PDA

View Full Version : Local Group Census



wstevenbrown
2005-Jun-21, 02:45 PM
Some time ago I whined that there didn't seem to be a resource that listed all the known data about our LG galaxies. I got so tired of looking for it that I compiled it. It is available as a Windows spreadsheet, and I will update it periodically, as new/altered data come in. If you are interested, e-mail me for a copy. Steve

antoniseb
2005-Jun-21, 04:03 PM
Originally posted by wstevenbrown@Jun 21 2005, 02:45 PM
It is available as a Windows spreadsheet, and I will update it periodically, as new/altered data come in.
Hi Steve,

I don't especially need it just now, but I am glad you are putting it together. I saw an arXiv paper in the last two days about two new ones that were discovered, but I couldn't tell if this was two NEW ones, or references to ones found in the last year or so.

If the galaxies in the local group, how many are not mere satellites of the MW and M31?

John L
2005-Jun-21, 04:17 PM
Here (http://www.ing.iac.es/WFS/LGC/targets.html) is a lit of Local Group galaxies from the Isaac Newton Group's Wide Field Survey program.

Here (http://spiff.rit.edu/classes/phys230/lectures/local_group/local_group.html) is a site with images of Local Group objects with an excellent 3D map of the Local Group at the bottom of the web page.

And here (http://www.seds.org/messier/more/local.html) is the site I had seen before and was looking for. It has a very comprehensive list of Local Group galaxies with details about their locations and galaxy types.

Nereid
2005-Jun-21, 04:31 PM
Originally posted by John L@Jun 21 2005, 04:17 PM
Here (http://www.ing.iac.es/WFS/LGC/targets.html) is a lit of Local Group galaxies from the Isaac Newton Group's Wide Field Survey program.

Here (http://spiff.rit.edu/classes/phys230/lectures/local_group/local_group.html) is a site with images of Local Group objects with an excellent 3D map of the Local Group at the bottom of the web page.

And here (http://www.seds.org/messier/more/local.html) is the site I had seen before and was looking for. It has a very comprehensive list of Local Group galaxies with details about their locations and galaxy types.
The last one is the best, IMHO. Not only does it give a comprehensive list, but also lots of links, and references to papers on particular objects.

The problem with all these is how frequently (and comprehensively) they're updated. For example, have all the SDSS objects been added?

Finally, who's keeping track of the gas clouds (if there are no stars, we don't call it a galaxy; yet the H clouds certainly contain mass, are probably either loose LG members, or satellites of the MW, M31, or M33)?

wstevenbrown
2005-Jun-22, 09:37 PM
IMHO, my list is more comprehensive and more up-to-date. One source listed Willman I, which Ms Willman herself refers to as UMa dSph-- the second Uma dSph, referred to by her under its survey name SDSS J1049+5103, is not in any of the lists. I have purposely left out population survey data like 'metallicity indices', and useless stuff like integrated visual magnitude. And IV has been definitely discounted as a background galaxy seen thru the disk of M31, at a distance of 8Mpc.

My dialup service does not support the pretty pictures-- if I try to load that page, and go off to dinner, the system administrator truncates the download because I am not surfing. (Except for cultural centers, central VA is still in the '80's.)

I only give the two most common designations for the galaxies, prioritized as NGC, IC, UGC, DSO, and common or trade name. You'd be amazed how much confusing nomenclature there is, and how schismatic astronomers are about it. Sometimes only the celestial coordinates will tell you that two names are the same object.

This has been a worthwhile endeavor, even if it only benefits the narrowing of my own ignorance. S

aeolus
2005-Jun-22, 10:14 PM
Originally posted by John L@Jun 21 2005, 04:17 PM
Here (http://spiff.rit.edu/classes/phys230/lectures/local_group/local_group.html) is a site with images of Local Group objects with an excellent 3D map of the Local Group at the bottom of the web page.
That 3D pic is great. Too bad it doesn't keep zooming in to the scale of the solar system and Earth, for completeness.

wstevenbrown
2005-Jun-22, 10:39 PM
If the galaxies in the local group, how many are not mere satellites of the MW and M31?

Discounting M33, which may be bound to M31 (and looking more likely as M31 grows more massive), and outlying subgroups (Scuptor Group, Camelopardis Group, Maffei I & II, and 1Zw18, a void galaxy) of the Local Volume, there are 13:

Cetus,WLM, DDO210, LeoA, Tucana, SagDIG, NGC3109, Antlia, Sextans A. Sextans B, IC 5152, KKR 25, and GR 8 (DDO 155). Some of them may be bound to each other (the italicized subgroup).

For my use, I am expanding the compendium to include the outlier groups, as the local mass is uncertain within a factor of 2, and the local group is defined in terms of a zero-velocity sphere whose radius is dependent on mass. Just trying to keep track of the neighborhood-- there are intermittent reports of 'foreground' effects on the WMAP data, which may depend directly on local mass...

Best regards-- Steve