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RE: NGC 5194
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Black hole caught 'burping' galactic gas supply

Astronomers have spotted two huge waves of gas being "burped" by the black hole at the heart of a nearby galaxy.
The swathes of hot gas, detected in X-ray images from Nasa's Chandra space telescope, appear to be sweeping cooler hydrogen gas ahead of them.
This vast, rippling belch is taking place in NGC 5194 - a small, neglected sibling of the "Whirlpool Galaxy", 26 million light years away.

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Title: Star Formation in NGC 5194 (M51a). II. The Spatially-Resolved Star Formation Law
Authors: Robert C. Kennicutt Jr., Daniela Calzetti, Fabian Walter, George Helou, David J. Hollenbach, Lee Armus, George Bendo, Daniel A. Dale, Bruce T. Draine, Charles W. Engelbracht, Karl D. Gordon, Moire K.M. Prescott, Michael W. Regan, Michele D. Thornley, Caroline Bot, Elias Brinks, Erwin de Blok, Duilia de Mello, Martin Meyer, John Moustakas, Eric J. Murphy, Kartik Sheth, J.D.T. Smith

We have studied the relationship between the star formation rate (SFR) surface density and gas surface density in the spiral galaxy M51a (NGC 5194), using multi-wavelength data obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS). We introduce a new SFR index based on a linear combination of H-alpha emission-line and 24 micron continuum luminosities, that provides reliable extinction-corrected ionising fluxes and SFR densities over a wide range of dust attenuations. The combination of these extinction-corrected SFR densities with aperture synthesis HI and CO maps has allowed us to probe the form of the spatially-resolved star formation law on scales of 0.5 to 2 kpc. We find that the resolved SFR vs gas surface density relation is well represented by a Schmidt power law, which is similar in form and dispersion to the disk-averaged Schmidt law. We observe a comparably strong correlation of the SFR surface density with the molecular gas surface density, but no significant correlation with the surface density of atomic gas. The best-fitting slope of the Schmidt law varies from N = 1.37 to 1.56, with zeropoint and slope that change systematically with the spatial sampling scale. We tentatively attribute these variations to the effects of area sampling and averaging of a nonlinear intrinsic star formation law. Our data can also be fitted by an alternative parameterisation of the SFR surface density in terms of the ratio of gas surface density to local dynamical time, but with a considerable dispersion.

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