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THE ASTRONOMICAL SOCIETY OF AUSTRALIA INC. |
Annual Scientific Meeting 1st to 5th July, 2007 |
| Program |  All Days |
Sunday |
Monday |
Tuesday |
Wednesday |
Thursday |
Posters |
| Abstracts | Posters A-K |
Posters L-Z |
Monday |
Tuesday |
Wednesday |
Thursday |
Lunch Meetings |
Abstracts - Monday
Session One
09:15-10:30
Ellery Lecture
The Photometric Revolution - the past and the future
Mike Bessell
Later this year, the SkyMapper telescope will commence operation at Siding Spring Observatory. With a field of almost 6 degrees with half arcsec pixels, it will produce photometry and maps of the southern sky in unprecedented precision for stars and galaxies between 8th and 21st magnitude. Within a few years, the S4 survey will be producing absolute fluxes, temperatures, gravities, metallicities and proper motions for millions of stars, an amazing prospect. It is therefore appropriate to look back over the past 40 years and review the immense changes that have taken place in spectroscopy and photometry in that time coupled with advances in theoretical stellar model atmospheres and stellar evolution.
A revolution has been underway for the last five years and in a further
five years will be complete. Quantitative measurement of stellar and
galaxy fluxes in the future will not be obtained by going to a telescope
but by using the Virtual Observatory to mine the databases generated by
SkyMapper, PANSTARRS and LSST.
The Central Molecular Zone around Sagittarius B2
Paul Jones
Using the new capabilities of the MOPS digital filter bank on the Mopra telescope,
we have mapped a 5 x 5 arcmin area of the Sagittarius B2 molecular cloud complex. We have covered nearly all of the 83.5 to 113.5 GHz frequency range with 4 tunings of the 8 GHz wide-band mode to image over 50 spectral lines, and have also observed 24 of these lines with the zoom mode (3 tunings) at higher velocity resolution. This shows substantial differences in chemical and physical conditions within the complex. This is the first part of a larger study of the Central Molecular Zone (CMZ) in the inner few degrees around the Galactic Centre. The coverage is now being extended to the 0.3 deg x 1.1 deg area including Sgr A and Sgr B2 between 85.3 and 93.3 GHz.
Session Two - Cosmology
11:00-12:30
Globular Cluster - Galaxy connections in early-type galaxies
Kenji Bekki
Based on high-resolution cosmological simulations with formation
models of globular clusters (GCs), we discuss the origin of the
observered correlations between galaxy properties (e.g., magnitudes)
and GCS ones (e.g., total GC number per galactic luminosity). In
particular, we discuss the origin of the luminosity-metallicity relation
between galactic luminosties and metallicities of their GCs in the
context of the cosmic reionization at high redshifts (z > 6). We try to
give some constraints on the epoch of the reionization based on
comparision between the simulations and the corresponding
observations.
X-ray "Cold Fronts" - a novel method for detection of a recent major cluster merger
Matt Owers
Our current understanding of large scale structure formation in the Universe
suggests that objects such as clusters of galaxies form hierarchically through
the accumulation of smaller systems. Rarely, two roughly equal mass clusters
will coalesce in a major merger. Major mergers have a profound effect on the
cluster constituents - many interesting physical phenomena can be studied
in this environment on the scales of galaxies to that of the entire
Intra-Cluster medium. However, these studies are hindered by the difficulties
in determining whether a cluster is a relaxed system, or if it has undergone
some form of recent major merging, whilst major and minor mergers are difficult
to disentangle. An effective signpost of a recent major merger is required,
and thanks to the excellent spatial resolution of the Chandra X-ray satellite
a solution may be at hand with the detection of "Cold Fronts" - thought
to be evidence of a recent merger. In order to gain confidence in the use of
cold fronts as a merger cue, we have constructed a sample of "Cold Front"
clusters using archival Chandra images and are conducting follow up
observations at optical and radio wavelengths to establish definitively their
link with merger activity. In this talk, I will describe the cold front
phenomenon, its application to cluster selection, and the sample that has been
selected. I will also present and discuss the initial results to come from our
follow up spectroscopy obtained with the AAOmega and MMT/Hectospec
spectrographs. In particular, I will focus on the sub-structure detection
analysis and the promising indications that cold fronts are robust indicators
of major cluster mergers.
A 30 Jy radio burst of extragalactic origin
Matthew Bailes, Lorimer, McLaughlin, Narkevic, Crawfield
We have serendipitously discovered a short-duration radio burst of
extragalactic origin. The burst is only a few milliseconds in duration but
clearly extra-terrestrial in origin exhibiting the classic cold-plasma
dispersion law and showing evidence for intergalactic scattering. The nature
of the source is unclear, but fascinating to speculate on.
Physical contributions to the observed variance in the Ly&alpha opacity of the IGM at high redshift
Jhan A Srbinovsky
The optical depth to Lyα transmission has been measured from the absorption spectra of high
redshift quasars along different sight-lines and shows significant scatter in excess of observational uncertainty.
Does this scatter reflect the inhomogeneity of the ionizing background due to discrete sources, the structure of
the density and peculiar velocity fields in the IGM, or a combination of both? To address this question, we
generate an ensemble of artificial Lyα spectra. We use large volume (943 cMpc) cosmological
simulations to describe the density and peculiar velocity fields, and identify bound halos within these volumes.
We then assign luminosities to these halos using a simple semi-analytic model, and construct a background
radiation field. The scatter in optical depth is then determined in the presence of both a uniform ionizing
background and the fluctuating background field described by our model. We find that a fluctuating ionizing background is needed in addition to the inhomogeneous density and velocity fields in order to describe the
observed scatter. We also consider the effect of dwarf galaxy suppression following reionization on the
scatter in the optical depth.
Rapid matter power spectrum estimation for dark energy cosmologies
Matthew J. Francis
For dynamical dark energy cosmologies we carry out a series of
N-body gravitational simulations, achieving percent level accuracy in
the relative mass power spectra at any redshift. Such accuracy in
the power spectrum is necessary for next generation
cosmological mass probes. Our matching procedure reproduces the CMB
distance to last scattering and delivers subpercent level power spectra
at z = 0 and z ≈ 3. We discuss the physical implications for
probing dark energy with surveys of large scale structure.
The host mass vs. black hole mass relation
Stephen Fine
Correlations between the mass of black holes found at the centre of galaxies and the
properties of their host galaxies point to a link between the growth of super-massive black holes
and the evolution of their hosts. I will discuss one of the first attempts to directly compare the
mass of SMBHs to their host dark halo mass. This comparison is made with QSOs out to a redshift z~2.5
and we find no evidence for evolution in the relation.
Session Three - Cosmology
13:45-15:30
Black hole masses in quasar host galaxies from IFU spectroscopy
Rob Sharp
I report Integral Field Spectroscopy observations aimed at determining the
dynamics and stellar populations of a large sample of low redshift X-ray selected AGN
previously imaged at high resolution with the Hubble Space Telescope.
Specifically we have used the AAOmega+SPIRAL IFU
on the AAT to perform spatially resolved spectroscopy of a sample of
AGN host galaxies at redshifts z = 0.03-0.15 which have a wide range in
nuclear luminosities (-24 < MB < -16).
This data will enable us to: 1)
detect evidence in the kinematics or star-formation history of the
hosts for recent mergers and measure the relative importance of
merging vs. small-scale stochastic accretion as a function of
luminosity 2) determine the bulge velocity dispersion (σ) and
Black Hole Mass, (MBH) to measure the MBH-σ
relation in these
sources 3) determine the accretion efficiency based on a comparison to
the nuclear luminosities at optical and X-ray wavelengths.
Black Hole Accretion Disks and Relativistic Jets in Blazars
Geoffrey Bicknell
Magnetic Fields mediate both turbulent accretion into black holes
and the launching of relativistic jets. Using a theory for magnetized
accretion developed by Kuncic and Bicknell one can estimate the magnetic
field in an accretion disk as a function of the accretion rate. One can then
extrapolate this magnetic field to the high energy emission region of a
blazar using a model for the initial propagation of a relativistic jet. The
comparison of these two estimates provides us with checks on the physics of
magnetic accretion, jet propagation and blazar emission. Models for blazar
emission also involve different assumptions on the source of the soft
photons that are upscattered to high energies. In this paper, estimates of
the magnetic fields in three blazars obtained from Synchrotron Self Compton
(SSC) and Local Inverse Compton (LIC) models are compared with the disk
extrapolated values. (LIC emission is a variant of External Inverse Compton
emission in which soft photons external to the high energy electrons are generated locally.)
Internal consistency with the magnetic field extrapolated from the disk is
obtained when the blazar emission is LIC emission.
The evolution of AGN and their hosts
Scott Croom
I will discuss constraints on the formation and evolution of QSOs and their hosts from new large surveys.
In particular, I will discuss the 2df-SDSS QSO and LRG (2SLAQ) survey, presenting results on the luminosity
distribution and clustering of faint QSO at z < 2.5. I will also show preliminary results from the AAOmega
UKIDSS SDSS (AUS) which aims to study faint QSOs at z > 2.5.
A colour bimodality in quasar host galaxies
David Floyd
Active galaxies are an important probe of the evolving universe, being implicated in the truncation of star-formation in massive galaxies, proposed as a possible solution to the "Cooling Flow" problem, and even as a possible explanation of the "Red Sequence".
We present recent work on imaging the host galaxies of quasars and
radio galaxies between redshift 0 and 2. In particular, new rest-
frame U-V colours for 20 optically matched radio-loud and radio-quiet
quasar hosts at z~1 and z~2. The results demonstrate that radio-loud
galaxies are found in systematically redder galaxies than radio-
quiets, the former being consistent with a passively evolving ancient
stellar population (zform = 5). The radio-quiets meanwhile are
consistent with a younger stellar population, and apparently less
massive host galaxies, but are found in similar cluster environments
at z>1. This suggests that radio-loud objects are found in older
systems and/or are able to truncate the star-formation in their host
galaxies.
Redshifted 21cm Emission from Quasar HII regions in a Percolating IGM
Paul Geil
We anaylse the ability of planned Low-Frequency Telescopes to detect the HII regions
surrounding luminous high redshift quasars before the end of the epoch of reionization. Our approach
is to implement a semi-numerical scheme to calculate the 3-dimensional structure of ionized regions
surrounding a massive halo at high redshift, including the ionizing influence of a luminous quasar.
We calculate mock spectra along the line-of-sight towards the high redshift quasar, and estimate the
ability of planned Low-Frequency Telescopes to detect the presence of an HII region. At times when
the neutral fraction is ~30% or greater (after which the typical HII region becomes comparable
to that generated by the quasar), the quasar will imprint a detectable signature that is distinct
from a region of typical IGM. We find that the average level of neutral gas surrounding a single 5Mpc
quasar HII region will be detectable in 1000 hours, while a detection will be possible in 100 hours
for a stack of 10 smaller 3Mpc HII regions.
A Multi-wavelength Study of the Extremely Luminous VLBI Scale Hotspot of PKS 1421-490
Leith Godfrey
Using the Australian Long Baseline Array, we have obtained an exquisite high resolution
image of the North-Eastern Hotspot of PKS 1421-490. The hotspot is very compact (400pc across)
given its extreme luminosity, and exhibits a smooth surface brightness distribution. A protrusion
at the leading edge of the hotspot resembles the morphology expected from the 'dentist drill effect'.
By combining our VLBI data with single dish fluxes for this source, we are able to constrain the
low energy cutoff in the electron energy distribution. A one-zone synchrotron self Compton model
provides a good fit to the radio, optical and X-ray flux and yields a robust estimate of the magnetic
field strength and electron density within the hotspot. I will discuss our findings and the
implications of these results for the interpretation of hotspot X-ray emission.
Search for Gravitational lenses in the Southern Hemisphere using the ATCA
Rajan Chhetri
The data collected for the Australia Telescope 20 GHz Survey (AT20G survey done
between 0 to -90 degrees latitude) can be used to look for extendedness in detected sources.
By using this method on compact sources (sources with flat spectrum) we are looking for Strong
Gravitational lenses in the Southern hemisphere. I would like to present the work we have done in this respect and the candidates we have come up with, which will be followed up later.
Session Four - Galaxies: Clustering, Formation and Evolution
16:00-17:45
Dynamics of the Horologium-Reticulum Supercluster
Melanie Johnston-Hollitt
The Horologium-Reticulum Supercluster (HRS) is the second largest mass concentration in the Southern
sky and represents an ideal test bed for understanding aspects of large-scale structure evolution.
We have amassed a large, multi-wavelength dataset of the region including radio data at 0.8, 1.4 and 2.4 GHz
and X-ray images of individual cluster members and nearly 10,000 spectroscopic optical observations over
the superlcuster. This gives us an unprecedented dataset to study the role that environment plays on constituent
galaxies. In addition to the wealth of information collected on the hierarchical merging occurring in the centre
of the supercluster and the overall bimodal structure, we compute the radio luminosity functions of the central
part of the HRS and examine the way environment shapes the radio population. I will review the work done to
date on understanding the dynamics of the HRS using this dataset including comparisons to similar, smaller
studies of the Shapley supercluster.
Morphology and Star Formation in the Supercluster Environment
Jason Moore
Filaments of galaxies between neighbouring clusters are the ideal regime
for studying galaxy evolution processes, as they provide a wide range of
galaxy environments as well as the particular environments where
processes begin to occur. In the past, studies had not considered a
non-isotropic accretion of galaxies when producing such results as the
'morphology-density relation'. This presentation will reiterate how
vital it is to consider filaments of galaxies when studying galaxy
evolution, review recent work which has done so and present the current
results of our own project.
WiggleZ Survey: Small-scale clustering of emission line galaxies
Russell Jurek
The WiggleZ Dark Energy Survey is an ambitious, three and a half year project being carried
out on the Anglo-Australian Telescope,using the 2dF-AAOmega instrument. The goal of this survey is to
measure the quantity w, that parametrises the dark energy equation of state, P = wρ, relatively free
of systematics to an accuracy of 10% at z = 0.8. To achieve this, the WiggleZ Dark Energy Survey is measuring
the redshifts of approximately 240,000 emission line galaxies.
Extracting the imprint of baryonic acoustic oscillations (BAOs) from the large-scale clustering of these emission
line galaxies will enable us to measure the angular distance to z = 0.8 and the value of the Hubble constant at
z = 0.8. As both of these quantities explicitly depend on w, from them we will be able to measure w at z = 0.8
to the desired accuracy.
Having almost completed the first year of the survey we are now in a position to investigate the small-scale
clustering of emission line galaxies. This will analysis will be carried out on the largest ever sample of
high-redshift emission line galaxies. From the small-scale clustering we have already obtained an improved
estimate of the clustering length and bias of high-redshift emission line galaxies, r0 = 6.0 h-1 Mpc
and b = 1.3 respectively. In this talk I will briefly review the current status of the WiggleZ Dark Energy
Survey; and present the results of our analysis of the small-scale clustering of high-redshift emission line galaxies.
The Evolution of Cosmic Neutral Hydrogen with Time
Chris Power
I will present theoretical predictions for the cosmic abundance and distribution of cosmic neutral
hydrogen as a function of redshift. I will briefly describe semi-analytical galaxy formation modelling and
how the resulting predictions can help in the design of HI surveys on next generation radio telescopes.
Star formation density and Halpha luminosity function of an emission line selected galaxy sample at z ~ 0.24
Eduard Westra
We select a sample of emission line galaxies at 0.20 < z < 1.22 in two fields covering 0.5 sq. qdeg. Spectroscopic follow-up is used to select a sub-sample of Halpha emitting galaxies and determine the Halpha luminosity function and star formation at z~0.24. Corrections are made for imaging and spectroscopic incompleteness, extinction and interloper contamination on the basis of the spectroscopy. The fields differ by 0.2 in the faint end slope alpha and by 0.2 in the luminosity log L*. Compared to other recent surveys, our sample has a comparable faint end slope, but a fainter L* turn-over. We conclude that systematic uncertainties and differences in selection criteria dominate the uncertainty between Halpha luminosity functions at this redshift.
We also investigate average star formation rates as a function of local environment. The values are typical and consistent with the field densities we probe, in agreement with previous results. However, we find tentative evidence for an increase in star formation rate with respect to the local density of star forming galaxies, consistent with the scenario that galaxy-galaxy interactions are triggers for bursts of star formation.
The Influence of Mass and Star-Formation Timescale on the Stellar Populations in Early-Type Galaxies
Craig Harrison, Matthew Colless, Warrick Couch, and Bruce Peterson
Through analyses of their absorption-line indices and stellar population parameters age, metallicity, and α-element abundance ratio ([α/Fe]), we investigate the stellar populations of early-type galaxies in low-redshift clusters and track their evolution over the last 30% of the Hubble time. These analyses reveal that early-type galaxies in clusters form a relatively homogeneous class of objects that follow trends of increasing metallicity and [α/Fe] with increasing velocity dispersion (i.e. mass). The distribution of ages is consistent with a down-sizing scenario, with age indirectly correlated with mass through star-formation timescale (i.e. the [α/Fe]-σ relation). The intrinsic scatters in their metallicity and [α/Fe] distributions are remarkably small, and can be accounted for by the distribution of galaxies along the trends with velocity dispersion together with the intrinsic scatter about these trends, which we suggest is a down-sizing parameter (namely the amount of late star formation as a function of velocity dispersion). The low-redshift cluster galaxies are consistent with being passively evolved versions of the galaxies in the intermediate-redshift cluster A0370.
This general homogeneity of the stellar populations in early-type galaxies is broken only by the differences found between the [α/Fe] distributions in A3558 and Coma, and the spread of ages observed in all low-redshift clusters. The former we attribute to the differing dynamical states of the clusters, while the latter we attribute to the in-fall of low-mass galaxies, consistent with a down-sizing scenario.
The overall picture of the formation of the stellar populations in
early-type galaxies that emerges is one of rapid early formation producing a
homogeneous class of objects whose properties are largely (but not solely)
determined by their mass, and which are subsequently partially modified by
wet mergers that are increasingly important for lower-mass galaxies and
those in clusters with extended assembly histories.
HI Galaxies and the SFR-Density Relation
Marianne Doyle
We present the result of investigations into two theories to explain the star formation rate-density relationship. For regions of high galaxy density, either there are fewer star-forming galaxies or galaxies capable of forming stars are present but some physical process is suppressing their star formation. We use HI Parkes All Sky Survey's (HIPASS) HI detected galaxies, their optical counterparts and IR and radio fluxes to investigate SFRs and efficiencies with respect to local surface density.
Harley Wood Lecture
19:00-20:30
Millisecond Pulsars and Einstein's Universe
Matthew Bailes
Using 3D virtual reality technologies Professor Bailes will explain how astronomers are using giant radio telescopes to discover millisecond pulsars, objects only 20km in diameter, but with masses some 500,000 times that of Earth. These stars rotate up to 700 times a second, and emit powerful beams of radio emission. Australian astronomers are using millisecond pulsars to test Einstein's laws of gravitation and search for gravitational waves produced by inspiralling supermassive black holes. This talk is aimed at the general public and understandable by children and adults alike. The impact of exciting new telescopes currently being designed for construction in Western Australia will also be discussed.
| Program | All Days |
Sunday |
Monday |
Tuesday |
Wednesday |
Thursday |
Posters |
| Abstracts | Posters A-K |
Posters L-Z |
Monday |
Tuesday |
Wednesday |
Thursday |
Lunch Meetings |
For further information (and additions or corrections), contact: qap@physics.mq.edu.au