Sky & Telescope - April 2023 QR - 24

GARY IMM (2)
Targets in Virgo
NGC 4731 is a member of the NGC 4697 group, which is
a subcomponent of the Virgo II Groups. Photographs show
twisted, extended arms that may be the result of gravitational
interactions with a nearby galaxy.
Slewing 4° east-southeast of NGC 4731 we come to
NGC 4958, a bright (magnitude 10.7), lens-shaped lenticular.
It's classified as a barred galaxy, but the presence of a bar
is not confirmed, nor is it apparent visually. NGC 4958 is
elongated nearly exactly north-south and seemed impressively
bright in my 18-inch Dob. A 2019 paper outlined evidence
of an accretion disk around a supermassive black hole at its
center, typical of an AGN.
Turning back and moving 4.2° west-southwest we come to
another rather bright target. NGC 4699 is a 9.5-magnitude
spiral with a very prominent center seen at an intermediate
orientation and elongated northeast-southwest. It resides about
SUPERWINDS The starburst galaxy NGC 4666 is in the throes of
particularly intense episodes of star formation. Driving this activity is a
superwind - a massive displacement of gas from the galaxy's core into
intergalactic space. NGC 4666 might be interacting gravitationally with
NGC 4668, the dwarf galaxy at lower left, which may possibly be triggering
the starburst phase.
64 million light-years from Earth. William recorded it as being
" very brilliant. " Observing it in my 18-inch Dob, I described it
as a conspicuous oval with an abruptly brighter core.
The compact galaxy group Hickson 62 sits 1.1° east-southeast
of NGC 4699 and comprises four members ranging in
magnitude from 12.5 to 15.1. The main object of interest here
is the double galaxy, which William first identified, but apparently
did not see, as double. This Hickson group as a whole
- and the double galaxy in particular - has a rather tortured
history of misidentifications. (See page 57 for the Going Deep
column on observing select Hickson Groups.)
Corwin explains that the double galaxy has three designations
in the NGC. After William's original observation on
March 25, 1786, he included it in his Faint Nebulae category,
and the NGC later listed it as NGC 4759. When John observed
the galaxy pair, he saw it as two objects and assigned it two
different numbers in the General Catalogue of Nebulae and
Clusters of Stars. John Louis Emil Dreyer, compiler of the
NGC, assumed that John's pair was different from William's
object and so listed them as NGC 4776 and NGC 4778.
Contributing Editor Steve Gottlieb's informative NGC/IC
TWISTED DISK NGC 4753 exhibits a curious series of crisscrossing
dust lanes. Astronomers attribute this feature to a merger event, when the
galaxy subsumed a smaller companion. The accreted material fashioned
into a disk, and precession twisted the disk into the shape we see today.
bright ovate sprinkled with several stars. William wrote " . . .
the brightness breaks off abruptly so as to almost resemble a
resolvable nucleus consisting of 4 or 5 bright stars . . . . " An
11th-magnitude star lies 2.7' northeast of the core.
Continuing another 50′ southeast, we encounter the soft
glow of the nearly edge-on barred spiral NGC 4731. Of magnitude
11.5, it's fairly large and elongated almost east-west.
William described it as bright, but I find it to be rather faint,
which instead agrees with John's description of the object.
24 APRIL 2023 * SKY & TELESCOPE
site explains further that German astronomer Heinrich
Louis d'Arrest observed the object on March 30, 1867, with
an 11-inch refractor at Copenhagen Observatory. Along with
measuring an accurate position, he noted a 10th-magnitude
star that lies 1.5′ to the south. D'Arrest, however, did not
perceive it as double but rather saw it as a single nebulosity.
Fellow German astronomer Wilhelm Tempel, who instead
recognized the object as double, confirmed d'Arrest's position
using Arcetri Observatory's 11-inch refractor.
The Revised New Catalogue of Nonstellar Astronomical
Objects and the Morphological Catalogue of Galaxies identify
the two components as NGC 4759 and NGC 4761. Corwin,
however, has established that the galaxy that lies 1′ eastnortheast
of the southeastern component of the double, often
identified as NGC 4764, is properly NGC 4761.
The double galaxy comprises the two brightest members
of Hickson 62. The southeastern companion is the brighter
component designated HCG 62A. This galaxy should instead
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