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NGC 7479, Caldwell 44, Pegasus, Propeller Galaxy, 50% CROP
NGC 7479, Caldwell 44, Pegasus, Propeller Galaxy
NGC7479 is a distorted barred spiral galaxy in the constellation of Pegasus, discovered by W. Herschel in 1784. With apparent diameter of 4.4 arcmin, and apparent magnitude of 10.85 (V), visual observation calls for large apertures. However, its basic structures are evident photographically with modest telescopes. From its measurable properties we can derive light travel distance (lookback time) of 110 million light years, redshift recession velocity of 2,379 km/s, actual diameter of 140,000 ly, and absolute magnitude of -21.83 (V), approximately 1.5 times as bright as the Milky Way. NGC7479 has an active galactic nucleus (AGN) which is 8.5 times brighter in the near IR (z filter) than in the visible band, and which emits narrow spectral lines of weakly ionized elements. These characteristics classify it as a Seyfert 2 and a LINER galaxy. It is powered by an actively accreting central supermassive black hole (SMBH) obscured by a large, dense cloud of light-absobing gas and dust. The nucleus is also active at radio frequencies, suggesting the SMBH has polar jets emitting synchrotron radiation. Bright blue floccules in the spiral arms and even within the bar are OB Associations, or vast clusters of recently formed blue giant stars which emit most of their energy in the ultraviolet band. NGC7479 is an isolated field galaxy with no nearby neighbors. Starburst activity, several stellar streams, and gravitational distortion in the W spiral arm are thought to have been caused by a merger with one or more dwarf satellite galaxies between 300 and 100 million years ago.
As the annotated image illustrates, different spectral bands reveal different details within a galaxy. In the ultraviolet band (GALEX), the most prominent features are OB associations, starburst regions, and reflection nebulae. The compact, round UV signal overlapping the N arm of the bar may be the remnant nucleus of a merged dwarf galaxy. The NGC7479 nucleus is not prominent because it is surrounded by a thick layer of gas and dust which absorb and scatter predominantly UV light. However, the brightest feature on the infrared (2MASS) image of the galaxy is precisely the main galactic nucleus with a central SMBH, because longer wavelengths are less obsured. The bulge and the bar are also distinctive due to the presence of ancient cool and red Population II stars. Radio frequency imaging of the galaxy reveals the presence of a bright jet-like feature, centered on the nucleus, and extending through the bar about 20,000 light years in the N and in the S direction. The jet's spiral morphology mildly curves in the direction opposite to that of the stellar and gaseous spiral arms, suggesting that the two structures may be counter-rotating. Jet bending can be caused by precession of the central SMBH accretion disk, by the presence of a binary central SMBH, and/or an off center merger with another galaxy. Based on the rate of expansion and the maximum distance from the nucleus, the jet is felt to be less than 10 million years old.
A large galaxy cluster is visible in the remote background at an estimated light travel distance of 1.5 to 2 billion light years. Only two of these have assigned identifiers. Their measurable and derived properties are listed in the chart on the annotated image.
Image details:
-Remote Takahashi TOA 150 x 1105 mm, Paramount GT GEM,
-OSC 34 x 300 sec, 2x drizzle, 50% linear crop,
-Software: DSS, XnView, StarNet++ v2, StarTools v1.3 and 1.7, Cosmological Calculator v3
NGC 7479, Caldwell 44, Pegasus, Propeller Galaxy, 50% CROP
NGC 7479, Caldwell 44, Pegasus, Propeller Galaxy
NGC7479 is a distorted barred spiral galaxy in the constellation of Pegasus, discovered by W. Herschel in 1784. With apparent diameter of 4.4 arcmin, and apparent magnitude of 10.85 (V), visual observation calls for large apertures. However, its basic structures are evident photographically with modest telescopes. From its measurable properties we can derive light travel distance (lookback time) of 110 million light years, redshift recession velocity of 2,379 km/s, actual diameter of 140,000 ly, and absolute magnitude of -21.83 (V), approximately 1.5 times as bright as the Milky Way. NGC7479 has an active galactic nucleus (AGN) which is 8.5 times brighter in the near IR (z filter) than in the visible band, and which emits narrow spectral lines of weakly ionized elements. These characteristics classify it as a Seyfert 2 and a LINER galaxy. It is powered by an actively accreting central supermassive black hole (SMBH) obscured by a large, dense cloud of light-absobing gas and dust. The nucleus is also active at radio frequencies, suggesting the SMBH has polar jets emitting synchrotron radiation. Bright blue floccules in the spiral arms and even within the bar are OB Associations, or vast clusters of recently formed blue giant stars which emit most of their energy in the ultraviolet band. NGC7479 is an isolated field galaxy with no nearby neighbors. Starburst activity, several stellar streams, and gravitational distortion in the W spiral arm are thought to have been caused by a merger with one or more dwarf satellite galaxies between 300 and 100 million years ago.
As the annotated image illustrates, different spectral bands reveal different details within a galaxy. In the ultraviolet band (GALEX), the most prominent features are OB associations, starburst regions, and reflection nebulae. The compact, round UV signal overlapping the N arm of the bar may be the remnant nucleus of a merged dwarf galaxy. The NGC7479 nucleus is not prominent because it is surrounded by a thick layer of gas and dust which absorb and scatter predominantly UV light. However, the brightest feature on the infrared (2MASS) image of the galaxy is precisely the main galactic nucleus with a central SMBH, because longer wavelengths are less obsured. The bulge and the bar are also distinctive due to the presence of ancient cool and red Population II stars. Radio frequency imaging of the galaxy reveals the presence of a bright jet-like feature, centered on the nucleus, and extending through the bar about 20,000 light years in the N and in the S direction. The jet's spiral morphology mildly curves in the direction opposite to that of the stellar and gaseous spiral arms, suggesting that the two structures may be counter-rotating. Jet bending can be caused by precession of the central SMBH accretion disk, by the presence of a binary central SMBH, and/or an off center merger with another galaxy. Based on the rate of expansion and the maximum distance from the nucleus, the jet is felt to be less than 10 million years old.
A large galaxy cluster is visible in the remote background at an estimated light travel distance of 1.5 to 2 billion light years. Only two of these have assigned identifiers. Their measurable and derived properties are listed in the chart on the annotated image.
Image details:
-Remote Takahashi TOA 150 x 1105 mm, Paramount GT GEM,
-OSC 34 x 300 sec, 2x drizzle, 50% linear crop,
-Software: DSS, XnView, StarNet++ v2, StarTools v1.3 and 1.7, Cosmological Calculator v3