arXiv subjects

Ray P. Norris

Publications and source records attributed to Ray P. Norris.

At least 109 records · Page 6Linked to original sources

arXiv2011

The radio core of the Ultraluminous Infrared Galaxy F00183-7111: watching the birth of a quasar

F00183-7111 is one of the most extreme Ultra-Luminous Infrared Galaxies known. Here we present a VLBI image which shows that F00183-7111 is powered by a combination of a radio-loud Active Galactic Nucleus surrounded by vigorous starburst activity. Although already radio-loud, the quasar jets are only 1.7 kpc long, boring through the dense gas and starburst activity that confine them. We appear to be witnessing this remarkable source in the brief transition period between merging starburst and radio-loud "quasar-mode" accretion.

astro-ph.CO↗

arXiv2011

EMU: Evolutionary Map of the Universe

EMU is a wide-field radio continuum survey planned for the new Australian Square Kilometre Array Pathfinder (ASKAP) telescope. The primary goal of EMU is to make a deep (rms ~ 10 microJy/beam) radio continuum survey of the entire Southern Sky at 1.3 GHz, extending as far North as +30 degrees declination, with a resolution of 10 arcsec. EMU is expected to detect and catalogue about 70 million galaxies, including typical star-forming galaxies up to z~1, powerful starbursts to even greater redshifts, and AGNs to the edge of the visible Universe. It will undoubtedly discover new classes of object. This paper defines the science goals and parameters of the survey, and describes the development of techniques necessary to maximise the science return from EMU.

astro-ph.CO↗

arXiv2011

An unbiased sample of bright southern Compact Steep Spectrum and Gigahertz Peaked Spectrum Sources

Compact Steep Spectrum (CSS) and Gigahertz Peaked Spectrum (GPS) sources are classes of compact, powerful, extragalactic objects. These sources are thought to be the earliest stages in the evolution of radio galaxies, capturing the ignition (or, in some cases, re-ignition) of the AGN. As well as serving as probes of the early stages of large-scale radio sources, these sources are good, stable, amplitude calibrators for radio telescopes. We present an unbiased flux density limited (>1.5 Jy at 2.7 GHz) catalogue of these objects in the Southern Hemisphere, including tabulated data, radio spectra, and where available, optical images and measurements. The catalogue contains 26 sources, consisting of 2 new candidate and 15 known CSS sources, and 9 known GPS sources. We present new Australia Telescope Compact Array (ATCA) data on ten of these 26 sources, and data on a further 42 sources which were excluded from our final sample. This bright sample will serve as a reference sample for comparison with subsequent faint (mJy level) samples of CSS and GPS candidates currently being compiled.

astro-ph.CO↗

arXiv2011

Eclipses in Australian Aboriginal Astronomy

We explore 50 Australian Aboriginal accounts of lunar and solar eclipses to determine how Aboriginal groups understood this phenomenon. We summarise the literature on Aboriginal references to eclipses, showing that many Aboriginal groups viewed eclipses negatively, frequently associating them with bad omens, evil magic, disease, blood and death. In many communities, Elders or medicine men were believed to have the ability to control or avert eclipses by magical means, solidifying their role as provider and protector within the community. We also show that many Aboriginal groups understood the motions of the sun-earth-moon system, the connection between the lunar phases and tides, and acknowledged that solar eclipses were caused by the moon blocking the sun.

physics.hist-ph↗

arXiv2011

Deep Spitzer observations of infrared-faint radio sources: high-redshift radio-loud AGN?

Infrared-faint radio sources (IFRSs) are a rare class of object which are relatively bright at radio wavelengths but very faint at infrared and optical wavelengths. Here we present sensitive near-infrared observations of a sample of these sources taken as part of the Spitzer Extragalactic Representative Volume Survey (SERVS). Nearly all the IFRSs are undetected at a level of ~ 1 μ$Jy in these new deep observations, and even the detections are consistent with confusion with unrelated galaxies. A stacked image implies that the median flux density is $S_{3.6μm} ~ 0.2$ μ$Jy or less, giving extreme values of the radio-infrared flux density ratio. Comparison of these objects with known classes of object suggests that the majority are probably high-redshift radio-loud galaxies, possibly suffering from significant dust extinction.

astro-ph.CO↗

arXiv2011

"Bridging the Gap" through Australian Cultural Astronomy

For more than 50,000 years, Indigenous Australians have incorporated celestial events into their oral traditions and used the motions of celestial bodies for navigation, time-keeping, food economics, and social structure. In this paper, we explore the ways in which Aboriginal people made careful observations of the sky, measurements of celestial bodies, and incorporated astronomical events into complex oral traditions by searching for written records of time-keeping using celestial bodies, the use of rising and setting stars as indicators of special events, recorded observations of variable stars, the solar cycle, and lunar phases (including ocean tides and eclipses) in oral tradition, as well as astronomical measurements of the equinox, solstice, and cardinal points.

physics.hist-ph↗

arXiv2011

No Evidence for Evolution in the Far-Infrared-Radio Correlation out to z ~ 2 in the eCDFS

We investigate the 70 um Far-Infrared Radio Correlation (FRC) of star-forming galaxies in the Extended Chandra Deep Field South (ECDFS) out to z > 2. We use 70 um data from the Far-Infrared Deep Extragalactic Legacy Survey (FIDEL), which comprises the most sensitive (~0.8 mJy rms) and extensive far-infrared deep field observations using MIPS on the Spitzer Space Telescope, and 1.4 GHz radio data (~8 uJy/beam rms) from the VLA. In order to quantify the evolution of the FRC we use both survival analysis and stacking techniques which we find give similar results. We also calculate the FRC using total infrared luminosity and rest-frame radio luminosity, qTIR, and find that qTIR is constant (within 0.22) over the redshift range 0 - 2. We see no evidence for evolution in the FRC at 70 um which is surprising given the many factors that are expected to change this ratio at high redshifts.

astro-ph.CO↗

arXiv2011

Data Challenges for Next-generation Radio Telescopes

Radio-astronomy is about to embark on a new way of doing science. The revolution that is about to take place is not due to the enormous sensitivity of the Square Kilometre Array, which is still a decade away, but due to its pathfinders, which are pioneering new ways of doing radio-astronomy. These new ways include multi-pixel phased-array feeds, the goal of producing science-ready images from a real-time pipeline processor, and from the vast amounts of survey data that will be available in the public domain soon after observing. Here I review the data challenges that need to be addressed if we are to reap all the science that potentially resides in SKA Pathfinder data. Some challenges are obvious, such as petabytes of data storage, and some are less obvious, such as the techniques we have yet to develop to perform cross- identifications on millions of galaxies.

astro-ph.IM↗

arXiv2010

The radio properties of infrared-faint radio sources

Infrared-faint radio sources (IFRS) are objects that have flux densities of several mJy at 1.4GHz, but that are invisible at 3.6um when using sensitive Spitzer observations with uJy sensitivities. Their nature is unclear and difficult to investigate since they are only visible in the radio. High-resolution radio images and comprehensive spectral coverage can yield constraints on the emission mechanisms of IFRS and can give hints to similarities with known objects. We imaged a sample of 17 IFRS at 4.8GHz and 8.6GHz with the Australia Telescope Compact Array to determine the structures on arcsecond scales. We added radio data from other observing projects and from the literature to obtain broad-band radio spectra. We find that the sources in our sample are either resolved out at the higher frequencies or are compact at resolutions of a few arcsec, which implies that they are smaller than a typical galaxy. The spectra of IFRS are remarkably steep, with a median spectral index of -1.4 and a prominent lack of spectral indices larger than -0.7. We also find that, given the IR non-detections, the ratio of 1.4GHz flux density to 3.6um flux density is very high, and this puts them into the same regime as high-redshift radio galaxies. The evidence that IFRS are predominantly high-redshift sources driven by active galactic nuclei (AGN) is strong, even though not all IFRS may be caused by the same phenomenon. Compared to the rare and painstakingly collected high-redshift radio galaxies, IFRS appear to be much more abundant, but less luminous, AGN-driven galaxies at similar cosmological distances.

astro-ph.CO↗

arXiv2010

Comets in Australian Aboriginal Astronomy

We present 25 accounts of comets from 40 Australian Aboriginal communities, citing both supernatural perceptions of comets and historical accounts of bright comets. Historical and ethnographic descriptions include the Great Comets of 1843, 1861, 1901, 1910, and 1927. We describe the perceptions of comets in Aboriginal societies and show that they are typically associated with fear, death, omens, malevolent spirits, and evil magic, consistent with many cultures around the world. We also provide a list of words for comets in 16 different Aboriginal languages.

physics.hist-ph↗

arXiv2010

Next-generation Astronomy

Fundamental changes are taking place in the way we do astronomy. In twenty years time, it is likely that most astronomers will never go near a cutting-edge telescope, which will be much more efficiently operated in service mode. They will rarely analyse data, since all the leading-edge telescopes will have pipeline processors. And rather than competing to observe a particularly interesting object, astronomers will more commonly group together in large consortia to observe massive chunks of the sky in carefully designed surveys, generating petabytes of data daily. We can imagine that astronomical productivity will be higher than at any previous time. PhD students will mine enormous survey databases using sophisticated tools, cross-correlating different wavelength data over vast areas, and producing front-line astronomy results within months of starting their PhD. The expertise that now goes into planning an observation will instead be devoted to planning a foray into the databases. In effect, people will plan observations to use the Virtual Observatory. Here I examine the process of astronomical discovery, take a crystal ball to see how it might change over the next twenty years, and identify further opportunities for the future, as well as identifying pitfalls against which we must remain vigilant.

astro-ph.IM↗

arXiv2010

Astronomical Symbolism in Australian Aboriginal Rock Art

Traditional Aboriginal Australian cultures include a significant astronomical component, perpetuated through oral tradition and ceremony. This knowledge has practical navigational and calendrical functions, and sometimes extends to a deep understanding of the motion of objects in the sky. Here we explore whether this astronomical tradition is reflected in the rock art of Aboriginal Australians. We find several plausible examples of depictions of astronomical figures and symbols, and also evidence that astronomical observations were used to set out stone arrangements. However, we recognise that the case is not yet strong enough to make an unequivocal statement, and describe our plans for further research.

physics.hist-ph↗

arXiv2010

Australian Aboriginal Geomythology: Eyewitness Accounts of Cosmic Impacts?

Descriptions of cosmic impacts and meteorite falls are found throughout Australian Aboriginal oral traditions. In some cases, these texts describe the impact event in detail, sometimes citing the location, suggesting that the events were witnessed. We explore whether cosmic impacts and meteorite falls may have been witnessed by Aboriginal Australians and incorporated into their oral traditions. We discuss the complications and bias in recording and analysing oral texts but suggest that these texts may be used both to locate new impact structures or meteorites and model observed impact events. We find that, while detailed Aboriginal descriptions of cosmic impacts are abundant in the literature, there is currently no physical evidence connecting these accounts to impact events currently known to Western science.

physics.hist-ph↗

arXiv2010

Wide-angle tail galaxies in ATLAS

We present radio images of a sample of six Wide-Angle Tail (WAT) radio sources identified in the ATLAS 1.4 GHz radio survey, and new spectroscopic redshifts for four of these sources. These WATs are in the redshift range of 0.1469 - 0.3762, and we find evidence of galaxy overdensities in the vicinity of four of the WATs from either spectroscopic or photometric redshifts. We also present follow-up spectroscopic observations of the area surrounding the largest WAT, S1189, which is at a redshift of ~0.22. The spectroscopic observations, taken using the AAOmega spectrograph on the AAT, show an overdensity of galaxies at this redshift. The galaxies are spread over an unusually large area of ~12 Mpc with a velocity spread of ~4500 km/s. This large-scale structure includes a highly asymmetric FRI radio galaxy and also appears to host a radio relic. It may represent an unrelaxed system with different sub-structures interacting or merging with one another. We discuss the implications of these observations for future large-scale radio surveys.

astro-ph.CO↗

arXiv2009

Cosmic Evolution of Radio Sources in ATLAS

The Australia Telescope Large Area Survey (ATLAS), which is the widest deep field radio survey so far attempted, aims to probe the evolution of radio galaxies out to the edge of the Universe. Using AAOmega on the Anglo-Australian Telescope we have successfully obtained spectroscopic redshifts for 395 of the ATLAS radio galaxies. Coupled with 169 redshifts from the existing literature, we now have 564 spectroscopic redshifts for ATLAS sources.

astro-ph.CO↗

arXiv2009

Distinguishing between AGN and Star-Forming Galaxies in ATLAS

The Australia Telescope Large Area Survey (ATLAS) is the widest deep radio survey ever attempted, covering 7 square degrees of sky in two separate fields, with extensive multi-wavelength data. The primary aim of this research is to investigate all possible discriminants between active galactic nuclei (AGN) and star-formation (SF) in ATLAS, with the goal of comparing discriminants, identifying the strengths and weaknesses, and establishing an optimum technique given the available data. Ultimately, all possible discriminants will be utilized, including optical/infrared SEDs, spectroscopic line widths, optical line ratios, radio spectral indices, variability, morphology, polarization and the radio/FIR correlation. A preliminary investigation using only the available spectroscopic data in ATLAS is ongoing. Results from this investigation are presented, exploring the proportion of AGN/SF galaxies as a function of radio flux density down to 150 microJy. Three faint GPS candidates are also presented, as a preliminary result from ATLAS.

astro-ph.CO↗

arXiv2009

ASKAP-EMU: Overcoming the challenges of wide deep continuum surveys

Next-generation continuum surveys will be strongly constrained by dynamic range and confusion. For example, the ASKAP-EMU (Evolutionary Map of the Universe) project will map 75% of the sky at 20cm to a sensitivity of 10 microJy - some 45 times deeper than NVSS, and is likely to be challenged by issues of confusion, cross-identification, and dynamic range. Here we describe the survey, the issues, and the steps that can be taken to overcome them. We also explore ways of using multiwavelength data to penetrate well beyond the classical confusion limit, using multiwavelength data, and an innovative outreach approach to cross-identification.

astro-ph.CO↗

arXiv2009

Co-evolution of AGN and Star-forming Galaxies in the Australia Telescope Large Area Survey

ATLAS (Australia Telescope Large Area Survey) is a wide deep radio survey which is distinguished by its comprehensive multi-wavelength approach. ATLAS is creating a large dataset of radio-selected galaxies for studying the evolution and inter-relationship of star-forming and active galaxies. Although the project is far from complete, we are already starting to answer some of these questions, and have stumbled across three surprises along the way: * FRI/FRII radio-loud AGN embedded within spiral galaxies, * radio-bright AGN which are unexpectedly faint in the infrared, and which may be at high redshift * IR-luminous radio-quiet AGN which are partly responsible for the wide variations in reported values of the radio-infrared ratio These and other observations suggest that the AGN activity and star formation become increasingly inter-dependent at high redshifts.

astro-ph.CO↗