TY - JOUR
T1 - An extremely metal-poor star complex in the reionization era
T2 - Approaching Population III stars with JWST
AU - Vanzella, E.
AU - Loiacono, F.
AU - Bergamini, P.
AU - Mestriac, U.
AU - Castellano, M.
AU - Rosati, P.
AU - Meneghetti, M.
AU - Grillo, C.
AU - Calura, F.
AU - Mignoli, M.
AU - Bradač, M.
AU - Adamo, A.
AU - Rihtaršič, G.
AU - Dickinson, M.
AU - Gronke, M.
AU - Zanella, A.
AU - Annibali, F.
AU - Willott, C.
AU - Messa, M.
AU - Sani, E.
AU - Acebron, A.
AU - Bolamperti, A.
AU - Comastri, A.
AU - Gilli, R.
AU - Caputi, K. I.
AU - Ricotti, M.
AU - Gruppioni, C.
AU - Ravindranath, S.
AU - Mercurio, A.
AU - Strait, V.
AU - Martis, N.
AU - Pascale, R.
AU - Caminha, G. B.
AU - Annunziatella, M.
AU - Nonino, M.
N1 - Publisher Copyright:
© 2023 The Authors.
PY - 2023/10/1
Y1 - 2023/10/1
N2 - 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 ), along with a remarkably weak [O III]λλ4959, 5007 at S/N 4. LAP1 shows a large ionizing photon production efficiency, log(ξion[erg Hz1]) > 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.
AB - 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 ), along with a remarkably weak [O III]λλ4959, 5007 at S/N 4. LAP1 shows a large ionizing photon production efficiency, log(ξion[erg Hz1]) > 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.
KW - Galaxies: high-redshift
KW - Galaxies: star formation
KW - Gravitational lensing: strong
KW - Stars: Population III
UR - http://www.scopus.com/inward/record.url?scp=85176111714&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/202346981
DO - 10.1051/0004-6361/202346981
M3 - Article
AN - SCOPUS:85176111714
SN - 0004-6361
VL - 678
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A173
ER -