Galactic Ecosystem Research Articles

Making Sense of Legitimacy Across Universities: Ecocritical Ontological Perspective

This paper reflects on research methodological considerations of how legitimacy of publicly funded universitiesoccurs. From an ecocritical ontological perspective the paper uses a metaphor and sense-making techniques to shed light into effective modalities universities use to connect with local economies. The Milky way Galactic ecosystem metaphor is used not only to make sense of the ecocritical ontological stance taken to make sense of legitimacy but is used as a metaphor to make sense of the findings. The paper asserts that the legitimacy theoretical lens is particularly appropriate to probe universities’ legitimacy and connectedness to the local communities they are embedded in. The rationale behind this assertion is that legitimacy is only conferred to the extent the actions of an entity are perceived as desirable, efficient, proper, or appropriate by the ecosystem stakeholders. The theory is thus useful for examining connectedness of publicly funded universities to its local community. The paper argues that the university system that is delinked from local economic development is like a Milky way Galaxy delinked from its Galactic ecosystem. Against this backdrop, the paper juxtaposes Mondragon University, located in a rural part of Northern Spain with two South African universities embedded in poverty stricken rural South Africa. Mondragon University is presented as a hallmark of success when it comes to local community legitimacy. The paper is centered around the following question: (1) how does university legitimacy yield impactful local community outcomes? Using the Milky way Galaxy metaphor, the findings show a considerable variety in local community connectedness depending on bureaucratic arrangements of the universities. The findings also showed that alternative income sources, outside the public purse, just like the gravitational force in the galactic ecosystem, is the key force that determines legitimacy in a university setting. The paper contributes to business research methods by fusing metaphorical as well as sense-making research techniques to bring to sharp focus permeability of the university space to enable local economic development.

Evolution and distribution of superbubbles in simulated Milky Way-like galaxies

ABSTRACT Stellar feedback plays a crucial role in regulating baryon cycles of a galactic ecosystem, and may manifest itself in the formation of superbubbles in the interstellar medium. In this work, we used a set of high-resolution simulations to systematically study the properties and evolution of superbubbles in galactic environments. The simulations were based on the SMUGGLE galaxy formation framework using the hydrodynamical moving-mesh code arepo, reaching a spatial resolution of $\sim 4 \, \rm pc$ and mass resolution of $\sim 10^3 \, \rm M_{\odot }$. We identified superbubbles and tracked their time evolution using the parent stellar associations within the bubbles. The X-ray luminosity-size distribution of superbubbles in the fiducial run is largely consistent with the observations of nearby galaxies. The size of superbubbles shows a double-peaked distribution, with the peaks attributed to early feedback (radiative and stellar wind feedback) and supernova feedback. The early feedback tends to suppress the subsequent supernova feedback, and it is strongly influenced by star formation efficiency, which regulates the environmental density. Our results show that the volume filling factor of hot gas (T > 105.5 K) is about $12~{{\ \rm per\ cent}}$ averaged over a region of 4 kpc in height and 20 kpc in radius centred on the disc of the galaxy. Overall, the properties of superbubbles are sensitive to the choice of subgrid galaxy formation models and can, therefore, be used to constrain these models.

Abundance and temperature of the outer hot circumgalactic medium

Context. Despite their vital importance to understanding galaxy evolution and our own Galactic ecosystem, our knowledge of the physical properties of the hot X-ray emitting phase of the Milky Way is still inadequate. However, sensitive SRG/eROSITA large area surveys are now providing us with the long-sought data needed to mend this state of affairs. Aims. Our aim is to constrain the properties of the Milky Way hot halo emission toward intermediate Galactic latitudes close to the Galactic anti-center. Methods. We analyzed the spectral properties of the integrated soft X-ray emission observed by eROSITA in the relatively deep eFEDS field. Results. We observe a flux of 12.6 and 5.1 × 10−12 erg cm−2 s−1 deg−2 in the total (0.3–2) and soft (0.3–0.6 keV) band. We measure the temperature and metal (oxygen) abundance of the hot circumgalactic medium (CGM) to be within kTCGM = 0.153–0.178 keV and ZCGM = 0.052–0.072 Z⊙, depending on the contribution of solar wind charge exchange (SWCX). Slightly higher CGM abundances ZCGM = 0.05–0.10 Z⊙ are possible, considering the uncertain extrapolation of the extragalactic cosmic X-ray background (CXB) emission below ~1 keV. To recover CGM abundances as high as ZCGM = 0.3 Z⊙, the presence of an additional component must be postulated, likely associated with the warm-hot intergalactic medium, providing ~15–20% of the flux in the soft X-ray band. We observe line widths of the CGM plasma smaller than Δυ ≤ 500 km s−1. The emission in the soft band is dominated (~47%) by the circumgalactic medium (CGM), whose contribution reduces to ~30% if heliospheric SWCX contributes at the level of ~15% also during solar minimum. The remaining flux is provided by the CXB (~33%) and the local hot bubble (~18%). Moreover, the eROSITA data require the presence of an additional component associated with the elusive Galactic corona plus a possible contribution from unresolved M dwarf stars. This component has a temperature of kT ~ 0.4– 0.7 keV, a considerable (~ kiloparsec) scale height, and might be out of thermal equilibrium. It contributes ~9% to the total emission in the 0.6—2 keV band, and is therefore a likely candidate to produce part of the unresolved CXB flux observed in X-ray ultra-deep fields. We also observe a significant contribution to the soft X-ray flux due to SWCX, during periods characterized by stronger solar wind activity, and causing the largest uncertainty on the determination of the CGM temperature. Conclusions. We constrain temperature, emission measure, abundances, thermal state, and spectral shape of the outer hot CGM of the Milky Way.

Star-formation-rate estimates from water emission

Context. The star-formation rate (SFR) quantitatively describes the star-formation process in galaxies throughout cosmic history. Current ways to calibrate this rate do not usually employ observational methods accounting for the low-mass end of stellar populations as their signatures are too weak. Aims. Accessing the bulk of protostellar activity within galactic star-forming regions can be achieved by tracing signposts of ongoing star formation. One such signpost is molecular outflows, which are particularly strong at the earliest stages of star formation. These outflows are bright in molecular emission, which is readily observable. We propose to utilize the protostellar outflow emission as a tracer of the SFR. Methods. In this work, we introduce a novel version of the galaxy-in-a-box model, which can be used to relate molecular emission from star formation in galaxies with the SFR. We measured the predicted para-water emission at 988 GHz (which is particularly bright in outflows) and corresponding SFRs for galaxies with LFIR = 108 − 1011 L⊙ in a distance-independent manner, and compared them with expectations from observations. Results. We evaluated the derived results by varying star-forming parameters, namely the star formation efficiency, the free-fall time scaling factor, and the initial mass function. We observe that for the chosen water transition, relying on the current Galactic observations and star formation properties, we are underestimating the total galactic emission, while overestimating the SFRs, particularly for more starburst-like configurations. Conclusions. The current version of the galaxy-in-a-box model only accounts for a limited number of processes and configurations, that is, it focuses on ongoing star formation in massive young clusters in a spiral galaxy. Therefore, the inferred results, which underestimate the emission and overestimate the SFR, are not surprising: known sources of emission are not included in the model. To improve the results, the next version of the model needs to include a more detailed treatment of the entire galactic ecosystem and other processes that would contribute to the emission. Thus, the galaxy-in-a-box model is a promising step toward unveiling the star-forming properties of galaxies across cosmic time.

Dust entrainment in galactic winds

ABSTRACT Winds driven by stellar feedback are an essential part of the galactic ecosystem and are the main mechanism through which low-mass galaxies regulate their star formation. These winds are generally observed to be multiphase with detections of entrained neutral and molecular gas. They are also thought to enrich the circumgalactic medium around galaxies with metals and dust. This ejected dust encodes information about the integrated star formation and outflow history of the galaxy. Therefore it is important to understand how much dust is entrained and driven out of the disc by galactic winds. Here, we demonstrate that stellar feedback is efficient in driving dust-enriched winds and eject enough material to account for the amount of extraplanar dust observed in nearby galaxies. The amount of ejected dust depends on the sites from where they are launched, with dustier galaxies launching more dust-enriched outflows. Moreover, the outflowing cold and dense gas is significantly more dust enriched than the volume filling hot and tenuous material. These results provide an important new insight into the dynamics, structure, and composition of galactic winds and their role in determining the dust content of the extragalactic gas in galaxies.

Dynamic localized turbulent diffusion and its impact on the galactic ecosystem

Modelling the turbulent diffusion of thermal energy, momentum, and metals is required in all galaxy evolution simulations due to the ubiquity of turbulence in galactic environments. The most commonly employed diffusion model, the Smagorinsky model, is known to be over-diffusive due to its strong dependence on the fluid velocity shear. We present a method for dynamically calculating a more accurate, locally appropriate, turbulent diffusivity: the dynamic localised Smagorinsky model. We investigate a set of standard astrophysically-relevant hydrodynamical tests, and demonstrate that the dynamic model curbs over-diffusion in non-turbulent shear flows and improves the density contrast in our driven turbulence experiments. In galactic discs, we find that the dynamic model maintains the stability of the disc by preventing excessive angular momentum transport, and increases the metal-mixing timescale in the interstellar medium. In both our isolated Milky Way-like galaxies and cosmological simulations, we find that the interstellar and circumgalactic media are particularly sensitive to the treatment of turbulent diffusion. We also examined the global gas enrichment fractions in our cosmological simulations, to gauge the potential effect on the formation sites and population statistics of Population III stars and supermassive black holes, since they are theorised to be sensitive to the metallicity of the gas out of which they form. The dynamic model is, however, not for galaxy evolution studies only. It can be applied to all astrophysical hydrodynamics simulations, including those modelling stellar interiors, planetary formation, and star formation.

Simulating galactic dust grain evolution on a moving mesh

Interstellar dust is an important component of the galactic ecosystem, playing a key role in multiple galaxy formation processes. We present a novel numerical framework for the dynamics and size evolution of dust grains implemented in the moving-mesh hydrodynamics code AREPO suited for cosmological galaxy formation simulations. We employ a particle-based method for dust subject to dynamical forces including drag and gravity. The drag force is implemented using a second-order semi-implicit integrator and validated using several dust-hydrodynamical test problems. Each dust particle has a grain size distribution, describing the local abundance of grains of different sizes. The grain size distribution is discretised with a second-order piecewise linear method and evolves in time according to various dust physical processes, including accretion, sputtering, shattering, and coagulation. We present a novel scheme for stochastically forming dust during stellar evolution and new methods for sub-cycling of dust physics time-steps. Using this model, we simulate an isolated disc galaxy to study the impact of dust physical processes that shape the interstellar grain size distribution. We demonstrate, for example, how dust shattering shifts the grain size distribution to smaller sizes resulting in a significant rise of radiation extinction from optical to near-ultraviolet wavelengths. Our framework for simulating dust and gas mixtures can readily be extended to account for other dynamical processes relevant in galaxy formation, like magnetohydrodynamics, radiation pressure, and thermo-chemical processes.

Radio Stars and Their Lives in the Galaxy

ABSTRACTThis article summarizes the 3-day international workshop Radio Stars and Their Lives in the Galaxy, held at the Massachusetts Institute of Technology Haystack Observatory on 2012 October 3–5. The workshop was organized to provide a forum for the presentation and discussion of advances in stellar and solar astrophysics recently (or soon to be) enabled by the latest generation of state-of-the-art observational facilities operating from meter to submillimeter wavelengths. The meeting brought together both observers and theorists to discuss how radio wavelength observations are providing new and unique insights into the workings of stars and their role in the Galactic ecosystem. Topics covered included radio emission from hot and cool stars (from the pre- to post-main-sequence), the Sun as a radio star, circumstellar chemistry, planetary nebulae, white dwarf binaries and novae, supernova progenitors, and radio stars as probes of the Galaxy.

XMM–Newton/Reflection Grating Spectrometer detection of the missing interstellar O vii Kα absorption line in the spectrum of Cyg X-2

The hot interstellar medium is an important part of the Galactic ecosystem and can be effectively characterized through X-ray absorption line spectroscopy. However, in a study of the hot medium using the accreting neutron star X-ray binary, Cyg X-2, as a background light source, a mystery came about when the putatively strong O vii Kα line was not detected in Chandra grating observations, while other normally weaker lines such as O vii Kβ as well as O vi and O viii Kα are clearly present. We have investigated the grating spectra of Cyg X-2 from 10 XMM–Newton observations, in search of the missing line. We detect it consistently in nine of these observations, but the line is absent in the remaining one observation or is inconsistent with the detection in others at a ∼4σ confidence level. This absence of the line resembles that seen in the Chandra observations. Similarly, the O vi Kα line is found to disappear occasionally, but not in concert with the variation of the O vii Kα line. All these variations are most likely due to the presence of changing O vii and O vi Kα emission lines of Cyg X-2, which are blurred together with the absorption ones in the X-ray spectra. A re-examination of the Chandra grating data indeed shows evidence for a narrow emission line slightly off the O vi Kα absorption line. We further show that narrow N v emission lines with varying centroids and fluxes are present in far-ultraviolet spectra from the Cosmic Origins Spectrograph aboard the Hubble Space Telescope. These results provide new constraints on the accretion around the neutron star and on the X-ray-heating of the stellar companion. The understanding of these physical processes is also important to the fidelity of using such local X-ray binaries for interstellar absorption line spectroscopy.

Supernovae and the Galactic Ecosystem

AbstractSupernovae are the dominant source of stellar feedback, which plays an important role in regulating galaxy formation and evolution. While this feedback process is still quite uncertain, it is probably not due to individual supernova remnants as commonly observed. Most supernovae likely take place in low-density, hot gaseous environments, such as superbubbles and galactic bulges, and typically produce no long-lasting bright remnants. I review recent observational and theoretical work on the impact of such supernovae on galaxy ecosystems, particularly on hot gas in superbubbles and galactic spheroids.

A Close Look at the Galactic Ecosystem: the Canadian Galactic Plane Survey

AbstractEnergy and mass interchanges in the interstellar medium are driven by the life-cycle of stars. They appear in our own Galaxy over a broad range of scales, from point-like injection from stars to global input on the scale of spiral density waves. Understanding this Galactic Ecosystem requires observations of the different phases of the ISM over this large angular dynamic range. The Canadian Galactic Plane Survey (CGPS) is a project to combine radio, millimeter, and infrared surveys of the Galactic plane, providing arcminute-scale images of all major components of the interstellar medium over a large portion of the Galactic disk.

The interstellar environment of our galaxy

This article reviews the current knowledge and understanding of the interstellar medium of our galaxy. The author first presents each of the three basic constituents---ordinary matter, cosmic rays, and magnetic fields---of the interstellar medium, with emphasis on their physical and chemical properties as inferred from a broad range of observations. The interaction of these interstellar constituents, both with each other and with stars, is then discussed in the framework of the general galactic ecosystem.

Simulations of the supernova-dominated interstellar medium in disk galaxies

A three-dimensional simulation of the evolution of an SNR-dominated ISM from an initially homogeneous, uniform substrate is presented. Systems with only bremsstrahlung cooling are compared with those cooled by radiation from metals. This distinction translates into a size difference in the resulting SNRs, and thus in the ability of isolated SNRs to affect the evolution of the galactic ecosystem. At a given SN rate, correlating the SNe decreases the global evolution of the galaxy if the SNRs individually can affect the system. It is shown that, when the density of the ISM varies widely, the N(R) test can give the reverse of standard expectations. It is shown that strong SNRs can impede interstellar tunnel production because of their ability to transport material and fill a previously evacuated volume, and that cloud size affects the final picture of the system.

The effects of induced star formation on the evolution of the galaxy. II - The galactic ecosystem

view Abstract Citations (42) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The effects of induced star formation on the evolution of the galaxy. II - The galactic ecosystem Shore, S. N. Abstract The deterministic dynamical systems approach of Paper I is here generalized to the case of a disk galaxy with star-induced star formation. It is shown that the cases of a rigidly rotating axisymmetric and nonaxisymmetric, and a differentially rotating galaxy model can be solved explicitly. The results are compared with stochastic simulations. A wave of star formation, propagating outward from the central portion of an active region, is found. The velocity and properties of this star formation front are examined. A two-phase model with time delays is also presented, which can be used for modeling sequential star formation. In this case, critical initial gas and star fractions are presented. Finally, a brief discussion is presented of the stochastic generalization of the one-zone model for a two-phase galaxy with and without infall. Publication: The Astrophysical Journal Pub Date: February 1983 DOI: 10.1086/160664 Bibcode: 1983ApJ...265..202S Keywords: Astronomical Models; Disk Galaxies; Galactic Evolution; Galactic Rotation; Star Distribution; Star Formation; Dwarf Galaxies; Dynamic Models; Galactic Structure; Spiral Galaxies; Stochastic Processes; Time Lag; Astrophysics full text sources ADS |