1. R. Meijerink, P. van der Werf, F. Israel and the HEXGAL team HERSCHEL OBSERVATIONS OF Edo Loenen, Leiden Observatory EXTRA GALACTIC STAR FORMATIONMESSIER 82

2. HEXGAL  Herschel EXtraGALactic Key Program  13 sub-programs using HIFI & PACS  Molecular spectroscopy of dense gas in galactic nuclei  Cooling lines in 10 starbursts with HIFI: CO & 13 CO [C I ], [C II ] & [N II ]

3. why CO?  It’s high abundance  CO ladder reflects the physical condition of the ISM  Only low-J lines (<6) observable from ground Low(er) density gas  Herschel HIFI: J=5-4 up to J=13-12 Dense gas = sites of star formation! Determine conditions of those sites

4. Observations  M82: archetypical starburst SFR ~150 M ʘ yr -1 Very nearby: 3.9 Mpc  Herschel HIFI (total time ~1.5 hrs) : CO J=5-4... 10-9 + J=13-12 13 CO J=5-4... 10-9 2 x [C I ], [C II ] & [N II ] Focussed on nucleus

5. Spectra

6. A third component?  2 main components: NE & SW lobes  3rd component @ high-J CO and 13 CO?

7. A third component CO(3-2) JCMT t?  2 main components: NE & SW lobes  3rd component @ high-J CO and 13 CO?

8. A third component CO(6-5) JCMT O? t?  2 main components: NE & SW lobes  3rd component @ high-J CO and 13 CO

9. CO excitation  Use integrated line fluxes Corrected for beam size using 450 µm map  Combine with other data: Low-J (<5) lines from ground (Ward+ 2003) High-J (>4) lines from SPIRE (Panuzzo+ 2010) Excellent agreement HIFI & SPIRE (<10%)  PDR models of Meijerink & Spaans (2005): Chemical & thermal balance in 1D cloud Radiative transfer  line fluxes

10. CO excitiation ground based (Ward+ 2003) Herschel SPIRE (Panuzzo+ 2010)

11. CO excitiation n=10 5, G 0 =10 2.75 n=10 3.5, G 0 =10 2 40% : 60%

12. CO excitiation n=10 6, G 0 =10 3.25 n=10 5, G 0 =10 2.75 n=10 3.5, G 0 =10 2 70% : 29% : 1%

13. Conclusions  Need 3 components to fit CO ladder  Most gas has “normal” properties: 70% shielded diffuse gas 29% dense irradiated gas (SF regions)  3rd component: 1%, but dominates J>7 CO and 13 CO J>3 100 km/s feature...  Super Orion Bar?