Integral Field Spectroscopy

Universidad de Almeria

Viernes de Ciencia

14 January 2011

S.F.Sánchez (CAHA)

IFS or 3D Spectroscopy Is the spectroscopic technique that samples a

quasi-continous area in the sky (FOV). The FOV is sampled by small aperture elements

named spaxels, which correspond to pixels of an image.

Light coming through each spaxel is transported to the entrance of an spectrograph.

The image/plane and focal/plane are completely decoupled: Lot of software is required to reconstruct the orginal spatial shape at each wavelength.

Different kind of spaxels. Is the spectroscopic technique that samples a

quasi-continous area in the sky (FOV). The FOV is sampled by small aperture elements

named spaxels, which correspond to pixels of an image.

Light coming through each spaxel is transported to the entrance of an spectrograph.

The image/plane and focal/plane are completely decoupled: Lot of software is required to reconstruct the orginal spatial shape at each wavelength.

How to send the light to the Spectrograph?

Image Slicers: Light is “sliced” in small continous pseudo-slits: SINFONI, MUSE...

Lensarrays: Continous lensarray is focused in separated apertures: SAURON, TIGER...

Fiber-Bundles (+lensarrays): Lights is conducted by fibers: PMAS/PPAK, VIMOS, GMOS...

Fiber Feed IFS technique

The Raw data of FF IFUs

The Raw data of FF IFUs

FF IFU: Data Reduction (I) Continuum exposure used to find and trace

the location of the spectra in the CCD. The FWHM of the spectra projected in the

cross-dispersion axis determined. Gaussian extraction performed. Comparison Arc used to determine the

distorsion correction and wavelength solution, latter applied to the data.

FF IFU: Data Reduction (II)

Sky-frames taken during the twilight used to correct for the differentical transmission fiber to fiber (wavelength dependent).

Spectrophotometric calibration standard star exposure used to determine the flux calibration, applied to the science frames.

Science (331), Sky (36) and calibration spectra (15) are separated in different frames, once reduced.

Sky spectrum is derived for each frae (median+3sigma clipping of the 36 sky-spectra) and the subtracted to the data.

FF IFU: Data Reduction (III) Re-arrange the dithered pointings in a single

row-stacked spectra frame, plus the complementary Position Table.

Mask the spectral pixel strongly affected by the vignetting.

Interpolate the final Mosaic into a common grid datacube of 1”/pixel.

When available, perform a flux recalibration based on broad-band photometry.

The Raw data of FF IFUs

Tracing process (I)

Tracing process (II)

Extraction: How to Add flux?

Extraction: cross-talk?

Extraction: The final product

Distorsions: Shifting lines.

Dispersion:Which line are you?

Fiber-to-Fiber transmission

Sky subtraction... If possible.

Where my spectra comes from?.

PMAS/PPAK: Dithering.

• 3 position dither pattern per pointing.

• Complete spatial covering of the FOV.

• Increase of the spatial resolution.

• Fully implemented in R3D.

WF-IFS Mosaics Experiment

Matching the pointings.

The pointings overlap, in at least 11 spectra. The change in transparency is critical Accuracy of the telescope offsets is also critical.

Results: Orion (Sánchez et al. 2006)

Results: M74 (Sánchez et al. 2010)

CALIFA: Introduction

Survey of ~600 Galaxies in the Local Universe, using Integral Field Spectroscopy, with PPAK mounted at the 3.5m Telescope.

Proposed by 53 researchers from 8 countries: PI:S.F.Sánchez. Board: R. Kennicutt (Chair), A. Gil de Paz (co-

PI), J.M. Vilchez, L. Wisotzki, G. Van den Ven. 210 dark nights allocated in next 3 years. Started on July 1st 2010.

CALIFA: Science Goals

• Model the resolved stellar population in galaxies of any kind and trace the star formation history.

• Determine the nature of the ionized gas and its chemical abundance gradients.

• Determine the 2D kinematic structure of galaxies in the local Universe.

Results (I): Mother Sample

Characterization of the Sample: How are the galaxies we are going to observe?

Morphology, Spectral Type, Nuclear or Starformation activity…

Do we have any possible Bias and how we can control/correct them?

Results (II): Reduced Data

Pilot Studies: 43 objects observed in 2009: A) V300 (R~450); 1.5h Int.;

3700-7100 A. B) V600 (R~950); 1.5h Int.;

3800-6700 A. CALIFA First Runs (June-July 2009): 21 objects:

A) V500 (R~890); 45m int: 3700-7100 A.

B) V1200 (R~1850); 1.5h int: 3500-4100A. R at 5000 A

Results (III): Science

Diversity of the observed galaxies: Different colors, magnitudes, morphologies, gas content… a photograph of the Local Universe!

Resolved properties of the stellar populations. Stellar Kinematics. Properties of the Ionized gas. All included in the First Article (in prep.)

3D Spectroscopy Summary

• IFS is a common user technique (40% of the observations done with the 3.5m at CAHA, 80% of one of the UT/VLT).

• Many of proposed or new generations instruments are IFUs (MUSE, MEGARA).

• JWST will include an IFU.• There is science that can only be done with

IFUs.• Any future astronomer should be prepared

to use it.