THE MID-INFRARED EXTINCTION LAW IN THE OPHIUCHUS, PERSEUS, AND SERPENS MOLECULAR CLOUDS

By N. Chapman, L. Mundy, S. Lai, N. Evans II. 2008

141 citations recorded by the source corpus.

We compute the mid-IR extinction law from 3.6 to 24 μm in three molecular clouds—Ophiuchus, Perseus, and Serpens—by combining data from the “Cores to Disks” Spitzer Legacy Science program with deep JHKs imaging. Using a new technique, we are able to calculate the line-of-sight (LOS) extinction law toward each background star in our fields. With these LOS measurements, we create, for the first time, maps of the χ2 deviation of the data from two extinction law models. Because our χ2 maps have the same spatial resolution as our extinction maps, we can directly observe the changing extinction law as a function of the total column density. In the Spitzer Infrared Array Camera (IRAC) bands, 3.6–8 μm, we see evidence for grain growth. Below , our extinction law is well fitted by the Weingartner and Draine RV = 3.1 diffuse interstellar-medium dust model. As the extinction increases, our law gradually flattens, and for , the data are more consistent with the Weingartner and Draine RV = 5.5 model that uses larger maximum dust grain sizes. At 24 μm, our extinction law is 2–4 times higher than the values predicted by theoretical dust models, but is more consistent with the observational results of Flaherty et al. Finally, from our χ2 maps we identify a region in Perseus where the IRAC extinction law is anomalously high considering its column density. A steeper near-IR extinction law than the one we have assumed may partially explain the IRAC extinction law in this region.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/50a39b6b7f92dcc6ec42b70b408f7a2366b73e1a

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Citations in the corpus

STAR FORMATION RELATIONS IN NEARBY MOLECULAR CLOUDS (2014, methodology): “…for each background star by fitting SEDs to the Spitzer and 2MASS photometry, with stellar photospheric models from the SSC tool, “Star-Pet,” and the extinction law for RV = 5.5 of Weingartner & Draine (2001), which matches multi-wavelength data well for these clouds (Chapman et al. 2009).”
AN OPTICAL SPECTROSCOPIC STUDY OF T TAURI STARS. I. PHOTOSPHERIC PROPERTIES (2014, background): “The value for RV increases to 5.5 for larger dust grains found deep in molecular clouds when AV ∼ 20, far larger than any extinction measured in this optical sample (Indebetouw et al. 2005; Chapman et al. 2009).”
Star Formation in the Milky Way and Nearby Galaxies (2012, background): “The relation derived for diffuse gas is often applied in molecular clouds, but grain growth flattens the extinction curve, leading to larger values of RV , and a much flatter curve in the infrared (Flaherty et al. 2007; Chapman et al. 2009).”
SDC13 infrared dark clouds: longitudinally collapsing filaments? (2013, background): “One advantage provided by these two wavelengths is that they are similarly affected by extinction (Flaherty et al. 2007; Chapman et al. 2009), which implies that estimated values of α[8−24] are not much affected by extinction.”
YOUNG STELLAR OBJECTS IN THE GOULD BELT (2015, background): “The choice of this particular extinction law is motivated by results showing that it is appropriate for the dense molecular clouds in which stars form (e.g., Chapman et al. 2009).”
The CO-to-H2 Conversion Factor (2013, background): “In high surface density molecular gas RV may be closer to 5.5 (Chapman et al. 2009), and Eq.”
LIFTING THE DUSTY VEIL WITH NEAR- AND MID-INFRARED PHOTOMETRY. I. DESCRIPTION AND APPLICATIONS OF THE RAYLEIGH–JEANS COLOR EXCESS METHOD (2011, background): “For very dense interstellar clouds (explicitly excluded from Paper II but studied in, e.g., Chapman et al. 2009), which have the “flattest” (i.e., grayest) MIR extinction curves, the reddening-toextinction ratio is only 7% greater than the value we have adopted here.”
THE SPITZER c2d LEGACY RESULTS: STAR-FORMATION RATES AND EFFICIENCIES; EVOLUTION AND LIFETIMES (2008, methodology): “We used the extinction law with RV = 5.5 (Weingartner & Draine 2001), which reproduces reasonably well the data for molecular clouds (Flaherty et al. 2007; Chapman et al. 2009), to determine AV .”