Аннотация
We present VLT/X-Shooter and MUSE spectroscopy of an intrinsically faint
F814W=28.82+/-0.33 (Muv=-16.8), low mass (<~10^7 Msol) and compact (R_eff=67pc)
freshly star-forming galaxy at z=3.1169 magnified (20x) by the Hubble Frontier
Fields galaxy cluster Abell S1063. Gravitational lensing allows for a
significant jump toward low-luminosity regimes, in moderately high resolution
spectroscopy (R=łambda/d ~ 3000-7400). In particular, we measured
CIV1548-1550, HeII1640, OIII1661-1666, CIII1907-1909, Hb, OIII4959-5007,
emission lines with FWHM<~50 km/s and (de-lensed) fluxes spanning the interval
1.0x10^(-19) - 2x10^(-18) erg/s/cm2 at S/N=4-30. The double peaked Lya emission
with \Delta v(red-blue) = 280(+/-7)km/s and de-lensed fluxes
2_(blue)|7_(red)x10^(-18) erg/s/cm2 (S/N=38_(blue)|110_(red)) indicates a low
column density of neutral hydrogen gas (N_HI~10^(16-18.5)cm^-2), consistent
with an highly ionized interstellar medium as also inferred from the large
OIII5007/OII3727>10 ratio. We detect CIV1548-1550 resonant doublet in
emission, each component with FWHM <~ 45 km/s, and redshifted by +51(+/-10)
km/s relative to the systemic redshift. We interpret this as nebular emission
tracing an expanding optically-thin interstellar medium. Both CIV1548-1550 and
HeII1640 suggest the presence of hot and massive stars (with a possible faint
AGN). The ultraviolet slope is remarkably blue, =-2.95 (+/-0.20)
(F_łambda=łambda^\beta), consistent with a dust-free and young <~20 Myr
galaxy. We are witnessing an early episode of star-formation in which a
relatively low N_HI and negligible dust attenuation might favor a leakage of
ionizing radiation. This galaxy currently represents a unique low-luminosity
reference object for future studies of the reionization epoch with JWST and
ELT.
Описание
[1603.01616] High-resolution spectroscopy at the faintest limits: an "ELT-like" spectrum of a young optically-thin L=0.02L* star-forming galaxy at z=3.12
Линки и ресурсы
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