Object of the Week April 2nd 2023

NGC 3090

MCG 0-26-5, Z 8-16, PGC 28945

Constellation Sextans

Galaxy

R.A. 10h00m30.3s

Dec. -02°58'10"

Magnitude: 13.60 B

Size: 1.6' x 1.3'

After all the OOTW’s recently that really require Jimi’s 48” to see I thought I would go for something
easier this time. It is also getting harder to observe now at northern latitudes as the equinox weather
is never that good and it is starting to get light now at nights with the changes to DST and we really
only have another 4 weeks dark time. Hence, I am going to the constellation of Sextans and the
small galaxy group around NGC 3090. The 6 NGC galaxies in this group were discovered on the
22nd Jan 1865 by Albert Marth using William Lassell’s 48” telescope in Malta. This was one of the
last of the large speculum metal mirror telescopes. For further information on Marth’s work with
this telescope and his catalogue of nebulae see Alan Dowdell’s article in the Webb Society QJ 100, o
r of course Wolfgang’s monumental work on Observing and Cataloguing Nebulae and Clusters.
The group consists of NGC 3083, 3086, 3090, 3092,3093 and 3101.

Attachment 5093

It does appear to be a physical grouping and has the galaxy cluster catalogue number WBL 248.
The galaxy CGCG 8-18 is also part of this group. As listed in the WBL the group contains 7 galaxies.

Attachment 5094

These galaxies will be much more challenging to find as most of them are in the 13-15th magnitude
range. As expected, this is too faint to appear in most of the classic references such as the NSOG.
Most of the galaxies in the group are edge on (or close to it) spirals, with the odd lenticular thrown in.
NGC 3090 itself as an E4 galaxy, it is also classified as a cD (cluster dominant) galaxy. There appears
to be another object closely associated with NGC 3090 but it is not clear if this is a star or another galaxy.
If the distances published are correct then the group is at a distance of about 108 Mpc, which would give
NGC 3090 a diameter of maybe 200000 lyrs, about twice the size of the Milky Way. Recent observations of the
group taking into account dwarf galaxies suggest that the total cluster membership maybe nearer 20
galaxies. Many of these surveys however were based on algorithms to find cluster members and hence
they are based on statistical surveys, the galaxy group in this case was MZ 03587 from study done by
the 2DFGRS galaxy survey. The group is also known as MKW 1 from a survey of cD galaxies done by
Morgan, Keenan and White in 1975. If these studies are right then NGC 3090 is a true poor cluster and
it may well be a fossil cluster, the end of the merging process of a group of galaxies. Apart from the
clustering studies there does not appear to be much else on this group in the literature. Observations of
the group may well be hampered by the two 10th mag stars involved with it. This will particularly impact
NGC 3090 itself It will be interesting to see what size aperture is required to pick up all the NGC galaxies
in the group. The group is pretty compact and most, if not all of the galaxies in the group, will fit in a
high-power field using a modern hyperwide eyepiece.

As always give it a go and let us know

Object of the Week April 2nd 2023 - NGC 3090