36.2 GHz Methanol Masersin Sagittarius A

Loránt Sjouwerman, Ylva Pihlström & Vincent Fish

Outline

Introduction to Sagittarius A (Sgr A)

Introduction to 36.2 GHz methanol (CH3OH)

Previous methanol observations in Sgr A

New 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)

Summary

Sagittarius A (radio) scene

Galactic Center Black Hole

Sgr A*

Circumnuclear Disk Sgr 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 !

Sagittarius A (radio) scene

Galactic Center Black Hole

Sgr A*

Circumnuclear Disk Sgr 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 !

Methanol (CH3OH)

Class I and Class II methanol Class 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 gas

Single dish 36.2 GHz in Sgr A

Single dish observations Szczepanski 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 receivers

Expanded Very Large Array

NRAO is currently rebuilding the VLA e.g. new Ka band receivers

27 to 40 GHz 36.2 GHz CH3OH

Observe Sgr A at 36.2 GHz with (E)VLA !

Special call for proposals March 2009, in (incomplete) B configuration Only 9 antennas outfitted, VLA correlator New Observation Preparation Tool (OPT)

36.2 GHz in Sgr A using (E)VLA

Several 68” pointings With 7 antennas, 0.3”

Point sources only Many detections

Strong and narrow Emission in sidelobes Velocity 20-50 km/s

Brightness T >> 105 K Definitely maser ! (First time this is derived)

1720 MHz OH and 36.2 GHz CH3OH

Collisionally excited Similar gas

n(H) ~ 104 to 105 cm-3

Tk ~ 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.)

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

origins

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

origins

44.1 GHz and 36.2 GHz CH3OH

Both Class I, i.e. collisions or outflows

36.2 and 44.1 GHz may be cospatial (see “G”)

Single 44.1 GHz masers

Single 36.2 GHz masers Here not sensitive to

extended thermal methanol emission

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 ?

Summary

First interferometric observations at 36.2 GHz Excellent 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!