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