SAGE survey

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Survey the Agents of Galaxy Evolution

Imaging survey of LMC, 7 deg by 7 deg.

Instruments used from Spitzer Space Telescope:

IRAC: 3.6, 4.5, 5.8, 8 micron and

MIPS: 24, 70, 160 micron.

Detection of diffuse ISM with column densities 1.2x10^21 H/cm^2 permits detailed studies of dust processes in the ISM.

Reporting regions near N79 and N83.

Various surveys done on LMC are shown in Figure 1.

Note that Smith, Cornett, Hill have done a UV survey in 1987. N79/N83 region is outlined by a box in IRAS 100 micron image.

The ISM in the Milky Way (MW) and in the Small Magellanic Cloud (SMC) is confused in infrared images due to crowding along the line of sight. In contrast, all LMC features are at approximately the same distance from the Sun, and there is typically only one substantial cloud along a given line of sight, so their relative masses and luminosities are directly measurable.

The Dust to Gas ratio has real variations, and is 2 to 4 times lower than in solar neighbourhood.

SAGE is more recent than IRAS, 2MASS, MSX and DENIS surveys. IRAS detected 1823 sources, and MSX detected 1806 with greater positional accuracy. These far-IR surveys revealed the most luminous dusty inhabitants of the LMC, super giants, AGB stars, HII regions and planetary nebulae. 2MASS and DENIS detected 820,000 and 1.3 million sources respectively, consisting of red giants, asymptotic giant branch stars and supergiants. The purpose of SAGE Survey is to push this IR Survey work to the fainter and more numerous dusty sources in the LMC.

section 2.1.3 ISM

1.Gordon et al (2003) have done UV extinction measurements and noticed that the dust properties in LMC vary spatially.

2. Most of the dust mass is in the largest grains. 3. Comparison with HI and CO data can give gas to dust ratio across LMC. 4. grain size distribution can be found using color ratios 5. using IRAC 3.6, 5.8 and 8 micron trace PAH emission 6. the MIPS 24 micron traces small grains, and MIPS 70+160 micron traces larger grains. 7. The analysis of IRAS data on LMC indicates a lower 12 micron diffuse emission in comparison to MilkyWay and suggests a deficit of very small dust grains, possibly due to intense UV radiation of LMC(Schwering 1989).

Region near N79 and N83

RA 4h 47m 39.3s and DEC -69deg 43min 6.7arcsec. Our observations are not close to these. These are HII regions with dozens of massive stars and possible star formation activity.

Section 4.1 shows how using different bands of MIPS and IRAC we can find out point sources, diffuse emission, warm coninuum dust emission, filamentary nature of turbulent ISM and cirrus dust emission in a qualitative manner.