QSO Absorbers in Radio Selected Samples

1
QSO Absorbers in Radio Selected Samples
Sara Ellison - University of Victoria
Paulina Lira - U. Chile Samantha Rix - ING Peter
Shaver - ESO Chuck Steidel - CalTech Jasper Wall
- UBC Lin Yan - IPAC
Max Pettini - Cambridge Chris Akerman -
Cambridge Chris Churchill - NMSU Pat Hall - York
U. Isobel Hook - Oxford Carole Jackson - ATNF
2
Survey Bias Due to Dust?
Theoretical motivation?
Vladilo Peroux (2005)

Churches, Nelson Edmunds (2004)
3
Survey Bias Due to Dust?
Simple calculation based on local extinction
laws. E.g., in the SMC
A150012.5 x E(B-V)
A150012.5 x N(HI)/4.4x1022

E.g., a z3 QSO with an intervening DLA of
N(HI) 1x1021 atoms/cm2 would suffer about 0.3
mags of extinction in the optical.
4
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 zlt1 emission line galaxy
abundances.
5
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 (gt0.25 Jy) and obtain complete optical
identifications. Obtain moderate resolution
optical spectroscopy for every QSO regardless of
optical magnitude.

Vital Statistics 66 QSOs zemgt 2.2 16.5 lt B mag lt
24 ?z56 19 (22) DLAs 1.8 lt zabs lt 3.8
6
?DLA, the mass density of neutral gas in good
agreement.
Ellison et al. (2001)
7
Statistics as a function of cumulative B band
magnitude. Seem to reach asymptote by about
B20 Eddington bias?
Small difference
N
Big difference
bright
faint
8
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 zlt1.5 select DLAs by MgII and FeII. DLA
candidate if EW(MgII, FeII)gt0.5 Å.
Rao Turnshek (2000)
9
Similar strategy to CORALS I optically complete,
radio selected sample. Line identification and
fit via automated search
Vital Statistics 73 QSOs ?z58.2 (0.6 Å) 47 MgII
systems 0.6 lt zabs lt 1.7 14 DLA candidates
10
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)
11
Inferences on n(z)DLA from 0.6ltzlt3.5
Ellison et al. (2004)
Assuming that 50 of our MgII selected DLA
candidates will be confirmed, we infer a number
density of DLAs at 0.6ltzlt1.6 consistent with
previous studies (but need UV follow-up to be
sure).
12
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 lt -1.0 ltZn/Hgt
-0.91 ltZn/Hgt -0.88
13
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.
14
ELGs ( )
Absorption galaxies( )
Schulte -Ladbeck et al (2003) Chen, Kennicutt
Rauch (2005) Ellison, Kewley Mallen-Ornelas
(2005)
Kobulnicky Zaritsky (1999) LillY, Carollo
Stockton (2003)
15
Optical - IR Colours of CORALS QSOs
Pat Hall, Paulina Lira
KS probability 25
Ellison, Hall Lira (2005)
16
Assume a fixed E(B-V) for every DLA
17
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) lt 0.05 (0.10).
18
E(B-V) lt 0.05 Log(NHI) Zn/H lt 20.46
Log(NHI) Zn/H lt 21 E(B-V) lt
0.17 (Prantzos Boissier 2000)
E(B-V) N(HI) x 10Zn/H/5.8e21
19
Summary

• WDLA 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 lt z lt
  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) lt 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.