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The Type 1 and Type 2 AGN dichotomy according to their ZTF optical variability

López-Navas, E. and Arévalo, P. and Bernal, S. and Graham, Matthew J. and Hernández-García, L. and Lira, P. and Sánchez-Sáez, P. (2023) The Type 1 and Type 2 AGN dichotomy according to their ZTF optical variability. Monthly Notices of the Royal Astronomical Society, 518 (1). pp. 1531-1542. ISSN 0035-8711. doi:10.1093/mnras/stac3174.

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The scarce optical variability studies in spectrally classified Type 2 active galactic nuclei (AGNs) have led to the discovery of anomalous objects that are incompatible with the simplest unified models (UMs). This paper focuses on the exploration of different variability features that allow to distinguish between obscured, Type 2 AGNs and the variable, unobscured Type 1s. We analyse systematically the Zwicky Transient Facility, 2.5-yr-long light curves of ∼15 000 AGNs from the Sloan Digital Sky Survey Data Release 16, which are generally considered Type 2s due to the absence of strong broad emission lines (BELs). Consistent with the expectations from the UM, the variability features are distributed differently for distinct populations, with spectrally classified weak Type 1s showing one order of magnitude larger variances than the Type 2s. We find that the parameters given by the damped random walk model lead to broader H α equivalent width for objects with τ_g > 16 d and long-term structure function SF_(∞, g) > 0.07 mag. By limiting the variability features, we find that ∼11 per cent of Type 2 sources show evidence for optical variations. A detailed spectral analysis of the most variable sources (∼1 per cent of the Type 2 sample) leads to the discovery of misclassified Type 1s with weak BELs and changing-state candidates. This work presents one of the largest systematic investigations of Type 2 AGN optical variability to date, in preparation for future large photometric surveys.

Item Type:Article
Related URLs:
URLURL TypeDescription
Arévalo, P.0000-0001-8503-9809
Graham, Matthew J.0000-0002-3168-0139
Hernández-García, L.0000-0002-8606-6961
Lira, P.0000-0003-1523-9164
Sánchez-Sáez, P.0000-0003-0820-4692
Additional Information:ELN and SB acknowledge support from Agencia Nacional de Investigación y Desarrollo / Programa de Becas/ Doctorado Nacional 21200718 and 21212344. ELN acknowledges the California Institute of Technology for its hospitality. PA, ELN, and PL acknowledge financial support from Millenium Nucleus NCN19_058 (TITANs). LHG acknowledges funds by ANID – Millennium Science Initiative Program – ICN12_009 awarded to the Millennium Institute of Astrophysics (MAS). PL acknowledges partial support from FONDECYT through grant Nº1201748. PSS acknowledges funds by ANID grant FONDECYT Postdoctorado Nº3200250. MJG acknowledges partial support from the NSF grant AST-2108402. Based on observations collected at the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant 12540303 (PI: Graham). DATA AVAILABILITY. The SDSS data underlying this article were accessed from SDSS DR16 ( The ZTF data underlying this article will be shared on reasonable request to the corresponding authors
Group:Zwicky Transient Facility
Funding AgencyGrant Number
Agencia Nacional de Investigación y Desarrollo (ANID)21200718
Agencia Nacional de Investigación y Desarrollo (ANID)21212344
Agencia Nacional de Investigación y Desarrollo (ANID)NCN19_058
Agencia Nacional de Investigación y Desarrollo (ANID)ICN12_ 009
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1201748
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)3200250
Heising-Simons Foundation12540303
Issue or Number:1
Record Number:CaltechAUTHORS:20230203-893210800.33
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:119027
Deposited By: Research Services Depository
Deposited On:28 Feb 2023 16:51
Last Modified:28 Feb 2023 16:51

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