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تسجيل مستخدم جديدBaryon Budget of the Hot Circumgalactic Medium of Massive Spiral Galaxies
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Jiang-Tao Li
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The baryon content around local galaxies is observed to be much less than is needed in Big Bang nucleosynthesis. Simulations indicate that a significant fraction of these missing baryons may be stored in a hot tenuous circum-galactic medium (CGM) around massive galaxies extending to or even beyond the virial radius of their dark matter halos. Previous observations in X-ray and Sunyaev-Zeldovich (SZ) signal claimed that $sim(1-50)%$ of the expected baryons are stored in a hot CGM within the virial radius. The large scatter is mainly caused by the very uncertain extrapolation of the hot gas density profile based on the detection in a small radial range (typically within 10%-20% of the virial radius). Here we report stacking X-ray observations of six local isolated massive spiral galaxies from the CGM-MASS sample. We find that the mean density profile can be characterized by a single power law out to a galactocentric radius of $approx 200rm~kpc$ (or $approx130rm~kpc$ above the 1~$sigma$ background uncertainty), about half the virial radius of the dark matter halo. We can now estimate that the hot CGM within the virial radius accounts for $(8pm4)%$ of the baryonic mass expected for the halos. Including the stars, the baryon fraction is $(27pm16)%$, or $(39pm20)%$ by assuming a flattened density profile at $rgtrsim130rm~kpc$. We conclude that the hot baryons within the virial radius of massive galaxy halos are insufficient to explain the missing baryons.
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