Spitzer Survey of the Large Magellanic Cloud: Surveying the Agents of a Galaxy’s Evolution (SAGE): Initial Results

Abstract

We are performing a uniform and unbiased imaging survey of the Large Magellanic Cloud (LMC, ~7°×7°), using the IRAC (3.6, 4.5, 5.8 and 8 µm) and MIPS (24, 70, and 160 µm) instruments on board the Spitzer Space Telescope (Spitzer) in order to survey the agents of a galaxy's evolution (SAGE), the interstellar medium (ISM) and stars in the LMC. This paper provides an overview of the SAGE legacy project including observing strategy, data processing and initial results. Three key science goals determined the coverage and depth of the survey. The detection of diffuse ISM with column densities >1.2x10 21 H cm -2 permits detailed studies of dust processes in the ISM. SAGE's point source sensitivity enables a complete census of newly formed stars with masses >3 M  that will determine the current star formation rate in the LMC. SAGE's detection of evolved stars with mass loss rates >1x10 -8 M  yr -1 will quantify the rate at which evolved stars inject mass into the ISM of the LMC. The observing strategy includes two epochs in 2005, separated by three months, that both mitigate instrumental artifacts and constrain source variability. The SAGE data are non-proprietary. The data processing includes IRAC and MIPS pipelines and a database for mining the point source catalogs, which will be released to the community in support of Spitzer proposal cycles 4 and 5. We present initial results on the epoch 1 data for a region near N79 and N83. The MIPS 70 and 160 µm images of the diffuse dust emission of the N79/N83 region reveal a similar distribution to the gas emissions, especially the HI 21 cm emission. The measured point source sensitivity for the epoch 1 data is consistent with expectations for the survey. The point source counts are highest for the IRAC 3.6 µm band and decrease dramatically towards longer wavelengths consistent with the fact that stars dominate the point source catalogs and that the dusty objects detected at the longer wavelengths are rare in comparison. The SAGE epoch 1 point source catalog has ~4×10 6 sources and more are anticipated when the epoch 1 and 2 data are combined. Using Milky Way (MW) templates as a guide, we adopt a simplified point source classification to identify three candidate groups, stars without dust, dusty evolved stars and young stellar objects, that offers a starting point for this work. We outline a strategy for identifying foreground MW stars, that may comprise as much as 18% of the source list, and background galaxies , that may comprise ~12% of the source list.

Akari Infrared Camera Survey of the Large Magellanic Cloud

“…Detailed properties of the survey are summarized in Table 1 of Shimonishi et al (2013) for the spectroscopic survey and Table 1 of Kato et al (2012) for the imaging survey. The present survey plays a complementary role to other infrared surveys such as SAGE or HERITAGE (Meixner et al, 2006(Meixner et al, , 2013. Based on the data obtained in the survey during the cold mission, we constructed the photometric and the spectroscopic catalogues of point sources in the LMC.…”

Akari Irc Survey of the Large Magellanic Cloud: An Overview of the Survey and a Brief Description of the Point Source Catalog

“…The coordinates of detected sources are calculated by reference to the Two Micron All Sky Survey Point Source Catalog (2MASS-PSC; Skrutskie et al, 2006) and Spitzer SAGE LMC point source catalog (Meixner et al, 2006). The equatorial coordinates of the 2MASS-PSC are based on the International Celestial Reference System (ICRS), and so are the SAGE-PSC via the 2MASS-PSC.…”

“…Difference in shapes of the marks is due to a difference in photometric survey data; black dots: Magellanic clouds optical photometric survey (Zaritsky et al, 2004), filled triangles: IRSF/SIRIUS near-infrared survey (Kato et al, 2007), filled stars: AKARI/LMC survey Kato et al, 2012), open circles: Spitzer SAGE survey (Meixner et al, 2006). As is evident in the figure, the IRC's 11 µm (S11) and 15 µm (L15) imaging bands fill the gap between the IRAC and MIPS onboard the Spitzer.…”

“…Two recent infrared satellites, the Spitzer Space Telescope (Werner et al, 2004) and AKARI (Murakami et al, 2007), provided a capability of deep midinfrared observations with better spatial resolutions. The Spitzer SAGE project (Meixner et al, 2006) carried out a uniform and unbiased imaging survey of a 49 deg 2 area of the LMC at 4 photometric bands from 3 to 10 µm with IRAC (Fazio et al, 2004) and 3 bands at 24, 70, and 160 µm with MIPS (Rieke et al, 2004), to which the SAGE-Spec performed follow-up spectroscopic observations in the MIR and far-infrared (FIR) (Kemper et al, 2010;van Loon et al, 2010). Recently Herschel Space Observatory also observed the whole LMC with a higher spatial resolution than Spitzer in the FIR (Meixner et al, 2010).…”

Infrared Supernova Remnants in the Large Magellanic Cloud

“…Recently, most of the LMC was observed by the Spitzer SAGE survey (7 Meixner et al, 2006), and AKARI has performed a large scale survey of the LMC (Ita et al, 2008). The AKARI telescope has continuous coverage of imaging from 2.5 − 26 µm, in particular, the 11 and 15 µm bands are unique.…”