Hot Extended Galaxy Halos around Local L* Galaxies from Sunyaev-Zeldovich Measurements

Most of the baryons in L* galaxies are unaccounted for and are predicted to lie in hot gaseous halos (T similar to 10(6.5) K) that may extend beyond R (200). A hot gaseous halo will produce a thermal Sunyaev-Zeldovich signal that is proportional to the product of the gas mass and the mass-weighted temperature. To best detect this signal, we used a Needlet Independent Linear Combination all-sky Planck map that we produced from the most recent Planck data release, also incorporating WMAP data. The sample is 12 L* spiral galaxies with distances of 3-10 Mpc, which are spatially resolved so that contamination from the optical galaxy can be excluded. One galaxy, NGC 891, has a particularly strong SZ signal, and when excluding it, the stack of 11 galaxies is detected at about 4 sigma (declining with radius) and is extended to at least 250 kpc (approximate to R (200)) at >99% confidence. The gas mass within a spherical volume to a radius of 250 kpc is 9.8 +/- 2.8 x 10(10) M (circle dot), for T (avg) = 3 x 10(6) K. This is about 30% of the predicted baryon content of the average galaxy (3.1 x 10(11) M (circle dot)), and about equal to the mass of stars, disk gas, and warm halo gas. The remaining missing baryons (approximate to 1.4 x 10(11) M (circle dot), 40%-50% of the total baryon content) are likely to be hot and extend to the 400-500 kpc volume, if not beyond. The result is higher than predictions, but within the uncertainties.

Automated summary

This study investigates the unaccounted baryons in L* galaxies using the latest Planck and WMAP data. The study finds that these unaccounted baryons are likely to exist in hot gaseous halos and occupy approximately 30% of the average galaxy mass, extending possibly to a range of 400-500 kpc.