Observing Dark Stars with JWST

Abstract

We study the capability of the James Webb Space Telescope (JWST) to detect Supermassive Dark Stars (SMDS). If the first stars are powered by dark matter heating in triaxial dark matter haloes, they may grow to be very large and very bright, visible in deep imaging with JWST and even Hubble Space Telescope (HST). We use HST surveys to place bounds on the numbers of SMDSs that may be detected in future JWST imaging surveys. We showed that SMDS in the mass range $10^6-10^7 M_\odot$ are bright enough to be detected in all the wavelength bands of the NIRCam on JWST . If SMDSs exist at z ~10, 12, and 14, they will be detectable as J-band, H-band, or K-band dropouts, respectively. With a total survey area of 150 arcmin^2 (assuming a multi-year deep parallel survey with JWST), we find that typically the number of $10^6 M_\odot$ SMDSs found as H or K-band dropouts is ~10^5\fsmds, where the fraction of early DM haloes hosting DS is likely to be small, \fsmds<<1. If the SDMS survive down to z=10 where HST bounds apply, then the observable number of SMDSs as H or K-band dropouts with JWST is ~1-30. While individual SMDS are bright enough to be detected by JWST, standard PopIII stars are not, and would only be detected in first galaxies with total stellar masses of ~$10^6-10^8 M_\odot$. Differentiating first galaxies at z>10 from SMDSs would be possible with spectroscopy: the SMDS (which are too cool produce significant nebular emission) will have only absorption lines while the galaxies are likely to produce emission lines as well. Of particular interest would be the 1640 HeII emission line as well as H{\alpha} lines which would be signatures of early galaxies rather than SMDSs. The detection of SMDSs would not only provide alternative evidence for WIMPs but would also provide possible seeds for the formation of supermassive black holes that power QSOs at z~6.