1. Massive Star Forming Activities in the Galactic Center Traced by the Radio
Cornelia C. Lang
University of Iowa
collaborators:
W.M. Goss, K.E. Johnson, M. Morris,
L.F. Rodriguez, Q.D. Wang, D. Figer,
and F. Yusef-Zadeh
toward Sagittarius in the optical band
New perspectives gained by combining the radio, near-IR and x-ray

2. Giant H II Regions Stellar winds
What can we learn about the interaction between the stellar and interstellar medium in the GC by combining near-IR, radio and X-ray observations?
Giant H II Regions
Stellar winds

3. Yusef-Zadeh, Morris & Chance (1984)
Radio Arc Region: best example of interplay between GC components
VLA 20 cm res ~ 5”
Yusef-Zadeh, Morris & Chance (1984)
Lang et al. (1999)
GCs are known to have
dense concentrations of
- massive stars
- molecular clouds
- ionized gas
- magnetic fields
- hot ISM
- SMBH
the *interplay* between
these components may
give rise to
ENERGETIC
EPISODIC
activities
on the kinds of scales
we detect in other nearby
galaxies ( > 1 kpc)
Sickle & Pistol
H II regions
Arched Filaments
H II Regions + +
25’~60 pc
Sgr A complex +

4. Ionization of the Sickle and Arched Filaments HII regions
Sickle HII
region
H92a line
Pistol Nebula
CS(2-1) line
(Lang, Goss & Morris 2002)
Lang, Goss & Wood 1997
NLyc(Quint.) ~ photons s-1
(Figer et al. 1999)
NLyc (radio continuum)
~ 3 x 1049 photons s-1
Quintuplet can easily ionize
edge of underlying molecular cloud
(Lang, Goss & Wood 1997)
NLyc(cluster) ~ 4x1051 ph. s-1
NLyc (radio continuum)
~ 3x1050 photons s-1
Arches cluster could be ~20 pc
away from molecular cloud
(Lang, Goss & Morris 2001)

5. Giant HII regions in GC are similar in morphology, energetics:
NGC 3603 & 30 Doradus in the LMC
cluster masses (~104 Mo)
cluster densities (~105 Mo pc-3)
cluster stellar types (W-R stars, peculiar O-stars)
ionizing fluxes (> photons s-1)
large surrounding, filamentary nebulae
strong stellar wind emission (~10-5 to 10-4 Mo yr-1)
red: X-ray
blue: UV stars
green: ionized
hydrogen
Wang 1999

6. VLA H92a velocity distribution
GC Radio Arc Cloud Kinematics
Arched Filaments and Sickle HII regions lie on surfaces of dense molecular clouds
Parent clouds are subject to large shear from GC region; don’t survive w/ clusters
- Arches and Sickle are likely to be edges of infalling, passerby clouds
-clusters themselves at ~30 pc will evaporate after < 10 Myr (Kim et al. 1999, 2000)
- stars and gas are moving with LARGE relative velocities > km/s!
VLA H92a velocity distribution
VLA H92a velocity distribution
Arches Region:
Vgas = +20 to -60 km/s
Vstars = +95 km/s
(Figer et al. 2002)
Sickle/Quint. Region:
Vgas = +30 to +50 km/s
Vgas (Pistol) = +125 km/s
Vstars = +130 km/s
(Figer et al. 1998)
+20 to -60 km/s
+25 to +130 km/s
(Lang, Goss & Morris 2001)
(Lang, Goss & Wood 1997)

7. Physical relationship between stars and gas in GC
radio continuum
HI absorption against continuum
molecular gas
ionized gas
stellar cluster radial velocities
view looking “down”
at the complex from above
colorscale: tHI over v = -23 to -29 km/s
Lang et al. (in prep)
Lang, Goss & Morris 2002

8. Stellar winds of massive GC stars
Such massive, highly-evolved stars have high mass loss rates (~ Mo yr-1)
Wind emission detectable in the radio continuum
- VLA observations of Quintuplet and Arches Clusters (1999 – present)
- multi-frequency, multi-epoch observations
- high resolution (A, BnA arrays) : 0.3-1”

9. Stellar Winds in the Quintuplet Cluster
10 sources detected
 ~ +0.2 to +0.9
Pistol Star has extended
radio nebula ( = -0.3)
+ represent near-IR
sources (Figer et al. 1999)
agreement within astrometric limits
high mass loss rates
~ 1 – 13 x 10-5 Mo yr-1
three sources (QR1-3)
do not have near-IR
counterparts – different
nature? UCHIIs?
Lang et al. (in prep)

10. Detections of Stellar Winds in the Arches Cluster
9 sources detected at
4.9, 8.3, 22, 43 GHz
 ~ +0.3 to +0.9
 ~ -0.7 (AR6)
+ represent near-IR
mass-losing sources
(Nagata et al. 95; Cotera et al. 96)
“V” sources show
10-30% variability
between epochs
high mass loss rates
~ 3 – 17 x 10-5 Mo yr-1
several non-thermal sources
combination of 1999 (Lang et al. 2001b) and 2002 observations

11. The Hot Component of the Arches Cluster
Arches: 3rd brightest GC X-ray point source in central 300 pc
(Wang, Gotthelf & Lang 2002)
Arches Cluster
3 X-ray point sources in cluster
+ surrounding X-ray diffuse emission
(Yusef-Zadeh et al. 2002)
Lx ( keV) ~ 1035 erg/s
coincident with several radio sources
largest mass-loss rates, extended
Law & Yusef-Zadeh 2003
Origin of X-ray Emission
point: colliding wind binaries
-diffuse: 107 K “cluster wind”?
(Canto et al. 2000; Raga et al. 2001)
Quintuplet cluster – point-like
X-ray sources (Law & Yusef-Zadeh 2003)
Yusef-Zadeh et al. 2003
contours: 1-10 keV emission (Wang, Gotthelf & Lang 2002)
colorscale: NICMOS near-IR image (A.Cotera)

12. Chandra X-ray Galactic Center Survey
Arches
Cluster
MSX Mid-IR 25 mm
Wang, Gotthelf & Lang 2002
 Massive star forming activites closely correlated with diffuse X-ray in GC Radio Arc
30 pc
Radio Arc
Region
Sgr B2

13. Conclusions
Clusters play important role in GC
- responsible for ionizing cloud edges
- young stars losing mass at high rates, collisions of winds
collective ‘cluster wind’
GC region is much more completely understood by incorporating massive
stars and their influence
- The Radio Arc environment is similar to NGC 3603 and 30 Dor
Overall diffuse hot emission in GC (traced by X-rays) likely to arise from massive star activities – SNR, winds
is our Galactic Center unique?
- identify and compare similar structures, interplay in nearby galaxies