Jennifer L. Karr

STRUCTURE AND COLORS OF DIFFUSE EMISSION IN THE SPITZER GALACTIC FIRST LOOK SURVEY

We investigate the density structure of the interstellar medium using new high-resolution maps of the 8, 24, and 70 μm surface brightness toward a molecular cloud in the Gum Nebula, made as part of the Spitzer Space Telescope Galactic First Look Survey. The maps are correlated with 100 μm images measured with IRAS. At 24 and 70 μm, the spatial power spectrum of surface brightness follows a power law with a spectral index of -3.5. At 24 μm, the power-law behavior is remarkably consistent from the ~02 size of our maps down to the ~5 spatial resolution. Thus, the structure of the 24 μm emission is self-similar even at milliparsec scales. The combined power spectrum produced from Spitzer 24 μm and IRAS 25 μm images is consistent with a change in the power-law exponent from -2.6 at spatial wavenumber k ~ 2 × 10-3 arcsec-1 to -3.5 at k ~ 4 × 10-3 arcsec-1. The decrease may be due to the transition from a two-dimensional to three-dimensional structure. Under this hypothesis, we estimate the thickness of the emitting medium to be 0.3 pc.

AN AGGREGATE OF YOUNG STELLAR DISKS IN LYNDS 1228 SOUTH

Using the Multiband Imaging Photometer for Spitzer (MIPS) and Infrared Array Camera (IRAC) instruments on the Spitzer Space Telescope, we have investigated an aggregate of at least nine candidate bright young stellar objects in the southern region of the Lynds 1228 cloud in Cepheus. The spectral energy distributions (SEDs) encompass both infrared Class II and Class III types, and at least one object has no excess at wavelengths shorter than 24 μm. There are five known IRAS sources in the region. We find that the fluxes of these sources are generally overestimated by IRAS because of confusion, and one appears in both the IRAS Point Source and Faint Source Catalogs. This small group of young stellar objects provides a good example of the power of Spitzer to resolve star-forming regions confused in the IRAS catalogs. The SEDs of these sources illustrate that there can be a diversity of disk evolutionary states within a coeval stellar aggregate.

Erratum: “Structure and Colors of Diffuse Emission in the Spitzer Galactic First Look Survey” (ApJS, 154, 281 [2004])

We have discovered an error in the scaling of our IRAC 8 m and MIPS 70 m data, which affected the caption for Figure 1 and the vertical axis scales for Figure 2. The original units in the images displayed in Figure 1 were MJy sr 1 for 8 m and Jy arcsec 2 for MIPS 24 and 70 m. We incorrectly multiplied our IRAC data by 0.0425 (the conversion from Jy arcsec 2 to MJy sr ), but neglected to multiply our MIPS 70 m data by that factor. (MIPS 24 m data were scaled correctly.) Thus, contrary to the caption of Figure 1, the gray levels for panels (a) and (b) actually range from 6.7 to 7.8 MJy sr , and the gray levels for panels (e) and ( f ) actually range from 0.85 to 20.8MJy sr . The power spectra in Figure 2 should have been normalized such that the integral over the spectrum equals the mean square image surface brightness. In the original paper, however, the IRAC power spectrumwas incorrectly multiplied by (0.0425), whereas theMIPS 70 m spectrum should have been multiplied by this factor but was not. We correct this in a revised version of Figure 2 included here. We thank Rick Arendt for calling our attention to this error.