The SZ flux-mass ($Y$-$M$) relation at low halo masses: improvements with symbolic regression and strong constraints on baryonic feedback

Kavli Affiliate: David N. Spergel

| First 5 Authors: Digvijay Wadekar, Leander Thiele, J. Colin Hill, Shivam Pandey, Francisco Villaescusa-Navarro

| Summary:

Ionized gas in the halo circumgalactic medium leaves an imprint on the cosmic
microwave background via the thermal Sunyaev-Zeldovich (tSZ) effect. Feedback
from active galactic nuclei (AGN) and supernovae can affect the measurements of
the integrated tSZ flux of halos ($Y_mathrm{SZ}$) and cause its relation with
the halo mass ($Y_mathrm{SZ}-M$) to deviate from the self-similar power-law
prediction of the virial theorem. We perform a comprehensive study of such
deviations using CAMELS, a suite of hydrodynamic simulations with extensive
variations in feedback prescriptions.
We use a combination of two machine learning tools (random forest and
symbolic regression) to search for analogues of the $Y-M$ relation which are
more robust to feedback processes for low masses ($Mlesssim 10^{14}, h^{-1}
, M_odot$); we find that simply replacing $Yrightarrow
Y(1+M_*/M_mathrm{gas})$ in the relation makes it remarkably self-similar. This
could serve as a robust multiwavelength mass proxy for low-mass clusters and
galaxy groups. Our methodology can also be generally useful to improve the
domain of validity of other astrophysical scaling relations.
We also forecast that measurements of the $Y-M$ relation could provide
percent-level constraints on certain combinations of feedback parameters and/or
rule out a major part of the parameter space of supernova and AGN feedback
models used in current state-of-the-art hydrodynamic simulations. Our results
can be useful for using upcoming SZ surveys (e.g. SO, CMB-S4) and galaxy
surveys (e.g. DESI and Rubin) to constrain the nature of baryonic feedback.
Finally, we find that the an alternative relation, $Y-M_*$, provides
complementary information on feedback than $Y-M$.

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