Revealing the hidden cosmic feast: A

Springer Link (Chiba Institute of Technology)

Abstract

We present the confirmation of a compact galaxy group candidate, CGG-z4, at z = 4.3 in the COSMOS field. This structure was identified by two spectroscopically confirmed z = 4.3 Ks-dropout galaxies with ALMA 870 μm and 3 mm continuum detections, surrounded by an overdensity of near infrared-detected galaxies with consistent photometric redshifts of 4.0 < z < 4.6. The two ALMA sources, CGG-z4.a and CGG-z4.b, have been detected with both CO(4–3) and CO(5–4) lines, whereby [CI](1–0) has been detected on CGG-z4.a, and H2O(11, 0–10, 1) absorption detected on CGG-z4.b. We modeled an integrated spectral energy distribution (SED) by combining the far-infrared-to-radio photometry of this group and estimated a total star formation rate of ∼2000 M⊙ yr−1, making it one of the most star-forming groups known at z > 4. Their high CO(5–4)/CO(4–3) ratios indicate that each respective interstellar medium (ISM) is close to thermalization, suggesting either high gas temperatures, high densities, and/or high pressure; whereas the low [CI](1–0)/CO(4–3) line ratios indicate high star formation efficiencies. With the [CI]-derived gas masses, we found the two galaxies have extremely short gas depletion times of 99 Myr and < 63 Myr, respectively, suggesting the onset of quenching. With an estimated halo mass of log(Mhalo [M⊙]) ∼ 12.8, we find that this structure is likely to be in the process of forming a massive galaxy cluster.

Authors 14

1. Malte Brinch
2. Shuowen Jin

   DTU Space · Technical University of Denmark

   Affiliation as printed

   Cosmic Dawn Center (DAWN) , Copenhagen , Denmark

   DTU Space , Technical University of Denmark , Elektrovej 327 , 2800 Kgs. Lyngby , Denmark

3. Raphael Gobat

   Pontificia Universidad Católica de Valparaíso

   Affiliation as printed

   Instituto de Física , Pontificia Universidad Católica de Valparaíso , Casilla 4059 , Valparaíso , Chile

4. Nikolaj B. Sillassen

   DTU Space · Technical University of Denmark

   Affiliation as printed

   Cosmic Dawn Center (DAWN) , Copenhagen , Denmark

   DTU Space , Technical University of Denmark , Elektrovej 327 , 2800 Kgs. Lyngby , Denmark

5. Hiddo Algera
6. Steven Gillman

   DTU Space · Technical University of Denmark

   Affiliation as printed

   Cosmic Dawn Center (DAWN) , Copenhagen , Denmark

   DTU Space , Technical University of Denmark , Elektrovej 327 , 2800 Kgs. Lyngby , Denmark

7. T. R. Greve

   DTU Space · Technical University of Denmark

   Affiliation as printed

   Cosmic Dawn Center (DAWN) , Copenhagen , Denmark

   DTU Space , Technical University of Denmark , Elektrovej 327 , 2800 Kgs. Lyngby , Denmark

8. Carlos Gómez-Guijarro

   Centre National de la Recherche Scientifique · Commissariat à l'Énergie Atomique et aux Énergies Alternatives · Université Paris-Saclay · Astrophysique, Instrumentation et Modélisation · Sorbonne Paris Cité · Université Paris Diderot

   Affiliation as printed

   AIM , CEA , CNRS , Université Paris-Saclay , Université Paris Diderot , Sorbonne Paris Cité 91191 , Gif-sur-Yvette , France

9. B. Gullberg

   DTU Space · Technical University of Denmark

   Affiliation as printed

   Cosmic Dawn Center (DAWN) , Copenhagen , Denmark

   DTU Space , Technical University of Denmark , Elektrovej 327 , 2800 Kgs. Lyngby , Denmark

10. Jacqueline Hodge Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory , Leiden University , NL-2300 RA Leiden , The Netherlands

11. Minju Lee

    DTU Space · Technical University of Denmark

    Affiliation as printed

    Cosmic Dawn Center (DAWN) , Copenhagen , Denmark

    DTU Space , Technical University of Denmark , Elektrovej 327 , 2800 Kgs. Lyngby , Denmark

12. DaiZhong Liu

    Chinese Academy of Sciences · Purple Mountain Observatory

    Affiliation as printed

    Purple Mountain Observatory , Chinese Academy of Sciences , 10 Yuanhua Road , Nanjing 210023 , China

13. G. Magdis
14. Francesco Valentino

    European Southern Observatory

    Affiliation as printed

    Cosmic Dawn Center (DAWN) , Copenhagen , Denmark

    European Southern Observatory , Karl-Schwarzschild-Str. 2 , 85748 Garching , Germany