Nested shells reveal the rejuvenation of the Orion-Eridanus superbubble

The Orion-Eridanus superbubble is the prototypical superbubble due to its proximity and evolutionary state. Here, we provide a synthesis of recent observational data from WISE and Planck with archival data, allowing to draw a new and more complete picture on the history and evolution of the Orion-Eridanus region. We discuss the general morphological structures and observational characteristics of the superbubble, and derive quantitative properties of the gas- and dust inside Barnard's Loop. We reveal that Barnard's Loop is a complete bubble structure which, together with the lambda Ori region and other smaller-scale bubbles, expands within the Orion-Eridanus superbubble. We argue that the Orion-Eridanus superbubble is larger and more complex than previously thought, and that it can be viewed as a series of nested shells, superimposed along the line of sight. During the lifetime of the superbubble, HII region champagne flows and thermal evaporation of embedded clouds continuously mass-load the superbubble interior, while winds or supernovae from the Orion OB association rejuvenate the superbubble by sweeping up the material from the interior cavities in an episodic fashion, possibly triggering the formation of new stars that form shells of their own. The steady supply of material into the superbubble cavity implies that dust processing from interior supernova remnants is more efficient than previously thought. The cycle of mass-loading, interior cleansing, and star formation repeats until the molecular reservoir is depleted or the clouds have been disrupted. While the nested shells come and go, the superbubble remains for tens of millions of years.Comment: 20 pages, 6 figures, accepted for publication in Ap

Jets and Outflows From Star to Cloud: Observations Confront Theory

In this review we focus on the role jets and outflows play in the star and planet formation process. Our essential question can be posed as follows: are jets/outflows merely an epiphenomenon associated with star formation or do they play an important role in mediating the physics of assembling stars both individually and globally? We address this question by reviewing the current state of observations and their key points of contact with theory. Our review of jet/outflow phenomena is organized into three length-scale domains: Source and Disk Scales ($0.1-10^2$ au) where the connection with protostellar and disk evolution theories is paramount; Envelope Scales ($10^2-10^5$ au) where the chemistry and propagation shed further light on the jet launching process, its variability and its impact on the infalling envelope; Parent Cloud Scales ($10^5-10^6$ au) where global momentum injection into cluster/cloud environments become relevant. Issues of feedback are of particular importance on the smallest scales where planet formation regions in a disk may be impacted by the presence of disk winds, irradiation by jet shocks or shielding by the winds. Feedback on envelope scales may determine the final stellar mass (core-to-star efficiency) and envelope dissipation. Feedback also plays an important role on the larger scales with outflows contributing to turbulent support within clusters including alteration of cluster star formation efficiencies (feedback on larger scales currently appears unlikely). A particularly novel dimension of our review is that we consider results on jet dynamics from the emerging field of High Energy Density Laboratory Astrophysics (HEDLA). HEDLA is now providing direct insights into the 3-D dynamics of fully magnetized, hypersonic, radiative outflows.Comment: Accepted for publication as a chapter in Protostars and Planets VI, University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C. Dullemond, Th. Hennin

Protostellar Feedback in Massive Star Forming Regions

We examine mechanical feedback mechanisms during the protostellar phase through jets and outflows. To do so, we make use of velocity-resolved CII observations at 158 $\mu$m taken with the SOFIA observatory. We identify CII emitting cavities at velocities ranging from 1-2 km s$^{-1}$ to 15 km s$^{-1}$ relative to the Veil shell ($v_\mathrm{LSR}$ = 13 km s$^{-1}$). The momentum and dynamical timescales of these cavities imply that the cavities in Orion were formed by fossil and active outflows from stars with luminosities ranging from 10$^3$ to 10$^5$ L$_\odot$. The momentum deposited during protostellar feedback is $\sim$1/6 of the momentum of the Veil shell deposited through winds from $\theta^1$ Ori C. By creating cavities, the fossil outflows may already have broken the Veil shell, and outflows from less massive stars may have made the Veil shell porous

Kinematics of elliptical galaxies with a diffuse dust component

Observations show that early-type galaxies contain a considerable amount of interstellar dust, most of which is believed to exist as a diffusely distributed component. We construct a four-parameter elliptical galaxy model in order to investigate the effects of such a smooth absorbing component on the projection of kinematic quantities, such as the line profiles and their moments. We investigate the dependence on the optical depth and on the dust geometry. Our calculations show that both the amplitude and the morphology of these quantities can be significantly affected. Dust effects should therefore be taken in consideration when interpreting photometric and kinematic properties, and correlations that utilize these quantities.Comment: 12 pages, 9 figures, accepted for publication in MNRA

Mapping the column density and dust temperature structure of IRDCs with Herschel

Infrared dark clouds (IRDCs) are cold and dense reservoirs of gas potentially available to form stars. Many of these clouds are likely to be pristine structures representing the initial conditions for star formation. The study presented here aims to construct and analyze accurate column density and dust temperature maps of IRDCs by using the first Herschel data from the Hi-GAL galactic plane survey. These fundamental quantities, are essential for understanding processes such as fragmentation in the early stages of the formation of stars in molecular clouds. We have developed a simple pixel-by-pixel SED fitting method, which accounts for the background emission. By fitting a grey-body function at each position, we recover the spatial variations in both the dust column density and temperature within the IRDCs. This method is applied to a sample of 22 IRDCs exhibiting a range of angular sizes and peak column densities. Our analysis shows that the dust temperature decreases significantly within IRDCs, from background temperatures of 20-30 K to minimum temperatures of 8-15 K within the clouds, showing that dense molecular clouds are not isothermal. Temperature gradients have most likely an important impact on the fragmentation of IRDCs. Local temperature minima are strongly correlated with column density peaks, which in a few cases reach NH2 = 1 x 10^{23} cm^{-2}, identifying these clouds as candidate massive prestellar cores. Applying this technique to the full Hi-GAL data set will provide important constraints on the fragmentation and thermal properties of IRDCs, and help identify hundreds of massive prestellar core candidates.Comment: Accepted for publication in A&A Herschel special issu

The hot and cold interstellar matter of early type galaxies and their radio emission

Over the last few years, the knowledge of the interstellar matter (ISM) of early type galaxies has increased dramatically. Many early type galaxies are now known to have ISM in three different phases: cold (neutral hydrogen (HI), dust and molecular material), warm (ionized) and hot (S-ray emitting) gas. Early type galaxies have smaller masses of cold ISM (10 to the 7th power - 10 to the 8th power solar mass; Jura et al. 1987) than later type spiral galaxies, while they have far more hot gas (10 to the 9th power - 10 to the tenth power solar mass; Forman et al. 1985, Canizares et al. 1987). In order to understand the relationship between the different phases of the ISM and the role of the ISM in fueling radio continuum sources and star formation, researchers compared observational data from a wide range of wavelengths

New Herbig-Haro Objects and Giant Outflows in Orion

We present the results of a photographic and CCD imaging survey for Herbig-Haro (HH) objects in the L1630 and L1641 giant molecular clouds in Orion. The new HH flows were initially identified from a deep H-alpha film from the recently commissioned AAO/UKST H-alpha Survey of the southern sky. Our scanned H-alpha and broad band R images highlight both the improved resolution of the H-alpha survey and the excellent contrast of the H-alpha flux with respect to the broad band R. Comparative IVN survey images allow us to distinguish between emission and reflection nebulosity. Our CCD H-alpha, [SII], continuum and I band images confirm the presence of a parsec-scale HH flow associated with the Ori I-2 cometary globule and several parsec-scale strings of HH emission centred on the L1641-N infrared cluster. Several smaller outflows display one-sided jets. Our results indicate that for declinations south of -6 degrees in L1641, parsec-scale flows appear to be the major force in the large-scale movement of optical dust and molecular gas.Comment: 14 pages, Latex using MN style, 21 figures in JPEG format. Higher resolution figures available from S.L. Mader. Accepted by MNRAS. Email contact for higher resolution images: [email protected]

Synthetic Molecular Clouds from Supersonic MHD and Non-LTE Radiative Transfer Calculations

The dynamics of molecular clouds is characterized by supersonic random motions in the presence of a magnetic field. We study this situation using numerical solutions of the three-dimensional compressible magneto-hydrodynamic (MHD) equations in a regime of highly supersonic random motions. The non-LTE radiative transfer calculations are performed through the complex density and velocity fields obtained as solutions of the MHD equations, and more than 5x10^5 synthetic molecular spectra are obtained. We use a numerical flow without gravity or external forcing. The flow is super-Alfvenic and corresponds to model A of Padoan and Nordlund (1997). Synthetic data consist of sets of 90x90 synthetic spectra with 60 velocity channels, in five molecular transitions: J=1-0 and J=2-1 for 12CO and 13CO, and J=1-0 for CS. Though we do not consider the effects of stellar radiation, gravity, or mechanical energy input from discrete sources, our models do contain the basic physics of magneto-fluid dynamics and non-LTE radiation transfer and are therefore more realistic than previous calculations. As a result, these synthetic maps and spectra bear a remarkable resemblance to the corresponding observations of real clouds.Comment: 33 pages, 12 figures included, 5 jpeg figures not included (fig1a, fig1b, fig3, fig4 fig5), submitted to Ap

Waves on the surface of the Orion molecular cloud

Massive stars influence their parental molecular cloud, and it has long been suspected that the development of hydrodynamical instabilities can compress or fragment the cloud. Identifying such instabilities has proved difficult. It has been suggested that elongated structures (such as the `pillars of creation') and other shapes arise because of instabilities, but alternative explanations are available. One key signature of an instability is a wave-like structure in the gas, which has hitherto not been seen. Here we report the presence of `waves' at the surface of the Orion molecular cloud near where massive stars are forming. The waves seem to be a Kelvin-Helmholtz instability that arises during the expansion of the nebula as gas heated and ionized by massive stars is blown over pre-existing molecular gas.Comment: Preprint of publication in Natur