Protoclusters, the progenitors of galaxy clusters, trace large scale structures in the early Universe and are important to our understanding of structure formation and galaxy evolution. To date, only a handful of protoclusters have been identified in the Epoch of Reionization. As one of the rarest populations in the early Universe, distant quasars that host active supermassive black holes are thought to reside in the most massive dark matter halos at that cosmic epoch and could thus potentially pinpoint some of the earliest protoclusters. In this Letter, we report the discovery of a massive protocluster around a luminous quasar at
We report the discovery of MAGAZ3NE J095924+022537, a spectroscopically confirmed protocluster at
- Award ID(s):
- 1815475
- NSF-PAR ID:
- 10362694
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 926
- Issue:
- 1
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 37
- Size(s):
- ["Article No. 37"]
- Sponsoring Org:
- National Science Foundation
More Like this
-
Abstract z = 6.63. This protocluster is anchored by the quasar and includes three [Cii ] emitters atz ∼ 6.63, 12 spectroscopically confirmed Lyα emitters (LAEs) at 6.54 <z ≤ 6.64, and a large number of narrow-band-imaging selected LAE candidates at the same redshift. This structure has an overall overdensity of within ∼35 × 74 cMpc2on the sky and an extreme overdensity ofδ > 30 in its central region (i.e.,R ≲ 2 cMpc). We estimate that this protocluster will collapse into a galaxy cluster with a mass of at the current epoch, more massive than the most massive clusters known in the local Universe such as Coma. In the quasar vicinity, we discover a double-peaked LAE, which implies that the quasar has a UV lifetime greater than 0.8 Myrs and has already ionized its surrounding intergalactic medium. -
Abstract We measure the CO-to-H2conversion factor (
α CO) in 37 galaxies at 2 kpc resolution, using the dust surface density inferred from far-infrared emission as a tracer of the gas surface density and assuming a constant dust-to-metal ratio. In total, we have ∼790 and ∼610 independent measurements ofα COfor CO (2–1) and (1–0), respectively. The mean values forα CO (2–1)andα CO (1–0)are and , respectively. The CO-intensity-weighted mean is 5.69 forα CO (2–1)and 3.33 forα CO (1–0). We examine howα COscales with several physical quantities, e.g., the star formation rate (SFR), stellar mass, and dust-mass-weighted average interstellar radiation field strength ( ). Among them, , ΣSFR, and the integrated CO intensity (W CO) have the strongest anticorrelation with spatially resolvedα CO. We provide linear regression results toα COfor all quantities tested. At galaxy-integrated scales, we observe significant correlations betweenα COandW CO, metallicity, , and ΣSFR. We also find thatα COin each galaxy decreases with the stellar mass surface density (Σ⋆) in high-surface-density regions (Σ⋆≥ 100M ⊙pc−2), following the power-law relations and . The power-law index is insensitive to the assumed dust-to-metal ratio. We interpret the decrease inα COwith increasing Σ⋆as a result of higher velocity dispersion compared to isolated, self-gravitating clouds due to the additional gravitational force from stellar sources, which leads to the reduction inα CO. The decrease inα COat high Σ⋆is important for accurately assessing molecular gas content and star formation efficiency in the centers of galaxies, which bridge “Milky Way–like” to “starburst-like” conversion factors. -
Abstract We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲
z ≲ 2.6 (z mean= 2.30), all chosen independent of emission-line strength. These galaxies have a median stellar mass of and a median star formation rate of . We measure the faint electron-temperature-sensitive [Oiii ]λ 4363 emission line at 2.5σ (4.1σ ) significance when considering a bootstrapped (statistical-only) uncertainty spectrum. This yields a direct-method oxygen abundance of ( ). We investigate the applicability at highz of locally calibrated oxygen-based strong-line metallicity relations, finding that the local reference calibrations of Bian et al. best reproduce (≲0.12 dex) our composite metallicity at fixed strong-line ratio. At fixedM *, our composite is well represented by thez ∼ 2.3 direct-method stellar mass—gas-phase metallicity relation (MZR) of Sanders et al. When comparing to predicted MZRs from the IllustrisTNG and FIRE simulations, having recalculated our stellar masses with more realistic nonparametric star formation histories , we find excellent agreement with the FIRE MZR. Our composite is consistent with no metallicity evolution, at fixedM *and SFR, of the locally defined fundamental metallicity relation. We measure the doublet ratio [Oii ]λ 3729/[Oii ]λ 3726 = 1.56 ± 0.32 (1.51 ± 0.12) and a corresponding electron density of ( ) when considering the bootstrapped (statistical-only) error spectrum. This result suggests that lower-mass galaxies have lower densities than higher-mass galaxies atz ∼ 2. -
Abstract We present the
z ≈ 6 type-1 quasar luminosity function (QLF), based on the Pan-STARRS1 (PS1) quasar survey. The PS1 sample includes 125 quasars atz ≈ 5.7–6.2, with −28 ≲M 1450≲ −25. With the addition of 48 fainter quasars from the SHELLQs survey, we evaluate thez ≈ 6 QLF over −28 ≲M 1450≲ −22. Adopting a double power law with an exponential evolution of the quasar density (Φ(z ) ∝ 10k (z −6);k = −0.7), we use a maximum likelihood method to model our data. We find a break magnitude of , a faint-end slope of , and a steep bright-end slope of . Based on our new QLF model, we determine the quasar comoving spatial density atz ≈ 6 to be . In comparison with the literature, we find the quasar density to evolve with a constant value ofk ≈ −0.7, fromz ≈ 7 toz ≈ 4. Additionally, we derive an ionizing emissivity of , based on the QLF measurement. Given standard assumptions, and the recent measurement of the mean free path by Becker et al. atz ≈ 6, we calculate an Hi photoionizing rate of ΓH I(z = 6) ≈ 6 × 10−16s−1, strongly disfavoring a dominant role of quasars in hydrogen reionization. -
Abstract M dwarfs are common host stars to exoplanets but often lack atmospheric abundance measurements. Late-M dwarfs are also good analogs to the youngest substellar companions, which share similar
T eff∼ 2300–2800 K. We present atmospheric analyses for the M7.5 companion HIP 55507 B and its K6V primary star with Keck/KPIC high-resolution (R ∼ 35,000)K -band spectroscopy. First, by including KPIC relative radial velocities between the primary and secondary in the orbit fit, we improve the dynamical mass precision by 60% and find , putting HIP 55507 B above the stellar–substellar boundary. We also find that HIP 55507 B orbits its K6V primary star with au ande = 0.40 ± 0.04. From atmospheric retrievals of HIP 55507 B, we measure [C/H] = 0.24 ± 0.13, [O/H] = 0.15 ± 0.13, and C/O = 0.67 ± 0.04. Moreover, we strongly detect13CO (7.8σ significance) and tentatively detect (3.7σ significance) in the companion’s atmosphere and measure and after accounting for systematic errors. From a simplified retrieval analysis of HIP 55507 A, we measure and for the primary star. These results demonstrate that HIP 55507 A and B have consistent12C/13C and16O/18O to the <1σ level, as expected for a chemically homogeneous binary system. Given the similar flux ratios and separations between HIP 55507 AB and systems with young substellar companions, our results open the door to systematically measuring13CO and abundances in the atmospheres of substellar or even planetary-mass companions with similar spectral types.