Disentangling the Halo: Joint Model for Measurements of the Kinetic Sunyaev-Zeldovich Effect and Galaxy-Galaxy Lensing

TL;DR

This paper presents the first joint analysis of the kSZ effect with galaxy-galaxy lensing (GGL) for CMASS galaxies, showing that combining these probes breaks degeneracies between baryons and dark matter in halo outskirts. An analytic halo model with a GNFW baryon density profile and an NFW dark-matter halo, plus a 2-halo term, is fit to both kSZ and GGL data, revealing tight constraints on the baryon density profile over $0.3$–$50\,h^{-1}\mathrm{Mpc}$ and informing comparisons to simulations. The joint fits yield a halo mass of $\log_{10}(M_{\rm halo,200m}/M_\odot)=13.44\pm0.12$ and indicate stronger-than-some-simulation baryonic feedback, as evidenced by a shallower outer slope $\beta$ of the baryon profile and corresponding suppression in $\Delta\Sigma$ at small scales. The publicly released glasz code enables broader application of kSZ+GGL joint analyses to test baryon physics and halo properties in current and future surveys.

Abstract

We present the first joint analysis of the kinetic Sunyaev-Zeldovich (kSZ) effect with galaxy-galaxy lensing (GGL) for CMASS galaxies in the Baryon Oscillation Spectroscopic Survey (BOSS). We show these complementary probes can disentangle baryons from dark matter in the outskirts of galactic halos by alleviating model degeneracies that are present when fitting to kSZ or GGL measurements alone. In our joint kSZ+GGL analysis we show that the baryon density profile is well constrained on scales from 0.3 to 50 Mpc/$h$. With our well constrained profile of the baryon density, we provide direct comparisons to simulations. For our model we find an outer slope of the baryon distribution that is shallower than predicted by some hydrodynamical simulations, consistent with enhanced baryonic feedback. We also show that not including baryons in a model for GGL can bias halo mass estimates low by $\sim 20\%$ compared to a model that includes baryons and is jointly fit to kSZ+GGL measurements. Our modelling code galaxy-galaxy lensing and kSZ (\texttt{glasz}) is publicly available at https://github.com/James11222/glasz.

Figures (7)

• Figure 1: Left: Sky footprints in equatorial coordinates of all surveys used in this work. Spectroscopic lenses are from the BOSS CMASS (purple) survey, photometric sources used for weak lensing come from DES Y3 (red) and KiDS-1000 (black), and the CMB backlight used for stacking the kSZ signal is from the ACT DR5 (orange) survey. We mask the full ACT footprint using the Planck$f_{\rm sky} = 60 \%$ galactic mask from Planck_2020_Maps. We estimate that DES Y3, KiDS-1000, and ACT have an overlap area of 777 deg$^2$, 409 deg$^2$, and 5737 deg$^2$ with BOSS respectively. Right: Redshift distributions for the galaxy surveys used in this analysis from Amon__Robertson_2023_GGL (BOSS scaled by $10^3$). The BOSS CMASS survey is divided into 2 samples C1 (pink) and C2 (purple) by redshift. DES Y3 and KiDS-1000 survey bins are coloured to indicate which lens bin they correspond to, such that the sources are sufficiently behind the lenses.
• Figure 2: The impact of model parameters on the quantities of interest: baryon density profile (left), kSZ temperature profile at 150 GHz (middle), and excess surface mass density $\Delta \Sigma$ (right). The model contains 6 parameters varied from top to bottom: halo mass $M_{\rm halo}$, core scale fraction $x_{\rm c}$, intermediate power law slope $\alpha$, outer power law slope $\beta$, inner power law slope $\gamma$, and the 2-halo amplitude factor $A_{\rm 2h}$. For our fiducial model we hold several parameters fixed to alleviate degeneracy between parameters. In the fiducial model we hold $\alpha = 1$ and $\gamma = 0.2$ fixed while using a concentration mass relation $c(M_{\rm halo})$. In the left most panel we show where $x = 1$ ($r = r_{\rm 200c}$). We found the halo mass $M_{\rm halo}$, the outer power law slope $\beta$, and the 2-halo amplitude $A_{\rm 2h}$ to be the most impactful parameters in the model given the scales we are probing with the kSZ effect and GGL. There are degeneracies between these parameters when only one measurement (kSZ or GGL) is being fit to which can be seen in either the $T_{\rm kSZ}$ or $R \Delta \Sigma$ panels.
• Figure 3: 68% and 95% constraints on the halo model parameters (halo mass $M_{\rm halo}$, core scale fraction $x_{\rm c}$, outer power law slope $\beta$, and 2-halo amplitude $A_{\rm 2h}$) for the analysis of the BOSS kSZ temperature profile measurements (kSZ, red), GGL excess surface mass density profile measurements (GGL, blue) and joint observations (kSZ+GGL, purple). Jointly fitting both the kSZ and GGL measurements allows for tighter constraints on dark matter and gas parameters compared to fits using only one of the datasets, effectively "disentangling" the dark matter from the gas. The GGL measurements tightly constrain the mass of the sample, and probe the matter density out to much larger scales than the kSZ measurements, which effectively pins the amplitude of the 2-halo term $A_{\rm 2h}$ alleviating degeneracies in the other free parameters.
• Figure 4: The baryon density profile (left), kSZ temperature profile at 150 GHz (top center) and 98 GHz (bottom center), and the GGL excess surface mass density profile (top right). We additionally show the fractional difference in $\Delta \Sigma$ relative to a model without any baryons (bottom right). The black points correspond to observations, the red corresponds to our fiducial model being fit to only the kSZ measurements, the blue corresponds to our fiducial model being fit to only the GGL measurements, and the purple corresponds to our joint fits to both the kSZ and GGL data. Dashed curves refer to the median (50th percentile) model of the posterior distribution and the bands denote the $\pm 1\sigma$ (32nd-68th percentiles) of the distribution of model curves. Lastly, solid curves denote the best-fit to the model. We show that the profile of the baryon density is tightly constrained by the joint fit relative to our kSZ or GGL only fits and qualitatively different compared to the data limited fits. We show that the joint fit of kSZ with GGL tightly constrains the baryon suppression in $\Delta \Sigma$ at small scales.
• Figure 5: Constraints on the halo mass from GGL where baryons are neglected (dark blue, $f_{\rm cdm} = 1$), where the baryon contribution and its uncertainty is modelled (blue, $f_{\rm cdm} = 1 - f_{\rm b}$) and where kSZ is jointly fit with the GGL to constrain the baryon parameters (purple). The prior range for the halo mass adopted by Bigwood_2024_kSZ_WL to encompass the uncertainty on the stellar masses and the SHMR spans beyond the extent of the plot.