When considering the distances of galaxies, it is very common for us to fail to comprehend the scale and distances involved.
Take Centaurus A for example. It is not a member of the Local Group but it is still relatively close to us at 12,000,000 light years (12 Mly) or as professional astronomers would prefer to say, 3.7 Mpc (3,700,000 parsecs).
My own image 2017-07-06 Centaurus A 3x4min ED120 840mm f7 ISO200 copyright R.Powell.
None of these huge distances give us much sense of scale.
Reducing them to our "normal" every day units such as kilometres makes it even worse.
Q. How many kilometres are travelled by light in 13.5 million years?
A. 1.072x1020km (107,200,000,000,000,000,000 km) - how can we even begin to comprehend that?
It's true that intergalactic distances can make the human brain boggle. I wish the astronomical community could adopt a simpler distance method, using smaller numbers (just as they do when describing the distance from the Earth to the Sun: 1 AU = mean Sun-Earth Distance). It is very helpful in understanding the distances of the other planets:
0.4 Mercury
0.7 Venus
1.0 Earth
1.5 Mars
5.2 Jupiter
9.5 Saturn
19.2 Uranus
30.7 Neptune
39.7 Pluto (yes, I know.....)
These numbers provide a sense of scale which can be easily understandable - we just need to grasp the basis of the Earth-Sun distance.
When considering interstellar space, astronomical units are too small. Our nearest star system, Alpha Centauri, is 277,616 AU. (In this case it may be easier to comprehend 4.1 light years) and at an intergalactic scale it gets even worse - but consider this:
The Milky Way galaxy is roughly 100,000 light years in diameter and if we can somehow come to grips with that and call it 1 Milky Way Diameter (MWD), then using it as a rough 'measuring stick' for intergalactic space makes it somewhat easier to visualise the scale of the vast galactic distances involved.
Using this approximation, I calculated these distances to some of the more well known local galaxies:
1.6 MWD Large Magellanic Cloud
25 MWD M31 (Andromeda)
120 MWD Centaurus A
280 MWD Sombrero
526 MWD Virgo Cluster
That gives a comprehensible sense of the local intergalactic scale and also helps us to understand that the space between galaxies in our neighbourhood, as a ratio of distance to size, is very small compared to the distances between stars using a similar ratio.