The Dark Sector and strong gravity
The DSA-2000 will spatially resolve galaxies in HI at z < 0.2 and enable the direct measurement of their dark matter contents through kinematic analysis. This is particularly important for the least massive galaxies; their properties depend sensitively on the nature of dark matter (e.g. warm vs. cold dark matter models). Cadenced DSA-2000 continuum data will yield an unprecedented sample of time-variable strong gravitational lenses for time-delay cosmography. In addition, the DSA-2000 will discover and characterize over 22,000 new Galactic radio pulsars, including highly accelerated systems that can transform our understanding of gravitational- and nuclear-physics theory.
Image: IncrediVFX
HI Kinematics and Rotation Curves
The DSA-2000 will uniquely constrain the HI kinematics and rotation curves to derive precise dark matter mass profiles for few × 10⁴ galaxies, delivering the most complete look yet at the connection between galaxies and their dark-matter halos. These data will, e.g., differentiate between cuspy and cored dark matter distributions. Crucially, the DSA-2000 will provide sufficient statistics to finally assess the ‘puzzling diversity’ of rotation curves.
Left: Forward-modeled HI imaging (HI intensity map color–coded by velocity). The dashed ellipse indicates the optical-galaxy size. The DSA-2000 will provide HI imaging and kinematics of similar quality for few × 10⁴ galaxies. Middle: These data will be used to construct high–quality rotation curves, which show great variety throughout the galaxy population (spiral galaxy NGC2403: flat rotation curve; dwarf galaxy IC 2574: solid body rotation curve). Right: The rotation curve shape plotted as a function of baryonic mass density shows a puzzling diversity at low densities, as indicated by the ‘region of interest’ box. The DSA-2000 survey will derive accurate dark-matter profiles for few × 10⁴ galaxies, improving over current studies by 100X.
Gravitational Lensing
Besides tracing the distribution of dark matter on the smallest scales, cadenced DSA-2000 continuum data will yield an unprecedented sample of time-variable strong gravitational lenses for time-delay cosmography. Among the largest extant uncertainties in observational cosmology is the H₀–tension: the 8% difference between estimates of H₀ from local-universe probes and the CMB. Multiple tracers of H₀ at different redshifts are critical to confirming this tension. Time-delay cosmography employs time-delays between different gravitationally lensed images of variable background sources, and redshift and lens-model analyses to directly measure H₀ using individual systems. The DSA-2000 will overcome uncertainties in lens modeling by detecting tens of thousands of strongly lensed compact AGN even with its native angular resolution, exceeding the yield of upcoming optical/IR surveys with Rubin/LSST and Euclid by virtue of a significantly deeper redshift distribution.
The DSA-2000 will discover a large number of strong gravitational lenses, including galaxy-galaxy lenses, group and cluster lenses, and time-domain lenses such as variable AGN and radio transients. Left: Mean lensing probability as a function of the total number of detected sources for seven surveys. Filled circles indicate past samples, open circles represent forecasts. The deep redshift distribution of DSA-2000 radio sources results in a large lensing probability. Right: Conceptual illustration of “time-delay cosmography”, whereby lensing delays can be used to determine cosmological parameters such as H₀. The DSA-2000 will discover and monitor several hundred such systems.
A Galactic Census of Radio Pulsars
The DSA-2000 will discover and characterize over 22,000 new Galactic radio pulsars, including highly accelerated systems that can transform our understanding of gravitational- and nuclear-physics theory. A yield of over 3,000 MSPs is anticipated, enabling dozens of new systems to be added to the DSA-2000 PTA. Searches for and confirmation of pulsars will occur commensally with the cadenced all-sky survey.
The relativistic BNS systems discovered and timed by the DSA-2000 will yield a transformative range of gravity tests and EoS measurements. The measurement of first-order post-Keplerian binary parameters is a well-established means of testing GR. The enhanced timing precision of the DSA-2000 will also enable measurements of higher-order post-Keplerian parameters that include the effects of independently measured pulsar spins, enabling an order of magnitude increase in the possible GR tests, including measurements of geodetic precession. Measurements of the Lense-Thirring effect, so far only measured in pulsar–white-dwarf binaries, will deliver the first measurements of the neutron star moment of inertia yielding new EoS constraints. Finally, DSA-2000 PTA data will yield the most sensitive tests of alternate theories of gravity that predict additional GW polarization states and modified GW dispersion relations.
Left: The phase space of existing and upcoming tests of gravity theories. Dynamical tests that additionally probe GWs and radiation-reaction are highlighted. It is critical to validate GR in all possible regimes. The DSA-2000 PTA will probe strong gravity and non-GR polarization modes of GWs in the low-curvature region by observing GWs from individual SMBHBs. The DSA-2000 will substantially increase the known population of pulsars (PSRs) in binary systems, and will discover PSR–BH binaries. Pulsar binaries with additional bound stars (e.g., PSR J0337+1715) also enable tests of the Einstein equivalence principle, and PSR-BH binaries enable tests of BH models (e.g., cosmic censorship conjecture). Right: The DSA-2000 will increase the number of known pulsars, including in binary systems, by a factor of seven.