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

Author:

López-Navas E12,Arévalo P12,Bernal S1,Graham Matthew J3ORCID,Hernández-García L41,Lira P52ORCID,Sánchez-Sáez P64

Affiliation:

1. Instituto de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso , Gran Bretaña 1111, Valparaíso, Chile

2. Millennium Nucleus on Transversal Research and Technology to Explore Supermassive Black Holes (TITANS)

3. California Institute of Technology , 1200 E. California Blvd, Pasadena, CA 91125, USA

4. Millennium Institute of Astrophysics (MAS) , Nuncio Monseñor Sótero Sanz 100, Providencia, Santiago, Chile

5. Departamento Astronomía, Universidad de Chile , Casilla 36D, Santiago, Chile

6. European Southern Observatory , Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany

Abstract

ABSTRACT 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 τg > 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.

Funder

ANID

California Institute of Technology

NCN

MAS

FONDECYT

NSF

Heising-Simons Foundation

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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