Early structure formation from cosmic string loops in light of early JWST observations

Cosmic strings, if they exist, source nonlinear and non-Gaussian perturbations all the way back to the time of equal matter and radiation (and earlier). Here, we compute the mass function of halos seeded by a scaling distribution of cosmic string loops, and we compare the results with the predictions of the standard Gaussian $\mathrm{\Lambda }$ cold dark matter model. Assuming a simple linear relation between stellar mass and halo mass, we also compute the stellar mass function. The contribution of cosmic strings dominates at sufficiently high redshifts $z>z_c$ where $z_c$ depends on the mass of the halo and on the mass per unit length $\mu$ of the strings and is of the order $z_c\sim 12$ for $G\mu ={10}^{-8}$. We find that strings with this value of $G\mu$ can explain the preliminary James Webb Space Telescope (JWST) data on the high-redshift stellar mass density. Based on an extreme value statistic, we find that the mass of the heaviest expected string-seeded galaxy for the current JWST sky coverage is compatible with the heaviest detected galaxy. Given the uncertainties in the interpretation of the JWST data, we discuss predictions for higher redshift observations.

Figure 1

Comparison of the contribution of cosmic string loops to both the halo and stellar mass functions $dn/d\ln M$ with the predictions of the $\mathrm{\Lambda }\mathrm{CDM}$ model for $G\mu ={10}^{-10},{10}^{-9}$, and ${10}^{-8}$, from top to bottom, respectively. The values of the cosmic string parameters are given in the text.

Figure 2

Cumulative stellar mass density at redshift $z\simeq 8$: Predictions of the cosmic string model vs preliminary JWST results. The four colorful lines are cumulative stellar mass densities of loop-seeded galaxies for $G\mu ={10}^{-10}$ (blue), ${10}^{-9}$ (orange), and ${10}^{-8}$ (green), separately. The black line with shaded region is the inferred mass density in the redshift bin $7<z<8.5$ from JWST data [20]. We are assuming a simple linear scaling between halo mass and stellar mass with star formation efficiency $\epsilon =1$.

Figure 3

Cumulative stellar mass density at redshift $z\simeq 9$: Predictions of the cosmic string model vs preliminary JWST results [20].

Figure 4

Predicted cumulative stellar mass density at redshift $z=16$.

Figure 5

Stellar mass function as a function of redshift for two representative values of the mass related to the high-redshift galaxy candidates detected by JWST: Predictions of the cosmic string vs $\mathrm{\Lambda }\mathrm{CDM}$ model. The black lines are the predictions of the $\mathrm{\Lambda }\mathrm{CDM}$ model, and the colored curves are the predictions of the string model, with $G\mu ={10}^{-10}$ (blue), $G\mu ={10}^{-9}$ (orange), and $G\mu ={10}^{-8}$ (green). Note the accidental overlap between the blue solid curve and the green dashed line.

Figure 6

The $1\sigma$ (dashed) and $2\sigma$ (solid) confidence intervals of the EVS PDF of the expected largest solar mass halo predicted by the cosmic string model as a function of $G\mu$ evaluated for the angular and redshift coverage corresponding to the preliminary JWST data. The horizontal axis is the mass, the vertical axis is $G\mu$. The blue lines correspond to redshift $z=10$ and the red lines are $z=16$.

Figure 7

Expected largest solar mass halo for a survey with the sky and redshift coverage of the preliminary JWST analyses. The vertical axis represents the cosmic string distribution parameter $N$ plotted in units of its canonical value $N_0=570$, and the horizontal axis is the stellar mass. One and two sigma confidence intervals are shown. The colors correspond to the same three different values of $G\mu$ used earlier (see text). The predictions are for redshift $z\ge 10$. The vertical black lines with gray shaded region correspond to the inferred stellar mass of galaxy 14924, which is the heaviest high-redshift galaxy from JWST.

Figure 8

The same as in Fig. (7), but for redshift $z\ge 16$. The shaded region corresponds to the JWST galaxy CEERS-1749.