GeminiFocus October 2018 | Page 12

Figure 3. Top panel: The two- dimensional GMOS spec- trum showing the strong emission feature detected in the radio galaxy TGSS J1530 + 1049. The size of the emission region is a bit less than 1 arc- second. Lower panel: One-dimensional plot of the spectrum of TGSS J1530 + 1049 (black line) is compared to a simple, symmetric Gaussian fit (orange line) to the emis- sion feature. The asym- metry of the data with respect to the Gaussian fit indicates that the emis- sion is Lyman-α at red- shift of z = 5.72, making TGSS J1530 + 1049 the most distant radio galaxy known to date. (Figure reproduced from Saxena, et al., MNRAS, 480: 2733, 2018.) 10 galaxy known as AGC 208457 has a velocity consistent with the HI velocity at its loca- tion within the extended tidal feature asso- ciated with the interacting galaxy pair NGC 3166/3169. The galaxy’s metal abundance and star formation rate inferred from the optical emission lines indicate that it formed recently from enriched material processed within the larger galaxies. In addition, the study finds that there is no evidence for a significant amount of dark matter. Thus, AGC 208457 has all the characteristics of a genu- ine tidal dwarf galaxy. Targeting a second system, the study con- firms the physical association of gaseous knots and star clusters with the extended tidal tail of NGC 4747, a disturbed galaxy that likely experienced a recent interaction with its larger neighbor NGC 4725. Like AGC 208457, these stellar aggregates likewise have relatively high metallicities, but they GeminiFocus are in an earlier stage of evolution. Thus, they may represent a tidal dwarf galaxy in the process of formation. By using a combi- nation of radio data, wide-field imaging, and GMOS spectroscopy to confirm the nature of these objects, this work significantly ex- pands the limited sample of well document- ed tidal dwarf galaxies. Confirmation of the Most Distant Known Radio Galaxy More than a dozen galaxies have been re- ported at redshifts beyond 7. These tend to be highly magnified star-forming objects found at infrared wavelengths, seen when the Universe was less than 5% of its current age. However, radio emission from such ob- jects has not yet been detected. This is mainly because the vast distances and extreme red- shifting will make any radio signal difficult to October 2018