Transcript Molecules in high-mass star

Molecules in high-mass
star-forming regions –
probing protostellar environments
Karl M. Menten
(MPIfR)
Orion:
Most low-mass stars
from together with
high-mass stars
We know very little about high
mass star formation, and
the earlier the stages and
the smaller the spatial scales
the less we know.
How does one
find HMPOs?
• Infrared surveys
Historically first in
NIR (starting with
the AFGL survey)
Willner et al. 1982
The Willner et al. protostars became a
bonanza for spectroscopists when ISO
came and even before
ISO SWS spectra of hot water (2 bending mode)
Tex  250 K,
5 10-6 < X(H2O) < 6 10-5
Boonman & van Dishoeck 2003
Also gas phase SO2, CO2:
Keane et al. 2001, Bonnman et al. 2003
What about less developed objects
than the Willner et al. protostars?
Expected to be deeply embedded
 NIR-quiet
Such objects were indeed found:
Hot Cores
• hot (>150 K)
• dense (>106 cm-3)
• compact (< a few thousand AU)
Finding High-Mass Protostellar Objects:
Problem:
Most known HMPO
candidates (hot cores)
were found (serendipitously) near HII regions
Cesaroni et. 1998
NH3 (4,4)
Needed: A sample of pristine & isolateds HMPOs
Systematic surveys for HMPOs:
From the mid 1990s on high-mass protostellar objects were
discovered in systematic surveys.
Major efforts:
• Molinari et al. (1996, 1998, 2000, see also Brand et al.
2001)
• Sridharan/Beuther et al. (2002 a – d).
Selection criteria included:
• IRAS colors identifying compact HII regions
• dense gas tracers, e.g.
• emission in the NH3 inversion lines (Molinari) or
• CS J = 2-1 transition (Sridharan/Beuther; based on the
CS survey by Bronfman et al.), and
• (Sridharan/Beuther) absence of strong radio continuum
emission (to exclude already developed compact HII
regions).
HMPO surveys find, both, “genuine”
HMPOs and UCHIIRs
Some results:
• Massive high velocity outflows are found in 21 out of 26
sources mapped in CO (2-1) transition@11" resolution
(Beuther et al. 2002)
HMPOs: bolometer maps: > 10000 AU size dust cores:
 Massive dense envelopes
Beuther et al. 2002
Surveys for HMPOs signposted by class II
methanol masers:
Class II methanol masers (in the 6.7 and 12.2
GHz lines) are unambiguous tracers of highmass star formation
Multi-wavelength study by Minier et al. finds class 0-like YSO
clusters (Lsubmm/Lbol>1%, Td=30 K) to hot molecular cores
(Lsubmm/Lbol=0.1%, Td=40 – 200 K).
Unbiased Galactic plane survey for class II CH3OH masers
• Szymczak et al. 2002
• Ellingsen et al. 1996
So far limited sensitivity/coverage: big improvement with
Jodrell Bank multi-beam array RX
Find many more
HMPOs!
Unbiased, large area
searches
• LABOCA@APEX Galactic
Plane survey
• (perhaps in conjunction)
with Herschel surveys
• SCUBA-2
Present day Example:
Large-scale bolometer map
of Cygnus-X star forming
region
(MAMBO/IRAM 30m)
Motte et al.
Interestingly, submillimeter dust and
molecule observations showed that many of
the Willner et al. near-IR-loud protostars
looked at (sub)millimeter wavelengths in,
both, dust and continuum emission very
similar to near-IR-quiet protostars
van der Tak et al. 2000a,b
Could the near-IR loudness or silence be a
viewing angle effect, as in the unified model
for AGN?
Dusty
envelope
 NIRQ protostar
Torus
Disk
Collimated
outflow

NIRL protostar
What is the nature of the NIR emission in NIR-loud
protostars?
AFGL 2591
NIR speckle imaging resolves
inner wall of circumstellar
material at the dust sublimation radius (r = 40 AU)
Preibisch et al. 2003
AFGL 2591 also has a compact radio source of similar
size!
(van der Tak & Menten 2005)
Orion-KL
SMA
VLA 
Orion - I
SiO masers + 43.2 GHz
continuum
45 AU
Greenhill, Chandler et al.
Reid & Menten
Chandler,
Greenhill,
et al.
Chandler, Greenhill,
et al.
… plus:
• large scale
H2O outflow
• large-scale
shocked H2
• HH objects
SiO
Greenhill et al.
W49N H2O masers:
• Bipolar high velocity outflow
• Proper motion measurements via VLBI
Another
excretion disk?
1000 AU
Gwinn,
Moran, &
Reid 1992
Radio continuum emission from HMPOs
Recently, compact, weak, steep, rising thermal
spectrum (S~2) radio emission (similar to
Orion-I) has been found toward a number of
other high-mass protostars.
Dust
Free-free
beam = 50 mas!
Menten & van der Tak 2004: CRL 2136
Van der Tak & Menten 2005: AFGL 2591, W33A, NGC 7538-IRS9
Orion-I
Beuther et al. 2005
Radio emission from High-Mass Protostars
• No obvious relationship between radio luminosity
and total luminosity - Panagia (1973) doesn't
work!
• Radio emission is “choked off” (Walmsley 1995)
for high enough (“critical”) mass accretion rates:
• Radio luminosity is only a tiny fraction of total
luminosity
• Almost certainly is the protostar itself!
To study the immediate neighborhood
of HMPOs (disks), one needs
 High resolution observations
• To study innermost regions (< 100 AU)
need B< 0.05”
• Problem: Brightness sensitivity
TB(K) = 5 105  S(mJy)/2(GHz)
• With today's interferometers you reach rms
noise levels of a few mJy (for lines)
 TB of dozens tens of K
… and prohibitive noise levels at higher
resolutions (even if you could realize them).
Beating Rayleigh-Jeans with ALMA:
collecting area does it!!
Because of Rayleigh-Jeans, only maser lines
can presently studied at “interesting”
resolutions
High (< 0.1”) spatial resolution spectroscopy
of thermal lines has to await ALMA
Surveys found lots of Hot Cores
* With astonishing chemical diversity
* small-scale structure
Orion-KL
2000 AU
Blake et al. 1996
Hot cores around dusty HMPO(s) and UCHIIRs
Chemical Diversity: The W3(OH) Region
(Turner & Welch
1984)
dust
free-free
(Wyrowski et al. 1999)
Hot core chemistry around protostars
revp
Van Dishoeck & Blake 1998, ARA&A
r(D=1) > revp
r(D=1) < revp
r(D=1) = f[,mD]
revp = f(L*)
(D=1) “somewhere” in the far-infrared –
submillimeter range
r(D=1) > r(n > ncrit)
r(D=1) < r(n > ncrit)
r(n > ncrit) = f(mgas,)
r(n = ncrit) “somewhere” in the far-infrared
– submillimeter range
You cannot see molecular
emission from within the
dust photosphere!
Sgr B2
In molecules:
• (almost) only absorption
• only simple species (hydrides, C-chains)
• from extended envelope, not from hot core
Goicoechea & Cernichao 2004
Poster
Why does ISO not see hot core molecules in Sgr B2?
http://www.ph1.uni-koeln.de/cgi-bin/cdmsinfo?file=e032504.cat
Why does ISO not see hot core molecules in Sgr B2?
• dust photosphere/critical density sphere effect
unclear
• beam dilution?
ISO
Herschel
80” (150 m)
20” (300 m)
• spectral dilution?
ISO LWS
Grating
max 300
Herschel
Fabry-Perot
10000
300000
The Big Question:
Will dust photosphere or critical density barrier
prohibit studies of hot, very dense regions at farinfrared wavelengths?
Should be addressed now!
Far-reaching consequences on the scientific
program for Herschel and the case for farinfrared space interferometry, and ALMA.
Not only for high-mass star-forming regions, but
also, e.g., for the inner regions of ULIRGs and
AGN accretion disks/tori.
So you’ve found lots of HMPOs – what do
you do now?
Of course: Follow up with ALMA
But how does one do this?
Problems:
• structure on many scales from <0.01”
• to tens of arc seconds (continuum) or
• to arcseconds (hot lines)
 multi-configuration imaging
• Very many lines from many molecules –
and one doesn’t want maps of S (or TB)
but
maps of Tkin, n, X and fit dynamical models
IRAM 30m telescope Sgr B2-N
“Large Molecule Heimat”
3 mm region (70 – 116 GHz) in 500 MHz chunks
2000 – 3000 lines!!!!
10 minutes per spectrum
 confusion limit
(Belloche, Comito, Hieret, Leurini, Menten, Schilke)
With ALMA it will be possible to observe that whole
spectral range within 10 minutes to confusion limit
To do science with (3D) line surveys one needs
very advanced data analysis tools:
• Automatic line identification and information extraction
(fluxes, velocities)
• requires up-tp-date “living” molecular spectroscopy
database
• LTE analysis
 maps of N(X), Trot
• non-LTE analysis (LVG/Monte Carlo least sqares method;
see Leurini et al. 2004 for CH3OH)
 maps of n, Tkin, [X/H2]
• Fit dynamical models
What do we have now?
• Not even a software package that
provides basic imaging capability!
• Dispersed (and very low manpower level)
efforts to develop data modeling and smart
analysis tools
• Uncertain future for spectroscopy databases
Even more basic…
Apart from smart data analysis tools, we need:
For observing, calibration, & imaging:
• computer-aided observation preparation
* (semi)automatic setup tools for frequency
selection, mosaicing, …
• (largely) automatic
* calibration
* imaging + selfcalibration,
* mosaicing, multi-configuration combination,
0-spacing addition
… and we don’t even have aips++ working!
To end on a positive note…
Considerable effort is put into
Herschel/HIFI observing and data
analysis software
Thanks for your attention
Simultaneous Flaring in both strong Class II methanol maser
lines
6.7 GHz
12.2 GHz
Maximum: 1.48 cycles/yr = 240 +/- 6 days
Flare Behaviour
12.2 GHz
4 flares folded
(modulo 240 d)
Steep rise
6.7 GHz
5 flares folded
Remarkably all flares have the same temporal behaviour:
Steep (~10 d) rise and slow (~100 d) decline
“E ”
S(15 GHz) = 15 mJy
Class II MMs
Garay et al. 1993
Minier et al. (2003) VLBA
X
X
Goedhart et al. (2003)
Minier et al. (2003) VLBA
30 days = 5200 AU = 70 mas => D = 74 kpc!! => something's wrong!
Surveys are useful …
... aber der Teufel liegt im Detail
 High resolution observations
• To study innermost regions (< 100 AU)
need B< 0.05”
• Problem: Brightness sensitivity
TB(K) = 5 105  S(mJy)/2(GHz)
• With today's interferometers you reach rms
noise levels of a few mJy (for lines)
 TB of several tens of K
… and prohibitive noise levels at higher
resolutions (even if you could realize them).
Beating Rayleigh-Jeans with ALMA:
collecting area does it!!
Because of Rayleigh-Jeans, only maser lines
can presently studied at “interesting”
resolutions
High (< 0.1”) spatial resolution spectroscopy
of thermal lines has to await ALMA
Radio emission from High-Mass Protostars
• No obvious relationship between radio luminosity
and total luminosity - Panagia (1973) doesn't
work!
• Radio emission is “choked off” (Walmsley 1995)
for high enough (“critical”) mass accretion rates:
• Radio luminosity is only a tiny fraction of total
luminosity
• Almost certainly is the protostar itself!