Little Red Dots or Brown Dwarfs? NIRSpec Discovery of Three Distant Brown Dwarfs Masquerading as NIRCam-Selected Highly-Reddened AGNs

Abstract

Cold, substellar objects such as brown dwarfs have long been recognized as contaminants in color-selected samples of active galactic nuclei (AGNs). In particular, their near- to mid-infrared colors (1-5 $\mu$m) can closely resemble the V-shaped ($f_{\lambda }$) spectra of highly-reddened accreting supermassive black holes ("little red dots"), especially at $6<z<7$. Recently, a NIRCam-selected sample of little red dots over 45 arcmin${}^2$ has been followed up with deep NIRSpec multi-object prism spectroscopy through the UNCOVER program. By investigating the acquired spectra, we identify three of the 14 followed-up objects as T/Y dwarfs with temperatures between 650 and 1300 K and distances between 0.8 and 4.8 kpc. At $4.8_{-0.1}^{+0.6}$ kpc, Abell2744-BD1 is the most distant brown dwarf discovered to date. We identify the remaining 11 objects as extragalactic sources at $z_{\mathrm{spec}}\gtrsim 5$. Given that three of these sources are strongly-lensed images of the same AGN (Abell2744-QSO1), we derive a brown dwarf contamination fraction of $25\%$ in this NIRCam-selection of little red dots. We find that in the near-infrared filters, brown dwarfs appear much bluer than the highly-reddened AGN, providing an avenue for distinguishing the two and compiling cleaner samples of photometrically selected highly-reddened AGN.

Published in ApJ Letters

References in corpus (21)

• CEERS Key Paper I: An Early Look into the First 500 Myr of Galaxy Formation with JWST
• A CEERS Discovery of an Accreting Supermassive Black Hole 570 Myr after the Big Bang: Identifying a Progenitor of Massive z > 6 Quasars
• GA-NIFS: A massive black hole in a low-metallicity AGN at $z\sim 5.55$ revealed by JWST/NIRSpec IFS
• A massive quiescent galaxy at redshift 4.658
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope II. Multi-object spectroscopy (MOS)
• A JWST/NIRCam Study of Key Contributors to Reionization: The Star-forming and Ionizing Properties of UV-faint $z\sim 7-8$ Galaxies
• The Field Substellar Mass Function Based on the Full-sky 20-pc Census of 525 L, T, and Y Dwarfs
• JWST UNCOVER: Extremely red and compact object at$z_{\mathrm{phot}}\simeq 7.6$ triply imaged by Abell 2744
• A Census of the Bright z=8.5-11 Universe with the Hubble and Spitzer Space Telescopes in the CANDELS Fields
• A Candidate of a Least-Massive Black Hole at the First 1.1 Billion Years of the Universe
• Searching for Extremely Blue UV Continuum Slopes at $z=7-11$ in JWST/NIRCam Imaging: Implications for Stellar Metallicity and Ionizing Photon Escape in Early Galaxies
• UNCOVERing the extended strong lensing structures of Abell 2744 with the deepest JWST imaging
• CEERS Key Paper VI: JWST/MIRI Uncovers a Large Population of Obscured AGN at High Redshifts
• The Sonora Substellar Atmosphere Models. II. Cholla: A Grid of Cloud-free, Solar Metallicity Models in Chemical Disequilibrium for the JWST Era
• The First JWST Spectral Energy Distribution of a Y dwarf
• EPOCHS VII: Discovery of high redshift ($6.5<z<12$) AGN candidates in JWST ERO and PEARLS data
• The Hawaii Infrared Parallax Program. V. New T-Dwarf Members and Candidate Members of Nearby Young Moving Groups
• JWST/NIRCam discovery of the first Y+Y brown dwarf binary: WISE J033605.05$-$014350.4
• Early results from GLASS-JWST. XIII. A faint, distant, and cold brown dwarf
• First Observations of the Brown Dwarf HD 19467 B with JWST
• A T-Dwarf Candidate from JWST Early Release NIRCam data

Cited by in corpus (11)

• RUBIES: A Spectroscopic Census of Little Red Dots; All V-Shaped Point Sources Have Broad Lines
• MIRI Deep Imaging Survey (MIDIS) of the Hubble Ultra Deep Field
• Exploring over 700 massive quiescent galaxies at z = 2-7: Demographics and stellar mass functions
• JWST/MIRI reveals the true number density of massive galaxies in the early Universe
• Euclid: Early Release Observations -- A glance at free-floating new-born planets in the sigma Orionis cluster
• JWST ERS Program Q3D: The pitfalls of virial BH mass constraints shown in a z = 3 quasar with an ultramassive host
• Lonely Little Red Dots: Challenges to the AGN-nature of little red dots through their clustering and spectral energy distributions
• What is the nature of Little Red Dots and what is not, MIRI SMILES edition
• Mysteries of Capotauro: investigating the puzzling nature of an extreme F356W-dropout
• A census of quiescent galaxies across $0.5<z<8$ with JWST/MIRI: Mass-dependent number density evolution of quiescent galaxies in the early Universe
• Serendipitous observation of a white dwarf companion to a JWST/MIRI coronagraphic calibrator