Indigenous Australian artists and astrophysicists come together to communicate science and culture via art

During the International Year of Astronomy in 2009, we initiated a collaboration between astrophysicists in Western Australia working toward building the largest telescope on Earth, the Square Kilometre Array (SKA), and Indigenous artists living in the region where the SKA is to be built. We came together to explore deep traditions in Indigenous culture, including perspectives of the night sky, and the modern astrophysical understanding of the Universe. Over the course of the year, we travelled as a group and camped at the SKA site, we sat under the stars and shared stories about the constellations, and we talked about the telescopes we wanted to build and how they could sit on the Indigenous traditional country. We found lots of interesting points of connection in our discussions and both artists and astronomers found inspiration. The artists then produced > 150 original works of art, curated as an exhibition called "Ilgarijiri - Things belonging to the Sky" in the language of the Wadjarri Yamatji people. This was exhibited in Geraldton, Perth, Canberra, South Africa, Brussels, the U.S.A., and Germany over the course of the next few years. In 2015, the concept went further, connecting with Indigenous artists from South Africa, resulting in the "Shared Sky" exhibition, which now tours the ten SKA member countries. The exhibitions communicate astrophysics and traditional Indigenous stories, as well as carry to the world Indigenous culture and art forms. The process behind the collaboration is an example of the Reconciliation process in Australia, successful through thoughtful and respectful engagements, built around common human experiences and points of contact (the night sky). This Commentary briefly describes the collaboration, its outcomes, and future work

Absorption variability as a probe of the multiphase interstellar media surrounding active galaxies

© 2016 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. We examine a model for the variable free-free and neutral hydrogen absorption inferred towards the cores of some compact radio galaxies in which a spatially fluctuating medium drifts in front of the source. We relate the absorption-induced intensity fluctuations to the statistics of the underlying opacity fluctuations. We investigate models in which the absorbing medium consists of either discrete clouds or a power-law spectrum of opacity fluctuations. We examine the variability characteristics of a medium comprised of Gaussian-shaped clouds in which the neutral and ionized matter are co-located, and in which the clouds comprise spherical constant-density neutral cores enveloped by ionized sheaths. The cross-power spectrum indicates the spatial relationship between neutral and ionized matter, and distinguishes the two models, with power in the Gaussian model declining as a featureless power-law, but that in the ionized sheath model oscillating between positive and negative values. We show how comparison of the H I and free-free power spectra reveals information on the ionization and neutral fractions of the medium. The background source acts as a low-pass filter of the underlying opacity power spectrum, which limits temporal fluctuations to frequencies ? ? ???/?src, where ??? is the angular drift speed of the matter in front of the source, and it quenches the observability of opacity structures on scales smaller than the source size ?src. For drift speeds of ~103 km s-1 and source brightness temperatures ~1012 K, this limitation confines temporal opacity fluctuations to time-scales of order several months to decades

PKS 1018-42: A Powerful Kinetically Dominated Quasar

We have identified PKS 1018-42 as a radio galaxy with extraordinarily powerful jets, over twice as powerful as any 3CR source of equal or lesser redshift except for one (3C196). It is perhaps the most intrinsically powerful extragalactic radio source in the, still poorly explored, Southern Hemisphere. PKS 1018-42 belongs to the class of FR II objects that are kinetically dominated, the jet kinetic luminosity, $Q \sim 6.5 \times 10^{46}\mathrm{ergs/s}$ (calculated at 151 MHz), is 3.4 times larger than the total thermal luminosity (IR to X-ray) of the accretion flow, $L_{bol} \sim 1.9 \times 10^{46}\mathrm{ergs/s}$. It is the fourth most kinetically dominated quasar that we could verify from existing radio data. From a review of the literature, we find that kinetically dominated sources such as PKS 1018-42 are rare, and list the 5 most kinetically dominated sources found from our review. Our results for PKS 1018-42 are based on new observations from the Australia Telescope Compact Array

Ten milliparsec-scale structure of the nucleus region in Centaurus A

We present the results of a VLBI Space Observatory Programme (VSOP) observation of the subparsec structure in Centaurus A at 4.9 GHz. Owing to its proximity, our Centaurus A space-VLBI image is one of the highest spatial resolution images of an AGN ever made -- 0.01 pc per beam. The elongated core region is resolved into several components over 10 milli-arcseconds long (0.2 pc) including a compact component of brightness temperature 2.2x10^10K. We analyze the jet geometry in terms of collimation. Assuming the strongest component to be the core, the jet opening angle at ~ 5,000 r_s (Schwarzchild radii) from the core is estimated to be ~ 12 degree, with collimation of the jet to ~ 3 degree continuing out to ~ 20,000 r_s. This result is consistent with previous studies of the jet in M87, which favor MHD disk outflow models. Future space VLBI observations at higher frequencies will probably be able to image the collimation region, within 1,000 r_s of the center of Centaurus A, together with the accretion disk itself.Comment: 12 pages, 6 figures, accepted for publication in PASJ, Vol.57 No.6, VSOP special issu