Astrophysics at Southampton

Lead Research Organisation: University of Southampton
Department Name: School of Physics and Astronomy

Abstract

Understanding accretion onto, and emission from, compact objects, including the relationship between high energy (X and Gamma-ray) emission and optical and radio emission, with particular emphasis on time domain studies, remains an important part of group research. Previously our main strengths were in the study of solar-mass scale compact objects, eg X-ray binary sources (XRBs). Whilst we retain this strength, the recent expansion of the group, coupled with considerable turnover of staff, has enabled us to enhance our research in the extragalactic and cosmological areas where previously we were less strong. Thus, overall, the group is more balanced.

On the most local scales, we are expanding our studies of the earth's magnetosphere to encompass that of other planets within our own solar system, particularly Saturn, to improve our understanding of magnetospheric field line reconnection. Magnetic fields are important in jet formation so we will be investigating the magnetic field line strengths in jets in star-forming regions and young stellar objects to improve our understanding of protostellar evolution. On small 'compact object' scales we are modelling the evolution of the strange Super Fast X-ray Transients (SFXTs), originally discovered by the ESA Gamma-ray/hard X-ray observatory, INTEGRAL, whose development we led. We also wish to understand the physics behind magnetic accretion onto rotating neutron stars in XRBs and model the 3D accretion structures. We also wish to understand the transition from accretion powered neutron stars in XRBs to rotation powered radio pulsars at lower accretion rates. We will study, by observation and modelling, whether the behaviour of accretion physics at near the maximum possible (Eddington) accretion rate is the same for systems of all black hole (BH) masses.

We are carrying out a deep eMERLIN radio legacy survey (LeMMINGs) of a complete sample of 280 nearby galaxies to determine whether the local environment (ie galaxy type) or BH mass affects the accretion onto the supermassive BH in the nucleus. We will also discover the exact relationship between BH mass, radio and X-ray luminosities in different galaxy types. For X-ray bright AGN we are quantifying the geometry of their central X-ray sources and surrounding material, eg accretion discs, in the strong gravitational fields around black holes by General Relativistic modelling of the time lags between X-ray energy bands. We are also trying to understand the relationship between the X-ray emission in AGN and that in the optical and radio bands.

Much of the observed behaviour of compact objects on all scales may be explained by surrounding outflows which modify and reprocess the nuclear emission, producing optical/uv emission lines and resulting in variable X-ray absorption. We are developing a wind model to explain these observations for AGN. Jets from AGN, through feedback of energy, can seriously affect the growth and appearance of surrounding galaxies and clusters. We are carrying out the first survey to determine how this interaction actually occurs at high redshift (z > 1). To provide a cosmological framework into which our other work can fit, we are modelling the large scale evolution of galaxies and their distribution via semi-analytic techniques, including energy input from AGN. These models will be compared with the evolving luminosity functions of AGN and SFGs we will derive from the deepest eMERLIN survey (eMERGE). On the very largest scales we are measuring the geometry of the universe itself using Supernovae as standard candles.

Although our work is mostly based on observations, almost all cases now contain a substantial fraction of theoretical or computer modelling. This modelling is obvious in the galaxy evolution and QSO wind cases but is also very important, eg, in SFXTs and neutron star XRBs and in AGN X-ray lags.

Planned Impact

The work of the Southampton Astronomy Group addresses some of the biggest questions in modern astrophysics, bringing benefits through public understanding and curiosity, providing cultural enrichment via collaborations between our scientists and the arts, and through links with industrial partners to provide economic prosperity. This new grant will consolidate and broaden the variety and scope of this impact.

Astronomy remains at the forefront of public engagement in science with a high profile and almost insatiable public interest. In total, our group directly reaches over 18,000 students and members of the public each year, across all its outreach and public engagement activities. Our highlights are the departmental "astrodome", which has visited 90 schools and reached over 20,000 students from Primary to A-level age over the last 2.5 years years. We also hold annual astronomy events for BBC Stargazing Live in January, and Science and Engineering week in March, and over the last 3 years have reached over 1,700 members of the public. At the University 60-year anniversary event (60@60) in June 2012, our LOFAR planetarium showcased our research to over 150 members of the public

In June and Sept 2013 we showcased UoS astrophysics research at the Cheltenham Science Festival and the Bestival music festival. The main focus of our Research Roadshow stand was the research of the INTEGRAL telescope and the spin off company Symetrica. At these 2 festivals we engaged with over 1400 members of the public, of all ages and over 400 people participated in a quiz on our research subjects.

While these activities have traditionally focussed on the general public and students, more recently there have been targetted opportunities to give support to teachers, such as the School's partnership with the local Science Learning Centre. This support has long-term value for their future teaching of basic scientific principles. Our outreach activities are also enhanced through the new Winchester Science Centre and Planetarium, in which we play a significant role.

Although our scientists also participate in standard outreach activities (e.g., local science cafes, regional astronomical societies, blogs and social media), we also look beyond these to reach new audiences. This includes group members actively seeking collaborations with the arts and other vehicles for cultural impact, including contributions to exhibits in Tate Modern ("All the dead stars"), musical compositions based on astrophysical spectral time-series, poetry inspired by dark matter, and art installations based on pulsars using the frequency of pulsars as a musical frequency.

Exploiting astronomy research in completely different environments has always been important in the Astronomy Group. For example, the Astronomy group has a distinguished body of work on the design of technology for gamma-ray detection and imaging, and has informed new counter-terrorism practices. Technological advances arising from the research have been crucial to delivering significant benefits in the fields of homeland security and nuclear safety, the latter particularly in the wake of the 2011 Fukushima disaster. A spin-out company, Symetrica, currently employs 26 people in the UK and the US, has a forecast turnover of more than £10m for 2013-14, and has been recognised as an example of best practice. It is a technological leader in the field of radioactive isotope identification.

We also provide a significant source of trained, skilled PhD graduates for non-academic professions. Our astronomy/astrophysics PhDs, with their analytical and data skills, remain sought after in industry. Southampton-trained graduates have entered fields related to imaging systems (including radiation imaging), big financial data projects (identifying patterns of money laundering), Symetrica, and the
education sector.

Publications

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Higginbottom N (2019) The luminosity dependence of thermally driven disc winds in low-mass X-ray binaries in Monthly Notices of the Royal Astronomical Society

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Higginbottom N (2020) Thermal and radiation driving can produce observable disc winds in hard-state X-ray binaries in Monthly Notices of the Royal Astronomical Society

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Heesen V (2016) Advective and diffusive cosmic ray transport in galactic haloes in Monthly Notices of the Royal Astronomical Society

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Harwood JJ (2016) FR II radio galaxies at low frequencies - I. Morphology, magnetic field strength and energetics. in Monthly notices of the Royal Astronomical Society

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Harwood JJ (2016) FR II radio galaxies at low frequencies - I. Morphology, magnetic field strength and energetics. in Monthly notices of the Royal Astronomical Society

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Harwood J (2017) FR II radio galaxies at low frequencies - II. Spectral ageing and source dynamics in Monthly Notices of the Royal Astronomical Society

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Harwood J (2015) Spectral ageing in the lobes of cluster-centre FR II radio galaxies in Monthly Notices of the Royal Astronomical Society

 
Description We carried out a number of projects based around observational and theoretical studies of galaxies and of 'active galactic nuclei (AGN)', ie accreting super-massive black holes (SMBHS) in the nuclei of galaxies.

We observed all 280 northern galaxies from the 'Palomar Sample' with the UK-based eMERLIN high resolution radio telescope array. This was the second largest 'legacy' observing programme carried out by eMERLIN. The Palomar sample is the most statistically complete sample of nearby galaxies and a wealth of data exists in other wavebands. We found many new, low luminosity, radio sources in the nuclei of these galaxies, half of which showed clear jets. We found very small, but complex and extended, radio structures in many galaxies, which are more common than previously thought. We found that core radio luminosities correlate with mass of the SMBHs for masses down to 10 million solar masses, but not below. We found that as long as they showed a radio jet, starforming galaxies, whose radio properties had not previously been greatly studied, followed the 3D relationship between black hole mass, radio and X-ray luminosity that had previously been demonstrated for the so-called 'active' galaxies, ie Seyferts and LINERS.

The origin of supermassive black holes and the connection with their host galaxies remains highly debated. We performed Monte Carlo simulations which suggest that it's not the stellar mass, but rather the velocity of the stars ("velocity dispersion") that is the true driver behind the relationship between black holes and their host galaxies. These findings strongly favour "energy-driven" (also known as ''quasar feedback") rather than "merger-driven" models of black hole growth. Merger-driven models predict a strong correlation between SMBH mass and the stellar mass of the bulge of the galaxy whereas energy-driven models predict, as observed, a stronger relationship between SMBH mass and stellar velocity dispersion. The Royal Astronomical Society put out a press release on this work in 2016.

Over the course of the grant period, we made excellent progress towards our ultimate goal of developing a full radiation-hydrodynamic model of disk winds in quasars and X-ray binaries. We have been proceeding quite systematically, starting with the implementation of realistic heating and cooling rates (calculated by our radiative transfer code) into hydrodynamic simulations of thermally driven disk wind. We then succeeded in coupling our radiative transfer code directly to a hydrodynamics code, allowing us to simulate such disk winds self-consistently for the first time. We have also continued to collaborate on other applications of our radiative transfer code, using it to model the spectroscopic signatures of quasar disk winds, as well as their reverberation signatures.
Exploitation Route There is still much work to be done in extending our hydrodynamic model to explain the observed multiwavelength variability of AGN. Cosmological modelling also needs to be revamped to take account of our working showing that velocity dispersion is a major driver of the link between AGN and galaxies. There is also much more work to be done in both the interpretation of our radio observations of nearby galaxies and in extending the observational work to higher frequencies where the AGN should be more dominant.
Sectors Education

URL http://adsabs.harvard.edu/abstract_service.html