1. Mrk 1018 returns to the shadows
Rebecca McElroy, Bernd Husemann, Scott Croom,
and the CARS team
Hi Everyone, my name is Rebecca McElroy and I am a third year PhD student here at the University of Sydney
Today I am going to tell you about a very interesting and strange active galaxy we discovered as part of the Close AGN Reference Survey that challenges our understanding of AGN physics
@re_mcelroy

2. The Close AGN Reference Survey (CARS)
Sample is drawn from the Hamburg ESO Survey
40 type 1 AGN
Observed with the MUSE IFU on the VLT
The Close AGN Reference Survey is a survey of nearby type 1 AGN.
The aim of CARS is to combine as much multiwavelength data as possible to fully understand the complex interplay between AGN and their host galaxies.
The sample was drawn from the Hamburg ESO Survey and observed with the MUSE IFU on the VLT.

3. The Close AGN Reference Survey (CARS)
3 colour image
24 spectrographs
90,000 spectra
I am just quickly going to brag about the quality of the MUSE data.
This ** is not an image, this is a collapsed MUSE-IFU data cube turned into a 3 colour image. Each one of these pixels is a spectrum
So as you can see, the data is amazing – and this is just one of the datasets that is part of the survey.

4. Type 1 & 2 AGN Broad Balmer lines Strong continuum Narrow Balmer lines
Weak continuum
AGN are usually split into two creatively named types – type I and type II
Type I AGN are characterised by their strong continuum emission and very broad Balmer lines.
Type II, or obscured, AGN have narrow lines and no continuum emission.

5. Type 1 & 2 AGN Jet Broad line region Accretion disk Black hole Torus
Narrow line region
These types are usually explained by a geometrical effect
I am sure most of you have seen a variant of this diagram before.
We have the black hole, accretion disk, and broad line region in the centre. An obscuring torus surrounding them, further out is the narrow line region. And sometimes there is a jet.
Urry & Padovani 1995

6. Type 1 & 2 AGN Type 1 Jet Broad line region Accretion disk Black hole
Torus
Narrow line region
Type 1 AGN you have a direct view onto the accretion disk and BLR
Urry & Padovani 1995
Type 1
Urry & Padovani 1995

7. Type 1 & 2 AGN Type 2 Type 1 Jet Broad line region Accretion disk
Black hole
Torus
Narrow line region
And in type 2’s this is blocked by an obscuring torus.
But, don’t put too much stock in this as I am about to show that this isn’t always the case
Urry & Padovani 1995
Type 1
Urry & Padovani 1995

8. Mrk 1018
SDSS – 2000
SDSS – 2000
The particular galaxy I am going to talk about today is Mrk 1018
This is a spectrum taken by SDSS in 2000, you can see the strong continuum emission and broad Balmer lines characteristic of Type 1 AGN
This is what we expected to see when we examined our new data

9. Mrk 1018 – ‘changing look’ AGN
SDSS – 2000
MUSE – 2015
But, Mrk 1018 didn’t look like this any more – and had lost most of its broad emission lines and continuum emission and looked more like a type 2 AGN.
This is what we call a changing look AGN.
We then dug around in the literature and found that this wasn’t the first time Mrk 1018 had changed spectral type.

10. Mrk 1018 – ‘changing look’ AGN
SDSS – 2000
MUSE – 2015
Uminn – 1984
Lick – 1979
When it was first observed in 1979 it looked like a type 2 AGN, then when reobserved in 1984 it had changed to a type 1. This was one of the earliest discovered changing look AGN.
There are quite a number of AGN that have changed type once known, maybe ~20
This galaxy has changed spectral type not one, but twice. Only 2 or 3 other galaxies have been shown to do this, and neither are as dramatic a change as this.
To hammer this point home – this is extremely exciting discovery! So exciting that we were awarded Chandra, VLA, and HST directors discretionary time to follow up.

11. Type 2 Type 1 Type 2 Mrk 1018 – ‘changing look’ AGN High state
SDSS – 2000
High state
MUSE
Liverpool Telescope
30 years
To summarize what we have seen
Mrk 1018 transitioned from type 2 to type 1 in the space of 5 years in the 80’s, stayed there for 30 years, then began to decline in luminosity and transition back to a type 2 AGN around 2011.
Type 2
Type 1
Type 2

12. What could cause this?

13. Tidal disruption event (TDE)
Massive star is tidally disrupted by SMBH
National Geographic
The first option that a massive star was tidally disrupted by the central black hole
The star temporarily provides fuel for the AGN

14. Tidal disruption event (TDE)
Massive star is tidally disrupted by SMBH
National Geographic
Expect a defined peak in luminosity
But this would cause a defined peak in luminosity

15. Tidal disruption event (TDE)
Massive star is tidally disrupted by SMBH
National Geographic
Expect a defined peak in luminosity
Shouldn’t last more than a few years
And a star could only provide fuel for a few years before it is destroyed or too far away.

16. Tidal disruption event (TDE)
Massive star is tidally disrupted by SMBH
National Geographic
Expect a defined peak in luminosity
Shouldn’t last more than a few years
We see a fairly constant luminosity in the bright phase.
We see a fairly constant luminosity over 30 years, which makes this scenario highly unfeasible.

17. Obscuration Gas & dust A new column of gas and
dust along our line of sight to the AGN
SDSS – 2000
Alternatively, could there be new gas and dust between us and the AGN blocking our view merely obscuring the emission from the accretion disk and broad line region

18. Obscuration Gas & dust A new column of gas and
dust along our line of sight to the AGN
Do not see evidence for increased extinction in optical spectrum
SDSS – 2000
But this would cause reddening due to extinction by dust in our observed spectrum.
Which means that the ratios of the hydrogen emission lines would change.
But we do not observe this

19. Obscuration Gas & dust A new column of gas and
dust along our line of sight to the AGN
Do not see evidence for increased extinction in optical spectrum or in the X-ray spectra
SDSS – 2000
We were awarded directors discretionary time with Chandra to follow up this galaxy.
Comparing the archival and new spectrum shows us that there is no new absorption along our line of sight.

20. Declining luminosity of the accretion disk
SDSS – 2000
phys.org
It is possible that the luminosity of the accretion disk is declining, and this has caused the observed change in type.
But as the luminosity of the AGN drops we expect the regions of the broad line region that are ionised to be closer to the nucleus, and therefore moving faster
This means that as the luminosity of the broad lines fall, we expect the velocity dispersion to increase

21. Declining luminosity of the accretion disk
SDSS – 2000
phys.org
Do not see broadening of emission lines
But we do not see broadening of the emission line, they actually appear narrower.

22. Declining luminosity of the accretion disk
SDSS – 2000
phys.org
Do not see broadening of emission lines
Implies the virial factor has changed, or the BLR is not in equilibrium
This could imply that the virial factor has changed
The BLR is not in equilibrium
Or that something strange has happened to the kinematics in the nucleus.

23. Kinematic disruption Late stage merger – second SMBH?
SDSS – 2000
As you can see from this r-band image, Mrk 1018 is a late stage merger
SDSS r-band image

24. Kinematic disruption Late stage merger – second SMBH? Tidal features
SDSS – 2000
Tidal features
With strong tidal features
So there is always the possibility that there is a second super massive black hole that has fallen to the centre of the system
Such a massive object close to the accretion disk would disrupt the accretion disk and broad line region, and could lead to our observations
SDSS r-band image

25. Kinematic disruption Late stage merger – second SMBH? Wind?
SDSS – 2000
Tidal features
Or it is possible that a less exciting kinematic disturbance, like a wind, could have caused this
SDSS r-band image

26. What could cause this? Tidal disruption event Obscuration
SDSS – 2000
Tidal disruption event
Obscuration
Declining luminosity of the accretion disk
Kinematic disruption
So to summarise, these are the possible causes

27. What could cause this? Tidal disruption event Obscuration
SDSS – 2000
Tidal disruption event
Obscuration
Declining luminosity of the accretion disk
Kinematic disruption
In order to look for evidence of feedback we selected 27 of the most luminous AGN at redshift < 0.1 These galaxies were selected from SDSS based on their [OIII] luminosity. They were required to the AGN region of a BPT diagram, and above the canonical LINER line.
Selected as a complimentary sample to the SAMI Galaxy Survey (which is an unbiased volume limited IFS survey – please come and talk to me about SAMI) as these objects are too rare in the SAMI volume.
They were observed with the SPIRAL IFU, which was the previous IFU on the AAT and luckily has very similar spectral and spatial resolution.

28. What could cause this? Tidal disruption event Obscuration
SDSS – 2000
Tidal disruption event
Obscuration
Declining luminosity of the accretion disk
Kinematic disruption
And we have ruled out these two

29. What could cause this? Tidal disruption event Obscuration
SDSS – 2000
Tidal disruption event
Obscuration
Declining luminosity of the accretion disk
Kinematic disruption
McElroy et al. (2016) & Husemann et al (2016)
So we are left with these two scenarios.
What I have talked about so far is in a paper I recently submitted, and a follow up led by the PI of the survey Bernd Husemann

30. What is Mrk 1018 doing now? Watch this space!
SDSS – 2000
Declining luminosity of the accretion disk
Liverpool telescope (photometry)
VIMOS & NIFS (IFU-spectroscopy)
Kinematic disruption
VLBA data to resolve the nucleus in detail
(2nd SMBH?)
Watch this space!
In order to look for evidence of feedback we selected 27 of the most luminous AGN at redshift < 0.1 These galaxies were selected from SDSS based on their [OIII] luminosity. They were required to the AGN region of a BPT diagram, and above the canonical LINER line.
Selected as a complimentary sample to the SAMI Galaxy Survey (which is an unbiased volume limited IFS survey – please come and talk to me about SAMI) as these objects are too rare in the SAMI volume.
They were observed with the SPIRAL IFU, which was the previous IFU on the AAT and luckily has very similar spectral and spatial resolution.