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?