Shantanu Desai

We present cosmological constraints from the Planck PSZ2 cosmological cluster sample, using weak-lensing shear profiles from Dark Energy Survey (DES) data and X-ray observations from the Chandra telescope for the mass calibration. We compute hydrostatic mass estimates for all clusters in the PSZ2 sample with a scaling relation between their integrated Sunyaev-Zeldovich signal and X-ray-derived hydrostatic mass, calibrated with the Chandra data. We introduce a method to correct these masses with a hydrostatic mass bias using shear profiles derived from wide-field galaxy surveys. We simultaneously fit the number counts of the PSZ2 sample and the mass calibration with the DES data, finding Ω _m = 0.312 ^+0.018 _−0.024 , σ ₈ = 0.777 ± 0.024, S ₈ ≡ σ ₈ √Ω _m /0.3 = 0.791 ^+0.023 _−0.021 , and (1− b ) = 0.844 ^+0.055 _−0.062 for our baseline analysis when combined with baryon acoustic oscillation data. When considering a hydrostatic mass bias evolving with mass, we find Ω _m = 0.353 ^+0.025 _−0.031 , σ ₈ = 0.751 ± 0.023, and S ₈ = 0.814 ^+0.019 _−0.020 . We verify the robustness of our results by exploring a variety of analysis settings, with a particular focus on the definition of the halo centre used for the extraction of shear profiles. We compare our results with a number of other cosmological analyses, in particular two recent analyses of cluster samples obtained from SPT and eROSITA data that share the same mass calibration data set. We find that our results are in overall agreement with most late-time probes, in very mild tension with CMB results (1.6 σ ), and in significant tension with results from eROSITA clusters (2.9 σ ). We confirm that our mass calibration is consistent with the eROSITA analysis by comparing masses for clusters present in both Planck and eROSITA samples, eliminating it as a potential cause of tension. We also compare our results with previous studies of the PSZ2 sample, finding a good agreement between the constraints derived in this work and previous constraints derived with the same sample, validating the use of wide-field lensing data for cluster mass calibration.

We test whether the Efron-Petrosian (E-P) method can recover the inverse-square law dependence of the radio pulsar flux, using a synthetic catalog generated according to the specifications of the Parkes Multi-beam survey using the PsrPopPy software. We find that the E-P method cannot automatically reproduce the inverse-square scaling law for the radio pulsar flux, even though this scaling is built into the synthetic data by construction , except over a narrow range of flux thresholds, and even here we don't get pristine agreement. The main reason for the deviation is that the synthetic radio pulsar catalog is truncated based on a cut on the pulsar signal to noise ratio (SNR), which has a non-linear dependence on the flux along with considerable scatter. We show that the disagreement is exacerbated as we raise the SNR threshold. We then demonstrate that if we create a synthetic catalog based on a flux cut (instead of an SNR-based threshold), we can recover the true distance exponent, with an accuracy ranging from pristine agreement to within ± 1 σ depending on the chosen flux threshold. Therefore, the E-P method cannot be used to determine the correct scaling of radio pulsar flux with distance. Our results also demonstrate that the E-P method breaks down when the detection threshold scales non-linearly with flux along with scatter .

We present 29 successfully recovered C iv time lags in Active Galactic Nuclei from the complete Dark Energy Survey Reverberation Mapping campaign. The AGN in this sample span a redshift range of 1.9 < z < 3.5. We successfully measure the velocity dispersion from the C iv spectral linewidth for 25 of these 29 sources, and use these to calculate new high-redshift black hole mass estimates, finding masses between 0.8 and 1.3 billion solar masses. We also identify a selection effect due to the duration of the survey that can impact the radius-luminosity relation derived from this and other (high-redshift) data. This paper represents the culmination of the OzDES C iv campaign.