UGC 07451, VCC 0613, PGC 040179, MCG +01-32-032[1]
NGC 4324 is alenticular galaxy[3] located about 85 millionlight-years away[4] in the constellationVirgo. It was discovered by astronomerHeinrich d'Arrest on March 4, 1862.[5] NGC 4324 has astellar mass of 5.62 × 1010M☉, and abaryonic mass of 5.88 × 1010M☉. The galaxy's total mass is around 5.25 × 1011M☉.[2] NGC 4324 is notable for having a ring of star formation surrounding its nucleus.[6][7][8] It was considered a member of theVirgo II Groups until 1999, when its distance was recalculated and it was placed in theVirgo W Group.[9][10]
First discovered in 1957 by Russian astronomerKirill Ogorodnikov and described byOgorodnikov as "a system of planet-like concentrations similar to beads" and as "equally-spaced bead-like concentrations of equal size and brightness similar to the annular nebula ofKant-Lapace nebular hypothesis.",[11] NGC 4324 features an innerring that surrounds the nucleus. The ring appears complete[12] but broken on opposite sides of its diameter[11] which led to Burstein et al. suggesting that the ring is not a ring at all but instead tightly wound spiral arms and that NGC 4324 is a misclassifiedspiral orlenticular galaxy.[13] Despite this, the ring is considered to be a true ring. The ring hosts most of themolecular gas observed in NGC 4324 with roughly 1.7 billionM☉ ofHI (neutral hydrogen) and 9 × 107M☉ ofHII (singly-ionised hydrogen).[7] Despite this, HI was detected by Duprie et al. in 1996 that extends roughly 2 optical diameters suggesting that atomic hydrogen is not only concentrated in the ring.[6]
InUltraviolet light, the ring is bright, due to the presence ofstar formation[6][7][8] that is occurring at an estimated rate of roughly 0.052 ± 0.021M☉ per year,[14] with star formation being segregated in the ring.[6] In between the ring and the bulge of NGC 4324, there are tightly wound spiral arms that are defined mostly by dust.[12][15]
In the center of NGC 4324, the stellar population has a mean age of about 8 billion years, with anabundance ratio that is close to the sun, at [Mg/Fe] 0, and ametallicity that is slightly supersolar, at [Z/H] ~ +0.1. This suggests continuous effective star formation in the nucleus of NGC 4324. In the bulge of NGC 4324, the mean age of the stellar population is around 13 billion years, with abundance ratio of [Mg/Fe] = +0.15, and a metallicity of [Z/H] = −0.2 L −0.3. In the inner part of the disk of NGC 4324, the stellar population is old, with an abundance ratio of [Mg/Fe] = +0.2, and a metallicity of [Z/H] < −0.33. Such characteristics imply a brief singlestarburst took place more than 10 billion ago and formed the stellar disk of NGC 4324. In the ring-dominated area of the disk, the dominant stellar population is also old, despite being slightly younger than in the inner disk, and has chemical properties similar to the stars of the inner disk.[7]
NGC 4324 is classified as aSeyfert Galaxy[16][17] and as aLINER galaxy.[18][16] Despite being classified as a Seyfert galaxy, NGC 4324 has no delectable nuclear radio continuum emission lines, suggesting that the emission lines that led to its classification as a Seyfert come from stellar processes such asphotoionization driven bysupernova remnants and/orplanetary nebulae which can mimic the high-ionization nebular emission characteristic of the nuclei of other observed Seyfert Galaxies. This is despite the fact that NGC 4324 is host to asupermassive black hole with an estimated mass of 2.187 millionM☉.[19]
