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Why do we need a VLST for studying QSO absorption lines?. So that we can go deeper…. Brilliant!. A Genius!!. sublime…. 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 a , weak metal lines)} 

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A Genius!!


The Critics agree….

qso absorption lines and a vlst
QSO absorption lines and a VLST

My top-three topics for QAL studies in the UV:

{detailed probing of the `cosmic web’ (Lya, weak metal lines)} 

metallicity of nearby galaxies

QSO absorption lines from QSOs (briefly)

what about metallicity
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 Lya-forest clouds to Damped Lya systems (DLAs)
what about metallicity1

13.5-5.8 Gyr

5.8 – 1.2 Gyr

Pettini (2003)

What about metallicity?

Kinda surprising…. expect `gas’ in the universe to be getting more enriched with time as galaxies evolve and pollute

  • DLAs in particular don’t approach solar at z=0

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)

NGC 4319, v=1405 km s-1

QSO absorption lines from nearby galaxies

Mrk 205, z=0.071

time for one example to show what can be done and how far we ve got
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


Ed Jenkins,

Todd Tripp,

Max Pettini



DSS image


HS 1543+5921





HII region,


(2700 km s-1)

APO 3.5m, R, 15 min


& Hagen 98




HST STIS (clear), 800s


F(1200) = 2.6x10-15 pretty hard even with first-order gratings; fortunately CVZ object (15 orbits)

[S/H] = -0.4

Higher than





Pettini (2003)

Compare Zs with DLA samples

what could we do with a vlst
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
what could we do with a vlst1
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



==30 STIS orbits

Nice edge-on galaxy probe outer disk


Gal: NGC3184

cz = 592 km/s

QSO: 1015+416

sep = 11 kpc

V=17.7 – 19.1?


chance to probe edge of huge HI envelope…

…compare to metallicties from HII regions…


Gal: NGC470

cz = 2374 km/s

QSO: Q0117+031

sep = 10 kpc



NGC 474



Gal: NGC3079

cz = 1125 km/s

QSO: Q0957+558

sep = 8 kpc




2.5 hrs, F658N, WFPC2

Great way to study outflows!

or multiple qsos
…or multiple QSOs!

NGC 3628

(cz=843 km/s)

QSOs have ‘O’ mags between 18.7 and 20.7

4 X-ray sources

near M65

Arp et al 2002


…or multiple multiple QSOs!

(narrow metal lines

instead of DLAs)

  • 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
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
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


19 h-1 kpc




j0836 48411
  • 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

  • - outflowing gas from jet
  • companion fuelling QSO
  • unrelated galaxy in
  • QSO cluster
a future project
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….