1. IRAC/MIPS view of the ISM: PAHs dominate in IRAC Li & Draine (2001) dust emissivity model; only very strong (> 10 3 x avg.) radiation fields contribute to thermal emission at 8  m Our entire mosaic is remarkably constant in CH4/Ch3 ratio (~ 3) => PAH- dominated with a few exceptions near HII regions

2. Massive stars are rare, but once a single massive star forms, the game changes. L ~ 10 5 – 10 6 L  Intense EUV, FUV radiation Powerful winds Supernova This energy input quickly reshapes the environment, dominating all that goes on there, perhaps including low- mass star formation.

3. NOT Star formation near massive stars is NOT Taurus-Auriga writ large!!!! Disks in Orion Disks in Taurus-Auriga

4. Structure of H II region carved by radiation from massive stars. Dark – Molecular gas Blue – Hot (~10 4 K), tenuous (~30 cm -3 ), ionized cavity. The H II region interior. Massive stars Red – Ionization front pushing into and evaporating dense gas Dense gas compressed in advance of the ionization front

5. Isolated star formation, such as that seen in Taurus-Auriga is atypical. The majority of low-mass, Sun-like stars form instead in rich clusters and in proximity to massive stars. Short-Lived Radionuclides (SLRs) require that the Sun formed near a massive star. Solar mass stars form in dense gas, then are soon uncovered by the ionization front, leaving young disks sitting in a hot, tenuous region near one or more massive stars. Direct counts E.g., Lada & Lada, 2003, Ann. Rev. Astron. Astrophys, 41, 57 Complete survey of embedded clusters out to 2 kpc: - 70 – 90% of stars form in dense clusters - Of these, 75% currently near massive stars Triggered Star Formation may be the standard mode of star formation, even in turbulent environments.

6. Embedded YSOs - 4 kpc* < 2 Msun 2 < Msun < 5 > 5 Msun *Assuming GLIMPSE sensitivities

7. Limitations of Color-Color Analysis You need to detect the source in all four IRAC bands Does not work well in crowded regions There is significant ambiguity in interpreting the results –Does not discriminate different masses well –Although the effects of extinction are much smaller at these wavelengths, there are still degeneracies typical for stars at the GC Solution: Fit ALL the SEDs

8. Radiation Transfer Models: Embedded Massive YSO (Whitney et al. 2003a,b;2004, Robatille et al. 2006) 3e490 5360 60 AvAv i L * =40000 T * =30000 M * =17.5 M=10 -4 M d =1.

9. Tests on M16 data EmbeddedDiskEmbedded or disk

10. M16: SED Fitter at Work (Whitney et al. 2003a,b,2004; Indebetouw et al. 2006; Robitaille et al. 2006) Stage I: Yellow Stage II: Green Stage III: Blue A by-product of the fitting program is a best-fit extinction to each source Includes the MS and Giant stars