Fwd: LBA possibilities...
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From: <John.Dickey_at_email.protected>
Date: Fri, 21 May 2010 17:12:22 +1000
Dear Folks,
I thought we should all think about the point Frank raises in his
email below, so with his permission I'm forwarding it. Frank did a
lot of work on VLBI of high redshift HI lines back in the 80's and
90's. He is certainly right that he ASKAP FLASH survey will turn up a
lot of candidates for follow-up with the LBA.
cheers,
jd
Begin forwarded message:
>From: Frank Briggs <fbriggs_at_mso.<!--nospam-->anu.edu.au>
>Date: 21 May 2010 4:41:40 PM
>To: Philip.Edwards_at_csiro.<!--nospam-->au
>Cc: Elaine Sadler <ems_at_physics.<!--nospam-->usyd.edu.au>, John.Dickey_at_utas.<!--nospam-->edu.au
>Subject: LBA possibilities...
>
>
>Something that the LBA community might do well to consider (in the
>context of ASKAP spectral line surveys) is whether the array (or a
>significant subset) can be equipped with a receiver set that would
>allow follow-up of redshifted HI and OH absorption systems that will
>result from the supported ASKAP survey that Elaine is coordinating.
>So... 500-1400MHz.
>This could be very interesting to obtain structural info for both
>types of absorbers (associated with AGNs, as coccoon around GPS and
>CSO, for example, and with intervening galaxies). For the latter
>systems, the greatest interest is likely to be in absorbers in front
>of extended radio galaxies, rather than compact background sources,
>so shorter baselines on the 50-100km are possibly more important
>than long ones. For the associated absorbers, all lengths are
>good.
>
>One issue that may be somewhat fatal is that, at these frequencies,
>it's hard to feed shaped reflectors that ordinarily rely on Cassegrain
>feeds.
>
>Further comment: You can actually do some interesting work with just
>a limited number of antennas equipped with broadband receivers. Once
>you have some good continuum maps at standard frequencies, you can
>use those to model the continuum structure, and because you only
>see absorption where there is continuum, the only free parameter in
>modelling the VLBI spectra is the optical depth against the model
>components. (A little old-fashioned and harps back to the days of
>the Caltech package, but it can be effective.)
>
>cheers,
>Frank
>
Received on 2010-05-21 17:12:56
Date: Fri, 21 May 2010 17:12:22 +1000
Dear Folks,
I thought we should all think about the point Frank raises in his
email below, so with his permission I'm forwarding it. Frank did a
lot of work on VLBI of high redshift HI lines back in the 80's and
90's. He is certainly right that he ASKAP FLASH survey will turn up a
lot of candidates for follow-up with the LBA.
cheers,
jd
Begin forwarded message:
>From: Frank Briggs <fbriggs_at_mso.<!--nospam-->anu.edu.au>
>Date: 21 May 2010 4:41:40 PM
>To: Philip.Edwards_at_csiro.<!--nospam-->au
>Cc: Elaine Sadler <ems_at_physics.<!--nospam-->usyd.edu.au>, John.Dickey_at_utas.<!--nospam-->edu.au
>Subject: LBA possibilities...
>
>
>Something that the LBA community might do well to consider (in the
>context of ASKAP spectral line surveys) is whether the array (or a
>significant subset) can be equipped with a receiver set that would
>allow follow-up of redshifted HI and OH absorption systems that will
>result from the supported ASKAP survey that Elaine is coordinating.
>So... 500-1400MHz.
>This could be very interesting to obtain structural info for both
>types of absorbers (associated with AGNs, as coccoon around GPS and
>CSO, for example, and with intervening galaxies). For the latter
>systems, the greatest interest is likely to be in absorbers in front
>of extended radio galaxies, rather than compact background sources,
>so shorter baselines on the 50-100km are possibly more important
>than long ones. For the associated absorbers, all lengths are
>good.
>
>One issue that may be somewhat fatal is that, at these frequencies,
>it's hard to feed shaped reflectors that ordinarily rely on Cassegrain
>feeds.
>
>Further comment: You can actually do some interesting work with just
>a limited number of antennas equipped with broadband receivers. Once
>you have some good continuum maps at standard frequencies, you can
>use those to model the continuum structure, and because you only
>see absorption where there is continuum, the only free parameter in
>modelling the VLBI spectra is the optical depth against the model
>components. (A little old-fashioned and harps back to the days of
>the Caltech package, but it can be effective.)
>
>cheers,
>Frank
>
Received on 2010-05-21 17:12:56