GHz Methanol Masers in Sagittarius A Loránt Sjouwerman Ylva Pihlström amp Vincent Fish Outline Introduction to Sagittarius A Sgr A Introduction to 362 GHz methanol CH3OH ID: 338748
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Slide1
36.2 GHz Methanol Masersin Sagittarius A
Loránt Sjouwerman, Ylva Pihlström & Vincent FishSlide2
Outline
Introduction to Sagittarius A (Sgr A)Introduction to 36.2 GHz methanol (CH3OH)Previous methanol observations in Sgr ANew receivers at the EVLA
(Ka band: 27-40 GHz)
36.2 GHz methanol is
indeed a
maser
Comparison with:
OH, HCN,
44.1
GHz
CH3OH, NH3(3,3)
SummarySlide3
Sagittarius A (radio) scene
Galactic CenterBlack HoleSgr A*Circumnuclear DiskSgr A West or CND
Supernova Remnants
Sgr
A East, G359.02-0.09
Lots of stars and gas
M-0.02-0.07, M-0.23-0.08
Interactions
e.g. 1720 MHz
OH
50-70 km/s
Complex !Slide4
Sagittarius A (radio) scene
Galactic CenterBlack HoleSgr A*Circumnuclear DiskSgr A West or CND
Supernova Remnants
Sgr
A East, G359.02-0.09
Lots of stars and gas
M-0.02-0.07, M-0.23-0.08
Interactions
e.g. 1720 MHz
OH
50-70 km/s
Complex !Slide5
Methanol (CH
3OH)Class I and Class II methanolClass I: mostly near outflows and shock regions: collisionally pumped
(e.g. 36.2 GHz, 44.1 GHz)
Class II
: mostly
at and in
star forming regions:
radiatively
pumped
(e.g. 6.7 GHz, 12.2 GHz)
Thermal and/or masers
36.2 GHz only single dish; 36.2 GHz
masers ?
36.2 GHz CH3OH and 1720 MHz OH:
similar gasSlide6
Single dish 36.2 GHz in Sgr A
Single dish observationsSzczepanski et al. 1989
,
1991
Large scale distribution
M-0.13-0.08, M-0.02-0.07
High-density gas
Interaction and/or
infall
?
Small scale distribution?
Need
interferometer
No
36.2 GHz receiversSlide7
Expanded Very Large Array
NRAO is currently rebuilding the VLAe.g. new Ka band receivers27 to 40 GHz36.2 GHz CH3OHObserve Sgr A at 36.2 GHz with (E)VLA !Special call for proposalsMarch 2009, in (incomplete) B
configuration
Only 9 antennas outfitted, VLA
correlator
New
Observation Preparation Tool
(OPT)Slide8
36.2 GHz in Sgr A using (E)VLA
Several 68” pointingsWith 7 antennas, 0.3”Point sources onlyMany detectionsStrong and narrowEmission in
sidelobes
Velocity
20-50
km/s
Brightness T >>
10
5
K
Definitely maser !
(First time this is derived)Slide9
1720 MHz OH and 36.2 GHz CH3OH
Collisionally excitedSimilar gasn(H) ~ 104 to 105 cm-3T
k
~ 80 to 100 K
Nearby, but
Not co-spatial (>6.5”)
Velocities differ
Different tracers
Different
shocks
(in
l.o.s
.)
Different
regions
(in
l.o.s
.)Slide10
HCN and 36.2 GHz CH3OH
Dense HCN clumps (red)Star formation sites ?44.1 GHz methanol (
o
)
and 22.2 GHz H2O masers
(
+
)
Yusef-Zadeh
et al. 2008
36.2 GHz methanol
(
x
)
Debatable:
GBT has ~15” beam
No young massive stars
No
radiatively
pumped CH3OH or OH masers
H2O maser has many originsSlide11
HCN and 36.2 GHz CH3OH
Dense HCN clumps (red)Star formation sites ?44.1 GHz methanol (
o
)
and 22.2 GHz H2O masers
(
+
)
Yusef-Zadeh
et al. 2008
36.2 GHz methanol
(
x
)
Debatable:
GBT has ~15” beam
No young massive stars
No
radiatively
pumped CH3OH or OH masers
H2O maser has many originsSlide12
44.1 GHz and 36.2 GHz CH3OH
Both Class I, i.e. collisions or outflows36.2 and 44.1 GHz may be cospatial (see “G”)Single 44.1 GHz masersSingle 36.2 GHz masers
Here not sensitive to
extended thermal
methanol emissionSlide13
NH3(3,3) and 36.2 GHz CH3OH
HCN contours (i.e. CND)Montero-
Castaño
et al.
2009
NH3(3,3) colors
McGary
et al.
2001
36.2 GHz CH3OH masers at NH3(3,3) peaks, tips of extensions toward CND
Also 44.1 GHz at NH3(3,3) peak
Gas
infall
, where it collides with CND ?Slide14
Summary
First interferometric observations at 36.2 GHzExcellent new EVLA Ka band receivers (27-40 GHz)36.2 GHz methanol
maser emission
36.2 GHz methanol and 1720 MHz OH probably trace
different shock
regions
(in
Sgr
A)
Class I 44.1 and 36.2 GHz methanol may coexist
No clear relation to HCN clumps or star formation
Correlated with NH3(3,3), dense cloud collisions ?
New science with EVLA is coming!