The wide-field multiband imaging and slitless spectroscopy survey to be carried out by the Survey Space Telescope of China Manned Space Program

Abstract

<p indent=0mm>The 2 m-aperture Survey Space Telescope (also known as the China Space Station Telescope, CSST) is a major science project of China Manned Space Program. It is expected to start science operations around 2024 and has a nominal mission lifetime of <sc>10 years.</sc> During observations, CSST will fly independently in the same orbit as the space station while maintaining a large distance apart. It can dock with the space station for refueling and servicing as scheduled or as needed. With a Cook-type three-mirror anastigmat design, CSST can achieve superior image quality within a large field of view (FoV), which gives it an advantage for survey observations. Being an off-axis telescope without any obstruction, its point spread function (PSF) is not affected by diffraction of mirror support structures and is thus helpful for weak-lensing shear measurements. The radius encircling 80% energy of the PSF within CSST’s central 1.1 square degrees of FoV is required to be no more than 0.15″, including all wavefront errors in the optics and instruments and dynamical effects such as the telescope’s attitude control and vibration. CSST will be launched with 5 first-generation instruments including a survey camera, a terahertz receiver, a multichannel imager, an integral field spectrograph, and a cool planet imaging coronagraph. The survey camera is equipped with 30 9k×9k detectors for science observations, each with a filter or grating mounted above, a defocused 9k×9k detector for flux calibration in r band, 8 640×512 near-infrared detectors, fine guide sensors, and wavefront sensors. The primary task of CSST is to carry out a high-resolution large-area multiband imaging and slitless spectroscopy survey covering the wavelength range of <sc>255–1000 nm.</sc> Precision cosmology is the main science driver of the survey, and, therefore, the main area of sky selected for observation is at median-to-high galactic latitude and median-to-high ecliptic latitude. It will take the survey camera roughly <sc>7 years</sc> of operation accumulated over <sc>10 years</sc> of orbital time to image roughly 17500 square degrees of the sky in NUV, u, g, r, i, z, and y bands and take slitless spectroscopy of the same sky in 3 bands. The point-source 5σ limiting magnitudes in g and r bands can reach 26 (AB mag) or higher. The spectral resolution (<italic>R</italic>=<italic>λ</italic>/Δ<italic>λ</italic>) of the slitless spectrograph is specified to be on average no less than 200, and the wide-band-equivalent limiting magnitudes in GV <sc>(400–620 nm)</sc> and GI <sc>(620–1000 nm)</sc> bands will reach 23 or higher. In addition, a number of deep fields will be selected for more observations to reach at least one magnitude deeper than the wide-area survey. The combined advantage of its angular resolution, depth, wavelength range, capability of both imaging and spectroscopy and large-area sky coverage makes the CSST survey highly competitive, and, at the same time, its observations are also highly complementary with other large projects of its time, such as Vera Rubin Observatory, Euclid, and Roman Space Telescope. These projects will provide extremely rich datasets for potential breakthroughs in studies from the solar system to cosmology and beyond.