Journal
ASTROPHYSICAL JOURNAL LETTERS
Volume 855, Issue 2, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/2041-8213/aab2af
Keywords
intergalactic medium; galaxies: evolution; galaxies: fundamental parameters; galaxies: halos; galaxies: spiral; X-rays: galaxies
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Funding
- NASA [NNX15AM93G, NNX15AV24G]
- SOFIA [05-0020]
- Chandra [18610344]
- XMM-Newton [080073]
- NASA [796583, 799903, NNX15AM93G, NNX15AV24G] Funding Source: Federal RePORTER
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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 circumgalactic 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-Zel'dovich (SZ) signals claimed that similar to(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 approximate to 200 kpc (or approximate to 130 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 (8 +/- 4)% of the baryonic mass expected for the halos. Including the stars, the baryon fraction is (27 +/- 16)%, or (39 +/- 20)% by assuming a flattened density profile at r greater than or similar to 130 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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