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ABSTRACT Characterizing the structural properties of galaxies in high-redshift protoclusters is key to our understanding of the environmental effects on galaxy evolution in the early stages of galaxy and structure formation. In this study, we assess the structural properties of 85 and 87 Hα emission-line candidates (HAEs) in the densest regions of two massive protoclusters, BOSS1244 and BOSS1542, respectively, using the Hubble Space Telescope (HST) H-band imaging data. Our results show a true pair fraction of 22 ± 5 (33 ± 6) per cent in BOSS1244 (BOSS1542), which yields a merger rate of 0.41 ± 0.09 (0.52 ± 0.04) Gyr−1 for massive HAEs with log (M*/M⊙) ≥ 10.3. This rate is 1.8 (2.8) times higher than that of the general fields at the same epoch. Our sample of HAEs exhibits half-light radii and Sérsic indices that cover a broader range than field star-forming galaxies. Additionally, about 15 per cent of the HAEs are as compact as the most massive (log (M*/M⊙) ≳ 11) spheroid-dominated population. These results suggest that the high galaxy density and cold dynamical state (i.e. velocity dispersion of <400 km s−1) are key factors that drive galaxy mergers and promote structural evolution in the two protoclusters. Our findings also indicate that both the local environment (on group scales) and the global environment play essential roles in shaping galaxy morphologies in protoclusters. This is evident in the systematic differences observed in the structural properties of galaxies between BOSS1244 and BOSS1542.
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MAMMOTH: confirmation of two massive galaxy overdensities at z = 2.24 with Hα emitters
ABSTRACT Massive galaxy overdensities at the peak epoch of cosmic star formation provide ideal testbeds for the formation theories of galaxies and large-scale structure. We report the confirmation of two massive galaxy overdensities at z = 2.24, BOSS1244 and BOSS1542, selected from the Mapping the Most Massive Overdensities Through Hydrogen (MAMMOTH) project using Lyα absorption from the intergalactic medium over the scales of 15−30 h−1 Mpc imprinted on the quasar spectra. We use Hα emitters (HAEs) as the density tracer and identify them using deep narrow-band H2S(1) and broad-band Ks imaging data obtained with the wide-field infrared camera (WIRCam) at the Canada–France–Hawaii Telescope. In total, 244 and 223 line emitters are detected in these two fields, and 196 ± 2 and 175 ± 2 are expected to be HAEs with an Hα flux of >2.5 × 10−17 erg s−1 cm−2 (corresponding to a star formation rate of >5 M⊙ yr−1). The detection rate of HAE candidates suggests an overdensity factor of δgal = 5.6 ± 0.3 and 4.9 ± 0.3 over the volume of 54 × 32 × 32 co-moving Mpc3. The overdensity factor increases two to three times when focusing on the high-density regions of scales 10–15 co-moving Mpc. Interestingly, the HAE density maps reveal that BOSS1244 contains a dominant structure, while BOSS1542 manifests as a giant filamentary structure. We measure the Hα luminosity functions (HLFs), finding that BOSS1244’s HLF is nearly identical to that of the general field at the same epoch, while BOSS1542 shows an excess of HAEs with high Hα luminosity, indicating the presence of enhanced star formation or active galactic nuclei activity. We conclude that the two massive MAMMOTH overdensities are undergoing a rapid galaxy mass assembly.
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- Award ID(s):
- 1908284
- PAR ID:
- 10292624
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 500
- Issue:
- 4
- ISSN:
- 0035-8711
- Page Range / eLocation ID:
- 4354 to 4364
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1093/mnras/staa2882
