Speaker
Description
Understanding the morphological evolution of radio-loud quasars (RLQs) across cosmic time offers unique insights into the physical conditions of the early Universe, the interaction of these RLQs with their surrounding medium, and the underlying mechanisms driving galaxy formation and evolution. Previous works, e.g., Barthel & Miley (1988, Nature), have laid the foundational understanding of the distortions in high-redshift RLQs, suggesting a more bent and distorted appearance compared to their lower-redshift counterparts. These studies have pointed towards an epoch-dependent interaction of the radio jets with an evolving interstellar or intergalactic medium. Saikia (1989, ESO) has stressed the importance of comparing sources of similar sizes as small sources are often found to be more distorted due to the effects of both the external environment and orientation. In addition, the limitation in the size of the samples and the depth of the surveys has called for further investigation with larger and more diverse quasar populations.
Our study aims to systematically characterize the properties of these RLQs, such as sizes, bending angles, and degrees of distortion, and to compare these features across size bins and redshift bins. Employing newer and significantly larger samples will not only ensure more robust statistical analyses of sources within each bin but also enable a comprehensive analysis of morphological evolution and its dependence on cosmic time. Building on the insights from Barthel & Miley (1988) and Saikia (1989), we intend to explore the relationship between quasar distortion and linear size, the fraction of emission from the core, and the misalignment angles, all while accounting for potential projection effects and orientation biases. Notably, previous studies (e.g. Barthel & Miley (1988)), included sources with redshifts up to ~2.6. We intend to significantly extend this investigation to encompass much higher redshifts, an ambition now feasible due to the exceptional sensitivity offered by LoTSS, coupled with the availability of deep spectroscopic surveys like DESI/ HETDEX. This expansion into higher redshift domains promises to illuminate the evolutionary trajectory of RLQs across a broader expanse of cosmic time, enhancing our understanding of their growth and the dynamics in the early Universe.
We have undertaken a comprehensive study using the LoTSS (deepest wide-sky area low-frequency radio survey), which provides an unprecedented opportunity to extend this line of inquiry to a broader and deeper cosmological scale. LoTSS, with its superior sensitivity and resolution at low frequencies, allows for the identification of RLQs across all redshifts up to z~6 (as demonstrated recently by Gloudemans et al. 2022 A&A), encompassing a wide variety of radio morphologies, including Fanaroff-Riley type II (FRII) sources. Our preliminary analysis has already revealed 36 RLQs with Fanaroff-Riley type II (FRII) morphology with z>3 from a careful manual inspection of 3000 candidate RLQs from the LoTSS, marking the largest sample of its kind to date. These 36 high-z RLQs exhibit a range of sizes from 40 to 800 kpc, among which three qualify as giants—representing the highest redshift giants identified to date. Interestingly, 70% of the 36 RLQs predominantly display asymmetric morphologies, with the core being situated closer to one lobe than the other. This observation marks the first instance of such reporting for FRII RLQs and their properties within this previously unexplored redshift regime. Additionally, these sources provide us with a unique opportunity to further investigate the effect of inverse Compton scattering from the Cosmic Microwave Background (CMB), given their location at very high redshifts. This aspect of our study is particularly significant, as it offers insights into the interaction between the relativistic electrons within the quasar jets and the increasingly energetic CMB photons in the early Universe. Understanding this interaction is crucial for elucidating the energy loss mechanisms and the overall impact on the observed radio morphology of RLQs across different epochs.
While the automated identification of large samples of Fanaroff-Riley type II (FRII) radio sources has demonstrated promising progress through the application of machine learning techniques, the automated measurement of sizes, distortion, and bending angles of radio sources remains a challenge. Consequently, these tasks still necessitate meticulous manual inspection and measurements, a process that is both time-consuming and labour-intensive. In response to this, our efforts are being concentrated on developing a semi-automated package designed to streamline the classification and measurement of the properties of thousands of sources. We have already conducted tests and identified properties for nearly 1000 sources, with ~0.3 ≤ z ≤3. This innovative approach aims to expedite the creation of an extensive sample of FRII RLQs from the LoTSS (aided by FIRST and VLASS), encompassing the widest possible range of redshifts. Through this, we anticipate significantly enhancing the efficiency and accuracy of our analyses, paving the way for important discoveries.
In the near future, our sample will benefit from data obtained from high-frequency surveys (matched in sensitivity and resolution), enabling us to ascertain the radio spectral properties and analyze their relationship with redshift.
By using the capabilities of LoTSS, this study promises to significantly advance our understanding of the evolutionary trajectory of RLQs and their interaction with the cosmic environment. The insights gained could have profound implications for models of galaxy evolution, the physics of radio sources, and the nature and evolution of the Universe's large-scale structure. By meticulously analysing the largest sample of FRII RLQs to date, we anticipate uncovering nuanced trends and relationships that were previously unattainable. In the oral presentation, we will present the results mentioned above, delve into their implications, and highlight the significant progress made in our study.
