Masers as evolutionary tracers of high-mass star formation

Shari Breen Simon Ellingsen

Bolton Fellow James Caswell

15th September 2010

Masers as evolutionary traces of star formation?

• Historically, attempts to construct a sequential timeline for the common maser species uncovered mixed/contradictory results

• Typically derived from biased searches with poor sensitivities and positional accuracies or limited to ‘special’ sources

CSIRO. Masers as evolutionary tracers of high-mass star formation

• Different species of masers trace different physical conditions (e.g. Cragg et al. 2005)• Arise in different locations within e.g. GMCs

Breen et al. 2007

Masers as evolutionary traces of star formation?

• Water masers present prior to OH emission (Forster & Caswell 1989)

• 6.7 GHz methanol masers present prior to detectable UCHII emission (Walsh et al.1998)

• Water masers can be present prior to emission from methanol maser emission (Garay & Lizano 1999)

• Methanol masers more sensitive to the ignition of the central object than water masers (e.g. Beuther et al. 2002)

• Ellingsen et al. 2007 present a ‘straw man’ model of the relative evolutionary phases that the different maser species are tracing

CSIRO. Masers as evolutionary tracers of high-mass star formation

Maser observations

• 12 GHz maser observations with Parkes• towards a complete sample of 6.7 GHz methanol masers (~600

sources)

• Additional 12 GHz maser observations towards 1.2 mm dust sources of Hill et al. (2005) (~50 additional sources)

• Water maser observations with the ATCA• Water maser observations completed with the ATCA towards 294

of the 1.2 mm dust clumps

• Water maser towards OH and methanol masers (~300 targets)

• For 1.2 mm dust clump sources we know:• 6.7, 12.2 GHz methanol masers, water masers, radio continuum

(Walsh et al. 1998) and OH masers (Caswell 1998)

CSIRO. Masers as evolutionary tracers of high-mass star formation

1.2 mm dust Hill et al. (2005)

6.7 GHz methanol(MMB)

Water (Breen et al. 2010)

OH (Caswell et al. 2010)

8 GHz cont (Walsh 1998)

12 GHz methanol masers towards the MMB sources

• Definitive, sensitive search for 12 GHz sources towards an unbiased sample of 6.7 GHz sources (subsample – Breen et al. (2010a))

• 250 detections 43 % detection rate, present at the later stages of the 6.7 GHz maser lifetime

• Both flux density and velocity ranges of the methanol masers increase as they evolve

• 6.7 GHz sources increase more rapidly than the 12 GHz sources

• Lower luminosity 12 GHz sources are more variable and are rarely associated with OH masers

• Complete searches of OH (Caswell 1998), 6.7 (MMB) and 12 GHz methanol masers allow relative lifetimes of sources to be derived

CSIRO. Masers as evolutionary tracers of high-mass star formation

12 GHz methanol masers towards the MMB sources

• Definitive, sensitive search for 12 GHz sources towards an unbiased sample of 6.7 GHz sources (subsample – Breen et al. (2010a))

• 250 detections 43 % detection rate, present at the later stages of the 6.7 GHz maser lifetime

• Both flux density and velocity ranges of the methanol masers increase as they evolve

• 6.7 GHz sources increase more rapidly than the 12 GHz sources

• Lower luminosity 12 GHz sources are more variable and are rarely associated with OH masers

• Complete searches of OH (Caswell 1998), 6.7 (MMB) and 12 GHz methanol masers allow relative lifetimes of sources to be derived

CSIRO. Masers as evolutionary tracers of high-mass star formation

CSIRO. Masers as evolutionary tracers of high-mass star formation

Water masers towards 1.2 mm dust clumps

• 294 of the 404 Hill et al. (2005) sample targeted for water masers with the ATCA

• 165 detections towards 128 clumps -> 44 % detection rate

• Positions of the water masers are consistent with the peak positions of most of the dust clumps.

• More dust clumps show ‘only water’ than ‘only methanol’

Water maser can be present even earlier than methanol masers

Water masers towards 1.2 mm dust clumps

• Increase in both flux density and velocity range from

mm only methanol methanol + cont• Flux density may ‘turn over’ towards the end of their lifetime• Water masers associated with bigger, brighter more massive

1.2 mm dust clumps• Properties of the 1.2 mm dust

also suggest that the water

maser increase in luminosity

as they evolve

CSIRO. Masers as evolutionary tracers of high-mass star formation

Water masers towards OH masers

• Breen et al. (2010b) -> large catalogue of water masers

• 379 water masers detected towards a complete sample of OH masers and a selection of methanol maser sources

• 128 associated with both OH and methanol masers• 33 associated only with OH masers• 70 associated with methanol masers• 148 sources are solitary (these are also the most variable and weakest)

• Average flux density and velocity range higher than for 1.2 mm dust clump sample

• 62 % associated with GLIMPSE point sources (less for solitary sources and those associated with continuum)

• Solitary sources colder? Or have 4.5 um excess?

• 63 sources coincident with an EGO• Highest coincidence rate with sources showing

water+OH+methanol

CSIRO. Masers as evolutionary tracers of high-mass star formation

CSIRO. Masers as evolutionary tracers of high-mass star formation

Evolutionary scheme for the common maser species

Contact UsPhone: 1300 363 400 or +61 3 9545 2176

Email: enquiries@csiro.au Web: www.csiro.au

Thank you

CSIRO Astronomy and Space ScienceShari BreenBolton Fellow

Phone: 02 9372 4325Email: Shari.Breen@csiro.auWeb: www.atnf.csiro.au

CSIRO. Masers as evolutionary tracers of high-mass star formation