Galactic WG Summary so far (comments please!)

rlw@stsci.edu
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Joined: Mon Mar 03, 2014 6:42 pm

Re: Galactic WG Summary so far (comments please!)

Postby rlw@stsci.edu » Thu Apr 03, 2014 12:07 am

lsjouwerman wrote:I guess the key phrase here is "for quite some time in the future". I don't think we should use a VLASS allocation of a few thousand hours to do - and potentially can be done much better - what is in the pipeline with SKA, etc, even if that has to wait another 10 years. Better try to go for something that otherwise never ever will happen anywhere.


I'll repeat this here in case people are not reading the Programmatics group.

Just one comment on this: while I agree that the long-term value and impact of a JVLA survey should be one criterion for defining its impact, we have a clear counterexample to the argument that the survey must be "absolutely unique" compared to any existing or planned future survey. Just look at the NVSS and FIRST! They were carried out at the same time, with the same telescope and receivers. They observed at the same frequency. The sky covered by FIRST was also completely covered by NVSS. FIRST is only about 2.5 times deeper than NVSS for point sources, and the sensitivity difference is even less for extended sources.

And yet both FIRST and NVSS have thrived, and both have had a demonstrably large impact on radio and multi-wavelength science. How can that be?

The answer is that the higher resolution of FIRST (with a beam 8 times smaller than NVSS) is essential in doing cross-matches to SDSS and other deep imaging observations. Science with NVSS depends on its larger sky coverage and on the more accurate fluxes that come from a low-resolution survey.

Even though these surveys were carried out and released essentially simultaneously, and even though they had many characteristics in common, it took only one difference --- resolution --- to distinguish them and make them both widely used to this day.

So while I agree that it is important to consider the VLASS survey in the context of current planned surveys and not to duplicate those surveys, I definitely do not agree that it is necessary to push to the extreme limits of the JVLA parameter space (e.g., very high frequencies and the highest possible spatial resolution) in order to distinguish it from coming low-frequency, low-resolution surveys by the SKA pathfinders.

gsivakoff
Posts: 17
Joined: Tue Mar 25, 2014 11:28 am

Re: Galactic WG Summary so far (comments please!)

Postby gsivakoff » Thu Apr 03, 2014 11:36 am

rlw@stsci.edu wrote:
And yet both FIRST and NVSS have thrived, and both have had a demonstrably large impact on radio and multi-wavelength science. How can that be?

The answer is that the higher resolution of FIRST (with a beam 8 times smaller than NVSS) is essential in doing cross-matches to SDSS and other deep imaging observations. Science with NVSS depends on its larger sky coverage and on the more accurate fluxes that come from a low-resolution survey.

Even though these surveys were carried out and released essentially simultaneously, and even though they had many characteristics in common, it took only one difference --- resolution --- to distinguish them and make them both widely used to this day.

So while I agree that it is important to consider the VLASS survey in the context of current planned surveys and not to duplicate those surveys, I definitely do not agree that it is necessary to push to the extreme limits of the JVLA parameter space (e.g., very high frequencies and the highest possible spatial resolution) in order to distinguish it from coming low-frequency, low-resolution surveys by the SKA pathfinders.


I think you raise an important point about the complementary nature of FIRST/NVSS. My take away as I think about VLASS and the other sky surveys is to find the properties that would be complementary. I definitely think we want to push the VLASS to better resolution than can be achieved with the other surveys for the direct analogue to FIRST. Thus, I do see the need to push the VLASS towards higher resolution, like 1-2" beams. I am also seeing that combining both a low and high frequency aspect of VLASS will have complementary characteristics, both between the sub-surveys and between other surveys.

By the way, I think I have a decent acronymn for such a Galactic effort, working off of Lorant's GUTS, Galactic kU and S-band Thermal Observer (GUSTO)


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