A different way of looking at galaxy magnitudes

Published galaxy magnitudes can be very misleading to visual observers for various reasons. Even properly determined visual magnitudes are not always very useful. Many observers look at a combination of the total V magnitude and the average surface brightness, but even that can fail in cases where the brightness distribution is unusual.

Using techniques similar to those used by researchers in this field, I have derived total visual magnitudes, magnitudes for a grid of apparent sizes, and other information for a sample of galaxies. I also give total visual magnitudes and sizes derived from the 3rd Reference Catalog of Bright Galaxies (RC3) and that information should be useful even if you don't like the extra analysis I've done. Plus, if you are a beginner, I have used this analysis to identify the most easily detected galaxies. I have put together a more detailed description of the basic problem, the data sources, and my analysis. The main point being that when you merely detect a galaxy, you will only be seeing the brightest core region and integrated magnitudes and average surface brightnesses do not always accurately predict the detectability or visibility of that core.

As a start to this project, I have put together data for galaxies in the Messier and Herschel 400 lists. That's a total of 260 galaxies, of which 258 have at least limited data, and about 95% have significant useful data. You can check out a few sample fits, which show the raw data and the best fit to this data.

This data may or may not be useful to you. As I see it, the main use would involve observing some galaxies, noting how easily they were detected, and compare your visibility data with V(1.0), etc. If you barely saw a galaxy with V(1.0)=11.0, then you will probably have trouble detecting any galaxy with V(1.0) much fainter than 11.0. I.e. maybe you are trying to see all the H400 objects with a small telescope under dark skies, or a large telescope under poor skies, etc. Note again that this list is geared toward the detection of a galaxy and not the amount of detail you might see if you have a large enough aperture and/or dark enough skies.

My personal goal is to see as many galaxies as possible with my 6" telescope from dark skies in the next year or two. I've observed all of the objects on the list I'm providing, plus many fainter galaxies. There are more than 2000 galaxies on the full Herschel list, plus hundreds of other NGC and IC galaxies that may be within reach. Nearly 3000 galaxies have enough photometry for me to do my full analysis, and hundreds of others have partial data. I intend to use this data to help weed out galaxies that I have no hope of detecting. If you use the following data in the same way, please be conservative in assuming that you can't see a galaxy. You may surprise yourself and sometimes the data is simply wrong!

As you might guess, much of this data was put together in an automated manner, so there may be a few stupid mistakes lurking.

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File last modified: 17 December 2004

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