12th Birmingham-Nottingham Extragalactic Workshop
27-28th September 2010
Variable High-Energy Emission from M 87 Across the Years: Radio to TeV from 2005 to 2010
The nearby AGN M 87 was the first radio galaxy detected in very-high energy gamma-rays. After the detection of rapid TeV variability by the H.E.S.S. telescopes in 2005, M 87 was the target of a series of monitoring programs across the eletromagnetic spectrum, from radio to gamma-rays. These unprecedented studies have provided a wealth of new information on the structure and physics of the inner jet of this object, which will be reviewed in this talk and allow us to constrain the sites of particle acceleration in relativistic extragalactic jets. Preliminary results on optical and X-ray data of the recent multiwavelength campaign conducted during strong TeV activity earlier this year will also be presented. This new campaign is the first to include polarimetric data as part of its monitoring program, which was obtained with the RINGO-II polarimeter at the Liverpool Telescope.
Radio source populations at z<1
I'll consider the energetic importance of low-luminosity radio-loud AGN in the nearby Universe, in particular distinguishing the roles of `quasar-like' and `low-excitation' radio sources. I'll further examine the evolution of the low-luminosity radio AGN population out to z~1, and discuss the relevance of this for understanding the evolving importance of radio-AGN feedback.
The Co-Evolution of Massive Galaxies and their Supermassive Black Holes over the past 12 Billion Years
Supermassive black holes (SMBHs) are now thought to be a ubiquitous constituent of massive galaxies. Despite their relatively small contribution to the mass of galaxies (< 1/1000) they exert a powerful influence over their evolution, possibly triggering star formation and being ultimately responsible for shutting this star formation off. Tight relationships are found to exist in the local Universe between global properties of host galaxies (such as luminosity, stellar mass and velocity dispersion) and the mass of the central SMBH. This suggests a causal connection between galaxies and SMBHs, the nature of which is still poorly understood. I will introduce my approach to investigate this causal connection through probing the redshift evolution in the M_BH - M_* relation. We utilize NIR imaging from the HST GOODS NICMOS Survey (a 180 orbit HST program to image the GOODS field in the H band) and the POWIR Survey and combine this to the deepest available Chandra X-ray data. (truncated)
AGN Environments to z~1.5 in the UKIDSS Ultra-Deep Survey
Using angular cross-correlation techniques, we find that both X-ray
and radio-loud AGN preferentially reside in overdense environments in
the redshift range 1
Galaxy-scale radio-loud AGN outflows
Most well-studied radio galaxies, particularly those most often considered in the context of AGN feedback, extend over hundreds of kiloparsecs, influencing and being influenced by the surrounding intragroup or intracluster medium. However, we are finding an increasing number of smaller, galaxy-scale radio-loud AGN with signs of strong effects on their host galaxies, such as small-scale shocks surrounding AGN outflows. I will discuss some individual examples of dramatic jet/environment interactions on galaxy scales, as well as showing preliminary results of a survey to determine the importance of this feedback process for the galaxy population as a whole.
What we learn about AGN from black hole binary systems
I will review the properties of the accretion flow (and its associated jet) in XRB and how these change with mass accretion rate. Scaling these up to AGN mass black holes shows that both the radio jet and ionising spectrum should change dramatically as a function of mass accretion rate. This can explain some of the diverse emission line properties seen in unobscured AGN of similar mass (LINER, Seyfert 1 and Narrow Line Seyfert 1s). This may also go some way to explaining radio loud/radio quiet behaviour, as shown in full cosmological simulations which track the growth of black hole mass and spin together with the hierarchical growth of galaxies.
AGN feedback within AMR cosmological simulations
AGN feedback is thought to solve some of the long-standing issues of the numerical modeling of galaxy formation. It offers a nice explanation of the regulation of the cold baryon component in early-type galaxies, and can possibly explain the non-cooling cores observed in some galaxy clusters. I will show, with some cosmological AMR simulations, how the growth of Black Holes is regulated by the feedback from AGN jets. And I will discuss how this kinetic feedback is able to change the cold baryon content of galaxies, and modify the properties of the Intra-Cluster Medium.
Cosmic Feedback from AGN
I'll introduce feedback with some simple arguments and will then spend some time on the kinetic mode in clusters etc.
The Environments of z~1 AGN at 3.6 microns
We present an analysis of a large sample of AGN environments at z~1 using stacked Spitzer data at 3.6um. The sample contains type-1 and type-2 AGN in the form of quasars and radio galaxies, and spans a large range in both optical and radio luminosity. We find, on average, that 2 to 3 massive galaxies containing a substantial evolved stellar population lie within a 200-300 kpc radius of the AGN, constituting a >8-sigma excess relative to the field. Secondly, we find evidence for the environmental source density to increase with the radio luminosity of AGN, but not with black-hole mass. This is shown first by dividing the AGN into their classical AGN types, where we see more significant over-densities in the fields of the adio-loud AGN. If instead we dispense with the classical AGN definitions, we find that the source over-density as a function of radio luminosity for all our AGN exhibits a positive correlation. One interpretation of this result is that the Mpc-scale environment is in some way influencing the radio emission that we observe from AGN. This could be explained by the confinement of radio jets in dense environments leading to enhanced radio emission or, alternatively, may be linked to more rapid black-hole spin brought on by galaxy mergers.
Low-frequency radio maps for the REXCESS cluster sample
Black holes in the cosmic web: host galaxies and large-scale environments of AGN
Large extragalactic surveys allow us to trace, in a statistical sense, how supermassive black holes, their host galaxies, and their dark matter halos evolve together over cosmic time. I will review some recent studies from large surveys that have found significant links between the accretion states of black holes and stellar populations, star formation histories, local environments, and obscuration by gas and dust. I will then discuss observational opportunities with Herschel and the proposed Wide Field X-ray Telescope mission.
Anti-hierarchical growth of black holes
Our aim is to understand the origin of the anti-hierarchical growth of black holes as it is found by many observational surveys. However, currently favored structure formation models imply a hierarchical formation of galaxies and their black holes. Using semi-analytic models based on N-body-simulations (Millennium-simulation) we study the effect of different models for black hole growth on the evolution of AGN number densities in different luminosity ranges. We find that a redshift dependent Eddington ratio as well as an additional accretion channel due to disk instabilities might be important physical processes governing the evolution of high and low luminosity AGN.
Cosmological Evolution of Radio Galaxies and Radio-loud Quasars
The High Redshift Evolution of Radio Source Properties from CENSORS and other Complete Radio Samples.
Jet-ISM interaction
I will present results from 3-D hydrodynamical simulations on the interaction of a bi-polar jet with the surrounding turbulent ISM in a disc galaxy. Our results show that the jet will naturally develop asymmetries for characteristic values for density fluctuations in the ISM. I will present a simple analytic model that can approximate the jet asymmetry and discuss the various stages during the interaction of the jet with the surrounding ISM.
Jet power: What do you do with it?
We have carried out simulations of jets with Fanaroff-Riley (FR) class I & II morphology, and the interaction with their environment. We find that the largest fraction of energy goes into heating and displacing the environment, followed by gravitational uplifting, if the source is cluster-central. A few percent is left to turbulence in the cocoon (lobes). The kinetic jet power can be best inferred by shocks in the ambient medium, which works to high accuracy in the simulations. There are observed examples where cocoon turbulence seems to be able to accelerate cold gas, which also constrains the energetics. We reproduce X-ray cavities in FR I & II sources. We find a total jet power of order a few times the cavity power, depending on type and state of the jet.
Stellar disc-active galactic nucleus alignments in the SDSS DR7
We study the intrinsic shapes and orientations of type I and II AGN galaxies in the spectroscopic sample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), with the aim of investigating the link between AGN and host galaxy alignments and testing the accretion model. We define control samples of non-AGN galaxies that mimic the colour, luminosity and concentration distributions of the AGN population, taking into account the effects of dust extinction and reddening. We characterise the intrinsic shapes of these control samples by studying the distribution of projected axis ratios separated into spiral and elliptical galaxies. We find that the structural parameters of these samples are consistent with that of the full galaxy population of the SDSS DR7, and are not affected by the Seyfert type they mimic. Assuming that AGN populations have the same underlying shapes as their corresponding control samples we find that the type I AGN population is strongly biased toward face-on galaxies, while the spiral type II AGN toward edge-on galaxies. Ellipticals show a much weaker tendency, consistent with random orientations in the case of the type I AGN hosted by ellipticals. These tendencies can be explained with a central obscuring torus of ~40 degrees of azimuthal height located preferentially in the galactic plane. We also find that a subset of AGN (of both Seyfert types) with point-source detections in the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) catalogue also tend to be face-on, possibly indicating that radio jets tend to be parallel to the galaxy disc angular momentum. I will discuss how these findings help to gain insight on the accretion model mainly through the comparison with the semi-analytic model by Lagos, Padilla & Cora.
Constraints on the spin of SMBHs from AGN jets
Overview of the X-ray timing properties of both large and small black hole systems, bringing out the scaling relationships between the two and considering the implications for the origin of the variability. Relationship between larger-scale galaxy properties (optical/radio) and X-ray variability properties.
The impact of AGN feedback on galaxy groups
The properties of galaxy groups are very sensitive to cosmic feedback. I will describe the results of a comparison between observed group properties and the properties of groups in the OWLS simulations - a suite of cosmological simulations specially designed to explore different prescriptions for feedback. We find that significant feedback from AGN is required, and I will briefly describe the rather surprising way in which it operates in the OWLS simulations.
Numerical Models of AGN Feeding and Feedback from First Principles
Evidence for a shocked outflow in NGC 4051
A new 600 ks XMM observation of the bright Seyfert galaxy NGC 4051 has revealed a rich absorption line spectrum indicating the presence of a photo-ionised outflow with a wide range of velocities and ionisation parameter. The velocity and ionisation structure are consistent with an initial high velocity wind running into the ISM or previous ejecta. Although much of the kinetic energy is lost in the resulting strong shock, conservation of momentum in the flow would maintain the potential of such AGN winds as an important feedback process.
The effects of radiation pressure on the absorption in the Chandra Deep Field
The presence of gas around the central engine of an Active Galactic Nuclei (AGN) is a common feature of these objects. Recent work has looked at the effect of the dust component of the gas, and how it enhances radiation pressure in a way that dusty gas can have a lower effective Eddington limit than ionised gas. In this work, we use multi-wavelength data and X-ray spectra from the 2 Ms exposures of the Chandra Deep Field North and Chandra Deep Field South surveys, to characterise the AGN in terms of their Eddington ratio and hydrogen column density. Their distribution are then compared with what is predicted when considering a coupling between dust and gas. We find that most of the AGN in our sample tend to be found at low Eddington ratios (typically between 10^-4 and 10^-2) and high column densities (>1e22 cm-2) with black hole masses in the range (10^8 - 10^9) solar masses. Their distribution is in agreement with predictions from the enhanced radiation pressure model, avoiding the area where we would expect the presence of outflows. We also investigate the behaviour of clouds in the galactic bulge, and predict how the transition from long-lived obscuration to outflows in AGN could be studied in future observations with the International X-Ray Observatory (IXO).
The link between AGN activity and the star formation
The link between AGN activity and the star formation history of their hosts is explored through studies of a sample of SDSS early-type galaxies. In particular, I will focus on galaxies showing dust features. Stellar population and AGN ages places these objects on an evolutionary sequence, and they are argued to be largely post-starburst galaxies with recent star formation diven by a gas-rich minor merger. Implications for AGN feedback in quenching star formation are discussed.
Star Formation in Powerful High Redshift Radio Galaxies
High-redshift radio galaxies (HzRGs) are unique markers of the most powerful galaxies in the early Universe, showing signatures of both highly accreting AGNs and extreme starbursts. As HzRGs have massive host galaxies we are likely observing the coeval formation of the most massive systems in the local Universe. The presence of a powerful radio jet indicates a special time in the formation of a massive galaxy, but exactly how the jet effects the evolution of the host galaxy remains unknown. I will review current and future efforts to study star formation and the physical conditions in the host galaxies of HzRGs. In particular I will include recent, and up-coming results with the Herschel Space Observatory, an important tool in understanding the galaxy/black hole connection over the next few years.
Triggering luminous AGN in galaxy mergers and interactions
This would present new Gemini imaging observations for samples of luminous radio-loud and radio-quiet AGN, along with results on their star formation histories based on ground-based optical spectra and Spitzer photometry/spectra. The results show that galaxy mergers and interactions are likely to be a major driver for luminous AGN activity, although the triggering of such activity does not solely occur in a single phase of a particular type of galaxy interaction/merger.
We investigate the properties of 70um selected sources in the Chandra Deep Field South, where there is extensive multi-wavelength data we are able to exploit. The 70um catalogue used in the study combines all the publicly available 70um Spitzer data, which we combine and re-reduced using techniques similar to Frayer et al. (2009). This makes our 70um catalogue currently one of the deepest, which contains sources with fluxes > 2.8mJy at 5 igma. In order to search for X-ray counterparts we combine that 2Ms CDFS catalogue (Luo et al. 2008) and the Extended Chandra Deep Field South catalogue (Lehmer et al. 2005). We find X-ray counterparts for ~33% of our 70um sources. We then determine the X-ray luminosity and the total infrared luminosity for each source, and compare to the star- formation relationship of Ranalli et al. (200?). We assume that sources with X-ray luminosity > 10^{42} erg/s host an AGN, and we find that the AGN fraction increases with an increase in the total infrared luminosity. The total infrared luminosity increases with redshift, we also find that sources with X-ray luminosities > 10^{42} erg/s are typically at the highest redshifts. We also look at the optical colours of the 70um sources with X-ray emitting AGN and compare these to the optical colours of other 70um sources.
Energy exchange mediated by radio galaxies: one size doesn't fit all
I will use data taken primarily from Chandra and the VLA, to show different examples of energy releases where radio plasma acts as the mediator for the deposition of energy at galaxy-scale distances from a supermassive black hole. Energy may be released on galaxy scales either promptly after accretion (e.g., via jet propagation) or in delayed processes (e.g., where a reservoir of energy is later released through a merger). Such a range of delays, coupled with evidence for intermittent AGN activity, suggests that the controlling parameters of feedback should be sought over integrated timescales that are a significant fraction of the lifetime of galaxies.