WFC3 slitless spectroscopy Harald Kuntschner Martin Kümmel, Jeremy Walsh (ST-ECF) Howard Bushouse (STScI) Grism Workshop, STScI November 15, 2010

WFC3 Filter wheels with WFC3 grisms UV Channel IR Channel

WFC3 Filters and Grisms UV channel IR channel

WFC3 grism parameters WFC3 Data Handbook version 2.1 (Cycle 18) IR FoV: 123” x 136” at 0.13”/pix UVIS FoV: 163” x 162” at 0.04”/pix

The science spectra are extracted G102 - Flux std GD153 0th order +1st order +2nd order lkjdsfklj F098M G102 R≈210 The science spectra are extracted from the +1st order

The science spectra are extracted G141 - Flux std GD153 0th order +1st order +2nd order +3rd order F140W G141 R≈130 The science spectra are extracted from the +1st order

The science spectra are extracted Which one is it actually? G280 – Wavelength std WR14 F300X G280 R≈70 The science spectra are extracted from the +1st order Which one is it actually?

UVIS G280 grism – star WR14 4096 pix G280 grism image +1st +2nd +3rd +4th -1st -2nd 0th Complex overlapping by many orders – very strong 0th order Trace and dispersion solution show complex variation across FoV

Extracting real WFC3 IR grism data in the CDFS 4 grism exposures – total of ~4200 seconds ~ 500 spectra per grism can be extracted F098M drizzled image G102 single grism Straughn et al. 2010, AJ, in press; arXiv:1005.3071

Registration Target position – grism spectrum Superimposed direct + grism image The position of the target (reference point) sets the full geometry of the spectral extraction No shifts between direct and grism image! Need for direct image when re-acquiring guide star Reference point: Xref, Yref

WFC3 grism calibrations Throughput of the instrument Traces as function of 2D position Wavelength solution as function of 2D position Global background … The calibrations are an integral part of the aXe software

WFC3 IR grism total throughput Peak 41% at 1100nm; >10% for 805 – 1150 nm Peak: 48% at 1450nm; >10% for 1080 -1690 nm 1st order 1st order +2nd order <=4% +2nd order <=7%

G102 trace & wavelength calibration Target: Planetary Nebula HB12 Many other (point) sources provide nice 2D trace coverage GOAL: ~0.1 pix accuracy for all calibrations Full WFC3 IR FoV

Field-dependent trace: G102 Roughly linear traces Significant variation of offset and slope with field position Accuracy of trace: <0.2 pix ST-ECF ISR WFC3-2009-17 ST-ECF ISR WFC3-2009-18 Reference: Xref, Yref

G102 wavelength calibration PN Vy2-2

G102: 2-dim dispersion calibration Wavelength Zeropoint Dispersion Roughly linear disp. solution; accuracy: <0.25 pixel G102: Dispersion varies from 23.6 – 25.1 Å/pixel over FoV G141: Dispersion varies from 45.0 – 47.7 Å/pixel over FoV

Master sky background High S/N master skies created from >100 publicly available WFC3 grism observ. Average flux levels vary: G102 = 0.4 – 1.6 e/s; G141 = 0.9 – 2.4 e/s Significant large scale structure as well as localized detector effects Significant improvement of spectral extraction G141 Master sky Before Subtraction of scaled global sky After Kümmel et al. , ISR in prep.

WFC3 IR grism sensitivity Limiting magnitudes for 1h exposure, average background and S/N=5 in the continuum Emission line sources have been detected down to m(F140W)AB ≈ 24.5 in 2 orbits WFC3 IR grism Magnitude G102 JAB = 22.6 G141 HAB = 22.9 See e.g. van Dokkum & Brammer 2010, ApJ, 718, 73 (two objects from ERS dataset) Atek et al. 2010, ApJ, 723, 104 (WISP survey) Straughn et al. 2010, AJ, in press; arXiv:1005.3071 (ERS dataset)

Extracting spectra with aXe See next talk by Martin Kümmel Extracting spectra with aXe Using a semi-automatic software (aXe) The software is already successfully being used for ACS + NICMOS grisms since 2003 Direct image position is reference point (wavelength zero-point) Need for field dependent trace, dispersion and flat-field calibration Extraction of source spectra and conversion to flux scale and uniform dispersion

Conclusions IR grisms show high sensitivity and are well calibrated UVIS G280 shows complex overlapping and calibration for survey-use is very challenging aXe software provides semi-automatic means of extracting several 100 source spectra taking into account cross-contamination of sources All calibration and reference files published on the Web http://www.stecf.org/instruments/WFC3grism/

The Tutorial and the Cookbook Harald Kuntschner Martin Kümmel, Jeremy Walsh Grism Workshop, STScI November 15, 2010

Aims Practical example of a typical slitless data reduction with aXe Challenge conception of “difficult slitless spectroscopy” Explain main aXe concepts and applications Provide some tips and tricks Warning about common pitfalls

Did you install the software? The Cookbook Did you install the software? IRAF version 2.14 STSDAS 3.12 with aXe aXe 2.1 aXeSIM 1.4 aXe2web 1.2 Step-by-step guide through a G141 grism data-reduction Using the STSDAS PYRAF environment aXe software package Reduce (aXe) Visualize (aXe2web) Simulate (aXeSIM) Data: WFC3 Early Release Science (ERS) II campaign (PID: 11359, PI: R. O’Connell) G141 observations in CDFS

The data

Extracting real WFC3 IR grism data in the CDFS 4 grism exposures – total of ~4200 seconds ~ 500 spectra per grism can be extracted F098M drizzled image G102 single grism Straughn et al. 2010, AJ, in press; arXiv:1005.3071

The reduction process

Example instructions from Cookbook

Tuesday, 9:00: Feedback session Cookbook Feedback Please let us know what you liked about the cookbook … did not like … Errors …? What is missing …? What else do you need to carry out your science? Tuesday, 9:00: Feedback session

aXe data reduction aXe source list co-added direct image direct images MultiDrizzle iolprep aXe data reduction Input Object Lists grism images direct images co-added direct image SExtractor axeprep Configuration & calibration files axecore source list drzprep manual modification axeprep aXe source list grism stamp images 1D spectra

Visualization browsable html-pages co-added direct image aXe source list grism stamp images 1D spectra aXe2web browsable html-pages

‘Helper’ slides for tutorial

Object Naming BEAMS and spectral orders 0th order +1st order +2nd order +3rd order BEAM_1B BEAM_1A BEAM_1C BEAM_1D Object number from SExtractor catalogue e.g. BEAM_234A, BEAM_415A Configuration file: BEAM A

Contamination Direct F140W image New Sources G141 Grism 0th order -1st order +1st order +2nd order +1st order +2nd order +3rd order G141 Grism

aXe configuration and reference files Type WFC3.IR.G141.V1.0.conf Configuration file (instrument setup) WFC3.IR.G141.1st.sens.1.fits Throughput for +1st order WFC3.IR.G141.1st.sens.2.fits Throughput for +2nd order … WFC3.IR.G141.flat.fits Flat-field cube WFC3.IR.G141.sky.V1.0.fits Master sky-background

aXe data reduction aXe source list co-added direct image direct images MultiDrizzle iolprep aXe data reduction Input Object Lists grism images direct images co-added direct image SExtractor axeprep Configuration & calibration files axecore source list drzprep manual modification axeprep aXe source list grism stamp images 1D spectra

Visualization browsable html-pages co-added direct image aXe source list grism stamp images 1D spectra aXe2web browsable html-pages

Output file types .SPC.fits .STP.fits .MEF.fits Extracted 1-dim spectra Multi extension binary FITS tables .STP.fits Extracted and rectified 2-dim spectra Multi extension FITS images Restricted usage and information .MEF.fits Extracted and fully rectified (drizzled) 2-dim spectra Full spatial and wavelength coordinate system Auxiliary info on errors, contamination …

Multi ext. binary FITS tables SPC.fits Multi ext. binary FITS tables 1-dim spectra

Restricted use – only meant for quick display and visualization STP.fits DS9 display of “BEAM_237A” Multi ext. FITS images 2-dim spectra Restricted use – only meant for quick display and visualization NOT FOR SCIENCE!

MEF.fits FITS images Fully calibrated 2-dim spectra “SIENCE READY” SCI CON “SIENCE READY”

Predicted source traces Contamination image ib6o23s0q_flt_2.CONT.fits A typical 1000s exposure in G141 is “full” of traces WFC3/G141 goes very deep!

Visualization How to look at ~500 spectra? aXe2web offers a convenient way to get an overview

Simulations Useful for Proposal preparation (Phase 1) Phase 2 submission Post observation verification Detection limits Emission line limits