An official website of the United States government
Abstract The observed large-scale scatter in Ly α opacity of the intergalactic medium at z < 6 implies large fluctuations in the neutral hydrogen fraction that are unexpected long after reionization has ended. A number of models have emerged to explain these fluctuations that make testable predictions for the relationship between Ly α opacity and density. We present selections of z = 5.7 Ly α -emitting galaxies (LAEs) in the fields surrounding two highly opaque quasar sightlines with long Ly α troughs. The fields lie toward the z = 6.0 quasar ULAS J0148+0600, for which we reanalyze previously published results using improved photometric selection, and toward the z = 6.15 quasar SDSS J1250+3130, for which results are presented here for the first time. In both fields, we report a deficit of LAEs within 20 h −1 Mpc of the quasar. The association of highly opaque sightlines with galaxy underdensities in these two fields is consistent with models in which the scatter in Ly α opacity is driven by large-scale fluctuations in the ionizing UV background or by an ultra-late reionization that has not yet concluded at z = 5.7.
more »
« less
The Relationship between IGM Lyα Opacity and Galaxy Density near the End of Reionization
Abstract Observed scatter in the Lyαopacity of quasar sightlines atz< 6 has motivated measurements of the correlation between Lyαopacity and galaxy density, as models that predict this scatter make strong and sometimes opposite predictions for how they should be related. Our previous work associated two highly opaque Lyαtroughs atz∼ 5.7 with a deficit of Lyαemitting galaxies (LAEs). In this work, we survey two of the most highly transmissive lines of sight at this redshift toward thez= 6.02 quasar SDSS J1306+0356 and thez= 6.17 quasar PSO J359-06. We find that both fields are underdense in LAEs within 10h−1Mpc of the quasar sightline, somewhat less extensive than underdensities associated with Lyαtroughs. We combine our observations with three additional fields from the literature and find that while fields with extreme opacities are generally underdense, moderate opacities span a wider density range. The results at high opacities are consistent with models that invoke UV background fluctuations and/or late reionization to explain the observed scatter in intergalactic medium (IGM) Lyαopacities. There is tension at low opacities, however, as the models tend to associate lower IGM Lyαopacities with higher densities. Although the number of fields surveyed is still small, the low-opacity results may support a scenario in which the ionizing background in low-density regions increases more rapidly than some models suggest after becoming ionized. Elevated gas temperatures from recent reionization may also be making these regions more transparent.
more »
« less
- PAR ID:
- 10465628
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 955
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 138
- Size(s):
- Article No. 138
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Observations of quasar absorption spectra provide strong evidence that reionization extended belowz= 6. The relationship between Lyαforest opacity and local galaxy density (the opacity-density relation) is a key observational test of this scenario. Using narrow-band surveys ofz≈ 5.7 Lyαemitters (LAEs) centered on quasar sight lines, ref. [1] showed that two of the most transmissive Lyαforest segments at this redshift intersect under-densities in the galaxy distribution. This result is in tension with models of a strongly fluctuating ionizing background, including some models of late reionization, which predict that the vast majority of these segments should intersect over-densities where the ionizing intensity is strongest. In this paper, we use radiative transfer simulations to explore in more detail the opacity-density relation predicted by late reionization models. We find that fields like the one toward quasar PSO J359-06 — the more under-dense of the two transmissive sight lines in ref. [1] — are typically associated with recently reionized gas inside of cosmic voids where the hotter temperatures and rarefied densities enhance Lyαtransmission. The opacity-density relation's transmissive end is sensitive to the amount of neutral gas in the voids, as well as its morphology, set by the clustering of reionization sources. These effects are, however, largely degenerate with each other. We demonstrate that models with very different source clustering can nonetheless yield nearly identical opacity-density relations when their reionization histories are calibrated to match Lyα forest mean flux measurements atz< 6. In models with fixed source clustering, a lower neutral fraction increases the likelihood of intersecting hot, recently reionized gas in the voids, increasing the likelihood of observing fields like PSO J359-06. For instance, the probability of observing this field is 15% in a model with neutral fractionxHI= 5% atz= 5.7, three times more likely than in a model withxHI= 15%. The opacity-density relation may thus provide a complementary probe of reionization's tail end.more » « less
-
Abstract Understanding when and how reionization happened is crucial for studying the early structure formation and the properties of the first galaxies in the Universe. Atz> 5.5, the observed intergalactic medium (IGM) optical depth shows a significant scatter, indicating an inhomogeneous reionization process. However, the nature of the inhomogeneous reionization remains debated. A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) is a JWST Cycle 1 program that has spectroscopically identified >400 [Oiii] emitters in 25 quasar fields atz> 6.5. Combined with deep ground-based optical spectroscopy of ASPIRE quasars, the ASPIRE program provides the current largest sample for IGM-galaxy connection studies during cosmic reionization. We present the first results of IGM effective optical depth measurements around [Oiii] emitters using 14 ASPIRE quasar fields. We find the IGM transmission is tightly related to reionization era galaxies to the extent that a significant excess of Lyαtransmission exists around [Oiii] emitters. We measure the stacked IGM effective optical depth of IGM patches associated with [Oiii] emitters and find they reach the same IGM effective optical depth at leastdz∼ 0.1 ahead of those IGM patches where no [Oiii] emitters are detected, supporting earlier reionization around [Oiii] emitters. Our results indicate an enhancement in IGM Lyαtransmission around [Oiii] emitters at scales beyond 25h−1cMpc, consistent with the predicted topology of reionization from fluctuating UV background models.more » « less
-
ABSTRACT The presence of excess scatter in the Ly-α forest at z ∼ 5.5, together with the existence of sporadic extended opaque Gunn-Peterson troughs, has started to provide robust evidence for a late end of hydrogen reionization. However, low data quality and systematic uncertainties complicate the use of Ly-α transmission as a precision probe of reionization’s end stages. In this paper, we assemble a sample of 67 quasar sightlines at z > 5.5 with high signal-to-noise ratios of >10 per ≤15 km s−1 spectral pixel, relying largely on the new XQR-30 quasar sample. XQR-30 is a large program on VLT/X-Shooter which obtained deep (SNR > 20 per pixel) spectra of 30 quasars at z > 5.7. We carefully account for systematics in continuum reconstruction, instrumentation, and contamination by damped Ly-α systems. We present improved measurements of the mean Ly-α transmission over 4.9 < z < 6.1. Using all known systematics in a forward modelling analysis, we find excellent agreement between the observed Ly-α transmission distributions and the homogeneous-UVB simulations Sherwood and Nyx up to z ≤ 5.2 (<1σ), and mild tension (∼2.5σ) at z = 5.3. Homogeneous UVB models are ruled out by excess Ly-α transmission scatter at z ≥ 5.4 with high confidence (>3.5σ). Our results indicate that reionization-related fluctuations, whether in the UVB, residual neutral hydrogen fraction, and/or IGM temperature, persist in the intergalactic medium until at least z = 5.3 (t = 1.1 Gyr after the big bang). This is further evidence for a late end to reionization.more » « less
-
Abstract The Hobby–Eberly Telescope Dark Energy Experiment (HETDEX) is designed to detect and measure the redshifts of more than 1 million Lyαemitting galaxies (LAEs) 1.88 <z< 3.52. In addition to its cosmological measurements, these data enable studies of Lyαspectral profiles and the underlying radiative transfer. Using the roughly half a million LAEs in the HETDEX Data Release 3, we stack various subsets to obtain the typical Lyαprofile for thez∼ 2–3 epoch and to understand their physical properties. We find clear absorption wings around Lyαemission, which extend ∼2000 km s−1both redward and blueward of the central line. Using far-UV spectra of nearby (0.002 <z< 0.182) LAEs in the COS Legacy Archive Spectroscopic Survey treasury and optical/near-IR spectra of 2.8 <z< 6.7 LAEs in the Multi Unit Spectroscopic-Wide survey, we observe absorption profiles in both redshift regimes. Dividing the sample by volume density shows that the troughs increase in higher-density regions. This trend suggests that the depth of the absorption is dependent on the local density of objects near the LAE, a geometry that is similar to damped Lyαsystems. Simple simulations of Lyαradiative transfer can produce similar troughs due to absorption of light from background sources by Higas surrounding the LAEs.more » « less
