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ARP 140, NGC 274 and NGC 275 Interacting Galaxies, Cetus
ARP 140, NGC 274 and NGC 275 Interacting Galaxies, Cetus
In 1966, American astronomer Halton Arp published a catalog of 338 peculiar galaxies under the assumption that the distorted shapes were due to large galactic ejections. It was soon demonstrated that the majority of the objects are in fact interacting galaxies, deforming each other by tidal forces. Entry number 140 is an example of two such galaxies, NGC 274 and NGC 275 in the constellation of Cetus, which appear to be in the early stages of merging. NGC 274 is a lenticular galaxy discovered by William Herschel in 1785. Although NGC 275 is in the same field of view, and of nearly the same brightness and identical contrast index, there is no mention of it in any of his observation notes. It is not unlikely that he mistook the pair for a single object. NGC 275 was first identified as a separate galaxy by his son, John Herschel in 1828.
Distance measurements of extragalactic objects are essential in estimating their physical properties, and are usually based on the redshift for very distant objects. However, redshift is dependent on two velocity components. One is due to the expansion of space, and the second to the object's "peculiar velocity" through space relative to the observer. It is generally accepted that "redshift-independent distances" are more accurate for redshifts lower than 0.01. In the case of ARP 140, redshift-independent distances are questionable on several levels. As listed in the NED database, the number of measurements is statistically too low. The range of results is too large, and varies by several hundred percent between low and high values. Distance calculations are based on outdated Hubble parameter (Ho) values. And, mean distance estimates for the two galaxies place them very widely apart, though they convincingly appear to be interacting in close contact. For these reasons, galaxy properties in the attached chart are calculated on the basis of their redshift derived distances.
Using the redshift method, NGC 274 lies at a distance of 80.84 Mly, receding at 1,746 km/s. Its actual diameter is about 37,200 ly, and absolute magnitude -19.46. It is approximately one third in size and brightness as our Milky Way galaxy. SIMBAD database classifies it as E/S0, an intermediate between an elliptical and a lenticular galaxy, while the NED database describes it as SAB0(r) pec, which is an intermediate spiral with a ring and a peculiar morphology. On my low magnification image I can barely visualize a full oval ring once my attention is drawn to it. On close examination, a couple of delicate features are present which suggest gravitational interaction. One is slight eccentricity of the galaxy relative to its nucleus. Another one is the presence of three wispy stellar streamers between the two galaxies. These features are better appreciated on Halton Arp's negative, high contrast, embossed original image.
NGC 275 is classified as SB(rs)cd pec, indicating a loosely wound barred spiral galaxy with an incomplete ring and a peculiar morphology. Its redshift based distance is 80.57 Mly, recession velocity 1,740 km/s, actual diameter approximately 37,700 ly, absolute magnitude -19.28, and brightness about one quarter that of the Milky Way. Even at low magnification, this galaxy shows markedly disrupted spiral arms and numerous bright blue floccules of starburst activity. While few references describe ARP 140 as a widely separated line-of-sight pair, it might be difficult to explain away peculiar features in both galaxies consistent with close gravitational interaction.
The attached image also includes a very distant galaxy, LEDA 1026074, lying at a distance of 1.5 billion light years, which is about half the size and brightness of the Milky Way. The background is strewn with numerous remote galaxies marked with letter "G" on the annotated image. Unfortunately, they have neither measurable properties nor identifiers listed in SIMBAD and NED databases. Based on their angular size alone, they would lie at distances between 1.5 and 3 billion light years. Of course, many of them might be dwarf galaxies, in which case they would be much closer. Without redshift information, there is no way to know.
The most remote object is quasar (QSO) SDSS J005134.95-065841.7, which presents barely above the limiting magnitude. Its apparent magnitude is presently about 0.5 mag brighter than listed. Quasars commonly manifest short and long term variability depending on the matter available to them for accretion. Based on its redshift of 1.38400, it lies at a light travel distance (lookback time) of 9.1 billion light years, and is about 70 times brighter than our Galaxy. When the light we are now recording was emitted, the object was receding from our location at 210,080 km/s. In the present cosmological epoch, its "proper recession velocity" is 292,040 km/s - very nearly the speed of light. When its proper recession velocity becomes superluminal, it will have crossed the cosmic event horizon and, over the next 9 billion years, its light will forever fade away into the infrared and radio waves.
Image Details:
-Remote Takahashi TOA 150 x 1105 mm
-OSC 32 x 300 sec, 2x drizzle, 30% linear crop
Software:
DSS, XnView, StarNet++ v2, Star Tools v1.8
Extragalactic Cosmological Calculator v2
www.cloudynights.com/gallery/image/169610-extragalactic-c...
ARP 140, NGC 274 and NGC 275 Interacting Galaxies, Cetus
ARP 140, NGC 274 and NGC 275 Interacting Galaxies, Cetus
In 1966, American astronomer Halton Arp published a catalog of 338 peculiar galaxies under the assumption that the distorted shapes were due to large galactic ejections. It was soon demonstrated that the majority of the objects are in fact interacting galaxies, deforming each other by tidal forces. Entry number 140 is an example of two such galaxies, NGC 274 and NGC 275 in the constellation of Cetus, which appear to be in the early stages of merging. NGC 274 is a lenticular galaxy discovered by William Herschel in 1785. Although NGC 275 is in the same field of view, and of nearly the same brightness and identical contrast index, there is no mention of it in any of his observation notes. It is not unlikely that he mistook the pair for a single object. NGC 275 was first identified as a separate galaxy by his son, John Herschel in 1828.
Distance measurements of extragalactic objects are essential in estimating their physical properties, and are usually based on the redshift for very distant objects. However, redshift is dependent on two velocity components. One is due to the expansion of space, and the second to the object's "peculiar velocity" through space relative to the observer. It is generally accepted that "redshift-independent distances" are more accurate for redshifts lower than 0.01. In the case of ARP 140, redshift-independent distances are questionable on several levels. As listed in the NED database, the number of measurements is statistically too low. The range of results is too large, and varies by several hundred percent between low and high values. Distance calculations are based on outdated Hubble parameter (Ho) values. And, mean distance estimates for the two galaxies place them very widely apart, though they convincingly appear to be interacting in close contact. For these reasons, galaxy properties in the attached chart are calculated on the basis of their redshift derived distances.
Using the redshift method, NGC 274 lies at a distance of 80.84 Mly, receding at 1,746 km/s. Its actual diameter is about 37,200 ly, and absolute magnitude -19.46. It is approximately one third in size and brightness as our Milky Way galaxy. SIMBAD database classifies it as E/S0, an intermediate between an elliptical and a lenticular galaxy, while the NED database describes it as SAB0(r) pec, which is an intermediate spiral with a ring and a peculiar morphology. On my low magnification image I can barely visualize a full oval ring once my attention is drawn to it. On close examination, a couple of delicate features are present which suggest gravitational interaction. One is slight eccentricity of the galaxy relative to its nucleus. Another one is the presence of three wispy stellar streamers between the two galaxies. These features are better appreciated on Halton Arp's negative, high contrast, embossed original image.
NGC 275 is classified as SB(rs)cd pec, indicating a loosely wound barred spiral galaxy with an incomplete ring and a peculiar morphology. Its redshift based distance is 80.57 Mly, recession velocity 1,740 km/s, actual diameter approximately 37,700 ly, absolute magnitude -19.28, and brightness about one quarter that of the Milky Way. Even at low magnification, this galaxy shows markedly disrupted spiral arms and numerous bright blue floccules of starburst activity. While few references describe ARP 140 as a widely separated line-of-sight pair, it might be difficult to explain away peculiar features in both galaxies consistent with close gravitational interaction.
The attached image also includes a very distant galaxy, LEDA 1026074, lying at a distance of 1.5 billion light years, which is about half the size and brightness of the Milky Way. The background is strewn with numerous remote galaxies marked with letter "G" on the annotated image. Unfortunately, they have neither measurable properties nor identifiers listed in SIMBAD and NED databases. Based on their angular size alone, they would lie at distances between 1.5 and 3 billion light years. Of course, many of them might be dwarf galaxies, in which case they would be much closer. Without redshift information, there is no way to know.
The most remote object is quasar (QSO) SDSS J005134.95-065841.7, which presents barely above the limiting magnitude. Its apparent magnitude is presently about 0.5 mag brighter than listed. Quasars commonly manifest short and long term variability depending on the matter available to them for accretion. Based on its redshift of 1.38400, it lies at a light travel distance (lookback time) of 9.1 billion light years, and is about 70 times brighter than our Galaxy. When the light we are now recording was emitted, the object was receding from our location at 210,080 km/s. In the present cosmological epoch, its "proper recession velocity" is 292,040 km/s - very nearly the speed of light. When its proper recession velocity becomes superluminal, it will have crossed the cosmic event horizon and, over the next 9 billion years, its light will forever fade away into the infrared and radio waves.
Image Details:
-Remote Takahashi TOA 150 x 1105 mm
-OSC 32 x 300 sec, 2x drizzle, 30% linear crop
Software:
DSS, XnView, StarNet++ v2, Star Tools v1.8
Extragalactic Cosmological Calculator v2
www.cloudynights.com/gallery/image/169610-extragalactic-c...