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QSO Absorbers in Radio Selected Samples Sara Ellison - University of Victoria Max Pettini - Cambridge Chris Akerman - Cambridge Chris Churchill - NMSU Pat Hall - York U. Isobel Hook - Oxford Carole Jackson - ATNF Paulina Lira - U. Chile Samantha Rix - ING Peter Shaver - ESO Chuck Steidel - CalTech Jasper Wall - UBC Lin Yan - IPAC Survey Bias Due to Dust? Theoretical motivation? Vladilo & Peroux (2005) Churches, Nelson & Edmunds (2004) Survey Bias Due to Dust? Simple calculation based on local extinction laws. E.g., in the SMC: A1500=12.5 x E(B-V) A1500=12.5 x N(HI)/4.4x1022 E.g., a z=3 QSO with an intervening DLA of N(HI)= 1x1021 atoms/cm2 would suffer about 0.3 mags of extinction in the optical. Survey Bias Due to Dust? Observational evidence?: • • Anti-correlation of N(HI) and [Zn/H] Lack of marked [M/H] evolution Prantzos & Boissier 2000 DLA metallicities and z<1 emission line galaxy abundances. The Complete Optical and Radio Absorption Line System (CORALS) Survey: Lin Yan, Isobel Hook, Max Pettini, Jasper Wall, Peter Shaver Strategy: Select radio loud quasars from the PKS catalogs (>0.25 Jy) and obtain complete optical identifications. Obtain moderate resolution optical spectroscopy for every QSO regardless of optical magnitude. Vital Statistics: 66 QSOs zem> 2.2 16.5 < B mag < 24 z=56 19 (22) DLAs 1.8 < zabs < 3.8 DLA, the mass density of neutral gas in good agreement. Ellison et al. (2001) Statistics as a function of cumulative B band magnitude. Seem to reach asymptote by about B~20: Eddington bias? Small difference N Big difference faint bright CORALS II: The Low Redshift Sequel. Chris Churchill, Sam Rix, Max Pettini However, perhaps the more serious issue is at low z when most of the stellar mass has assembled and stars are major contributors of dust. At z<1.5 select DLAs by MgII and FeII. DLA ‘candidate’ if EW(MgII, FeII)>0.5 Å. Rao & Turnshek (2000) Similar strategy to CORALS I: optically complete, radio selected sample. Line identification and fit via automated search Vital Statistics 73 QSOs z=58.2 (0.6 Å) 47 MgII systems 0.6 < zabs < 1.7 14 DLA candidates Calculate the number density of MgII absorbers above a certain EW threshold and compare with previous surveys: Excellent agreement with the large SDSS sample of absorbers (Nestor, Turnshek & Rao 2005) No evidence for a previous systematic under-estimate of MgII absorption systems. Ellison et al. (2004) Inferences on n(z)DLA from 0.6<z<3.5 Ellison et al. (2004) Assuming that 50% of our MgII selected DLA candidates will be confirmed, we infer a number density of DLAs at 0.6<z<1.6 consistent with previous studies (but need UV follow-up to be sure). CORALSZ: Metallicity Follow-up at High z Chris Akerman, Max Pettini, Chuck Steidel High resolution follow-up (mostly with either VLT/UVES or Keck/ESI) of the DLAs in the CORALS sample. Vital Statistics 20/22 DLAs w/ abundances 8 Zn detections 12 Zn limits ~< -1.0 <[Zn/H]> ~ -0.91 [<Zn/H>] ~ -0.88 Akerman et al (2005) CORALS metallicities maybe marginally higher, although it depends how the limits are treated. At most the CORALS average is larger by about 0.2 dex than optical samples. ELGs ( ): Kobulnicky & Zaritsky (1999) LillY, Carollo & Stockton (2003) Absorption galaxies( ): Schulte -Ladbeck et al (2003) Chen, Kennicutt & Rauch (2005) Ellison, Kewley & Mallen-Ornelas (2005) Optical - IR Colours of CORALS QSOs Pat Hall, Paulina Lira KS probability = 25% Ellison, Hall & Lira (2005) Assume a fixed E(B-V) for every DLA: Ellison, Hall & Lira (2005) Most probable E(B-V) for SMC (MW) dust = 0.02(0.05). 3 sigma (99% confidence) limit E(B-V) < 0.05 (0.10). E(B-V) < 0.05 Log(NHI) + [Zn/H] < 20.46 Log(NHI) + [Zn/H] < 21 E(B-V) < 0.17 (Prantzos & Boissier 2000) E(B-V) = N(HI) x 10[Zn/H]/5.8e21 Summary • DLA in high z DLAs at most a factor 2 higher than magnitude limited surveys - no significant bias. • n(z) of DLAs and MgII systems from 0.6 < z < 3.5 similarly not significantly higher than previous surveys. • Metallicity marginally higher (0.2 dex), but no systems in the “forbidden” high N(HI) high [Zn/H] zone. • From B-K colours, E(B-V) < 0.05 for SMC dust, best fit E(B-V) ~ 0.02 Overall, observations point to mild reddening and small differences in DLA statistics compared with optically selected samples.