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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 Koekemoer, Anton M. and Miyatake, Hironao (2021) Joint Survey Processing I: Compact oddballs in the COSMOS field -- low-luminosity Quasars at z > 6? . (Unpublished)

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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 >25mag, 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/HSC and HST/ACS. We create a deconfused catalog over the 1.64 deg² of the COSMOS field, after accounting for spatial varying PSFs and astrometric differences between the two datasets. 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. We estimate that late-type stars could contribute up to 50% to our sample. Our constraints on the faint end of the quasar luminosity function at z~6.4 suggests 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:Report or Paper (Discussion Paper)
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
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:Attribution 4.0 International (CC BY 4.0). We thank E. Merlin for providing an updated TPhot version and technical support. 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.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:Surveys (1671), Quasars (1319), High-redshift galaxies (734), Photometry (1234), Astronomical techniques (1684)
Record Number:CaltechAUTHORS:20210323-151326953
Persistent URL:
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:24 Mar 2021 21:02

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