Neighbours in the Cosmos

The discovery of a pair of AGN engaged in a cosmic dance

Super-massive black holes (SMBHs) are thought to lie at the centre of galaxies throughout time, sucking up the gas and stars from their whirling hosts. This process of a super-massive black hole eating away at the core of galaxy can produce copious amounts of energy when at it’s most ravenous. Much of this energy is emitted as light, such that super-massive black holes in galactic centres drown out the star-light from their host galaxies when at their most active. These powerfully emitting super-massive black holes are termed Active Galactic Nuclei (or AGN), with the brightest of all classed as Quasars.

The MUSE data from which Jil was originally detected. In this zoomed out image, Jil’s light is lost in the bright light of LBQS 0302–0019 (the brightest source in the image).

Given our Universe is dynamic and steadily evolving with galaxies moving around, and towards, each other under the influence of gravity, a natural question is to ask what happens when these SMBHs meet? Durham astronomers are involved in a number of studies looking for meetings between distant AGN or Quasars to better understand the evolution of galaxies and their SMBHs. One such study recently published in the Monthly Notices of the Royal Astronomical Society [1], has found one such meeting, with an AGN approaching close by to a distant bright Quasar. This pair, lying at almost 100 million light years from the Earth, represents one of the closest known pairings of two active super-massive black holes. The Quasar, bright enough to have been known for a few decades already, was hiding in the outskirts of it’s bright light, a fainter SMBH which has only now been discovered due to recent advances in technology and in particular the MUSE integrated field spectrograph on the VLT in Chile. LBQS 0302–0019, as the bright QSO is known, was observed as part of the Durham-led VLT LBG Redshift Survey (VLRS [2,3]) and with these observations, the study identified the counterpart AGN due to light emitted from Helium ions around it’s centre, and christened it JIl, (or to translate from Klingon: neighbour).

An image from the KMOS integral field spectrograph showing emission from oxygen ions from Jil (circled) and the extremely close (and extremely bright) Quasar LBQS 0302–0019.

In this latest paper, the team have confirmed JIl to be a genuine source using the (partially Durham-developed) KMOS infrared spectrograph on the VLT, identifying the presence of Oxygen ions in the AGN via their bright emission at optical wavelengths [4]. JIl is separated from its close neighbour by 17,000 light years, which is smaller than the extent of our own galaxy, the Milky Way.

JIl represents an excellent opportunity to understand what happens when active galaxies approach each other in the early Universe, and understand how SMBHs and their host galaxies coming together can contribute and potentially accelerate the growth of these massive beasts.

* Possibly translates from the original Klingon as — “May your star have a close neighbour”.

[1] Husemann et al. (2018a) “Discovery of a dual AGN at z~3.3 with 20kpc separation” (arxiv:1801.05442)

[2] Bielby et al. (2013) “The VLT LBG Redshift Survey — III. The clustering and dynamics of Lyman-break galaxies at z ~ 3” (arXiv:1204.3635)

[3] Bielby et al. (2017) “The VLT LBG redshift survey — VI. Mapping H I in the proximity of z ~ 3 LBGs with X-Shooter” (arXiv:1610.09144)

[4] Husemann et al. (2018b) “A cosmic dance at z~3: Detecting the host galaxies of the dual AGN system LBQS 0302–0019 and Jil with HAWK-I+GRAAL” (arxiv:1805. 09845)

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