Parallel Session P31: 1045-1230, Friday 16th April 2010

The Role of Feedback in Galaxy Evolution

Location: Bute


Feedback processes, both from supernovae and AGN, are believed to be an important process in shaping the galaxy luminosity function, with different mechanisms being important at different mass scales. This session will address feedback from both observational and theoretical perspectives and investigate the energetics of the processes at work. Mechanisms for the triggering and termination of star formation and AGN activity will be explored.


  • Chris Simpson (Liverpool John Moores University)



16 April, 10:45The impact of feedback on the orbital content of dark matter haloes.
Sarah Bryan (University of Manchester)
16 April, 11:00Disk Heating: Comparing the Milky Way with Cosmological Simulations
Elisa House (Jeremiah Horrocks Institute, UCLan)
16 April, 11:15The role of feedback in Milky Way satellite galaxy formation using high resolution simulations
Sam Geen (Oxford Astrophysics)
16 April, 11:30Stellar Feedback in SPH Galaxy Formation Simulations
Greg Stinson (Jeremiah Horrocks Institute, UCLan)
16 April, 11:45Super star cluster feedback from local to galaxy scales
Mark Westmoquette (UCL)
16 April, 12:00The Enviroments of AGN at z~1
James Falder (University of Hertfordshire)
16 April, 12:15The Co-Evolution of Massive Galaxies and their Supermassive Black Holes over the last 11.5 Gyrs
Asa Bluck (University of Nottingham)


The Multi-faceted X-ray activity of the complete 3CRR AGN sample at z < 0.1
Elizabeth Mannering (University of Bristol)

Searching for Compton Thick AGN at z~2 in deep X-ray fields
Cyprian Rangel (Imperial College London)

Momentum driven feedback from stellar nuclei
Rachael McQuillin (Keele University)

Stability and evolution of cluster galaxies in MOND
Xufen Wu (Physics and Astronomy, University of St Andrews)

The Cold Gas Content of Bulgeless Disk Galaxies
Kate Pilkington (Jeremiah Horrocks Institute, UCLan)

Cluster and Galaxy Environments of Quasars
Kathryn Harris (Jeremiah Horrocks Institute, UCLan)

The orientation of accretion disks and jets in quasars
Emily Down (UK Gemini Support Group)

Talk Abstracts

The impact of feedback on the orbital content of dark matter haloes.
Bryan, Sarah, Scott T. Kay, Shude Mao
University of Manchester
16 April, 10:45

Galaxies are thought to form hierarchically, through the merging and accretion of smaller systems. As such, there should be observational signatures of these merging processes in the remnant galaxy, providing dynamical information about its formation history. We investigate the orbital content of dark matter haloes in order to explore what observational signatures may result. To do this, we have used the OverWhelmingly Large Simulations, a set of state-of-the-art high resolution cosmological hydrodynamical simulations run with different physical prescriptions for the feedback processes. We quantify the effects of the feedback prescriptions on the dynamics and orbits of the dark matter and stellar particles, by comparing runs with no feedback, with stellar feedback and with feedback from AGN. We compare results of spectral analysis of the orbital content of these simulations and quantify the change in fraction of box orbits as different implementations of feedback are considered, illustrating the influence of feedback processes on the orbital content of the haloes. We also investigate how the orbital content of these haloes depend on several key parameters such as their mass, redshift and dynamical state.

Disk Heating: Comparing the Milky Way with Cosmological Simulations
House, Elisa, C. B. Brook, B. K. Gibson, P. Sanchez-Blazquez, S. Courty
Jeremiah Horrocks Institute, UCLan
16 April, 11:00

We present the analysis of five simulations run with different particle and grid-based cosmological hydrodynamical codes and compare them with observational data of the Milky Way. We study the velocity dispersion versus age for disk stars at z = 0 and find that three of the simulations are more consistent with observations by Holmberg et al. (2008) where the stellar disk appears to undergo continual/secular heating. The other two simulations are in better agreement with the Quillen & Garnett (2001) observations that suggest a ``saturation" in the heating profile for young stars in the disk. We also analyse the kinematics of disk stars at the time of their birth for different epochs in the galaxy's evolution and find that in some simulations stars are born cold within the disk and heat due to a combination of physical and/or numerical processes, while other simulations possess stellar populations which present little or no heating with time. Two of the models which are in better agreement with observations of the Milky Way's stellar disk undergo significantly lower minor-merger/assembly activity after the last major merger, i.e. once the disk has formed. All of the simulations are significantly ``hotter" than the Milky Way disk, a problem likely rooted in the underlying treatment of the heating and cooling of the interstellar medium, and the resolution-dependent density threshold for star formation.

The role of feedback in Milky Way satellite galaxy formation using high resolution simulations
Geen, Sam, Adrianne Slyz, Julien Devriendt
Oxford Astrophysics
16 April, 11:15

We use sub-parsec resolution hydrodynamic simulations of the Milky Way at high redshift to investigate the formation of the Milky Way satellite galaxies. We analyse the influence of supernova feedback on dwarf galaxy formation, and the efficiency of reionisation in suppressing star formation in the smallest galaxies. By locating galaxies in our high redshift simulation and tracking them to z=0 using a halo merger tree, we can compare our results to present-day observations and comment on the hypothesis that reionisation halts star formation in the lowest mass halos. We also consider the effect of adding gas physics to simulations of the formation of dwarf dark matter halos, and the impact this has on the missing satellite problem.

Stellar Feedback in SPH Galaxy Formation Simulations
Stinson, Greg, Chris Brook (UCLan), Jeremy Bailin (Michigan), Sarah Nicerkson (McMaster), Hugh Couchman (McMaster), James Wadsley (McMaster)
Jeremiah Horrocks Institute, UCLan
16 April, 11:30

We present a study of galaxies and their accompanying satellite dwarf galaxies found in the McMaster Unbiased Galaxy Simulations, a series of 15 cosmological SPH simulations of MW massed objects. In these simulations that form a range of galaxy morphologies, we find that the satellite luminosity functions are similar to what is found in the Local Group when effective stellar feedback is utilized. One of the problems with the galaxies formed in these simulations is the dense central concentration of matter found in every galaxy. We explore possible solutions to this problem using alternate star formation and stellar feedback recipes.

Super star cluster feedback from local to galaxy scales
Westmoquette, Mark
16 April, 11:45

Understanding starburst-driven outflows is important for many reasons within the context of galaxy evolution. However, to understand outflows on the large scale, the details of feedback mechanisms from individual star clusters must first be understood. I will discuss recent results from a number of high spatial and spectral resolution integral field spectroscopic studies of the ionized gas environment within a sample of nearby starbursts. These studies are allowing us to build up a picture of (1) how power is fed from super star clusters into the surrounding ISM, (2) how the ISM properties affect how this power is directed, and (3) how the gas outflows evolve structurally and energetically towards the larger-scales.

The Enviroments of AGN at z~1
Falder, James, Jason Stevens, Matt Jarvis
University of Hertfordshire
16 April, 12:00

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 radio-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.

The Co-Evolution of Massive Galaxies and their Supermassive Black Holes over the last 11.5 Gyrs
Bluck, Asa, Christopher Conselice, Omar Almaini, Elise Laird, Kirpal Nandra, Mark Dickinson
University of Nottingham
16 April, 12:15

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. By constructing a volume limited sample of 120 active galaxies at z < 3, we constrain the possible evolution in M_BH – M_* to be less than a factor of 2. Moreover, we use Eddington arguments to calculate the total fraction of massive galaxies that will undergo an active phase in their evolution since z = 3, finding that greater than 25% of all massive galaxies will achieve X-ray luminosities in the Seyfert regime or brighter. From this we deduce that the the total energy released by AGN since z = 3 is greater than 15 times the total binding energy of all massive galaxies in the Universe, within this redshift range. This colossal release of energy must have profound implications on the evolution of galaxies, with many ramification still to be properly understood.

Poster Abstracts

The orientation of accretion disks and jets in quasars
Down, Emily, Steve Rawlings, Devinder Sivia, Jo Baker
UK Gemini Support Group

I will describe how the orientation of a sample of 19 high-z quasars was measured by (i) fitting the broad H-alpha line with a model which includes the emission from a flattened, extended accretion disk; and (ii) by modelling the radio spectral energy distribution with the assumption that the jets are Doppler-boosted. Results are: (i) The opening angle of the obscuring torus is consistent with predictions of the receding torus model; (ii) A possible z-dependent velocity offset between the narrow line region and the accretion disk is found; (iii) Misaligned accretion disks and radio jets, a possible signature of a recent galaxy merger, are rare.

Cluster and Galaxy Environments of Quasars
Harris, Kathryn, R.G. Clowes, I.K. Sochting, G.M. Williger, L. Haberzettl, L.E. Campusano, M.J. Graham
Jeremiah Horrocks Institute, UCLan

Using galaxy clusters and quasars it is possible to look at the large scale environment of quasars and therefore infer which formation mechanisms (e.g., mergers, hot gas theory, galaxy harassment) are most likely to occur. Looking at this over a range of redshifts and quasar luminosities gives an indication of any evolution of this relationship.

Using Canada-France-Hawaii Telescope (CFHT), Cosmic Evolution Survey (COSMOS) and Imamori Magellan Areal Camera and Spectrograph (IMACS) data, galaxy cluster redshifts, positions, and shapes were determined. Where possible, directional information was conserved in order to give more environmental information. This data covers an area of 4 sq. degrees in total and extends to a redshift of 0.8 for the IMACS data and 1.3 for the COSMOS data.

Preliminary results show the quasars appear to lie preferentially in a direction perpendicular to the major axis of the cluster associated with it. This does not change over the redshift range 0.2-0.8. Preliminary results also suggest that at higher redshifts (z<0.5) quasars lie further away from the clusters than at lower redshifts, with quasars at redshifts less than 0.25 lying on average between two and four Mpc from the cluster and for z>0.5 the average is three to six Mpc.These distances are project 2D distance and taken at the redshift of the quasar.

The Multi-faceted X-ray activity of the complete 3CRR AGN sample at z < 0.1
Mannering, Elizabeth, M. Birkinshaw, D.M. Worrall, D.A. Evans, M. Hardcastle, R.P. Kraft, E.S. Perlman
University of Bristol

We present Chandra images of 9 previously X-ray unobserved sources to complete observations of the 3CRR low-redshift radio galaxy sample. The 36 sources of the complete sample also have excellent multi-wavelength radio data and have been imaged with Spitzer (3.5-160 microns) and with HST. The sample spans the important transition in radio luminosities and morphology from FRI to FRII type. The imaging and spectroscopy of the cores, jets, hot spots and atmospheres will be of permanent legacy value. This poster gives a first look at these data and indicates how we plan to investigate particle acceleration mechanisms, interactions between radio plasma and the ISM and IGM, the emission mechanism of hot spots, and AGN fuelling

Momentum driven feedback from stellar nuclei
McQuillin, Rachael
Keele University

In the last decade observations with the Hubble Space Telescope (HST) have revealed the presence of massive star clusters at the centres of the majority of low and intermediate mass galaxies. An unexpected observational result is that nuclear cluster mass, $M_nc$, scales with the velocity dispersion of the host galaxy bulge, $\sigma$. The $M_nc - \sigma$ relation is analogous to that between the masses of central supermassive black holes (SMBHs) and the velocity dispersions of their host galaxy bulges. The observed $M – sigma$ relation can be understood as a consequence of momentum conserving feedback from the nucleus which sweeps the ambient medium into a shell that expands into the galaxy. There is a critical mass of the nucleus for which the shell can escape the galaxy hence cutting off the growth of the nucleus and locking in the $M – \sigma$ dependence. Previous work has modelled this process in galaxies with singular isothermal dark-matter haloes. In this contribution, we extend this work and investigate the $M – \sigma$ relation that results from nuclear feedback in galaxies with more realistic dark-matter and gas density profiles.

The Cold Gas Content of Bulgeless Disk Galaxies
Pilkington, Kate, Brad Gibson, Chris Brook, Greg Stinson, Francesco Calura
Jeremiah Horrocks Institute, UCLan

We present an analysis of the neutral hydrogen (HI) properties of a set of fully cosmological hydrodynamical dwarf galaxy simulations. As reported recently by Governato et al. (2010), these simulations are the first of their kind to result in the successful reproduction of a (dwarf) spiral galaxy, without any associated stellar bulge.  In a blind experiment, we have now set out to compare in detail the HI distribution and kinematics of these simulated bulgeless disks with those of three comparable dwarfs from the THINGS (The HI Nearby Galaxy Survey) archive.  We wish to answer the question "Are the gas properties of the first successfully simulated bulgeless dwarfs consistent with observations?".  To do so, we have thus far extracted from the simulations, radial and vertical density profiles, scalelengths, and spatially-resolved maps of scaleheights (eg. flaring, warping) and velocity dispersion (eg. velocity ellipsoid, turbulence).  Our highest resolution dwarf shows several unique and challenging characteristics (relative to the THINGS observations of comparable dwarfs) which we are in the midst of quantifying, including (i) a high-density cold gas core within the inner 1kpc (10 times the density at one HI disk scalelength), (ii) significant, and continual, disk flaring from the inner to the outer HI disk (factor of 10 increase in scaleheight per dex increase in radius), and (iii) a significantly (kinematically) colder HI disk (factor of 5 lower lines-of-sight velocity dispersions, relative to HoII, NGC4214, and IC2574).  We will discuss the ramifications of our preliminary analyses in terms of the defining roles played by energy feedback and star formation thresholds in such cosmological hydrodynamical simulations.

Searching for Compton Thick AGN at z~2 in deep X-ray fields
Rangel, Cyprian, Kirpal Nandra, Elise Laird, James Aird
Imperial College London

Currently the X-ray emission from AGN fails to fully account for the observed X-ray Background (XRB) at harder energies. It has been theorized this is due to a population of obscured AGN that we have yet to observe. Compton Thick (CT) AGN have obscuring gas of the surrounding torus with $N_H>10^{24}$ cm$^{-2}$, thus the X-ray emission from the central source is heavily suppressed. We present the results of a search for CT AGN at z~2 in deep X-ray fields. We identify X-ray detected AGN through Likelihood Ratio (LR) matching of optical and NIR photometry to X-ray data. Sometimes CT AGN are detected via scattered or reflected X-ray emission from the central source, but at z~2 such these processes may be too faint to yield a detection. Stacking is therefore used to test for the presence of X-ray emission from candidate CT sources selected via their multi-wavelength properties.

Stability and evolution of cluster galaxies in MOND
Wu, Xufen, HongSheng Zhao, Yougang Wang, Benoit Famaey, Martin Feix
Physics and Astronomy, University of St Andrews

Following Schwarzschild's approach, we construct a series of Hernquist models embedded in external fields in the framework of MOdified Newtonian Dynamics (MOND). These models represent medium-mass elliptical galaxies with mild cusps within a galaxy cluster, providing a MONDian external field on the order of $g_{\rm ext}\approx a_0$. Using N-body simulations, we further test the stability of these models. We find that the Schwarzschild models are not in rigorous equilibrium. The outskirts of the galaxies develop lopsided shapes along the external field's direction, and the radii containing $90$\% of the total mass increase by a factor of $2$ during $60$ simulation times (Newtonian Keplerian times at scale length of $1$kpc) after which the models seem to settle to a stable equilibrium. Comparing our results to an isolated galaxy model, the Schwarzschild models in external fields are less self-consistent and stable.