Getting to know the Lindsay-Shapley Ring

In order to really know a galaxy, one has to understand the neighborhood. This page provides some context for the Heritage release of the HST/ACS 14th anniversary images of what John A. Graham first positively identified as "a peculiar southern ring galaxy". The image data displayed below show the environment around the RN nuclear ring galaxy VV785 (a.k.a. AM0644-741, the Lindsay-Shapley Ring, or Graham's Ring Galaxy) in ground-based radio, IR, and optical wavelengths. Just as color photographs provide much more information about a scene than does a black-and-white photo, by examining a region of the sky in more than one wavelength, much can be gleaned about what is going on. Below, a brief tour of the region around AM0644-741 is given by successively stepping through multi-wavelength data collected from various astronomical facilities. We start at very long wavelengths (radio), and proceed on up through the optical. Although a wealth of other wavelength data is available, we will show only that where the ring galaxy stands out prominently.

Eric Lindsay was the first to publish on the existence of the eccentric elliptical ring in 1960, however because of its proximity to the Large Magellanic Cloud and the lack of confirming radial velocity data, he suggested it might be some sort of stellar remenant.

The pictures below are all 0.25 degrees on a side (about half the width of the moon). At the 90 megaparsec distance of the ring galaxy (290 million light years), this corresponds to a field of view about 380 kiloparsecs or 1.2 million light years square. This is about 10-times the full diameter of the Milky Way Galaxy, about 50 times the distance between our sun and the Milky-Way's center, and about half the distance between the Milky Way and our nearest large neighbor, the Andromeda Galaxy. So, on this scale, if our galaxy were in the center, Andromeda could be as much as 4-times further away than the frame edge, so it is likely that many other companions to this ring galaxy are not in the field of view. The relative three-dimensional configuration of the companions which are visible is unknown, however work is underway to try to clarify this and identify the impactor which triggered the ring to appear.

All images on this page are provided courtesy of GSFC's SkyView virtual observatory engine.

At above left is the 843 MHz (356mm) Sydney University Molonglo Sky Survey (SUMSS) data is displayed. With a little imagination, the position of four companion galaxies can be discerned even though noise appears to contaminate the upper third of the frame (compare this with the optical images displayed at the bottom of the page).

IRAS was one of the first space telescopes sensitive to thermal infrared wavelengths. It was launched in the early 1980s and before its liquid helium cryogen boiled away, it surveyed the entire sky at four different wavelengths.

Above are images produced from the IRAS 100 micron (left) and 60 micron (right) surveys. What is possibly a star in our own galaxy surrounded by a large and distant shell of very cold (approximately 5 kelvin) gas and dust can be seen prominently in foreground of the upper left quadrant of the 100 and 60 micron images. Below the 25 micron (left) and 12 micron survey data are shown.

Resolution in all four wavelengths is the same because a single detector with a fixed pixel size was used. Although the pixels were about 100,000 light-years across at the distance of this small cluster of galaxies, the existence of the ring galaxy as a strong source is clearly detectable. At these wavelengths, the heat from the dust and gas from which the active star formation in the ring and other parts of the galaxy derive its fuel glow bright enough to be visible well above the background.

The Two Micron All Sky Survey completed its first full-sky map in the early 2000s and provided the first uniform dataset of the sky's appearance at near-infrared wavelengths (1.6-2.2 microns). By comparing the single-band images below, one can see subtle brightness differences between stars in the pictures. The ring is faint but visible in all these images.

Above are the 2MASS K (2.17 microns) and J (1.25 microns) band images. Below is the H-band (1.65 microns) image.

H-alpha (6563 angstroms) maps show emission or absorption by neutral hydrogen atoms. Old gas- and dust-free galaxies show little neutral hydrogen content, however ones with abundant star formation have enough to display strong emission. The Southern H-Alpha Sky Survey Atlas is the product of a wide-angle digital imaging survey of the H-alpha emission from the warm ionized interstellar gas primarily from the Milky Way Galaxy. The Lindsay-Shapley ring can be seen glowing faintly above our own galaxy and the gas surrounding the LMC in the SHASSA images.

Above are the SHASSA Continuum (left) and H-alpha images of the field around the ring galaxy.

The Digital Sky Survey Data taken by Royal Observatory Edinburgh(Southern Sky), Oschin Schmidt Telescope, and the Anglo Australian Observatories, and digitized at the Space Telescope Science Institute, partially in support of the HST Project.

Above are the DSS Blue (left) and Red (right) images. At least 4 elliptical-type galaxies which are members of the same cluster containing AM0644-741 are identifiable.

Okay, now that you have seen that, check out the power of HST:

Neat, huh?