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- 2019
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Tidskriftsartikel (refereegranskat)
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- Vanzella, E., et al.
(författare)
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An extremely metal-poor star complex in the reionization era : Approaching Population III stars with JWST
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 678
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Tidskriftsartikel (refereegranskat)abstract
- We present JWST/Near Infrared Spectrograph (NIRSpec) integral field spectroscopy (IFS) of a lensed Population III candidate stellar complex (dubbed Lensed And Pristine 1, LAP1), with a lensing-corrected stellar mass of ≲104 M⊙ and an absolute luminosity of MUV > −11.2 (mUV > 35.6), confirmed at redshift 6.639 ± 0.004. The system is strongly amplified (μ ≳ 100) by straddling a critical line of the Hubble Frontier Field galaxy cluster MACS J0416. Although the stellar continuum is currently not detected in the Hubble and JWST/Near Infrared Camera (NIRCam) and Near Infrared Imager and Slitless Spectrograph (NIRISS) imaging, arclet-like shapes of Lyman and Balmer lines, Lyα, Hγ, Hβ and Hα are detected with NIRSpec IFS with signal-to-noise ratios (S/N) of approximately 5 − 13 and large equivalent widths (> 300 − 2000 Å), along with a remarkably weak [O III]λλ4959, 5007 at S/N ≃ 4. LAP1 shows a large ionizing photon production efficiency, log(ξion[erg Hz−1]) > 26. From the metallicity indexes R23 = ([O III] + [O II])/Hβ ≲ 0.74 and R3 = ([O III]/Hβ) = 0.55 ± 0.14, we derive an oxygen abundance of 12 + log(O/H)≲6.3. Intriguingly, the Hα emission is also measured in mirrored subcomponents where no [O III] is detected, providing even more stringent upper limits on the metallicity if in situ star formation is ongoing in this region (12 + log(O/H) < 6). The formal stellar mass limit of the subcomponents would correspond to ∼103 M⊙ or MUV fainter than −10. Alternatively, this metal-free, pure line-emitting region could be the first case of a fluorescing H I gas region induced by transverse escaping ionizing radiation from a nearby star complex. The presence of large equivalent-width hydrogen lines and the deficiency of metal lines in such a small region make LAP1 the most metal-poor star-forming region currently known in the reionization era and a promising site that may host isolated, pristine stars.
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- Cook, D. O., et al.
(författare)
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Star cluster catalogues for the LEGUS dwarf galaxies
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 484:4, s. 4897-4919
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Tidskriftsartikel (refereegranskat)abstract
- We present the star cluster catalogues for 17 dwarf and irregular galaxies in the HST Treasury Program 'Legacy ExtraGalactic UV Survey' (LEGUS). Cluster identification and photometry in this sub-sample are similar to that of the entire LEGUS sample, but special methods were developed to provide robust catalogues with accurate fluxes due to low cluster statistics. The colours and ages are largely consistent for two widely used aperture corrections, but a significant fraction of the clusters are more compact than the average training cluster. However, the ensemble luminosity, mass, and age distributions are consistent suggesting that the systematics between the two methods are less than the random errors. When compared with the clusters from previous dwarf galaxy samples, we find that the LEGUS catalogues are more complete and provide more accurate total fluxes. Combining all clusters into a composite dwarf galaxy, we find that the luminosity and mass functions can be described by a power law with the canonical index of -2 independent of age and global SFR binning. The age distribution declines as a power law, with an index of approximate to -0.80 +/- 0.15, independent of cluster mass and global SFR binning. This decline of clusters is dominated by cluster disruption since the combined star formation histories and integrated-light SFRs are both approximately constant over the last few hundred Myr. Finally, we find little evidence for an upper-mass cut-off (< 2 sigma) in the composite cluster mass function, and can rule out a truncation mass below approximate to 10(4.5)M(circle dot) but cannot rule out the existence of a truncation at higher masses.
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