Story
First galaxy ultraviolet luminosity function limits on dark matter-proton scattering
Key takeaway
By studying faint distant galaxies, scientists have placed new limits on how dark matter could interact with normal matter, which helps narrow the search for the mysterious substance that makes up most of the universe's mass.
Quick Explainer
This work uses observations of high-redshift galaxies' ultraviolet luminosity functions to constrain the scattering between dark matter and protons. By modeling the effects of this interaction on the galaxy luminosity functions, and combining this with other cosmological data, the researchers were able to set improved limits on the dark matter-proton scattering cross section compared to previous bounds from satellite galaxies and the cosmic microwave background. The key components are modifying the halo mass function, relating galaxy UV luminosity to halo mass, and interfacing with a modified Boltzmann solver to capture the impact of interacting dark matter on the luminosity functions.
Deep Dive
Technical Deep Dive: First Galaxy UV Luminosity Function Limits on Dark Matter-Proton Scattering
Overview
This work uses high-redshift (z~4-10) ultraviolet galaxy luminosity functions (UVLFs) observed by the Hubble Space Telescope to set constraints on the dark matter (DM)-proton scattering cross section. The authors employ an adjusted implementation of the GALLUMI code combined with the modified Boltzmann solver CLASS DMeff to model the effect of interacting DM on the UVLFs. They incorporate both blank and lensed UVLF data, as well as Planck CMB and Pantheon supernova data, in a Bayesian analysis framework.
Problem & Context
Scattering between DM and protons can lead to suppressed small-scale matter fluctuations, with implications for various cosmological observables. The authors investigate this effect using high-redshift UVLFs as a probe, exploring three different scenarios for the DM-proton momentum transfer cross section: velocity-independent (n=0), velocity-dependent (n=2), and higher-order dipole interactions (n=4).
Methodology
The key components of the modeling approach are:
- Modifications to the halo mass function to account for the cutoff and oscillatory features introduced by interacting DM models
- Parameterization of the galaxy UV luminosity as a function of halo mass, incorporating effects like supernovae feedback and photoionization
- Interface with the DMeff modified version of the Boltzmann code CLASS to study the impact of interacting DM on the UVLFs
The authors perform a Bayesian MCMC analysis, combining the UVLF data with Planck CMB and Pantheon supernova likelihoods.
Data & Experimental Setup
The UVLF data used in this work comes from both blank and lensed Hubble fields, spanning redshifts z~4-10. The lensed data probes fainter galaxies and smaller scales compared to the blank fields.
The authors account for observational effects like cosmic variance, dust attenuation, and the Alcock-Paczynski effect in their analysis.
Results
The key findings are:
- Inclusion of the lensed UVLF data significantly improves the constraints on the DM-proton cross section for n>0 models, surpassing existing bounds from Milky Way satellite abundance and CMB anisotropies.
- For m_χ=1 MeV, the authors set upper bounds of 1.1×10^{-25} cm^2 for n=2 and 2.1×10^{-22} cm^2 for n=4.
- For n=0, the bounds are within an order of magnitude of those from the Lyman-α forest and Milky Way satellites.
Interpretation
The UVLF-dominated constraints derived here roughly match those from Milky Way satellites, despite the latter being known to probe smaller scales. This is attributed to the approximation used in the Milky Way satellite analysis, which compared the IDM matter power spectrum to that of warm dark matter, rather than fully exploiting the small-scale sensitivity of the satellites.
The authors show that UVLFs can potentially compete with Lyman-α forest constraints on n=0 models by probing fainter galaxies corresponding to smaller scales.
Limitations & Uncertainties
- The analysis does not account for the possible impact of DM-baryon scattering on astrophysical processes of galaxy formation, which could lead to additional signatures on the UVLFs.
- The reliability of the Sheth-Tormen halo mass function at the highest redshifts (z~14) probed by JWST may be limited, as recent studies suggest it could underpredict the halo abundance.
What Comes Next
Future UVLF observations from the JWST, reaching fainter galaxies at higher redshifts, are expected to significantly improve the constraints on interacting DM models. Additionally, the 21cm signal from upcoming experiments like HERA, LOFAR, and the SKA holds exceptional promise for probing even smaller scales than accessible with galaxy surveys.
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