Methanol Masers in the NGC6334F Star Forming Region

Simon Ellingsen & Anne-Marie Brick

University of Tasmania

Centre for Astrophysics of Compact Objects

Methanol Masers in the NGC6334F Star Forming Region

Overview• NGC6334, a very well studied star forming

region.• Methanol masers in NGC6334F - so many

transitions• Multi-transition methanol maser studies at high

resolution :– LBA observations 6.7 and 12.2 GHz– VLBA observations 12.2 and 23.1 GHz

• The polarization properties of the methanol masers in NGC6334F

Methanol Masers in the NGC6334F Star Forming Region

NGC6334• The Southern star forming region NGC6334 is one of the

most active OB star forming regions in the Galaxy.• It contains 6 different high-mass star forming sites

detected at radio/infrared wavelengths, and different evolutionary phases.

• The sources in the north-eastern part of the complex are the most deeply embedded in the infrared and the most compact radio sources => The youngest regions.

• NGC6334F (also known as NGC6334I) is a cometary ultra-compact HII region with strong methanol masers.

• NGC6334I(N) is only detected at sub-mm wavelengths, but has strong thermal ammonia, class I methanol and weaker class II methanol masers.

Methanol Masers in the NGC6334F Star Forming Region

NGC6334 : The Cat’s Paw Nebula.

Optical emission nebula taken with the Blanco 4m Cerro Tololo Inter-American Observatory

Methanol Masers in the NGC6334F Star Forming Region

SCUBA 850m (contours) and optical (greyscale) from Matthews et al. 2008

Methanol Masers in the NGC6334F Star Forming Region

NGC6334• The Southern star forming region NGC6334 is one of the

most active OB star forming regions in the Galaxy.• It contains 6 different high-mass star forming sites

detected at radio/infrared wavelengths, and different evolutionary phases.

• The sources in the north-eastern part of the complex are the most deeply embedded in the infrared and the most compact radio sources => The youngest regions.

• NGC6334F (also known as NGC6334I) is a cometary ultra-compact HII region with strong methanol masers.

• NGC6334I(N) is only detected at sub-mm wavelengths, but has strong thermal ammonia, class I methanol and weaker class II methanol masers.

Methanol Masers in the NGC6334F Star Forming Region

NGC6334F/NGC6334I• Is a strong, cometary UCHII region (integrated

flux density ~2.8 Jy at 8.5 GHz).• It is one of the strongest 6.7 GHz methanol maser

sources (peak flux density of around 3300 Jy).• It shares many characteristics with the archetypal

star forming region W3(OH).• It shows maser emission in a large number of class

II methanol maser transitions, many of which are rarely seen in other sources.

• In addition to the transitions shown here, class II methanol masers are also observed from the 37.7, 38.2 and 38.4 GHz transitions.

Methanol Masers in the NGC6334F Star Forming Region

NGC6334F : ATCA 8.5 GHz radio continuum with the location of 6.7 GHz methanol masers indicated with blue crosses (Ellingsen, Norris & McCulloch 1996)

Methanol Masers in the NGC6334F Star Forming Region

NGC6334F/NGC6334I• Is a strong, cometary UCHII region (integrated flux

density ~2.8 Jy at 8.5 GHz).• It is one of the strongest 6.7 GHz methanol maser sources

(peak flux density of around 3300 Jy).• It shares many characteristics with the archetypal star

forming region W3(OH).• It shows maser emission in a large number of class II

methanol maser transitions, many of which are rarely seen in other sources.

• In addition to the transitions shown here, class II methanol masers are also observed from the 37.7, 38.2 and 38.4 GHz transitions.

Methanol Masers in the NGC6334F Star Forming Region

NGC6334F : At least 8 different class II methanol maser transitions are observed towards this source, 5 of these are shown here (Ellingsen et al. 2004)

Methanol Masers in the NGC6334F Star Forming Region

NGC6334F/NGC6334I• Is a strong, cometary UCHII region (integrated flux

density ~2.8 Jy at 8.5 GHz).• It is one of the strongest 6.7 GHz methanol maser sources

(peak flux density of around 3300 Jy).• It shares many characteristics with the archetypal star

forming region W3(OH).• It shows maser emission in a large number of class II

methanol maser transitions, many of which are rarely seen in other sources.

• In addition to the transitions shown here, class II methanol masers are also observed from the 37.7, 38.2 and 38.4 GHz transitions.

Methanol Masers in the NGC6334F Star Forming Region

Multi-transition modelling• Cragg et al. (2001) and Ellingsen et al. (2004) have used

the observations of multiple class II methanol maser transitions to test pumping models and constrain physical conditions.

• These models suggest the following physical parameters for the masing region : nH2 = 106 cm-3, Tgas = 30K, Tdust = 150K, beaming factor around 10.

• These parameters are all very plausible for young high-mass star formation regions.

• The modeling assumes that the emission from the different transitions is coincident/cospatial and ignores temporal variability.

• The first of these is the most critical and can be tested through VLBI observations.

Methanol Masers in the NGC6334F Star Forming Region

LBA Observations• VLBI observations of NGC6334F at 6.7 and 12.2 GHz

were made using the LBA in May 1992 with a MKII system (Parkes, Mopra, ATCA, Hobart, Tid).

• They reveal 3 clusters of masers at 6.7 and 2 at 12.2 GHz.• Approximately half of the 6.7 GHz methanol maser spots

are coincident with a 12.2 GHz maser at the same velocity (RMS positional different 4 mas).

• The 6.7 GHz masers are typically a factor of 3 - 10 greater in integrated flux density.

• Class II methanol masers start to become resolved on baselines of 100 km or less.

• Typically only a few percent of the single-dish peak flux density is detected on baselines of 1000 km or longer (scales of < 10 mas).

Methanol Masers in the NGC6334F Star Forming Region

NGC6334F : ATCA 8.5 GHz radio continuum with the location of 6.7 GHz methanol masers indicated with blue crosses (Ellingsen, Norris & McCulloch 1996)

NW

C

S

Methanol Masers in the NGC6334F Star Forming Region

LBA Observations• VLBI observations of NGC6334F at 6.7 and 12.2 GHz

were made using the LBA in May 1992 with a MKII system (Parkes, Mopra, ATCA, Hobart, Tid).

• They reveal 3 clusters of masers at 6.7 and 2 at 12.2 GHz.• Approximately half of the 6.7 GHz methanol maser spots

are coincident with a 12.2 GHz maser at the same velocity (RMS positional different 4 mas).

• The 6.7 GHz masers are typically a factor of 3 - 10 greater in integrated flux density.

• Class II methanol masers start to become resolved on baselines of 100 km or less.

• Typically only a few percent of the single-dish peak flux density is detected on baselines of 1000 km or longer (scales of < 10 mas).

Methanol Masers in the NGC6334F Star Forming Region

NGC6334F : Comparison of the 6.7 and 12.2 GHz methanol masers shows that the real situation is complex.

Methanol Masers in the NGC6334F Star Forming Region

LBA Observations• VLBI observations of NGC6334F at 6.7 and 12.2 GHz

were made using the LBA in May 1992 with a MKII system (Parkes, Mopra, ATCA, Hobart, Tid).

• They reveal 3 clusters of masers at 6.7 and 2 at 12.2 GHz.• Approximately half of the 6.7 GHz methanol maser spots

are coincident with a 12.2 GHz maser at the same velocity (RMS positional different 4 mas).

• The 6.7 GHz masers are typically a factor of 3 - 10 greater in integrated flux density.

• Class II methanol masers start to become resolved on baselines of 100 km or less.

• Typically only a few percent of the single-dish peak flux density is detected on baselines of 1000 km or longer (scales of < 10 mas).

Methanol Masers in the NGC6334F Star Forming Region

Visibility versus baseline for the strongest 6.7 and 12.2 GHz masers in NGC6334F. The visibility versus baseline information is not consistent with a Gaussian spatial distribution.

Methanol Masers in the NGC6334F Star Forming Region

VLBA Observations• Phase referenced VLBA observations of NGC6334F at

12.2 and 23.1 GHz were made May 1997.• The purpose of these observations was to both investigate

the polarization properties of the 12.2 GHz masers and the relative positions of the emission from the two transitions.

• Obtaining full-polarization products, adversely impacted the spectral resolution.

• A total of nine 12.2 GHz spots were detected in 1992, eight of these were also observed in 1997.

• The 23.1 GHz maser was found to be coincident with the strongest 6.7/12.2 GHz maser in the central cluster.

• The 23.1 GHz maser is highly resolved and only detected on the shortest baselines

Methanol Masers in the NGC6334F Star Forming Region

Visibility versus baseline for the strongest 12.2 and 23.1 GHz methanol masers from the VLBA observations. Note: the amplitude scale for the 23.1 GHz observations is not calibrated.

Methanol Masers in the NGC6334F Star Forming Region

Polarization of NGC6334F masers

• The ATCA has been used to measure the polarization properties of a number of 6.7 GHz methanol masers, including NGC6334F (Ellingsen 2002).

• Linear polarization at levels of a few percent is commonly observed in strong 6.7 GHz methanol masers.

• In NGC6334F the some spectral features show up to 10% linear polarization (comparable to the highest level observed in a 6.7 GHz methanol maser).

• Other spectral features have no linear polarization at the 0.5% level.

• The polarization can be used to infer the magnetic field direction (perpendicular to the P.A.). Here it shows the field is perpendicular to the elongation in the spatial dist.

Methanol Masers in the NGC6334F Star Forming Region

From the top : Stokes I, Q, U and V

I

Q

V

U

I

Q

V

U

Methanol Masers in the NGC6334F Star Forming Region

Polarization of NGC6334F masers

• The ATCA has been used to measure the polarization properties of a number of 6.7 GHz methanol masers, including NGC6334F (Ellingsen 2002).

• Linear polarization at levels of a few percent is commonly observed in strong 6.7 GHz methanol masers.

• In NGC6334F the some spectral features show up to 10% linear polarization (comparable to the highest level observed in a 6.7 GHz methanol maser).

• Other spectral features have no linear polarization at the 0.5% level.

• The polarization can be used to infer the magnetic field direction (perpendicular to the P.A.). Here it shows the field is perpendicular to the elongation in the spatial dist.

Methanol Masers in the NGC6334F Star Forming Region

Methanol Masers in the NGC6334F Star Forming Region

SMA observations by Hunter et al. (2006). Blue symbols = water masers, Black squares = methanol masers, Green symbols = ammonia, Greyscale = 1.3mm continuum

Methanol Masers in the NGC6334F Star Forming Region

Conclusions• The assumption that the intensity distribution of co-spatial

maser spots is the same appears to be incorrect.

• The two main methanol maser clusters in NGC6334F trace quite different objects.

• The B field inferred from the maser polarization is roughly perpendicular to the elongation in the spatial distribution (should be checked with polarization VLBI).

• We are in the process of measuring the proper motion/parallax to NGC6334F (observations in Nov 08 and Feb 09).

• This will shed further light on the kinematics and physics of this fascinating source.

Methanol Masers in the NGC6334F Star Forming Region

NGC6334 : The Cat’s Paw Nebula.

2MASS image

Methanol Masers in the NGC6334F Star Forming Region

NGC6334 :

450 m APEX image. The central bright peak is NGC6334F (also known as NGC6334I) and north of that is NGC6334I(N)

Methanol Masers in the NGC6334F Star Forming Region

NGC6334F :

GLIMPSEII 3 colour image (3.6, 5.8 and 8.0 m. The red crosses show the location of the C, NW and I(N) associated 6.7 GHz methanol masers.