|Right ascension||23h 48m 54.6s|
|Declination||−16° 32′ 27″|
|Apparent magnitude (V)||13.5|
|Apparent size (V)||1.549′ × 1.122′|
|Right ascension||23h 48m 54.6s|
|Declination||−16° 32′ 27″|
|Apparent magnitude (V)||13.5|
|Apparent size (V)||1.549′ × 1.122′|
NGC 7582 is a spiral galaxy of the Hubble type SBab in the constellation Grus. It has an angular size of 5.0' × 2.1' and an apparent magnitude of 11.37. It has a diameter of about 100,000 light years; the galaxy is classified as a type of active galaxy. This galaxy is in the upper middle west part of the virgo supercluster; the supermassive black hole at the core has a mass of 5.5+2.6−1.9×107 M☉
NGC 7552 is a barred spiral galaxy in the constellation Grus. It is at a distance of circa 60 million light years from Earth, given its apparent dimensions, means that NGC 7552 is about 75,000 light years across, it forms with three other spiral galaxies the Grus Quartet. NGC 7552 was discovered and reported in 1826 by James Dunlop and John Herschel added it in the General Catalogue of Nebulae and Clusters as number 3977. However, Lewis Swift reported the galaxy independently in on October 22, 1897, at right ascention 9 arcseconds off the location of the galaxy and was included in Index Catalogue as IC 5294. NGC 7552 is a barred spiral galaxy, with two spiral arms forming an outer pseudo-ring; the galaxy is seen nearly face on, at an inclination of ∼ 28°. The one arm is more prominent and the less prominent arm shows no clear continuation with the bar; the bar is dusty, four huge HII regions are detected in it. The disk features numerous scattered HII regions in an asymmetric pattern; the total infrared luminosity of the galaxy is 1011.03 L☉, thus is categorised as a luminous infrared galaxy.
In 1994, Forbes et al. observed a partial starburst ring with 1 kpc radius at Br-gamma with various hot spots. They detected a small-scale molecular bar and a large reservoir of molecular material, however, no evidence of current activity was detected at the nucleus; the ring is more than 100 parsec wide. The ring is brighter north of the nucleus and there is inhabited by the younger star populations. Brandl et al. detected in near- and mid-infrared nine prominent structures within the ring they identified as star clusters with stellar ages ranging between 5.5 Myr and 6.3 Myr. These clusters account for the 75% of the bolometric luminosity of the starburst ring, with total luminosity of the clusters 2.1 × 1010 L⊙. Numerous supernova remnants have been observed in the ring. Further observations of the galaxy in radio waves showed that NGC 7552 contains three star forming rings of radii 1.0 kpc, 1.9 kpc, 3.4 kpc as observed by the Very Large Array at 46.9 MHz and the Australia Telescope Compact Array.
NGC 7552 belongs in NGC 7582 group known as Grus group. Others members of the group include the spiral galaxies of NGC 7599, NGC 7590, NGC 7582, which along with NGC 7552 form the Grus Quartet. A large tidal extension of HI reaches from NGC 7582 to NGC 7552, indicative of interactions between the group members, yet NGC 7552 hasn't disturbed morphology. NGC 7552 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images
NGC 7742 known as Fried Egg Galaxy is a face-on unbarred spiral galaxy in the constellation Pegasus. The galaxy is unusual in. Bars are needed to produce a ring structure; the bars' gravitational forces move gas to the ends of the bars, where it forms into the rings seen in many barred spiral galaxies. In this galaxy, however, no bar is present, so this mechanism cannot be used to explain the formation of the ring. O. K. Sil'chenko and A. V. Moiseev proposed that the ring was formed as the result of a merger event in which a smaller gas-rich dwarf galaxy collided with NGC 7742; as evidence for this, they point to the unusually bright central region, the presence of inclined central gas disk, the presence of gas, counterrotating with respect to the stars. Two Type II supernovae, SN 1993R and SN 2014cy, have been detected in NGC 7742. NGC 7217 - a face-on spiral galaxy with identical characteristics Sombrero Galaxy - a similar galaxy with a dust ring NGC 7742 at ESA/Hubble NGC 7742 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images
NGC 7674 is a spiral galaxy located in the constellation Pegasus. It is located at a distance of circa 350 million light years from Earth, given its apparent dimensions, means that NGC 7674 is about 125,000 light years across, it was discovered by John Herschel on August 16, 1830. The galaxy is seen nearly face-on, at an inclination of 31 degrees; the central bar-shaped structure, measuring 15×5 arcseconds is made up of stars. The galaxy has two spiral arms. One arm vanishes at the point it overlaps with the nearby galaxy NGC 7674A; the shape of NGC 7674, including the long narrow streamers emanating northeast and northwest of the galaxy can be accounted for by tidal interactions with its companions. There is no dwarf galaxy seen inside the streamers, it is featured in Arp's Atlas of Peculiar Galaxies as number 182, in the category "galaxies with narrow filaments". NGC 7674 has a powerful active nucleus of the kind known as a type 2 Seyfert, fed by gas drawn into the center through the interactions with the companions.
Using spectropolarimetry, emission characteristic of a hidden broad-line region, visible only in the polarized flux spectrum was detected, implying that the nucleus of NGC 7674 is an obscured type 1 Seyfert, hidden by a dust torus. In the center of NGC 7674 lies a supermassive black hole whose mass is estimated to be nearly 3.63×107 M☉ based on stellar velocity dispersion. When observed in radio waves, NGC 7674 features two radio jets with an S-shape, 0.7 kpc long. The reason for this shape may be a change in the black hole spin axis due to a minor merger, the presence of a binary black hole or due to interactions with the interstellar medium. Two radio sources with characteristics similar to accreting supermassive black holes have been observed in the centre of NGC 7674, at a projected separation of 0.35 parsec. NGC 7674 falls into the family of luminous infrared galaxies, with its infrared luminosity being 1011.54 L☉. The luminous infrared; the total star formation rate in NGC 7674 is estimated to be 54 M☉ per year, the star formation rate at the nucleus is 4.3 M☉ per year.
Two supernovae have been observed in NGC 7674, SN SN 2011hb. NGC 7674 is the brightest and largest member of the isolated Hickson 96 compact group of galaxies, consisting of four galaxies. NGC 7674 forms a pair with its smaller companion NGC 7674A. NGC 7675, an elliptical galaxy, lies 2.2 arcminutes to the east. This article incorporates text available under the CC BY 3.0 license. NGC 7674 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Sky Map and images NGC 7674 on SIMBAD
NGC 7723 is a barred spiral galaxy located in the constellation Aquarius. It is located at a distance of circa 90 million light years from Earth, given its apparent dimensions, means that NGC 7723 is about 95,000 light years across, it was discovered by William Herschel οn November 27, 1785. The galaxy is included in the Herschel 400 Catalogue, it lies one and a half degrees north-northwest from Omega1 Aquarii. It can be seen with a 4-inch telescope under dark skies. NGC 7723 is a barred spiral galaxy, it has a boxy bulge. In the centre of the galaxy lies a supermassive black hole whose mass is estimated to be ×106 M☉ based on the spiral arm pitch angle; the bar emerges from the opposite sides of the bulge. Straight dust lanes are observed along the one smooth and the other appearing broken; the bar has a maximum apparent length 64 arcseconds. At the end of the bar the spiral arms form a pseudoring with diameter of 71 arcseconds. Based on observations in far ultraviolet and Hα there is active star formation at the pseudoring.
Based on the B-I color profile of the galaxy the bar finishes at 23 arcseconds, at the same distance where there is a population of older stars, thus is suggested to be the corotation radius of NGC 7723. The structure of the arms is complex; the arm that emanates from the southwest part of the bar is well defined for a quarter of a revolution and after that it becomes more diffuse and fades after reaching half a revolution. The other arm emanates from a feature about 60 degrees northwest of the bar and brightens after passing the end of the bar, it splits in two; the inner part forms the southwest part of the pseudoring and bifurcates after winding for about 120 degrees after the bar end, with the inner part being the brightest. The other arm becomes diffuse and of low surface brightness. One supernova has been observed in NGC 7723, SN 1975N, a type Ia supernova with peak magnitude of 13.8. NGC 7723 belongs to a small groups of galaxies known as the NGC 7727 group. Other members of the group include NGC 7727 and NGC 7724.
A lenticular galaxy is a type of galaxy intermediate between an elliptical and a spiral galaxy in galaxy morphological classification schemes. They contain large-scale discs but they do not have large-scale spiral arms. Lenticular galaxies are disc galaxies that have used up or lost most of their interstellar matter and therefore have little ongoing star formation, they may, retain significant dust in their disks. As a result, they consist of aging stars. Despite the morphological differences and elliptical galaxies share common properties like spectral features and scaling relations. Both can be considered early-type galaxies that are passively evolving, at least in the local part of the Universe. Connecting the E galaxies with the S0 galaxies are the ES galaxies with intermediate-scale discs. Lenticular galaxies are unique in that they have a visible disk component as well as a prominent bulge component, they have much higher bulge-to-disk ratios than typical spirals and do not have the canonical spiral arm structure of late-type galaxies, yet may exhibit a central bar.
This bulge dominance can be seen in the axis ratio distribution of a lenticular galaxy sample. The distribution for lenticular galaxies rises in the range 0.25 to 0.85 whereas the distribution for spirals is flat in that same range. Larger axial ratios can be explained by observing face-on disk galaxies or by having a sample of spheroidal galaxies. Imagine looking at two disk galaxies edge-on, one with a bulge and one without a bulge; the galaxy with a prominent bulge will have a larger edge-on axial ratio compared to the galaxy without a bulge based on the definition of axial ratio. Thus a sample of disk galaxies with prominent spheroidal components will have more galaxies at larger axial ratios; the fact that the lenticular galaxy distribution rises with increasing observed axial ratio implies that lenticulars are dominated by a central bulge component. Lenticular galaxies are considered to be a poorly understood transition state between spiral and elliptical galaxies, which results in their intermediate placement on the Hubble sequence.
This results from lenticulars having bulge components. The disk component is featureless, which precludes a classification system similar to spiral galaxies; as the bulge component is spherical, elliptical galaxy classifications are unsuitable. Lenticular galaxies are thus divided into subclasses based upon either the amount of dust present or the prominence of a central bar; the classes of lenticular galaxies with no bar are S01, S02, S03 where the subscripted numbers indicate the amount of dust absorption in the disk component. The surface brightness profiles of lenticular galaxies are well described by the sum of a Sérsic model for the spheroidal component plus an exponentially declining model for the disk, a third component for the bar. Sometimes there is an observed truncation in the surface brightness profiles of lenticular galaxies at ~ 4 disk scalelengths; these features are consistent with the general structure of spiral galaxies. However, the bulge component of lenticulars is more related to elliptical galaxies in terms of morphological classification.
This spheroidal region, which dominates the inner structure of lenticular galaxies, has a steeper surface brightness profile than the disk component. Lenticular galaxy samples are distinguishable from the diskless elliptical galaxy population through analysis of their surface brightness profiles. Like spiral galaxies, lenticular galaxies can possess a central bar structure. While the classification system for normal lenticulars depends on dust content, barred lenticular galaxies are classified by the prominence of the central bar. SB01 galaxies have the least defined bar structure and are only classified as having enhanced surface brightness along opposite sides of the central bulge; the prominence of the bar increases with index number, thus SB03 galaxies have well defined bars that can extend through the transition region between the bulge and disk. The properties of bars in lenticular galaxies have not been researched in great detail. Understanding these properties, as well as understanding the formation mechanism for bars, would help clarify the formation or evolution history of lenticular galaxies.
In many respects the composition of lenticular galaxies is like that of ellipticals. For example, they both consist of predominately older, hence redder, stars. All of their stars are thought to be older than about a billion years, in agreement with their offset from the Tully–Fisher relation. In addition to these general stellar attributes, globular clusters are found more in lenticular galaxies than in spiral galaxies of similar mass and luminosity, they have little to no molecular gas and no significant hydrogen α or 21-cm emission. Unlike ellipticals, they may still possess significant dust. Lenticular galaxies share kinematic properties with elliptical galaxies; this is due to the significant disk nature of lenticulars. The bulge component is similar to elliptical galaxies in that it is pressure supported by a central velocity dispersion; this situation is analogous to a balloon, where the motions of the air particles are dominated by random motions. However, the kinematics of lenticular galaxies are dominated
The apparent magnitude of an astronomical object is a number, a measure of its brightness as seen by an observer on Earth. The magnitude scale is logarithmic. A difference of 1 in magnitude corresponds to a change in brightness by a factor of 5√100, or about 2.512. The brighter an object appears, the lower its magnitude value, with the brightest astronomical objects having negative apparent magnitudes: for example Sirius at −1.46. The measurement of apparent magnitudes or brightnesses of celestial objects is known as photometry. Apparent magnitudes are used to quantify the brightness of sources at ultraviolet and infrared wavelengths. An apparent magnitude is measured in a specific passband corresponding to some photometric system such as the UBV system. In standard astronomical notation, an apparent magnitude in the V filter band would be denoted either as mV or simply as V, as in "mV = 15" or "V = 15" to describe a 15th-magnitude object; the scale used to indicate magnitude originates in the Hellenistic practice of dividing stars visible to the naked eye into six magnitudes.
The brightest stars in the night sky were said to be of first magnitude, whereas the faintest were of sixth magnitude, the limit of human visual perception. Each grade of magnitude was considered twice the brightness of the following grade, although that ratio was subjective as no photodetectors existed; this rather crude scale for the brightness of stars was popularized by Ptolemy in his Almagest and is believed to have originated with Hipparchus. In 1856, Norman Robert Pogson formalized the system by defining a first magnitude star as a star, 100 times as bright as a sixth-magnitude star, thereby establishing the logarithmic scale still in use today; this implies that a star of magnitude m is about 2.512 times as bright as a star of magnitude m + 1. This figure, the fifth root of 100, became known as Pogson's Ratio; the zero point of Pogson's scale was defined by assigning Polaris a magnitude of 2. Astronomers discovered that Polaris is variable, so they switched to Vega as the standard reference star, assigning the brightness of Vega as the definition of zero magnitude at any specified wavelength.
Apart from small corrections, the brightness of Vega still serves as the definition of zero magnitude for visible and near infrared wavelengths, where its spectral energy distribution approximates that of a black body for a temperature of 11000 K. However, with the advent of infrared astronomy it was revealed that Vega's radiation includes an Infrared excess due to a circumstellar disk consisting of dust at warm temperatures. At shorter wavelengths, there is negligible emission from dust at these temperatures. However, in order to properly extend the magnitude scale further into the infrared, this peculiarity of Vega should not affect the definition of the magnitude scale. Therefore, the magnitude scale was extrapolated to all wavelengths on the basis of the black-body radiation curve for an ideal stellar surface at 11000 K uncontaminated by circumstellar radiation. On this basis the spectral irradiance for the zero magnitude point, as a function of wavelength, can be computed. Small deviations are specified between systems using measurement apparatuses developed independently so that data obtained by different astronomers can be properly compared, but of greater practical importance is the definition of magnitude not at a single wavelength but applying to the response of standard spectral filters used in photometry over various wavelength bands.
With the modern magnitude systems, brightness over a wide range is specified according to the logarithmic definition detailed below, using this zero reference. In practice such apparent magnitudes do not exceed 30; the brightness of Vega is exceeded by four stars in the night sky at visible wavelengths as well as the bright planets Venus and Jupiter, these must be described by negative magnitudes. For example, the brightest star of the celestial sphere, has an apparent magnitude of −1.4 in the visible. Negative magnitudes for other bright astronomical objects can be found in the table below. Astronomers have developed other photometric zeropoint systems as alternatives to the Vega system; the most used is the AB magnitude system, in which photometric zeropoints are based on a hypothetical reference spectrum having constant flux per unit frequency interval, rather than using a stellar spectrum or blackbody curve as the reference. The AB magnitude zeropoint is defined such that an object's AB and Vega-based magnitudes will be equal in the V filter band.
As the amount of light received by a telescope is reduced by transmission through the Earth's atmosphere, any measurement of apparent magnitude is corrected for what it would have been as seen from above the atmosphere. The dimmer an object appears, the higher the numerical value given to its apparent magnitude, with a difference of 5 magnitudes corresponding to a brightness factor of 100. Therefore, the apparent magnitude m, in the spectral band x, would be given by m x = − 5 log 100 , more expressed in terms of common logarithms as m x