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High-z galaxy masses from spectroastrometry

Alessio GnerucciDepartment of Physics and Astronomy

University of Florence

13/12/2009- Obergurgl

Collaborators: A. Marconi, R. Maiolino, F. Mannucci, G. Cresci and many others

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High redshift galaxies dynamics and masses

Galaxies formation ad cosmological evolution•Structures formation•Dark matter•Star formation history

•Many theoretical models that need to be constrained with data.•Dynamics is directly related to the models of galaxy formation and it is the most direct way to probe the content of dark matter.•Dynamical studies are important for assessing the cases of mergers, rotating disk or turbulence dominated object.•3D spectroscopy is a key technique for these studies.•In literature there are few dynamical studies of high-z galaxies (z~2: Genzel+06,08, Forster-Schreiber+06,09, Cresci+09, Erb+06) (z>2.5: Nesvabda+06,07,08, Jones+09, Law+09, Lemoine-

Busserolle+09,Swimbank+07,09)

Forster-Schreiber+09

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Gas dynamics on z~3 galaxiesGas dynamics from Integral field spectra

Projects AMAZE (PI: R.Maiolino) and LSD (PI: F.Mannucci)

z~3 galaxies sample

deep SINFONI (VLT) Integral field spectra

~ 6 Rotating objects (~21%)

~13 Non rotating objects (~47%)

~9 Unresolved objects (~32%)

AMAZE sample: 28 objects

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Gas dynamics on z~3 galaxies

Dynamical modeling

LINE O

F NODES

LINE OF SIGTH

SKY PLANE

DISKAXIS

i

DISKPLANE

Model(Marconi et al. 2006, Cresci et al. 2009)

•Rotating thin disk.

•Mass distribution modeled as “exponential disk”.

•Instrumental effects (beam smearing, pixel size, spectral resolution).

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Gas dynamics on z~3 galaxies

Some examples of the fit for the rotating objects

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Gas dynamics on z~3 galaxies

In the case of unresolved objects it is not possible to perform the dynamical modeling.

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Virial mass estimates

Virial Theorem

Characteristic radius estimated as half light radiusof the continuum (or line) emission (corrected for beam smearing)

Vc

FWHM

WavelengthIn

tens

ity

Integrated source spectrum

(corrected for instrumental response)

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Virial mass estimates

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Wavelength

Pos

ition

alo

ng t

he s

lit

Fixed slit position 1D image

Fixed wavelength (velocity)1D image

Wavelength centroid Position centroid

Rotation curve Spectroastrometric curve

A. Gnerucci, A. Marconi et al.: Spectroastrometry of rotating gas disks and the detection of supermassive black holes in galactic nuclei. (A&A accepted)

Spectroastrometry in principle

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Spectroastrometry in principle

Wav

elen

gthY d

irect

ion

X direction

Integral field spectrum

Fixed wavelength2D image

Image: Stephen Todd (ROE) and Douglas Pierce-Price (JAC)

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Overcoming the spatial resolution

DHWHM PSFSLIT

Two unresolved point sources

Position along the slit

Inte

nsity

SLIT HWHM PSFD

V1

V2

It is possible to get the centroid position with an accuracy better than the PSF FWHM

D

Position along the slit

Inte

nsity

Inte

nsity

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Spectroastrometry and virial mass estimates“Classical” virial mass estimator

Characteristic radius estimated as half light radiusof the continuum (or line) emission

D

(Xr,Yr)(Xb,Yb)

Vc

FWHM

Wavelength

Inte

nsity

Integrated source spectrum

Velocity map

“Spectroastrometric” virial mass estimator

Blue side

Red side

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Spectroastrometric mass estimatorBlue image

Red image

PSF size

~0.6”(FWHM)

pixel size ~0.125”

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Calibration of the mass estimator

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stesso discorso con le masse viriali classiche

This method isinstrument-independent,

it needs only the“cube” data format.Useful with ALMA!

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•We study the gas kinematics of the AMAZE and LSD objects from VLT SINFONI data.

•For a subsample of “rotating” objects we perform a complete dynamical modeling.

•We introduce the spectroastrometry technique and observe that the power of spectroastrometry is the capability to overcome the spatial resolution.

•We use of spectroastrometry to improve the virial mass estimate.

•We calibrate the spectroastrometric mass estimator using dynamical masses for some AMAZE object obtained by complete dynamical modeling, observing a better correlation between fitted dynamical mass and the estimator on respect of classical virial estimate.

We introduced an estimator of the dynamical mass of high z galaxies, based on the “spectroastrometric” technique, that can be useful in the cases of poor spatial resolution or signal to noise ratio.

This estimator correlate very well with more robust estimates of the dynamic mass.

Although based on SINFONI data, this method is instrument-independent and indeed has been used many times by radio and sub-mm astronomers.It can be useful even with ALMA data.

Summary and conclusion

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Gas dynamics on z~3 galaxies

Gas turbulence