SPHEREx: an all-sky NIR spectral survey

Abstract

SPHEREx, a mission in NASA's Medium Explorer (MIDEX) program recently selected for Phase-A implementation, is an all-sky survey satellite that will produce a near-infrared spectrum for every 6 arcsecond pixel on the sky. SPHEREx has a simple, high-heritage design with large optical throughput to maximize spectral mapping speed. While the legacy data products will provide a rich archive of spectra for the entire astronomical community to mine, the instrument is optimized for three specific scientific goals: to probe inflation through the imprint primordial non-Gaussianity left on today's large-scale cosmological structure; to survey the Galactic plane for water and other biogenic ices through absorption line studies; and to constrain the history of galaxy formation through power spectra of background fluctuations as measured in deep regions near the ecliptic poles. The aluminum telescope consists of a heavily baffled, wide-field off-axis reflective triplet design. The focal plane is imaged simultaneously by two mosaics of H2RG detector arrays separated by a dichroic beamsplitter. SPHEREx assembles spectra through the use of mass and volume efficient linear variable filters (LVFs) included in the focal plane assemblies, eliminating the need for any dispersive or moving elements. Instead, spectra are constructed through a series of small steps in the spacecraft attitude across the sky, modulating the location of an object

J-PAS: forecasts on dark energy and modified gravity theories

“…An intermediate regime is represented by the so-called spectro-photometric surveys (COMBO-17 (Wolf et al 2003), ALHAMBRA (Moles et al 2008), COSMOS (Ilbert et al 2009), MUSYC (Cardamone et al 2010), CLASH (Postman et al 2012), SHARDS (Pérez-González et al 2013), PAU (Martí et al 2014), J-PLUS (Cenarro et al 2019a), J-PAS (Benitez et al 2014) and SPHEREx (Korngut et al 2018)), that combine deep imaging with multi-color information obtained through combination of broad, medium and narrow band filters. In this way, a low-resolution spectrum (also known as "pseudospectrum") is obtained for every pixel in the survey's footprint, and in particular for each and all sources present in the joint catalogue extracted from the combination of all bands.…”

SPHEREx: NASA's near-infrared spectrophotometric all-sky survey

“…SPHEREx's unprecedented all sky spectroscopic survey will open an important new spectroscopic window on the Universe, and we expect that the SPHEREx data will be used for scientific investigations going far beyond the three important science themes which define the mission. The progress reported by Korngut et al (2018) 1 and in this paper shows that the SPHEREx design and technology are well in hand, leading to launch currently targeted for 2024. SPHEREx will then become an important participant in a new era of astronomical exploration which has been called "The Decade of the Surveys".…”

Superresolution Reconstruction of Severely Undersampled Point-spread Functions Using Point-source Stacking and Deconvolution

“…In order to test and characterize these algorithms, simulated images of the sky are necessary. We simulate images of undersampled point sources consistent with the SPHEREx expectation (Korngut et al 2018) according to the following prescription. First, we generate a grid that represents the r-times finer grid or pixelized image.…”

“…As a case study, we examine this PSF reconstruction algorithm as it may apply to the Spectro-Photometer for the History of the universe, Epoch of Reionization, and ices Explorer (SPHEREx), an upcoming spectroscopic survey mission designed to image every 6.2×6.2 arcsec 2 pixel over the entire sky for 0.75 < λ < 4.8 μm. Accurate photometry with methodological uncertainties <1% is required to help attain SPHEREx's ambitious scientific goals, but the PSF is intentionally designed to be underresolved by the pixel grid with an optical FWHM of 2 01 at 0.75 μm, which is consistent with Korngut et al (2018) when manufacturing tolerance and aberrations are included. This gives a sampling rate of ∼0.3 pixels per FWHM, well below the Nyquist rate.…”