Reaching for the stars - JWST/NIRSpec spectroscopy of a lensed star candidate at z = 4.76

Publication date: 
Main author: 
Furtak, Lukas J.
IAA authors: 
Jiménez-Teja, Yolanda
Furtak, Lukas J.;Meena, Ashish K.;Zackrisson, Erik;Zitrin, Adi;Brammer, Gabriel B.;Coe, Dan;Diego, José M.;Eldridge, Jan J.;Jiménez-Teja, Yolanda;Kokorev, Vasily;Ricotti, Massimo;Welch, Brian;Windhorst, Rogier A.;Abdurro'uf;Andrade-Santos, Felipe;Bhatawdekar, Rachana;Bradley, Larry D.;Broadhurst, Tom;Chen, Wenlei;Conselice, Christopher J.;Dayal, Pratika;Frye, Brenda L.;Fujimoto, Seiji;Hsiao, Tiger Y. -Y.;Kelly, Patrick L.;Mahler, Guillaume;Mandelker, Nir;Norman, Colin;Oguri, Masamune;Pirzkal, Norbert;Postman, Marc;Ravindranath, Swara;Vanzella, Eros;Wilkins, Stephen M.
Monthly Notices of the Royal Astronomical Society
Publication type: 
We present JWST/NIRSpec observations of a highly magnified star candidate at a photometric redshift of z<SUB>phot</SUB> ≃ 4.8, previously detected in JWST/NIRCam imaging of the strong lensing (SL) cluster MACS J0647+7015 (z = 0.591). The spectroscopic observation allows us to precisely measure the redshift of the host arc at z<SUB>spec</SUB> = 4.758 ± 0.004, and the star's spectrum displays clear Lyman- and Balmer-breaks commensurate with this redshift. A fit to the spectrum suggests a B-type super-giant star of surface temperature $T_{\mathrm{eff,B}}\simeq 15\, 000$ K with either a redder F-type companion ($T_{\mathrm{eff,F}}\simeq 6\, 250$ K) or significant dust attenuation (A<SUB>V</SUB> ≃ 0.82) along the line of sight. We also investigate the possibility that this object is a magnified young globular cluster rather than a single star. We show that the spectrum is in principle consistent with a star cluster, which could also accommodate the lack of flux variability between the two epochs. However, the lack of a counter image and the strong upper limit on the size of the object from lensing symmetry, r ≲ 0.5 pc, could indicate that this scenario is somewhat less likely - albeit not completely ruled out by the current data. The presented spectrum seen at a time when the Universe was only ~1.2 Gyr old showcases the ability of JWST to study early stars through extreme lensing.
ADS Bibcode: 
gravitational lensing: micro;gravitational lensing: strong;stars: individual: MACS0647-star-1;stars: massive;galaxies: high-redshift;galaxies: star clusters: general;Astrophysics - Astrophysics of Galaxies;Astrophysics - Cosmology and Nongalactic Astrophysics;Astrophysics - Solar and Stellar Astrophysics