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Our Cosmic History

Our Cosmic History

The DSA will detect and characterize radio continuum emission in over a billion radio sources and 21 cm HI line emission in millions of galaxies. These will pinpoint active supermassive black holes and star-forming galaxies spread throughout the history of the Universe, and provide an HI census through half to the Universe’s age. DSA observations will be used to answer fundamental questions regarding the formation and evolution of black holes and galaxies, and the cosmic-ray lifecycle.

Image: THINGS

HI Census Through Half of the Universe’s Age

The DSA will provide a transformative full tomographic view of HI from our Galaxy out to redshift z = 1, via the 21 cm spin-flip emission line. A ‘Galactic’ HI zoom band with 0.2 km/s velocity resolution will directly link the cold and warm-neutral ISM to the star-formation process as a function of all environments, providing a crucial benchmark for modern ISM models, including in environments beyond the Galactic thin disk. Out to 100 Mpc, with sensitivity to HI masses 100 times below the knee of the HI mass function, the DSA will increase the number of high-quality kpc-resolution HI maps of galaxies by about 3 orders of magnitude, crucially capturing HI and its kinematics in all galactic environments encountered in the nearby Universe.

As the radio equivalent of the optical Rubin/LSST, the DSA will transform our understanding of the baryon cycle by detecting HI in millions of galaxies out to z = 1, uniquely measuring the cosmic HI content within the past 8 Gyr. HI mass functions will be measured down to masses low enough to enable a test of feedback prescriptions in numerical simulations the DSA will finally provide a full census of gas–rich dwarf galaxies beyond our Local Group (groups vs. field), complementing major efforts in the optical regime.

Left: The DSA neutral-hydrogen (HI) all-sky and deep-drilling surveys will increase the sensitivity and survey volume (grey curves) compared to previous and ongoing HI surveys by orders of magnitude. Right: Simulated distribution of the millions of galaxies the DSA will detect in HI at >10 σ, from the Local Group out to redshift z = 1. As the HI luminosity function at significant redshifts is currently unconstrained, we show two realizations based on: red: local scaling relations, blue: the SURFS simulations, the SHARK semi-analytic model of galaxy evolution, and the STINGRAY mock sky builder. The DSA will map the gas content of the Universe in unprecedented ways, including its large-scale structure imprinted on the underlying dark matter distribution.

The Cosmic-Ray Lifecycle

The DSA continuum images of nearby galaxies will have unprecedented sensitivity to sources of cosmic-ray feedback. This will enable central assumptions of galaxy-formation models to be tested. The DSA will deliver a census of nuclear activity in ~32,000 galaxies within 100 Mpc to orders of magnitude lower luminosities than presently accessible. In the more distant Universe, the DSA will detect > 109 individual radio sources down to 3.5 μJy (7σ) over the entire sky, uniquely characterizing the occurrence of AGN and star formation activity throughout cosmic time. In addition, Faraday rotation-measure observations of a grid of ~107 background sources will enable direct mapping of magnetic fields extending beyond galaxies. This provides sensitivity to magnetic-field seeding in the Universe.

Left: The main sequence of galaxies at < 100 Mpc from the NED Local Volume Sample. 32,000 galaxies are cataloged and characterized, representing > 90% of the total population. For each galaxy, the DSA will map continuum and polarized emission with sensitivity to 2.5 μJy/beam over ≲ 1 kpc scales. Right: Radio-synchrotron images made from FIRE-2 simulations of Milky Way-like galaxies with different assumptions for CR transport microphysics. The left (right) figure corresponds to the constant-diffusion (extrinsic turbulence) assumption. DSA will be sensitive to surface brightnesses of ~10^4.1 Jy/sr, easily distinguishing between these models.