PowerPoint-Pr

1
The structure of the nuclear stellar cluster of
the Milky Way
IAU Assembly Prague August 2006
and A. Eckart, R. Genzel,D. Merritt, T.
Alexander, A. Sternberg, J. Moultaka, T. Ott, C.
Straubmeier, F. Kul, L. Meyer
2
Stellar Cusps around Supermassive Black Holes

• age of a galaxy nucleus gt relaxation time
• steady state solution of Fokker-Planck equation
• predicts stellar cusp
• single mass ?r -7/4 (Bahcall Wolf, 1976
  Lightman Shapiro 1977)
• multiple masses ?r -3/2-7/4 (depending on
  stellar mass)
• size of cusp 0.1-0.2 rinfluence, BH

• relaxation time in center of Milky Way a few 109
  yr
• we expect to observe a stellar cusp
• GC is only such system that can be resolved into
  individual stars.

3
First AO results with NACO/VLT
distance from Sgr A (arcsecs)
4
New Analysis of GC Stellar Cluster

• use of uniform data sets seeing limited AO
  assisted
• extent of cusp/location of break radius?
• spatially variable extinction taken into account
• Refined methods
• PSF fitting with spatially variable PSF
• analysis of number counts and background light
• no binning of counts
• 2D structure of cluster, symmetry of cluster

Above all ... to convince the remaining skeptics!
5
Seeing Limited Imaging
ISAAC/VLT 2.09 ?m FWHM 0.4 (color image from
J2.09 ?m imaging)
Point source extraction and background
estimation with StarFinder (Diolaiti et al.,
2000)
6
Background light density inner 2.5 pc
broken power-law good fit!
7
AO Imaging Data
NACO/VLT adaptive optics resolution
0.06 40?40 FOV 10000 stars with magK
17.5
8
Extinction in the Central pc
IRS 7
Extinction derived from narrow-band imaging
(2.00, 2.06, 2.24, 2.27 ?m, ? 0.06
?m) assumption stars are blackbodies with T
5000 K, AK?-1.75 AK 1.8 - 3.6 mag (contours
AK 0.2 mag)
Sgr A
IRS 13
Outflow directed SSW from IRS 16/Sgr A? (see
poster by K. Muzic)
IRS 16
Schödel et al., subm. to AA
9
2D extinction corrected density map
Adaptively smoothed 40 stars for each
pixel smoothing radius 0.5 near Sgr A 1
near edge of image
Some clumps appear to be present in the
cluster. One of them is the well- known
co-moving group IRS 13E. (see Maillard et al.,
2004 Schödel et al., 2005)
Sgr A
Schödel et al., subm. to AA
10
Stellar surface number density inner 0.5 pc
magK 9.75 - 17.75
11
Horizontal branch/red clump stars
magK 14.75 - 15.75
see also Genzel et al. (2003), Paumard et al.
(2006)
12
Summary
1. Extinction New method for deriving
extinction Indications for
outflow? No significant
influence on number counts
1. Extinction New method for deriving
extinction Indications for
outflow? No significant
influence on number counts 2. Structure of
Cluster Clearly a broken power-law!
Presence of clumps -
relation to
recent star formation?
1. Extinction New method for deriving
extinction Indications for
outflow? No significant
influence on number counts 2. Structure of
Cluster Clearly a broken power-law!
Presence of clumps -
relation to
recent star formation? 3. Cusp Detected with
high significance shallower than
Bahcall-Wolf (?R-0.75) solution (due to
mixing of different masses)
Extent of cusp 7 (0.25 pc)
Effects of mass segregation.
1. Extinction New method for deriving
extinction Indications for
outflow? No significant
influence on number counts 2. Structure of
Cluster Clearly a broken power-law!
Presence of clumps -
relation to
recent star formation? 3. Cusp Detected with
high significance shallower than
Bahcall-Wolf (?R-0.75) solution (due to
mixing of different masses/classes)
Extent of cusp 7 (0.25 pc)
Effects of mass segregation. Results are in
good agreement with theory. Models can now be
fine-tuned with the exact values for the GC
cluster.
13
Thank you for your attention!