arXiv subjects

Affan Khadir

Publications and source records attributed to Affan Khadir.

4 recordsLinked to original sources

arXiv2026

Evidence for Enhancement in the Rate of Fast Radio Bursts Toward Galaxy Clusters

Massive galaxy clusters can introduce gravitational lensing and populations of suppressed star formation member galaxies into the line of sight, potentially changing the distribution of observable sources toward them from that of the average sky. As a result, Fast Radio Bursts (FRBs) aligned with galaxy clusters can provide a unique window into parameter spaces of the FRB population that other lines of sight do not afford. In this study, we demonstrate that the second CHIME/FRB baseband catalog contains FRBs emitted from within or behind clusters identified from the latest DECaLS data release; we isolate a sample of 26 FRBs where this is likely, including one repeating FRB and two FRBs that intersect the Coma cluster. Comparing our results against a range of simulated FRB populations, we conclude that the number of these associations represents a $3\sigma$ rate enhancement toward galaxy clusters, constituting $1.4\pm0.4\%$ of the FRBs detected in the second CHIME/FRB baseband catalog. We suggest that this enhancement is caused by an equal proportion of member galaxies hosting additional FRBs, and gravitational lensing magnifying background sources. We demonstrate that such contributions are sensitive to alternative progenitor channels and high redshift evolution in the FRB population, providing a future avenue for constraining these features. Considering the redshifts and masses of the associated clusters, we identify FRB 20211113A, which is aligned with the strong gravitational lens Abell 2218 as a potential lensed candidate for further consideration.

astro-ph.CO↗

arXiv2025

Revealing the magnetization of the intracluster medium of Abell 3581 using background Faraday rotation measures from the POSSUM survey

The line-of-sight magnetic field of galaxy clusters can be probed using Faraday rotation measure (RM) data. However, our understanding of cluster magnetism is limited due to the scarcity of polarized background radio sources, with most previous studies being constrained to $\sim 10$ sources per cluster. Leveraging the increased source density of the POlarisation Sky Survey of the Universe's Magnetism (POSSUM), we probe the magnetic field properties of the galaxy cluster Abell 3581 {(A3581)} with 111 RMs. We find that the standard deviation in the RM declines monotonically with increasing radius up to 0.75 Mpc{, agreeing with a radially declining magnetic field and electron density profile modeled as Gaussian and lognormal random fields, respectively. {We compare our observations of the inner 0.75 Mpc of A3581 to various semi-analytic models of the magnetic field and electron density, and obtain several best-fit models.} For the first time, we compare the observed RMs in a cluster to full magnetohydrodynamic simulated clusters from TNG-Cluster and find that the non-monotonic trend in RM standard deviation past 0.75 Mpc in A3581 is likely caused by past or present merger activity. We identify a possible candidate for a merger to be the galaxy group [DZ2015b] 276, which would be the first group detected in RMs that is not strongly emitting in X-rays. We find a possible merger axis of A3581 with this group at a position angle of $\theta = 52\pm 4$ deg.

astro-ph.GA↗

arXiv2024

Interpolation techniques for reconstructing Galactic Faraday rotation

The line-of-sight structure of the Galactic magnetic field (GMF) can be studied using Faraday rotation measure (RM) grids. We analyze how the choice of interpolation kernel can affect the accuracy and reliability of reconstructed RM maps. We test the following kernels: inverse distance weighting (IDW), natural neighbour interpolation (NNI), inverse multiquadric interpolation (IM), thin-plate spline interpolation (TPS), and a Bayesian rotation measure sky (BRMS); all techniques were tested on two simulated Galactic foreground RMs (one assuming the GMF has patchy structures and the other assuming it has filamentary structures) using magnetohydrodynamic simulations. Both foregrounds were sampled to form RM grids with densities of $\sim$40 sources deg$^{-2}$ and area $\sim$144 deg$^2$. The techniques were tested on data sets with different noise levels and Gaussian random extragalactic RM contributions. The data set that most closely emulates expected data from current surveys, such as the POlarization Sky Survey of the Universe's Magnetism (POSSUM), had extragalactic contributions and a noise standard deviation of $\sim 1.5$ rad m$^{-2}$. For this data set, the accuracy of the techniques for the patchy structures from best to worst was: BRMS, NNI, TPS, IDW and IM; while in the filamentary simulate foreground it was: BRMS, NNI, TPS, and IDW. IDW is the most computationally expensive technique, while TPS and IM are the least expensive. BRMS and NNI have the same, intermediate computational cost. This analysis lays the groundwork for Galactic RM studies with large radio polarization sky surveys, such as POSSUM.

astro-ph.IM↗

arXiv2024

Cosmic Reionization on Computers: The Evolution of Ionizing Background and Mean Free Path

Observations of the end stages of reionization indicate that at $z\approx 5-6$, the ionizing background is not uniform and the mean free path (MFP) changes drastically. As MFP is closely related to the distribution of Lyman Limit Systems and Damped Lyman-alpha Systems (LLSs and DLAs, or ionizing photon "sinks"), it is important to understand them. In this study, we utilize the CROC simulations, which have both sufficient spatial resolution to resolve galaxy formation and LLSs alongside a fully coupled radiative transfer to simulate the reionization processes. In our analysis, we connect the evolution of the ionizing background and the MFP. We analyze two CROC boxes with distinct reionization histories and find that the distribution of ionizing background in both simulations display significant skewness that deviate from log-normal. Further, the ionizing background in late reionization box still displays significant fluctuations ($\sim 40\%$) at $z\approx5$. We also measure the MFP along sightlines that start 0.15 pMpc away from the center of potential quasar hosting halos. The evolution of the MFP measured from these sightlines exhibits a break that coincides with when all the neutral islands disappear in the reionization history of each box (the `ankle' of the reionization history of the box). In the absence of LLSs, the MFP will be biased high by $\approx 20\%$ at $z\approx 5$. We also compare the MFP measured in random sightlines. We find that at $z\approx 5$ the MFP measured in sightlines that start from massive halos are systematically smaller by $\approx 10\%$ compared with the MFP measured in random sightlines. We attribute this difference to the concentration of dense structures within 1 pMpc from massive halos. Our findings highlight the importance of high fidelity models in the interpretation of observational measurements.

astro-ph.CO↗