The Carousel Lens I: A Spectroscopic Survey of the Carousel Lens Field

TL;DR

This work leverages deep VLT/MUSE and Gemini/GMOS spectroscopy to exploit the Carousel lens as a multi-source-plane cluster for cosmography. By expanding the lensed-source catalog to 13 and assembling a 57-object redshift catalog (49 cluster members), the authors obtain a precise cluster velocity dispersion $\sigma_{\text{gal}} \approx 1.1\times10^{3}$ km s$^{-1}$ and a corresponding $M_{200c} \approx 1.2\times10^{15}$ M$_{\odot}$, while identifying four Ly$\alpha$ emitters with central images that strongly constrain the inner mass distribution. The combination of a simple lens mass model, numerous high-redshift sources, and central images enhances the potential of Carousel for constraining $w$ and $Ω_m$ via multi-source-plane cosmography, and the study highlights the value of deep infrared follow-up to further refine lens models and source positions.

Abstract

We present a spectroscopic survey of field galaxies and lensed sources in the vicinity of the strong lensing galaxy cluster known as the Carousel lens at z=0.49. Using both Gemini/GMOS slitmask spectra and deep VLT/MUSE observations, we bring the total number of lensed sources up to 13, including three which were not previously known from imaging observations but are apparent in the MUSE data as emission-line sources. Of these sources, 10 have confident redshifts, and an additional 2 have tentative redshifts from likely Ly$α$ emission (including seven new redshifts determined here adding to those presented previously in Sheu et al. (2024)). The lensed sources span a redshift range from z=0.96 to 4.09 with most of them showing 3-5 images, including four sources displaying central or radial images. In total, we identify 43 images of these 13 sources. This lens system is remarkably symmetric and well-modeled by a simpler lens model than typical cluster lenses, and the large number of sources and their large range of redshifts make this cluster ideal for constraining cosmological parameters such as $w$ and $Ω_m$ as well as the cluster density profile. Additionally, we present a catalog of 57 unlensed field galaxies with confident redshifts, of which 49 are associated with the cluster. We measure a cluster velocity dispersion of about 1100 km s$^{-1}$ from which we estimate a halo mass $M_{200c} \approx 1.2 \times 10^{15} M_\odot$.

Figures (10)

• Figure 1: Spectral FOV Comparison: A comparison of the fields-of-view of GMOS slitmasks and MUSE observations used in this work. The cyan region simply shows the size of the GMOS slitmask for scale, not the actual orientation used in our four masks. The compass arrows in the bottom-right are each 1.5' long.
• Figure 2: All Sources: All known lensed sources in the Carousel system, overlaid on HST imaging with color coding as follows. Magenta: Known sources with redshifts presented in Paper 0 Sheu.Cikota.ea2024; White: Previously known sources with redshifts presented in this work; Cyan: Newly discovered sources, with extended emission observed in MUSE data; Yellow: Sources which do not yet have confident redshifts. Sources 8, 11, 12, and 13 display contours of Ly$\alpha$ emission.
• Figure 3: Known sources: Spectra of sources previously identified in imaging data. Left: MUSE data, with regions of extracted spectra overlaid. Right: Extracted spectra of each lensed source, identifying spectral features and redshift. For clarity, the spectrum of each lensed image is offset vertically. For Source 7, we include the Early Type Galaxy MARZ template match in red. For source 9, we additionally show a GMOS spectrum of image 9a exhibiting a clear [O II] doublet. Wavelengths contaminated by poor sky subtraction are indicated in vertical gray bands.
• Figure 4: Lyman $\alpha$ Emitters: Spectra and newly reported redshifts of strongly-lensed LAEs discovered in MUSE data. Left Column: RGB image of the MUSE data, with regions used for each object overlaid. Right Column: Extracted spectra of each object. In each plot, the left panel shows Ly$\alpha$ emission visible in each image, offset and scaled for clarity. The right panels show the stacked spectrum of all images, demonstrating faint features. Grey shaded regions at the bottom show the uncertainty. Features labeled in green (purple) are expected in absorption (emission).
• Figure 5: Sources 12 and 13: The spatial distribution of Ly$\alpha$ emission from sources 12 and 13, with each image labeled.