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A rain-on-snow event in June 2022 led to extreme flooding in northern Yellowstone National Park (YNP). Extensive erosion and overbank deposition altered stream morphology and destroyed park infrastructure including campgrounds, facilities, and roadways. In northern Yellowstone, the previous flood of record was in 1918. The aim of this project is to compare the magnitude of the 1918 flood with the 2022 flooding event. We studied the Lamar River (LR), Soda Butte Creek (SBC), and Pebble Creek (PC) in the summer of 2023. These reaches are the same reaches used by Meyer (2001) to estimate the 1918 peak discharge. Pebble Creek and Soda Butte Creek are tributaries of the Lamar River, which has its headwaters in northern YNP. The reach of the Lamar River surveyed was upstream of the confluence with Pebble Creek and Soda Butte Creek. We used cm-scale RTK GPS to survey channel cross-sections and stage indicators. We used an acoustic doppler velocimeter to calculate current discharge to estimate channel roughness. We then reconstructed the 2022 peak discharges in HEC-RAS. Our models produced estimated peak discharges of 80-90 m3/s at PC, 120-170 m3/s at SBC, and 104-172 m3/s at the LR. Meyer (2001) estimated the peak discharge of the 1918 flood to be 55-75 m3/s at PC, 110-260 m3/s at SBC, and 450-550 m3/s at LR. Based on these estimates, the 2022 peak discharges in PC and SBC exceed those of the 1918 flood, making it the new flood of record on those reaches. The 2022 LR peak discharge, however, was lower than the 1918 estimate. This could be attributed to lower precipitation and less snowmelt in the Lamar Basin that drains the northern Absaroka Range relative to the basins of Pebble Creek and Soda Butte Creek that drain the Beartooth Range. Late spring and early summer rain-on-snow events that cause extreme flooding are likely to occur more frequently in the future because of climate change. Considering the lower relative precipitation in the Lamar Basin during the 2022 flooding, there is potential for greater magnitude flooding in the future during more spatially extensive rain-on-snow events that would increase runoff in the Lamar drainage. 

Abstract Tight relationships exist in the local Universe between the central stellar properties of galaxies and the mass of their supermassive black hole (SMBH)^1–3. These suggest that galaxies and black holes co-evolve, with the main regulation mechanism being energetic feedback from accretion onto the black hole during its quasar phase^4–6. A crucial question is how the relationship between black holes and galaxies evolves with time; a key epoch to examine this relationship is at the peaks of star formation and black hole growth 8–12 billion years ago (redshifts 1–3)⁷. Here we report a dynamical measurement of the mass of the black hole in a luminous quasar at a redshift of 2, with a look back in time of 11 billion years, by spatially resolving the broad-line region (BLR). We detect a 40-μas (0.31-pc) spatial offset between the red and blue photocentres of the Hα line that traces the velocity gradient of a rotating BLR. The flux and differential phase spectra are well reproduced by a thick, moderately inclined disk of gas clouds within the sphere of influence of a central black hole with a mass of 3.2 × 10⁸ solar masses. Molecular gas data reveal a dynamical mass for the host galaxy of 6 × 10¹¹ solar masses, which indicates an undermassive black hole accreting at a super-Eddington rate. This suggests a host galaxy that grew faster than the SMBH, indicating a delay between galaxy and black hole formation for some systems. 

We report the time-resolved spectral analysis of a bright near-infrared and moderate X-ray flare of Sgr A ⋆ . We obtained light curves in the M , K , and H bands in the mid- and near-infrared and in the 2 − 8 keV and 2 − 70 keV bands in the X-ray. The observed spectral slope in the near-infrared band is νL ν  ∝  ν 0.5 ± 0.2 ; the spectral slope observed in the X-ray band is νL ν  ∝  ν −0.7 ± 0.5 . Using a fast numerical implementation of a synchrotron sphere with a constant radius, magnetic field, and electron density (i.e., a one-zone model), we tested various synchrotron and synchrotron self-Compton scenarios. The observed near-infrared brightness and X-ray faintness, together with the observed spectral slopes, pose challenges for all models explored. We rule out a scenario in which the near-infrared emission is synchrotron emission and the X-ray emission is synchrotron self-Compton. Two realizations of the one-zone model can explain the observed flare and its temporal correlation: one-zone model in which the near-infrared and X-ray luminosity are produced by synchrotron self-Compton and a model in which the luminosity stems from a cooled synchrotron spectrum. Both models can describe the mean spectral energy distribution (SED) and temporal evolution similarly well. In order to describe the mean SED, both models require specific values of the maximum Lorentz factor γ max , which differ by roughly two orders of magnitude. The synchrotron self-Compton model suggests that electrons are accelerated to γ max  ∼ 500, while cooled synchrotron model requires acceleration up to γ max  ∼ 5 × 10 4 . The synchrotron self-Compton scenario requires electron densities of 10 10 cm −3 that are much larger than typical ambient densities in the accretion flow. Furthermore, it requires a variation of the particle density that is inconsistent with the average mass-flow rate inferred from polarization measurements and can therefore only be realized in an extraordinary accretion event. In contrast, assuming a source size of 1  R S , the cooled synchrotron scenario can be realized with densities and magnetic fields comparable with the ambient accretion flow. For both models, the temporal evolution is regulated through the maximum acceleration factor γ max , implying that sustained particle acceleration is required to explain at least a part of the temporal evolution of the flare.