Galactic Survey observing frequency

Posts: 1
Joined: Fri Mar 07, 2014 1:01 pm

Galactic Survey observing frequency

Postby lsjouwer » Fri Mar 07, 2014 1:26 pm

In my opinion, the way to make a Galactic sky survey most beneficial to the entire Galactic community - from ISM through stars - and have the best legacy value, also for e.g. the transient observers, is to make a completely new contribution to the existing surveys (NVSS, CGPS, CORNISH, etc) by surveying the Galactic plane at roughly arcsecond angular resolution and at the highest observing frequency that is feasible. Unfortunately Q band seems too high to ask for... This will serve any Galactic study over multiple wavebands (radio, OIR, high-energy - ground and space based) and not focus on a single/limited research topic and/or group of investigators.

Posts: 3
Joined: Wed Oct 05, 2011 3:39 pm

Re: Galactic Survey observing frequency

Postby sbhatnag » Tue Mar 11, 2014 5:11 pm

Thinking in terms of "what is new and unique scientific product that VLASS can provide", I feel L or S-band or L+S-Band will be also a good frequency range covering a range of scientific topics. E.g., it gives a reasonable handle on questions involving physical properties via non-thermal wide-and continuum emission, polarization (RM synthesis), spectral index maps, and covers a host of "low-frequency" spectral lines (RRLs in particular) that probe low-density ionized medium. Spectral index destribution, mapping of the RRL emission (via stacking a number of transitions in the band) and perhaps better RM synthesis will be unique scientific products from such a survey which are otherwise hard to get via regular proposals. Combination of new wide-band wide-field imaging algorithms, instantaneous wide-band widths and simultaneous continuum+spectral line observations is demonstrably unique advantage that EVLA provides. Lower frequency ranges also have a higher survey speed (though lower bands also suffer from higher RFI nuisance).

The surveyed area and the required integration time can be achieved by multiple visits separated by a a couple of timescales which are interesting from a Galactic transient-studies point of view. Building the sensitivity and uv-coverage over time has other technical advantages as well.

The cost of computing in the Galactic plane (at any frequency band) is however, in my mind, an important parameter which will determine (if not force) the parameters of a Galactic survey. While this may be an issue for Technical Working Group, decisions for the GWC will probably not be totally independent of it.


Posts: 21
Joined: Mon Jul 18, 2011 3:49 pm

Re: Galactic Survey observing frequency

Postby lsjouwerman » Tue Mar 11, 2014 6:20 pm

Sanjay, see my posting on the science case topic on this forum

Posts: 13
Joined: Tue Mar 11, 2014 3:58 pm

Re: Galactic Survey observing frequency

Postby elisabethmills » Tue Mar 11, 2014 7:12 pm


As this is not my speciality, I would like to know more about how the community will use such data products as RM synthesis maps.
While I agree that they are unique (at least inasmuch as this is also science that LOFAR is doing at lower frequencies?), they are somewhat a specialist data product, and I am curious what their impact would be for the community, apart from a set of papers reporting these products.

Is the use the community will get out of these data enough to justify an L-band survey of ~1300 hours as a part of the VLASS rather than a PI-led project?
How much of what is possible at L-band is entirely unique from what has been done before or is already being done by PIs? (e.g, THOR is already doing simultaneous wide-band continuum + spectral line mapping, RRL stacking, and mapping HI and OH-- but perhaps without full polarization?)

Posts: 13
Joined: Tue Mar 11, 2014 3:58 pm

Re: Galactic Survey observing frequency

Postby elisabethmills » Tue Mar 11, 2014 7:18 pm

Another issue closely tied to the choice of frequency is the choice of array configuration.

Should a Galactic plane survey necessarily involve the GBT? Is D-configuration a must, both for single-dish combination and for imaging the extended ISM, or will a Galactic plane survey realistically be to shallow to consider spectral lines other than masers, for which point source sensitivity is the primary consideration?

Are multiple array configurations on the table?

Return to “Galactic Working Group”

Who is online

Users browsing this forum: No registered users and 1 guest