标题： 红移约为2的类星体周围星系际介质中的堆叠Lyman-α发射轮廓 显示英文标题

标题： The Stacked Lyman-Alpha Emission Profile from the Circum-Galactic Medium of z~2 Quasars

摘要： 在 FLASHLIGHT 巡天的背景下，我们利用 Gemini-South 上的 GMOS 获取了 15 个$z\sim2$类星体的深窄带图像，旨在测量从中心类星体数百千秒差距范围内的星系际和星系间气体产生的 Ly$\alpha$发射线。 我们没有检测到来自任何源的明亮的大尺度（Ly$\alpha$ 星云，SB~10$^{-17}$ erg s$^{-1}$ cm$^{-2}$ 弧分$^{-2}$，距离 >50 kpc），尽管我们常规地（$\simeq47$%）在这一 SB 水平上检测到来自距离 <50 kpc 的较小尺度的 Ly$\alpha$辐射，这些辐射要么来自类星体驱动的扩展窄发射线区，要么来自宿主星系中的恒星形成活动。 我们堆叠了15幅深场图像，以研究围绕$z\sim2$类星体的平均扩展Ly$\alpha$面亮度分布轮廓，仔细地从未分辨辐射成分中减去点扩散函数，并密切关注系统误差来源。 我们的分析达到了前所未有的深度，揭示了在距离类星体 50 千秒差距到 500 千秒差距的环状区域内，表面亮度为 SB$_{\rm Ly\alpha}\sim10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ （在 $\sim200$ 千秒差距处），并且在 SB$_{\rm Ly\alpha}=(5.5\pm3.1)\times10^{-20}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ 的表面亮度下检测到了 Ly$\alpha$ 辐射，其检出信号显著性为$2.3\sigma$。 假设这种 Ly$\alpha$辐射是由明亮中心类星体照亮的高电离气体发出的荧光驱动的，我们推断出在这些大尺度上体积密度平均为$n_{\rm H}=0.6\times10^{-2}$ cm$^{-3}$。我们的结果与巨大质量（$M\simeq10^{12.5}M_\odot$）类星体宿主的宇宙流体力学模拟所建议的密度大致一致，然而它们表明，这些红移处的典型类星体周围被包围的气体密度比我们团队最近发现的围绕类星体的巨大明亮 Ly$\alpha$气体晕（~1 cm$^{-3}$）的密度低约100倍。 显示英文摘要

摘要： In the context of the FLASHLIGHT survey, we obtained deep narrow band images of 15 $z\sim2$ quasars with GMOS on Gemini-South in an effort to measure Ly$\alpha$ emission from circum- and inter-galactic gas on scales of hundreds of kpc from the central quasar. We do not detect bright giant Ly$\alpha$ nebulae (SB~10$^{-17}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ at distances >50 kpc) around any of our sources, although we routinely ($\simeq47$%) detect smaller scale <50 kpc Ly$\alpha$ emission at this SB level emerging from either the extended narrow emission line regions powered by the quasars or by star-formation in their host galaxies. We stack our 15 deep images to study the average extended Ly$\alpha$ surface brightness profile around $z\sim2$ quasars, carefully PSF-subtracting the unresolved emission component and paying close attention to sources of systematic error. Our analysis, which achieves an unprecedented depth, reveals a surface brightness of SB$_{\rm Ly\alpha}\sim10^{-19}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ at $\sim200$ kpc, with a $2.3\sigma$ detection of Ly$\alpha$ emission at SB$_{\rm Ly\alpha}=(5.5\pm3.1)\times10^{-20}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$ within an annulus spanning 50 kpc <R< 500 kpc from the quasars. Assuming this Ly$\alpha$ emission is powered by fluorescence from highly ionized gas illuminated by the bright central quasar, we deduce an average volume density of $n_{\rm H}=0.6\times10^{-2}$ cm$^{-3}$ on these large scales. Our results are in broad agreement with the densities suggested by cosmological hydrodynamical simulations of massive ($M\simeq10^{12.5}M_\odot$) quasar hosts, however they indicate that the typical quasars at these redshifts are surrounded by gas that is a factor of ~100 times less dense than the (~1 cm$^{-3}$) gas responsible for the giant bright Ly$\alpha$ nebulae around quasars recently discovered by our group.