A recurring changing state AGN discovered in the SAMI Galaxy Survey and SDSS

Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: I'm Vera.

Jocelyn: And I'm Jocelyn, here with Subrahmanyan.

Vera: We're looking at the paper: "A recurring changing state AGN discovered in the SAMI Galaxy Survey and SDSS".

Jocelyn: Here's the gist of the paper. The gist J0853 has gone through at least one full changing-look AGN cycle, from type 1.9 in 2001 to type 1 in 2015 and 2021, and then type 1.9 again in 2022 The Phenomenon of Changing-Look AGN Active Galactic Nuclei (AGN) can undergo dramatic spectral shifts, losing or gaining broad emission lines and optical continuum emission over mere months to years, which are termed ‘Changing Look AGN’ (CLAGN).

Vera: These rapid variations cannot be explained by static orientation-based unification models, making CLAGN crucial laboratories for probing short-term accretion disk instabilities, dynamic obscuration, and complex unknown physics in real-time.

Jocelyn: Ricci and Trakhtenbrot (2023) proposed that CLAGN actually contain two distinct populations: Changing-State AGN (CSAGN) and Changing-Obscuration AGN (COAGN).

Vera: The former transition between observed spectral type due to intrinsic changes in the ionising radiation from the accretion disc, while the latter appear to change spectral type due to varying obscuration along the line of sight between the observer and the core of the AGN.

Title and authors: Vera: Let's talk about the title again, "A recurring changing state AGN discovered in the SAMI Galaxy Survey and SDSS." It’s important to note that this paper highlights how large statistical samples from surveys like SDSS and SAMI have allowed us to find these recurring events >

Jocelyn: They’re not just looking at one isolated event anymore; they are finding a subset of these, which they call RCLAGN, that transition multiple times over time across different epochs >

Subrahmanyan: From a theoretical standpoint, finding recurring transitions in AGN behavior tells us that the physics governing accretion disk instabilities isn't always steady; it suggests there are feedback mechanisms operating on timescales shorter than we might have previously assumed >

Vera: It means that when we try to model these systems, we can’t just assume a static picture of the accretion flow; things are constantly shifting their state >

Jocelyn: And the authors mention that early discoveries were limited to isolated chance finds like Mrk one thousand eighteen and Mrk five hundred ninety but now with these larger surveys, they are seeing more examples of these recurring changes > <ref:2610.30816#pg2,were limited to isolated chance>

The paper's summary: Vera: So, what’s the core finding here? The paper summarizes that J0853 is a prime example of a Changing-State AGN, and it has cycled from type one point nine in two thousand one to type one in both two thousand fifteen and two thousand twenty-one before going back to type one point nine in two thousand twenty-two > <ref:2610.30816#pg1,from type 1.9 in 2001 to type 1 in>

Jocelyn: That cycle is key because it shows the object can switch between different spectral types based on intrinsic changes within the accretion disk, rather than just a simple change in obscuration along the line of sight >

Subrahmanyan: The summary emphasizes that this object isn't consistent with a single component responding to central luminosity changes; instead, there are at least two separate components within the Broad Line Region >

Vera: That complexity is what they highlight. They use WISE light curve evolution and W1-W2 colors as evidence that rules out purely obscuration models because those color evolution trends match a physical state change >

Jocelyn: The paper also noted that the low-state spectra have significantly higher dust extinction, with E(B minus V) values around six to eight magnitudes, compared to the high-state spectra which are much lower, at about zero point six to zero point seven magnitudes >

The paper's improvements: Vera: Now let's look at what the authors suggest for future work. They want to improve how we classify these objects by integrating both intrinsic spectral state changes and physical obscuration models into their prediction algorithms using AI >

Jocelyn: That sounds like they are trying to build an AI system that can use the WISE color evolution, which shows a shift from normal galaxy colors in the low state to colors typical of AGN in the high state, to predict these transitions before they happen >

Subrahmanyan: From a theoretical side, this is about improving our ability to model how these disks behave under different accretion rates or instabilities; it’s moving us toward a more complex physical picture >

Vera: They also suggest developing models for the Broad Line Region structure that go beyond simple single-component fits, because they found J0853’s BLR is not consistent with one component responding to luminosity change >

Jocelyn: And they want to get better at estimating black hole mass by using kinematic data from different epochs, recognizing that different epochs don't provide consistent values for the black hole mass >

Conclusion: Vera: So, wrapping this up, the recurring changing state AGN discovered in the SAMI Galaxy Survey and SDSS shows us that these objects have complex internal physics driving their spectral shifts across multiple cycles >

Jocelyn: It means we need multi-wavelength data, not just optical spectra, to truly understand what’s happening around the supermassive black hole because optical evolution alone isn't enough to determine the nature of a state change >

Subrahmanyan: And for cosmology, this recurring behavior in AGN suggests that the processes fueling SMBH growth are inherently noisy and subject to internal dynamics that we need better simulations to capture properly >

Vera: We’re moving toward systems where we can distinguish between Changing-State AGN and Changing-Obscuration AGN based on how WISE colors evolve compared to optical shifts, which is a big step >

Jocelyn: And for Jocelyn, the next step is tracking these transitions using time-domain radio observations to see if we can find similar patterns in other sources >

Subrahmanyan: I’m just thinking that this recurring activity in J0853 tells us that the environment around the SMBH is dynamic and not just a static structure, which is something we need to keep pushing for confirmation with future observations >