An official website of the United States government
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.
more »
« less
Precisely measuring the cosmic reionization history from IGM damping wings towards quasars
ABSTRACT We introduce a new approach for analysing the intergalactic medium (IGM) damping wings imprinted on the proximity zones of quasars in the epoch of reionization (EoR). Whereas past work has typically forgone the additional constraining power afforded by the blue side continuum ($$\lambda \lesssim 1280\,$$ Å) and/or opted not to model the large correlated IGM transmission fluctuations in the proximity zone ($$\lambda \lesssim 1216\,$$ Å), we construct a generative probabilistic model for the entire spectrum accounting for all sources of error – the stochasticity induced by patchy reionization, the impact of the quasar’s ionizing radiation on the IGM, the unknown intrinsic spectrum of the quasar, and spectral noise. This principled Bayesian method allows us to marginalize out nuisance parameters associated with the quasar’s radiation and its unknown intrinsic spectrum to precisely measure the IGM neutral fraction, $$\langle x_{\rm H\,\small{I}}\rangle$$. A key element of our analysis is the use of dimensionality reduction (DR) to describe the intrinsic quasar spectrum via a small number of nuisance parameters. Using a large sample of 15 559 SDSS/BOSS quasars at $$z \gtrsim 2.15$$ we trained and quantified the performance of six distinct DR methods, and find that a six parameter principal component analysis model (five coefficients plus a normalization) performs best, with complex machine-learning approaches providing no advantage. By conducting statistical inference on 100 realistic mock EoR quasar spectra, we demonstrate the reliability of the credibility contours that we obtain on $$\langle x_{\rm H\,{\small{I}}}\rangle$$ and the quasar lifetime, $$t_{\rm Q}$$. The new method introduced here will transform IGM damping wings into a precision probe of reionization, on the same solid methodological and statistical footing as other precision cosmological measurements.
more »
« less
- Award ID(s):
- 2307180
- PAR ID:
- 10586980
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 539
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 2621-2653
- Size(s):
- p. 2621-2653
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
ABSTRACT Recent quasar absorption line observations suggest that reionization may end as late as $$z \approx 5.3$$. As a means to search for large neutral hydrogen islands at $$z\ \lt\ 6$$, we revisit long dark gaps in the Ly $$\beta$$ forest in Very Large Telescope/X-Shooter and Keck/Echellette Spectrograph and Imager quasar spectra. We stack the Ly $$\alpha$$ forest corresponding to both edges of these Ly $$\beta$$ dark gaps and identify a damping wing-like extended absorption profile. The average redshift of the stacked forest is $z=5.8$. By comparing these observations with reionization simulations, we infer that such a damping wing-like feature can be naturally explained if these gaps are at least partially created by neutral islands. Conversely, simulated dark gaps lacking neutral hydrogen struggle to replicate the observed damping wing features. Furthermore, this damping wing-like profile implies that the volume-averaged neutral hydrogen fraction must be $$\langle x_{\rm H\,{\small {I}}} \rangle \ge 6.1 \pm 3.9~{{\ \rm per\ cent}}$$ at $z = 5.8$. Our results offer robust evidence that reionization extends below $z=6$.more » « less
-
ABSTRACT We measure the mean free path ($$\lambda _{\rm mfp,H\, \small {I}}$$), photoionization rate ($$\langle \Gamma _{\rm H\, \small {I}} \rangle$$), and neutral fraction ($$\langle f_{\rm H\, \small {I}} \rangle$$) of hydrogen in 12 redshift bins at 4.85 < z < 6.05 from a large sample of moderate resolution XShooter and ESI QSO absorption spectra. The fluctuations in ionizing radiation field are modelled by post-processing simulations from the Sherwood suite using our new code ‘EXtended reionization based on the Code for Ionization and Temperature Evolution’ (ex-cite). ex-cite uses efficient Octree summation for computing intergalactic medium attenuation and can generate large number of high resolution $$\Gamma _{\rm H\, \small {I}}$$ fluctuation models. Our simulation with ex-cite shows remarkable agreement with simulations performed with the radiative transfer code Aton and can recover the simulated parameters within 1σ uncertainty. We measure the three parameters by forward-modelling the Lyα forest and comparing the effective optical depth ($$\tau _{\rm eff, H\, \small {I}}$$) distribution in simulations and observations. The final uncertainties in our measured parameters account for the uncertainties due to thermal parameters, modelling parameters, observational systematics, and cosmic variance. Our best-fitting parameters show significant evolution with redshift such that $$\lambda _{\rm mfp,H\, \small {I}}$$ and $$\langle f_{\rm H\, \small {I}} \rangle$$ decreases and increases by a factor ∼6 and ∼104, respectively from z ∼ 5 to z ∼ 6. By comparing our $$\lambda _{\rm mfp,H\, \small {I}}$$, $$\langle \Gamma _{\rm H\, \small {I}} \rangle$$ and $$\langle f_{\rm H\, \small {I}} \rangle$$ evolution with that in state-of-the-art Aton radiative transfer simulations and the Thesan and CoDa-III simulations, we find that our best-fitting parameter evolution is consistent with a model in which reionization completes by z ∼ 5.2. Our best-fitting model that matches the $$\tau _{\rm eff, H\, \small {I}}$$ distribution also reproduces the dark gap length distribution and transmission spike height distribution suggesting robustness and accuracy of our measured parameters.more » « less
-
ABSTRACT Proximity zones of high-redshift quasars are unique probes of their central supermassive black holes as well as the intergalactic medium (IGM) in the last stages of reionization. We present 22 new measurements of proximity zones of quasars with redshifts between 5.8 and 6.6, using the enlarged XQR-30 sample of high-resolution, high-SNR quasar spectra. The quasars in our sample have ultraviolet magnitudes of M1450 ∼ −27 and black hole masses of 109–1010 M⊙. Our inferred proximity zone sizes are 2–7 physical Mpc, with a typical uncertainty of less than 0.5 physical Mpc, which, for the first time, also includes uncertainty in the quasar continuum. We find that the correlation between proximity zone sizes and the quasar redshift, luminosity, or black hole mass, indicates a large diversity of quasar lifetimes. Two of our proximity zone sizes are exceptionally small. The spectrum of one of these quasars, with z = 6.02, displays, unusually for this redshift, damping wing absorption without any detectable metal lines, which could potentially originate from the IGM. The other quasar has a high-ionization absorber ∼0.5 pMpc from the edge of the proximity zone. This work increases the number of proximity zone measurements available in the last stages of cosmic reionization to 87. This data will lead to better constraints on quasar lifetimes and obscuration fractions at high redshift, that in turn will help probe the seed mass and formation redshift of supermassive black holes.more » « less
-
ABSTRACT The attenuation of Lyα photons by neutral hydrogen in the intergalactic medium (IGM) at z ≳ 5 continues to be a powerful probe for studying the epoch of reionization. Given a framework to estimate the intrinsic (true) Lyα emission of high-z sources, one can infer the ionization state of the IGM during reionization. In this work, we use the enlarged XQR-30 sample of 42 high-resolution and high signal-to-noise quasar spectra between $$5.8\lesssim \, z\lesssim \, 6.6$$ obtained with VLT/X-shooter to place constraints on the IGM neutral fraction. This is achieved using our existing Bayesian QSO reconstruction framework which accounts for uncertainties such as the: (i) posterior distribution of predicted intrinsic Lyα emission profiles (obtained via covariance matrix reconstruction of the Lyα and N v emission lines from unattenuated high-ionization emission line profiles; C iv, Si iv + O iv], and C iii]) and (ii) distribution of ionized regions within the IGM using synthetic damping wing profiles drawn from a 1.63 Gpc3 reionization simulation. Following careful quality control, we used 23 of the 42 available QSOs to obtain constraints/limits on the IGM neutral fraction during the tail-end of reionization. Our median and 68th percentile constraints on the IGM neutral fraction are: $$0.20\substack{+0.14 -0.12}$$ and $$0.29\substack{+0.14 -0.13}$$ at z = 6.15 and 6.35. Further, we also report 68th percentile upper limits of $$\bar{x}_{\mathrm{H\, {\small I}}{}} \lt 0.21$$, 0.20, 0.21, and 0.18 at z = 5.8, 5.95, 6.05, and 6.55. These results imply reionization is still ongoing at $$5.8\lesssim \, z\lesssim \, 6.55$$, consistent with previous results from XQR-30 (dark fraction and Lyα forest) along with other observational probes considered in the literature.more » « less
