此处提出的观察结果是JADES41的一部分，这是由JWST42,43 NIRCAM44和NIRSPEC45,46保证的时间观察仪器科学团队进行的联合调查。如Robertson等人所述。10。Nat。astron。7，611–621（2023）。λobs在JWST计划1180（PI：Eisenstein）下进行了0.8至5μm（在F200W中达到MAB 30 MAG），在伟大的观察者起源深度调查中，在65个Arcmin2的区域中，South（Goods South）（商品S），其中包括公共中的中等范围的extral in Medim-Band sefters jw。（JEMS49； JWST计划，1963年，PI：WILLIAMS）和首次回报时期的光谱完整调查（FRESCO50； JWST计划1895年，PI：Oesch），通过合并了来自Hubble Space telescope的大量公开可用的辅助数据这些NIRCAM选择的源的多对象光谱51在Prism/透明光谱构型中使用MSA52进行，覆盖光谱范围为0.6至5.3μm，并通过解决功率r 100进行。三分点点点点数用于与MSA降低的敏捷效果，以提高敏捷的敏感性和迅速效应，并迅速降低了范围的效果，并迅速降低了范围的效率，并迅速降低了范围的准确性效率，并表明了频率的准确性效率，并取得了动力的效果。探测器的差距和抖动点的去除是由三个点头的四个序列组成的。访问，使整合时间为27.9 h（表1）， 而其他目标的暴露时间在9.3至27.9 h之间。在扩展数据中显示了Jades-GS-Z6-0的光谱能量分布（SED）和Jades-gs-Z6-0的虚拟颜色图像覆盖了NIRSPEC MSA百叶窗位置。

　　通过欧洲航天局的NIRSPEC科学运营团队和NIRSPEC保证的时间观察团队开发的管道获得了通过通量校准的二维光谱和一维光谱提取，将在即将发表的论文中详细讨论。该管道通常在官方太空望远镜科学研究所管道中应用相同的算法，该管道生成了Mikulski档案库用于太空望远镜产品。采用每个分辨率元件具有5个光谱像素的不规则波长网格，以避免在短波长（λOBS1μM）下过采样线扩散函数。用5像素孔覆盖整个快门尺寸以恢复整个发射，将一维光谱提取。但是，如Curtis-Lake等人27所示，我们考虑了3像素孔径的额外提取，以测试我们发现的鲁棒性，如紫外线凸起检测的鲁棒性所述。鉴于此处考虑的高红移星系的紧凑尺寸（扩展数据图1），在假定位于每个星系的相对弹盘位置位于点样源的假设下应用了缝隙较差校正。我们注意到，缝隙减小校正中的系统不确定性是波长的平稳函数，因此不会影响紫外线凸起签名，而紫外线凸起签名则依赖于检测到相对较小的λemit=2,175Å的紫外斜率弯曲（如下一节所讨论的那样）。在快门大小的光圈中进行提取以恢复所有发射。关于目标选择和数据减少的更多详细信息将在前面的Jades Works 27,41，10。Nat中进行广泛讨论。astron。7，611–621（2023）。“ href =” https://www.nature.com/articles/s41586-023-06413-w#ref-cr47“ id =” ref-link-section-d4869124e3007> 47,48,51。

　　在风笛中运行自动光谱拟合程序（贝叶斯对物理推理和参数估计的星系分析）53之后，通过视觉检查，至少有两个团队成员独立地进行视觉检查确认了光谱红移的估计。如Curtis-Lake等人27中所述，通过随后的分析（在PrEP。中详细描述）通过随后的分析（在PrEP。中详细描述）确定最终红移值，但具有延迟的呈延迟的无红色组合，并结合了一个狭窄的分布，并在狭窄的范围内组成，并确定beagle（贝叶斯分析）54。红移。我们选择了Z> 4上方具有自信光谱红移的对象，以确保其余的紫外线覆盖范围包括Lyman-α断裂。基于形式的不确定性，我们进一步选择了中位信噪比的光谱，在该区域中至少为3个，对应于1,268Å的静止帧波长< λemit < 2,580 Å.

　　We then performed several Bayesian power-law fitting procedures to the rest-frame UV continuum with a Python implementation55 of the MultiNest56 nested sampling algorithm. To identify spectra exhibiting a UV bump, we fitted power laws in four adjacent wavelength windows defined by Noll et al.57 (with corresponding power-law indices γ1 to γ4), excluding the region 1,920 Å < λemit < 1,950 Å to avoid contamination by the C  doublet. In the presence of the UV bump, the spectral shape of the rest-frame UV is characterized by a strong turnover in the power-law slope directly blue- and redwards of 2,175 Å covered by regions 3 and 4 respectively, resulting in a negative γ34 ≡ γ3 − γ4 value. Before fitting these separate wavelength windows in the individual spectrum, we applied a running median filter over 15 spectral pixels that cover three times the spectral resolution. We estimated the uncertainty on the running median with a bootstrapping procedure in which we randomly perturbed each of the 15 spectral pixels according to their formal uncertainty for 100 iterations.

　　In the fitting algorithm, a likelihood was calculated based on the inverse-variance weighted squared residuals between a given model and the observed spectrum within the adopted spectral regions. We chose flat prior distributions for the power-law indices (in the range −5 < γi < 1) and normalization at the centre of each wavelength window (between 0 and twice the maximum value of the spectrum in the fitting regions). Best-fit values of γ34, whose posterior distribution was obtained from simultaneously fitting γ3 and γ4, are shown in Extended Data Fig. 2 as the 50th percentile (the median) with 16th and 84th percentiles as a ±1σ confidence range. A selection of galaxies with a median value of γ34 < −1, in addition to γ34 < 0 within the 1σ uncertainty range, led to the identification of ten galaxies (including JADES-GS-z6-0) with evidence for a UV bump (the ‘bump sample’). Next, we discuss the physical properties of this subsample in the context of the full sample. Coordinates and other properties of these ten galaxies are reported in Extended Data Table 1.

　　We consistently used a flat lambda cold dark matter (ΛCDM) cosmology based on the results of the Planck collaboration58 (that is, H0 = 67.4 km s−1 Mpc−1 and Ωm = 0.315). Several of the main physical properties of the full sample are presented in Extended Data Fig. 2. Extended Data Table 1 lists the observed properties of the ten individual galaxies in the bump sample. Extended Data Table 2 reports median values for the bump sample, the sample of galaxies not contained in the bump sample (the ‘non-bump sample’) and the full sample, as well as values measured from the stacked spectra.

　　We derived UV magnitudes directly from NIRCam photometric data points probing a rest-frame wavelength of approximately 1,500 Å (F115W for JADES-GS-z6-0; see Table 1), if available. Note that several targets fall outside the NIRCam footprint. We fitted an overall UV slope βUV to the rest-frame UV continuum probed by the NIRSpec PRISM measurements using a similar Bayesian power-law fitting procedure as described in Sample selection. We adopted the spectral windows defined by Calzetti et al.59, which were designed to exclude several UV emission and absorption features. Indeed, no strong emission lines were observed within these spectral regions of our low-resolution spectra. importantly, they explicitly exclude the bump region and C  emission lines. We chose a Gaussian prior distribution for the power-law index (centred on μβ = −2 with a width of σβ = 0.5) and a flat prior on the normalization at λemit = 1,500 Å (between 0 and twice the maximum value of the spectrum in the fitting regions). The resulting UV slope of JADES-GS-z6-0 is reported in Table 1.

　　Emission line fluxes in the NIRSpec PRISM measurements of the individual galaxies in our sample were obtained using the pPXF software60 (for details, refer to Curti et al.20). We converted Hα/Hβ line ratios into a nebular extinction E(B − V)neb with the Cardelli et al.61 extinction curve, assuming an intrinsic ratio Hα/Hβ = 2.86 appropriate for case-B recombination, Te = 104 K and ne = 100 cm−3 (for example, ref. 62). Note that for JADES-GS+53.13423-27.76891 at z = 7.0493, the Hα line is precisely on the edge the PRISM spectral coverage, causing the measured Hα/Hβ ratio to appear significantly below the theoretical value of Hα/Hβ = 2.86 expected in the absence of dust. Moreover, we caution that potential wavelength-dependent slit-loss effects could bias the Hα/Hβ measurements (although minimally, as the objects in this analysis are only marginally resolved) and that the stellar and nebular extinctions have a non-trivial dependence. However, despite such systematic uncertainties, galaxies strongly obscured by dust are still expected to be identifiable via their elevated Hα/Hβ line ratios.

　　The gas-phase oxygen abundances in our sample were derived primarily by exploiting the detection of multiple emission lines, where available, in NIRSpec medium-resolution (R  1,000) grating/filter configurations (G140M/F070LP, G235M/F170LP and G395M/F290LP) taken alongside the PRISM spectroscopic observations (details are discussed in Curti et al.20). For targets that were not covered by R  1,000 observations, the PRISM spectra were considered. More specifically, we required a minimum 3σ detection of [O ] λ 5,008 Å, [O ] λ 3,727, 3,730 Å, [Ne ] λ 3,870 Å and Hβ before we included these lines in the metallicity calculation. For the detected emission lines, we combined information from the R3, R23, O32 and Ne3O2 line-ratio diagnostics, adopting the calibrations described in Nakajima et al.63. When only [O ] λ 5,008 Å and Hβ were detected, and therefore, R3 was the only available line ratio, upper limits on [O ] λ 3,727, 3,730 Å and [N ] λ 6,584 Å were exploited to discriminate between the high- and low-metallicity solutions of the double-branched R3 calibration. The full procedure is described in more detail in Curti et al.20. We quote the gas-phase metallicity (Zneb) in units of solar metallicity (Z), assuming 12 + (O/H) = 8.69 as the solar oxygen abundance64.

　　We further explored the rest-frame optical properties of our samples by considering composite spectra around the strong optical emission lines in Extended Data Fig. 3. These stacked spectra were obtained equivalently as described in Spectral stacking, but with bins of ∆λemit = 10 Å given the increased spectral resolution of NIRSpec at longer wavelengths45. To study the Balmer decrement, we included only galaxies for which Hα is observable (that is, we did not consider objects at z > 7.1, leaving out one source in the bump sample). We obtained fluxes of the main emission lines (that is, [O ] λ 3,727, 3,730 Å, [O ] λ 4,960, 5,008 Å, Hβ and Hα) by fitting Gaussian profiles, as shown in Extended Data Fig. 3. The measured line ratios are reported in Extended Data Table 2.

　　We employed the BAGPIPES code53 to model the SED, which is simultaneously probed by NIRSpec PRISM measurements and NIRCam photometry, for which we used a conservative 10% error floor. For the underlying stellar models, we used the Binary Population and Spectral Synthesis (BPASS31) v2.2.1 stellar population synthesis models, which include binary stars. We used the default BPASS initial mass function with a slope of −2.35 (for M >0.5 m）和一系列恒星质量从1 m到300M。目标是一个简单但能够捕获较老的恒星种群的模型，我们采用了一个恒定的SFH，其最小年龄在0（即持续的恒星形成）和500 MYR之间，并且最大年龄在1 Myr之间变化。形成的总恒星质量在0到1015 m之间变化，而恒星金属性在0到1.5 z之间。使用电离参数参数（-3< log10 U < −0.5). We chose a flexible Charlot and Fall66 dust attenuation prescription with varying visual extinction (0 < AV < 7 mag) and power-law slope (0.4 < n < 1.5). We fixed the fraction of attenuation arising from stellar birth clouds to 60% (the remaining fraction originating in the diffuse interstellar medium; for example, see ref. 67). Note that the Calzetti et al.59 dust attenuation curve yielded consistent results. A first-order Chebyshev polynomial (described in Carnall et al.68) was included to account for aperture and flux-calibration effects in the spectroscopic data. The detailed properties of JADES-GS-z6-0 are reported in Table 1. Moreover, the resulting stellar masses (M), star formation rates (SFRs) averaged over the last 30 Myr (SFR30), and mass-weighted stellar ages (t) inferred from SED models of the entire sample are presented in Extended Data Fig. 2. Median values of all properties for the galaxy sample with and without evidence for a UV bump are reported in Extended Data Table 2.

　　Further, we explored whether the apparent absence of a significantly older stellar population (t > 300 Myr) could be explained by an ‘outshining effect’ due to a more recent burst of star formation69. Indeed, there is evidence that a substantial fraction (20% to 25%) of reionization-era galaxies (z  6) host such evolved stellar populations70,71. Taking the best-fitting parameter values in our BAGPIPES model, we added an instantaneous burst of star formation to the original model with a single (constant) SFH component. Comparing the reduced chi-squared values between the original, single-component model and the new, two-component model (accounting for an additional three model parameters, namely stellar mass, metallicity and age of the burst), we inferred, from a stellar population synthesis modelling point of view, how large a stellar mass can be while being ‘disguised’ in an evolved stellar population. This is illustrated in Extended Data Fig. 4, which shows the age-sensitive 4000 Å (Balmer) break. To avoid systematic uncertainties due to flux calibration or slit losses in the spectrum, we restricted the chi-squared analysis to the photometry. We determined the difference in reduced chi-squared values as , where () is the reduced chi-squared metric of the single-component (two-component) model. From this conservative estimate, we cannot definitively rule out the existence of an additional population of evolved stars. For example, for (that is, at 2σ or 95% confidence), up to 5.5 × 107 M (9.6 × 107 M) or 0.55× (0.95×) of the inferred stellar mass of JADES-GS-z6-0 could have been produced in a 250 (500)-Myr-old burst of star formation. This scenario, however, where a galaxy builds up more than half of its stellar mass following an extended period (that is, more than 250 Myr) with little or no star formation, is physically implausible given the smooth SFH expected for relatively massive galaxies in this early epoch (M  108 M)72. Even a more stochastic mode of star formation is not likely to undergo such a lengthy quiescent period, suggesting that the SEDs should reveal detectable signatures of stars with intermediate ages (approximately 100 Myr), if star formation activity can truly be traced back over a time period required for AGB stars to produce substantial amounts of dust. Instead, we constrain any additional 100-Myr-old component to have at most 0.31× the current stellar mass (approximately 3 × 107 M; 2σ). This suggests that more than half, if not most, of the stellar mass in JADES-GS-z6-0 was built up in less than 100 Myr. Finally, we note that stacked rest-frame optical spectra (discussed in Spectroscopic rest-frame optical properties), when normalized to the continuum at λemit  3600 Å, equally do not reveal a strong Balmer break either in the bump sample or in the full sample, further supporting the finding that these galaxies have relatively young stellar populations.

　　To search for additional signatures of dust obscuration, we considered archival Atacama Large Millimeter/submillimeter Array (ALMA) 1.2 mm and 3 mm continuum imaging taken in GOODS-S. All sources in our sample were contained within the combined 1.2 mm data of the ALMA twenty-six arcmin2 survey of GOODS-S at one millimeter (ASAGAO73; ALMA project code 2015.1.00098.S, PI: K. Kohno), which includes the ALMA Hubble Ultra Deep Field survey74 (project code 2012.1.00173.S, PI: J. Dunlop) and the GOODS-ALMA survey75 (project code 2015.1.00543.S, PI: D. Elbaz) and reaches a continuum sensitivity of approximately 78 μJy (3σ). A further 15 sources, including three sources in the bump sample (JADES-GS+53.17022-27.77739, JADES-GS+53.16743-27.77548 and JADES-GS+53.16660-27.77240), are covered by the ALMA Spectroscopic Survey (ASPECS76,77; project code 2013.1.00146.S, PI: F. Walter), reaching a 3σ continuum sensitivity of approximately 38 μJy at 1.2 mm and approximately 11.4 μJy at 3 mm. None of the 49 sources in our sample, however, show a significant detection (3.5σ) in either dataset. A stacking procedure, similarly, does not yield any detectable continuum emission, neither for the sources in the bump sample nor for the full sample, indicating that the non-detections can be explained by the relatively low sensitivity of the ALMA mosaics. Indeed, we have verified that for a typical SFR of a few solar masses per year (as inferred for JADES-GS-z6-0), even a conservatively high fraction (50%) of dust-obscured star formation results in an infrared luminosity that requires several tens of hours to secure a confident detection (LIR  1010 L, translating to a continuum flux density of Fν  5 μJy in band 6).

　　Given an observed flux density profile Fλ, we parametrized the UV bump profile by defining the excess attenuation as in Shivaei et al.13: Aλ,bump = −2.5 log10 (Fλ/Fλ,cont). For the individual spectrum of JADES-GS-z6-0, we took the power-law fit with UV slope βUV measured outside the bump region as the attenuated spectrum without a bump, Fλ, cont. When considering the excess attenuation in the individual spectrum of JADES-GS-z6-0, we again used the running median and corresponding uncertainty (described in Sample selection), which was additionally used to compute the significance of the negative flux excess of the spectrum with respect to the power-law fit alone (Fig. 1c). Note that the formal uncertainty of each spectral pixel is scaled upwards to include the effects of covariance between adjacent pixels. We have verified that a similarly high significance is found when bootstrapping a spectrum first rebinned to match the spectral resolution element (thereby largely negating the effects of correlated noise). Using the MultiNest56 nested sampling algorithm, we fitted the excess attenuation Aλ,bump with a Drude profile78, which has been shown to appropriately describe the spectral shape of the bump13,18,79. Centred on rest-frame wavelength λmax, it is parametrized as

　　where the full-width at half-maximum is γλmax2. We fixed γ = 250 Å/(2,175 Å)2 which, if λmax = 2,175 Å, corresponds to a full-width at half-maximum of 250 Å, in agreement with what has been found for z  2 star-forming galaxies13,18. Again motivated by the spectral windows defined by Calzetti et al.59, we fitted the data in a region of 1,950 Å ≤ λemit ≤ 2,580 Å (reflecting the γ3 and γ4 regions discussed in Sample selection), which excludes the C  doublet. As a prior for the bump amplitude Aλ,max, we conservatively chose a gamma distribution with shape parameter a = 1 and scale θ = 0.2, which favours the lowest amplitudes (noting that a flat prior yields comparable results). For the central wavelength, we adopted a flat prior in the range 2,100 Å < λmax < 2,300 Å.

　　For the spectral stacking analysis, we shifted each spectrum to rest-frame wavelengths λemit and normalized it to the value of the power-law fit at λemit = 2,175 Å. The individual continuum spectra and corresponding uncertainties are rebinned to bins of ∆λemit = 20 Å using SpectRes80. Stacked continuum profiles were created by weighting each binned data point by its inverse variance, although note that we obtained similar results with an unweighted average. The stacked continuum profile Fλ of the ten galaxies with evidence for a UV bump was converted to an excess attenuation, as described in Bump parametrization and fitting procedure, where for the ‘bumpless’ profile (Fλ,cont), we refitted a power-law continuum to the stacked continuum profile of the ten galaxies, noting the difference in slope (measured to be β  −1.95) compared to the stacked spectrum of the full sample of 49 galaxies (with β  −2.12; Extended Data Table 2). To ensure good agreement with the observed continuum outside the region used in the bump fitting procedure, this power law was determined from the Calzetti et al.59 windows bluewards of λemit = 1,850 Å (explicitly excluding the C  doublet region), whereas at wavelengths beyond the bump region, we consider the windows 2,500 Å < λemit < 2,600 Å and 2,850 Å < λemit < 3,000 Å (avoiding potential Mg  doublet emission at λemit  2,800 Å). Fitting a Drude profile78 yields an amplitude of mag and a central wavelength Å. Note that the amplitude remains effectively unchanged if we instead fix the central wavelength to λmax = 2,175 Å.

　　To test the robustness of the identification of the UV bump in JADES-GS-z6-0, we extracted one-dimensional spectra from the three separate observing visits to show that the feature around 2,175 Å is not dominated by a single observation. This is illustrated in Extended Data Fig. 5, which shows measurements from each individual visit normalized to its power-law fit. We furthermore tested our extraction of the one-dimensional spectra using different apertures on the reduced two-dimensional spectra (see Data and parent sample). This slightly lowered the average continuum flux level and signal-to-noise ratio, but we found no significant changes to the rest-frame UV spectrum. We also compared NIRCam apodized photometry (the total background-subtracted NIRCam flux passing through the NIRSpec MSA slit) to synthetic photometry obtained from convolving the PRISM spectra with NIRCam filters. We verified that for most sources, the two fluxes are offset by a constant factor with offsets smoothly varying as a function of wavelength. Finally, note that the attenuation feature is a highly localized region in the low-resolution PRISM spectra (a rest-frame width of 250 Å is sampled by approximately six independent spectral resolution elements at a resolution of R(λobs  1.7 μm)  50) such that its magnitude is not significantly affected by the absolute flux calibration. Moreover, this wavelength range was probed by more than ten native detector pixels, indicating that the chances that this feature was produced by correlated detector noise or other artefacts are minimal.

　　In this section, we discuss the robustness of the identification of the bump feature in our stacked spectra. First, we randomly split our bump sample into two subsamples and confirmed the bump signature is present in both, implying that the stacked spectrum is not dominated by a single source. Further, we verified that performing an analogous stacking procedure at a different wavelength (2,475 Å) for a subset of sources selected based on the continuum shape around 2,475 Å in an equivalent manner as the γ34 selection described in Sample selection does not produce a significant broad absorption feature as in Fig. 2. Instead, the result was a narrow negative excess with positive excess on the edge of our fitting window, hence yielding a substantially lower amplitude when fitted with a Drude profile.

　　We now explore various properties of the different samples measured by NIRSpec and NIRCam to test whether the bump signature could purely be due to random noise fluctuations, in which case the ten selected galaxies are expected to simply be a random subset of the parent sample. As seen in Extended Data Fig. 2, we found a significant correlation (p < 0.05 for the null hypothesis that the data are uncorrelated) between on the one hand the UV slope inflection around 2,175 Å, γ34, and on the other hand, the absolute UV magnitude MUV. Our selected bump sample is measured to be intrinsically fainter in the rest-frame UV (higher MUV, independent of the SED modelling). This may be indicative of the absence of young stellar populations, in line with the theoretically predicted trend of decreasing bump strength with increasing star formation activity, and hence the intensity and hardness of the UV radiation field81. Moreover, several of the median properties hint at systematically different physical conditions in the galaxies part of the bump sample. In particular, these objects exhibit a significantly enhanced Hα/Hβ ratio, indicating that on average the nebular emission in these galaxies experiences a higher degree of dust obscuration, with nebular extinction values comparable to those of z  2 galaxies with a UV bump18. Moreover, their slightly elevated gas-phase oxygen abundances indicate that they are more highly enriched in metal (Extended Data Table 2). Interestingly, however, the stellar masses of the bump sample are substantially lower than their z  2 counterparts, as illustrated in Fig. 3. Note that other factors, such as geometry, could play an important role in determining the strength of the UV bump, although larger samples are needed to confirm these trends.

　　To avoid potential biases in the correlations based on individual galaxy properties due to contaminants in our γ34-selected sample, we explored the stacked spectra. For instance, note that the bump and non-bump samples appear to be characterized by a comparable median UV slope, as measured in the individual spectra, which is confirmed by the agreement with the UV slopes in the unweighted stacked spectra. However, the weighted stacked spectrum shown in Fig. 2 reveals that the bump sample has a significantly redder UV continuum (as discussed in Spectral stacking). From the stacked spectra around the strong optical emission lines in Extended Data Fig. 3, we again found the Hα/Hβ ratio in the bump sample was significantly higher, translating to a nebular extinction E(B −V )neb a factor of approximately 2 higher than in the stacked spectrum of the full sample. This indicates that the bump sample preferably contains dustier galaxies, strongly favouring the interpretation that the observed excess attenuation around 2,175 Å is due to dust absorption. Moreover, we found evidence for a mildly higher metallicity in the bump sample through an enhanced line ratio of [O ] λ 5,008 Å to Hβ. Although this line ratio follows a double-branched metallicity solution (for example, ref. 20), a low-metallicity solution that monotonically increases with [O ]/Hβ should be appropriate for the current sample of galaxies, given the [O ]/[O ] line ratio of approximately 10 (both in the full sample and the subset of sources selected as the bump sample). Note that such differences in the Hα/Hβ and [O ]/Hβ line ratios are absent in the control sample discussed above, which was selected based on the continuum shape around 2,475 Å.

　　Finally, we verified that a blind selection from the parent sample of sources with the highest Balmer decrements and reddest UV slopes resulted in a tentative detection of the UV bump. Specifically, requiring a Balmer decrement of Hα/Hβ  4 and a UV slope of βUV  −2.2 yielded a sample of four sources all contained within the bump sample (namely JADES-GS+53.16871-27.81516, JADES-GS+53.13284-27.80186, JADES-GS+53.17022-27.77739 and JADES-GS+53.16743-27.77548; Extended Data Table 1) but notably excluded JADES-GS-z6-0. Without any preselection for the continuum shape around 2,175 Å, the stacked spectrum of these four galaxies produced a tentative (approximately 4σ) bump feature.

　　As discussed in Shivaei et al.13, the adopted parametrization of bump amplitude in the excess attenuation (that is, Aλ,max; see Bump parametrization and fitting) includes the extinction in the absence of the bump E(B − V) to avoid propagating the large uncertainties of this parameter that stem from the not well-constrained assumptions on the attenuation curves of high-redshift galaxies. Note that a direct measurement of the Balmer recombination line ratios can, in principle, constrain the nebular extinction82, but its relation with stellar extinction carries uncertainty in addition to suffering from wavelength-dependent slit-loss effects (also discussed in Spectroscopic rest-frame optical properties). In Fig. 3, we directly compare these excess attenuation strengths, taking into account the underlying extinction E(B − V) for bump strengths measured for the Milky Way, Large Magellanic Cloud and Small Magellanic Cloud extinction curves. In terms of the commonly used Fitzpatrick and Massa40,78,83 parametrization, Aλ,max = c3/γ2E(B − V). We retrieve E(B − V) from the measured total-to-selective extinction RV = AV/E(B − V) for each extinction curve, assuming a range of 0.1 mag < AV < 0.5 mag. Data points from Noll et al.18 and Heintz et al.39 (and references therein) were similarly converted to a consistent bump amplitude Aλ,max using their measured values of E(B − V). Measurements from Noll et al.18 represent the stacked spectra of three subsamples that were selected based on their UV slope βUV and bump strength parametrized by the γ34 parameter (Sample selection). The upwards-pointing triangle in Fig. 3 has βUV < −1.5 and γ34 > −2, the diamond has βUV >-1.5和γ34> -2，向下的三角形具有γ34<-2。请注意，Heintz等人的39测量γ射线爆发吸收器有效地沿着星系线有效地沿视线，而Shivaei等人13和Noll等。18测量结果，例如这项工作中的测量值，基于星系的总体整合光。相对于星系中恒星的灰尘分布会影响后者的紫外线24,84的综合观察结果。