SIMLA: The Spitzer Infrared Spectrograph Mapping Legacy Archive

TL;DR

SIMLA addresses the lack of ready-to-use Spitzer/IRS mapping-mode cubes by building a uniform, background-subtracted archive. It introduces a three-component background model—zodiacal emission, tailored baseline frames, and time-varying dark shard stacks—and integrates this with CUBISM to produce spectral cubes with quantified uncertainties. The approach is validated through dark-region spectra and cross-checks with WISE W3 photometry, confirming reliable flux scales down to the background floor. The results provide the community with a large, accessible set of MIR spectral cubes that contextualize JWST and enable detailed ISM and galaxy studies.

Abstract

We present the Spitzer/IRS Mapping Legacy Archive (SIMLA); a complete set of mid-infrared spectral cubes built from low-resolution mapping-mode fixed-target observations from Spitzer/IRS (5.2-38μm, R~60-130). Contained in this dataset are spectral maps for several hundred spatially-resolved and unresolved objects, including galaxies, molecular clouds, supernova remnants, HII regions, and more. Each cube has been carefully treated to remove astronomical foregrounds and backgrounds as well as detector effects using a novel pipeline we describe here. Cube assembly was facilitated by the CUBISM code, which included automatic detection and removal of bad pixels. We describe the SIMLA pipeline for reducing and validating the cubes. SIMLA will soon be available at the NASA/IPAC Infrared Science Archive.

Figures (17)

• Figure 1: The distribution of SIMLA maps on-sky. Red and blue squares indicate SL and LL cubes, respectively. The size of these markers do not represent the real fields of view, but are logarithmically scaled to the covered fields of view with an arbitrary scale factor applied to all. In this IRS sample, there is a total area on sky of 2.94 deg$^2$. The total unique area covered by SL is 0.9 deg$^2$ and by LL, 2.34 deg$^2$.
• Figure 2: Three-color images made using mosaics of SIMLA spectral cubes of the Eagle Nebula (top), the Antennae galaxies (bottom left), and the Cassiopeia A supernova remnant (bottom right). For each image, the pixel values of each color correspond to the slice of a SIMLA cube mosaic at the listed wavelength.
• Figure 3: Example spectra from SIMLA spectral cubes of the Galactic Hii region G43 (blue), the star-forming galaxy M101 (orange), the luminous infrared galaxy NGC 7469 (green), and the binary Herbig Ae stars PDS144 (red).
• Figure 4: Basic calibrated data (BCD) example images for Spitzer/IRS with major sections labeled. The left and right panels show BCDs for the short-low (SL) and long-low (LL) modules, respectively. For both, the red and blue sections highlight the wavesamp regions for the sub-slits within either module. The green sections are the "bonus orders" (SL3, LL3), on which light from the 2nd slit (SL2, LL2) is sampled within a wavelength range overlapping the red and blue ranges. BCDs for SL contain the light from the peak-up (PU) photometer arrays. Both of these BCDs are from pointings containing no bright sources and they have minimal zodiacal emission intensity. Note the spatially and spectrally-varying artifact in the SL BCD that persists throughout the spectral orders as well as into the inter-order region.
• Figure 5: Schematic of the SIMLA pipeline to produce a cube. Blue boxes indicate SIMLA intermediate products derived from more basic inputs shown as yellow rounded boxes. Green hexagons are operations. Note that most of the SIMLA pipeline is oriented towards producing backgrounds.