NGC 3227
A Seyfert spiral interacting with a dwarf elliptical companion.
NGC 3227 is an intermediate spiral galaxy that lies in the constellation Leo, locked in a gravitational dance with its smaller neighbor, the dwarf elliptical galaxy NGC 3226. This pair is one of several spiral-and-dwarf-elliptical combinations cataloged in the Atlas of Peculiar Galaxies. Both galaxies belong to the NGC 3227 Group, which itself is part of the larger Leo II Groups—a chain of galaxies and clusters stretching from the edge of the Virgo Supercluster.
Sir William Herschel first noted them as a "double nebula," and they appear together as Holm 187 in the Catalogue of Double and Multiple Galaxies and as Arp 94 in the Atlas of Peculiar Galaxies. With a telescope and about 100× magnification, amateur observers can spot them, located 50 arcminutes east of the bright double star Gamma Leonis, also known as Algieba.
At the heart of NGC 3227 lies a Seyfert nucleus—a type of active galactic nucleus (AGN) powered by a supermassive black hole. Like many AGNs, its nucleus emits variable X-rays, fluctuating over timescales from hours to months. These changes likely stem from shifts in the density or ionization of gas and dust near the black hole, which absorb the X-rays. Much of this absorbing gas sits within 0.4 parsecs (1.3 light-years) of the nucleus. Observations in 2000 and 2001 revealed a change in the X-ray spectrum, suggesting some of that gas lies even closer—within 10 to 100 light-days. The nucleus reached peak luminosity in 1977, when evidence emerged of long-lived gas streams flowing in one or both directions.
X-rays from the central accretion disk are reprocessed into optical light within one to two days. Infrared emission from the hot dust torus lags behind the optical light by about 20 days. In NGC 3227 and similar galaxies, the dust torus reaches temperatures between 1500 K and 1800 K. This galaxy was studied using the Multicolor Active Galactic Nuclei Monitoring 2-meter telescope.
One supernova has been observed in NGC 3227: SN 1983U, a Type Ia event reaching magnitude 12, discovered by Vladimir Pronik on 4 November 1983.
Quick Facts
- Constellation Name
- Leo
- Epoch
- J2000
- Ra
- 10 · 23 · 30.6
- Dec
- +19 · 51 · 54
- Dist Ly
- 77 ± 9 Mly (24 ± 3 Mpc)
- Z
- 1157 ± 3 km/s
- Appmag V
- 11.1
- Names
- UGC 5620, PGC 30445, Arp 94
Facts from the source article.
Lore & Background
Sir William Herschel recognized NGC 3227 and NGC 3226 as a 'double nebula', and they were jointly cataloged as Holm 187 in the Catalogue of Double and Multiple Galaxies and as Arp 94 in the Atlas of Peculiar Galaxies. The pair lies 50 arcminutes east of the double star Gamma Leonis (Algieba) and can be discerned in amateur telescopes at about 100× magnification.
The nucleus of NGC 3227 is a Seyfert active galactic nucleus containing a supermassive black hole. Its X-ray emission varies on timescales from hours to months, likely due to changes in absorbing gas and dust near the nucleus. A substantial portion of this absorbing gas lies within 0.4 parsec (1.3 light-years) of the nucleus, and an observed change in the X-ray spectrum in 2000 and 2001 suggests some gas is within 10–100 light-days. The nucleus reached peak luminosity in 1977, when evidence of long-lived one-sided or two-sided gas streams was obtained. Optical light from the accretion disk is reprocessed in one to two days, while infrared emission from the hot dust torus lags optical light by about 20 days; the dust torus temperature is estimated at 1500–1800 K.
Reader's Guide
NGC 3227 is significant as a nearby example of an interacting spiral galaxy with a Seyfert nucleus, offering insights into galaxy interactions and active galactic nucleus (AGN) physics. Its pairing with NGC 3226 provides a case study for how dwarf ellipticals interact with larger spirals, a configuration highlighted in the Atlas of Peculiar Galaxies. The galaxy's variable X-ray emission, studied on timescales from hours to months, helps constrain the location and behavior of absorbing material near the supermassive black hole. The detection of a lag between optical and infrared light—about 20 days—allows measurement of the inner radius of the dust torus, a key parameter for AGN models. The 1977 luminosity maximum and associated gas streams indicate dynamic activity in the nucleus. The single observed supernova, SN 1983U, adds to its observational record. NGC 3227 was studied by the Multicolor Active Galactic Nuclei Monitoring 2m telescope, contributing to long-term monitoring of AGN variability.
Did You Know?
- NGC 3227 and NGC 3226 were jointly cataloged as Holm 187 and Arp 94.
- The nucleus of NGC 3227 reached maximum luminosity in 1977.
- Infrared light from the dust torus lags optical light from the nucleus by about 20 days.
- One supernova, SN 1983U (Type Ia, mag. 12), was observed in NGC 3227.
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