Spitzer Observations of the Supergiant Shell Region in IC 2574

Cannon, John M., Walter, Fabian, Bendo, George J., Calzetti, Daniela, Dale, Daniel A., Draine, Bruce T., Engelbracht, Charles W., Gordon, Karl D., Helou, George, Kennicutt, Robert C., Jr., Murphy, Eric J., Thornley, Michele D., Armus, Lee, Hollenbach, David J., Leitherer, Claus, Regan, Michael W., Roussel, Hélène, & Sheth, Kartik
2005, The Astrophysical Journal, 630, L37


We present spatially resolved Spitzer Space Telescope imaging of the supergiant shell region of the M81 group dwarf galaxy IC 2574 obtained as part of the Spitzer Infrared Nearby Galaxies Survey. This region harbors one of the best nearby examples of a kinematically distinct H I shell, with an associated remnant stellar cluster; the shell is initiating sequential star formation as it interacts with the surrounding interstellar medium. This region dominates the infrared luminosity of IC 2574 and is spatially resolved in all Spitzer imaging bands. We study the differences in dust temperature as a function of local environment and compare local star formation rates as inferred from Hα and total infrared luminosities. We find that the strong Hα sources are associated with regions of warm dust; however, the most luminous infrared and Hα sources are not necessarily cospatial. The coolest dust is found in the regions farthest from the rim of the shell; these regions show the best agreement between star formation rates derived from Hα and from total infrared luminosities (although discrepancies at the factor of 3-4 level still exist). There is considerable variation in the radio-far-infrared correlation in different regions surrounding the shell. The low dust content of the region may influence the scatter seen in these relations; these data demonstrate that the expanding shell is dramatically affecting its surroundings by triggering star formation and altering the dust temperature.

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