Messier 106
A nearby spiral galaxy with a supermassive black hole and water megamaser.
Messier 106, also cataloged as NGC 4258, is an intermediate spiral galaxy located in the constellation Canes Venatici. French astronomer Pierre Méchain first spotted it in 1781. This galaxy lies between 22 and 25 million light-years from Earth and is one of the largest and brightest galaxies in our cosmic neighborhood, comparable in size and brightness to the Andromeda Galaxy.
At its center, M106 hosts an active nucleus classified as a Type 2 Seyfert. Radio observations of a rotating disk of molecular gas within the innermost light-year around the core have confirmed the presence of a supermassive black hole, with a mass of about 39 million times that of the Sun. The galaxy also has a slightly warped, thin, nearly edge-on Keplerian disk on a subparsec scale surrounding this central region.
Beyond its two visible spiral arms, M106 features two additional "anomalous arms" that are only detectable with X-ray telescopes. A possible companion galaxy, NGC 4217, is associated with it.
M106 contains a powerful water vapor megamaser—a galactic-scale equivalent of a laser operating in the microwave spectrum—emitting at the 22-GHz line of ortho-H2O. This maser signals the presence of dense, warm molecular gas and is valuable for studying nuclear accretion disks in active galaxies. The water masers in M106 provided the first direct measurement of the distance to a galaxy, offering an independent calibration point for the cosmic distance ladder.
The galaxy has also been crucial for refining distance measurements using Cepheid variable stars. Because Cepheids in other galaxies often have different metallicities than those in the Milky Way, their distances were difficult to determine directly. M106 contains Cepheids with metallicities similar to both the Milky Way and other galaxies. By measuring the distance to Cepheids with Milky Way-like metallicities in M106, astronomers can recalibrate the distances of Cepheids with different metallicities elsewhere—a key step in improving distance estimates to other galaxies.
Two supernovae have been observed in M106: SN 1981K (Type II, magnitude 17), reported by E. Hummel and confirmed by Paul Wild from archival photos taken on 3 November 1981; and SN 2014bc (Type II, magnitude 14.8), discovered by the PS1 Science Consortium 3Pi survey on 19 May 2014.
Quick Facts
- Epoch
- J2000
- Ra
- 12 · 18 · 57.5
- Dec
- +47 · 18 · 14
- Dist Ly
- 23.7 +/-
- Z
- 448 ± 3 km/s
- Appmag V
- 8.4
- Constellation Name
- Canes Venatici
- Notes
- Megamaser galaxy, Seyfert II galaxy.
- Names
- M 106, NGC 4258, UGC 7353, PGC 39600.
Facts from the source article.
Lore & Background
Messier 106 was discovered by Pierre Méchain in 1781. It is an intermediate spiral galaxy located in the constellation Canes Venatici, at a distance of about 22 to 25 million light-years from Earth. The galaxy contains an active nucleus classified as a Type 2 Seyfert, and the presence of a central supermassive black hole has been demonstrated from radio-wavelength observations of the rotation of a disk of molecular gas orbiting within the inner light-year around the black hole. NGC 4217 is a possible companion galaxy. Besides its two visible arms, M106 has two 'anomalous arms' detectable using an X-ray telescope.
M106 has a water vapor megamaser—the equivalent of a laser operating in the microwave spectrum on a galactic scale—seen by the 22-GHz line of ortho-H2O, which evidences dense and warm molecular gas. These water masers are useful for observing nuclear accretion disks in active galaxies. The water masers in M106 enabled the first case of a direct measurement of the distance to a galaxy, providing an independent anchor for the cosmic distance ladder. The galaxy has a slightly warped, thin, almost edge-on Keplerian disc on a subparsec scale, surrounding a central area with mass 4×10⁷ M☉. The supermassive black hole at the core has a mass of (3.9±0.1)×10⁷ M☉.
Two supernovae have been observed in M106: SN 1981K (Type II, mag. 17), reported by E. Hummel and verified by Paul Wild from archival photos dated 3 November 1981; and SN 2014bc (Type II, mag. 14.8), discovered by the PS1 Science Consortium 3Pi survey on 19 May 2014.
Reader's Guide
Messier 106 has played an important role in calibrating the cosmic distance ladder. Before its study, Cepheid variables from other galaxies could not be used to measure distances because they cover ranges of metallicities different from the Milky Way's. M106 contains Cepheid variables similar to both the metallicities of the Milky Way and other galaxies' Cepheids. By measuring the distance of the Cepheids with metallicities similar to our galaxy, astronomers are able to recalibrate the other Cepheids with different metallicities—a key fundamental step in improving quantification of distances to other galaxies in the universe. Additionally, the water masers in M106 enabled the first direct measurement of the distance to a galaxy, providing an independent anchor for the cosmic distance ladder. The galaxy's active nucleus and supermassive black hole, with a mass of (3.9±0.1)×10⁷ M☉, make it a significant object for studying accretion processes and galactic dynamics. Its two anomalous arms, visible only in X-rays, add to its uniqueness among nearby galaxies.
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