The Grus Quartet is a group of four interacting galaxies located in the southern constellation of Grus (the Crane). The four spiral galaxies – NGC 7552, NGC 7582, NGC 7590, and NGC 7599 – appear close to each other in the sky and are known to be gravitationally bound. They can be observed in larger telescopes in good conditions.
The four galaxies are part of the NGC 7582 Group, which contains at least nine members. In addition to the Grus Quartet, the group includes NGC 7496, NGC 7531, NGC 7632, IC 5325, and ESO 291-24.
Three of the galaxies in the Grus Quartet – NGC 7582, NGC 7590, and NGC 7599 – are sometimes called the Grus Triplet. These galaxies occupy only 10 arcminutes of the apparent sky, while NGC 7552 appears a bit further away.
Grus Quartet, image credit: Michael Sidonio/Wikisky (CC BY 4.0)
The galaxies of the Grus Quartet form a compact galaxy group with the low surface brightness galaxy (LSBd) catalogued as HIPASS J2318-42a S4. The faint galaxy was identified by a team of astronomers led by Sarah M. Sweet, School of Mathematics and Physics, University of Queensland, Australia, in 2013. It appears near NGC 7582 in the sky.
The fifth galaxy was identified based on the Survey for Ionization in Neutral Gas Galaxies (SINGG) with the Cerro Tololo Inter-American Observatory (CTIO) 1.5 and 0.9 m telescopes. The astronomers selected galaxies based on their neutral hydrogen (HI) mass obtained in the H I Parkes All-Sky Survey (HiPASS).
The Grus Quartet galaxies are members of the same larger group of galaxies known as the Grus cloud. The nearby IC 1459 Group belongs to the same cloud. This is a loose group of galaxies named after its brightest member, the giant elliptical galaxy IC 1459. The large radio galaxy appears north of the Grus Quartet, in the direction of the bright Fomalhaut in Piscis Austrinus. Members of the IC 1459 Group include NGC 7418, NGC 7418A, NGC 7421, IC 5264, IC 5269, IC 5269B, IC 5270 and IC 5273.
Galaxies in the Grus Quartet, image credit: ESO/Digitized Sky Survey 2 (CC BY 4.0)
NGC 7552
NGC 7552 (IC 5294) is the brightest of the four galaxies that form the Grus Quartet. It is a barred spiral galaxy located approximately 56 million light years away. It appears nearly face-on. The galaxy has an apparent magnitude of 11.2 and an angular size of 3.4 by 2.7 arcminutes. It is smaller than our own Milky Way. It has an estimated diameter of around 55,700 light-years.
The two spiral arms of NGC 7552 form a pseudo-ring around the galaxy. One of the arms is more prominent than the other. The galaxy has a dusty bar that contains four known large HII regions.
NGC 7752 is classified as a luminous infrared galaxy (LIRG). It has an infrared luminosity of 1011.03 solar luminosities. It is listed as a Seyfert I galaxy and has a very bright, quasar-like active nucleus.
Many LIRGs are galaxies that are in the process of interacting with their neighbours. As a result, they can appear disrupted and tend to have high rates of star formation, which contributes to the high level of luminosity.
NGC 7752 contains a partial starburst ring more than 326 light years wide. Astronomers have identified many supernova remnants and very young star clusters in the ring. These clusters have estimated ages between 5.5 and 6.3 million years. Observations with the Very Large Array (VLA) and the Australia Telescope Compact Array (ATCA) in 2008 revealed three star forming rings with radii of 3,261, 6,197, and 11,089 light-years.
NGC 7552 hosted a luminous red nova in 2014. Catalogued as AT 2014ej, the nova shone at magnitude 18.0. The galaxy also hosted a recent Type Ia supernova, SN 2017bzc, discovered in March 2017. The supernova had an apparent magnitude of 12.8.
Even though it is interacting with other members of the Grus Quartet, NGC 7552 does not appear highly disturbed. However, astronomers have detected a large tidal tail of neutral hydrogen that stretches from NGC 7552 to NGC 7582, which has provided evidence of interactions between the galaxies.
NGC 7552 by the Hubble Space Telescope, image credit: NASA/ESA and Hubble; processing: Judy Schmidt (CC BY 2.0)
NGC 7582
NGC 7582 is a barred spiral galaxy located 69.1 million light-years away. It has an apparent visual magnitude of 11.37 and an apparent size of 5.0 by 2.1 arcminutes, corresponding to a physical diameter of 331,200 light-years.
Like NGC 7552, NGC 7582 is an active galaxy. It is classified as a Seyfert 2 galaxy. It has the characteristic bright core, both at optical and infrared wavelengths, and an active galactic nucleus (AGN) with a supermassive black hole. The central black hole of NGC 7582 has an estimated mass of 5.5 × 107 M☉ (55 million solar masses).
In 2005, observations with the Australia Telescope Compact Array revealed a mass of 2.1 × 109 solar masses of neutral atomic hydrogen (H I) to be dragged from NGC 7582 into intergalactic space. Astronomers found 1.34 billion solar masses of H I gas contained in a tidal tail emanating from the northwestern disk of NGC 7582 and extending for 277,233 light-years. The tidal tail does not have a counterpart in optical images.
Spiral galaxy NGC 7582 is the brightest member of the Grus Quartet of galaxies, some 60 million light-years distant traveling together through space. In this near-infrared image, FLAMINGOS-2 resolved its high quantity of dust that line NGC 7582’s arms as well as regions rich in star formation. Field of view: 2.5 x 1.7 arcmin. Image: Gemini Observatory/AURA (CC BY 4.0)
NGC 7590
NGC 7590 is a spiral galaxy with an apparent magnitude of 11.37. It lies either 64.1 million light years away (Hubble distance) or 84.50 million light-years away, based on 12 non-redshift measurements.
Like NGC 7752, it is a Seyfert I galaxy with a bright Seyfert core. It has a diameter of 83,700 light years and an apparent size of 5.0 by 2.1 arcminutes.
NGC 7590 forms a pair with the nearby NGC 7599. The two galaxies are separated by less than 5 arcminutes in the sky. Astronomers have detected a bridge of hydrogen gas stretching between the two galaxies, indicating that they are interacting.
NGC 7590 and NGC 7599, image: Legacy Surveys / D. Lang (Perimeter Institute), NERSC (CC BY 4.0)
NGC 7599
NGC 7599 (IC 5308) is a barred spiral galaxy located around 62.7 million light-years away. It has an apparent magnitude of 11.5 and an apparent size of 4.4 by 1.3 arcminutes, corresponding to a linear diameter of 94,000 light-years.
NGC 7599 has a small nucleus that is not particularly bright. It has multiple spiral arms and a prominent dark dust lane on one side. It contains a central supermassive black hole with an estimated mass of 106.48 ± 0.56 solar masses.
Facts
The Grus Quartet was discovered by the Scottish astronomer James Dunlop from Paramatta (now Parramatta) in New South Wales, Australia, in July 1826. Dunlop spotted NGC 7552 and NGC 7582 on July 7, and NGC 7590 and NGC 7599 on July 14, 1826.
English astronomer John Herschel observed the galaxies on September 2, 1836. Based on his observations, the galaxies were included as NGC 7552, NGC 7582, NGC 7590 and NGC 7599 in the New General Catalogue, compiled by Danish astronomer John Louis Emil Dreyer in 1888.
Location
The Grus Quartet appears close to the triple star Theta Gruis in the sky, close to the imaginary line connecting Ankaa (Alpha Phoenicis), the brightest star in the constellation Phoenix, and Aldhanab (Gamma Gruis), the third brightest star in Grus.
At declination -42° 35′, the Grus Quartet is best seen from the southern hemisphere. It never rises above the horizon for observers north of the latitude 47° N.
The best time of the year to observe the Grus Quartet and other deep sky objects in Grus is during the month of October, when the celestial Crane appears higher above the horizon in the early evening.
Location of the Grus Quartet, image: Stellarium
Grus Quartet
| Constellation | Grus |
| Object type | Compact group of galaxies |
| Right ascension | 23h 16m 10.800s |
| Declination | -42° 35′ 05.00″ |
| Names and designations | Grus Quartet, AM 2315-423, SCG2 2315-4241, [SMD2013] HIPASS J2318-42a |
NGC 7552
| Object type | Barred spiral galaxy |
| Morphological type | (R’)SB(s)ab |
| Right ascension | 23h 16m 10.7287s |
| Declination | −42° 35′ 04.881″ |
| Apparent magnitude | 11.2 |
| Apparent size | 3.4′ × 2.7′ |
| Distance | 56 million light years (17.2 megaparsecs) |
| Redshift | 0.005407 |
| Heliocentric radial velocity | 1608 ± 5 km/s |
| Size | ~55,700 ly (17.07 kpc) |
| Names and designations | NGC 7752, IC 5294, LEDA 70884, PGC 70884, ESO 291- G 012, ESO 291-12, ESO-LV 291-0120, MCG -07-47-028, VV 440, IRAS 23134-4251, IRAS F23133-4251, 2MASX J23161076-4235053, HIPASS J2316-42, EQ 2313-43, SPASS J231611-423528, ATPMN J231610.6-423504, Cul 2313-428, SGC 231325-4251.4, 1E 2313.4-4251, 2E 4704, 2E 2313.4-4251, PKS 2313-428, PKS J2316-4235, [DML87] 732, 6dFGS gJ231610.7-423505, GLEAM J231611-423503, ISOSS J23161-4234, PMN J2316-4234, PSCz Q23134-4251, SUMSS J231610-423506, TGSSADR J231610.6-423503, [SLK2000] 113, [SLK2004] 1862, 2XMM J231610.7-423505, [CHM2007] HDC 1238 J231610.76-4235053, [CHM2007] LDC 1559 J231610.76-4235053, [VDD93] 252, [VV2000c] J231611.2-423501, [VV2003c] J231611.2-423501, [VV2006c] J231610.8-423505, [VV2010c] J231610.8-423505, [VV98c] J231611.2-423501, [ZM98] NGC 7582 4 |
NGC 7582
| Object type | Barred spiral galaxy |
| Morphological type | SA(rs)bc? |
| Right ascension | 23h 18m 23.5s |
| Declination | −42° 22′ 14″ |
| Apparent magnitude | 11.37 |
| Apparent size | 5.0′ × 2.1′ |
| Distance | 69.1 ± 6.719 million light-years (21.2 ± 2.060 megaparsecs) |
| Redshift | 0.00524908 |
| Heliocentric radial velocity | 1570 ± 150 km/s |
| Size | 331,220 light years (101,600 parsecs) |
| Names and designations | NGC 7582, LEDA 71001, PGC 71001, MCG -07-47-029, ESO 291-16, ESO-LV 291-0160, IRAS 23156-4238, IRAS F23156-4238, 2MASX J23182362-4222140, ATPMN J231823.6-422213, 6dFGS gJ231823.6-422214, 1E 2315.6-4238, 2E 4706, 2E 2315.6-4238, INTREF 1104, GLEAM J231823-422207, SWIFT J2318.4-4223, SWIFT J2318.4-4221, SUMSS J231823-422212, PBC J2318.3-4221, PKS 2315-426, 2XMM J231823.5-422213, PMN J2318-4221, TGSSADR J231823.5-422214, QDOT B2315381-423841, XSS J23178-4236, PSCz Q23156-4238, SGC 231538-4238.6, SINGG HIPASS J2318-42a S1, [HB91] 2315-426, [DML87] 734, [VDD93] 253, [CHM2007] HDC 1238 J231823.62-4222140, [CHM2007] LDC 1559 J231823.62-4222140, [A81] 231538-4239, [HSN2016] J349.59-42.37, [VV2000c] J231823.5-422214, [VV2003c] J231823.5-422214, [VV2006c] J231823.5-422214, [VV2010c] J231823.5-422214, [VV98c] J231823.5-422214, [ZM98] NGC 7582 5 |
NGC 7590
| Object type | Spiral galaxy |
| Morphological type | SA(rs)bc? |
| Right ascension | 23h 18m 54.7949760192s |
| Declination | −42° 14′ 20.515300476″ |
| Apparent magnitude | 11.37 |
| Apparent size | 5.0′ × 2.1′ |
| Distance | 64.1 ± 4.6 million light-years (19.66 ± 1.40 megaparsecs) or 84.50 ± 3.99 Mly (25.908 ± 1.222 Mpc) |
| Redshift | 0.005255 |
| Heliocentric radial velocity | 1575 ± 5 km/s |
| Size | ~83,700 ly (25.65 kpc) |
| Names and designations | NGC 7590, LEDA 71031, PGC 71031, ESO 347- G 033, ESO 347-33, ESO-LV 347-0330, MCG -07-47-030, IRAS 23161-4230, IRAS F23161-4230, 2MASX J23185483-4214206, HIPASS J2318-42a, SINGG HIPASS J2318-42a, SINGG HIPASS J2318-42a S2, 1E 2316.2-4230, 2E 4708, 2E 2316.1-4230, 6dFGS gJ231854.8-421421, ISOSS J23189-4214, PSCz Q23161-4230, QDOT B2316097-423048, SGC 231610-4230.7, [CHM2007] HDC 1238 J231854.83-4214206, [CHM2007] LDC 1559 J231854.83-4214206, [DML87] 735, [HB91] 2316-425, [SLK2004] 1865, [VV2000c] J231855.0-421417, [VV2003c] J231855.0-421417, [VV2006c] J231854.8-421421, [VV2010c] J231854.8-421421, [VV98c] J231855.0-421417, [ZM98] NGC 7582 1, [VDD93] 254A, Gaia DR3 6536139165866767232 |
NGC 7599
| Object type | Barred spiral galaxy |
| Morphological type | SB(s)c |
| Right ascension | 23h 19m 31.055s |
| Declination | −42° 15′ 25.24″ |
| Apparent magnitude | 11.5 |
| Apparent size | 4.4′ × 1.3′ |
| Distance | 62.7 ± 7.4 Mly (19.2 ± 2.3 Mpc) |
| Redshift | 0.005508 ± 0.000017 |
| Heliocentric radial velocity | 1,651 ± 5 km/s |
| Size | ~94,000 ly (28.9 kpc) |
| Names and designations | NGC 7599, IC 5308, LEDA 71066, PGC 71066, ESO 347- G 034, ESO 347-34, ESO-LV 347-0340, MCG -07-47-033, HIPASS J2318-42b, SINGG HIPASS J2318-42a S3, IRAS 23166-4231, IRAS F23165-4231, 2MASX J23192114-4215246, SGC 231636-4231.8, 6dFGS gJ231921.0-421526, 2E 4711, 2E 2316.6-4232, ISOSS J23193-4216, QDOT B2316364-423149, PSCz Q23166-4231, [CHM2007] HDC 1238 J231921.14-4215246, [CHM2007] LDC 1559 J231921.14-4215246, [ZM98] NGC 7582 2, [VDD93] 254B, [SLK2004] 1867 |
Images
Gemini GMOS image of the barred spiral galaxy NGC 7552. The picture consists of separate images taken with different filters: H-alpha (red), g (blue), r (green), and i (yellow). Image credit: International Gemini Observatory/NOIRLab/NSF/AURA/B. Reynolds (Sutherland Shire Christian School)/T. Rector (University of Alaska, Anchorage)/Australian Gemini Office (CC BY 4.0)
NGC 7552 captured by the Spitzer space telescope, image: NASA/JPL-Caltech/K. Gordon (Space Telescope Science Institute) and SINGS Team (PD)
Lurking about 70 million light years away from Earth in the constellation Grus, you will find the galaxy NGC 7582 — a spiral galaxy harbouring a supermassive black hole at its core. These images were captured as part of a study using the MUSE instrument on ESO’s Very Large Telescope (VLT) to uncover the effect of an active black hole on the formation of stars in the galaxy. The galaxy contains an active galactic nucleus (AGN) — an extremely energetic central engine powered by the supermassive black hole gobbling up material in its immediate surroundings. Matter heats up in this process, launching huge amounts of energy and powerful winds into the surrounding area. But what effect does this have on the galaxy at large? To find out, a recent study, led by Stéphanie Juneau from NOIRLab in the USA, looked at the distribution of different ionised elements in the galaxy. The image on the right shows oxygen, nitrogen and hydrogen in blue, green and red respectively. The red glowing areas are regions of high star formation activity, whereas the dominant blue regions show the cone-shaped material flowing out of the AGN. The image on the left, which covers the same area, shows a more classical view of this galaxy, with dust lanes obscuring blue and orange starlight. MUSE also allowed the team to map the motion of the stars and gas. They discovered that NGC 7582 may have a structure surrounding its central supermassive black hole that shields the rest of the galaxy from the harsh outflow of energy coming from the AGN, diverting it away from it in the form of an extremely powerful wind. image credit: ESO / Juneau et al. (CC BY 4.0)
Color image of the barred spiral galaxy NGC 7582 which hosts a hidden black hole. MUSE observations (inset) reveal emission from a hot gaseous wind (in green) that is ionized and launched by the black hole. Credit: Stefan Binnewies and Josef Pöpsel of Capella Observatory (background image); Stephanie Juneau of NOAO and CEA-Saclay (inset) (CC BY 4.0)