2018RAA....18...53D

We present a detailed analysis of the soft X-ray emission of 3C 445 using an archival Chandra High Energy Transmission Grating (HETG) spectrum. Highly-ionized H- and He-like Mg, Si and S lines, as well as a resolved low-ionized Si Kα line, are detected in the high resolution spectrum. The He-like triplets of Mg and Si are resolved into individual lines, and the calculated R ratios indicate a high density for the emitter. The low values of G ratios indicate the lines originate from collisionally ionized plasmas. However, the detection of a resolved narrow Ne X radiative recombination continua (RRC) feature in the spectrum seems to prefer a photoionized environment. The spectrum is subsequently modeled with a photoionization model, and the results are compared with those of a collisional model. Through a detailed analysis of the spectrum, we exclude a collisional origin for these emission lines. A one-component photoionization model provides a great fit to the emission features. The best-fit parameters are $logξ= 3.3^{+0.4}_{-0.3}$ erg cm s$^{-1}$, $n_H=5^{+15}_{-4.5}×10^{10}$ cm$^{-3}$, and $N_H = 2.5^{+3.8}{-1.7}×10^{20}$ cm$^{-2}$. According to the calculated high density for the emitter, the measured velocity widths of the emission lines and the inferred radial distance (6 x 10$^{14}$ - 8 x 10$^{15}$ cm), we suggest the emission lines originating from matter are located in the broad line region (BLR).