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Methanol Maser
Associated Outflows
Antonio Chrysostomou
University of Hertfordshire
Helena (Lientjie) de Villiers, Mark Thompson,
James Urquhart, Simon Ellingsen,
and the MMB team
de Villiers et al. (2014) MNRAS, 444, 566
de Villiers et al. (2015) MNRAS, 449, 119
Introduction
Massive stars play a key and fundamental role in the Universe
•
regulate the dynamics, chemical evolution and heating
of molecular clouds
•
the light that we see at cosmological distances is
dominated by massive stars
Despite this, they are difficult to observe in detail
•
the IMF dictates that they are few in number so they tend
to be found at large distances from the Sun
•
embedded in molecular clouds, clustered and evolve
rapidly
Milky Way Astrophysics from Wide-Field Surveys
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Introduction
The big question: how do massive stars form?
•
they reach the ZAMS while they are still accreting
•
intense radiation pressure should halt normal accretion rates seen in LMSF
•
increase the accretion rate to large enough values, ~ 10-3 M⊙/yr (McKee & Tan 2003)
•
similar to low-mass star formation (but bigger) where the star
accumulates mass via an accretion disk?
•
can grow protostars up to ~ 140 M⊙ (Kuiper et al. 2010)
Finding disks directly is very difficult (at least before ALMA)
•
so we search for evidence indicative of disks → outflows
•
insights to the formation process → links & trends with LMSF
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Introduction
Is there evidence of disks around HMSF regions?
•
6.7 GHz methanol masers emission from NGC7538
Keplerian disk model.
Pestalozzi et al. (2004)
Milky Way Astrophysics from Wide-Field Surveys
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Introduction
Is there evidence of disks around HMSF regions?
•
outflow/disk system around IRAS20126+4104
•
H2 emission and HCO+ (1-0) outflow
•
3.6 cm continuum and C34S (5-4) velocity field
•
7mm continuum and H2O maser spots
see Cesaroni et al. (2007, PPV)
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Evolutionary scheme for HMSF?
A possible scenario for the evolutionary cycle of a massive
star (Zinnecker & Yorke 2007)
Cold
core in
IRDCs
Hot
Molecular
Cores
Hyper/Ultra
Compact HII
regions
Compact/
Classical
HII regions
Hot molecular cores become molecular complex
•
methanol masers begin to appear during this phase
Maser : Y
Outflow : N
Codella et al. 2004
Maser : N
Outflow : Y
Maser : Y
Outflow : Y
Maser : N
Outflow : N
Time
Milky Way Astrophysics from Wide-Field Surveys
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Evolutionary scheme for HMSF?
A possible scenario for the evolutionary cycle of a massive
star (Zinnecker & Yorke 2007)
Cold
core in
IRDCs
Hot
Molecular
Cores
Hyper/Ultra
Compact HII
regions
Compact/
Classical
HII regions
Hot molecular cores become molecular complex
•
methanol masers begin to appear during this phase
•
methanol masers signposts of early phases of HMSF
Milky Way Astrophysics from Wide-Field Surveys
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The MMB Survey
Methanol Multibeam (MMB) Survey started as a systematic
survey for methanol masers in the Galaxy
•
map the (southern) Galactic plane for the 6.7GHz
maser line with the Parkes telescope
•
followed up detections with ATCA to get accurate
(~0.4”) positions
•
published MMB includes 186˚ < l < 20˚ ; |b| < 2˚ (Green et al. 2010; Caswell et al. 2010)
•
full survey currently being prepared for publication
(Breen et al.)
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The MMAO survey
In 2007 we began a JCMT follow up programme of MMB
sources
•
original sample of 70 sources drawn from MMB
•
located between 20˚ < l < 34˚, observable by JCMT
• 13CO
•
and C18O J=3-2 observations with HARP
quality control : 70 → 54 sources (58 clumps)
•
all 58 were found to be associated with high velocity emission ⇒ outflows
MMAO = Methanol Maser Associated Outflows
•
associated if the maser falls within 18” of the C18O clump
•
MMAO criterion : 58 → 44 sources
Milky Way Astrophysics from Wide-Field Surveys
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Milky Way Astrophysics from Wide-Field Surveys
Not MMAO!
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MMAO properties
Physical properties of the outflows were calculated
•
distances, mass, flux, momentum, kinematic timescale
Clump masses were obtained by cross matching to the
ATLASGAL 850µm survey (Urquhart et al. 2014)
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MMAO properties
The C18O is assumed optically thin
•
use that to define the core emission
•
fit a gaussian and scale to 13CO
•
remove to reveal the wing emission
Milky Way Astrophysics from Wide-Field Surveys
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MMAO properties
Outflow
mass
Outflow
mass flux
0.6
MMAO : Mout = 0.9 Mclump
M
0.8
Beuther et al. (2002) : Mout = 0.1 Mclump
M
6 orders of magnitude
0.8
Sanchez-Monge et al. (2013) : Mout = 0.3 Mclump
M
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MMAO properties
Is this evidence for
independent power
laws for low/high
MSF?
Outflow
power
Duarte-Cabral et al. (2013)
Cygnus-X
Different physics governing their
formation, or the need for more
data at intermediate masses?
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MMAO properties
How do the properties of MMAOs compare with other
samples of HMSF?
•
we compared against:
•
Beuther et al. 2002
•
Wu et al. 2004 (only the high mass population was chosen)
•
Zhang et al. 2005 & Kim et al. 2006
Reminder: we have a clear bias in MMAO sample
•
association with methanol masers
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Mass
Momentum
Milky Way Astrophysics from Wide-Field Surveys
Dynamical age
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If younger sources are
present in the sample, we
would have detected them.
Assume all sources are same size
as beam (i.e. youngest outflows
we could possibly detect)
Jack-knife test shows no (weak?)
evidence of Malmquist bias
Milky Way Astrophysics from Wide-Field Surveys
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Codella et al. 2004
Maser : Y
Outflow : N
Maser : Y
Outflow : Y
Maser : N
Outflow : Y
Maser : N
Outflow : N
Maser : N
Outflow : Y
Maser : N
Outflow : N
Time
Maser : N
Outflow : Y
Maser : Y
Outflow : Y
MMAOs 2014
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Summary
MMAOs are a sample of outflows from HMSF that are
closely associated with methanol masers
•
this means that they are selected to exist within a
specific slice of HMSF evolution
•
basic properties are in line with other outflow surveys
•
trends to LMSF outflows seem to hold over 6 orders of
magnitude
•
dynamical ages suggests that methanol masers switch
on after the onset of the outflow
•
consistent with hot molecular core chemical evolution models
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