Cross-correlating galaxies and cosmic dispersion measures: Constraints on the gas-to-halo mass relation from 2MASS galaxies and 133 localized fast radio bursts

TL;DR

We address the distribution of hot gas around galaxies by cross-correlating 2MASS galaxies with dispersion measures from 133 localized FRBs, measuring the real-space statistic $\xi_\mathrm{gd}(R)$ over $0.01<R<1\,h^{-1}$Mpc. The analysis uses a halo-model framework with electron-density profiles from IllustrisTNG-300 to predict the signal and finds a null result at small scales, indicating that halos with masses $M\sim10^{12-13}\,M_\odot$ host less hot gas than in the TNG300 prediction. By introducing a phenomenological gas-to-halo mass modification (and testing an alternative electron-density profile), the data constrain the hot-gas fraction to $f_{gas,hot}\lesssim0.03$ (about 10% of the global baryon fraction), consistent with SZ/X-ray studies and challenging several feedback implementations in simulations. This work demonstrates that FRB–galaxy cross-correlations provide a powerful, direct probe of baryonic feedback and gas content in halos, with strong potential for future surveys to tighten these constraints.

Abstract

We conduct a cross-correlation analysis between large-scale structures traced by the Two Micron All Sky Survey (2MASS) galaxy catalog and the cosmic dispersion measures of 133 localized fast radio bursts (FRBs). The cross-correlation signal is measured as a function of the comoving separation $R$ between 2MASS galaxies and background FRB sightlines, making full use of the available redshift information for both datasets. Our measurements are consistent with a null detection over the range $0.01 < R\, [h^{-1}\mathrm{Mpc}] < 1$. Using a halo-based model in which free-electron density profiles are drawn from the hydrodynamical simulation IllustrisTNG-300 (TNG300), we show that the null signal at $R \sim 0.01\, h^{-1}\mathrm{Mpc}$ is inconsistent with the TNG300 prediction. This discrepancy indicates that the hot-gas mass fraction in halos with masses of $10^{12-13}\, M_\odot$ hosting 2MASS galaxies must be lower than that predicted by TNG300. A simple phenomenological modification of the TNG300 model suggests that the hot-gas mass fraction in halos of $10^{12-13}\, M_\odot$ should be below $\sim 10\%$ of the global baryon fraction in the nearby universe, implying the need for stronger feedback in this mass range. Our constraints are consistent with those inferred from X-ray emission and Sunyaev-Zel'dovich measurements in galaxies, while providing a direct estimate of the hot-gas mass fraction that does not rely on electron-temperature measurements. These results demonstrate that galaxy-FRB cross correlations offer a powerful probe of feedback processes in galaxy formation.

Figures (5)

• Figure 1: Redshift and angular distributions of our dataset. The upper panel summarizes the histogram of 2MASS-galaxy and FRB redshifts with the bin width of $\Delta z=0.01$, while colored points and black cross symbols in the lower panel represent the angular positions of 2MASS galaxies and 133 localized FRBs, respectively. We adopt the equatorial coordinate system in the lower panel. Note that the different colors in the lower panel highlight 40 jackknife subdivisions of the 2MASS galaxy catalog. Those subregions are used for the covariance estimation in our cross-correlation measurements. Alt text: Graphs and data on spatial information of galaxies and fast radio bursts.
• Figure 2: A summary of our cross-correlation measurements. The top, middle upper, middle lower, and bottom panels show the cross-correlation functions between 2MASS and FRB dispersion measures, the ratio of the jackknife errors to the random-shuffling shot noises, the number of galaxy-FRB pairs at each radial bin, and the boost factor (a diagonistic quantity for secure selections of background FRBs), respectively. Different colored points in this figure highlight that our measurements rely on the four different estimates of MW dispersion measures. The gray filled regions in the top two panels represent the jackknife-based estimate of statistical errors at $R>1\, h^{-1}\mathrm{Mpc}$ is not appropriate for scientific analyses. Note that our analysis will be subject to misidentification of background FRBs or/and observational selection effects of FRBs when the boost factor significantly deviates from unity. We describe the boost factor and its role in Section \ref{['subsec:boost']}. Alt text: Graphs and data on our cross-correlation measurements.
• Figure 3: The derivative of the one-halo cross power spectrum (defined in Eq. \ref{['eq:pk_1h']}) with respect to halo masses. In this figure, the blue solid, orange dashed, and green dashed-dotted lines represent the results for three scales of $1$, $10$, and $100\, h\mathrm{Mpc}^{-1}$, respectively. We here set the redshift to be 0.03 as an effective redshift of the 2MASS galaxies. Alt text: Three line graphs.
• Figure 4: Comparions of our measurement with several model predicitons. The blue points with error bars show the measured cross correlation functions beween the 2MASS galaxies and 133 localized FRBs, while the black solid line stands for our fiducial model prediciton based on the electron density profiles extracted from the TNG300-1 simulation. The orange dashed line represents the prediction based on the TNG300 outputs but we reduced the electron abundance $f_\mathrm{e}$ in halos with $M$ by a phenomenological function of $\tanh(M_{500}/10^{13.9} M_\odot)$. The green dashed-dotted line is an alternative to the TNG300 electron density profiles with observationally inferred ones in 2024arXiv241116555P. Note that the gray region in this figure highlights our covariance estimate of the cross correlation may be underestimated. Alt text: Graphs and data on the comparison with our cross-correlation measurements and theoretical predictions.
• Figure 5: The limit of gas-to-halo mass relations by our cross correlation measurements along with others. The orange filled region shows our constraint with a 95% confidence level, while the cyan filled, black hatched, gray filled regions and pink points with error bars represent the observational limits based on 2021MNRAS.504.5131L, 2022PASJ...74..175A, 2024MNRAS.534..655B, and 2024arXiv241116555P, respectively. For reference, we also plot the model predictions based on different hydrodynamical simulations; gray dashed line stands for the TNG300, while brown, green, purple, yellow lines correspond to the predictions for the FABLE and XFABLE suite 2018MNRAS.479.5385H2025MNRAS.542.3206H, the FLAMINGO suite 2023MNRAS.526.4978S2023MNRAS.526.6103K, the BAHAMAS suite 2017MNRAS.465.2936M, and the SIMBA 2019MNRAS.486.2827D, respectively. The black solid horizontal line represents the global baryon fraction with the best-fit values inferred from the Planck observation 2020AA...641A...6P. Alt text: Graphs and data on constraints of the gas-to-halo mass relation.