Hierarquical Stellar Systems

La Galaxia en un PetabyteMahón, October 2009

Emilio J. Alfaro et al. “Group of Stellar Systems”

Instituto de Astrofísica de AndalucíaConsejo Superior de Investigaciones Científicas

M33 Engargiola et al. (2004) LMC HI + CO 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)

MotivationNew born stars

Initial conditions: GMCs, clouds, clumpsISM structure (environmental variables?)

Star formation

Hierarchical structure,masses, sizes, …

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 !!!???

Df=2.3 Df=2.6

miprogramita.f

well-defined Df

miotroprogramita.fDper , Dm , Dc , …

• Proyection effects• Image resolution• Opacity• Noise

Dper=1.35 Dper=1.35 Df = 2.6 +/- 0.1 !!! Df = 2.6 +/- 0.1 !!!Sanchez et al. 2005

Application to emission maps

Ophiuchus, Perseus (COMPLETE, Ridge et al. 2006)

Orion (Nobeyama, Tatematsu et al. 1993)

13CO maps

Df=2.6-2.8 (Universal?)

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 thefractal 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 = 1.0For ε = 0.1 we get alpha_M ≈ 1.2 +/- 0.2(Salpeter = 1.35)

Sanchez et al. 2006

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)∼ ∼

Df=2.3 vs Df=2.6

Dc=1.64 Dc=1.82 Dc=1.79

HII regions in disk galaxies

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 LGDBlue = O-B3Red = B4-B6

GB-early: Df = 2.68 +/- 0.04GB-late: Df = 2.85 +/- 0.04LGD-early: Df = 2.89 +/- 0.06LGD-late: Df = 2.84 +/- 0.06

Sanchez et al. 2007b

Stars in open clusters

Sanchez et al. 2009

Minimum spanning tree(Q parameter)

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 (Maíz-

Apellániz 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 = 31 ± 4 pc

• hDGL = 34 ± 5 pc

• Z0CG = -15 ± 12 pc

• Z0DGL = -12 ± 12 pc

• iCG = 14º ± 1º

• ΩCG = 287º ± 6º

• iDGL = 2º ± 2º

• ΩDGL = 352º ± 28º

-1000 -500 0 500 1000-1000

-500

0

500

1000

X (pc)

Y (

pc)

-1000 -500 0 500 1000-1000

-500

0

500

1000

X (pc)

Y (

pc)

DGL

CG

Alfaro et al. 2009Elias 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/8microns 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

MPE/ESO

50 light days 14 light days

UCLA/Keck

Mass of Sagittarius A*: 4.0±0.1 106 M

Size of Sagittarius A* < 1 AU

➔ Sagittarius A* must be a black hole.

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.

The black hole at the Galactic center

Velocity dispersion at the Galactic Center

Sgr A* would hardly be detectable ifit 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

Sánchez et al. (2009) (referee)

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 CrewCulpables:

– 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