Cosmology with the SPHEREX All-Sky Spectral Survey

Abstract: SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer) ( http://spherex.caltech.edu ) is a proposed all-sky spectroscopic survey satellite designed to address all three science goals in NASA's Astrophysics Division: probe the origin and destiny of our Universe; explore whether planets around other stars could harbor life; and explore the origin and evolution of galaxies. SPHEREx will scan a series of Linear Variable Filters systematically across the entire sky. The SPHEREx data set will contain R=40 spectra fir 0.75$<\lambda<$4.1$\mu$m and R=150 spectra for 4.1$<\lambda<$4.8$\mu$m for every 6.2 arc second pixel over the entire-sky. In this paper, we detail the extra-galactic and cosmological studies SPHEREx will enable and present detailed systematic effect evaluations. We also outline the Ice and Galaxy Evolution Investigations.

• The paper demonstrates that SPHEREx significantly improves constraints on primordial non-Gaussianity by mapping redshifts for over 300 million galaxies.
• It employs near-infrared spectroscopy with resolutions of R=40–150 across 0.75–4.8 μm to probe the physics of inflation and the universe's structure.
• The mission also maps interstellar ices and galactic evolution, complementing Euclid and WFIRST to provide a comprehensive cosmic census.

Cosmology with the SPHEREx All-Sky Spectral Survey

The paper "Cosmology with the SPHEREX All-Sky Spectral Survey" explores the comprehensive scientific goals and methodologies of the SPHEREx mission, a proposed all-sky survey satellite designed to fulfill NASA's mandate of understanding the universe's origins, the potential for life on other planets, and the evolution of galaxies. The SPHEREx mission, utilizing a near-infrared spectral approach, aims to create a legacy of cosmological data that spans a wide spectral range, capturing R=40 spectra for 0.75 $<\lambda<$ 4.1 $\mu$m and R=150 spectra for 4.1 $<\lambda<$ 4.8 $\mu$m across the sky.

Scientific Implications

The SPHEREx project will probe the universe's origins by exploring the physics of inflation, a rapid expansion following the Big Bang. By analyzing the large-scale distribution of matter through galaxy redshifts, SPHEREx will provide pivotal data to complement existing high-redshift surveys. This will aid in constraining models of inflation, particularly by measuring the parameter $f_{\rm NL}^{\rm loc}$, which relates to primordial non-Gaussianity in cosmic microwave background fluctuations.

On a galactic scale, SPHEREx will investigate water and biogenic molecules' origins and abundance in interstellar ices, crucial for understanding the formation of planetary systems and the potential for life on exoplanets. This involves spectroscopic studies across the galaxy, targeting over two million obscured stars and protostars, gathering a statistically significant spectrum of ices like H$_2$O, CO, and CH$_3$OH.

From an extragalactic perspective, SPHEREx will assess the evolution of galaxies by mapping the large-scale structure and analyzing the integrated light from all galaxies. This project also promises insights into the epoch of reionization, leveraging its spectral capabilities to examine the universe’s reionization history through fluctuations in the extragalactic background light (EBL).

Methodology and Instrumentation

SPHEREx will employ a 20 cm all-aluminum telescope equipped with four 2k x 2k HgCdTe detector arrays, cooled to optimize sensitivity and precision. The mission's design ensures consistent spectral mapping, relying heavily on the Earth's atmospheric opacity to make the necessary infrared observations space-based. This comprehensive approach allows SPHEREx to benefit from high spectral throughput, mapping cosmic structures in detail and reducing systematic errors encountered in ground-based surveys.

Expected Outcomes and Comparisons

Quantitatively, SPHEREx anticipates determining redshifts for over 300 million galaxies, yielding a substantial improvement in the constraints on $f_{\rm NL}^{\rm loc}$ by a factor of ten compared to Planck's measurements. The power spectrum and bispectrum analyses target a margin of error lower than one in $f_{\rm NL}^{\rm loc}$, differentiating between competing inflationary models. Moreover, SPHEREx's collaboration with missions like Euclid and WFIRST will fortify its position as a pivotal instrument in completing the cosmic census, while addressing challenges in photometric and spectroscopic galaxy classifications alongside these missions' datasets.

Conclusion

SPHEREx’s expected contributions to cosmology are multifaceted, reinforcing our understanding of the universe through enhanced spectral imaging and innovative data integration across cosmic phenomena. This ambitious all-sky survey, by emphasizing inflation physics, interstellar and galactic evolution, and the cosmic dawn, will not only fulfill NASA's astrophysical goals but will also provide a robust spectral dataset for future astronomical investigations. The mission stands poised to significantly refine cosmological models and contribute to a coherent, data-driven narrative of the universe’s history and structure.