We study the spectrophotometric properties of a highly magnified (Î¼ â¤ 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 (mUV â¤ 30.6), young (â²100 Myr), low-mass (<107 Mâ), low-metallicity (12 + Log (O/H) â¤ 7.7, or 1/10 solar), and compact (30 pc effective radius) stellar systems separated by â¤ 300 pc after correcting for lensing amplification. We measured several rest-frame ultraviolet and optical narrow (Ïv â² 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 LyÎ± emission (e.g., C IV/LyÎ± > 15), despite the fact that the LyÎ± line flux is expected to be 150 times brighter (inferred from the HÎ² flux). A spatially offset, strongly magnified (m > 50) LyÎ± emission with a spatial extent â²7.6 kpc2 is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent LyÎ± 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 mUV > 34 de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without LyÎ± emission-suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the LyÎ± detection.
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|Titolo:||Magnifying the Early Episodes of Star Formation: Super Star Clusters at Cosmological Distances|
|Data di pubblicazione:||2017|
|Appare nelle tipologie:||03.1 Articolo su rivista|