J/A+A/694/A127 Spectroscopy of AGNs in low-mass galaxies (Bernal+, 2025)
The success of optical variability in uncovering active galactic nuclei in
low-stellar mass galaxies.
Bernal S., Sanchez-Saez P., Arevalo P., Bauer F.E., Lira P., Sotomayor B.
<Astron. Astrophys. 694, A127 (2025)>
=2025A&A...694A.127B 2025A&A...694A.127B (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Redshifts ; Equivalent widths ; Optical ;
Spectroscopy
Keywords: galaxies: active - galaxies: general - galaxies: Seyfert
Abstract:
The origins of supermassive black holes (SMBHs) at the centers of
massive galaxies are a topic of intense investigation. One way to
address this subject is to identify the seeds of SMBHs as
intermediate-mass black holes (IMBHs; 100M☉<MBH<106M☉).
IMBHs are expected to be found at the centers of low stellar mass
galaxies (LSMGs).
Our goal is to complete the census of SMBHs in LSMGs. In this work our
aim is to establish the purity of active galactic nucleus (AGN)
selection by algorithms based on optical variability and to
characterize the black hole population found through this method.
We used random forest algorithms to classify all objects in a large
portion of the sky, using optical light curves obtained from, or built
from images provided by, the Zwicky Transient Facility (ZTF). We
compared different selection sets based on alerts (flux changes with
at least 5σ significance) or complete light curves derived from
different photometric selection algorithms. The AGN candidates thus
selected were cross-matched with objects in the NASA-Sloan Atlas (NSA)
of local galaxies, with M*<2x1010M☉. The AGN nature of these
candidates was verified and characterized using archival optical
spectra from SDSS. We further established the fraction of candidates
with counterparts in the eROSITA Data Release 1 catalog of X-ray
sources.
From an initial sample of 506 candidates, 415 have good-quality
spectra. Among these 415 objects we found significant broad Balmer
lines in the spectra for 86% (357) of the candidates. When considering
BPT classifications, five additional candidates were confirmed,
resulting in 87% (362) confirmed candidates. Specifically, broad
Balmer lines were detected in 94%-98% of the AGN candidates selected
from complete light curves and in 80% of those selected from the less
frequent ZTF alerts. The black hole masses estimated from the spectra
range from 2.2x106M☉ to 4.2x107M☉, reaching
lower values for the candidates selected using the more sensitive
light curves. The black hole masses obtained cluster around 0.1% of
the stellar mass of the host from the NSA catalog. Two-thirds of the
AGN candidates are classified as Seyfert or composite by their narrow
emission line ratios (BPT diagnostics), while the rest are
star-forming. Almost all the candidates classified as Seyfert and over
50% of those classified as star-forming have significant broad
emission lines (BELs). We found X-ray counterparts for 67% of the
candidates that fall in the footprint of the eROSITA-DE DR1.
Considering only the candidates with significant BELs, the matches
increase to 75%, regardless of where they appear in the BPT
diagnostics diagrams.
Description:
We present the results of characterizing the spectra of AGN candidates
in low-stellar-mass galaxies. The candidates were selected using a
Hierarchical Random Forest algorithm applied to ZTF photometry data
products, and cross-matched with the NASA-Sloan Atlas catalog
(v1.0.1). The spectroscopic data were retrieved from the SDSS
archives. Parameters derived from spectral fitting and calculated
using single-epoch relations are provided in this table. Additionally,
coordinates and parameters from the NASA-Sloan Atlas v1.0.1 catalog
are included.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table4.dat 673 415 Values of the different estimated magnitudes
for 415 AGN candidates
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See also:
J/A+A/682/A34 : SRG/eROSITA all-sky survey catalogs (eRASS1) (Merloni+, 2024)
https://www.sdss4.org/dr17/manga/manga-target-selection/nsa/ :
NASA-Sloan Atlas Home Page (NSA)
Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- Name Object ID in NSAv1.0.1,
JHHMMSS.ss+DDMMSS.s (IAUNAME)
21- 30 F10.6 deg RAdeg Right ascension (J2000) (RA)
32- 41 F10.6 deg DEdeg Declination( J2000) (Dec)
43- 54 F12.10 --- zNSA Redshift in NSAv1.0.1 (Redshift_NSA)
56- 68 F13.1 Msun MSersic Galaxy mass (SERSIC_MASS) (1)
70- 75 A6 --- SDSSClass SDSS pipeline class (SDSS_class)
77- 86 F10.8 --- z Redshift in SDSS (Z)
88 I1 --- ZTFAlertsset [0/1] Included in the set 1=yes 0=no
(ZTFAlertsset)
90 I1 --- ForcedPhotset [0/1] Included in the set 1=yes 0=no
(ForcedPhotometryset)
92 I1 --- ZTFDR11gband [0/1] Included in the set 1=yes 0=no
(ZTFDR11gband)
94 I1 --- ZTFDR11rband [0/1] Included in the set 1=yes 0=no
(ZTFDR11rband)
96-104 F9.3 km/s FWHMbr BEL component FWHM (FWHM_br) (2)
106-114 F9.3 km/s bFWHMbr FWHMbr percentil 16 (FWHMbrp16)
116-124 F9.3 km/s BFWHMbr FWHMbr percentil 84 (FWHMbrp84)
126-132 F7.3 --- EWHabr Equivalent Width Ha (EWHabr) (2)
134-140 F7.3 --- bEWHabr EWHabr percentil 16 (EWHabr_p16)
142-148 F7.3 --- BEWHabr EWHabr percentil 84 (EWHabr_p84)
150-158 F9.3 10-20W/m2 FluxHabr Flux Halpha BEL (FluxHabr) (2)
160-168 F9.3 10-20W/m2 bFluxHabr FluxHabr 16th (FluxHabr_p16)
170-178 F9.3 10-20W/m2 BFluxHabr FluxHabr 84th (FluxHabr_p84)
180-201 E22.17 10-7W Lum5100 AGN-cont luminosity at 5100Å
(Lum_5100)
203-224 E22.17 10-7W bLum5100 Lum5100 16th (Lum5100p16)
226-247 E22.17 10-7W BLum5100 Lum5100 84th (Lum5100p84)
249-253 F5.3 [Msun] BHMass BH Mass using Eq.1 (BH_Mass)
255-259 F5.3 [Msun] e_BHMass BH Mass negative error (BHMasse1)
261-265 F5.3 [Msun] E_BHMass BH Mass positive error (BHMasse2)
267-271 F5.3 --- LREdd Eddintong Ratio (LREdd)
273-277 F5.3 --- e_LREdd LREdd negative error (LREdd_e1)
279-283 F5.3 --- E_LREdd LREdd positive error (LREdd_e2)
285-293 F9.3 10-20W/m2 FluxHbbr Flux Hbeta BEL (FluxHbbr) (2)
295-303 F9.3 10-20W/m2 bFluxHbbr FluxHabr 16th (FluxHbbr_p16)
305-313 F9.3 10-20W/m2 BFluxHbbr FluxHabr 84th (FluxHbbr_p84)
315-321 F7.3 --- EWHbbr Equivalent Width Hb (EWHbbr) (2)
323-329 F7.3 --- bEWHbbr EWHbbr 16th (EWHbbr_p16)
331-337 F7.3 --- BEWHbbr EWHbbr 84th (EWHbbr_p84)
339-347 F9.3 10-20W/m2 Flux[OIII] Flux [OIII] NEL (Flux_[OIII]) (3)
349-357 F9.3 10-20W/m2 bFlux[OIII] Flux[OIII] 16th (Flux[OIII]p16)
359-367 F9.3 10-20W/m2 BFlux[OIII] Flux[OIII] 84th (Flux[OIII]p84)
369-376 F8.3 10-20W/m2 FluxHbnr Flux Hbeta NEL (FluxHbnr) (3)
378-385 F8.3 10-20W/m2 bFluxHbnr FluxHbnr 16th (FluxHbnr_p16)
387-394 F8.3 10-20W/m2 BFluxHbnr FluxHbnr 84th (FluxHbnr_p84)
396-404 F9.3 10-20W/m2 FluxHanr Flux Halpha NEL (FluxHanr) (3)
406-414 F9.3 10-20W/m2 bFluxHanr FluxHanr 16th (FluxHanr_p16)
416-424 F9.3 10-20W/m2 BFluxHanr FluxHanr 84th (FluxHanr_p84)
426-433 F8.3 10-20W/m2 Flux[NII] Flux [NII] NEL (Flux_[NII]) (3)
435-442 F8.3 10-20W/m2 bFlux[NII] Flux[NII] 16th (Flux[NII]p16)
444-451 F8.3 10-20W/m2 BFlux[NII] Flux[NII] 84th (Flux[NII]p84)
453-460 F8.3 10-20W/m2 Flux[SII]d Flux [SII]d NEL (Flux_[SII]d) (3)
462-469 F8.3 10-20W/m2 bFlux[SII]d Flux[SII]d 16th (Flux[SII]dp16)
471-478 F8.3 10-20W/m2 BFlux[SII]d Flux[SII]d 84th (Flux[SII]dp84)
480-487 F8.3 10-20W/m2 Flux[OI] Flux [OI] NEL (Flux_[OI]) (3)
489-496 F8.3 10-20W/m2 bFlux[OI] Flux[OI] 16th (Flux[OI]p16)
498-505 F8.3 10-20W/m2 BFlux[OI] Flux[OI] 84th (Flux[OI]p84)
507-515 A9 --- BPT[NII]Ha BPT class (BPT[NII]Ha) (4)
517-524 A8 --- BPT[SII]Ha BPT class (BPT[SII]Ha) (4)
526-533 A8 --- BPT[OI]Ha BPT class (BPT[OI]Ha) (4)
535-539 F5.3 --- rAGNc5100 AGN/continuum at 5100Å (rAGN_c5100)
541-546 F6.3 --- AGNslope AGN component slope (AGN_slope)
548-552 F5.3 [Msun] BHMassHa BH Mass from Ha-Lum (BHMass(Ha))
554-576 E23.17 10-7W LHatotal ?=-999 NEL+BEL Luminosity (LHa_total)
578-600 A23 --- eRASS IAUNAME in eRASSv1.1,
1eRASS JHHMMSS.s+DDMMSS (eRASS_IAUNAME)
602-624 E23.17 mW/m2 Flux2.8keV ?=-99999 eRASS MLFLUXP4+P5
(Flux28_keV) (5)
626-648 E23.17 10-7W Lum2.8keV ?=-99999 Luminosity for 2-8keV
(Lum28_keV)
650-656 A7 --- FitModel Model name used to fit (Fitted_Model)
658-673 A16 --- FFparam Fixed parameters (FF_parameters) (6)
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Note (1): Galaxy Mass obtained from NSAv1.0.1 using h=2 in the original table.
Note (2): Values for Broad Emission Lines components.
Note (3): Values for Narrow Emission Lines components.
Note (4): BPT classification using the [OIII]/Hbeta vs the emission lines ratio
in the column name (e.g., BPT[NII]Ha for diagram [OIII]/Hb vs [NII]/Ha).
Note (5): Values of -99999.0 are used for objects with no X-ray counterpart.
Note (6): Fixed parameters as follows:
AF = All Free; all parameters free for fitting
Ha_nV = Fixed velocity for Ha(>6300Å) NELs component
Ha_nVd = Fixed velocity dispersion for Ha(>6300Å) NELs component
HanVnVd = Ha_nV + Ha_nVd
Hb_nV = Fixed velocity for Hb(<6300Å) NELs component
Hb_nVd = Fixed velocity dispersion for Ha(<6300Å) NELs component
HanVd-HbnV_nVd = Ha_nVd + Hb_nV + Hb_nVd
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Acknowledgements:
Santiago Bernal, santiago.bernal(at)postgrado.uv.cl
(End) Santiago Bernal [IFA-UV, Chile], Patricia Vannier [CDS] 18-Dec-2024