probing the imf

Probing the IMF

Star Formation in Massive Clusters

Probing the IMF: Goals

• Quantify the IMF in rich, dense star-forming regions

• Understand the relationship between IMF; initial conditions

– locate the stellar birthline/region

– link to mass accretion rate

– explore linkage to thermal + turbulent pressure

Critical to modeling star-formation in the early universe

Probing the IMF: Measurements

• JHK photometry– MCAO images at high Strehl (~0.5 at J-band)

• IFU spectroscopy at R ~ 1000• MCAO photometry can probe

– 0.3 to 100 Msun in Arches cluster; R 136• define birthline location + IMF

– 5 to 100 Msun in clusters out to ~1 Mpc• quantify slope of upper IMF

• IFU spectroscopy can probe brightest stars


= 7”

Stellar density ~ 100x Orion Nebula Cluster

Galactic Center Superclusters: d = 10 kpc


R 136

20”

Stellar density ~ 10x Orion Nebula Cluster

LMC Massive Cluster: d = 200 kpc


M82 Superclusters: d = 4 Mpc


High dMacc/dt

Low dMacc/dt

Stellar Birthlines for Differing dMacc/dt

How is dMacc/dt related to [Fe/H]; stellar density?

Probing the IMF: Ancillary Science

• Quantify the spatial distribution for stars of different masses & ages– Do massive stars form preferentially near the cluster center?– If so, does this imply a different formation mechanism?

• Quantify stellar multiplicity in dense clusters– What role do dynamical interactions play in influencing

multiplicity?– What are the relevant timescales and environmental conditions?

Probing the IMF: Current Status

With current 6-10m class telescopes + HST:

• Crowding limits IMF probe to M > 2 Msun in Arches; R 136

• IMF probes in regions more distant than ~1 Mpc is precluded by

crowding

Probing the IMF: Need for GSMT

Key issue is crowding (not photon collection)

With a 30m GSMT, K-band diffraction limit is 0.015”

• Arches clusters can be studied throughout the M33 disk

– Probe birthlines; IMF for wide range of metallicities

• R 136 clusters can be studied out to M82 (upper end of IMF)

Probing the IMF: Requirements

• MCAO-fed near IR imager with ~1’ FOV

– Deliver Strehl ~ 0.5 at J-band

• MCAO-fed IFU spectrograph with R ~ 3000

Probing the IMF: Trades

• Ability to probe IMF to larger distances; lower masses

increases dramatically as aperture increases

– Directly linked to reduced crowding

• Adequate sampling of IMF may not require MCAO

correction over maximum achievable field (~2’)

13

Effects of Crowding on Photometry

GSMT with MCAO

20”

M 32 (Gemini/Hokupaa)NGST

Probing the IMF: GSMT v NGST et al

• NGST is limited by crowding (see previous slide)

• ALMA could probe initial conditions in Galactic regions

Probing the IMF: Needed Simulations

• Quantify crowding vs aperture trade

• Simulate variable extinction & nebular background

• Understand Strehl vs photometric precision trade

• Understand optimum field of view

• Model time variations of Strehl during exposure

probing the imf

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