Seminar

Unifying X-ray Scaling Relations from Galaxies to Clusters

We examine a sample of ~250 000 "locally brightest galaxies" selected from the Sloan Digital Sky Survey by the Planck Collaboration to be central galaxies within their dark matter halos. We stack the X-ray emission from these halos using data from the ROSAT All-Sky Survey. We detect emission across almost our entire sample, including extended emission in the (0.15-1)xR500 annulus around a range of galaxies spanning 1.2 dex in stellar mass (corresponding to two orders of magnitude in halo mass) down to M* = 10^{10.8} Msun (M500= 10^{12.5} Msun). Across this range, the X-ray luminosity can be fit with a power-law, either as a function of stellar mass or halo mass. From this, we infer a single unified scaling relation between mass and LX which applies for galaxies, galaxy groups, and galaxy clusters. This relation has a slope steeper than expected for self-similarity, showing the importance of non-gravitational heating, and the lack of a break in the relation suggests the influence of self-regulated AGN feedback. Our relation is consistent with established measurements of the LX-LK relation for elliptical galaxies as well as the LX-M500 relation for galaxy clusters. However, our LX-M500 relation has a normalization about twice as low as most previous relations, which have relied on galaxy clusters selected by their X-ray flux. We argue that optical selection offers a more unbiased measurement of the intrinsic LX-M500 relation.

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