Download Document

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.