Download Sanchez et al. 2009

Hierarquical Stellar Systems
Emilio J. Alfaro et al.
“Group of Stellar Systems”
Instituto de Astrofísica de Andalucía
Consejo Superior de Investigaciones Científicas
La Galaxia en un Petabyte
Mahón, October 2009
M33 Engargiola et al. (2004)
HI + CO
LMC
Hα + U + V
Scales of star formation
Pattern recognition:
Stellar Complexes
A wider concept
• Stellar Complexes represent the largest globular scale in the hierarquical
structure of star forming systems, going from double and trapezium
systems to fragments of spiral arms in flocculent galaxies.
•
Larger scales evolve slower than t ~ L0.5.
Efremov & Elmegreen 1998
The current scientific project
• Three years ago we started a scientific project with
the main objective of studying:
– The behaviour of the star forming processes at different
spatial scales.
• In particular we focussed on four different scales
showing different state equations and different
physical mechanisms:
– Molecular Clouds
– Massive Stars (Binary and Trapezium systems)
– Stellar Clusters
– Stellar Complexes
Geometry & Physics
• The interstellar medium (ISM) shows a fractal structure
(Elmegreen & Falgarone 1996), with a fractal dimension wich
appears to be nearly constant for different physical states of
the gas and different chemical species. (Sánchez et al. 2005,
2007)
• How does the internal structure of the clouds induce or
control the main properties of the emerging stellar
population?
• Is the spatial pattern of the recent born stars a mimic of the
internal structure of the parent cloud?
• How does the stellar spatial pattern evolve with time?
• Is it scale invariant?
Sandra Ocando (Grad thesis); Néstor Sánchez (Poster)
Motivation
Star formation
Initial conditions: GMCs, clouds, clumps
ISM structure (environmental variables?)
Hierarchical structure,
masses, sizes, …
New born stars
???
IMF, spatial distribution,…
Objective/Systematic characterization/study
Fractal ISM
• Maps of nearby complexes show a hierarchical
and self-similar structure → underlying
fractal structure
Taurus Molecular Cloud
(IRAS 100μ emission)
Taurus complex: integrated emission in
12CO (Falgarone et al. 1991)
Df(ISM) ≈ 2.3 = universal !!!???
miprogramita.f
well-defined Df
Df=2.3
miotroprogramita.f
Df=2.6
Dper , Dm , Dc , …
•
•
•
•
Proyection effects
Image resolution
Opacity
Noise
Sanchez et al. 2005
Dper=1.35  Df = 2.6 +/- 0.1 !!!
Application to emission maps
13CO maps
Ophiuchus, Perseus (COMPLETE, Ridge et al. 2006)
Df=2.6-2.8 (Universal?)
Orion (Nobeyama, Tatematsu et al. 1993)
Sanchez et al. 2007a
- What is the relationship between the physical properties of
the interstellar clouds and their fractal structure?
- Are the observed properties in agreement with relatively high
fractal dimension values?
Clump mass spectra:
Simple random sampling through the
fractal yields alpha_M = 1.
Observations (as always, a problem!!):
0.6 < alpha_M < 0.8 (E&F96)
0.3 < alpha_M < 1.1 (others)
If Df = 2.6 then alpha_M ≈ 0.55 for ε = 1.0
For ε = 0.1 we get alpha_M ≈ 1.2 +/- 0.2
(Salpeter = 1.35)
Sanchez et al. 2006
Df=2.3 vs Df=2.6
Federrath et al. 2009:
Stochastic forcing term f as source term in equations of hydrodynamics
compressive modes (nabla x f = 0) and solenoidal (nabla · f = 0)
D∼2.3 for compressive and D∼2.6 for solenoidal forcing (M=5.5)
HII regions in disk galaxies
Dc=1.64
Dc=1.82
Dc=1.79
Dc,ave=1.81  Df(3D),ave=2.73
Significant Dc variations among galaxies!!!
1.5 < Dc < 2.0 (2.4 < Df < 3.0)
Faintest galaxies  smallest Dc values
Sanchez et al. 2008
New-born stars
• Df(ISM)  Df (star distribution)
• Application to the Gould Belt
(closest star formation complex):
GB-early:
GB-late:
LGD-early:
LGD-late:
Df = 2.68 +/- 0.04
Df = 2.85 +/- 0.04
Df = 2.89 +/- 0.06
Df = 2.84 +/- 0.06
GB
LGD
Blue = O-B3
Red = B4-B6
Sanchez et al. 2007b
Stars in open clusters
Minimum spanning tree
(Q parameter)
Sanchez et al. 2009
Stars in open clusters
Sanchez et al. 2009
Stars in open clusters
Sanchez et al. 2009
Dc = 1.74  Df ~ 2.0 << 2.6-2.7 ???
• Perhaps some clusters may develop some kind of substructure starting from an initially more
homogeneous state (Goodwin & Whitworth 2004).
• This difference could be a consequence of a more clustered distribution of the densest gas from
which stars form at the smallest spatial scales in the molecular cloud complexes, according to a
multifractal scenario (Chappell & Scalo 2001).
• Another explanation is that the fractal dimension in the Galaxy does not have a universal value
and therefore some regions form stars distributed following more clustered patterns.
• Finally, maybe the star formation process itself modifies in some (unknown) way the underlying
geometry generating distributions of stars that can be very different from the distribution of gas in
the parental clouds.
Massive Stars & Low-Number
Groupings
• Question:
How do the massive stars form?
• Primary Objectives
– Expand the Galactic O-star catalogue (MaízApellániz 2004)
– Generate a catalogue of Galactic early-type stars
from Tycho-2 and 2MASS data bases
Alfredo Sota (PhD); J. Maíz-Apellániz (poster)
Some spectra
Some Special Stellar Complexes
• Gould Belt (supposed to be our closest stellar
complex)
Federico Elias (PhD, 2006)
• Super-bubble in NGC 6946 (contains a young
SSC with 106 solar masses and shows a
diameter close to 700 pc)
Carmen Sánchez Gil (PhD)
Corrección de completitud
•
•
•
•
•
fCG
= 0.58 ± 0.06
hCG =
hDGL =
31 ± 4 pc
34 ± 5 pc
Z0
iCG
CG
500
0
-500
Z0CG = -15 ± 12 pc
DGL
1000
Y (pc)
•
-1000
-1000
-500
500
1000
X (pc)
= -12 ± 12 pc
=
0
1000
14º ± 1º
DGL
•
ΩCG
= 287º ± 6º
•
iDGL
=
•
ΩDGL = 352º ± 28º
2º ± 2º
Y (pc)
500
0
-500
-1000
-1000
-500
0
X (pc)
500
1000
Alfaro et al. 2009
Elias et al. 2009
Gould Belt (??)
NGC 6946
Sánchez Gil et al 2009
Age maps of spiral galaxies
Age maps of spiral galaxies
Sánchez Gil et al. 2009 (in preparation)
Velocity corrugations in face-on
galaxies
PMS stars in open clusters
• Main Objective: Search and characterization of
PMS members in young open clusters
– UBVRIJHK + Hα photometry + models
– Mainly focussed on AF star
PMS stars in open clusters
Colour
composite of
30’X30' from
AAO/UKST-Hα
survey image
(blue) and
Spitzer/IRAC/8
microns image
(red) (Sh-2 284)
Delgado et al. 2009
(referee)
PMS stars in open clusters
• Two stellar
populations
Kinematics and mass of
Sagittarius A* and the nuclear
star cluster of the Milky Way
The black hole at the Galactic center
50 light days
14 light days
Mass of Sagittarius A*: 4.0±0.1 × 106 M
Size of Sagittarius A* < 1 AU
➔ Sagittarius A* must be a black hole.
MPE/ESO
UCLA/Keck
e.g. Eckart & Genzel (1996); Ghez et al. (1998, 2003,2008); Genzel et al.
(2000); Eckart et al. (2002); Schödel et al. (2002, 2003, 2009); Reid et al.
(2004); Eisenhauer et al. (2003, 2005); Gillessen et al. (2009); Doeleman et
al. (2008) etc.
Velocity dispersion at the Galactic Center
Sgr A* would hardly be detectable if
it were located in another galaxy.
At R>0.5 pc the extended mass of the
cluster becomes visible in the kinematics
(deviation from Kepler law).
v~r-0.5
Modeling the enclosed mass
• Extended mass is detected for the first time
unambiguously from the stellar dynamics in the
central parsec.
• Cluster rotation confirmed
• Extended mass in central parsec:
M★(r<1pc) = 1.5×106 M☉ for M/L = const.
Consistent with normal stars.
Schödel, Merritt & Eckart (2009,
A&A)
Searching for new stellar systems
• Looking inside astrometric + photometric
catalogues
• Clusters, associations & streams
• Development of new tools
• Detailed studies for special systems
Starting point: Carte du Ciel (revisited), see
poster by Belén Vicente
ALHAMBRA & GAIA
• Characterization of ALHAMBRA photometric
system
• Calibration strategy
• Determination of stellar physical parameters
from ALHAMBRA colors
See poster by Teresa Aparicio (PhD)
SSG & GAIA
• Searching for new Galactic subsystems
• Stellar Clusters (Galaxy dynamics,
Membership studies, Internal structure and
evolution with time)
• Massive Stars (Binarity)
The Crew
Culpables:
– E. J. Alfaro
– T. Aparicio
– A. J. Delgado
– T. Gallego
– J. Maíz-Apellániz
– N. Sánchez
– C. Sánchez-Gil
– R. Schoedel
– A. Sota
– B. Vicente
Cómplices Necesarios:
•A.A Djupvik
•N. Walborn
•J. L. Yun
Sospechos Habituales:
• A. Eckart
• Y. N. Efremov
• R. Gamen
• N. Morrell
• S. Ocando
• E. Pérez