The Incredible 6.7 GHz Methanol Masers:A key to understanding high-mass star formation.

Jimi Green (for Gary Fuller)CSIRO Astronomy & Space Science, ATNF (Jodrell Bank Centre for Astrophysics, University of Manchester)

Great Barriers in Massive Star Formation

13th September 2010, Townsville

THE METHANOL MULTIBEAM SURVEY:SURVEYING THE MASSIVE STAR FORMATION IN OUR GALAXY

• Galactic plane survey (±2° latitude) for 6.7-GHz methanol masers.

• Parkes:• ~140 days, -174o < l < 60o • 3 sigma sensitivity of ~0.7 Jy.• Completeness of 100% at 1 Jy. • 0.09 kms-1 spectral resolution.

• Australia Telescope Compact Array: • comparable spectral resolution to

Parkes• 40-60 mJy per channel.• positional accuracy of ~0.4 arcsec.

• Velocity coverage is full range of CO

The Methanol Multibeam (MMB) Survey

The MMB collaboration: J. L. Caswell, G. A. Fuller, A. Avison, S. Breen, K. Brooks, M. G. Burton, A. Chrysostomou, J. Cox, P. J. Diamond, S. Ellingsen, M. D. Gray, M. G.

Hoare, M. R. W. Masheder, N. McClure-Griffiths, M. Pestalozzi, C. Phillips, L. Quinn, M. Thompson, M. Voronkov, A. Walsh, D. Ward-Thompson, D. Wong-McSweeney,

J. A. Yates and R. J. Cohen.

Class II 6.7-GHz methanol masers

• Models and observations (Pestalozzi et al. 2002, Minier et al. 2003, Xu et al. 2008) show these masers are confined to regions of high-mass star formation.

• Methanol forms on ice mantles and evaporates.

• Masers originate in gas surrounding the forming star, pumped by mid IR emission from heated dust.

• Require high density and methanol abundance (>10-8) and dust temperatures ~100-200 K.

• Associated with hot-core like sources.

Cragg et al. 2002

Catalogue Papers & Maser Distribution

• I. +345°<l<+6° Caswell, Fuller, Green et al. 2010, MNRAS• 183 masers (86 new)

• II. +6°<l<+20° Green, Caswell, Fuller et al. 2010, MNRAS• 119 masers (42 new)

• |l|<1° • 28 sources (11 in Sgr B2) and only 4 (15%) new (cf. Caswell 1996)• CO covers velocities from -206 km/s to +280 km/s, but masers only occur

with velocities -60 km/s to +77 km/s, implying no high-mass star formation at these high velocities.

• |l|<6°: only one source |b|>1° but l <-6°: b distribution wider

+ masers, ▲ Sgr B2, ● 3kpc arm

Location of masers

• R<3 kpc, 1.8 masers/kpc2 (excl. GCZ)• GCZ 55 masers/kpc2• Spiral arms ~ 20 masers/kpc2• GCZ has higher star formation rate but

comparable to spiral arms

3.5 to 13 kpc

R<3 kpc

R<3 kpc

R<3 kpc

3kpc arm

3kpc arm

Sun

Longitude-velocity domain structure studies

Structure & Nature of sources (A. Avison PhD Thesis)

Velocity gradient across source

Two clumps shifted in velocity

Colour-LuminosityMIPSGAL (24um) – Hi-GAL PACS (70um)

Use Robitaille models to fit SED from 3.6um to 500um

Class II masers in Hi-GAL l=30o SDP (Molinari et al. 2010) (Not (yet) MMB

sources). Only 7 masers in field.

+ non-maser maser

Circumstellar Gas(Fuller et al. follow-up)

• Mopra 45 GHz and Parkes NH3 surveys of 240 MMB

sources

• Observed complete sample in 3 longitude ranges.

Species Fraction Tracing

CS 95% Dense gas, vel

SiO 33% Shocks/outflows

HNCO 15% Hot cores

CH3OH 62%

(1,1)

CH3OH CH

3OH SiO

(1,1)

(2,2)

(3,3)NH3

Summary

• Southern Galactic plane survey complete:

• -174°< l < 60°

• Detected 954 masers, of which 598 previously known, 356 new.

• Methanol Multibeam Publications:

• Magellanic Cloud Survey (Green et al. 2008)

• Techniques (Green et al. 2009)

• High-mass star formation in 3-kpc arms (Green et al. 2009)

• Catalogue I: Galactic Centre region (Caswell et al. 2010)

• Catalogue II: +6°< l < +20° (Green et al. 2010)

• Catalogue III: 330° < l < 345° (coming soon!)

• Extensive follow-up programme underway

• GLIMPSE IR association (Poster 20)

• 12 GHz masers (Shari Breen talk on Wednesday)

• Ground-state OH & magnetic fields (MAGMO talk on Thursday)

Jimi Green/Gary FullerJames.green@csiro.au/g.fuller@manchester.ac.uk

Thank you

http://www.jb.man.ac.uk/research/methanolhttp://www.astromasers.org