Malin 1 - an Extreme observational challenge

[madbadgalaxyman (Robert)]

A fairly recent paper in the Publications of the Astronomical Society of Australia gives some good information about Malin 1, which may be the most extreme known example of the "giant Low Surface Brightness galaxy population". The reference is : Moore and Parker,(2006), PASA, 23, p.165
[[ PASA is available online from CSIRO Publishing. This journal is an excellent source of information about southern objects. The access policy is not really restrictive, as it used to be in the past! ]]

Unfortunately, Malin 1 has turned out to be a singular object, in that most of the genuine Low Surface Brightness galaxies are physically small objects. A few other Gigantic L.S.B. galaxies do exist, but they are not as extreme as
Malin 1.

[ There exists a formal definition of the population of low surface brightness galaxies, which is in use by professional astronomers, and this relates to the fact that the disk-component surface brightness of a genuine LSB galaxy must be fainter than some specific surface brightness. If anyone is interested, I can provide a precise definition of the concept of a "Low Surface Brightness galaxy". ]

Malin 1 is a very very difficult observational challenge for imagers, and while its extremely low-surface-brightness outer disk/spiral component is faintly visible in images, it is hard to make out the structure of this galaxy even when viewing deep imaging material.

The innermost part of Malin 1 is not too hard to detect, and it takes the form of a central bulge and bar, together with some smooth Inner spiral arms. See the attached I-band Hubble Space Telescope image which comes from this reference: (2007), AJ, 133, 1085 .
The filename is: Malin 1_F814W(log scale) (.......)

This inner morphology has been characterized as being of the Hubble Type SB0-a

Outside of this bright Inner Spiral is a gigantic & diffuse Extremely Low Surface Brightness envelope; which constitutes the outer disk component of this galaxy, and which also manifests some spiral structure.
The observations of Moore and Parker traced this very faint outer component to a radius of 77 arcseconds along the major axis, which implies an overall galaxy diameter of 2 and a half arcminutes.
Malin 1 is therefore a remarkably diffuse and remarkably physically large spiral galaxy.......the angular diameter of this galaxy corresponds to about 800,000 light years !!
(for an assumed distance of 330 Mpc , which is derived from a Hubble Constant of 75 km/s/Mpc )

This supergiant galaxy has, for some reason, formed on a much larger physical scale than your typical large spiral galaxy, and its very low Surface Brightness is simply due to the fact that its constituent stars are further apart than is normally the case in a spiral galaxy. Malin 1 is often characterized as being in an unevolved state, as it contains gigantic quantities of gas which may one day form into stars.

At the outermost galactocentric radius at which Moore & Parker measured the surface brightness of the gigantic diffuse Disk Component of Malin 1, this galaxy has an R-band surface brightness of 27.5 R magnitude per square arcsecond.
But who knows how far this galaxy extends, at even lower surface brightness??

I attach a further image of Malin 1, made with the INT. It is from the website of Simon P. Driver.
Its filename is: Malin 1_with the INT (........)

Southern astronomers are fortunate to have easy access to another genuine Low Surface Brightness galaxy: NGC 289
This is a much easier object than Malin 1 !!
NGC 289 has an easy-to-see inner disk together with a very faint outer disk. [ The contrast between the bright spiral structure in its inner zone and the faint spiral structure in the outer zone is well shown in Rob Gendler's image at: www.robgendlerastropics.com ]

Cheers,

madbadgalaxyman

[ballaratdragons (Ken)]

Very interesting subject.

Thank you Robert for posting this.
I have a fascination with faint very distant galaxies, and both of these (Malin1 & NGC289) are beautiful examples.

Please keep us informed of any more information in this particular field.

NGC 289 http://www.robgendlerastropics.com/NGC289.html

[madbadgalaxyman (Robert)]

I thought it was worth re-issuing this post from the message archive. While Malin 1 is not spectacular in images, a galaxy that is nearly a million light years across is one of the weirdest things that we know of in the cosmos.

cheers,
madbadgalaxyman