Holwerda, B. W. and Meyer, M. and Regan, M. and Calzetti, D. and Gordon, K. D. and Smith, J. D. and Dale, D. and Engelbracht, C. W. and Jarrett, T. and Thornley, M. and Bot, C. and Buckalew, B. and Kennicutt, R. C. and González, R. A. (2007) Gaps in the Cloud Cover? Comparing Extinction Measures in Spiral Disks. Astronomical Journal, 134 (4). pp. 1655-1661. ISSN 0004-6256 http://resolver.caltech.edu/CaltechAUTHORS:20091112-145949340
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Dust in galaxies can be mapped either by the FIR/submillimeter emission, the optical or infrared reddening of starlight, or the extinction of a known background source. We compare two dust extinction measurements for a set of 15 sections in 13 nearby galaxies to determine the scale of the dusty interstellar medium (ISM) responsible for disk opacity: one using stellar reddening and the other a known background source. In our earlier papers, we presented extinction measurements of 29 galaxies, based on calibrated counts of distant background objects identified though foreground disks in Hubble Space Telescope WFPC2 images. For the 13 galaxies that overlap with the Spitzer Infrared Nearby Galaxies Survey, we now compare these results with those obtained from an I - L color map. Our goal is to determine whether or not a detected distant galaxy indicates a gap in the dusty ISM, and hence to better understand the nature and geometry of the disk extinction. We find that distant galaxies are predominantly in low-extinction sections marked by the color maps, indicating that their number depends both on the cloud cover of Spitzer-resolved dust structures, mostly the spiral arms, and a diffuse, unresolved underlying disk. We note that our infrared color map [E(I - L)] underestimates the overall dust presence in these disks severely because it implicitly assumes the presence of a dust screen in front of the stellar distribution.
|Additional Information:||© 2007 The American Astronomical Society. Received 2007 May 31; accepted 2007 July 19. The authors would like to thank T. Jarrett, for making his aperture corrections available, and B. Sugerman, for his help with the construction of the extinction maps. The authors would like to thank the referee, D. Elmegreen, for her comments; they helped tremendously to improve the paper. This work is based in part on archival data obtained with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. This work is also based on observations with the NASA/ESA Hubble Space Telescope, obtained at the STScI, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS5-26555. Support for this work was provided by NASA through grant number c3886 to D. Calzetti.|
|Subject Keywords:||dust; extinction; galaxies : individual (NGC 925, NGC 2841, NGC 3198, NGC 3351, NGC 3621, NGC 3627, NGC 4321, NGC 4536, NGC 4559, NGC 5491, NGC 6946, NGC 7331); galaxies : ISM; galaxies : spiral; infrared : galaxies; infrared : ISM; ISM : structure|
|Official Citation:||Gaps in the Cloud Cover? Comparing Extinction Measures in Spiral Disks B. W. Holwerda, M. Meyer, M. Regan, D. Calzetti, K. D. Gordon, J. D. Smith, D. Dale, C. W. Engelbracht, T. Jarrett, M. Thornley, C. Bot, B. Buckalew, R. C. Kennicutt, and R. A. González 2007 The Astronomical Journal 134 1655-1661 doi: 10.1086/521824|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||25 Nov 2009 19:06|
|Last Modified:||26 Dec 2012 11:33|
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