Super star clusters Super star clusters andand star-formation in interacting galaxiesstar-formation in interacting galaxies

Zara RANDRIAMANAKOTO Zara RANDRIAMANAKOTO

SA SKA Annual Bursary ConferenceSA SKA Annual Bursary Conference December, 2009December, 2009

SupervisorsSupervisors: Petri Vaisanen (SAAO): Petri Vaisanen (SAAO) Sarah Blyth (UCT)Sarah Blyth (UCT)

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ObjectivesObjectives

Estimate star formation rate (SFR) in interacting luminousEstimate star formation rate (SFR) in interacting luminous

infrared galaxies (LIRGs) from a study of SSCs LFsinfrared galaxies (LIRGs) from a study of SSCs LFs

Establish a spatial distribution of star formation (SF)Establish a spatial distribution of star formation (SF)

over the whole galaxyover the whole galaxy

Derive the Derive the first everfirst ever significant sample of K-band luminosity significant sample of K-band luminosity

functions (LFs) of extragalactic super star clusters (SSCs)functions (LFs) of extragalactic super star clusters (SSCs)

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Key science in Astronomy:Key science in Astronomy: Understand the UniverseUnderstand the Universe

Relevances of the projectRelevances of the project

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Galaxy evolutionGalaxy evolution(LIRGs)(LIRGs)

Relevances of the projectRelevances of the project

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SF via SSCsSF via SSCs

Relevances of the projectRelevances of the project

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LIRGsLIRGs

Why LIRGs ?Why LIRGs ?

Generally, anGenerally, an interacting interacting system system

High SFRHigh SFR

Large number of SSCsLarge number of SSCs

Good laboratory for probing galaxy evolution and SFGood laboratory for probing galaxy evolution and SF

Elmegreen et al., 2006, ApJ 642, 158

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SSCsSSCs

Why SSCs ?Why SSCs ?

Found whenever there is vigorous SF such as interactingFound whenever there is vigorous SF such as interacting

LIRGs (Whitmore et al., 2000)LIRGs (Whitmore et al., 2000)

CharacteristicsCharacteristics::

Whitmore et al., 2000; Elmegreen, 2002

Location:Location:

MassiveMassive

YoungYoung

LuminousLuminous

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SSCsSSCs

Why SSCs ?Why SSCs ?

Found whenever there is vigorous SF such as interactingFound whenever there is vigorous SF such as interacting

LIRGs (Whitmore et al., 2000)LIRGs (Whitmore et al., 2000)

CharacteristicsCharacteristics::

Whitmore et al., 2000; Elmegreen, 2002

Location:Location:

MassiveMassive

YoungYoung

LuminousLuminous

SSCs provide insight to the mechanisms of SF

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Challenges:Challenges: SSCs are located in the obscured optical region of the galaxiesSSCs are located in the obscured optical region of the galaxies

It is difficult to differentiate individual SSCs to its surrounding dusty regionsIt is difficult to differentiate individual SSCs to its surrounding dusty regions

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Challenges:Challenges: SSCs are located in the obscured optical region of the galaxiesSSCs are located in the obscured optical region of the galaxies

It is difficult to differentiate individual SSCs to its surrounding dusty regionsIt is difficult to differentiate individual SSCs to its surrounding dusty regions

SolutionSolution: Observe in Observe in K-bandK-band using near infrared using near infrared adaptive opticsadaptive optics

imagingimaging

K-band K-band : observation suffers less of the dust effect: observation suffers less of the dust effect

AO AO : will resolve individual SSCs to large distances than before: will resolve individual SSCs to large distances than before

(a small field with high resolution) (a small field with high resolution)

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SolutionSolution: Observe in Observe in K-bandK-band using NIR using NIR adaptive opticsadaptive optics imaging

A region of IRAS 18293-3413, close to the nucleus ( Vaisanen et al., 2009).

HST/ACS VLT/NACO

4.5”

2”

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SolutionSolution: Observe in Observe in K-bandK-band using NIR using NIR adaptive opticsadaptive optics imaging

A region of IRAS 18293-3413, close to the nucleus ( Vaisanen et al., 2009).

HST/ACS VLT/NACO

4.5”

2”

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MethodologyMethodology

SSCs LFs

Multi-wavelength observations

Data reduction of a ten local LIRGs

from VLT/NACO and GEMINI/ALTAIR

(using K-band NIR AO, survey in progress)

Imaging archival data for optical (HST/ACS) mid- and far-infrared(MIPS and IRAC) radio (VLA) wavelengths

Spatial distribution of SFSpatial distribution of SF

SFRSFR

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AchievementsAchievements

Data reduction (IRAF)

GEMINI/ALTAIR Individual frames

Final combined imageFinal combined image

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GeminiGeminico-added imagesco-added images

CGCG 049-057

NGC 3690

IRAS F17138-1017

IRAS F17578-0400

MCG +08-11-002

IRAS F16516-0948 IC 694

UGC 8387

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AchievementsAchievements

Data reduction (IRAF)

Photometry calibration

Mag_zeropoint

Aperture correction

Aperture photometry (IRAF)

Objects detection (Sextractor)

Selection criteria SSCs LFsSSCs LFs

GEMINI/ALTAIR Individual frames

Astrometry calibration (IRAF)Final combined imageFinal combined image

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Preliminary resultsPreliminary resultsK-band SSCs LFs

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Preliminary resultsPreliminary resultsK-band SSCs LFs

LFs exhibit a turnover at the faint end:

Observational incompleteness (Anders et al., 2007)

Small number of SSCs with lower luminosity

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Preliminary resultsPreliminary resultsK-band SSCs LFs

LFs exhibit a turnover at the faint end:

Observational incompleteness (Anders et al., 2007)

Small number of SSCs with lower luminosity

Solution:Solution: Use Monte-Carlo simulation to determine the completeness fraction

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Preliminary resultsPreliminary resultsK-band SSCs LFs

Theoretical observations: LFs shape follow a power-law distribution (de Grijs et al., 2003)

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Preliminary resultsPreliminary results

K-band SSCs LFs

Slope slightly deviates from 2 Effect from photometric uncertainties or some statistical fluctuations It can be real (the goal of the project)

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Preliminary resultsPreliminary results

K-band SSCs LFs

Slope slightly deviates from 2 Effect from photometric uncertainties or some statistical fluctuations It can be real (the goal of the project)

SSCs LFs systematic variations: Steeper at higher luminosities (Whitmore et al., 1999; Larsen, 2002) Steeper in redder filters (Elmegreen et al., 2002; Haas et al., 2008)

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Preliminary resultsPreliminary resultsK-band SSCs LFs: shift of the peak

The fainter the brightest star cluster,

the lower its SFR

Larsen, 2002; Bastian, 2008

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Preliminary resultsPreliminary resultsK-band SSCs LFs: shift of the peak

The fainter the brightest star cluster,

the lower its SFR

Expect that

Larsen, 2002; Bastian, 2008

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SSCs LFs

Multi-wavelength observations

Data reduction of a ten local LIRGs

from VLT/NACO and GEMINI/ALTAIR

(using K-band NIR AO, survey in progress)

Imaging archival data for optical (HST/ACS) mid- and far-infrared(MIPS and IRAC) radio (VLA) wavelengths

Spatial distribution of SFSpatial distribution of SF

SFRSFR

Future outlookFuture outlook

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SSCs LFs

Multi-wavelength observations

Data reduction of a ten local LIRGs

from VLT/NACO and GEMINI/ALTAIR

(using K-band NIR AO, survey in progress)

Imaging archival data for optical (HST/ACS) mid- and far-infrared(MIPS and IRAC) radio (VLA) wavelengths

Spatial distribution of SFSpatial distribution of SF

SFRSFR

Future outlookFuture outlook

GMRT/ATCAobservations

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ExpectationsExpectations

Reason of the turnover in LF at the faint end

In the local Universe, only a small fraction of the global SF density is contributed by LIRGs. However, at higher redshift, the fraction becomes dominant (Iono et al., 2009).