Searching for high-brightness temperature AGN cores in surveys using high-resolution radio data


October 2024


e-MERLIN observations of OH masers confirm outflowing gas in Zw049.057

Some of the most luminous galaxies in our (local) universe are covered by thick layers of gas and dust, rendering them only visible at radio and millimeter wavelengths. Recent observations are uncovering that behind the curtain of dust lie dynamical systems, where gas flows inward to fuel the supermassive black hole, while powerful outflows expel gas out of the galaxy.

Observations using the e-MERLIN telescope have now revealed a powerful tracer of these processes. In the dynamical galaxy nucleus of the luminous infrared galaxy Zw049.057, hydroxyl (OH) molecule emissions are amplified through a laser-like process, forming OH megamasers. While these OH megamasers are well known to emanate from luminous galaxies, high-resolution e-MERLIN observations were able to give the first interferometric confirmation that the OH megamaser is coming from outflowing gas.

In combination with ALMA data, Lankhaar et al. (2024) were able to make a reconstruction of the complex gas flows within Zw049.057. They discovered that the OH megamaser traces a slow, wide-angle outflow that is enveloping a faster, collimated outflow detected through HCN emission. These two distinct outflows illustrate the dynamic processes in the galaxy’s nucleus, with the slower outflow likely falling back into the galaxy, while the faster outflow may escape into the intergalactic medium. The combination of inflows and outflows in Zw049.057 provides key insights into the evolution and powering of such luminous, dust-enshrouded galaxies.

Read the full article here (Lankhaar et al. 2024).


A new astrophysics centre for Multimessenger studies in Europe – ACME


September 2024


e-MERLIN joins a new EU-funded project dedicated to multi-messenger astronomy

On the 16th and 17th of September 2024 the kick-off meeting for the Astrophysics Centre for Multimessenger studies in Europe (ACME) was held in Paris. This EU-funded project is coordinated by Centre national de la recherche scientifique (CNRS) and aims to realise an ambitious coordinated European-wide optimization of the accessibility and cohesion between multiple leading astroparticle and astronomy research infrastructures. The e-MERLIN/VLBI National facility which the University of Manchester operates on behalf of STFC, and expertise from the UK’s SKA Regional Centre will be key part of this project, offering access to instruments, data and expertise, focused on the new science of multi-messenger astrophysics.

With 40 world-class collaborating institutions, from 15 countries, including the Jodrell Bank Centre for Astrophysics, ACME brings together the astroparticle and astronomy communities in a joint effort to forge a basis for strengthened long-term collaboration between these research infrastructures irrespective of location and level-up access opportunities across Europe and beyond.

The ACME project coordinator Prof. Antoine Kouchner (CNRS/Université Paris Cité), and co-coordinator Paolo D’Avanzo (INAF), represent each community to ensure balance and drive cross-domain collaboration.

“ACME is an incredibly exciting opportunity. This project will bring together a wide range of world-class researchers and astronomical research infrastructure spanning astroparticle and gravitational wave facilities along the entire electromagnetic spectrum, with a common focus to advance multi-messenger astrophysics,” says Prof Rob Beswick who co-leads ACME’s transnational access programme and the University of Manchester’s involvement.

ACME will also develop six new multi-messenger Centres of Excellence across Europe. These will be new hubs of expertise supporting all researchers in all aspects of direct and multimessenger science programmes (from proposals to data analysis and science interpretation). Dr David Williams-Baldwin, who leads JBCA’s involvement in these new Centres of Excellence says “The ACME project will bring many infrastructures and groups together across Europe in a unique collaboration to provide the astronomy and astro particle communities unprecedented access to data, workflows and expertise. ACME will revolutionise how researchers in multi-messenger fields work and collaborate in the future.”

You can find out more at the project page here.


e-MERLIN Cycle 18 results announcement


July 2024


The e-MERLIN Time Allocation Group met on 5th July 2024 to consider proposals for Cycle-18. Proposals were received for L-Band (1.3-1.7 GHz), C-Band (4.5-7.5GHz), and K-Band (19-25 GHz). The amount of time approved is set by existing programme observation requirements, scheduling and engineering constraints, and by EVN commitments within the Cycle-18 period.

The e-MERLIN Cycle 18 call for proposals list of accepted proposals is below (in no particular order). The next call for proposals is anticipated in Autumn 2024.

  • Coordinated e-MERLIN and Chandra Observations of BZ Cam: Accretion and Outflows in Nova-likes
  • An e-MERLIN quest for the persistent radio emission associated with FRBs
  • Radio counterparts of the GW sky with e-MERLIN
  • Precise calorimetry of large-scale jets from black hole X-ray binaries
  • Was LSXPS J0956 a tidal disruption event with a structured jet?
  • Flaring and polarization of 4.765 GHz exOH and 6.7 GHz methanol masers in Mon R2
  • Resolving the sub-kpc structures in red quasars
  • Unveiling the nature of X-ray Flashes in the Einstein Probe era
  • On the origin of the kpc-scale radio emission in AT2021hdr
  • Resolving kpc-scale relativistic jets at high redshift
  • Localising repeating FRBs with VLBI -- continued need for eMERLIN
  • Monitoring the new-born jet in changing-look AGN 1ES 1927+654
  • e-MERLIN monitoring of the changing angle jets from GRS 1915+105
  • Feedback in LINERs: connecting the radio emission and the ionised gas
  • Continued eMERLIN monitoring of ZTF22aaajecp/AT2022cmc: the first jetted tidal disruption event in a decade
  • High-resolution observations of short GRBs beyond the LIGO horizon
  • Peering into the heart of the young AGN in HCG15
  • Catching the delayed and fast rising radio emission from a faint TDE in a dwarf galaxy
  • Revealing episodic jet ejections from a candidate relativistic TDE in a starforming galaxy
  • Long term observation of SN2017eaw
  • Chasing high-redshift gamma-ray bursts with e-MERLIN
  • Catching the formation of accretion disks and jets in black hole X-ray binaries


New insights on the high-mass star formation using methanol and water masers in G59.783+0.065


June 2024


20 years of monitoring using MERLIN, e-MERLIN, KVN, VERA and EVN have enabled a reconstruction of the complex structures surrounding the high mass star.

The processes that form high-mass stars can be probed by high-resolution studies of Methanol masers, which are bright tracers of the 3D structure of the disk-like accretion flow. Methanol masers are excited closer to high-mass protostars and can be used to infer the location of the star and study the circumstellar kinematics. However, the distribution of observed Methanol masers is often complex when observed with VLBI which may indicate the aforementioned rotating disc-like structures or in some cases expanding and/or infalling motions. In addition some Methanol masers can be excited by outflows, so ascertaining the direct cause of the maser is often difficult and may point to multiple processes.

In this work by Momotaro Nakamura, Kazuhito Motogi and colleagues, archival MERLIN and new e-MERLIN data from 2019 were combined with VERA and JVN observations of the methanol (at 6.7 GHz) and water (at 22 GHz) masers in a high-mass star forming region named G59.783+0.065 to study the distribution of masering components. Two decades worth of data enabled the researchers to see how the maser clusters changed over a prolonged period. For example, archival MERLIN data (Darwish et al. 2020) only saw the western cluster of water masers, but the first, second and third epochs of the new data confirmed a ‘pair-like’ distribution with an eastern cluster, which disappeared in the fourth epoch along with the water masers. However, the distribution of methanol masers remained stable throughout all epochs from 2004 to 2019, despite some individual spots only showing up for short periods. This suggests that the environment for pumping the methanol masers has remained consistent over a long time period, whereas the water masers were only found in the western cluster in pairs in specific epochs, suggesting episodic mass accretion leading to an outflow/shocks producing the water masers.

In context, the variety of structures and clusters of the eastern and western methanol and water masers provides evidence for: 1) a bipolar outflow, traced mostly by the water masers; 2) the methanol masers in the eastern structure show some inward motions which may be explained by them being produced at the edge of the outflow and the infalling envelope; 3) the western methanol masers are perpendicular to the outflow which may indicate that they are in a rotating disc-like structure. These multi-epoch, multi-frequency observations studying the different types of maser have produced the schematic model in the figure above, which can only be performed with high-resolution high-sensitivity VLBI arrays.

Read the full article here (Nakamura et al. 2023).


Submit an abstract for the SKA Pathfinders session at NAM!


May 2024


Join a plethora of other SKA Pathfinder scientists including e-MERLIN at NAM 2024 in Hull.

We are happy to announce a parallel session entitled “Era of SKAO Pathfinders – Pushing the Boundaries of the Radio Sky” will be held at NAM 2024 hosted in Hull. The session has 2, 2-hour slots on the Monday of the conference (15th July) and we are accepting abstracts with the deadline of 3rd June.

The Square Kilometre Array Observatory (SKAO) will revolutionise our understanding of the radio sky and with the SKAO-Mid prototype dish having achieved first light, the future of radio astronomy is in sight. To prepare for such an impressive instrument, SKAO pathfinders (such as, LOFAR, e-MERLIN, MeerKAT) have already pushed, and are continuing to push, the boundaries of what is possible. It is important to show the wider astronomical community the vast science that has been conducted at low to mid radio frequencies and what has already been done to prepare for the transformative results the SKAO will bring.

This session will enable the UK astronomy community, particularly early-career researchers (ECRs), to present their cutting-edge research conducted using SKAO precursors. We will welcome a wide scope of science to this session to emphasize the widespread impact that current radio facilities are having on science topics such as galaxy evolution, AGN, transients, pulsars and cosmic magnetism as well as technical challenges such as the confrontation of large data sets in radio imaging. Discussion of how such research prepared us for the SKAO will help us understand the path toward its survey operations.

Find out more about the NAM here.


The paradigm of U/LIRGs with e-MERLIN and VLA


April 2024


Using a novel method to decompose AGN activity from star formation, the star formation rate is found to be higher than previous studies in four Ultra-Luminous Infrared Galaxies.

The class of objects called Ultra-Luminous and Luminous Infrared Galaxies (U/LIRGs) are bright infrared emitters. They are characteristic of massive merger interactions and high rates of star formation, at different spatial scales, both in nuclear regions (<0.2-1 kpc) and on large-scale structures. Understanding how star formation takes place in these systems plays a pivotal role in studying their dynamics and evolution. Alongside this, characterising local U/LIRGs with high-angular resolution helps us to understand the star-formation and mass assembly of the Universe at higher red-shifts.

The radio emission in the nuclear regions of these systems is a mixture of AGN activity, starburst, jets and star formation. Decoupling these individual processes to study them separately has proven difficult and led to inaccurate measurements of star formation rates or AGN power. The PARADIGM project, alongside with the e-MERLIN Legacy Project LIRGI, aims to measure the radio emission on 10s pc-scales, thus disentangling the emission mechanisms.

In this recent work, Geferson Lucatelli and collaborators investigated an alternative approach that uses combined interferometric arrays (e-MERLIN + VLA) at 6 GHz to obtain a multi-scale tracer for star-formation. Using e-MERLIN, the compact AGN emission is disentangled from the nuclear extended radio emission, and was thus used to quantify the nuclear star-formation. The VLA data helped to probe the larger-scale emission, translating it to star formation without the contamination from possible AGN emission, which was removed with the e-MERLIN data.

The main result of the pilot study showed that the total star formation rate (SFR) of these sources can be significantly higher when using a multi-scale metric, since it takes into account the nuclear star formation. This effect provides a boost to the total SFR output, and in some occasions, dominates the large-scale SFR.

The next phase of this work, is to expand the same concepts for the full LIRGI sample (42 U/LIRGs), and using multi-wavelength observations, separate different emission mechanisms (thermal and non-thermal) across various frequency and spatial scales, on a component-by-component basis.

Read the full article here (Lucatelli et al. 2024). The source code can be found at Github


Milliarcsecond Localisation of the Hyperactive Repeating FRB 20220912A


March 2024


An astonishingly active repeating fast radio burst source has been pinpointed to milliarcsecond precision, thanks to an ad hoc array of European VLBI Network and e-MERLIN dishes.

The majority of fast radio bursts (FRBs) are observed as single, millisecond-duration radio pulses originating from extragalactic distances. While a small fraction (~3%) of these sources repeat sporadically and infrequently, FRB 20220912A stands out as one of the most active FRB sources known to date. Discovered by the Canadian Hydrogen Intensity Mapping Experiment FRB project (CHIME/FRB), this single source contributed a few percent of the entire all-sky rate of FRBs above a fluence threshold of 100 Jy ms during its peak activity! Consequently, it has become the focus of numerous follow-up campaigns, including localization efforts involving e-MERLIN.

In a recent paper, Danté Hewitt and colleagues from the PRECISE FRB-localisation programme, detected 150 bursts from the hyperactive repeater FRB 20220912A, allowing it to be pinpointed to a precision of a few milliarcseconds - hundreds of times more precise than previous localisations. This revealed that FRB 20220912A resides closer to (albeit still offset from) the center of its host galaxy, which was earlier identified using a localisation from the Deep Synoptic Array 110 (DSA-110). The observations also ruled out the presence of a compact persistent radio source at the FRB location, a phenomenon observed in some other active repeaters, and theorised to be hypernebulae powered by neutron stars. Instead, the persistent radio emission on larger angular scales is most likely due to star formation in the host galaxy.

PRECISE (Pinpointing REpeating ChIme/frb Sources with EVN dishes) is a project to localise repeating FRBs to the best-possible precision by making use of ad-hoc arrays of radio telescopes. Approximately half of these dishes also form part of e-MERLIN. Typically, angular resolution on the order of milliarcseconds is achieved in PRECISE FRB localisations. In the past this has facilitated not only the identification of host galaxies of FRB sources, but also enabled detailed studies of their local environments using, e.g., the Hubble Space Telescope. Such milliarcsecond localizations will prove particularly valuable in the coming era, where optical telescopes like the Extremely Large Telescope will match the milliarcsecond resolution of VLBI, allowing us to zoom-in on the local environments of FRB sources at the (sub-)parsec level in their host galaxy; perhaps even leading to the discovery of extragalactic stellar counterparts to FRB sources.

Read the full article here (Hewitt et al. 2024).


Searching for high-brightness temperature AGN cores in surveys using high-resolution radio data


March 2024


Extragalactic Survey fields provide a rich hunting ground for Active nuclei, but multiple resolution interferometers are needed to tell them apart from star formation.

Deep radio surveys of extragalactic legacy fields trace a large range of spatial and brightness temperature sensitivity scales, and therefore have differing biases to radio-emitting physical components within galaxies. This is particularly true of radio surveys performed at ≲1 arcsec angular resolutions, and so robust comparisons are necessary to better understand the biases present in each survey.

Ann Njeri and her team performed a multi-resolution analysis of 24 sources detected in a new Very Long Baseline Array (VLBA) survey of the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey Great Observatories Origins Deep Survey-North field. This VLBA data were augmented by ~0.1-1 arcsec angular resolution data provided by the European VLBI Network, the Very Large Array (VLA) and the enhanced-Multi Element Remotely Linked Interferometry Network (e-MERLIN).

The high brightness temperatures of these sources (> 1 million Kelvin) confirm AGN cores as measured by VLBI. These sources would often be missed or ambiguous in lower-resolution radio data of the same sources. By combining VLA and VLBI measurements, they find evidence that most of the extended radio emission is also AGN dominated, with only ~13% of the sources showing a likelihood of being star formation-dominated. Combining e-MERLIN and VLBI reveals potentially hybrid systems that are missed in either individual surveys. This survey demonstrates the importance of wide-field multi-resolution (arcsecond-to-milliarcsecond) coverage of the faint radio source population, for a complete picture of the multiscale processes within these galaxies.

Read the full article here (Njeri et al. 2024).


ORP Multi-facility call announced


March 2024


An opportunity to propose for 18 facilities simultaneously in the radio and optical has been announced through the Opticon RadioNet Pilot programme.

The Opticon RadioNet Pilot (ORP) has launched as new Multi-Facility Call for Proposals to use multiple observatories for the same scientific project. 18 radio and optical facilities are available and proposers are asked to submit for time on more than one facility as part of this call. The deadline is the 9th April 2024 at 1400UTC.

Find out more about the multi-facility call here.


e-MERLIN Data School announcement


March 2024


The 2nd e-MERLIN data school has been announced, taking place in Manchester from 13-15 May 2024

e-MERLIN support staff, with funding support from the Opticon RadioNet Pilot, will be running a data school at the University of Manchester from 13-15 May 2024. The purpose of this school is to show participants how to reduce e-MERLIN data using the e-MERLIN CASA Pipeline. The school is designed for those with some radio astronomy knowledge. Priority will be given to PhD students and early career researchers. The three-day school will include calibration, imaging and self-calibration tutorials, with an opportunity to bring your own data (BYOD) to get expert help with your own e-MERLIN projects. We expect to be able to have space for up to 10 participants.

Find out more about the 2nd e-MERLIN data school here.


OH MegaMasers in Arp 220 at intermediate resolution, using MERLIN + EVN


February 2024


The complex OH line activity in Arp 220 has been detected by combining MERLIN and EVN data.

Arp 220 is a nearby system comprised of two merging galaxies triggering significant star formation in the merger. It was the first system to be detected with hydroxyl (OH) MegaMaser emission, afterwards identified as an archetypal Ultra-Luminous infrared Galaxy (ULIRG). Since that first discovery many more ULIRGs have been discovered with OH MegaMaser emission. ULIRGs tend to be found at higher redshift, making Arp 220 a useful nearby laboratory for the ULIRG population.

In this work by Willem Baan and colleagues, observations obtained in 2003 using MERLIN and EVN have been analysed and combined to study the multiple masering components in Arp 220. The data combination was performed in order to make an intermediate resolution dataset to provide a clearer view of the source. MERLIN on its own does not provide the requisite resolution but detects the larger scale regions; EVN resolves those extended emission regions and only detects higher brightness temperature components.

At intermediate resolution with MERLIN and EVN, the spectral line emission in Arp 220 separates into compact and extended regions distributed across the two nuclei. The strong compact components represent star-formation-related maser sources and provide the first accurate estimate of the systemic velocities of these two very obscured nuclei. On the other hand, the more dominant extended emission regions belong to foreground material at a much lower velocity that is part of the surrounding debris structures, generated by the galactic merger. The far-infrared radiation field from the ongoing star-formation in the nuclear regions serves to excite the OH molecules in those foreground regions. In turn, this results in maser amplification of the radio background as well as re-amplification of the compact components in the nuclear regions.

The results of the MERLIN/EVN synthesis have provided a detailed look at the masering process in Arp 220 showing that indeed excited foreground material can result in amplification of the radio background in the galaxy. This can generate the observed powerful MegaMaser emissions not only of OH, but also those of other masering molecular species. Such a scenario has been proposed along with the first discovery of the OHMM emission in Arp 220, but it had not been verified in detail.

Read the full article here (Baan et al. 2023).


UK SKA regional centre webinar series commences


February 2024


Join the UK SKA regional centre for their first webinar on 7th March 2024!

The UK's SKA regional centre (UKSRC) are starting a monthly webinar series focussing on topics related to the UKSRC and SKAO, including (but not limited to) demonstrator cases; SKA science topics; career pathways; relevant software; tools and data; SKAO Science Data Challenges and project updates. The inaugural webinar is on March 7th 2024 at 12:00 (GMT), with the title "Introducing UKSRC" and led by co-directors Louise Chisholm and Rob Beswick.

For more information about the upcoming webinars and stay up to date, please visit the UKSRC webpage. Also follow the UKS on Twitter & LinkedIn


Re-visiting NGC 1068 with the upgraded e-MERLIN and VLA telescopes


January 2024


By combining new datasets with the upgraded VLA and e-MERLIN telescopes, new images of NGC 1068 show the full jet structure for the first time.

NGC1068 is an archetypal Seyfert galaxy with an active nucleus producing large-scale jet structures. These structures, first observed in the 1980s and 1990s with MERLIN and the old VLA, have compact components and larger diffuse lobes north and south of the core region which interact with the gas and dust in the galaxy. As NGC1068 is a nearby galaxy, the study of it's radio jets is important for understanding how galaxies and active black holes co-evolve. Multiple studies with ALMA show molecular clouds that are shaped and plausibly powered by the radio jet structures. More recently, neutrino emission has been found to be co-incident with NGC1068, suggesting that either the active black hole or the jet is responsible for neutrino emission. New data obtained over the last ten years with the upgraded VLA and e-MERLIN interferometers now enable new studies to find the origin of this emission and study in-depth the affect the radio jet has on the molecular gas.

By combining the VLA and e-MERLIN high sensitivity data, Isaac Mutie, a PhD student at Technical University Kenya has created new images which show the full jet structure at multiple spatial resolutions simultaneously for the first time (see figure above). The new images are more sensitive than the previous observations and reveal a new component, S2a, south of the nucleus. In addition, component C was shown to be variable over the observing timeline between previous studies in the 1990s and the new data from the last ten years. It is still unclear what is causing this variability. Finally, it was shown that the NE jet lobe is powerful enough to drive the molecular outflows observed in ALMA data, showing further the need for multi-wavelength observations of this important source.

Read the full article here (Mutie et al. 2024).


Dealing with irregular PSFs in radio images using e-MERLIN and VLA


January 2024


Simulations of e-MERLIN and the VLA examine a systematic error present in all radio interferometric images employing CLEAN-based deconvolution methods.

An interferometer acts like the lens in an optical telescope, focusing the incoming radio waves. However, it differs in that one can conceptualize it as a telescope with perforations in the lens, preventing the generation of a clear image of the sky. Often this distortion is due to the point-spread function, which distorts the light across the image. The PSF is present in every single observation. The effect of the PSF is removed through a process called deconvolution which typically employs the CLEAN group of algorithms (see below). In these algorithms, the PSF is removed from the flux of the source and an estimate of the instrumental response (known as restoration) with a filled aperture (a lens without the holes) is used to produce the image.

Nevertheless, the restoration step introduces a systematic error in measured flux densities, particularly when dealing with a highly irregular PSF. This occurs when the estimate of the filled aperture response is inaccurate, as highlighted by Jörsäter and van Moorsel (1995). Historically, this effect has been overlooked, thanks to the excellent imaging performance and well-behaved PSFs of many contemporary interferometers. However, the forthcoming generation of instruments may face challenges in this regard. Radcliffe et al. addressed this issue by quantifying the impact of an irregular or poorly behaved PSF and the subsequent deconvolution process on the measured flux densities of astronomical objects. Their findings revealed potential errors that can range from a few per cent to over 250 per cent, a substantial discrepancy that demands consideration (see the figure below).

This paper underscores the critical importance of correcting for this effect. The authors present various solutions, enabling astronomers to accurately measure the brightness of their favourite astronomical objects despite the challenges posed by irregular PSFs and the deconvolution process.

Read the full article here (Radcliffe et al. 2024).


e-MERLIN Cycle 17 results announcement


December 2023


The e-MERLIN Time Allocation Group met on 11th December 2023 to consider proposals for Cycle-17. Proposals were received for L-Band (1.3-1.7 GHz), C-Band (4.5-7.5GHz), and K-Band (19-25 GHz). The amount of time approved is set by existing programme observation requirements, scheduling and engineering constraints, and by EVN commitments within the Cycle-17 period.

The e-MERLIN Cycle 17 call for proposals list of accepted proposals is below (in no particular order). The next call for proposals is anticipated in Spring 2024.

  • Accretion in Bipolar PN Hb12
  • Imaging the Central Engine of AGN powered Outflows
  • Finding the "Missing Flux" in PG 1149-110
  • The e-MERLIN view of the radio counterpart of GW events during O4
  • Comprehensive Study of a Dual AGN System J104454+354055 with e-MERLIN and LOFAR-VLBI: Probing AGN Jets, Lobe Emission, and Dynamics
  • High-resolution view on a kilo-parsec scale radio jet at z=6.1
  • The lensed radio-quiet quasar WISE2329-1258
  • Localising repeating FRBs with VLBI -- the need for eMERLIN
  • A radio view of the first changing multiplicity lensed quasar
  • Revealing dense circumnuclear regions with observations of an extreme coronal line emitting TDE
  • e-MERLIN monitoring of newly discovered slow jets from GRS 1915+105
  • Searching for the radio emission from the nucleus of M31 with e-MERLIN
  • Continued eMERLIN monitoring of ZTF22aaajecp/AT2022cmc: the first jetted tidal disruption event in a decade
  • Spectral evolution properties of a nuclear radio outburst from a massive quiescent galaxy
  • e-MERLIN observations of radio-quiet quasars for revealing the multi-scale radio emission structure
  • E-MERLIN Observations for Super-Eddington Accreting Quasar
  • The jewel in the crown, T Corona Borealis: the nearest recurrent nova poised to go into outburst
  • Mini-AGN NGC 4395: a pc-scale thermal outflow with a termination shock?


e-MERLIN detects the anticipated radio-optical offsets in high redshift candidates of sub-kpc dual SMBHs


November 2023


Gaia astrometric jitter was used to select dual SMBH candidates and the method shows promise with e-MERLIN follow up observations

Dual super massive black holes (SMBH) may appear in the post-merger stage of galaxies, which could play a key role in galaxy formation and evolution. As time goes by, dual SMBHs would get closer to each other due to dynamical friction, form binary SMBHs with a compact orbit and finally coalesce. Searching for close (∼kpc or sub-kpc) dual SMBHs, the progenitors of coalescing SMBHs, thus are essential to probe their dynamical evolution as well as the process of galaxy merging, especially at high redshifts when galaxy mergers occur much more frequently. Such dual SMBHs may appear as a dual AGN (active galactic nuclei) if both SMBHs are accreting, or an off-nucleus AGN, if only one SMBH is active. However dual and off-nucleus AGN were previously found mostly at low redshifts or large separations (> 10 kpc).

In a recent work, Haochen Wang and his team obtained high resolution e-MERLIN images of 5 candidates of high redshift dual SMBHs. These candidate quasars (luminous AGN) were pre-selected with clear astrometric jitters in Gaia EDR3, as the stochastic flux variabilities of the dual or off-nucleus quasar could yield astrometric variation of the photocenter of the dual-SMBH system. e-MERLIN observations revealed a single compact radio source for each candidate. Remarkably, four of them exhibit significant radio-optical offsets, which represent for the anticipated separations between one radio loud nucleus and the optical photocenter of a dual-SMBH system. Such radio-optical offsets are hardly seen in normal quasars, thus strongly favor the scenario of dual or off-nucleus quasars. The team confirms the projected separations of the candidate dual SMBHs could be as small as sub-kpc, and highlights the unique capability of high-resolution radio images to investigate close dual SMBHs.

Read the full article here (Wang et al. 2023).


VLBI Observations of a sample of Palomar-Green quasars


October 2023


Combining e-MERLIN with other VLBI arrays provides insight into radio-quiet quasars radio emission mechanisms

Very long baseline interferometry can be a powerful tool for providing insights into the origins of the nuclear radio emission in quasars. In radio-quiet quasars (RQQs), it is especially important as the radio emission can be due to the presence of a radio jets from an accreting AGN, winds, star formation, coronae, or a combination of the above. In lower-resolution studies, it is hard to disentangle these processes, but at sub-arcsecond resolution, a high-brightness temperature core can be attributed to the presence of jets or coronae from an accreting AGN, rather than star formation or winds. The spectral index, morphology and flux densities of the source also give clues to the source of the emission too. By combining the information from multiple arrays, it is possible to get a statistical understanding of the contribution of these different processes to the observed radio emission.

In these works, published by Monthly Notices of the Royal Astronomical Society, Ailing Wang and her team observed 20 quasars, comprising 4 radio loud (RLQs) and 16 RQQs, from the Palomar Green sample, using the VLA, VLBA, and EVN+e-MERLIN measurements at different resolution scales. In 10/16 RQQ cases, radio emission was unequivocally detected in the VLBA data, with 8 of those exhibiting a compact core. They noticed a division in the RLQs and the RQQs at ~30mJy, with RQQs likely due a combination of star formation and AGN activity. Moreover, the RQQs in their study proved to be highly resolved, due to extended jets or relic emission. One source, PG 0050+124, which was observed with EVN+e-MERLIN demonstrates this well. The combination of longer exposure time, and use of intermediate and long baselines from the e-MERLIN/EVN antennas enabled a noise level of 9µJy/beam, about 2.5 times lower than the noise in the VLBA image at a comparable frequency. Thanks to its impressive sensitivity, the EVN+eMERLIN image of PG 0050+124 unveils a more intricate jet structure.

Read the first article here (Wang et al. 2023a).

Read the second article here (Wang et al. 2023b).


LeMMINGs VI: Investigating the influence of the bulge on AGN activity and host galaxy evolution with Hubble and e-MERLIN


September 2023


Hubble and e-MERLIN observations link AGN and bulge properties in the LeMMINGs survey

The active galactic nucleus (AGN) at the galaxy centre and star formation in the bulge play a crucial role in moderating the growth and evolution of galaxies. The relationship between the mass of the bulge and the mass of the central accreting supermassive black hole powering the AGN is firmly established, with the two growing together. For nearby galaxies, distinguishing between the AGN and the bulge is possible due to the AGN's much higher central surface brightness in the optical, but this is not true for low-luminosity AGN. Furthermore, other nuclear features, e.g., rings and bars can complicate matters, but using high resolution e-MERLIN radio data and Hubble optical data, it is possible to discriminate the AGN from other sources of emission. The resolution of Hubble is comparable to that of e-MERLIN at 1.5 GHz, making the two a perfect synergetic pair for exploring the effect that bulge properties have on AGN, which is one of the goals of the LeMMINGs survey.

The e-MERLIN legacy project (LeMMINGs) provides high sensitivity radio observations of 280 nearby galaxies at 1.5 and 5 GHz, with a milli-arcsecond resolution to detect nuclear radio emission, identifying low-luminosity AGN and supernova remnant shells which can trace star formation. As part of this project, the LeMMINGs team has recently published 1.5 GHz e-MERLIN radio data for the full sample of 280 nearby galaxies. In a subsequent study, the team used data from the Hubble Science Archive and performed multi-component decompositions of optical images for 173 out of 280 galaxies and quantify the impact of various galaxy components (bulge, disc, AGN, bar, ring, spiral arms, and star clusters) on the optical galaxy profile. This allowed them to accurately measure optical bulge properties. In this work, Bil Dullo and the LeMMINGs team investigated the link between the radio core luminosity and the properties of the host bulge as well as its surrounding environment. When compared to the radio data, bulge dominance is linked to brighter radio core luminosities, with the both AGN and radio detection fractions increasing with the bulge mass. Furthermore, the analysis reveals a transition from AGN-dominated radio emission in massive bulges to stellar-driven processes in low-mass bulges. Radio-loud hosts preferred early-type morphology, but no obvious dependence on environment was found for radio loudness, nuclear radio activity, and the AGN fraction at a fixed bulge mass. Radio-loud and radio-quiet hosts are indistinguishable in terms of the Sersic index and ellipticity of the bulge.

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