Type Ia supernova remnant shell at z = 3.5 seen in the three sightlines toward the gravitationally lensed QSO B1422+231

Abstract

Using the Subaru 8.2m Telescope with the IRCS Echelle spectrograph, we obtained high-resolution (R= 10,000) near-infrared (1.01-1.38 μm) spectra of images A and B of the gravitationally lensed QSO B1422+231 (z = 3.628) consisting of four known lensed images. We detected Mg II absorption lines at z = 3.54, which show a large variance of column densities (0.3 dex) and velocities (10kms-1) between sightlines A and B with a projected separation of only 8.4h -170 pc at that redshift. This is the smallest spatial structure of the high-z gas clouds ever detected after Rauch et al. found a 20pc scale structure for the same z = 3.54 absorption system using optical spectra of images A and C. The observed systematic variances imply that the system is an expanding shell as originally suggested by Rauch et al. By combining the data for three sightlines, we managed to constrain the radius and expansion velocity of the shell (50-100pc, 130kms-1), concluding that the shell is truly a supernova remnant (SNR) rather than other types of shell objects, such as a giant H II region. We also detected strong Fe II absorption lines for this system, but with much broader Doppler width than that of α-element lines. We suggest that this Fe II absorption line originates in a localized Fe II-rich gas cloud that is not completely mixed with plowed ambient interstellar gas clouds showing other α-element low-ion absorption lines. Along with the Fe richness, we conclude that the SNR is produced by an SNIa explosion. © 2012. The American Astronomical Society. All rights reserved..