Spectroscopic characterisation of gravitationally lensed stars at high redshifts

Abstract

Deep imaging of galaxy cluster fields have in recent years revealed tens of candidates for gravitationally lensed stars at redshifts $z\approx$ 1-6, and future searches are expected to reveal highly magnified stars from even earlier epochs. Multi-band photometric observations may be used to constrain the redshift, effective temperature $T_{\mathrm{eff}}$ and dust attenuation along the line of sight to such objects. When combined with an estimate of the likely magnification, these quantities may be converted into a constraint on the stellar luminosity and, for an adopted set of stellar evolutionary tracks, the initial stellar mass. Further characterization is, however, difficult without spectroscopic observations, which at the typical brightness levels of high-redshift lensed stars becomes extremely challenging for even the largest existing telescopes. Here, we explore what spectral features one can realistically hope to detect in lensed stars with peak brightness in the range 26-28 AB mag, $T_{\mathrm{eff}}=$ 4000-50 000 K and redshifts $z=$1-10, using spectroscopy with the James Webb Space Telescope (JWST) and the forthcoming Extremely Large Telescope. We find that a majority of detectable lines appear in the rest UV-range for stars with $T_{\mathrm{eff}}\ge$15 000 K. The strongest detectable spectral lines are the C IV $\lambda$ 1550 Å line and the Si IV $\lambda \lambda$1393, 1403 Å-doublet at $T_{\mathrm{eff}}=$30 000 K. For lower temperatures, the calcium H- and K-lines at $T_{\mathrm{eff}}=$6000 K are among the most readily detectable. In limited wavelength ranges, ELT is expected to provide more sensitive spectroscopic observations, and with higher resolution than JWST. We find that variations of both mass loss rate and metallicity lead to noticeable effects in the detectability of certain spectral lines with both JWST and ELT.

12 pages, 6 figures, accepted in A&A

References in corpus (11)

• Understanding caustic crossings in giant arcs: characteristic scales, event rates, and constraints on compact dark matter
• A Highly Magnified Star at Redshift 6.2
• JWST Imaging of Earendel, the Extremely Magnified Star at Redshift $z=6.2$
• Two lensed star candidates at $z\simeq 4.8$ behind the galaxy cluster MACS J0647.7+7015
• JWST's PEARLS: a new lens model for ACT-CL J0102$-$4915, "EL Gordo'', and the first red supergiant star at cosmological distances discovered by JWST
• Uncovering a population of gravitational lens galaxies with magnified standard candle SN Zwicky
• JWST's PEARLS: Mothra, a new kaiju star at z=2.091 extremely magnified by MACS0416, and implications for dark matter models
• Early results from GLASS-JWST VIII: An Extremely Magnified Blue Supergiant Star at Redshift 2.65 in the Abell 2744 Cluster Field
• Spectroscopy of the first resolved strongly lensed Type Ia supernova iPTF16geu
• Raising the observed metallicity floor with a 3D non-LTE analysis of SDSS J102915.14+172927.9
• Extremely strong CIV 1550 nebular emission in the extremely low-metallicity star-forming galaxy J2229+2725

Cited by in corpus (2)

• Explanations for the two-component spectral energy distributions of gravitationally lensed stars at high redshifts
• Kinematic Mapping of Giant Arcs: A New Method to Locate Lensing Critical Curves