Monte Carlo Predictions of Far-Infrared Emission from Spiral Galaxies

We present simulations of Far Infrared (FIR) emission by dust in spiral galaxies, based on the Monte Carlo radiative transfer code of Bianchi, Ferrara & Giovanardi (1996). The radiative transfer is carried out at several wavelength in the Ultraviolet, optical and Near Infrared, to cover the range of the stellar Spectral Energy Distribution (SED). Together with the images of the galactic model, a map of the energy absorbed by dust is produced. Using Galactic dust properties, the spatial distribution of dust temperature is derived under the assumption of thermal equilibrium. A correction is applied for non-equilibrium emission in the Mid Infrared. Images of dust emission can then be produced at any wavelength in the FIR. We show the application of the model to the spiral galaxy NGC 6946. The observed stellar SED is used as input and models are produced for different star-dust geometries. It is found that only optically thick dust disks can reproduce the observed amount of FIR radiation. However, it is not possible to reproduce the large FIR scalelength suggested by recent observation of spirals at 200 um, even when the scalelength of the dust disk is larger than that for stars. Optically thin models have ratios of optical/FIR scalelengths closer to the 200um observations, but with smaller absolute scalelengths than optically thick cases. The modelled temperature distributions are compatible with observations of the Galaxy and other spirals. We finally discuss the approximations of the model and the impact of a clumpy stellar and dust structure on the FIR simulations.Comment: 19 pages, 6 figures, accepted by A&

SCUBA imaging of NGC 7331 dust ring

We present observations of the spiral galaxy NGC 7331 using the Sub-millimetre Common User Bolometer Array (SCUBA) on the James Clark Maxwell Telescope. We have detected a dust ring of 45 arcsec radius (3.3 kpc) at wavelengths of 450 and 850-micron. The dust ring is in good correspondence with other observations of the ring in the mid-infrared (MIR), CO and radio-continuum, suggesting that the observed dust is associated with the molecular gas and star formation. A B-K colour map shows an analogous ring structure with an asymmetry about the major axis, consistent with the extinction being produced by a dust ring. The derived temperature of the dust lies between 16 and 31 K and the gas-to-dust ratio between 150 and 570, depending on the assumed dust emission efficiency index (beta=1.5 or 2.).Comment: 5 pages, 6 figures, to be published in MNRA

Abundant dust found in intergalactic space

Galactic dust constitutes approximately half of the elements more massive than helium produced in stellar nucleosynthesis. Notwithstanding the formation of dust grains in the dense, cool atmospheres of late-type stars, there still remain huge uncertainties concerning the origin and fate of galactic stardust. In this paper, we identify the intergalactic medium (i.e. the region between gravitationally-bound galaxies) as a major sink for galactic dust. We discover a systematic shift in the colour of background galaxies viewed through the intergalactic medium of the nearby M81 group. This reddening coincides with atomic, neutral gas previously detected between the group members. The dust-to-HI mass ratio is high (1/20) compared to that of the solar neighborhood (1/120) suggesting that the dust originates from the centre of one or more of the galaxies in the group. Indeed, M82, which is known to be ejecting dust and gas in a starburst-driven superwind, is cited as the probable main source.Comment: 5 pages, 3 figures, 1 table. ApJ Letters in pres

Could a CAMELS downgrade model improve off-site surveillance?

The Federal Reserve’s off-site surveillance system includes two econometric models that are collectively known as the System for Estimating Examination Ratings (SEER). One model, the SEER risk rank model, uses the latest financial statements to estimate the probability that each Fed-supervised bank will fail in the next two years. The other component, the SEER rating model, uses the latest financial statements to produce a “shadow” CAMELS rating for each supervised bank. Banks identified as risky by either model receive closer supervisory scrutiny than other state-member banks.> Because many of the banks flagged by the SEER models have already tumbled into poor condition and, hence, would already be receiving considerable supervisory attention, we developed an alternative model to identify safe-and-sound banks that potentially are headed for financial distress. Such a model could help supervisors allocate scarce on- and off-site resources by pointing out banks not currently under scrutiny that need watching.> It is possible, however, that our alternative model improves little over the current SEER framework. All three models—the SEER risk rank model, the SEER rating model, and our downgrade model—produce ordinal rankings based on overall risk. If the financial factors that explain CAMELS downgrades differ little from the financial factors that explain failures or CAMELS ratings, then all three models will produce similar risk ratings and, hence, similar watch lists of one- and two-rated banks.> We find only slight differences in the ability of the three models to spot emerging financial distress among safe-and-sound banks. In out-of-sample tests for 1992 through 1998, the watch lists produced by the downgrade model outperform the watch lists produced by the SEER models by only a small margin. We conclude that, in relatively tranquil banking environments like the 1990s, a downgrade model adds little value in off-site surveillance. We caution, however, that a downgrade model might prove useful in more turbulent banking times.Bank supervision

Can feedback from the jumbo-CD market improve off-site surveillance of community banks?

We examine the value of feedback from the jumbo-certificate-of-deposit (CD) market in the off-site surveillance of community banks. Using accounting data, we construct proxies for default premiums on jumbo CDs. Then, we produce rank orderings of community banks -- defined as institutions holding less than $500 million in assets (constant 1999 dollars) -- based on these proxies. Next, we use an econometric surveillance model to generate rank orderings based on the probability of encountering financial distress. Finally, we compare these rank orderings as tools for flagging emerging problems. Our comparisons include eight out-of-sample test windows during the 1990s. We find that feedback from the jumbo-CD market would have added little value in community-bank surveillance during our sample period. Specifically, rank orderings based on output from the econometric model significantly outperformed rank orderings based on jumbo-CD default premiums. More important, the jumbo-CD orderings improved little over a random ordering. Other attempts to extract risk signals from the jumbo-CD data yielded similar results. Taken together, our findings validate current surveillance practices. We conclude by arguing that the robust economic environment of the 1990s probably plays a large role in our results.Community banks ; Bank supervision

Can feedback from the jumbo-CD market improve bank surveillance?

We examine the value of jumbo certificate-of-deposit (CD) signals in bank surveillance. To do so, we first construct proxies for default premiums and deposit runoffs and then rank banks based on these risk proxies. Next, we rank banks based on the output of a logit model typical of the econometric models used in off-site surveillance. Finally, we compare jumbo-CD rankings and surveillance-model rankings as tools for predicting financial distress. Our comparisons include eight out-of-sample test windows during the 1990s. We find that rankings obtained from jumbo-CD data would not have improved on rankings obtained from conventional surveillance tools. More importantly, we find that jumbo-CD rankings would not have improved materially over random rankings of the sample banks. These findings validate current surveillance practices and, when viewed with other recent empirical tests, raise questions about the value of market signals in bank surveillance.Finance ; Banks and banking ; Bank supervision

The role of a CAMEL downgrade model in bank surveillance

This article examines the potential contribution to bank supervision of a model designed to predict which banks will have their supervisory ratings downgraded in future periods. Bank supervisors rely on various tools of off-site surveillance to track the condition of banks under their jurisdiction between on-site examinations, including econometric models. One of the models that the Federal Reserve System uses for surveillance was estimated to predict bank failures. Because bank failures have been so rare during the last decade, the coefficients on this model have been "frozen" since 1991. Each quarter the surveillance staff at the Board of Governors provide the supervision staff in the Reserve Banks the probabilities of failure by the banks subject to Fed supervision, based on the coefficients of this bank failure model and the latest call report data for each bank. The number of banks downgraded to problem status in recent years has been substantially larger than the number of bank failures. During a period of few bank failures, the relevance of this bank failure model for surveillance depends to some extent on the accuracy of the model in predicting which banks will have their supervisory ratings downgraded to problem status in future periods. This paper compares the ability of two models to predict downgrades of supervisory ratings to problem status: the Board staff model, which was estimated to predict bank failures, and a model estimated to predict downgrades of supervisory ratings. We find that both models do about as well in predicting downgrades of supervisory ratings for the early 1990s. Over time, however, the ability of the downgrade model to predict downgrades improves relative to that of the model estimated to predict failures. This pattern reflects the value of using a model for surveillance that can be re-estimated frequently. We conclude that the downgrade model may prove to be a useful supplement to the Board's model for estimating failures during periods when most banks are healthy, but that the downgrade model should not be considered a replacement for the current surveillance framework.Bank supervision

Can feedback from the jumbo CD market improve bank surveillance?

Banks and banking