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arXiv 1507.06648astro-ph.GA
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$z=3.2$的极端[ OIII ]发射体:低金属丰度莱曼连续源

An extreme [OIII] emitter at $z=3.2$: a low metallicity Lyman continuum source

S. de Barros, E. Vanzella, R. Amorín, M. Castellano, B. Siana, A. Grazian, H. Suh, I. Balestra, C. Vignali, A. Verhamme, G. Zamorani, M. Mignoli, G. Hasinger, A… 展开作者

S. de Barros, E. Vanzella, R. Amorín, M. Castellano, B. Siana, A. Grazian, H. Suh, I. Balestra, C. Vignali, A. Verhamme, G. Zamorani, M. Mignoli, G. Hasinger, A. Comastri, L. Pentericci, E. Pérez-Montero, A. Fontana, M. Giavalisco, R. Gilli

摘要:

[摘要]我们研究了莱曼连续发射体候选者在$z=3.212$的物理性质,光度覆盖范围从$U$到MIPS 24 $μ$ m带和VIMOS/VLT和MOSFIRE/Keck光谱。UV光谱的研究证实了使用$S/N>5$的莱曼连续发射的直接光谱检测。系统红移处的非零Ly $α$通量和高Lyman-$α$逃逸分数表明低HI柱密度。弱的C和Si低电离吸收线也与沿视线的低覆盖分数一致。[OIII] $λ\lambda4959,5007+\mathrm{H}β$的等效宽度是在$z>3$($\mathrm{EW}([\mathrm{OIII}]λ\lambda4959,5007+\mathrm{H}β) \simeq 1600Å$,静止坐标系)上所报道的最大的星系之一,近红外光谱显示这主要是由于极强的[OIII]发射。观测到的大的[OIII]/[OII]比值($>10$)和高电离参数与光电离模型在密度有界星云情况下的预测一致。此外,$\mathrm{EW}([\mathrm{OIII}]λ\lambda4959,5007+\mathrm{H}β)$与最近在$z\sim7-9$报告的再电离时期的测量结果相当。我们还研究了活动星系核贡献的可能性,以解释电离辐射,但大多数活动星系核的识别诊断表明,恒星的排放占主导地位,而不是。这个来源是目前第一个高$z$的莱曼连续辐射源的例子,表现出莱曼连续泄漏的间接和直接证据,并具有与密度有界星云莱曼连续辐射理论预期一致的物理性质。

英文摘要:

[Abridged] We investigate the physical properties of a Lyman continuum emitter candidate at $z=3.212$ with photometric coverage from $U$ to MIPS 24$μ$m band and VIMOS/VLT and MOSFIRE/Keck spectroscopy. Investigation of the UV spectrum confirms a direct spectroscopic detection of the Lyman continuum emission with $S/N>5$. Non-zero Ly$α$ flux at the systemic redshift and high Lyman-$α$ escape fraction suggest a low HI column density. The weak C and Si low-ionization absorption lines are also consistent with a low covering fraction along the line of sight. The [OIII]$λ\lambda4959,5007+\mathrm{H}β$ equivalent width is one of the largest reported for a galaxy at $z>3$ ($\mathrm{EW}([\mathrm{OIII}]λ\lambda4959,5007+\mathrm{H}β) \simeq 1600Å$, rest-frame) and the NIR spectrum shows that this is mainly due to an extremely strong [OIII] emission. The large observed [OIII]/[OII] ratio ($>10$) and high ionization parameter are consistent with prediction from photoionization models in case of a density-bounded nebula scenario. Furthermore, the $\mathrm{EW}([\mathrm{OIII}]λ\lambda4959,5007+\mathrm{H}β)$ is comparable to recent measurements reported at $z\sim7-9$, in the reionization epoch. We also investigate the possibility of an AGN contribution to explain the ionizing emission but most of the AGN identification diagnostics suggest that stellar emission dominates instead. This source is currently the first high-$z$ example of a Lyman continuum emitter exhibiting indirect and direct evidences of a Lyman continuum leakage and having physical properties consistent with theoretical expectation from Lyman continuum emission from a density-bounded nebula.

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