Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSmoke in the Smoke Rings: ISO Observations of Dust in Collisional Ring Galaxies
147
0
0.0
(
0
)
Added by
Vassilis Charmandaris
Publication date
1999
fields
Physics
and research's language is
English
Authors
P. N. Appleton
Ask ChatGPT about the research
No Arabic abstract
Collisional ring galaxies probably result from a head-on collision between a compact companion galaxy and a gas-rich disk system. We present a review of the discovery of warm dust in five collisional rings observed by ISO which range in total Far-IR luminosity from 10$^{10}$~ $<$ ~L$_{FIR}$ ~$<$ ~10$^{11}$ L$odot$. The results show that in most cases, the mid-IR (MIR) flux is often a significant fraction of the total energy budget of star formation activity in these galaxies (at least 10% even in the least powerful cases). We argue that the MIR emission, when combined with optical and radio observations, allows us to build a more complete picture of activity in these collisional systems. Although not as extreme as ULIRGs, these collisional systems provide low-redshift examples of the early effects of galaxy collisions on the ISM and may be relevant to the collisional assembly of galaxy disk components at high redshift.
rate research
Read More
We present the first mid-infrared (Mid-IR) ($lambda5-15mu$m) and radio continuum ($lambdalambda$20,~6 and 3.6 cm) observations of the star-forming collisional ring galaxy VII Zw 466 and its host group made with the Infrared Space Observatory and the NRAO Very Large Array. A search was also made for CO line emission in two of the galaxies with the Onsala 20m radio telescope and upper limits were placed on the mass of molecular gas in those galaxies. The ring galaxy is believed to owe its morphology to a slightly off-center collision between an `intruder galaxy and a disk. An off-center collision is predicted to generate a radially expanding density wave in the disk which should show large azimuthal variations in overdensity, and have observational consequences. The radio continuum emission shows the largest asymmetry, exhibiting a crescent-shaped distribution consistent with either the trapping of cosmic-ray particles in the target disk, or an enhanced supernova rate in the compressed region. On the other hand, the ISO observations (especially those made at $lambda9.6mu$m) show a more scattered distribution, with emission centers associated with powerful star formation sites distributed more uniformly around the ring. Low-signal to noise observations at $lambda15.0mu$m show possible emission inside the ring, with little emission directly associated with the ion{H}{2} regions. The observations emphasize the complex relationship between the generation of radio emission and the development of star formation even in relatively simple and well understood collisional scenarios.
The propagation velocity of the first gas ring in collisional ring galaxies, i.e. the velocity at which the maximum in the radial gas density profile propagates radially in the galactic disk, is usually inferred from the radial expansion velocity of gas in the first ring. Our numerical hydrodynamics modeling of ring galaxy formation however shows that the maximum radial expansion velocity of gas in the first ring ($v_{gas}$) is invariably below the propagation velocity of the first gas ring itself ($v_{ring}$). Modeling of the Cartwheel galaxy indicates that the outer ring is currently propagating at $v_{ring} approx$ 100 km/s, while the maximum radial expansion velocity of gas in the outer ring is currently $v_{gas} approx$ 65 km/s. Modeling of the radial B-V/V-K color gradients of the Cartwheel ring galaxy also indicates that the outer ring is propagating at $v_{ring} ge $ 90 km/s. We show that a combined effect of inclination, finite thickness, and warping of the Cartwheels disk might be responsible for the lack of angular difference in the peak positions found for the azimuthally averaged $Halpha$, K and B surface brightness profiles of the Cartwheels outer ring. Indeed, the radial $Halpha$ surface brightness profiles obtained along the Cartwheels major axis, where effects of inclination and finite thickness are minimized, do peak exterior to those at K- and B-bands. The angular difference in peak positions implies $v_{ring}$ = 110 km/s, which is in agreement with the model predictions. We briefly discuss the utility of radio continuum emission and spectral line equivalent widths for determining the propagation velocity of gas rings in collisional ring galaxies.
(abridged) Methods: We derive maps of submillimeter dust optical depth and effective dust temperature from Herschel data that were calibrated against Planck. After calibration, we then fit a modified blackbody to the long-wavelength Herschel data, using the Planck-derived dust opacity spectral index beta, derived on scales of 30 (or ~1 pc). We use this model to make predictions of the submillimeter flux density at 850 micron, and we compare these in turn with APEX-Laboca observations. Results: A comparison of the submillimeter dust optical depth and near-infrared extinction data reveals evidence for an increased submillimeter dust opacity at high column densities, interpreted as an indication of grain growth in the inner parts of the core. Additionally, a comparison of the Herschel dust model and the Laboca data reveals that the frequency dependence of the submillimeter opacity, described by the spectral index beta, does not change. A single beta that is only slightly different from the Planck-derived value is sufficient to describe the data, beta=1.53+/-0.07. We apply a similar analysis to Barnard 68, a core with significantly lower column densities than FeSt 1-457, and we do not find evidence for grain growth but also a single beta. Conclusions: While we find evidence for grain growth from the dust opacity in FeSt 1-457, we find no evidence for significant variations in the dust opacity spectral index beta on scales 0.02<x<1 pc (or 36<x<30). The correction to the Planck-derived dust beta that we find in both cases is on the order of the measurement error, not including any systematic errors, and it would thus be reasonable to directly apply the dust beta from the Planck all-sky dust model. As a corollary, reliable effective temperature maps can be derived which would be otherwise affected by beta variations.
Simulating turbulent smoke flows is computationally intensive due to their intrinsic multiscale behavior, thus requiring relatively high resolution grids to fully capture their complexity. For iterative editing or simply faster generation of smoke flows, dynamic upsampling of an input low-resolution numerical simulation is an attractive, yet currently unattainable goal. In this paper, we propose a novel dictionary-based learning approach to the dynamic upsampling of smoke flows. For each frame of an input coarse animation, we seek a sparse representation of small, local velocity patches of the flow based on an over-complete dictionary, and use the resulting sparse coefficients to generate a high-resolution smoke animation sequence. We propose a novel dictionary-based neural network which learns both a fast evaluation of sparse patch encoding and a dictionary of corresponding coarse and fine patches from a sequence of example simulations computed with any numerical solver. Our upsampling network then injects into coarse input sequences physics-driven fine details, unlike most previous approaches that only employed fast procedural models to add high frequency to the input. We present a variety of upsampling results for smoke flows and offer comparisons to their corresponding high-resolution simulations to demonstrate the effectiveness of our approach.
Although the gulf between the theory and practice in Information Systems is much lamented, few researchers have offered a way forward except through a number of (failed) attempts to develop a single systematic theory for Information Systems. In this paper, we encourage researchers to re-examine the practical consequences of their theoretical arguments. By examining these arguments we may be able to form a number of more rigorous theories of Information Systems, allowing us to draw theory and practice together without undertaking yet another attempt at the holy grail of a single unified systematic theory of Information Systems.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
