J/A+A/699/A132 Catalog of Anomalous Quasars from SDSS DR16 (Tiwari+, 2025)
Spectroscopic quasar anomaly detection (SQuAD).
I. Rest-frame UV spectra from SDSS DR16.
Tiwari A., Vivek M.
<Astron. Astrophys. 699, A132 (2025)>
=2025A&A...699A.132T 2025A&A...699A.132T (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; QSOs ; Galaxies, peculiar ;
Spectra, ultraviolet ; Spectral types ; Ultraviolet
Keywords: catalogs - galaxies: active - galaxies: nuclei - quasars: general
Abstract:
We present the results of applying anomaly detection algorithms to a
quasar spectroscopic sub-sample from the SDSS DR16 quasar catalog,
covering the redshift range 1.88≤z≤2.47. Principal component
analysis (PCA) was employed for dimensionality reduction of the quasar
spectra, followed by hierarchical K-Means clustering in a
20-dimensional PCA eigenvector hyperspace. To prevent broad absorption
line (BAL) quasars from being identified as the primary anomaly group,
we conducted the analysis separately on BAL and Non-BAL QSOs,
comparing both categories for a clearer identification of other
anomalous quasar type. We identified 2066, anomalous quasars,
categorized into 10 broad groups. The anomalous groups include CIV
Peakers-quasars with extremely strong and narrow CIV emission
lines; Excess SiIV emitters-quasars where the SiIV line is as
strong as the CIV line; and SiIV deficient anomalies, which exhibit
significantly weaker SiIV emission compared to typical quasars. The
anomalous nature of these quasars is attributed to lower Eddington
ratios for CIV Peakers, super-solar metallicity for Excess SiIV
emitters, and sub-solar metallicity for Si iv deficient anomalies.
Additionally, we identified four groups of BAL anomalies: Blue BALs,
Flat BALs, reddened BALs, and FeLoBALs, distinguished primarily by the
strength of reddening in these sources. Further, among the non-BAL
quasars, we identified three types of reddened anomaly groups
classified as heavily reddened, moderately reddened, and
plateau-shaped spectrum quasars, each exhibiting varying degrees of
reddening. The detected anomalies are presented as a value-added
catalog.
Description:
Coordinates and labels of 2066 anomalous quasars derived from SDSS
DR16, by applying a spectroscopic quasar anomaly detection algorithm.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
catalog.dat 122 2066 SDSS_NAME, RA-DEC, Redshift, r band mag
(from SDSS DR16Q) and Anomaly Type for the
2066 detected anomalies (table 5)
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See also:
VII/289 : SDSS quasar catalog, sixteenth data release (DR16Q) (Lyke+, 2020)
Byte-by-byte Description of file: catalog.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- SDSS SDSS-designation (HHMMSS.ss+DDMMSS.s, J2000)
20- 39 F20.16 deg RAdeg Right ascension (J2000)
41- 61 F21.17 deg DEdeg Declination (J2000)
63- 80 F18.16 --- z Redshift (best estimate from DR16Q)
82-102 F21.15 mag rmag PSFMAG in r band
104-122 A19 --- AnomalyType Type of anomaly (Label)
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Acknowledgements:
Arihant Tiwari, arihant19(at)iiserb.ac.in
(End) Patricia Vannier [CDS] 16-May-2025