Radio-Excess IRAS Galaxies: PMN/FSC Sample Selection

A sample of 178 extragalactic objects is defined by correlating the 60 micron IRAS FSC with the 5 GHz PMN catalog. Of these, 98 objects lie above the radio/far-infrared relation for radio-quiet objects. These radio-excess galaxies and quasars have a uniform distribution of radio excesses and appear to be a new population of active galaxies not present in previous radio/far-infrared samples. The radio-excess objects extend over the full range of far-infrared luminosities seen in extragalactic objects. Objects with small radio excesses are more likely to have far-infrared colors similar to starbursts, while objects with large radio excesses have far-infrared colors typical of pure AGN. Some of the most far-infrared luminous radio-excess objects have the highest far-infrared optical depths. These are good candidates to search for hidden broad line regions in polarized light or via near-infrared spectroscopy. Some low far-infrared luminosity radio-excess objects appear to derive a dominant fraction of their far-infrared emission from star formation, despite the dominance of the AGN at radio wavelengths. Many of the radio-excess objects have sizes likely to be smaller than the optical host, but show optically thin radio emission. We draw parallels between these objects and high radio luminosity Compact Steep-Spectrum (CSS) and GigaHertz Peaked-Spectrum (GPS) objects. Radio sources with these characteristics may be young AGN in which the radio activity has begun only recently. Alternatively, high central densities in the host galaxies may be confining the radio sources to compact sizes. We discuss future observations required to distinguish between these possibilities and determine the nature of radio-excess objects.Comment: Submitted to AJ. 44 pages, 11 figures. A version of the paper with higher quality figures is available from http://www.mso.anu.edu.au/~cdrake/PMNFSC/paperI

A Joint Mid-Infrared Spectroscopic and X-Ray Imaging Investigation of Liner Galaxies

We present a comprehensive comparative high resolution mid-IR spectroscopic and X-ray imaging investigation of LINERs using archival observations from the ISO-SWS and the Chandra Advanced CCD Imaging Spectrometer. Although the sample is heterogenous and incomplete, this is the first comprehensive study of the mid-infrared fine structure line emission of LINERs. These results have been compared with similar observations of starburst galaxies and AGN. We find that LINERs very clearly fall between starbursts and AGN in their mid-IR fine structure line spectra, showing L_[OIV]26um/L_FIR and L_[OIV]26um/L_[NeII]12.8um ratios, both measures of the dominant nuclear energy source in dust-enshrouded galaxies, intermediate between those of AGN and starbursts. Chandra imaging observations of the LINERs reveal hard nuclear point sources morphologically consistent with AGN in most (67%) of the sample, with a clear trend with IR-brightness. Most LINERs that show a single dominant hard compact X-ray core are IR-faint ((L_FIR/L_B < 1), whereas most LINERs that show scattered X-ray sources are IR-bright. A comparative X-ray/mid-IR spectroscopic investigation of LINERs reveals some puzzling results. Objects that display strong hard nuclear X-ray cores should also display high excitation lines in the IR. However, we find two LINERs disagree with this expectation. The galaxy NGC 404 shows weak soft X-ray emission consistent with a starburst but has the most prominent highest excitation mid-IR spectrum of our entire sample. Using IR emission line diagnostics alone, this galaxy would be classified as hosting a dominant AGN. Conversely, the IR luminous LINER NGC 6240 has an extremely luminous binary AGN as revealed by the X-rays but shows weak IR emission lines.Comment: 17 pages, 12 figures, accepted for publication in A&

Materializing digital collecting: an extended view of digital materiality

If digital objects are abundant and ubiquitous, why should consumers pay for, much less collect them? The qualities of digital code present numerous challenges for collecting, yet digital collecting can and does occur. We explore the role of companies in constructing digital consumption objects that encourage and support collecting behaviours, identifying material configuration techniques that materialise these objects as elusive and authentic. Such techniques, we argue, may facilitate those pleasures of collecting otherwise absent in the digital realm. We extend theories of collecting by highlighting the role of objects and the companies that construct them in materialising digital collecting. More broadly, we extend theories of digital materiality by highlighting processes of digital material configuration that occur in the pre-objectification phase of materialisation, acknowledging the role of marketing and design in shaping the qualities exhibited by digital consumption objects and consequently related consumption behaviours and experiences

Ultraluminous Infrared Galaxies

Ever since their discovery in the 1970's, UltraLuminous InfraRed Galaxies (ULIRGs; classically Lir>10^12Lsun) have fascinated astronomers with their immense luminosities, and frustrated them due to their singularly opaque nature, almost in equal measure. Over the last decade, however, comprehensive observations from the X-ray through to the radio have produced a consensus picture of local ULIRGs, showing that they are mergers between gas rich galaxies, where the interaction triggers some combination of dust-enshrouded starburst and AGN activity, with the starburst usually dominating. Very recent results have thrown ULIRGs even further to the fore. Originally they were thought of as little more than a local oddity, but the latest IR surveys have shown that ULIRGs are vastly more numerous at high redshift, and tantalizing suggestions of physical differences between high and low redshift ULIRGs hint at differences in their formation modes and local environment. In this review we look at recent progress on understanding the physics and evolution of local ULIRGs, the contribution of high redshift ULIRGs to the cosmic infrared background and the global history of star formation, and the role of ULIRGs as diagnostics of the formation of massive galaxies and large-scale structures.Comment: Review article, published in "Astrophysics Update 2 - topical and timely reviews on astronomy and astrophysics". Ed. John W. Mason. Springer/Praxis books. ISBN: 3-540-30312-X. 53 pages, 5 figures. Higher quality figures available on reques