The Physical Parameters of the Micro-quasar S26 in the Sculptor Group Galaxy NGC 7793

NGC 7793 - S26 is an extended source (350 pc $\times$ 185 pc) previously studied in the radio, optical and x-ray domains. It has been identified as a micro-quasar which has inflated a super bubble. We used Integral Field Spectra from the Wide Field Spectrograph on the ANU 2.3 m telescope to analyse spectra between 3600--7000 \AA. This allowed us to derive fluxes and line ratios for selected nebular lines. Applying radiative shock model diagnostics, we estimate shock velocities, densities, radiative ages and pressures across the object. We show that S26 is just entering its radiative phase, and that the northern and western regions are dominated by partially-radiative shocks due to a lower density ISM in these directions. We determine a velocity of expansion along the jet of 330 km s$^{-1}$, and a velocity of expansion of the bubble in the minor axis direction of 132 km s$^{-1}$. We determine the age of the structure to be $4.1\times10^5$ yr, and the jet energy flux to be $(4-10)\times10^{40}$ erg s$^{-1}$ The jet appears to be collimated within $\sim0.25$ deg, and to undergo very little precession. If the relativistic $\beta \sim 1/3$, then some 4 M$_{\odot}$ of relativistic matter has already been processed through the jet. We conclude that the central object in S26 is probably a Black Hole with a mass typical of the ultra-luminous X-ray source population which is currently consuming a fairly massive companion through Roche Lobe accretion.Comment: Accepted for publication in MNRAS; 12 pages, 7 figures and 3 table

The structure of Herbig-Haro object 43 and Orion dark cloud extinction

New ultraviolet and optical observations of Herbig-Haro Object No. 43 are reported. Continuum and emission line fluxes in the range 1250 A equal to or less than lambda equal to less than 7350A have been measured. The continuum fluxes are best matched by an enhanced H two photon component added to H free bound emission, assuming theta Ori extinction curve with E(B-V) = 0.2, R = 5. The strucutre and dynamics of three components within the object are discussed. The object has a radiative output of equal to or greater than 0.23 infrared luminosity in ultraviolet and optical radiation combined. The energy requirements are discussed in terms of the production of shock waves by a collimated, supersonic mass outflow from a nearby infrared source

Galaxy-Wide Shocks in Late-Merger Stage Luminous Infrared Galaxies

We present an integral field spectroscopic study of two nearby Luminous Infrared Galaxies (LIRGs) that exhibit evidence of widespread shock excitation induced by ongoing merger activity, IC 1623 and NGC 3256. We show the importance of carefully separating excitation due to shocks vs. excitation by HII regions and the usefulness of IFU data in interpreting the complex processes in LIRGs. Our analysis focuses primarily on the emission line gas which is extensive in both systems and is a result of the abundant ongoing star formation as well as widespread LINER-like excitation from shocks. We use emission-line ratio maps, line kinematics, line-ratio diagnostics and new models as methods for distinguishing and analyzing shocked gas in these systems. We discuss how our results inform the merger sequence associated with local U/LIRGs and the impact that widespread shock excitation has on the interpretation of emission-line spectra and derived quantities of both local and high-redshift galaxies.Comment: 14 pages, 11 figures, Accepted to Ap

The Physical Conditions in Starbursts Derived from Bayesian Fitting of Mid-IR SEDS: 30 Doradus as a Template

To understand and interpret the observed Spectral Energy Distributions (SEDs) of starbursts, theoretical or semi-empirical SED models are necessary. Yet, while they are well-founded in theory, independent verification and calibration of these models, including the exploration of possible degeneracies between their parameters, are rarely made. As a consequence, a robust fitting method that leads to unique and reproducible results has been lacking. Here we introduce a novel approach based on Bayesian analysis to fit the Spitzer-IRS spectra of starbursts using the SED models proposed by Groves et al. (2008). We demonstrate its capabilities and verify the agreement between the derived best fit parameters and actual physical conditions by modelling the nearby, well-studied, giant HII region 30 Dor in the LMC. The derived physical parameters, such as cluster mass, cluster age, ISM pressure and covering fraction of photodissociation regions, are representative of the 30 Dor region. The inclusion of the emission lines in the modelling is crucial to break degeneracies. We investigate the limitations and uncertainties by modelling sub-regions, which are dominated by single components, within 30 Dor. A remarkable result for 30 Doradus in particular is a considerable contribution to its mid-infrared spectrum from hot ({\simeq} 300K) dust. The demonstrated success of our approach will allow us to derive the physical conditions in more distant, spatially unresolved starbursts.Comment: 17 pages, 10 figures. Accepted por publication in the Astrophysical Journa