R. Meijerink, P. van der Werf, F. Israel

and the HEXGAL team

HERSCHEL OBSERVATIONS OF

Edo Loenen, Leiden Observatory

EXTRA GALACTIC STAR FORMATIONMESSIER 82

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 & 13CO[CI] , [CII] & [NII]

why CO?

It’s high abundance CO ladder reflects the physical condition of

the ISM

Only low-J lines (<6) observable from groundLow(er) density gas

Herschel HIFI: J=5-4 up to J=13-12Dense gas = sites of star formation!Determine conditions of those sites

Observations

M82:archetypical starburstSFR ~150 Mʘ yr

-1

Very nearby: 3.9 Mpc

Herschel HIFI (total time ~1.5 hrs) :CO J=5-4 ... 10-9 + J=13-12 13CO J=5-4 ... 10-92 x [CI], [CII] & [NII]

Focussed on nucleus

Spectra

A third component?

2 main components: NE & SW lobes 3rd component @ high-J CO and 13CO?

A third component

CO(3-2) JCMT

t?

2 main components: NE & SW lobes 3rd component @ high-J CO and 13CO?

A third component

CO(6-5) JCMT

O?

t?

2 main components: NE & SW lobes 3rd component @ high-J CO and 13CO

CO excitation

Use integrated line fluxesCorrected 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 cloudRadiative transfer line fluxes

CO excitiation

ground based (Ward+ 2003)Herschel SPIRE (Panuzzo+ 2010)

CO excitiation

n=105, G0=102.75

n=103.5, G0=102

40% : 60%

CO excitiation

n=106, G0=103.25

n=105, G0=102.75

n=103.5, G0=102

70% : 29% : 1%

Conclusions

Need 3 components to fit CO ladder

Most gas has “normal” properties:70% shielded diffuse gas29% dense irradiated gas (SF regions)

3rd component:1%, but dominates J>7 CO and 13CO J>3100 km/s feature...

Super Orion Bar?