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Main Colloquium |
Prof. Heinz Andernach
| SCHEDULED |
Th"uringer Landessternwarte, Tautenburg, Germany, on leave from University of Guanajuato, Mexico
Giant Radio Galaxies (GRGs) with a projected linear extent over 1 Mpc
were first found in 1974, and over 5,000 are now known, plus another
5,000 larger than 0.7 Mpc, the currently adopted threshold for GRGs. I
present results based on my compilation of GRGs (a) from literature,
and
my own visual inspection of (b) large-scale radio surveys in general
(e.g. NVSS, SUMSS, RACS, LoTSS DR2, etc.), and of specific regions like
(c) the LoTSS Deep Fields (LDF), as well as (d) the equatorial
SWAG-X/eFEDS/LOFAR field. Although very time-consuming, systematic
visual inspection clearly provides a higher ratio of GRGs <1 Mpc to
those >1 Mpc than literature samples, which tend to disfavor smaller
GRGs. I also show examples of published mis-identifications based on
automated algorithms, lacking the necessary human control of the
results. In order to shed light on the open question why GRGs can reach
their large sizes, I look at (a) their location as function of
environment density in the LDF and SWAG-X fields, and (b) I select the
very largest 115 GRGs (from 3 to 6.6 Mpc), to study how they were
discovered (mostly by LOFAR), their distribution in redshift and radio
luminosity, and their bending angle, and compare these with GRGs of
more
modest sizes.