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arXiv 2410.03337astro-ph.GA
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两个明亮的z~7.5星系对再电离光子预算的贡献可忽略不计

A negligible contribution of two luminous $z$ ~ 7.5 galaxies to the ionizing photon budget of reionization

S. Gazagnes, J. Chisholm, R. Endsley, D. A. Berg, F. Leclercq, N. Jurlin, A. Saldana-Lopez, S. L. Finkelstein, S. R. Flury, N. G. Guseva, A. Henry, Y. I. Izotov… 展开作者

S. Gazagnes, J. Chisholm, R. Endsley, D. A. Berg, F. Leclercq, N. Jurlin, A. Saldana-Lopez, S. L. Finkelstein, S. R. Flury, N. G. Guseva, A. Henry, Y. I. Izotov, I. Jung, J. Matthee, D. Schaerer

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18 pages, Accepted MNRAS
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AI总结：

本文通过Mg II双线间接约束z~7.5处两个明亮星系GN 42912-NE和GN 42912-SW的电离光子逃逸分数，得到8.5%和14%的保守上限，表明它们对再电离纪元电离光子预算的贡献较小。

摘要：

我们对GN 42912系统的电离光子绝对逃逸分数（$f_{\rm esc}^{\rm LyC}$）提出了间接约束，该系统由两个位于$z\sim7.5$的明亮星系组成（$M_{\rm UV}$星等分别为-20.89和-20.37），即GN 42912-NE和GN 42912-SW，以确定它们对再电离纪元（EoR）电离光子预算的贡献。高分辨率詹姆斯·韦伯空间望远镜NIRSpec和NIRCam观测显示，这两个星系在天空上仅相距约0.1$''$（0.5 kpc），速度差为358 km s$^{-1}$。GN 42912-NE和GN 42912-SW在该红移处相对较大（log($M_\ast/M_\odot$)分别约为8.4和8.9），气相金属丰度分别为太阳值的18%和23%，O$_{32}$比值分别为5.3和$>5.8$，$\beta$斜率分别为$-1.92$和$-1.51$。我们利用Mg II$\lambda\lambda$2796,2803双线来约束$f_{\rm esc}^{\rm LyC}$。Mg II的电离势接近中性氢，在光学薄区域可作为LyC泄漏的间接示踪剂。我们对GN 42912-NE和GN 42912-SW建立了现实且保守的$f_{\rm esc}^{\rm LyC}$上限，分别为8.5%和14%。这些估计与在$z<4$处观测到的$f_{\rm esc}^{\rm LyC}$随$\beta$、O$_{32}$和H$\beta$等值宽度的变化趋势一致。推断出的两个星系周围的电离区域尺寸很小（$<0.3$ pMpc），表明它们尚未电离周围中性气体的显著部分。虽然这些$z>7$的$f_{\rm esc}^{\rm LyC}$约束不能决定性地确定特定的再电离模型，但它们支持这两个相对明亮的星系对EoR的贡献较小。

英文摘要：

We present indirect constraints on the absolute escape fraction of ionizing photons ($f_{\rm esc}^{\rm LyC}$) of the system GN 42912 which comprises two luminous galaxies ($M_{\rm UV}$ magnitudes of -20.89 and -20.37) at $z\sim7.5$, GN 42912-NE and GN 42912-SW, to determine their contribution to the ionizing photon budget of the Epoch of Reionization (EoR). The high-resolution James Webb Space Telescope NIRSpec and NIRCam observations reveal the two galaxies are separated by only ~0.1$"$ (0.5 kpc) on the sky and have a 358 km s$^{-1}$ velocity separation. GN 42912-NE and GN 42912-SW are relatively massive for this redshift (log($M_\ast/M_\odot$) $\sim$ 8.4 and 8.9, respectively), with gas-phase metallicities of 18 per cent and 23 per cent solar, O$_{32}$ ratios of 5.3 and $>5.8$, and $β$ slopes of $-1.92$ and $-1.51$, respectively. We use the Mg II$λλ$2796,2803 doublet to constrain $f_{\rm esc}^{\rm LyC}$. Mg II has an ionization potential close to that of neutral hydrogen and, in the optically thin regime, can be used as an indirect tracer of the LyC leakage. We establish realistic conservative upper limits on $f_{\rm esc}^{\rm LyC}$ of 8.5 per cent for GN 42912-NE and 14 per cent for GN 42912-SW. These estimates align with $f_{\rm esc}^{\rm LyC}$ trends observed with $β$, O$_{32}$, and the H$β$ equivalent width at $z<4$. The small inferred ionized region sizes ($<0.3$ pMpc) around both galaxies indicate they have not ionized a significant fraction of the surrounding neutral gas. While these $z>7$ $f_{\rm esc}^{\rm LyC}$ constraints do not decisively determine a specific reionization model, they support a minor contribution from these two relatively luminous galaxies to the EoR.

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