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Blog

Filtering by Tag: Academic

"The accretion history of dark matter haloes - III. A physical model for the concentration-mass relation" Correa et al. (2015c)

Alan Duffy

My student's third paper of a stunning 3-part series on the growth of dark matter structures. In this paper Camila finally demonstrated the long studied concentration of dark matter haloes was tied to the growth history of that halo and hence, through her other works, the basic cosmology of the universe. Reference: Correa, Wyithe, Schaye and Duffy 2015 MNRAS 452, 1217C

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"The accretion history of dark matter haloes - II. The connections with the mass power spectrum and the density profile" Correa et al. (2015b)

Alan Duffy

My student's second paper of a stunning 3-part series on the growth of dark matter structures. In this paper Camila tied the distribution of dark matter in haloes (i.e. the density profile) and initial power spectrum of the universe. This used detailed N-body simulations that Camila herself ran several of on supercomputer. Reference: Correa, Wyithe, Schaye and Duffy 2015 MNRAS 450, 1521C

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"The accretion history of dark matter haloes - I. The physical origin of the universal function" Correa et al. (2015a)

Alan Duffy

My student's first paper of her PhD was a stunning 3-part series on the growth of dark matter structures. In this paper Camila set up the analytic machinery that tied the mass accretion history of haloes to the underlying cosmology of the universe using linear structure formation theory. In particular she showed that the rapid exponential growth of haloes in the early universe slows to become a slower power law at late times thanks to Dark Energy. Reference: Correa, Wyithe, Schaye and Duffy 2015 MNRAS 450, 1514-1520

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"Low-mass galaxy formation and the ionizing photon budget during reionization" Duffy et al. (2014b)

Alan Duffy

The first paper from the "DRAGONS" team led by Prof Stuart Wyithe, investigating how the First Galaxies formed. Using a series of hydrodynamical simulations series known as Smaug we show that the first billion years after the Big Bang is a very exciting time, with the entire universe lit by a hidden population of small galaxies that current telescopes have yet to see. Reference: Duffy, Wyithe, Mutch, Poole 2014 MNRAS 443, 3435D.

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"Probing the nature of dark energy through galaxy redshift surveys with radio telescopes" Duffy (2014a)

Alan Duffy

I analysed the ability of radio and optical (visible light) telescopes to probe the nature of Dark Energy. I showed that radio telescopes are rapidly improving in capability and although starting from a low base they will rival the best optical telescopes by the time of the Square Kilometre Array (SKA). One issue is that the SKA demands such a large supercomputer that Moore's law might not get us such a machine by the time SKA is built. Reference: Duffy 2014 Annalen der Physik 526, 283D for the Special Issue "The Accelerating Universe".

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"Giant Radio Galaxies: I. Intergalactic Barometers" Malarecki et al. (2013)

Alan Duffy

A fascinating technique using the outbursts of supermassive blackholes as barometers to measure the pressure of the gas around the galaxies, as the outbursts inflate 'bubbles' of ionised gas. These pressures were then compared with the hydrodynamical simulations and found to be significantly rarer, over-pressurised regions than normal. Reference: Malarecki, Staveley-Smith, Saripalli, Subrahmanyan, Jones, Duffy, Rioja 2013 MNRAS 432 200M.

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"The impact of baryons on the spins and shapes of dark matter haloes" Bryan et al. (2013)

Alan Duffy

Sarah and myself started investigating the shape and spin properties of Dark Matter haloes just after I left Jodrell Bank. This then increased in scope when she started to consider the actions of the baryons (as featured in Duffy et al 2010) in changing these key properties of the collapsed Dark Matter structures. This work showed that the baryons strongly influence the halo, making it more spherical and rotating faster than the Dark Matter only predictions. This is a key result for Gravitational lensing and X-ray temperature mass estimates. Reference: Bryan, Kay, Duffy, Schaye, Dalla Vecchia, Booth 2013 MNRAS 429 3316B.

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"Predictions for ASKAP neutral hydrogen surveys" Duffy et al. (2012c)

Alan Duffy

Using one of the largest simulated universes in existence (the Millennium Simulation) we populated the Dark Matter haloes with detailed Neutral Hydrogen gas (which radio telescopes can detect). By 'observing' these objects with the expected performance of the Australian SKA Pathfinder telescope we created a series virtual surveys that ASKAP can be expected to detect. These catalogues are as detailed and real as we can hope to have until we turn the telescope on. Some incredible fly through movies and images are available (be warned they can be pretty large). Reference: Duffy, Meyer, Staveley-Smith et al 2012 MNRAS 426 3385D

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"Cosmological Surveys with the Australian Square Kilometre Array Pathfinder" Duffy et al. (2012b)

Alan Duffy

An analysis of the ability of the forthcoming Australian Square Kilometre Array Pathfinder to investigate the nature of Dark Energy. It will likely be the first radio telescope to make these kind of observations and is an exciting precursor to the type of science that the full Square Kilometre Array (SKA) can accomplish. Reference: Duffy, Moss, Staveley-Smith 2012 PASA 29 202D

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Radio Observations of Local Galaxies

Alan Duffy

This new high resolution study of neutral hydrogen (HI) in local galaxies, led by Baerbel Koribalska has a great name LVHIS (almost pronounced Elvis... which is reason enough to look at this work). It's also a fantastically thorough and exhaustive study into the kinematic properties of 12 nearby dwarf galaxies. The study of galaxy rotations using the HI line isn't anything new of course, but the dataset presented here represents the quality of data that we can routinely expect from the forthcoming Australian Square Kilometre Array Pathfinder (ASKAP) and hence is a valuable guide into the uses (and pitfalls) of high resolution kinematic data. 

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New Baryonic Acoustic Oscillation Measurements

Alan Duffy

This is a summary of 3 papers released today by the above authors (who all shuffle in order dependent on the exact paper) but basically it's a way to improve the measurements of the Baryonic Acoustic Oscillation (BAO) using the Sloan Digital Sky Survey Data Release 7 sample of galaxies... So of course the first question is, what's the BAO? 

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Impressive Citizen Science

Alan Duffy

The latest 'citizen science' project to hit the astronomical shelves is a really fun investigation into the HII (ionised hydrogen) bubbles that form around young, ionising stars or Supernovae explosions. The issue here is that they can be very complex shapes as the shock wave around such ionising sources will typically flow around dense interstellar gas. This means that identifying such objects will be difficult for automated systems but easy for humans with our pretty impressive pattern recognition skills. This is the idea of the project - harness the power of people for a problem that we can uniquely solve. 

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"Modelling neutral hydrogen in galaxies using cosmological hydrodynamical simulations" Duffy et al. (2012a)

Alan Duffy

Following on from Duffy et al. (2010) we considered the same simulated haloes when "Modelling neutral hydrogen in galaxies using cosmological hydrodynamical simulations". This studied the baryonic properties of simulated haloes; focussing on Neutral Hydrogen, but also Molecular Hydrogen and Stellar masses as a function of cosmic time, halo mass and baryonic physics. With this paper I made the Victorian State Finals for the Fresh Science Award. Reference: Duffy, Kay, Battye, Booth, Dalla Vecchia, Schaye 2012 MNRAS 420 2799

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"Impact of baryon physics on dark matter structures: a detailed simulation study of halo density profiles" Duffy et al. (2010)

Alan Duffy

My first SPH simulation paper on the "Impact of baryon physics on dark matter structures: a detailed simulation study of halo density profiles". It demonstrated that the physics of galaxy formation can (surprisingly) strongly affect the dark matter distribution. It won the "Best Paper by a UWA Early Career Researcher" award. Reference: Duffy, Schaye, Kay, Dalla Vecchia, Battye, Booth 2010 MNRAS 405 2161D

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"The physics driving the cosmic star formation history" Schaye et al. (2010)

Alan Duffy

This was the simulation paper for the OverWhelmingly Large Simulations (OWLS) effort that I was involved with during my PhD. This paper in particular focusses on the impact that different baryonic processes can have on the global star-formation rate, amongst many other effects. Reference: Schaye, Dalla Vecchia, Booth, Wiersma, Theuns, Haas, Bertone, Duffy, McCarthy, vd Voort 2010 MNRAS 402 1536-1560

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"Dark matter halo concentrations in the Wilkinson Microwave Anisotropy Probe year 5 cosmology" Duffy et al. (2008b)

Alan Duffy

My first N-body simulation paper (as well as Letter) on the topic of "Dark matter halo concentrations in the Wilkinson Microwave Anisotropy Probe year 5 cosmology" when I was based at Leiden Observatory. It demonstrated a fascinating inverse relation between the concentration (compactness) of a dark matter object and the mass of said object. Reference: Duffy, Schaye, Kay, Dalla Vecchia 2008 MNRAS 390L 64D

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"Galaxy redshift surveys selected by neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope" Duffy et al. (2008a)

Alan Duffy

My first publication in a journal, on the subject of "Galaxy redshift surveys selected by neutral hydrogen using the Five-hundred metre Aperture Spherical Telescope". The telescope will be a fantastic survey instrument, capable of detecting millions to hundreds of millions of galaxies around us for billions of light years. Reference: Duffy, Battye, Davies, Moss, Wilkinson 2008 MNRAS 383 150D

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