Ancillary science

 
Taipan Ancillary Science
The Taipan Galaxy Survey (http://www.taipan-survey.orgis an optical spectroscopic survey of the entire Southern sky. We are inviting expressions of interest for ancillary science. This page provides the full background and context including the details of the Taipan system, and the instructions for applications. Please carefully read all the information below before submitting an application. Please feel free to coordinate your application with a Taipan team member. The collaboration membership list is available from the team website.
 
The Taipan Galaxy Survey and the Taipan system
The planning and development for the Taipan galaxy survey is well underway. We currently expect survey operations to begin mid-2017. The Taipan observing system is a 150 (upgradable to 300) fibre multi-object spectrograph on the 1.2 m UKST, with a very wide field of view: 6 degrees in diameter. Taipan spectra span the visible spectru(370-870nm) with a resolution around R~2000 (similar to SDSS and GAMA). 
 
The ultimate vision for the Taipan galaxy survey is to obtain near-total (99+%) spectroscopic redshift completeness for an (optical) flux-limited sample of galaxies across the entire Southern sky. While the final details of sample selection are still being revised, the main galaxy sample is likely to be < ~17.0 (i.e., SDSS-like), with a footprint of Dec < +15, and |b| > 10 to avoid the Galactic plane (i.e., around 2 to 2.5 pi steradians).
 
The key scientific goals of the Taipan galaxy survey are: 
  • Determination of the Hubble parameter to within 1%, from z < 0.3 measurements of the BAO signature in the galaxy clustering power spectrum. 
  • Bulk flow measurements, from Fundamental Plane distance and peculiar velocity determinations for ~60000 early-type galaxies. 
  • Detailed studies of the life cycle of baryons within galaxies as a function of mass and environment, incorporating panchromatic data from Wallaby, WISE, VHS, etc.
 
Background to this call
Taipan sits in stark contrast to earlier multiobject survey ancillary science programs, such as 6dFGS, that used "spare fibres", which otherwise were not able to be used for science. Because of our relatively low fibre number compared to our target number density, Taipan is almost maximally efficient, with main targets able to be allocated to all fibres until essentially the very end of survey operations. As a result, Taipan ancillary science arising from additional targets that are not part of the main survey comes at a direct cost to main survey operations. We distinguish this from "priority science" that can be achieved through prioritising main survey targets or fields, which does not add extra cost to the overall survey. 

The Taipan team is keen to support a Priority and Ancillary Science program, recognising the value of enabling a broader range of science and providing opportunities for a wider community to participate in the Taipan program. We expect main survey operations to begin in mid-2017, and most approved ancillary science programs to begin in early 2018. 

In order to account for the cost to the main survey, we ask all ancillary science programs that request additional (non-main-survey) targets to provide in-kind or cash contributions as appropriate. All publications arising from ancillary science programs will fall under the Taipan survey publication policy, to give the broader Taipan team the opportunity to provide and be recognised for scientific contributions. 

 
Priority and Ancillary science considerations
Within our existing survey framework, we see three possible avenues for enabling complementary science projects with Taipan spectroscopy. 
1. Taipan will prioritise some field(s) or target(s) for early completion (Priority Science); and/or 
2. Repeat observations of some targets for monitoring, or additional S/N (Ancillary Science); and/or 
3. An expansion of the Taipan sample to include additional targets/samples (Ancillary Science).
We stress that only the first option (i.e., priority targeting of particular fields or targets that are within the nominal Taipan sample) comes at no additional cost to the main survey. Because Taipan will occupy essentially all of the dark time on the UKST for the ~5 year duration of the survey, we have a degree of freedom and flexibility in choosing how to schedule or prioritise which targets/fields to observe. These flexible scheduling structures allow us to specify targeting priorities on the basis of position, observable properties (e.g. colour, brightness), or derived properties (e.g. redshift, line flux, equivalent width). To the extent that it is possible to schedule these fields/targets, adjusting the priorities does not have a large impact on the final content of the survey, or of the survey duration.
 
We also stress that the second and third options (i.e. expanding the sample to include additional targets, or spending extra time on selected main survey targets) are less straightforward, and come at additional cost, for a few reasons:
  • We do not expect to be in a position to observe "spare fibre" targets, that is we do not expect to run short on main survey targets, until relatively late in the survey. Further, our simulations indicate that there will be a significantly smaller proportion of "spare fibres" than earlier surveys such as 6dFGS or GAMA. While we see the value in allocating some fraction of main survey time for these kinds of complementary projects, there is nonetheless significantly less scope than earlier programs to allocate fibres to extra targets without compromising our main survey goals.
  • With the large field of view (6 deg. in diameter), and the relatively low fibre density (150 fibres over ~28 sq deg.), any ancillary science using additional targets will need to operate with a relatively low sky density (on the order of 1-10 / sq. deg.) to be able to be folded into Taipan observing without significant impact on the main survey.
  • The Taipan main survey will target a magnitude-limited sample down to what can be reasonably observed with the 1.2m UKST, there is a narrow range of ancillary science additional targets where (1) there can be a reasonable prospect of obtaining useful data, and (2) that target is not already within the main survey. Potential targets would need to be brighter than our limit, but not galaxies (such as quasars, for example), or fainter than our limit, but with strong emission lines (perhaps radio or UV detections).
 
Additional information on survey operations
The thing that sets Taipan apart is the rapid reconfigurability of the autonomous starbug fibre positioning robots, which lets us target many, many more fields per night than other MOS facilities. Because Taipan is a many-pass survey, it is possible to re-visit individual targets multiple times in order to build up signal-to-noise.
Taipan spectra are expected to be taken in blocks of 3 x 5 minute integrations. The data are processed immediately, and tested against our data requirements. If main survey specifications are met, then the object is removed from the target pool; otherwise, it will be reobserved at a later time and continue to be reobserved with new spectra coadded into a final spectrum, until specifications (primarily on S/N) are met.  
This approach allows for different data requirements for different targets within the larger survey sample.  For example, in order to get the robust velocity dispersion measurements needed for Fundamental Plane distance measurements, we require a median S/N>10, but only for those galaxies that we identify as being early types at z < ~0.1.  Similarly, we will have a higher continuum S/N threshold for lower redshift galaxies, which are the focus of our galaxy evolution science, than for higher redshift galaxies, where our main interest is redshifts for BAO science.
It is thus possible for us to observe targets in multiples of 3x5 minute blocks, until some specification (a "success condition") is met. This specification can be phrased in terms of, e.g., integration time, redshift success, line/continuum S/N, or any other quantity that can be derived/inferred from the spectra, and any combination of these quantities. While not part of the existing Taipan data pipeline, ancillary science programs might consider different success conditions that the ancillary science team would be asked to help develop within the main survey pipeline framework.
 
Application process
Please send your expression of interest, limited to 1 page, to Andrew Hopkins (ahopkins@aao.gov.au) by 31 March 2017. The EoI should include the following: 
  • Whether you are requesting Priority Science (i.e., want to have the Taipan survey team prioritise an existing survey field or targets, please provide details), or Ancillary Science (i.e., you have an additional list of specific targets, or target types). 
  • If the latter, what kind and level of contribution you will agree to commit to, noting that the value of the contributions will be a factor in defining which ancillary programs are pursued:
    • direct effort on Taipan team activities as specified by the Taipan galaxy survey executive; 
    • a cash contribution described further below, but broadly at a level of $1000 per thousand spectra to offset UKST operational costs borne by the Taipan survey team; 
    • a combination of the above.
  • A short scientific justification (a couple of paragraphs) that demonstrates why the Taipan facility is the most suitable for your science, and shows the significance and impact of your expected results.

For cash contributions, the cost is basically $1 per spectrum but with the following requirements:

  • A minimum cash contribution of $5000 is required before it becomes cost effective for the Taipan team to adopt the necessary overheads. For samples smaller than 5000 targets, a minimum cost of $5000 is still required, although for very small samples the Taipan executive may be approached to consider waiving the cost.
  • For larger samples, a cost of $1000 for each additional thousand spectra or fraction thereof, so that costs increase in increments of $1000.
  • A "spectrum" here is defined as the output of a standard Taipan visit (presently anticipated to be 3 exposures of 5 minutes = 15 minute exposure in total). If ancillary science requests want longer exposures (multiple visits on a single target) each 15 minute dataset counts as a "spectrum" (so, e.g., a 60 minute exposure on a single target would be charged as 4 "spectra", even if subsequently combined into a single ancillary science spectrum). Shorter exposures (<15 min), if needed and we can accommodate them, would still count as a single "spectrum".
  • The charge is for spectra requested and targeted, not for spectra delivered, although the Taipan team will make all reasonable efforts to deliver on what is requested. This is because the impact on the main survey is the same whether or not we successfully acquire an ancillary spectrum, and multiple attempts would increase the impact on the main survey. (So, weather losses, for example, will impact ancillary science to the same degree as main survey targets.) The Taipan team can of course be requested to try again for further payment.
The Taipan executive will review EoIs during April 2017, contacting proposers with requests for more detail as needed. The Taipan executive will contact proposers with outcomes by June 2017.