QSO Absorbers in Radio Selected Samples

Sara Ellison - University of Victoria

Max Pettini - CambridgeChris Akerman - CambridgeChris Churchill - NMSUPat Hall - York U.Isobel Hook - OxfordCarole Jackson - ATNF

Paulina Lira - U. ChileSamantha Rix - INGPeter Shaver - ESOChuck Steidel - CalTechJasper Wall - UBCLin 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

DLA metallicities and z<1 emission line galaxy abundances.

Prantzos & Boissier 2000

The Complete Optical and Radio Absorption Line System (CORALS) Survey:

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 < 24z=56

19 (22) DLAs 1.8 < zabs < 3.8

Lin Yan, Isobel Hook, Max Pettini, Jasper Wall, Peter Shaver

Ellison et al. (2001)

DLA, the mass density of neutral gas in good agreement.

brightfaint

N

Small difference

Big difference

Statistics as a function of cumulative B band magnitude. Seem to reach asymptote by about B~20: Eddington bias?

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)

Vital Statistics73 QSOs

z=58.2 (0.6 Å)47 MgII systems 0.6 < zabs < 1.7

14 DLA candidates

Similar strategy to CORALS I: optically complete, radio selected sample. Line identification and fit via automated search

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)

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).

Inferences on n(z)DLA from 0.6<z<3.5

Ellison et al. (2004)

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 Statistics20/22 DLAs w/ abundances

8 Zn detections12 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.

Schulte -Ladbeck et al (2003) Chen, Kennicutt & Rauch (2005)Ellison, Kewley & Mallen-Ornelas (2005)

Kobulnicky & Zaritsky (1999)LillY, Carollo & Stockton (2003)

ELGs ( ): Absorption galaxies( ):

Optical - IR Colours of CORALS QSOs

Ellison, Hall & Lira (2005)

Pat Hall, Paulina Lira

KS probability = 25%

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).

Log(NHI) + [Zn/H] < 21 E(B-V) < 0.17(Prantzos & Boissier 2000)

E(B-V) < 0.05 Log(NHI) + [Zn/H] < 20.46

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.