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Studying the Ly- Absorber/Galaxy Connection at 21cm
Jessica L. Rosenberg


Theorists View of Gas in the Low-z Universe

G. L. Bryan & M. L. Norman


Observers View of Gas in the Low-z Universe

Flux


Observers View of Gas in the Low-z Universe

Damped absorbers (NHI > 2x1020) can be observed at 21cm and are associated with galaxy disks

Lyman- limit systems (2x10 20 >NHI > 1017) are associated with galaxy halos
> I~

High column density forest absorbers (W>0.3A, NH 1013.5) may also be associated with galaxy halos

Lower column density forest is associated with galaxy halos

Lower column density forest is associated with large scale filaments


Why ask about the Relationship between Galaxies and Low-NHI Absorbers?



Test and interpret theoretical models



Constraint on formation and evolution of galaxies



How large are galaxy halos?



How large are absorbing structures?



Are absorbers probing galaxy halos or filaments?


Absorption in a Galaxy Group

van Gorkom et al. 1996, AJ 112, 1397


Absorption from Galaxy Outflow?

McLin et al.


Arecibo Studies



Work in progress - results are yet to come



Have used Arecibo to map 0.5 x 0.5 regions around 21 low column density absorbers in 4 AGN sight lines





Mass sensitivities of 2x106 - 5x108 M for the nearby absorbers choosen for study

Area surveyed is 140 kpc - 1 Mpc around these nearby absorbers






Parkes HI data cube using the Multibeam Receiver


3C 273 and He1228 Field


What will the Arecibo Multibeam Contribute?



Examine large scale structure as defined by gas- rich galaxies around absorbers

Ў

Deep large area surveys will provide better understanding of the large scale environment



Search for gas- rich LSBs near sightlines

Ў

Provide a complement to optical searches to remove bias towards stellar- dominated galaxies


T he F u t u r e

COS, the next UV spectrograph on HST is scheduled to be launched in late 2004

COS will have 10-30 times the throughput of present instruments

A much larger sample of low-z absorbers will be available for statistical study

There will be AGN probes of galaxy halos

We must tie our understanding of low column density gas in the local universe to the distribution of higher column density gas in galaxies