A SPectroscopic Survey of Biased Halos in the Reionization Era (ASPIRE): JWST Reveals a Filamentary Structure around a z = 6.61 Quasar

Abstract

We present the first results from the JWST program A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE). This program represents an imaging and spectroscopic survey of 25 reionization-era quasars and their environments by utilizing the unprecedented capabilities of NIRCam Wide Field Slitless Spectroscopy (WFSS) mode. ASPIRE will deliver the largest ( ∼ 280 arcmin 2 ) galaxy redshift survey at 3–4 μm among JWST Cycle 1 programs and provide extensive legacy values for studying the formation of the earliest supermassive black holes, the assembly of galaxies, early metal enrichment, and cosmic reionization. In this first ASPIRE paper, we report the discovery of a filamentary structure traced by the luminous quasar J0305–3150 and 10 [O iii] emitters at z = 6.6. This structure has a 3D galaxy overdensity of δ gal = 12.6 over 637 cMpc3, one of the most overdense structures known in the early universe, and could eventually evolve into a massive galaxy cluster. Together with existing VLT/MUSE and ALMA observations of this field, our JWST observations reveal that J0305–3150 traces a complex environment where both UV-bright and dusty galaxies are present and indicate that the early evolution of galaxies around the quasar is not simultaneous. In addition, we discovered 31 [O iii] emitters in this field at other redshifts, 5.3 < z < 6.7, with half of them situated at z ∼ 5.4 and 6.2. This indicates that star-forming galaxies, such as [O iii] emitters, are generally clustered at high redshifts. These discoveries demonstrate the unparalleled redshift survey capabilities of NIRCam WFSS and the potential of the full ASPIRE survey data set.

A Mixture of LBG Overdensities in the Fields of Three 6 < z < 7 Quasars: Implications for the Robustness of Photometric Selection

“…On the other hand, Farina et al (2017) found one faint LAE companion within the arcminute field of view of MUSE, separated by 12 kpc (2″) and assumed to be undergoing a merger with the quasar host galaxy; this companion is detected with S/N = 2 in H 160 in these data, thus it was not included in our LBG list. Similarly, the overdensity reported by Wang et al (2023) shows an enhancement of bright [O III] emitters with f [O III] >5.0 × 10 −18 erg s −1 cm −2 within 10″ from the quasar, which had faint but visible counterparts in the HST data that did not meet our H 160 detection criteria. In a Subaru Suprime-Cam survey in the J0305 field, Ota et al (2018) also noted a dearth of faint LAEs and LBGs given their 50% completeness limit of m = 26.…”

“…J0305-3150, at z = 6.6, hosts the strongest overdensity in the sample with 42 LBGs, corresponding to δ gal = 8.8 ± 1.8. In a companion paper, Wang et al (2023) show a spectroscopically confirmed overdensity of [O III] emitters, 13 of which correspond to LBGs reported in this paper. Its coordinated parallel field shows a significant 3σ overdensity, which could be consistent with being part of the same structure.…”

“…We find that the strongest overdensity signal is when we center the search on z = 6.2, where the median z phot = 6.16. Here, we find a total of 49 LBGs, with 8 sources being unique from our reported J0305 QSO sample (3 of which are also reported as [O III] emitters in Wang et al 2023), yielding an overdensity δ gal = 10.9 ± 2.0. Given the uncertainties in photometric redshifts, 8 the strong 2D clustering of this filament could indicate association with the quasar or a separate overdensity along the line of sight.…”

“…Finally, Wang et al (2023) show a spectroscopic δ gal ∼ 13 overdensity of Hβ+[O III] emitters identified with JWST/ NIRCam WFSS; they find 41 galaxies at z > 5.4, 13 of which are within Δz = 0.03 from the quasar. Of these 41, 15 fall out of the WFC3 footprint and 7 are too faint to have visible counterparts in the HST data because the JWST data find the faintest [O III] emitters at 2 × 10 −18 erg s −1 cm −2 (Wang et al 2023).…”

“…Finally, Wang et al (2023) show a spectroscopic δ gal ∼ 13 overdensity of Hβ+[O III] emitters identified with JWST/ NIRCam WFSS; they find 41 galaxies at z > 5.4, 13 of which are within Δz = 0.03 from the quasar. Of these 41, 15 fall out of the WFC3 footprint and 7 are too faint to have visible counterparts in the HST data because the JWST data find the faintest [O III] emitters at 2 × 10 −18 erg s −1 cm −2 (Wang et al 2023). Thirteen [O III] sources are matched to 10 LBGs with 6 < z phot < 6.8 in this work (IDs 267 and 823 are resolved into three and two components, respectively, but were included in one Kron aperture in this work), all of which agree spectroscopically within 1σ of the best-fit EAZY redshift (2σ for the aforementioned blended sources).…”