ABSTRACT
We present a VLT/X-Shooter spectroscopy of the Lyman continuum (LyC) emitting galaxy Ion2 at z = 3.2121 and compare it to that of the recently discovered strongly lensed LyC emitter at ...z = 2.37, known as the Sunburst arc. Three main results emerge from the X-Shooter spectrum: (a) the Ly α has three distinct peaks with the central one at the systemic redshift, indicating a ionized tunnel through which both Ly α and LyC radiation escape; (b) the large O32 oxygen index (O iii λλ4959, 5007/O ii λλ3727, 3729) of $9.18_{-1.32}^{+1.82}$ is compatible to those measured in local (z ∼0.4) LyC leakers; (c) there are narrow nebular high-ionization metal lines with σv < 20 km s−1, which confirms the presence of young hot, massive stars. The He iiλ1640 appears broad, consistent with a young stellar component including Wolf–Rayet stars. Similarly, the Sunburst LyC emitter shows a triple-peaked Ly α profile and from VLT/MUSE spectroscopy the presence of spectral features arising from young hot and massive stars. The strong lensing magnification, (μ > 20), suggests that this exceptional object is a gravitationally bound star cluster observed at a cosmological distance, with a stellar mass M ≲ 107 M⊙ and an effective radius smaller than 20 pc. Intriguingly, sources like Sunburst but without lensing magnification might appear as Ion2-like galaxies, in which unresolved massive star clusters dominate the ultraviolet emission. This work supports the idea that dense young star clusters can contribute to the ionization of the IGM through holes created by stellar feedback.
We investigate the strongly lensed (
μ
≃ ×10 − 100) Lyman continuum (LyC) galaxy, dubbed Sunburst, at
z
= 2.37, taking advantage of a new accurate model of the lens. A characterization of the ...intrinsic (delensed) properties of the system yields a size of ≃3 sq. kpc, a luminosity of
M
UV
= −20.3, and a stellar mass of
M
≃ 10
9
M
⊙
; 16% of the ultraviolet light is located in a 3 Myr old gravitationally bound young massive star cluster (YMC), with an effective radius of ∼8 pc (corresponding to 1 milliarcsec without lensing) and a dynamical mass of ∼10
7
M
⊙
(similar to the stellar mass) – from which LyC radiation is detected (
λ
< 912 Å). The star formation rate and stellar mass surface densities for the YMC are Log
10
(Σ
SFR
M
⊙
yr
−1
kpc
−2
) ≃ 3.7 and Log
10
(Σ
M
M
⊙
pc
−2
) ≃ 4.1, with sSFR > 330 Gyr
−1
, consistent with the values observed in local young massive star clusters. The inferred outflowing gas velocity (> 300 km s
−1
) exceeds the escape velocity of the cluster. The resulting relative escape fraction of the ionizing radiation emerging from the entire galaxy is higher than 6−12%, whilst it is ≳46 − 93% if inferred from the YMC multiple line of sights. At least 12 additional unresolved star-forming knots with radii spanning the interval 3 − 20 pc (the majority of them likely gravitationally bound star clusters) are identified in the galaxy. A significant fraction (40−60%) of the ultraviolet light of the entire galaxy is located in such bound star clusters. In adopting a formation timescale of the star clusters of 20 Myr, a cluster formation efficiency Γ ≳ 30%. The star formation rate surface density of the Sunburst galaxy (Log
10
(Σ
SFR
) = 0.5
−0.2
+0.3
) is consistent with the high inferred Γ, as observed in local galaxies experiencing extreme gas physical conditions. Overall, the presence of a bursty event (i.e., the 3 Myr old YMC with large sSFR) significantly influences the morphology (nucleation), photometry (photometric jumps), and spectroscopic output (nebular emission) of the entire galaxy. Without lensing magnification, the YMC would be associated to an unresolved 0.5 kpc–size star-forming clump. The delensed LyC and UV magnitude
m
1600
(at 1600 Å) of the YMC are ≃30.6 and ≃26.9, whilst the entire galaxy has
m
1600
≃ 24.8. The Sunburst galaxy shows a relatively large rest-frame equivalent width of EW
rest
(H
β
+ O
III
λλ
4959, 5007) ≃ 450 Å, with the YMC contributing to ∼30% (having a local EW
rest
≃ 1100 Å) and ∼1% of the total stellar mass. If O-type (ionizing) stars are mainly forged in star clusters, then such engines were the key ionizing agents during reionization and the increasing occurrence of high equivalent width lines (H
β
+ O
III
) observed at
z
> 6.5 might be an indirect signature of a high frequency of forming massive star clusters (or high Γ) at reionization. Future facilities, which will perform at few tens milliarcsec resolution (e.g., VLT/MAVIS or ELT), will probe bound clusters on moderately magnified (
μ
< 5 − 10) galaxies across cosmic epochs up to reionization.
Abstract
We report on the serendipitous discovery of a z = 4.0, M1500 = −22.20 star-forming galaxy (Ion3) showing copious Lyman continuum (LyC) leakage (∼60 per cent escaping), a remarkable multiple ...peaked Ly α emission, and significant Ly α radiation directly emerging at the resonance frequency. This is the highest redshift confirmed LyC emitter in which the ionizing and Ly α radiation possibly share a common ionized channel (with NH I < 1017.2 cm−2). Ion3 is spatially resolved, it shows clear stellar winds signatures like the P-Cygni N vλ1240 profile, and has blue ultraviolet continuum (β = −2.5 ± 0.25, Fλ ∼ λβ) with weak low-ionization interstellar metal lines. Deep VLT/HAWKI Ks and Spitzer/IRAC 3.6 and 4.5μm imaging show a clear photometric signature of the H α line with equivalent width of 1000 Å rest-frame emerging over a flat continuum (Ks − 4.5μm ≃ 0). From the SED fitting, we derive a stellar mass of 1.5 × 109 M⊙, SFR of 140 M⊙ yr−1 and age of ∼10 Myr, with a low dust extinction, E(B − V) ≲ 0.1, placing the source in the starburst region of the SFR−M* plane. Ion3 shows similar properties of another LyC emitter previously discovered (z = 3.21, Ion2, Vanzella et al. 2016). Ion3 (and Ion2) represents ideal high-redshift reference cases to guide the search for reionizing sources at z > 6.5 with JWST.
We present VLT/X-Shooter and MUSE spectroscopy of a faint F814W = 28.60 + or - 0.33 (M sub(UV)=-17.0, low-mass (<, ~10 super(7)M sub(middo t in circle)), and compact (R sub(eff)= 62 pc) freshly ...star-forming galaxy at z= 3.1169 magnified (16x) 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= lambda /dlambda ~ 3000-7400). We measured C IV lambda 1548, 1550, He II lambda 1640, O IIIlambda 1661,1666, C IIIlambdalambda 1907,1909, Hbeta, OIIIlambdalambda 4959,5007 emission lines with <, ~ 50 km s super(-1) and (de-lensed) fluxes spanning the interval 1.0 x 10 super(-19)-2 x 10 super(-18) erg s super(-1) cm super(-2) at signal-to-noise ratio (S/N) = 4-30. The double-peaked Lyalpha emission with Deltanured - blue) = 280 (+ or -7) km s super(-1) and de-lensed fluxes 2.4 sub((blue)) 8.5 sub((red)) x 10 super(-18) erg s super(-1) cm super(-2)(S/N = 38 sub((blue)) 110 sub((red))) indicate a low column density of neutral hydrogen gas consistent with a highly ionized interstellar medium as also inferred from the large OIIIlambda 5007/ OIIlambda 3727 > 10 ratio. We detect C IV lambda 1548,1550 resonant doublet in emission, each component with FWHM <, ~ 45 km s super(-1) and redshifted by +51(+ or -10) km s super(-1) relative to the systemic redshift. We interpret this as nebular emission tracing an expanding optically thin interstellar medium. Both C IV lambda 1548,1550 and He II lambda 1640 suggest the presence of hot and massive stars (with a possible faint active galactic nucleus). The ultraviolet slope is remarkably blue, beta =-2.95 + or - 0.20 (F sub(lambda)= lambda super(beta)), consistent with a dust-free and young <, ~20 Myr galaxy. Line ratios suggest an oxygen abundance 12 + log(O/H) < 7.8. We are witnessing an early episode of star formation in which a relatively low N sub(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.
Abstract
We study the spectrophotometric properties of a highly magnified (
) 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 (
), young (
Myr), low-mass (
), low-metallicity (12 + Log(O/H) ≃ 7.7, or 1/10 solar), and compact (30 pc effective radius) stellar systems separated by
pc after correcting for lensing amplification. We measured several rest-frame ultraviolet and optical narrow (
km s
−1
) high-ionization lines. These features may be the signature of very hot (
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 Ly
α
emission (e.g., C
iv
/Ly
α
), despite the fact that the Ly
α
line flux is expected to be 150 times brighter (inferred from the H
β
flux). A spatially offset, strongly magnified (
) Ly
α
emission with a spatial extent
kpc
2
is instead identified 2 kpc away from the system. The origin of such a faint emission could be the result of fluorescent Ly
α
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
de-lensed). This is the first confirmed metal-line emitter at such low-luminosity and redshift without Ly
α
emission—suggesting that, at least in some cases, a non-uniform covering factor of the neutral gas might hamper the Ly
α
detection.
We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from ~0.03 to ~1.2 M⊙, but ...mostly with 0.1 M⊙<M⋆< 0.5 M⊙. Our aim is twofold: firstly, to analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (Lacc), and in turn the accretion rate (Ṁacc), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. We computed the flux and luminosity (Lline) of many emission lines of H , He , and Ca ii, observed simultaneously in the range from ~330 nm to 2500 nm. The luminosity of all the lines is well correlated with Lacc. We provide empirical relationships between Lacc and the luminosity of 39 emission lines, which have a lower dispersion than relationships previously reported in the literature. Our measurements extend the Paβ and Brγ relationships to Lacc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies of measuring Lacc and Ṁacc yield significantly different results: Hα line profile modelling may underestimate Ṁacc by 0.6 to 0.8 dex with respect to Ṁacc derived from continuum-excess measures. These differences may explain the probably spurious bi-modal relationships between Ṁacc and other YSOs properties reported in the literature. We derived Ṁacc in the range 2 × 10-12–4 × 10-8 M⊙ yr-1 and conclude that Ṁacc ∝ M⋆1.8(±0.2), with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Ṁacc, confirming previous suggestions that the geometry of the accretion flow controls the rate at which the disc material accretes onto the central star.
We present VLT/X-shooter observations of a sample of 36 accreting low-mass stellar and substellar objects (YSOs) in the Lupus star-forming region, spanning a range in mass from similar0.03 to ...similar1.2 M, but mostly with 0.1 M<Msub *< 0.5 M. Our aim is twofold: firstly, to analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (Lsubacc), and in turn the accretion rate (Msubacc ), was derived by modelling the excess emission from the UV to the near-infrared as the continuum emission of a slab of hydrogen. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Msubacc, confirming previous suggestions that the geometry of the accretion flow controls the rate at which the disc material accretes onto the central star.
ABSTRACT
We discovered a strongly lensed (μ ≳ 40) Ly α emission at z = 6.629 (S/N ≃ 18) in the MUSE Deep Lensed Field (MDLF) targeting the Hubble Frontier Field (HFF) galaxy cluster MACS J0416. ...Dedicated lensing simulations imply that the Ly α emitting region necessarily crosses the caustic. The arc-like shape of the Ly α extends 3 arcsec on the observed plane and is the result of two merged multiple images, each one with a de-lensed Ly α luminosity L ≲ 2.8 × 1040 erg s−1 arising from a confined region (≲150 pc effective radius). A spatially unresolved Hubble Space Telescope(HST) counterpart is barely detected at S/N ≃ 2 after stacking the near-infrared bands, corresponding to an observed (intrinsic) magnitude m1500 ≳ 30.8 (≳35.0). The inferred rest-frame Ly α equivalent width is EW0 > 1120 Å if the IGM transmission is TIGM < 0.5. The low luminosities and the extremely large Ly α EW0 match the case of a Population III (Pop III) star complex made of several dozens stars (∼104 M⊙) that irradiate an H ii region crossing the caustic. While the Ly α and stellar continuum are among the faintest ever observed at this redshift, the continuum and the Ly α emissions could be affected by differential magnification, possibly biasing the EW0 estimate. The aforementioned tentative HST detection tends to favour a large EW0, making such a faint Pop III candidate a key target for the James Webb Space Telescope and Extremely Large Telescopes.
ABSTRACT
We study the physical properties (size, stellar mass, luminosity, and star formation rate) and scaling relations for a sample of 166 star-forming clumps with redshift z ∼ 2–6.2. They are ...magnified by the Hubble Frontier Field galaxy cluster MACS J0416 and have robust lensing magnification (2 ≲ μ ≲ 82) computed by using our high-precision lens model, based on 182 multiple images. Our sample extends by ∼3 times the number of spectroscopically confirmed lensed clumps at z ≳ 2. We identify clumps in ultraviolet continuum images and find that, whenever the effective spatial resolution (enhanced by gravitational lensing) increases, they fragment into smaller entities, likely reflecting the hierarchically organized nature of star formation. Kpc-scale clumps, most commonly observed in field, are not found in our sample. The physical properties of our sample extend the parameter space typically probed by z ≳ 1 field observations and simulations, by populating the low mass (M⋆ ≲ 107 M⊙), low star formation rate (SFR ≲ 0.5 M⊙ yr−1), and small size (Reff ≲ 100 pc) regime. The new domain probed by our study approaches the regime of compact stellar complexes and star clusters. In the mass–size plane, our sample spans the region between galaxies and globular clusters, with a few clumps in the region populated by young star clusters and globular clusters. For the bulk of our sample, we measure star formation rates which are higher than those observed locally in compact stellar systems, indicating different conditions for star formation at high redshift than in the local Universe.
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