3D ISM-Shock Spectral Emission: X-ray models for Radio Galaxy SED Modeling

Galaxies form out of small fluctuations in a smoothly expanding Universe. However, the initial gravitational collapse phase is accompanied by the formation of supermassive black holes and clusters of massive stars. Black holes and star clusters generate powerful outflows in the form of jets and superwinds that interact with still infalling gas, possibly regulating the galaxy formation process, initiating new sites of star formation, and carrying chemically enriched gas to the intergalactic medium. Unfortunately, beyond this qualitative description our detailed theoretical understanding is poor. New results from 3D simulations of a GPS/CSS galaxy, with gravitational potentials included, shed some new light on the jet driven outflow process in particular. New code capabilites to predict detailed X-ray spectra from multi-dimensional time-dependent dynamics simulations of Galaxy Feedback, and will be useful for future interpretation of X-ray and radio SEDs of forming galaxies.Comment: 10 pages, 5 figures, Invited Conference Talk, The Spectral Energy Distribution of Gas Rich Galaxies: Confronting Models with Data, Heidelberg, Germany,October 4-8, 200

The Infrared Emission from the Narrow Line Region

We present models for the mid- and far- infrared emission from the Narrow Line Region (NLR) of Active Galactic Nuclei (AGN). Using the MAPPINGS III code we explore the effect of typical NLR parameters on the spectral characteristics of the IR emission. These include useful IR emission line ratio diagnostic diagrams for the determination of these parameters, as well as Star formation--AGN mixing diagnostics. We also examine emission line to continuum correlations which would assist in separating the IR emission arising from the NLR from that coming from the inner torus. We find for AGN like NGC 1068 and NGC 4151 that the NLR only contributes ~10% to the total IRAS 25 mum flux, and that other components such as a dusty torus are necessary to explain the total AGN IR emission.Comment: 15 pages, 12 figures, accepted for publication in A&A. Paper with full resolution figures available at http://www.mpa-garching.mpg.de/~brent/publications/bgrovesnlrIRpaper.pd

Ultrafaint Dwarfs - Star Formation and Chemical Evolution in the Smallest Galaxies

In earlier work we showed that a dark matter halo with a virial mass of $10^7$ M$_\odot$ can retain a large percentage of its baryons in the face of the pre-ionization phase and supernova explosion from a 25$M_\odot$ star. Here we expand on the results of that work, investigating the star formation and chemical evolution of the system beyond the first supernova. In a galaxy with a mass $M_{vir} = 10^7$M$_\odot$, sufficient gas is retained by the potential for a second period of star formation to occur. The impact of a central explosion is found to be much stronger than that of an off-centred explosion both in blowing out the gas and in enriching it, as in the off-centered case most of the supernova energy and metals escape into the IGM. We model the star formation and metallicity given the assumption that stars form for 100, 200, 400 and 600 Myr and discuss the results in the context of recent observations of very low mass galaxies. We show that we can account for most features of the observed relationship between [$\alpha$/Fe] and [Fe/H] in ultra-faint dwarf galaxies with the assumption that the systems formed at a low mass, rather than being remnants of much larger systems

Ultrafaint Dwarf Galaxies - the lowest mass relics from before reionization

New observations indicate that ultrafaint dwarf galaxies (UFD) -- the least luminous systems bound by dark matter halos (<10^5 Lsun) -- may have formed before reionization. The extrapolated virial masses today are uncertain with estimates ranging from 10^8 Msun to 10^9 Msun. We show that the progenitor halo masses of UFDs can be as low as Mvir = 10^7 Msun. Under the right conditions, such a halo can survive the energy input of a supernova and its radiative progenitor. A clumpy medium is much less susceptible to both internal and external injections of energy. It is less prone to SN sweeping because the coupling efficiency of the explosive energy is much lower than for a diffuse ISM. With the aid of the 3D hydro/ionization code Fyris, we show that sufficient baryons are retained to form stars following a single supernova event in dark matter halos down to Mvir ~ 10^7 Msun with radiative cooling. The gas survives the SN explosion, is enriched with the abundance yields of the discrete events, and reaches surface densities where low mass stars can form. Our highest resolution simulations reveal why cooling is so effective in retaining gas compared to any other factor. In the early stages, the super-hot metal-enriched SN ejecta exhibit strong cooling, leading to much of the explosive energy being lost. Consistent with earlier work, the baryons do *not* survive in smooth or adiabatic models in the event of a supernova. The smallest galaxies carry signatures of the earliest epochs of star formation, which may distinguish a small primordial galaxy from one that was stripped down to its present size through tidal interaction. We discuss these results in the context of local UFDs and damped Ly-alpha systems (z~2) at very low metallicity ([Fe/H] ~ -3). We show that both classes of objects are consistent with primordial low-mass systems that have experienced only a few enrichment events.Comment: 32 pages, 25 figures, accepted by Ap

The Magellanic Stream: break up and accretion onto the hot Galactic corona

The Magellanic HI Stream (~2x10^9 Msun [d/55 kpc]^2) encircling the Galaxy at a distance 'd' is arguably the most important tracer of what happens to gas accreting onto a disk galaxy. Recent observations reveal that the Stream's mass is in fact dominated (3:1) by its ionised component. Here we revisit the origin of the mysterious H-alpha recombination emission observed along much of its length that is overly bright (~150-200 milli-Rayleigh) for the known Galactic ultraviolet background (~20-40 mR / [d/55 kpc]^2). In an earlier model, we proposed that a slow shock cascade was operating along the Stream due to its interaction with the extended Galactic hot corona. We find that, for a smooth coronal density profile, this model can explain the bright H-alpha emission if the coronal density satisfies 2 < (n / 10^{-4} cm^{-3}) < 4 at d = 55 kpc. But in view of updated parameters for the Galactic halo and mounting evidence that most of the Stream must lie far beyond the Magellanic Clouds (d>55 kpc), we revisit the shock cascade model in detail. At lower densities, the HI gas is broken down by the shock cascade but mostly mixes with the hot corona without significant recombination. At higher densities, the hot coronal mass (including the other baryonic components) exceeds the baryon budget of the Galaxy. If the H-alpha emission arises from the shock cascade, the upper limit on the smooth coronal density constrains the Stream's mean distance to < 75 kpc. If, as some models indicate, the Stream is even further out, either the shock cascade is operating in a regime where the corona is substantially mass-loaded with recent gas debris, or an entirely different ionization mechanism is responsible.Comment: Significant expansion of the parameter space explored in response to referee's comments. ApJ accepte

The Centaurus A Northern Middle Lobe as a Buoyant Bubble

We model the northern middle radio lobe of Centaurus A (NGC 5128) as a buoyant bubble of plasma deposited by an intermittently active jet. The extent of the rise of the bubble and its morphology imply that the ratio of its density to that of the surrounding ISM is less than 10^{-2}, consistent with our knowledge of extragalactic jets and minimal entrainment into the precursor radio lobe. Using the morphology of the lobe to date the beginning of its rise through the atmosphere of Centaurus A, we conclude that the bubble has been rising for approximately 140Myr. This time scale is consistent with that proposed by Quillen et al. (1993) for the settling of post-merger gas into the presently observed large scale disk in NGC 5128, suggesting a strong connection between the delayed re-establishment of radio emission and the merger of NGC 5128 with a small gas-rich galaxy. This suggests a connection, for radio galaxies in general, between mergers and the delayed onset of radio emission. In our model, the elongated X-ray emission region discovered by Feigelson et al. (1981), part of which coincides with the northern middle lobe, is thermal gas that originates from the ISM below the bubble and that has been uplifted and compressed. The "large-scale jet" appearing in the radio images of Morganti et al. (1999) may be the result of the same pressure gradients that cause the uplift of the thermal gas, acting on much lighter plasma, or may represent a jet that did not turn off completely when the northern middle lobe started to buoyantly rise. We propose that the adjacent emission line knots (the "outer filaments") and star-forming regions result from the disturbance, in particular the thermal trunk, caused by the bubble moving through the extended atmosphere of NGC 5128.Comment: 38 pages, 13 figures, submitted to ApJ; a version with higher resolution figures is available at http://www.mso.anu.edu.au/~saxton/papers/cena.pd