kinematic properties of early-type galaxy haloes using...

Kinematic Properties of Early-Type GalaxyHaloes using Planetary Nebulae

by L. Coccato et al.

May 27, 2011

Outline

IntroductionBackgroundPlanetary Nebulae (PNe)

MethodsData obtainedIs the PNe sample a good sample?Smoothing

ResultsParametersRotation, Misalignment and TwistingRadial Velocity and Velocity DispersionAngular Momentum

Putting Constraints on Galaxy Formation

I The dynamics of galaxies give information on theirevolution.

I Until recently only measurements of the stellar component.I Numerical simulations of galaxy formation based on

different cosmological simulations predict particular valuesfor different quantities, which have to be checked againstreal data.

Outline




Why Planetary Nebulae (PNe)?

I PNe are easily detected at large radii from the centre, byvirtue of their relatively bright [OIII] emission line.

I They are believed to trace the main stellar population.

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PNe data and photometric data of the stellarcomponent

I The PNe data is obtained in two ways: new measurementswith the PNS at the WHT (six galaxies) and from theliterature (ten galaxies).

I Only PNe with velocities within 3σ of the mean velocity oftheir neighbours are used.

I HST photometry is used in the innermost 4-5 arcsec, whileground-based observations are used for r > 10-11 arcsec.

I In between, the average values are used.

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Completeness correction

I To compare the stellar surface brightness and PNe numberdensity, the incompleteness in PNe detection has to betaken into account. The noise has four contributions:

I sky surface brightnessI detector readout noiseI galaxy backgroundI presence of foreground stars

Completeness correction cont’d

I Generate artificial images with simulated sources ofdifferent magnitudes.

I Compute the luminosity function and check for whichmagnitude more than 80% (m < m80%) of the sources arerecovered.

I Put a distribution with m < m80% in the observed images.I Detect the artificial sources again and from this compute

the radial completeness factor. Loss of the sources is thendue only to the galaxy background and presence offoreground stars.

I Group the observed PNe into elliptical annuli, computeNc/A, corrected for the completeness factor.

I Compute the logarithmic PNe number densityρ(R) = −2.5 log10(Nc/A).

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Different parameters studied

I rotationI misalignment and twistingI radial velocityI velocity dispersionI angular momentum

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I The average value of V/σ is used to describe the relativeimportance of rotation and anisotropy for dynamicalequilibrium.

I Stellar V/σ are taken from the SAURON survey.

Figure: Red: flattened ellipticals. Black: Round ellipticals. Green: S0galaxies.

Outline




I λR measures the importance of rotation as a function ofradius and is thus related to the angular momentum perunit mass within radius R.

I Galaxies with λR < 0.1 are defined as slow rotators.I Galaxies with λR > 0.1 are defined as fast rotators.

Summary

I Kinematic twists and misalignments at large radii.I Average V/σ of the stellar component is smaller than the

PNe component, which means that the kinematics becomeincreasingly supported by rotation in the outer parts.

I Some galaxies turn from slow rotators to fast rotators in thehalo.

I This means that we can put constraints on the modelswhich take only into account the inner parts of the galaxies.

kinematic properties of early-type galaxy haloes using...

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