The Nancy Grace Roman Space Telescope's Wide Field Instrument (WFI) will have a large field of view (0.28 deg²), Hubble-like sensitivity and resolution over a wavelength range of 0.5 to 2.3 microns with broad-band imaging and slitless spectroscopy, and highly efficient survey operations, enabling survey speeds roughly 1000 times faster than achieved with Hubble. The observing program for the WFI on Roman will include both Core Community Surveys and General Astrophysics Surveys, defined by a community-led process and traditional peer-reviewed calls for proposals. The majority of observing time during the primary 5-year mission will be devoted to community-defined surveys.

The Core Community Surveys are the High Latitude Wide Area Survey, the High Latitude Time Domain Survey, and the Galactic Bulge Time Domain Survey. While Roman's Core Community Surveys are being undertaken in order to meet Roman's cosmology and exoplanet science requirements, the primary goal and responsibility of all the community-defined surveys is to enable a wide range of science investigations.

Galactic Bulge Time Domain Survey

The Galactic Bulge Time Domain Survey (GBTDS) is one of three core community surveys (CCS) to be executed by the Nancy Grace Roman Space Telescope. The primary science driver for the Roman GBTDS, and high priority goal for the field (as captured in the Astro2010 Decadal Report) is the demographics of cold exoplanets. This science will be enabled by obtaining high cadence (∼15 minute), high precision time series photometry using Roman's Wide Field Instrument (WFI) over a nominal ∼2-square degree field of view towards the Galactic bulge, in order to observe microlensing events caused by both bound and free- floating planets. The survey will have a total duration of ∼400 days spread over the 5-year prime mission.

Survey Component	Nominal Survey
Number of high-cadence seasons	6
Observing allocation per season (days)	68.5
Feasible season length (days)	72
Number of contiguous fields	6
Observing cadence (min)	14.8
Number of low-cadence seasons	4
Observing cadence (days)	5
Number of photometry snapshots	12
Number of grism snapshots	12

 

The proposed Nominal Field centers of the GBTDS. Click to enlarge the figure.

Galactic Longitude  l (deg) Galactic Latitude  b (deg) -0.622435 -1.200 -0.213461 -1.200 0.195513 -1.200 0.604487 -1.200 1.013461 -1.200 1.422435 -1.200 0.000000 -0.125

 

High Latitude Time Domain Survey

The High Latitude Time Domain Survey (HLTDS) is one of three core community surveys (CCS) that Roman will carry out during its nominal 5-year mission. The primary goal of the HLTDS is to use Type Ia supernovae (SNe Ia) as cosmological probes to measure the expansion history of the Universe. The light curves of SNe Ia are powerful "standardizable" candles: measurement of their peak luminosity, evolution time scale, and color can be used to infer reliable distances to these sources. As a result, SNe Ia offered the first evidence of the accelerating expansion of the Universe, commonly attributed to dark energy. With its large field-of-view, exceptional sensitivity, and near-infrared (NIR) band pass, Roman will be by far the most efficient discovery machine of SNe Ia at redshifts z > 1. Furthermore, the NIR transient sky has been less well explored to date, offering the opportunity for serendipitous discovery. The in-guide survey consists of a core component, a pilot component, and an extended component, with both wide-field imaging and prism spectroscopy.

Tier	Pointings   [North: South]	Area (deg2)   [North: South]	Pilot Component Time (days) [North:South]	Core Component Time (days) [North:South]	Extended Component Time (days) [North:South]
Wide Imaging	38 : 27	10.68: 7.59	3.73 : 2.58	33.99 : 23.53	0 : 0
Deep Imaging	7 : 16	1.97 : 4.50	2.17 : 4.96	19.79 : 45.23	2.17 : 4.96
Wide Spectroscopy	0 : 14	0 : 4.50	0 : 1.23	0 : 22.47	0 : 0
Deep Spectroscopy	0 : 2	0 : 0.56	0 : 0.70	0 : 12.86	0 : 0
Total Time (days)	...	...	15.36	157.84	7.12

The proposed In-Guide northern (ELAIS-N1; left) and southern (EDFS; right) fields of the HLTDS.

 

High Latitude Wide Area Survey

The High Latitude Wide Area Survey (HLWAS) has long been a central element of the Roman mission. One defining goal of the HLWAS is to probe the origin of cosmic acceleration with accurate and extremely precise measurements of weak gravitational lensing and galaxy clustering. While the cosmology objectives set the survey's most demanding technical requirements, a survey that meets those requirements supports an enormous variety of science investigations. The recommended in-guide survey consists of three tiers: a Medium Tier, a Wide Tier, and a Deep Tier. For cosmology, the Medium and Wide Tiers will yield measurements of ~6.2×10⁸ galaxy shapes for weak lensing, and grism spectroscopy in the Medium Tier will measure ~9.3×10⁶ galaxy redshifts at 1 < z < 2 and ~1.7×10⁶ galaxy redshifts at 2 < z < 3. The Deep Tier will provide the essential data for calibrating photometric redshifts and a wide range of shape measurements and spectroscopic incompleteness biases. (The parameters in the table below: n_eff is the weak lensing source density; N_shape is the number of galaxies with shape measurements; N_spec is the number of galaxies with secure spectral-based redshifts; n_spec is the comoving space density of galaxies with secure redshifts.)

Name	Area & Filters	Exposure times (sec)	Depth (AB mag/ erg cm-2 s-1)	Survey yields
Wide	2702 deg2 H	2x3x107 (H)	26.2 (H)	neff=26.7 arcmin-2 Nshape=260×106
Medium	2415 deg2 YJH + Grism	2×3×107 (YJH) 4×2×190 (Grism)	26.5 (Y)/26.4 (JH) 1.5×10-16 (Grism)	neff=41.3 arcmin-2 Nshape=360×106 Nspec=19.1×106 (tot)            9.3×106 (z=1-2)           1.7×106 (z=2-3) nspec=9.8×10-4 h3Mpc-3
Deep	19.2 deg2 WZYJHFK + Grism	+5×3×295  (WZYJHFK) +36×2×190 (Grism)	27.7 (ZY)/27.6 (J)/ 27.5 (H)/27.0 (F)/ 25.9 (K)/28.3 (W) 5.8×10-17 (Grism)	(for calibration)
Ultra Deep	5 deg2 YJH	+10×3×295 (YJH)	28.2 (YJ)/28.1 (H)	(for calibration)