Data for "JWST COMPASS Program: The 3--5$\mu$m transmission spectrum of LTT 1445 A b"

The search for an atmosphere on the closest rocky M dwarf planet, \ltt, has been the subject of intense investigation from both the ground and space. Here, we present the first JWST transmission spectrum of \ltt ~using a single visit spanning 3-5~$\mu$m using NIRSpec/G395H. We conduct two independent reductions of the data using both the \texttt{Eureka!} and \texttt{ExoTiC-JEDI} pipelines. Overall, we measure the NRS1 transit depths to a median precision of $\sim23$~ppm in 41 spectroscopic channels with uniform widths of 30 pixels ($\sim$ 0.02 $\mu$m), and the NRS2 transit depths to $\sim36$~ppm precision in 65 spectroscopic channels, also with uniform widths of 30 pixels. We rule out any statistically significant spectral features at this precision and place limits on atmospheric metallicity. Using NIRSpec/G395H alone, we find the atmospheric metallicity must be $\gtrsim350~\times$ Solar when considering cases with opaque pressure levels greater than 0.01~bars. We also conduct a combined analysis of JWST/NIRSpec and HST/WFC3 transmission data and find our atmospheric limits can be extended $\gtrsim500~\times$ Solar when considering both datasets.  If an atmosphere is present on \ltt, its atmosphere is likely high mean molecular weight. Future analyses both in transit and emission will uncover whether there are detectable atmospheric features.