUDY v07.02 to model 51 OVI systems . • Assumption : a) cloud is optically thin • b) cloud is in single phase ! • CLOUDY parameters : Stop column density : N(HI) = 15.0 cm-2 • HM-05 EGB at redshift 2.32 • log Z ~ -3.0 to -1.0 ; log nH~ -5.0 to -3.5 assuming photoionization !! QSO + GAL QSO

  20. Conclusions • There is no redshift evolution of NOVI between 1.9 < z < 2.9 . • There is no significant difference in column density distributions between OVI with and without CIV for NOVI > 13.5 cm-2 . • There is no significant difference in b-parameter distributions between OVI with and without CIV for b > 14.4 km/s . • Almost 75% cases we find bOVI > bCIV which indeed imply CIV and OVI probe different phases of the IGM . • Increase of multiphase ratio NHI /NOVI with NHI suggests that IGM has at least two phases (WHIM & WNM) and they are not well mixed . • Mild log b – log NOVI correlation is there with slope ~ 2.0 which is not due to any bias !! • b – NOVI correlation is possibly due to local physics of heating and cooling . • A simple model of the OVI systems gives metallicity ~ -3.0 to -1.0 in log and δ ~ 15 – 60 assuming photoionization by Haardt-Madau EGB.

  21. References • Fukugita, M ., Hogan, C. J., Peebles, P. J. E ., 1998, ApJ, 503, 518 • Cen, R., Ostriker, J. P., 1998, ApJ, 514, 1 • Dave´, R., et al., 2001, ApJ, 552, 473 • Fang, T. & Bryan, G. L., 2001, ApJ, 561, L31 • Danforth, C.W. & Shull, M.J., ApJ, 624:560, 2005 • Heckman., et al., ApJ, 577:691-700, 2002 • Bergeron, J., Aracil, B., Petitjean, P., Pichon, C., A&A 396,L11-15,02 • Bergeron, J. & Herbert-Fort., Proceeding IAU Colloquium No 199,2005 • Gnat, O. & Strenberg, A., ApJ, 168:213 – 230, 2007 • Fox, A. J., et al. A&A 465, 171-184(2007) • Haardt, F., & Madau, P. 1996, ApJ, 461, 20 • Ferland, G. J., et al., 1998, PASP, 110, 761

  22. Thank You ..

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