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Methanol Masers* as tools to study high-mass star formation
Michele Pestalozzi, University of Hertfordshire
http://star-www.herts.ac.uk/~michele

*In this talk: 12.2 and 6.7GHz galactic masers
Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Organisation of studies
(and of my talk!)
"Global" studies Lum. Function, structure of MW, maser modelling, ... Particular studies Discs, polarisation, location of protostars, ... NGC7538, IRAS20126, S255, ...
Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Masers

Hosts of SEDs, follow-up,... masers

Hosts of methanol masers (I)
Targeted searches have tried to characterise the hosts: High-mass stars in early stages of evolution

Wood & Churchwell 1989

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Hosts of methanol masers (I)

Some hosts are not really hosts of methanol masers: Difficult to study the hosts if the associations are not clear Not yet clear what kind of objects host methanol masers

Cesaroni et al. 2000
Global Masers Hosts Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Hosts of methanol masers (II)
S255 - S257: protocluster marked by methanol maser

Minier et al. 2005

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Methanol masers in the Milky Way

Pestalozzi et al. 2005

OB-associations

Methanol masers show same Galactic distribution as high-mass protostars

Bronfman et al. 2000
Global Masers Hosts Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Methanol masers in the Milky Way

Pestalozzi et al. 2005

Methanol masers are in a ring of r~5kpc and half-width ~1.5kpc

Global Masers Hosts

Particular

Pestalozzi et al. 2007

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Luminosity function: idea

N

*
Global Masers Hosts Particular

Lm

in

Lm

ax

L

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Real luminosity function?

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Real luminosity function?

More questions than answers: Is there a "switch-on" luminosity? What does lum function of the maser mean? ...

Single power-law, index between -1.5 and -2 Total number of sources ~1500-2000

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

NGC7538: prototype for case study
·11 IR sources ·Different ages: youngest lower left more evolved upper right ·UC HII region, IRS1 ·Many masers, IRS1
IRS 1,2,3
Pestalozzi et al., 2006

IRS 11 IRS 9 NGC7538 S
Global Masers Hosts Particular

·Positioning of the high-mass protostars ·Marking different stages of evolution? First MERLIN methanol observations
Michele Pestalozzi, IAU 242, Alice Springs, March 2007

The disc signature

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

The disc signature

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

The disc signature

6.7 GHz

12.2 GHz

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Particular study general conclusion
· Smooth, Symmetric, Continuous emission in space and LOS velocity: differential rotation · This excludes solid body rotation and a bipolar outflow geometry · Preliminary mass: 6-30 solar masses
Global Masers Hosts Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Still to be exploited
· Extended Emission

A C,D B,E

Methanol masers are not spots!

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Still to be exploited
· Proper motion
12 GHz May 1995. Log gain. 50, 60, 70, 80 , 90, 99 % peak 20

DEC [mas]

10 0 -10 -30 -20 -10 0 10 20 30 40 50 60 12 GHz Jan 1999. Log gain. 50, 60, 70, 80 , 90, 99 % peak 70 80

20

DEC [mas]

10 0 -10 -30 -20 -10 0 10 20 30 40 50 60 12 GHz April 2001. Log gain. 50, 60, 70, 80 , 90, 99 % peak 70 80

20

DEC [mas]

10 0 -10 -30 -20 -10 0 10 20 30 RA [mas] 40 50 60 70 80

Global Masers Hosts

Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

Summary and future
· Study of hosts requires unique associations · Statistical studies provide important insights for the maser studies · Particular studies can guide to general conclusions · MMB: ultimate census · Structure of the Galaxy, Multi wavelength follow-up · Identification of hosts on large samples
Global Masers Hosts Particular

Michele Pestalozzi, IAU 242, Alice Springs, March 2007

List of collaborators
A. Chysostomou and J. Collett (Univ of Herts, UK) V. Minier (Saclay, Paris, France) M. Elitzur (Univ. of Kentucky, USA) J. Conway, R. Booth, A. Jerkstrand (Onsala, Sweden) S. Kraus, G. Weigelt (MPIfR, Bonn) J. De Buizer, La Serena, Chile The MMB team

Thank you

Michele Pestalozzi, IAU 242, Alice Springs, March 2007