J/A+A/702/A57 RUBIES. Spectroscopic census of little red dots (Hviding+, 2025)
RUBIES: A spectroscopic census of little red dots.
All point sources with v-shaped continua have broad lines.
Hviding R.E., de Graaff A., Miller T.B., Setton D.J., Greene J.E.,
Labbe I., Brammer G., Bezanson R., Boogaard L.A., Cleri N.J., Leja J.,
Maseda M.V., McConachie I., Matthee J., Naidu R.P., Oesch P.A., Wang B.,
Whitaker K.E., Williams C.C.
<Astron. Astrophys. 702, A57 (2025)>
=2025A&A...702A..57H 2025A&A...702A..57H (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Redshifts ; Photometry, infrared ;
Spectroscopy
Keywords: galaxies: active - galaxies: high-redshift
Abstract:
The physical nature of Little Red Dots (LRDs), a population of
compact, red galaxies revealed by JWST, remains unclear. Photometric
samples are constructed from varying selection criteria with limited
spectroscopic follow-up available to test intrinsic spectral shapes
and prevalence of broad emission lines. We use the RUBIES survey, a
large spectroscopic program with wide color-morphology coverage and
homogeneous data quality, to systematically analyze the emission-line
kinematics, spectral shapes, and morphologies of ∼1500 galaxies at
z>3.1. We identify broad Balmer lines via a novel fitting approach
that simultaneously models NIRSpec/PRISM and G395M spectra, yielding
80 broad-line sources with 28 (35%) at z>6. A large subpopulation
naturally emerges from the broad Balmer line sources, with 36
exhibiting 'v-shaped' UV-to-optical continua and a dominant point
source component in the rest-optical; we define these as spectroscopic
LRDs, constituting the largest such sample to date. Strikingly, the
spectroscopic LRD population is largely recovered when either a broad
line or rest-optical point source is required in combination with a
v-shaped continuum, suggesting an inherent link between these three
defining characteristics. We compare the spectroscopic LRD sample to
published photometric searches. Although these selections have high
accuracy, 80%-95% down to F444W<26.5, only 50%-80% of the RUBIES LRDs
were photometrically identified, depending on the selection criteria
used. The remainder were missed due to a mixture of faint rest-UV
photometry, comparatively blue rest-optical colors, or highly
uncertain photometric redshifts. Our findings highlight that
well-selected spectroscopic campaigns are essential for robust LRD
identification, while photometric criteria require refinement to
capture the full population.
Description:
The JWST Cycle 2 program RUBIES (GO-4233; PIs: de Graaff & Brammer) is
a 60-hour spectroscopic survey with the NIR-Spec microshutter array
(MSA) that has observed ∼4500 high-redshift sources selected across
∼150arcmin2 from JWST Cycle 1 NIRCam imaging programs.
We present one of the largest spectroscopic samples of broad Balmer
line sources at high redshift to date, including 80 robust detections
at z>3.1, 28 (35%) of which lie at z>6.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 135 80 RUBIES zspec>3.1 broad Balmer line galaxies
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- Field [UDS EGS] Field name
5- 10 I6 --- ID Source ID
12- 30 F19.15 deg RAdeg Right ascension (J2000)
32- 50 F19.16 deg DEdeg Declination (J2000)
52- 55 F4.2 --- zsp Spectroscopic redshift (1)
57- 76 F20.15 --- dWAIC {DELTA}WAIC, Widely Applicable Information
Criterion
78- 95 F18.13 km/s FWHM Broad balmer line FWHM (2)
97-116 F20.16 km/s e_FWHM Broad balmer line FWHM error
118-135 F18.15 mag F444W F444W magnitude (3)
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Note (1): Based on the best DAWN JWST Archive (https://dawn-cph.github.io/dja/)
value.
Note (2): We caution that these values are derived from Gaussian fitting with
FWHM<2500km/s that may not best represent the spectral profile.
Note (3): Obtained from the Weibel et al. (2024MNRAS.533.1808W 2024MNRAS.533.1808W) catalogs.
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Acknowledgements:
Raphael Hviding, hviding(at)mpia.de
(End) Patricia Vannier [CDS] 07-Aug-2025