Download The origin of the high gas temperatures in Galactic Center molecular

The origin of the high gas temperatures
in Galactic Center molecular clouds
Katharina Immer
ESO, Germany
09.04.2016
From Stars to Massive Stars
Collaborators:
J. Kauffmann (MPIfR)
T. Pillai (MPIfR)
A. Ginsburg (ESO)
K. M. Menten (MPIfR)
Motivation
High gas temperatures (> 50 K) in many CMZ clouds (Ao et al. 2012, Ginsburg
et al. 2016)
High column densities, volume densities constrained to > 104 cm-3
Densities and temperatures comparable to those in the active regions of
starburst galaxies (Mangum et al. 2013a, b)
ATLASGAL, 870 μm
Schuller et al. 2009
Goals
Detailed gas temperature maps of seven molecular clouds in
the CMZ, using the H2CO thermometer and other temperature
tracers (CH3CN, CH3CCH, CH3OH)
●
What is the origin of the warm gas?
●
Is para-H2CO a trustworthy temperature probe?
●
What is the density of the warm gas?
Observations
On-the-fly maps of seven clouds in the CMZ
with the APEX telescope
A) Observed frequency ranges: 216.9–220.9,
278.5–282.5, 290.5–294.5 GHz
Covering: H2CO(3–2) and (4–3) Ka-ladders
Smoothed velocity resolution: 1 km/s
Smoothed beam size: ~33''
B) Observed frequency ranges: 163–167,
169.85–173.85, 175–179, 181.85–185.85,
189.9–193.9, 201.9–205.9 GHz
Covering: CH3CCH(10–9) and (12-11)
ladders, CH3CN(9–8) and (11–10) ladders
Smoothed velocity resolution: 1.1 km/s
Smoothed beam size: ~39''
Targets
ATLASGAL, 870 μm
Schuller et al. 2009
Dust temperatures: ~20 K
Total masses: ~105 Mʘ
Integrated Intensity Ratios
Temperature
Temperature
Density
Integrated Intensity Ratio Maps
R321
R422
R404
20 km/s cloud
-15–36 km/s
G0.411+0.050
10–30 km/s
Temperature Maps
218 GHz
291 GHz
20 km/s cloud
-15–36 km/s
G0.411+0.050
10–30 km/s
Temperature vs Density
Temperature vs Density
Density of warm gas constrained to 104 – 106 cm-3
Temperature vs Linewidth
Red: Temperatures at 218 GHz
Blue: Temperatures at 291 GHz
Positive correlation between
temperature and linewidth
→ Turbulence plays an
important role in the heating of
the gas
CH3CN/CH3CCH Temperatures
G0.253+0.016 36 –42 km/s
CH3CN
CH3CCH
TH2CO = 132 ± 3 K
CH3CN/CH3CCH Temperatures
CH3CN
SGRC -55 – -49 km/s
CH3CCH
TH2CO = 63 ± 2 K
Conclusion
Detailed gas temperature maps of seven clouds in the CMZ with
high gas temperatures
●
●
●
What is the origin of the warm gas?
Temperature vs linewidth correlation for H2CO line, gas seems to
be pre-dominantly heated by turbulence.
Is p-H2CO a trustworthy temperature probe?
CH3CN and CH3CCH rotational temperature diagrams are
consistent but they give different temperatures than H2CO
(preliminary results!).
What is the density of the warm gas?
We constrain the density of the warm gas to 104 – 106 cm-3.
H2CO Thermometry
H2CO = slightly asymmetric rotor molecule =>
rotational levels split into two energy levels: JK+1K-1
Mangum & Wootten 1993:
Integrated intensity ratio of two different Ka-levels of the same ΔJ=1
transition → kinetic gas temperature
Integrated intensity ratio of different ΔJ=1 transitions within the same Kaladder → gas density
Different Ka-ladders located close in frequency
p-H2CO thermometry successfully applied to CMZ gas (Ao et al. 2012,
Ginsburg et al. 2016)
Velocity components in 20 km/s cloud
Velocity components in G0.253+0.016
Temperature Maps – Vel. Components
0–6 km/s
-3–3 km/s
8–14 km/s
16–22 km/s
27–33 km/s
36–42 km/s
75–81 km/s
Temperature uncertainty maps
20 km/s cloud
-15–36 km/s
0–6 km/s
8–14 km/s
27–33 km/s
G0.253+0.016
G0.253+0.016
-6–54 km/s
-3–3 km/s
16–22 km/s
36–42 km/s
75–81 km/s