Wide-Field Galaxy Imaging

The night sky in the spring is packed with a plethora of galaxies just waiting to be observed and imaged. Recently I was browsing through my copy of Sky and Telescope's "Pocket Sky Atlas" by Roger W. Sinnott. I came across the pages that cover the constellations Virgo and Coma Berenices. After noticing how many "red" symbols were on the page representing galaxies in the area of these constellations, I had the idea of remotely imaging a particular area that would be condensed with some of these galaxies with a wide-field telescope.

Galaxy Group in the Virgo Cluster with NGC 4461 in the Center Image by Michael Petrasko and Muir Evenden

I then accessed the planetarium software on my computer, "Stellarium", to determine the best time to image a cluster of galaxies. After surveying the night sky in New Mexico in the software, setting the time of night roughly an hour and a half after sunset there, I found a grouping of island universes in Virgo that would be worth giving a shot at. I found a galaxy in the grouping that would be the "targeted center galaxy" for the image frame. This galaxy would be NGC 4461, a spiral galaxy in Virgo. I ended up taking a series of ten luminance images over a period of two nights on T14, a Takahashi FSQ Fluorite 160mm telescope with an SBIG STL-11000M CCD camera via the itelescope.net remote robotic telescope network. My associate, Muir Evenden, then processed the raw image files using the CCD image processing software PixInsight. What I found interesting about the results was all of the different types of spiral galaxies that were caught in the image.

This type of data gathering could be a fun and interesting exercise for students participating in astronomy education projects. Students could be tasked with identifying the designations and galaxy types in the image field utilizing astronomy software and/or star atlases as I did.

The galaxies caught in my image are located in the Virgo Cluster. This cluster of galaxies whose center is about 53.8 light-years away in the constellation Virgo. Comprising approximately 1300 (and possibly up to 2000) member galaxies, the cluster forms the heart of the larger Virgo Supercluster, of which the Local Group is an outlying member.

Many of the brighter galaxies in this cluster, including the giant elliptical galaxy Messier 87, were discovered in the late 1770s and early 1780s and subsequently included in Charles Messier's catalog of non-cometary fuzzy objects. Described by Messier as a nebula without stars, their true nature was not recognized until the 1920s.

The cluster subtends a maximum arc of approximately 8 degrees centered in the constellation Virgo. Many of the member galaxies of the cluster are visible with a small telescope. Its brightest member is the elliptical galaxy Messier 49; however, its most famous member is the also elliptical galaxy Messier 87, which unlike the former is located in the center of the cluster.

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Galaxies Galore

Since my independent discovery of SN1989B in the spiral galaxy, M66 in the constellation Leo back on February 11, 1989, I have always been fascinated with observing galaxies and galaxy clusters. Over this past weekend, Muir and I wanted to try to capture a few galaxy clusters in the spring sky using the remote robotic T-5 (Takahashi Epsilon 250mm) telescope in New Mexico Skies. Over the weekend we referenced the Stellarium astronomy program to find a field of view that may catch multiple galaxies in a single image. One group of galaxies that caught our attention in Stellarium was in the constellation of Coma Berenices. We chose one galaxy in the group that would make a good "center point" for the image. 

Galaxies in the Coma Cluster - Click to Enlarge

That object was NGC 4872. We scheduled a 300-second exposure at 2:45 am MDT when the galaxy was near transit. After examining the data we received post-processing, we noticed a few different galaxies in the frame. Using the Aladin Sky Atlas astronomy software, I loaded up the DSS color image of NGC 4872. As I zoomed into the Aladin image with NGC 4872 at the center, I observed numerous galaxies. Referring back to our image taken with the T-5, what I thought were faint stars were actually galaxies. After the excitement set in, I decided to use telescope T-11 (Planewave 20" CDK Astrograph) the next day to get a magnified image of the galaxy cluster. After waking up this morning around 5:00 am EDT (3:00 am MDT), I jumped on T-11 and acquired the image above. After processing the image, I magnified and saw the same detail in all of the galaxies I observed in the Aladin Sky Atlas software.

NGC 4872 and Surrounding Galaxies in the Coma Cluster Identified with Aladin Astronomy Software

There were so many galaxies in the field of view that I could not keep count. I then thought it would be a fun exercise to identify a few of the brighter and more interesting-looking galaxies using the SIMBAD Astronomical Database overlay in the Aladin Sky Atlas. I was able to successfully identify the galaxies in the image above using the technique pictured left.

A wide-field image of the Coma Cluster of galaxies taken at the 
Mount Lemmon SkyCenter using the 0.8m Schulman Telescope. 
Image courtesy Adam Block

The Coma Cluster (Abell 1656) is a large cluster of galaxies that contains over 1,000 identified galaxies. Along with the Leo Cluster (Abell 1367), it is one of the two major clusters comprising the Coma Supercluster. It is located in and takes its name from the constellation Coma Berenices. The cluster's mean distance from Earth is 321 million light-years. Its ten brightest spiral galaxies have apparent magnitudes of 12–14 that are observable with amateur telescopes larger than 20 cm. The central region is dominated by two giant elliptical galaxies: NGC 4874 and NGC 4889. The cluster is within a few degrees of the north galactic pole in the sky. Most of the galaxies that inhabit the central portion of the Coma Cluster are ellipticals. Both dwarf and giant ellipticals are found in abundance in the Coma Cluster. The image (right) shows some of the same galaxies that are in the field of view of the image (top of post) I obtained using the Planewave 20" telescope this morning.

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