Wide-Field Slitless Spectr scopy with NIRISS

Van DixonSTScI

TIPS/JIM2012 September 20

TIPS/JIM2012 September 20

NIRISS at a Glance

Parameter ValueArray Size 2048 x 2048 (2040 x 2040 active)

Pixel size 18 μm x 18 μm

Dark rate < 0.02 e-/s

Noise 23 e- (correlated double sample)

Gain 1.5 e-/ADU

Field of View 2.2’ x 2.2’

Plate scale in x 0.0654 arcsec/pixel

Plate scale in y 0.0658 arcsec/pixel

TIPS/JIM2012 September 20

Dual-Wheel Configuration

GR150R GR150C

TIPS/JIM2012 September 20

Dual-Wheel Configuration

GR150R GR150C

GR150C GR150R

TIPS/JIM2012 September 20

Blaze Function for GR150 Grisms

TIPS/JIM2012 September 20

First-Order Sensitivity: Emission LinesMinimum line flux to reach S/N = 10 in 10 ks

TIPS/JIM2012 September 20

First-Order Sensitivity: Emission Lines

z = 9 z = 17

Redshifted Lyman α

TIPS/JIM2012 September 20

The Software

The aXe software package was developed to support slitless spectroscopy with ACS and WFC3 (Kümmel et al. 2009).

aXeSIM generates synthetic direct and dispersed images of the sky.aXe extracts and calibrates spectra.

aXedrizzle allows for the combination of dithered images.aXe2web displays the extracted spectra in a convenient HTML format.

aXe was originally developed by the Space Telescope - European Coordinating Facility (ST-ECF). The code is now supported by STScI.

Source Extractor builds a catalog of objects from an astronomical image (Bertin & Arnouts 1996).

TIPS/JIM2012 September 20

Input for aXeSIM Configuration file

• Location, trace, and dispersion of each spectral order Sensitivity (including grating)

• e- per erg/cm2 Throughput (w/out grating; used to make direct image) Flat Field (may be wavelength-dependent) Master Sky Background Image Input Catalog (output from Source Extractor)

• Specify image size and shape or point to image file Postage-stamp images Spectra

TIPS/JIM2012 September 20

Location of Each Order (F150W)

-1 0 +1 +2 +3

-601 -512 -227 0 53 148 336 520 619 893

Direct Image

2040 pixels

1.03 1.3 1.7 (μm)

TIPS/JIM2012 September 20

Model Object Table

# 1 NUMBER Object number# 2 X_IMAGE X coordinate (pixels)# 3 Y_IMAGE Y coordinate (pixels)# 4 A_IMAGE Length of semi-major axis (pixels)# 5 B_IMAGE Length of semi-minor axis (pixels)# 6 THETA_IMAGE Angle of major axis# 7 MAG_F1537 Magnitude at 1537 nm (WFC3 F160W) # 8 SPECTEMP Key to spectral template# 9 Z Redshift# 10 MODIMAGE Key to model image 1 900.00 1500.00 0.6 0.6 0.0 22.5 0 0.0 0 2 900.00 1250.00 30.0 10.0 45.0 18.0 0 0.0 0 3 900.00 1000.00 18.0 10.0 -30.0 18.0 1 0.0 1 4 900.00 750.00 5.0 2.0 60.0 18.0 2 0.0 0 5 900.00 700.00 5.0 2.0 60.0 18.0 2 0.075 0 6 900.00 650.00 5.0 2.0 60.0 18.0 2 0.15 0 7 900.00 600.00 5.0 2.0 60.0 18.0 2 0.22 0

x y a b θ mag sp z image

TIPS/JIM2012 September 20

Dispersed Image (log stretch)

-1 0 +1 +2 +3

2040 pixels

TIPS/JIM2012 September 20

Millennium Run Observatory

H-band image using the WFC3/F160W bandpassOverzier et al. 2012 (MNRAS, in press)

Semi-analytic galaxy-formation models based on the Millennium Run dark-matter simulations

TIPS/JIM2012 September 20

Direct Image w/ NIRISS PSF

TIPS/JIM2012 September 20

Direct Image w/ Background (100 s)

TIPS/JIM2012 September 20

Source Extractor Apertures

TIPS/JIM2012 September 20

Dispersed Image: Horizontal

TIPS/JIM2012 September 20

Dispersed Image: Vertical

TIPS/JIM2012 September 20

aXe2web