Magnifying the Early Episodes of Star Formation: Super Star Clusters at Cosmological Distances
Journal
Date Issued
2017
Author(s)
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Caminha, G. B.
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Christensen, L.
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Rosati, P.
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Gronke, M.
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Dijkstra, M.
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De Barros, S.
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Caputi, K.
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Grillo, C.
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Balestra, I.
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Vignali, C.
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Zamorani, G.
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Brusa, M.
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Bergamini, P.
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Abstract
We study the spectrophotometric properties of a highly magnified (μ ≃ 40{--}70) pair of stellar systems identified at z = 3.2222 behind the Hubble Frontier Field galaxy cluster MACS J0416. Five multiple images (out of six) have been spectroscopically confirmed by means of VLT/MUSE and VLT/X-Shooter observations. Each image includes two faint ({m}{UV}≃ 30.6), young (≲ 100 Myr), low-mass (< {10}7 {M}☉ ), low-metallicity (12 + Log(O/H) ≃ 7.7, or 1/10 solar), and compact (30 pc effective radius) stellar systems separated by ≃ 300 pc after correcting for lensing amplification. We measured several rest-frame ultraviolet and optical narrow ({σ }v≲ 25 km s-1) high-ionization lines. These features may be the signature of very hot (T> {{50,000}} K) stars within dense stellar clusters, whose dynamical mass is likely dominated by the stellar component. Remarkably, the ultraviolet metal lines are not accompanied by Lyα emission (e.g., C IV/Lyα > 15), despite the fact that the Lyα line flux is expected to be 150 times brighter (inferred from the Hβ flux). A spatially offset, strongly magnified (μ > 50) Lyα emission with a spatial extent ≲ 7.6 kpc2 is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent Lyα induced by a transverse leakage of ionizing radiation emerging from the stellar systems and/or may be associated with an underlying and barely detected object (with {m}{UV}> 34 de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without Lyα emission—suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the Lyα detection.
Based on observations collected at the European Southern Observatory for Astronomical research in the southern hemisphere, under ESO programmes P095.A-0840, P095.A-0653, and P186.A-0798.
Volume
842
Issue
1
Start page
47
Issn Identifier
0004-637X
Ads BibCode
2017ApJ...842...47V
Rights
open.access
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