Integral Field Spectroscopy Sarah Brough AAO Integral Field

Integral Field Spectroscopy Sarah Brough (AAO)

Integral Field Spectroscopy What is an Integral Field Spectrograph? What can I study with an IFS? What kinds of IFS are there? How do I prepare IFS observations How do I reduce/view/analyse my data?

Integral Field Spectroscopy What is an Integral Field Spectrograph? What can I study with an IFS? What kinds of IFS are there? How do I prepare IFS observations How do I reduce/view/analyse my data?

What is an Integral Field Spectrograph? An IFS is an instrument that allows you to gather optical/NIR spectra over a two-dimensional field-of-view. The final product is a data-cube, with axes of RA, Dec and wavelength. DEC RA Wavelength Credit: Stephen Todd (ROE) and Douglas Pierce-Price (JAC)

Integral Field Spectroscopy What is an Integral Field Spectrograph? What can I study with an IFS? What kinds of IFS are there? How do I prepare IFS observations How do I reduce/view/analyse my data?

What can I study with an IFS? Any astronomical object where you require spatially resolved spectroscopic information is ideally suited for study with IFS. Where shocks occur Where star formation occurs Where dust is Rotation measures Angular momentum Where the oldest stars are Where the most metal rich stars and gas are • Dynamical mass measurements • •

Galaxy Winds: Emission-line integrated flux maps generated by single Gaussian fitting to individual spectra Line ratio maps Classic ionization diagnostic diagrams, starburst vs AGN excited vs shockexcitation – Sharp & Hawthorn (2010) *Also Fogarty+(2012), Ho+(2014, 2016)*

Where Star Formation occurs: Map of flux under Hα Emission Line, i. e. star formation. Brough et al. (2013) *Also Schaefer et al. (in prep)*

Whether galaxies are disc- or merger-dominated? Wiggle. Z Survey, z~1 Wisnioski et al. 2011 SINS survey, z~2 Förster Schreiber, et al. 2009 *Also Green et al. (2014) – DYNAMO, z~0. 1*

Stellar Rotation Stellar velocity across galaxy from cross-correlation to stellar templates (Brough et al. , 2011) Rotating

Projected stellar angular momentum l. R = < R|V| > / < R sqrt(V 2 + s 2) >, is a proxy for the observed projected stellar angular momentum per unit mass. Early-type galaxies are separated into slow and fast rotators, depending on their l. Re and ellipticity ATLAS 3 D Survey; Emsellem et al. (2011) *Also Jimmy+2013, Fogarty et al. (2014, 2015), van de Sande et al. (in prep)

Galaxy star formation histories: Mc. Dermid et al. (2015). * Also Scott et al. (in prep)

Where the oldest and most metal-rich stars are: SAURON sample. Stellar ages, metallicities and alpha-enhancements from singlestellar population models. Radial profiles are averaged along isophotes (Kuntchner et al. 2010). *Also Oliva-Altamirano et al. (2015)

Integral Field Spectroscopy What is an Integral Field Spectrograph? What can I study with an IFS? What kinds of IFS are there? How do I prepare IFS observations How do I reduce/view/analyse my data?

What kinds of IFS are there? An integral field spectrograph consists of two components: the spectrograph and an integral field unit (IFU). The job of the IFU is to divide the 2 D spatial plane into a continuous array. This division can be achieved in three ways: Credit: M. Westmoquette, adapted from Allington-Smith et al. 1998

Lenslet array The input image is split up by a microlens array (MLA). Light from each element of your observed object is concentrated into a small dot and dispersed by the spectrograph. Dots are small so that the spectra do not fall on top of each other, allowing the input image to be sampled contiguously. The disadvantage is that the length of spectrum that can be produced without overlapping is very small and the packing of the CCD is not efficient. Examples: VLT FLAMES(GIRAFFE)-IFU, Keck OSIRIS, WHT SAURON

Fibres (with/without lenslets) A 2 D bundle of optical fibres transfer the light to the slit of the spectrograph. Fibre flexibility allows the round/rectangular field-of-view to be reformatted into one (or more) "slits", from where the light is directed to the spectrograph. The spectra are obtained without wavelength shifts between them. Placing an array of contiguous lenslets in front of the fibre bundle to focus light into the fibre improves these IFUs as lenslets can be packed contiguously. Microlenses also slow the telescope focal beam so that FRD can be minimised. Examples, without lenslets: WHT Integral; WIYN Sparse. Pak with lenslets: AAOmega KOALA/SAMI; Gemini GMOS-IFU; VLT VIMOS

Image-slicer Datacube The input image is formed on a mirror that is segmented in thin horizontal sections, sending each 'slice' in different directions. A second segmented mirror is arranged to reformat the slices so that, instead of being above each other they are now laid out end to form the slit of the spectrograph. FRD is avoided and the slicing arrangement gives contiguous coverage of the field at potentially high spatial resolution. Examples: ANU 2. 3 m Wi. Fe. S; Gemini NIFS; VLT SINFONI/MUSE

Fabry-Pérots (tunable filters) Fabry-Pérot imaging spectrographs are different from what is usually meant by integral field spectroscopy, but the result is still a data-cube. Fabry-Pérots allow a large Fo. V (e. g. 5 arcmin) to be surveyed at high spatial resolution (e. g. 0. 3 arcmin/pixel) in a single exposure but only at a single wavelength — the required data volume (x, y, λ) is built up by scanning through the desired wavelength range. Time-inefficient and difficult to perform accurate flatfielding and flux calibration of the data.

Integral Field Spectroscopy What is an Integral Field Spectrograph? What can I study with an IFS? What kinds of IFS are there? How do I prepare IFS observations How do I reduce/view/analyse my data?

How do I prepare observations with an IFS? What are you looking at? What FOV/spatial and spectral resolution/wavelength coverage do you need? (http: //ifs. wikidot. com/instruments) Choose your IFS based on these (and the availability to you). Use ETC to calculate exposure times to get the S/N you need. Think about the calibration observations you will need (obviously bias/flat/arc, probably twilight flats for throughput correction, and spectro-photometric standard stars for flux calibration) Prepare finding charts: label your target, add the chart scale (about 5'x 5’) & indicate N&E, then print it out in b&w Think about vignetting and bad fibres and centering/dithering your target to avoid these issues.

Vignetted Footprint of VLT VIMOS-IFU in high-resolution mode -> 20*20 fibres * 4 quadrants

Integral Field Spectroscopy What is an Integral Field Spectrograph? What can I study with an IFS? What kinds of IFS are there? How do I prepare IFS observations How do I reduce/view/analyse my data?

How do I reduce these data? Basic Reduction Steps (reduce each observation separately): FYI: Your data will probably arrive as Raw Stacked Spectra (RSS) NOT a cube Create master bias by averaging bias frames TRACE the spectra. Create master spectroscopic flat by tracing spectra in flat field Create master lamp by subtracting bias & normalising by the flat arc frames. (Can wavelength calibrate from sky lines but not ideal) Subtract bias, and divide image by flat field (which also notes spectra positions) Extract 1 D spectra from 2 D image: Apply wavelength calibration and remove cosmic rays. Can check wavelength calibration with sky lines – see how much peak varies in wavelength from spectrum to spectrum and frame to frame. These processes are easily done within 2 dfdr for AAOmega data. For VLT VIMOS-IFU data using vipgi it’s a hands-on point and click exercise including flagging bad fibres! P 3 D is another open source software for these tasks.

IFS Specific Reduction: Some of these steps are possible within packages. I used IDL or python Take each observation (per quadrant if relevant and per observation): create a variance array for each spectrum (trust me, you want to know about your noise) Inverse gain = X electrons/ADU Variance = √(e-)/gain = √(count*gain)/gain = √(count/gain) + Read. Out. Noise scale for different fibre transmissions subtract sky Make into a cube Combine quadrants (if relevant) into 1 cube using known pixel mapping. If observations are dithered by integer spaxel offsets then combine spectra by known RA, DEC offset and scale for the relative throughput and noise of each observation. If dithered by part-spaxel shifts then you will need to resample your spectra into the new cube (See Sharp et al. 2015).

Reduced Data: Spectrum In central spaxel Image is RA x Dec. Each spaxel is summed along the wavelength direction.

How do I view these data At most of these points you’re going to want to look at your data, to see what it looks like. I used to plot parts of the spectrum from IDL or for later, science plots and map values (e. g. intensity/velocity dispersion) using SAURON plot_spaxels and plot_bins IDL code. PINGSoft is a series of IDL routines including basic tools to visualize spatially and spectrally the IFS data, to extract regions of interest by hand or within a given geometric aperture, to integrate the spectra within a given region, to read, edit and write RSS FITS files, and to perform simple analyses to the IFS data I am currently moving to Python. This is probably better.

How do I analyse these data? Depends on what you are interested in! Example 1. Galaxy Stellar Kinematics http: //www-astro. physics. ox. ac. uk/~mxc/software/: Voronoi 2 d tesselation: bins pixels to up a defined signal-tonoise (which you’ll need to calculate across your cube) PPXF: which fits stellar templates to calculate velocities at each spaxel. Emission lines can be excluded. SAURON PLOT_BIN: makes pretty colour plots of velocities I developed my own IDL script to calculate Lambda parameter. For SAMI analysis see van de Sande et al. (in prep).

Example 2. Galaxy Emission Lines LZIFU software fits emission lines (Ho et al. ) Fit the emission lines you’re interested in at each spaxel. You want to know their width, height, central wavelength and flux. With these information you can plot intensity and velocity maps of lines. You can also calculate emission line ratios and look at dust and ratio maps. You can plot the line ratio intensities on IDD and determine locations of shocks etc.

The FUTURE is HERE! SAMI (Sydney AAO MOS IFU) 13 deployable “hexabundle” fibres – 61 x 1. 6” fibres per bundle and ~14” per bundle across 1 deg field http: //sami-survey. org/