skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Submillimetre galaxies in two massive protoclusters at z  = 2.24: witnessing the enrichment of extreme starbursts in the outskirts of HAE density peaks
Title: Submillimetre galaxies in two massive protoclusters at z  = 2.24: witnessing the enrichment of extreme starbursts in the outskirts of HAE density peaks
ABSTRACT Submillimetre galaxies represent a rapid growth phase of both star formation and massive galaxies. Mapping SMGs in galaxy protoclusters provides key insights into where and how these extreme starbursts take place in connections with the assembly of the large-scale structure in the early Universe. We search for SMGs at 850 $$\rm{\mu m}$$ using JCMT/SCUBA-2 in two massive protoclusters at z = 2.24, BOSS1244 and BOSS1542, and detect 43 and 54 sources with S850 > 4 mJy at the 4σ level within an effective area of 264 arcmin2, respectively. We construct the intrinsic number counts and find that the abundance of SMGs is 2.0 ± 0.3 and 2.1 ± 0.2 times that of the general fields, confirming that BOSS1244 and BOSS1542 contain a higher fraction of dusty galaxies with strongly enhanced star formation. The volume densities of the SMGs are estimated to be ∼15–30 times the average, significantly higher than the overdensity factor (∼6) traced by H α emission-line galaxies (HAEs). More importantly, we discover a prominent offset between the spatial distributions of the two populations in these two protoclusters – SMGs are mostly located around the high-density regions of HAEs, and few are seen inside these regions. This finding may have revealed for the first time the occurrence of violent star formation enhancement in the outskirts of the HAE density peaks, likely driven by the boosting of gas supplies and/or starburst triggering events. Meanwhile, the lack of SMGs inside the most overdense regions at z ∼ 2 implies a transition to the environment disfavouring extreme starbursts.  more » « less
Award ID(s):
1908284
PAR ID:
10381311
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more » ; « less
Date Published:
Journal Name:
Monthly Notices of the Royal Astronomical Society
Volume:
512
Issue:
4
ISSN:
0035-8711
Page Range / eLocation ID:
4893 to 4908
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT Simulations predict that the galaxy populations inhabiting protoclusters may contribute considerably to the total amount of stellar mass growth of galaxies in the early universe. In this study, we test these predictions observationally, using the Taralay protocluster (formerly PCl J1001+0220) at z ∼ 4.57 in the COSMOS field. With the Charting Cluster Construction with VUDS and ORELSE (C3VO) survey, we spectroscopically confirmed 44 galaxies within the adopted redshift range of the protocluster (4.48 < z < 4.64) and incorporate an additional 18 galaxies from ancillary spectroscopic surveys. Using a density mapping technique, we estimate the total mass of Taralay to be ∼1.7 × 1015 M⊙, sufficient to form a massive cluster by the present day. By comparing the star formation rate density (SFRD) within the protocluster (SFRDpc) to that of the coeval field (SFRDfield), we find that SFRDpc surpasses the SFRDfield by Δlog (SFRD/M⊙yr−1 Mpc−3) = 1.08 ± 0.32 (or ∼12 ×). The observed contribution fraction of protoclusters to the cosmic SFRD adopting Taralay as a proxy for typical protoclusters is $$33.5~{{\ \rm per\ cent}}^{+8.0~{{\ \rm per\ cent}}}_{-4.3~{{\ \rm per\ cent}}}$$, a value ∼2σ higher than the predictions from simulations. Taralay contains three peaks that are 5σ above the average density at these redshifts. Their SFRD is ∼0.5 dex higher than the value derived for the overall protocluster. We show that 68 per cent of all star formation in the protocluster takes place within these peaks, and that the innermost regions of the peaks encase $$\sim 50~{{\ \rm per\ cent}}$$ of the total star formation in the protocluster. This study strongly suggests that protoclusters drive stellar mass growth in the early universe and that this growth may proceed in an inside-out manner. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, Monthly Notices of the Royal Astronomical Society)
    ABSTRACT Submillimetre galaxies (SMGs) are some of the most extreme star-forming systems in the Universe, whose place in the framework of galaxy evolution is as yet uncertain. It has been hypothesized that SMGs are progenitors of local early-type galaxies, requiring that SMGs generally reside in galaxy cluster progenitors at high redshift. We test this hypothesis and explore SMG environments using a narrow-band VLT/HAWK-I+GRAAL study of H $$\alpha$$ and [O iii] emitters around an unbiased sample of three ALMA-identified and spectroscopically confirmed SMGs at $$z \sim 2.3$$ and $$\sim 3.3$$, where these SMGs were selected solely on spectroscopic redshift. Comparing with blank-field observations at similar epochs, we find that one of the three SMGs lies in an overdensity of emission-line sources on the $$\sim 4$$ Mpc scale of the HAWK-I field of view, with overdensity parameter $$\delta _{g} = 2.6^{+1.4}_{-1.2}$$. A second SMG is significantly overdense only on $$\lesssim 1.6$$ Mpc scales and the final SMG is consistent with residing in a blank field environment. The total masses of the two overdensities are estimated to be $$\log (M_{h}/{\rm M}_{\odot }) =$$ 12.1–14.4, leading to present-day masses of $$\log (M_{h,z=0}/{\rm M}_{\odot }) =$$ 12.9–15.9. These results imply that SMGs occupy a range of environments, from overdense protoclusters or protogroups to the blank field, suggesting that while some SMGs are strong candidates for the progenitors of massive elliptical galaxies in clusters, this may not be their only possible evolutionary pathway. 
    more » « less
  3. ; ; ; ; ; ; ; ; ; ; et al (, Monthly Notices of the Royal Astronomical Society)
    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. 
    more » « less
  4. ; ; ; ; ; ; ; ; ; ; et al (, Monthly Notices of the Royal Astronomical Society)
    null (Ed.)
    ABSTRACT We present Gemini-S and Spitzer-IRAC optical-through-near-IR observations in the field of the SPT2349-56 proto-cluster at z = 4.3. We detect optical/IR counterparts for only 9 of the 14 submillimetre galaxies (SMGs) previously identified by ALMA in the core of SPT2349-56. In addition, we detect four z ∼ 4 Lyman-break galaxies (LBGs) in the 30 arcsec-diameter region surrounding this proto-cluster core. Three of the four LBGs are new systems, while one appears to be a counterpart of one of the nine observed SMGs. We identify a candidate brightest cluster galaxy (BCG) with a stellar mass of $$(3.2^{+2.3}_{-1.4})\times 10^{11}$$ M⊙. The stellar masses of the eight other SMGs place them on, above, and below the main sequence of star formation at z ≈ 4.5. The cumulative stellar mass for the SPT2349-56 core is at least (12.2 ± 2.8) × 1011 M⊙, a sizeable fraction of the stellar mass in local BCGs, and close to the universal baryon fraction (0.19) relative to the virial mass of the core (1013 M⊙). As all 14 of these SMGs are destined to quickly merge, we conclude that the proto-cluster core has already developed a significant stellar mass at this early stage, comparable to z = 1 BCGs. Importantly, we also find that the SPT2349-56 core structure would be difficult to uncover in optical surveys, with none of the ALMA sources being easily identifiable or constrained through g, r, and i colour selection in deep optical surveys and only a modest overdensity of LBGs over the more extended structure. SPT2349-56 therefore represents a truly dust-obscured phase of a massive cluster core under formation. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; (, Astronomy & Astrophysics)
    Context.Large-scale environment is one of the main physical drivers of galaxy evolution. The densest regions at high redshifts (i.e.z > 2 protoclusters) are gas-rich regions characterised by high star formation activity. The same physical properties that enhance star formation in protoclusters are also thought to boost the growth of supermassive black holes (SMBHs), most likely in heavily obscured conditions. Aims.We aim to test this scenario by probing the active galactic nucleus (AGN) content of SPT2349–56: a massive, gas-rich, and highly star-forming protocluster core atz = 4.3 discovered as an overdensity of dusty star-forming galaxies (DSFGs). We compare our results with data on the field environment and other protoclusters. Methods.We observed SPT2349–56 withChandra(200 ks) and searched for X-ray emission from the known galaxy members. We also performed a spectral energy distribution fitting procedure to derive the physical properties of the discovered AGNs. Results.In the X-ray band, we detected two protocluster members: C1 and C6, corresponding to an AGN fraction among DSFGs in the structure of ≈10%. This value is consistent with other protoclusters atz  =  2 − 4, but higher than the AGN incidence among DSFGs in the field environment. Both AGNs are heavily obscured sources, hosted in star-forming galaxies with ≈3 × 1010 M⊙stellar masses. We estimate that the intergalactic medium in the host galaxies contributes to a significant fraction (or even entirely) to the nuclear obscuration. In particular, C1 is a highly luminous (LX = 2 × 1045 erg s−1) and Compton-thick (NH = 2 × 1024 cm−2) AGN, likely powered by aMBH > 6 × 108 M⊙SMBH, assuming Eddington-limited accretion. Its high accretion rate suggests that it is in the phase of efficient growth that is generally required to explain the presence of extremely massive SMBHs in the centres of local galaxy clusters. Considering SPT2349–56 and DRC, a similar protocuster atz = 4, and under different assumptions on their volumes, we find that gas-rich protocluster cores atz ≈ 4 enhance the triggering of luminous (logLX/erg s−1 = 45 − 46) AGNs by three to five orders of magnitude with respect to the predictions from the AGN X-ray luminosity function at a similar redshift in the field environment. We note that this result is not solely driven by the overdensity of the galaxy population in the structures. Conclusions.Our results indicate that gas-rich protoclusters at high redshift boost the growth of SMBHs, which will likely impact the subsequent evolution of the structures. Therefore, they stand as key science targets to obtain a complete understanding of the relation between the environment and galaxy evolution. Dedicated investigations of similar protoclusters are required to definitively confirm this conclusion with a higher statistical significance. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email