Selection of high redshift quasars with SED fitting for 4MOST
In the 1980s, the discovery of the first quasar at z > 4 was made possible by digital large sky surveys, marking a significant advance in our understanding of the distant universe. (e.g., Fan et al. 2023). Since then, next-generation surveys such as WISE, 2MASS, Gaia, and Pan-STARRS have expanded our knowledge of the universe by using advanced technologies to map it across different wavelengths with unprecedented precision and depth. These digital large-area sky surveys, in combination with deep, multi-wavelength observations of smaller regions of the sky by projects like COSMOS, have led to significant discoveries and characterizations of AGN and quasars beyond the local universe (e.g., Scoville et al. 2007b, Salvato et al. 2009, Marchesi et al. 2015). The Rubin Observatory, Euclid, and Roman Space Telescope will provide new imaging surveys with unprecedented coverage and depth. Further progress in photometric redshift methods is needed to fully utilize these datasets.
One important estimation for determining the distance of an extragalactic object is to study its properties using the electromagnetic SED, which includes a continuum and emission/absorption lines. The best way of identifying and confirming the redshift of a sample would be to perform a spectroscopic follow-up. However, this may not be feasible due to the high cost of spectroscopic observation for large data samples. This makes photometric surveys stronger as they have the advantage of providing large imaging samples, making photo-z estimation a preferable and relatively cheaper alternative.
Then how to select high redshift quasar candidates with SED fitting in the southern hemisphere for next-generation spectroscopic surveys?
This project focuses on the SED fitting method used to identify high redshift AGN and estimate their photo-z. I am selecting high redshift quasar candidates through a SED fitting code that I developed. These sources will be spectroscopically followed, to confirm or discard their nature, as part of the 4MOST Chilean AGN/Galaxy Extragalactic Survey (ChANGES; Bauer et al. 2023). 4MOST is a multi-object spectroscopic facility that will be installed on the VISTA 4-meter telescope, which will observe ~2400 objects simultaneously. The goal of ChANGES is to acquire spectroscopy for a large, representative sample of AGN, selected primarily via optical variability and opt/NIR/MIR SED fitting over ~18,000 deg2 of the sky. In this context, we focus on the selection of new high-redshift (4.5 < z < 7) quasar candidates in the Southern Hemisphere, covering in particular the southernmost declinations, which are currently unexplored.
Currently, this project is in the final stage of being prepared to be submitted as a paper. To have an initial understanding of our selection, I had the opportunity to observe 5 objects from my catalog with NTT/EFOSC2, as part of an observing run of collaborators. The team submitted another proposal that aims to have another observation of high redshift quasar candidates from my candidates list with NTT at the end of November 2024.
Me in the observatory!
