Galactic Survey Design

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Joined: Tue Mar 11, 2014 3:58 pm

Galactic Survey Design

Postby elisabethmills » Mon Mar 17, 2014 5:17 pm

In an effort to start converging on a survey strategy, I would like to encourage people to put forward survey designs for discussion.

To quote Rachel: "The type of survey being envisioned may be a uniform one or tiered, can total to around 10,000 hours, and should be completable in about 5 years time. It should be more ambitious than something that could be done in up to 2000 hours (this could be proposed through the normal VLA proposal process)."

So far, I know of one such proposal that has been made for the Plane: GUTS, from the Sjouwerman et al. white paper. I believe that the Bhatnagar et al. white paper presents a second (although, one possible implementation of that survey is only 1300 hours of VLA time, and could be done as PI science?). Are there others to consider?

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

Re: Galactic Survey Design

Postby elisabethmills » Mon Mar 17, 2014 5:21 pm

Ku-band Galactic plane survey (GUTS; Sjouwerman et al. white paper)

WHERE will the survey coverage be:
-The entire observable northern Galactic plane (l=-20 to +260, b +/-5), matching the area of existing surveys from Spitzer, WISE and Planck, at a comparable 1'' resolution. The continuum sensitivity will be 130 microJy**

WHAT's new:
-Previous VLA surveys of the Galactic plane have been conducted at L and C bands; this would be the first Galactic plane survey conducted at high frequencies primarily sensitive to thermal sources, at arcsecond resolution***

-The coverage, resolution, and imaging quality of the data should make this the definitive high-frequency survey of the Galactic plane for the conceivable future. (MEERGAL may offer complementary coverage of the southern Galactic plane in the next decade, but likely at lower resolution)

This survey will yield:
--A catalog of thermal sources for follow-up, including planetary nebulae, AGB stars, and compact HII regions.
--Recombination line detections of many of these sources via stacking of the 10 lines in the band, free from pressure broadening.
--A baseline 'snapshot' of continuum emission in the plane for time-domain studies, including transient detection.
--A homogeneous, sensitive survey for the 12 GHz methanol maser, a tracer of early stages of star formation
--A significantly less-biased search for optically thick free-free emission sources, such as hypercompact HII regions
--A combination of high discovery and legacy value, as sensitive surveys of the plane at these frequencies have not previously been conducted, and there is no other existing or planned (northern-hemisphere) instrument capable of doing so.

WHO will benefit:
-Time-domain and transient studies will benefit from having a high-resolution baseline image of the Galactic plane continuum
-Non-radio observers will benefit from having a catalog of high-frequency (thermal) radio sources, at a resolution matched to existing infrared survey data, over the entire observable plane, enabling searches for radio counterparts.
-Radio observers will benefit from having ancillary data anywhere they might look in the Galactic plane
-High-frequency radio observers will benefit from a new catalog of high-frequency calibrators in the plane.

WHY do it now?
-The infrared and X-ray catalogs which these data will be compared to already exist; this survey does not depend upon the completion of future projects to be relevant

-Finding high-frequency calibrators is essential for efficient and successful high-frequency observing with the VLA and ALMA. yielding an immediate benefit to the observing community at the start of JVLA operations.

-The timing of the next array configurations (if they remain unchanged) is ideal for beginning the survey with observations of the inner galaxy, and following it up with observations of the northern plane in the next configuration.

-Aside from the maturation of on-the-fly-mapping, which will be needed by almost any aspect of the VLASS, completion of this survey and release of final data products does not depend upon the development of new software or algorithms for the data procession and analysis.

WHEN will it be done?
- As proposed in the Sjouwerman et al. white paper, observations would take ~3200 hours.
-If these observations were spread over 5 years (yielding completion in early 2020), the survey would impact less than 10% of the total time available to general observing.

HOW will it impact the community of VLA observers?
-These observations can be conducted in C-array, which is less oversubscribed than A-array (and offers less unique capabilities to observers than either A or D arrays)
-Observations will also be spread over LST, so will not disproportionately impact oversubscribed LST toward the inner galaxy.
-Observations can be conducted in relatively poor weather, so will not compete for the best-weather observing time.

Strengths: Uniqueness, legacy value, sensitivity to thermal emission, comparable resolution to other wavelengths
Weaknesses: Not sensitive to synchrotron emission. Frequency is not optimized to observe an ISM tracer (other than the 12 GHz methanol maser)

**Ku has the highest instantaneous continuum sensitivity of all of the VLA bands, including both X (lower frequency) and K (higher frequency)
***The GBT GPA survey was also conducted at 14 GHz, but with 400'' resolution; AMIGPS is also currently being conducted in Ku band, with ~arcminute resolution

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