NGC 1672
Barred spiral galaxy with an ambiguous nucleus and strong radio emissions.
NGC 1672 is a barred spiral galaxy located in the southern constellation Dorado. Scottish astronomer James Dunlop first observed it on 5 November 1826. Whether the galaxy belonged to the Dorado Group was long debated, but recent measurements using the tip of the red-giant branch method place it at the same distance as other group members, strongly indicating it is part of that group.
The galaxy features a large bar roughly 20 kiloparsecs across. Its nucleus, bar, and inner spiral arms emit very strong radio waves. The nucleus is classified as a Seyfert type II and is surrounded by a starburst region. The strongest polarized radio emission comes from the northeastern area, upstream of the galaxy’s dust lanes, and the magnetic field lines there run at large angles to the bar, curving smoothly toward the center.
Structurally, NGC 1672 has a bright central bar, from which four filament-like spiral arms extend. These arms are asymmetric: the northeastern arm is significantly brighter than its counterpart on the opposite side. Numerous star-forming regions dot the arms, some possibly quite large.
The galaxy’s nucleus does not fit neatly into the standard three-type classification scheme (nuclear H II region, Seyfert nucleus, or low-ionization emission-line region). Its spectrum appears intermediate, suggesting it may host both nuclear star formation and an active galactic nucleus. In some wavelengths, such as ultraviolet, the star-forming regions dominate the emission.
Two supernovae have been observed in NGC 1672: SN 2017gax, a Type Ib/c event discovered on 14 August 2017 by the Distance Less Than 40 Mpc Survey (DLT40), and SN 2022aau, a Type II supernova found by the same survey on 20 January 2022.
Quick Facts
- Epoch
- J2000
- Ra
- 04 · 45 · 42.5022
- Dec
- -59 · 14 · 50.162
- Dist Ly
- 15.86 ±
- Z
- 0.004440
- Appmag V
- 10.3
- Constellation Name
- Dorado
Facts from the source article.
Lore & Background
NGC 1672 has a large bar estimated to measure around 20 kpc. The galaxy exhibits very strong radio emissions from its nucleus, bar, and inner spiral arm region. The strongest polarized emissions come from the northeastern region, upstream from its dust lanes, and magnetic field lines lie at large angles relative to the bar, turning smoothly toward the center. The center contains a high surface brightness bar, and four filament-like spiral arms extend outward from its ends. The spiral arms are asymmetric, with one arm in the northeast significantly brighter than its counterpart. These arms contain numerous star formation regions, some of which may be as large as . The nucleus of NGC 1672 is uncertain in classification. Most galaxies are classified as having a nuclear H II region, a Seyfert nucleus, or a low-ionization nuclear emission-line region. NGC 1672, however, does not fit into this scheme, as its spectrum appears intermediary between these three classes. It may contain both nuclear star formation regions and an active galactic nucleus. In some wave bands, such as ultraviolet light, the star formation regions are the primary source of emission. Two supernovae have been observed in NGC 1672: SN 2017gax (Type Ib/c, mag. 17.0406) discovered by the Distance Less Than 40 Mpc Survey (DLT40) on 14 August 2017, and SN 2022aau (Type II, mag. 16.2788) discovered by DLT40 on 20 January 2022.
Reader's Guide
NGC 1672 is significant as a nearby barred spiral galaxy whose ambiguous nuclear classification challenges standard schemes for galactic nuclei. Its spectrum appears intermediary between nuclear H II regions, Seyfert nuclei, and low-ionization nuclear emission-line regions, suggesting it may host both star formation and an active galactic nucleus. This makes it a valuable object for studying the interplay between star formation and supermassive black hole activity. The galaxy's strong radio emissions from its nucleus, bar, and inner spiral arms, along with polarized emissions and magnetic field geometry, provide insights into magnetic field behavior in barred galaxies. Its membership in the Dorado Group, confirmed by TRGB distance measurements, helps establish the group's structure. The two supernovae observed in NGC 1672 contribute to studies of stellar evolution and explosion mechanisms. The galaxy's asymmetric spiral arms and large star formation regions also make it a target for understanding star formation processes in barred spirals. NGC 1672 is often compared to other barred spirals such as NGC 1300 and NGC 7552.
Did You Know?
- NGC 1672 was discovered by Scottish astronomer James Dunlop on 5 November 1826.
- Its nucleus does not fit standard classification schemes, appearing intermediary between H II regions, Seyfert nuclei, and LINERs.
More in Galaxy Clusters and Groups, Part 4 1-24
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