Why do we need a VLST for studying QSO absorption lines?
So that
we can
go deeper…
Brilliant! A Genius!! sublim
e….
The Critics agree….
QSO absorption lines and a VLST
My top-three topics for QAL studies in the UV:
{detailed probing of the `cosmic web’ (Ly, weak metal lines)}
metallicity of nearby galaxies QSO absorption lines from QSOs (briefly)
What about metallicity?
• Measurements from QSO absorption lines show little evolution from z=4 to ~1
• The lack of evolution appears to be largely independent of column density – from Ly-forest clouds to Damped Ly
systems (DLAs)
What about metallicity?
Pettini (2003)
• DLAs in particular don’t approach solar at z=0
5.8 – 1.2 Gyr
13.5-5.8 Gyr
Kinda surprising…. expect `gas’ in the universe to be getting more enriched with time as galaxies evolve
and pollute
Let’s measure metallicities from nearby galaxies…
Advantages of looking at nearby galaxies:
•determine wide range of galaxy properties (21cm, X-ray, etc.)
•select low luminosity galaxies that are hard to see at higher-z
•check for fainter interlopers close to any selected galaxy
•easier to examine the galaxy’s environment (isolated, group, cluster)
QSO absorption lines from nearby galaxies
NGC 4319, v=1405 km s-1
Mrk 205, z=0.071
Time for one example…… to show what can be done and how
far we’ve got
Used HST + STIS to measure abundances towards
HS1543+5921 / SBS1543+593
With:
Ed Jenkins,
Todd Tripp,
Max Pettini
10’
HS 1543+5921z=0.807
DSS image
SBS1543+593
APO 3.5m, R, 15 min
QSO
HII region,z=0.009
(2700 km s-1)
star
Reimers& Hagen 98
HST STIS (clear), 800s
QSO
star
Spectroscopy
F(1200) = 2.6x10-15 pretty hard even with first-order gratings; fortunately CVZ object (15 orbits)
[S/H] = -0.4
Higher than
expected?
Compare Zs with DLA samples
Pettini (2003)
HS1543+5921
PG1543+489
List of other suitable pairs which can be observed at high spectral resolution
with HST:
Name of QSO Name of f/g galaxy
What could we do with a VLST?
•There are plenty of QSO-galaxy pairs in the sky! Just too faint!
•Go deeper, the number of interesting pairs becomes substantial
STIS echelle
What could we do with a VLST?
•There are plenty of QSO-galaxy pairs in the sky! Just too faint!
•Go deeper, the number of interesting pairs becomes substantial
•Already know some QSO intercept large N(H I) from 21cm maps [knowing HI a priori helps choose a target to measure Z]
•Four examples, just to show what we’re missing out on….
•VLA maps from Womble (1993)
•optical images from DSS
Gal: IC1746
cz = 5201 km/s
QSO: 0151+045
sep = 10 kpc
V=14.8?
F(1220)=3e-15
==30 STIS orbits
Nice edge-on galaxy probe outer disk
CaII:
N(H I) ~ 7-13 e19 cm/2
Gal: NGC3184
cz = 592 km/s
QSO: 1015+416
sep = 11 kpc
V=17.7 – 19.1?
F(1220)=?
chance to probe edge of huge HI envelope…
…compare to metallicties from HII regions…
CaII:
N(H I) ~ 4e19 cm/2
Gal: NGC470
cz = 2374 km/s
QSO: Q0117+031
sep = 10 kpc
V=18.2
F(1220)=?
NGC 474
19.9
CaII:
N(H I) ~ 6-10 e20 cm/2
Gal: NGC3079
cz = 1125 km/s
QSO: Q0957+558
sep = 8 kpc
V=17.4
F(1220)=1e-15
2.5 hrs, F658N, WFPC2Great way to study outflows!
CaII: N(H I) ~ 3 e20 cm/2
…or multiple QSOs!
Arp et al 2002
NGC 3628
(cz=843 km/s)
QSOs have ‘O’ mags between 18.7 and 20.7
4 X-ray sources
near M65
…or multiple multiple QSOs!
(narrow metal lines
instead of DLAs)
Summary• There are plenty of QSO-galaxy pairs known:
– though number with 21cm maps and/or CaII/NaI observations is smaller– more behind galaxy disks to appear with GALEX presumably– … and using SDSS photo-z techniques
• Need UV telescope that can:– reach 10 km/s resolution down to 20 mag
• factor of 250 in flux over STIS G140M echelle– large wavelength range to cover many lines
• important for ionization corrections• …. and for studying relative abundunace patterns which can be used
to infer history of metal production – how about…. a LiF coated mirror and do < 1100A as well? i.e.
HST+FUSE
• Payoff: – detailed inventory of galaxy metallicities in the local universe– for individual galaxies:
• ability to compare ISM abundances with values from HII regions• variations of metallicities as a function of radius if multiple
sightlines available• kinematics and ionization structure of gas in the outer regions of
galaxies– probes of the interface between a galaxy and the IGM
QSO absorption lines from QSOs
Suppose instead of probing galaxies, could probe QSOs instead.
• QSOs are ejecting large amounts of metal-enriched gas into the IGM might expect:– metallicity of the gas around a QSO to be high– ionization of the gas to be high– absorption to be complex from outflows mixing with the
IGM
• By observing many QSO-QSO pairs, should be able to track the enrichment of the IGM with radius
• Compare absorption from a f/g QSO with associated absorption (zabs ~ zem) in the QSO’s spectrum– learn more about associated systems, compare structure,
ionization, and metallicity variations over small scales.
Available QSO-QSO pairs
• SDSS provides a large # of QSO pair candidates with the b/g QSO < 20th
• Often require follow-up spectra of one of the pairs from the ground– both from collaborators: Joe Hannawi, Gordon Richards
and Michael Strauss
J0836+4841
z=1.71
z=0.66
4.1”,
19 h-1 kpc
J0836+4841
•zabs = zQSO = 0.66 in SDSS spec
•Likely to be a DLA!
•Probably host galaxy
•Perhaps high metallicity?
J2313+1445
zbg = 1.52
zfg = 0.79
sep = 6.4” or
32 h-1 kpc
3e-16
- outflowing gas from jet
-companion fuelling QSO
- unrelated galaxy in
QSO cluster
A future project
• QSOs appear to cause the same kinds of MgII systems that field galaxies cause
• Will need a VLST to do the kinds of spectroscopy of interest….