NIRCam Deep Field Imaging with MIRI Imaging Parallels

 Example Science Program #22

This page outlines an example science program for deep field imaging with JWST NIRCam Imaging and MIRI Imaging in parallel. The overarching science goals are from the joint NIRCam and NIRSpec GTO program JADES (JWST Advanced Deep Extragalactic Survey). Here we describe the science motivation, followed by a Step-by-Step ETC Guide and Step-by-Step APT Guide to implement a portion of the JADES observing program using the Exposure Time Calculator Old and Astronomer's Proposal Tool.

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Science motivation

Main articles: JWST Parallel Observations
See also: Step-by-Step ETC Guide for NIRCam Deep Field Imaging with MIRI Imaging ParallelsStep-by-Step APT Guide for NIRCam Deep Field Imaging with MIRI Imaging Parallels

This example part of the JADES GTO program includes deep field imaging of the GOODS-S field (Figure 1). The goal is to study galaxy evolution from the first steps (> 10) through the end of the dark ages (7 < < 9) and through the epoch of galaxy assembly (2 < < 6).  Specific objectives include:

  • Construct luminosity functions at the highest redshifts to test galaxy formation models
  • Test ΛCDM by finding the highest redshift galaxies and estimating their masses
  • Determine the halo masses of these galaxies
  • Measure morphological parameters and assembly of stellar mass as a function of redshift
  • Measure metallicity as a function of redshift
  • Measure star formation histories
  • Look for surprises!

This example science program describes what data are required to achieve the program's objectives, including discussion of the required wavelengths, spatial resolution, sensitivity, and spatial coverage.

The Exposure Time Calculator (ETC) guide describes how to estimate the necessary imaging depth, and the Astronomer's Proposal Tool (APT) guide describes how to design the observation parameters. This program was presented as part of the JWST Proposal Planning Workshop at STScI in May 2017. Note that the program presented here is slightly different from the one presented at the workshop.

Step-by-Step Guide

Below we follow steps from the Imaging Roadmap to design an observing program. See also the General Proposal Planning Workflow.

Choose Instruments

Main articles: NIRCam ImagingMIRI Imaging
See also: NIRCam Imaging Recommended StrategiesMIRI Imaging Recommended Strategies

NIRCam Imaging (0.6–5.0 μm) is the primary observing mode for this program, with MIRI imaging (5.6–25.5 μm) in parallel.  The NIRCam observations will be deeper than the existing Hubble observations of GOODS-S and have superior spatial resolution at λ > 1 μm.  The MIRI sensitivity limits will be 10x those achieved with Spitzer and will have much better spatial resolution.

Check Feasibility

Main articles: NIRCam Imaging SensitivityMIRI Sensitivity

For general guidance on depth vs. exposure time, we refer to Imaging PerformanceNIRCam Imaging Sensitivity, and MIRI Sensitivity.  

For this program, we refer to calculations by Crowley et al. (2018).  Their simulations yielded expected number densities of galaxies at high redshifts, along with their detectability with NIRCam and MIRI imaging.  They determined that 167 square arcmin of NIRCam imaging with a depth of 100 ksec would yield 10 galaxies at z = 12.  A smaller NIRCam survey of 33 square arcmin at 10 ksec depth would yield 100 galaxies at z = 7.  Here, we choose to cover 25 square arcmin with NIRCam at 30–50 ksec depth.

Select Filters

Main articles: NIRCam FiltersMIRI Filters and Dispersers


To achieve maximum sensitivity, this program will use a combination of wide and medium NIRCam filters. Specifically, this program uses F090W, F115W, F150W, F200W, F277W, F356W, and F444W. F070W is not used because of its lower transmission. The medium filters used are F335M and F410M, which both overlap with a wide filter (F356W and F444W), helping to guard against emission lines in this wavelength region and providing additional redshift discrimination (Figure 2). The F410M filter is almost as sensitive as F444W, despite its narrower width, because the JWST background increases sharply at long wavelengths.

For the parallel images, this program uses only a single MIRI filter, F770W, to achieve sufficient depth.

Mosaic Strategy

Main article: JWST Mosaic Overview

The desired area (25 square arcmin) is larger than the NIRCam Field of View (~10 square arcmin).  We will use a 2 × 2 mosaic, as discussed in the accompanying APT Guide.

Dithering Strategy

Main article: NIRCam Primary DithersNIRCam Subpixel Dithers

Dithers are highly recommended for NIRCam imaging to protect against cosmic rays, improve the angular resolution, cover detector gaps, compensate for detector artifacts, and improve image quality. NIRCam is Nyquist sampled at 2 and 4 μm, so subpixel dithers are required for good spatial sampling for most of the wavelength coverage. Larger NIRCam dithers are also required to cover the detector gaps in the field of view (see below). MIRI is oversampled over most of its wavelength range and Nyquist sampled at F770W, so MIRI subpixel sampling is not required.  Dither patterns for this program are discussed in the APT Guide.

Calculate Required Exposure Times

The Step-by-Step ETC Guide shows how to use the Exposure Time Calculator (ETC) to determine exposure parameters appropriate for the science goals for this program.

Design the Observing Program

The Step-by-Step APT Guide demonstrates how to specify these observations in a JWST proposal using the Astronomer's Proposal Tool (APT).

Figure 1. The GOODS-S field

The GOODS-S field, with the coverage of the CANDELS footprint and ACS ultra-deep field (UDF) marked. The GTO program includes NIRCam, MIRI, and NIRSpec observations. This example science program describes the NIRCam and MIRI observations marked in red and pink, respectively. Note that this example program is similar to, but not exactly the same as, the GTO program.
Figure 2. Example galaxy spectrum

Example spectrum for a galaxy at redshift 8 and the estimated flux in several NIRCam filters. The red spectrum and red points exclude emission lines. Circles mark the expected sensitivities of the observations described here, while the diamonds mark the shallow survey, which is not included in this example.


References

Rieke, M. et al. 2019
Astro2020 Science White Paper: JWST GTO/ERS Deep Surveys

The JWST Advanced Extragalactic Survey (JADES)

Crowley, W, Baugh, C., Cole, S., Frenk, C., & Lacey, C., 2018, MNRAS, 474, 2352
Predictions for deep galaxy surveys with JWST from ΛCDM

CANDELS website

ACS Ultra Deep Field website

JWST Proposal Planning Workshop (May 2017) (See the "Agenda" tables for accompanying documents)




Published

 

Latest updates

  • Revisions include splitting ETC and APT guides into separate articles