Search for: All records

ABSTRACT We present optical and near-infrared (NIR) spectroscopic observations for a sample of 45 quasars at $$6.50 < z \le 7.64$$ with absolute magnitudes at 1450 Å in the range $$-28.82 \le M_{1450} \le -24.13$$ and their composite spectrum. The median redshift and $$M_{1450}$$ of the quasars in the sample are $$z_{\rm {median}}=6.71$$ and $$M_{1450,\rm {median}} \simeq -26.1$$, respectively. The NIR spectra are taken with Echelle spectrographs, complemented with additional data from optical long slit instruments, and then reduced consistently using the open-source Python-based spectroscopic data reduction pipeline PypeIt. The median of the mean signal-to-noise ratios per 110 km s$$^{-1}$$ pixel in the J, H, and K band [median $$\langle \rm {SNR}_{\lambda } \rangle$$] is median $$\langle \rm {SNR}_{J} \rangle =9.7$$, median $$\langle \rm {SNR}_{H} \rangle =10.3$$, and median $$\langle \rm {SNR}_{K} \rangle =11.7$$; demonstrating the good data quality. This work presents the largest medium-/moderate-resolution sample of quasars at $z>6.5$ from ground-based instruments. Despite the diversity in instrumental set-ups and spectral quality, the data set is uniformly processed and well-characterized, making it ideally suited for several scientific goals, including the study of the quasar proximity zones and damping wings, the Ly $$\alpha$$ forest, the intergalactic medium’s metal content, as well as other properties such as the distribution of SMBH masses and Eddington ratios. Our composite spectrum is compared to others at both high and low z from the literature, showing differences in the strengths of many emission lines, probably due to differences in luminosity among the samples, but a consistent continuum slope, which proves that the same spectral features are preserved in quasars at different redshift ranges. 

Abstract We present in this paper (Paper II of the series) a 35 arcmin²JWST/NIRCam imaging and wide-field slitless spectroscopy mosaic centered on J0305–3150, a luminous quasar atz= 6.61. The F356W grism data reveal 124 [Oiii]+Hβemitters at 5.3 < z < 7, 53 of which constitute a protocluster spanning (10 cMpc)²across 6.5 < z < 6.8. We find no evidence of any broad-line active galactic nucleus (AGN) in individual galaxies or stacking, reporting a median HβFWHM of 585 ± 152 km s⁻¹; however, the mass–excitation diagram and “little red dot” color and compactness criteria suggest that there are a few AGN candidates on the outskirts of the protocluster. We fit the spectral energy distributions (SEDs) of the [Oiii] emitters withProspectorandBagpipesand find that none of the SED-derived properties (stellar mass, age, or star formation rate) correlate with proximity to the quasar. While there is no correlation between galaxy age and local galaxy density, we find modest correlations of local galaxy density with increasing stellar mass, decreasing 10–100 Myr star formation rate ratios, and decreasing nebular line equivalent widths. We further find that the protocluster galaxies are consistent with being more massive, being older, and hosting higher star formation rates than the field sample at the 3σlevel, distributed in a filamentary structure that supports inside-out formation of the protocluster. There is modest evidence that galaxy evolution proceeds differently as a function of the density of local environment within protoclusters during the epoch of reionization, and the central quasar has little effect on the galaxy properties of the surrounding structure. 

Abstract A SPectroscopic survey of bIased halos in the Reionization Era is a quasar legacy survey primarily using JWST to target a sample of 25z > 6 quasars with NIRCam slitless spectroscopy and imaging. The first study in this series found evidence of a strong overdensity of galaxies around J0305−3150, a luminous quasar atz= 6.61, within a single NIRCam pointing obtained in JWST Cycle 1. Here we present the first results of a JWST Cycle 2 mosaic that covers 35 arcmin²with NIRCam imaging/wide-field slitless spectroscopy of the same field to investigate the spatial extent of the putative protocluster. The F356W grism data target [Oiii]+Hβat 5.3 < z < 7 and reveal a population of 124 line emitters down to a flux limit of 1.2 × 10⁻¹⁸erg s⁻¹cm⁻². Fifty-three of these galaxies lie at 6.5 < z < 6.8 spanning 10 cMpc on the sky, corresponding to an overdensity within a 2500 cMpc³volume of 12.5 ± 2.6, anchored by the quasar. Comparing to the [Oiii] luminosity function from the Emission line galaxies and Intergalactic Gas in the Epoch of Reionization project, we find a dearth of faint [Oiii] emitters at log(L/erg s⁻¹) < 42.3, which we suggest is consistent with either bursty star formation causing galaxies to scatter around the grism detection limit or modest suppression from quasar feedback. While we find a strong filamentary overdensity of [Oiii] emitters consistent with a protocluster, we suggest that we could be insensitive to a population of older, more massive Lyman break galaxies with weak nebular emission on scales >​​​​​​10 cMpc. 

Abstract Theoretical models predict thatz≳ 6 quasars are hosted in the most massive halos of the underlying dark matter distribution and thus would be immersed in protoclusters of galaxies. However, observations report inconclusive results. We investigate the 1.1 proper-Mpc²environment of thez= 7.54 luminous quasar ULAS J1342+0928. We search for Lyman-break galaxy (LBG) candidates using deep imaging from the Hubble Space Telescope (HST) in the Advanced Camera for Surveys (ACS)/F814W, Wide Field Camera 3 (WFC3)/F105W/F125W bands, and Spitzer/Infrared Array Camera at 3.6 and 4.5μm. We report a $z_{\mathrm{phot}}={7.69}_{-0.23}^{+0.33}$LBG with mag_F125W= 26.41 at 223 projected proper kpc (pkpc) from the quasar. We find no HST counterpart to one [Cii] emitter previously found with the Atacama Large millimeter/submillimeter Array (ALMA) at 27 projected pkpc andz_{[C II]}=7.5341 ± 0.0009 (Venemans et al. 2020). We estimate the completeness of our LBG candidates using results from Cosmic Assembly Near-Infrared Deep Extragalactic Legacy Survey/GOODS deep blank field searches sharing a similar filter setup. We find that >50% of thez∼ 7.5 Lyman-break galaxies (LBGs) with mag_F125W> 25.5 are missed due to the absence of a filter redward of the Lyman break in F105W, hindering the UV color accuracy of the candidates. We conduct a QSO-LBG clustering analysis revealing a low LBG excess of ${0.46}_{-0.08}^{+1.52}$in this quasar field, consistent with an average or low-density field. Consequently, this result does not present strong evidence of an LBG overdensity around ULAS J1342+0928. Furthermore, we identify two LBG candidates with az_photmatching a confirmedz= 6.84 absorber along the line of sight to the quasar. All these galaxy candidates are excellent targets for follow-up observations with JWST and/or ALMA to confirm their redshift and physical properties. 

ABSTRACT We present the high-z quasar candidate archive (HzQCA), summarizing the spectroscopic observations of 207 z ≳ 5 quasar candidates using Keck/LRIS, Keck/MOSFIRE, and Keck/NIRES. We identify 14 candidates as z ∼ 6 quasars, with 10 of them newly reported here and 63 candidates as brown dwarfs. In the remaining sources, 79 candidates are unlikely to be quasars; 2 sources are inconclusive; the others could not be fully reduced or extracted. Based on the classifications, we investigate the distributions of quasars and contaminants in colour space with photometry measurements from DELS (z), VIKING/UKIDSS (YJHKs/YJHK), and unWISE (W1W2). We find that the identified brown dwarfs are consistent with the empirical brown dwarf model that is commonly used in quasar candidate selection methods. To refine spectroscopic confirmation strategies, we simulate synthetic spectroscopy of high-z quasars and contaminants for all three instruments. The simulations utilize the spectroscopic data in HzQCA. We predict the required exposure times for quasar confirmation and propose an optimal strategy for spectroscopic follow-up observations. For instance, we demonstrate that we can identify a mJ = 21.5 at z = 7.6 or a mJ = 23.0 at z = 7.0 within 15 min of exposure time with LRIS. With the publication of the HzQCA, we aim to provide guidance for future quasar surveys and candidate classification. 

Abstract The variations in Lyαforest opacity observed atz> 5.3 between lines of sight to different background quasars are too strong to be caused by fluctuations in the density field alone. The leading hypothesis for the cause of this excess variance is a late, ongoing reionization process at redshifts below six. Another model proposes strong ionizing background fluctuations coupled to a short, spatially varying mean free path of ionizing photons, without explicitly invoking incomplete reionization. With recent observations suggesting a short mean free path atz∼ 6, and a dramatic improvement inz> 5 Lyαforest data quality, we revisit this latter possibility. Here, we apply the likelihood-free inference technique of approximate Bayesian computation (ABC) to jointly constrain the hydrogen photoionization rate Γ_HIand the mean free path of ionizing photonsλ_mfpfrom the effective optical depth distributions atz= 5.0–6.1 from XQR-30. We find that the observations are well-described by fluctuating mean free path models with average mean free paths that are consistent with the steep trend implied by independent measurements atz∼ 5–6, with a concomitant rapid evolution of the photoionization rate. 

Abstract Low-luminosity active galactic nuclei (AGNs) with low-mass black holes (BHs) in the early universe are fundamental to understanding the BH growth and their coevolution with the host galaxies. Utilizing JWST NIRCam Wide Field Slitless Spectroscopy, we perform a systematic search for broad-line Hαemitters (BHAEs) atz≈ 4–5 in 25 fields of the A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) project, covering a total area of 275 arcmin². We identify 16 BHAEs with FWHM of the broad components spanning from ∼1000 to 3000 km s⁻¹. Assuming that the broad line widths arise as a result of Doppler broadening around BHs, the implied BH masses range from 10⁷to 10⁸M_⊙, with broad Hα-converted bolometric luminosities of 10^44.5–10^45.5erg s⁻¹and Eddington ratios of 0.07–0.47. The spatially extended structure of the F200W stacked image may trace the stellar light from the host galaxies. The Hαluminosity function indicates an increasing AGN fraction toward the higher Hαluminosities. We find possible evidence for clustering of BHAEs: two sources are at the same redshift with a projected separation of 519 kpc; one BHAE appears as a composite system residing in an overdense region with three close companion Hαemitters. Three BHAEs exhibit blueshifted absorption troughs indicative of the presence of high column density gas. We find that the broad-line-selected and photometrically selected BHAE samples exhibit different distributions in the optical continuum slopes, which can be attributed to their different selection methods. The ASPIRE broad-line Hαsample provides a good database for future studies of faint AGN populations at high redshift. 

Abstract The formation of the first supermassive black holes is expected to have occurred in some most pronounced matter and galaxy overdensities in the early universe. We have conducted a submillimeter wavelength continuum survey of 54z∼ 6 quasars using the Submillimeter Common-User Bolometre Array-2 on the James Clerk Maxwell Telescope to study the environments aroundz∼ 6 quasars. We identified 170 submillimeter galaxies (SMGs) with above 3.5σdetections in 450 or 850μm maps. Their far-IR luminosities are (2.2–6.4) × 10¹²L_⊙, and their star formation rates are ∼400–1200M_⊙yr⁻¹. We also calculated the SMGs’ differential and cumulative number counts in a combined area of ∼620 arcmin². To a 4σdetection (at ∼5.5 mJy), SMGs’ overdensity is ${0.68}_{-0.19}^{+0.21}$(±0.19), exceeding the blank-field source counts by a factor of 1.68. We find that 13/54 quasars show overdensities (at ∼5.5 mJy) ofδ_SMG∼ 1.5–5.4. The combined area of these 13 quasars exceeds the blank-field counts with the overdensity to 5.5 mJy ofδ_SMG∼ ${2.46}_{-0.55}^{+0.64}$(±0.25) in the regions of ∼150 arcmin². However, the excess is insignificant on the bright end (e.g., 7.5 mJy). We also compare results with previous environmental studies of Lyαemitters and Lyman break galaxies on a similar scale. Our survey presents the first systematic study of the environment of quasars atz∼ 6. The newly discovered SMGs provide essential candidates for follow-up spectroscopic observations to test whether they reside in the same large-scale structures as the quasars and search for protoclusters at an early epoch. 

Abstract The [Cii] 158μm emission line and the underlying far-infrared (FIR) dust continuum are important tracers for studying star formation and kinematic properties of early galaxies. We present a survey of the [Cii] emission lines and FIR continua of 31 luminous quasars atz> 6.5 using the Atacama Large Millimeter Array (ALMA) and the NOrthern Extended Millimeter Array at sub-arcsec resolution. This survey more than doubles the number of quasars with [Cii] and FIR observations at these redshifts and enables statistical studies of quasar host galaxies deep into the epoch of reionization. We detect [Cii] emission in 27 quasar hosts with a luminosity range ofL_[CII]= (0.3–5.5) × 10⁹L_⊙and detect the FIR continuum of 28 quasar hosts with a luminosity range ofL_FIR= (0.5–13.0) × 10¹²L_⊙. BothL_[CII]andL_FIRare correlated (ρ≃ 0.4) with the quasar bolometric luminosity, albeit with substantial scatter. The quasar hosts detected by ALMA are clearly resolved with a median diameter of ∼5 kpc. About 40% of the quasar host galaxies show a velocity gradient in [Cii] emission, while the rest show either dispersion-dominated or disturbed kinematics. Basic estimates of the dynamical masses of the rotation-dominated host galaxies yieldM_dyn= (0.1–7.5) × 10¹¹M_⊙. Considering our findings alongside those of literature studies, we found that the ratio betweenM_BHandM_dynis about 10 times higher than that of localM_BH–M_dynrelation on average but with substantial scatter (the ratio difference ranging from ∼0.6 to 60) and large uncertainties. 

We present JWST/NIRSpec integral field data of the quasar PJ308-21 atz = 6.2342. As shown by previous ALMA and HST imaging, the quasar has two companion sources, interacting with the quasar host galaxy. The high-resolution G395H/290LP NIRSpec spectrum covers the 2.87 − 5.27 μm wavelength range and shows the rest-frame optical emission of the quasar with exquisite quality (signal-to-noise ratio ∼100 − 400 per spectral element). Based on the Hβline from the broad line region, we obtain an estimate of the black hole massM_BH, Hβ ∼ 2.7 × 10⁹ M_⊙. This value is within a factor ≲1.5 of the Hα-based black hole mass from the same spectrum (M_BH, Hα ∼ 1.93 × 10⁹ M_⊙) and is consistent with a previous estimate relying on the Mg IIλ2799 line (M_BH, MgII ∼ 2.65 × 10⁹ M_⊙). All theseM_BHestimates are within the ∼0.5 dex intrinsic scatter of the adopted mass calibrations. The high Eddington ratio of PJ308-21λ_Edd, Hβ ∼ 0.67 (λ_Edd, Hα ∼ 0.96) is in line with the overall quasar population atz ≳ 6. The relative strengths of the [O III], Fe II, and Hβlines are consistent with the empirical “Eigenvector 1” correlations as observed for low redshift quasars. We find evidence for blueshifted [O III]λ5007 emission with a velocity offset Δv_{[O III]} = −1922 ± 39 km s⁻¹from the systemic velocity and a full width at half maximum (FWHM)FWHM([O III]) = 2776₋₇₄⁺⁷⁵km s⁻¹. This may be the signature of outflowing gas from the nuclear region, despite the true values of Δv_{[O III]}andFWHM([O III]) likely being more uncertain due to the blending with Hβand Fe IIlines. Our study demonstrates the unique capabilities of NIRSpec in capturing quasar spectra at cosmic dawn and studying their properties in unprecedented detail.