Journal ArticleMicrophysics of Circumgalactic Turbulence Probed by Fast Radio Bursts and QuasarsOcker, Stella Koch (ORCID:0000000249415333); Chen, Mandy C (ORCID:0000000287393163); Oh, S Peng (ORCID:0000000210134657); Sharma, Prateek (ORCID:0000000326354643)<title>Abstract</title> <p>The circumgalactic medium (CGM) is poorly constrained at the subparsec scales relevant to turbulent energy dissipation and regulation of multiphase structure. Fast radio bursts are sensitive to small-scale plasma density fluctuations, which can induce multipath propagation (scattering). The amount of scattering depends on the density fluctuation spectrum, including its amplitude<inline-formula><tex-math><CDATA/></tex-math><math overflow='scroll'><msubsup><mrow><mi>C</mi></mrow><mrow><mi mathvariant='normal'>n</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math></inline-formula>, spectral index<italic>β</italic>, and dissipation scale<italic>l</italic>_i. We use quasar observations of CGM turbulence at ≳pc scales to infer<inline-formula><tex-math><CDATA/></tex-math><math overflow='scroll'><msubsup><mrow><mi>C</mi></mrow><mrow><mi mathvariant='normal'>n</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math></inline-formula>, finding it to be<inline-formula><tex-math><CDATA/></tex-math><math overflow='scroll'><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>16</mn></mrow></msup><mo>≲</mo><msubsup><mrow><mi>C</mi></mrow><mrow><mi mathvariant='normal'>n</mi></mrow><mrow><mn>2</mn></mrow></msubsup><mo>≲</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>9</mn></mrow></msup></math></inline-formula>m^−20/3for hot (<italic>T</italic>> 10⁶K) gas and<inline-formula><tex-math><CDATA/></tex-math><math overflow='scroll'><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>8</mn></mrow></msup><mo>≲</mo><msubsup><mrow><mi>C</mi></mrow><mrow><mi mathvariant='normal'>n</mi></mrow><mrow><mn>2</mn></mrow></msubsup><mo>≲</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow></msup></math></inline-formula>m^−20/3for cool (10⁴≲<italic>T</italic>≲ 10⁵K) gas, depending on the gas sound speed and density. These values of<inline-formula><tex-math><CDATA/></tex-math><math overflow='scroll'><msubsup><mrow><mi>C</mi></mrow><mrow><mi mathvariant='normal'>n</mi></mrow><mrow><mn>2</mn></mrow></msubsup></math></inline-formula>are much smaller than those inferred in the interstellar medium at similar physical scales. The resulting scattering delays from the hot CGM are negligible (≪1<italic>μ</italic>s at 1 GHz), but they are more detectable from the cool gas as either radio pulse broadening or scintillation, depending on the observing frequency and sightline geometry. Joint quasar-FRB observations of individual galaxies can yield lower limits on<italic>l</italic>_i, even if the CGM is not a significant scattering site. An initial comparison between quasar and FRB observations (albeit for different systems) suggests<italic>l</italic>_i≳ 750 km in ∼10⁴K gas in order for the quasar and FRB constraints to be consistent. If a foreground CGM is completely ruled out as a source of scattering along an FRB sightline, then<italic>l</italic>_imay be comparable to the smallest cloud sizes (≲pc) inferred from photoionization modeling of quasar absorption lines.</p>ApJ2025-07-1510678459The Astrophysical Journal9881690004-637Xhttps://doi.org/10.3847/1538-4357/ade0bc2407521National Science Foundation