High-resolution spectroscopy of a young, low-metallicity optically-thin L=0.02L* star-forming galaxy at z=3.12

TY - JOUR

T1 - High-resolution spectroscopy of a young, low-metallicity optically-thin L=0.02L* star-forming galaxy at z=3.12

AU - Vanzella, E.

AU - Barros, S. De

AU - Cupani, G.

AU - Karman, W.

AU - Gronke, M.

AU - Balestra, I.

AU - Coe, D.

AU - Mignoli, M.

AU - Brusa, M.

AU - Calura, F.

AU - Caminha, G. -B.

AU - Caputi, K.

AU - Castellano, M.

AU - Christensen, Lise Bech

AU - Comastri, A.

AU - Cristiani, S.

AU - Dijkstra, M.

AU - Fontana, A.

AU - Giallongo, E.

AU - Giavalisco, M.

AU - Gilli, R.

AU - Grazian, A.

AU - Grillo, C.

AU - Koekemoer, A.

AU - Meneghetti, M.

AU - Nonino, M.

AU - Pentericci, L.

AU - Rosati, P.

AU - Schaerer, D.

AU - Verhamme, A.

AU - Vignali, C.

AU - Zamorani, G.

N1 - 7 pages, 4 figures and 1 table; ApJL, accepted for publication

PY - 2016/4/20

Y1 - 2016/4/20

N2 - We present VLT/X-Shooter and MUSE spectroscopy of a faint F814W = 28.60 ± 0.33 (MUV = -17.0), low-mass (≲107M⊙), and compact (R eff = 62 pc) freshly star-forming galaxy at z = 3.1169 magnified (16×) 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 = λ/dλ ∼ ∼ 3000-7400). We measured C iv , He ii , O iii], C iii], Hβ, [O iii] emission lines with km s-1 and (de-lensed) fluxes spanning the interval erg s-1 cm-2 at signal-to-noise ratio (S/N) = 4-30. The double-peaked Lyα emission with (±7) km s-1 and de-lensed fluxes erg s-1 cm-2 (S/N = ) indicate a low column density of neutral hydrogen gas consistent with a highly ionized interstellar medium as also inferred from the large [O iii]/ [O ii] ratio. We detect C iv resonant doublet in emission, each component with km s-1 and redshifted by +51(±10) km s-1 relative to the systemic redshift. We interpret this as nebular emission tracing an expanding optically thin interstellar medium. Both C iv and He ii suggest the presence of hot and massive stars (with a possible faint active galactic nucleus). The ultraviolet slope is remarkably blue, β = -2.95 ± 0.20 (Fλ λβ), consistent with a dust-free and young ≲20 Myr galaxy. Line ratios suggest an oxygen abundance 12 + log(O/H). We are witnessing an early episode of star formation in which a relatively low N H i 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 the James Webb Space Telescope.

AB - We present VLT/X-Shooter and MUSE spectroscopy of a faint F814W = 28.60 ± 0.33 (MUV = -17.0), low-mass (≲107M⊙), and compact (R eff = 62 pc) freshly star-forming galaxy at z = 3.1169 magnified (16×) 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 = λ/dλ ∼ ∼ 3000-7400). We measured C iv , He ii , O iii], C iii], Hβ, [O iii] emission lines with km s-1 and (de-lensed) fluxes spanning the interval erg s-1 cm-2 at signal-to-noise ratio (S/N) = 4-30. The double-peaked Lyα emission with (±7) km s-1 and de-lensed fluxes erg s-1 cm-2 (S/N = ) indicate a low column density of neutral hydrogen gas consistent with a highly ionized interstellar medium as also inferred from the large [O iii]/ [O ii] ratio. We detect C iv resonant doublet in emission, each component with km s-1 and redshifted by +51(±10) km s-1 relative to the systemic redshift. We interpret this as nebular emission tracing an expanding optically thin interstellar medium. Both C iv and He ii suggest the presence of hot and massive stars (with a possible faint active galactic nucleus). The ultraviolet slope is remarkably blue, β = -2.95 ± 0.20 (Fλ λβ), consistent with a dust-free and young ≲20 Myr galaxy. Line ratios suggest an oxygen abundance 12 + log(O/H). We are witnessing an early episode of star formation in which a relatively low N H i 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 the James Webb Space Telescope.

KW - astro-ph.GA

U2 - 10.3847/2041-8205/821/2/L27

DO - 10.3847/2041-8205/821/2/L27

M3 - Journal article

SN - 2041-8205

VL - 821

JO - The Astrophysical Journal Letters

JF - The Astrophysical Journal Letters

M1 - L27

ER -