A Caltech Library Service

Joint Survey Processing. I. Compact Oddballs in the COSMOS Field—Low-luminosity Quasars at z > 6?

Faisst, Andreas L. and Chary, Ranga Ram and Fajardo-Acosta, Sergio and Paladini, Roberta and Rusholme, Benjamin and Stickley, Nathaniel and Helou, George and Weaver, John R. and Brammer, Gabriel and Koekemoer, Anton M. and Miyatake, Hironao (2022) Joint Survey Processing. I. Compact Oddballs in the COSMOS Field—Low-luminosity Quasars at z > 6? Astrophysical Journal, 929 (1). Art. No. 66. ISSN 0004-637X. doi:10.3847/1538-4357/ac59b3.

[img] PDF - Published Version
Creative Commons Attribution.

[img] PDF - Submitted Version
Creative Commons Attribution.


Use this Persistent URL to link to this item:


The faint-end slope of the quasar luminosity function at z ∼ 6 and its implication on the role of quasars in reionizing the intergalactic medium at early times has been an outstanding problem for some time. The identification of faint high-redshift quasars with luminosities of <10^(44.5) erg s⁻¹ is challenging. They are rare (few per square degree), and the separation of these unresolved quasars from late-type stars and compact star-forming galaxies is difficult from ground-based observations alone. In addition, source confusion becomes significant at >25 mag, with ∼30% of sources having their flux contaminated by foreground objects when the seeing resolution is ∼0''.7. We mitigate these issues by performing a pixel-level joint processing of ground and space-based data from Subaru/Hyper-SuprimeCam (HSC) and Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS). We create a deconfused catalog over the 1.64 deg² of the COSMOS field, after accounting for spatial varying point-spread functions and astrometric differences between the two data sets. We identify twelve low-luminosity (M_(UV) ∼ −21 mag) z > 6 quasar candidates through (i) their red color measured between ACS/F814W and HSC/i band and (ii) their compactness in the space-based data. Nondetections of our candidates in Hubble DASH data argues against contamination from late-type stars. Our constraints on the faint end of the quasar luminosity function at z ∼ 6.4 suggest a negligibly small contribution to reionization compared to the star-forming galaxy population. The confirmation of our candidates and the evolution of number density with redshift could provide better insights into how supermassive galaxies grew in the first billion years of cosmic time.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Faisst, Andreas L.0000-0002-9382-9832
Chary, Ranga Ram0000-0001-7583-0621
Fajardo-Acosta, Sergio0000-0001-9309-0102
Paladini, Roberta0000-0002-5158-243X
Rusholme, Benjamin0000-0001-7648-4142
Helou, George0000-0003-3367-3415
Weaver, John R.0000-0003-1614-196X
Brammer, Gabriel0000-0003-2680-005X
Koekemoer, Anton M.0000-0002-6610-2048
Miyatake, Hironao0000-0001-7964-9766
Alternate Title:Joint Survey Processing I: Compact oddballs in the COSMOS field -- low-luminosity Quasars at z greater than 6?
Additional Information:© 2022. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Received 2021 March 8; revised 2022 January 19; accepted 2022 February 28; published 2022 April 13. We thank E. Merlin for providing an updated TPhot version and technical support, and the anonymous referee for a constructive feedback on our manuscript. This research is partially funded by the Joint Survey Processing effort at IPAC/Caltech through NASA grant NNN12AA01C. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. The Hyper Suprime-Cam (HSC) collaboration includes the astronomical communities of Japan and Taiwan, and Princeton University. The HSC instrumentation and software were developed by the National Astronomical Observatory of Japan (NAOJ), the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU), the University of Tokyo, the High Energy Accelerator Research Organization (KEK), the Academia Sinica Institute for Astronomy and Astrophysics in Taiwan (ASIAA), and Princeton University. Funding was contributed by the Faint Images of the Radio Sky at Twenty cm (FIRST) program from Japanese Cabinet Office, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), the Japan Society for the Promotion of Science (JSPS), Japan Science and Technology Agency (JST), the Toray Science Foundation, NAOJ, Kavli IPMU, KEK, ASIAA, and Princeton University. This paper makes use of software developed for the Large Synoptic Survey Telescope. We thank the LSST Project for making their code available as free software at Based in part on data collected at the Subaru Telescope and retrieved from the HSC data archive system, which is operated by Subaru Telescope and Astronomy Data Center at National Astronomical Observatory of Japan. Software: Astropy 3 (Astropy Collaboration et al. 2013, 2018), Tractor (Lang et al. 2016a, 2016b; Weaver et al. 2022), Photutils (Bradley et al. 2019), SExtractor (Bertin & Arnouts 1996), PSFex (Bertin 2011), TPhot (Merlin et al. 2015, 2016), SkyMaker (Bertin 2009).
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:Surveys; Quasars; High-redshift galaxies; Photometry; Astronomical techniques
Issue or Number:1
Classification Code:Unified Astronomy Thesaurus concepts: Surveys (1671); Quasars (1319); High-redshift galaxies (734); Photometry (1234); Astronomical techniques (1684)
Record Number:CaltechAUTHORS:20210323-151326953
Persistent URL:
Official Citation:Andreas L. Faisst et al 2022 ApJ 929 66
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108539
Deposited By: Tony Diaz
Deposited On:24 Mar 2021 21:02
Last Modified:18 Apr 2022 18:17

Repository Staff Only: item control page