Community Science with the Nancy Grace Roman Space Telescope

K. Gilbert (kgilbert[at]stsci.edu) and N. Reid (inr[at]stsci.edu)

Executive Summary

A survey of the astronomical community reveals extensive interest in using observations with the Nancy Grace Roman Space Telescope for investigations across a wide range of scientific themes. Astronomy community interests in the Roman Space Telescope span all scales from solar system and exoplanet science, through stellar populations, Galactic science, and nearby galaxies to far-field cosmology, with a particular emphasis on transient phenomena. Roman's science program will reflect these diverse interests, and will directly benefit from community participation at all levels in designing the observations, with open access to all data. As the Science Operations Center, the Institute has a key role in ensuring strong community participation in defining the overall observing program and supporting the ensuing broad array of science investigations.

Introduction

The Nancy Grace Roman Space Telescope, planned for launch in the mid-2020s, will continue the legacy of NASA's Great Observatories. This survey telescope is equipped with a large-format camera for wide-field imaging and low-resolution grism and prism spectroscopy from 0.5 to 2.0 microns, together with a technology-demonstration coronagraph. With approximately 200 times the field of view of the WFC3/IR camera on Hubble Space Telescope and comparable sensitivity and angular resolution, the Roman Space Telescope will open a high-resolution wide-field window on the infrared universe (Fig. 1).

ROMAN's Field of View
Figure 1: The field of view of Roman's Wide Field Instrument superimposed on a ground-based image of the Eagle Nebula (M16), with an inset Hubble observation of the central star-forming region superimposed. The 18 detectors comprising the Wide Field Instrument will obtain images that cover an area nearly 100 times that of Hubble's ACS camera, and more than 200 times that of Hubble's WFC3/IR camera, with comparable resolution. Survey responses indicated a high level of community interest in Galactic targets. The ground-based image combines an image obtained by the 0.9 m telescope at NSF's Kitt Peak National Observatory and an image by Liam Murphy. Credits/Acknowledgements: L. Hustak (STScI), L. Murphy, T. A. Rector (NRAO/AUI/NSF and NOAO/AURA/NSF) and B. A. Wolpa (NOAO/AURA/NSF).

Roman's observing program will comprise a mix of Core Community Surveys (CCS), each enabling multiple scientific investigations, and General Observer (GO) targeted surveys. The CCS, which will be optimized based on community input, are anticipated to include:

  • A high galactic-latitude survey capable of exploring the nature of dark energy;
  • A survey for extragalactic transient sources capable of detecting and characterizing supernovae; and
  • A time-series survey of the Galactic Bulge capable of detecting exoplanet microlensing events.

All data, both CCS and GO, will be non-proprietary and available for Archival Research (AR) programs. All of the investigation teams will be selected through competitive review.

The Space Telescope Science Institute is the Science Operations Center for Roman. STScI will plan, schedule, and carry out observations; process and archive mission datasets; and engage and inform the astronomical community and the public. The Institute is working to design and develop science systems for Roman in collaboration with other Mission partners, including NASA's Goddard Space Flight Center, which manages the mission; the Jet Propulsion Laboratory (JPL), which is developing the Coronagraphic Instrument; and the Infrared Processing and Analysis Center (IPAC)/Caltech, which will support the Coronagraphic Instrument, process spectroscopic and microlensing Wide Field Instrument (WFI) data, conduct the GO/AR/Theory proposal calls, and engage the community and the public in these areas as the observatory's Science Support Center.

The STScI Director established the Roman Space Telescope Advisory Committee (RSTAC) to advise on all aspects of STScI's role for the Roman mission. Following the RSTAC's advice, the Institute circulated a survey to the community earlier this year to solicit input on the anticipated science drivers for the CCS and GO programs. This article summarizes the feedback generated by that survey.

Demographics of the respondents

The survey was circulated to the community in late May 2020 with responses requested by June 15th; 572 responses were submitted by the deadline. The demographic distribution of the respondents is shown in Figure 2. The 23 "other" respondents included undergraduates, research staff at observatories and government facilities, and emeritus astronomers.

The respondents include 93 current members of Roman Space Telescope Science Investigation Teams (SITs), approximately half of the SIT membership, and 16% of the total survey respondents. In general, the priorities expressed by the SIT members are consistent with those from the broader community. We summarize some examples illustrating the convergence below, as well as the responses to the questions.

 

Demographic chart
Figure 2: Demographics of survey respondents.
Community surveys
Figure 3: Interest in candidate Core Community Surveys.

 

Building the Core Community Surveys

The first questions centered on community support for different types of surveys. Almost half of the respondents expressed interest in a high galactic-latitude imaging survey, while a survey of nearby galaxies and/or an ultra-deep high-latitude survey also garnered strong interest (Fig. 3). Looking beyond the listed options, other suggestions included a high galactic-latitude spectroscopic survey, surveys of star clusters and star-formation regions, detailed surveys of specific nearby galaxies (including the Magellanic Clouds), additional time-series observations, and a coronagraphic survey of nearby stars.

Options for the high-latitude survey

While a high galactic-latitude survey is highly likely to constitute one CCS (Fig. 4), the exact form remains to be decided, and it is possible that a multi-tiered approach could be adopted. Respondents were asked to indicate their preferences among four generic options:

  • A wide, shallow survey, covering ~10,000–20,000 sq. deg. to AB ~ 24 magnitude;
  • A medium-wide, moderate-depth survey, covering ~2,000 sq. deg. to AB ~ 26.5;
  • A narrow, deep survey, covering ~20 sq. deg. to AB ~ 28; and
  • A pencil beam, ultra-deep survey, covering ~1 sq. deg. to AB ~ 30.
Roman's field of view
Figure 4: The field of view of Roman's Wide Field Instrument superimposed upon a ground-based image of galaxy cluster Abell 246, with an inset Hubble observation of NGC 1275 superimposed. A single Roman pointing will cover an area equivalent to the area of the largest galaxy survey undertaken with Hubble (CANDELS, PIs Faber and Ferguson; Grogin et al. 2011; and Koekemoer et al. 2011). The ground-based image combines data from the Digitized Sky Survey and an image by Petri Kehusmaa. Credits and acknowledgements: L. Hustak (STScI), Digitized Sky Survey, and P. Kehusmaa.

The results are shown in Figure 5, which plots separately the responses from the members of the SIT teams and the wider community. Overall, there is concordance, with support for all four options but a preference for the wider-angle surveys.

Types of beams
Figure 5: Preferences for the form of the high-latitude survey.

Roman Space Telescope characteristics

Roman will offer observations with a range of key characteristics, including a wide field of view, high angular resolution, a stable point-spread function, high sensitivity, and the availability of multiple filter passbands and grism spectroscopy. Respondents were asked to provide feedback on which aligned most closely with their scientific interests. Figure 6 shows that the community values all of those characteristics.

Roman Space Telescope characteristics
Figure 6: Survey characteristics.

Scientific interests

The Roman Space Telescope has its origins in the 2010 Decadal Survey and was conceived as a means to address specific questions in cosmology/dark energy and exoplanet science. With a Hubble-sized mirror and equivalent resolution, a field of view more than 200 times that of Hubble's current IR camera, and survey speeds up to 1000 times faster than Hubble, Roman has a far greater potential grasp—one equivalent to a Great Observatory. Figure 7 shows there is strong interest in applying Roman's capabilities over the full gamut of observational astronomy. Other categories highlighted in write-in responses included AGN/QSOs, gravitational lensing, kilonovae and brown dwarfs. Again, we note that there is general concordance between the interests of the SIT members and the broader community.

Scientific interests
Figure 7: Key science areas for Roman.

Transient science

Transients will represent a key component for Roman, which will serve as a space-based, near-infrared complement to the ground-based, optical Vera Rubin Observatory now under construction. One hundred fifty-one respondents (26.5%) indicated that time-series observations are an essential element of their science, while a further 193 (33.9%) indicated that the observations are beneficial. Breaking down those observations, interests span the full range from seconds to months in cadence and days to years in duration (Figs. 8 & 9).

Chart displaying observational cadence
Figure 8: Observational cadence.
Chart displaying observational duration
Figure 9: Observational duration.

 

As one might suspect, the cadence and duration are driven by the science goals for a particular program:

  • High cadence (minutes), very short duration (days) observations are required for follow-up observations of energetic phenomena such as gamma-ray bursts and kilonovae;
  • High cadence (minutes), short duration (1–3 weeks) observations are required for asteroseismology;
  • Moderate cadence (tens of minutes to hours), moderate duration (4–8 weeks) observations are required for monitoring sources such as variable stars and AGN; and
  • Low cadence (months), long duration (years) observations are tied to long-term astrometric investigations.

Community participation

Respondents were asked to estimate the likelihood that they would consider a formal role in developing a CCS (Fig. 10), and that they would submit a GO proposal or an archival research proposal as either a Principal Investigator, co-Principal Investigator, or co-Investigator (Figs. 11–12). Approximately 60–65% of the survey respondents indicated that they expect to participate in a GO or archival program.

Participation in a Core Community Survey program
Figure 10: The likelihood that survey respondents will consider a formal role in developing a Core Community Survey.
Participation in a GO program
Figure 11: The likelihood that survey respondents will participate in a GO program.
Participation in an archival program
Figure 12:  The likelihood that survey respondents will participate in an archival program.

 

Parameters for typical GO programs

The Wide Field Instrument on Roman will offer a field of view of approximately 0.28 square degrees. Given those parameters, respondents were asked to estimate the approximate contiguous sky coverage for a GO proposal likely to be required to tackle their prospective GO science investigations. Most respondents favored programs covering a relatively limited area, with one or two pointings, albeit covering multiple targets in the majority of cases (Fig. 13). Similarly, close to 65% of the respondents are considering submitting either small-scale (<50 hours) or medium-scale (50–200 hours) GO programs (Fig. 14).

Areal coverage anticipated for GO programs
Figure 13: Areal coverage anticipated for GO programs.
Anticipated scale of GO proposals
Figure 14: Anticipated scale of GO proposals.

Other factors

Finally, respondents were given an opportunity to provide input on other factors that they believed are important for consideration in specifying the broad attributes of the Core Community Surveys and the GO/AR program. Some 115 responses were received, and Figure 15 collects some themes from those responses.

Common themes from the free format responses
Figure 15: Common themes from the free format responses.

Summary

  1. The survey results show clear recognition of Roman's capabilities to address a broad range of science themes, and strong interest from a broad cross-section of the community in using Roman to investigate astrophysical phenomena on all scales. As the Science Operations Center, STScI has an obligation to provide systems that will enable the astronomical community to achieve their far-ranging science goals.
  2. The survey also shows strong interest in continued and broad community involvement in developing the CCS. The Institute will work with our Roman Mission partners to develop mechanisms for community engagement that can directly shape the number and range of investigations enabled by the CCS data.
  3. A majority of survey respondents envisage Roman as a successor to Hubble and NASA's other Great Observatories, with the expectation of submitting small- and medium-scale GO observing programs. At the same time, large-scale programs and surveys designed with scientific breadth in mind have the capability to open up numerous complementary investigations over a wide range of scientific topics. The Institute will work with our Roman Mission partners to engage the community in exploring how best to optimize the design of the CCS programs to maximize the overall scientific return.