Quasar photo
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Advances in Quasar Photometric Redshift Estimation and Cataloging
Introduction to Quasar Photometric Redshift Estimation
Quasars, the luminous active galactic nuclei powered by supermassive black holes, are critical for understanding the universe's structure and evolution. Estimating their redshifts accurately is essential for cosmological studies. Recent advancements have significantly improved the methods for photometric redshift (photo-z) estimation, leveraging both photometric data and images.
Q-PreNet: Integrating Images and Photometric Data
A novel approach to quasar redshift estimation is the Quasar Photometric Redshift Estimation Network (Q-PreNet). This method integrates optical and infrared data from the Sloan Digital Sky Survey (SDSS) and the Wide-field Infrared Survey Explorer (WISE) to enhance the richness of information. Q-PreNet employs an image feature extraction network (IfeNet) and a regression network (RegNet-z) to estimate photo-z with high accuracy. The fusion of image features and photometric data significantly improves the estimation performance, achieving a high proportion of accurate redshift predictions.
Southern Photometric Quasar Catalog from DES
The Dark Energy Survey (DES) has contributed a substantial catalog of 1.4 million photometrically selected quasar candidates in the southern hemisphere. This catalog combines optical photometry from DES with near-infrared (NIR) and mid-infrared (mid-IR) data. The selection algorithm assigns probabilities for quasars, galaxies, and stars, and calculates photo-z for quasar and galaxy candidates. The catalog achieves a high classification success rate and provides a comprehensive dataset for further studies.
Discovering High-Redshift Quasars
Efforts to discover high-redshift quasars have expanded with the inclusion of data from DES, VISTA Hemisphere Survey, and unWISE photometry. This approach has led to the discovery of six new luminous quasars at z > 6.4, including one at z = 7.02. These findings are crucial for understanding the early universe and the epoch of reionization.
Efficient Photometric Selection from SDSS
The Sloan Digital Sky Survey (SDSS) has produced a catalog of over one million quasar candidates using photometric imaging data. This catalog includes both UV-excess and high-redshift quasars, with a high efficiency in identifying bona fide quasars. The photometric redshift estimates provided are typically accurate to within Δz ± 0.3, making this catalog a valuable resource for statistical analyses and studies of the quasar luminosity function.
Gravitationally Lensed Quasars
Gravitational lensing of quasars provides unique opportunities to study the universe. The discovery of COOL J0335−1927, a quasar at z = 3.27 lensed into three images, highlights the potential of such systems for understanding cosmic structures. The lensing effect allows for detailed photometric and spectroscopic studies, revealing information about both the quasar and the intervening lensing galaxy.
Conclusion
The integration of photometric data and images has significantly advanced the field of quasar redshift estimation and cataloging. Methods like Q-PreNet and extensive surveys such as DES and SDSS have provided comprehensive datasets and improved accuracy in quasar identification and redshift estimation. These advancements are crucial for cosmological studies and our understanding of the universe's evolution.
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