Methanol Masers in the NGC6334F Star Forming Region

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Transcript Methanol Masers in the NGC6334F Star Forming Region

Methanol Masers in the
NGC6334F Star Forming Region
Simon Ellingsen & Anne-Marie Brick
University of Tasmania
Centre for Astrophysics of Compact
Objects
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
InterAmerican
Observatory
Methanol Masers in the NGC6334F
Star Forming Region
SCUBA 850m
(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 highmass 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
I
I
Q
Q
U
U
V
V
From the top : Stokes I, Q, U and V
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.
Methanol Masers in the NGC6334F
Star Forming Region