Hedgehog (galaxy)
Isolated dwarf galaxy
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Hedgehog is an isolated low surface brightness dwarf galaxy in the constellation Virgo. With no neighboring galaxies within 1 Mpc and located 1.7Mpc from the nearest massive galaxy group, Hedgehog is one of the most isolated quiescent dwarfs found to date.[1] It was discovered in 2024.
| Hedgehog | |
|---|---|
 The Hedgehog Galaxy (under different wavelengths) | |
| Observation data (J2000 epoch) | |
| Constellation | Virgo |
| Right ascension | 13h 22m 46.88s |
| Declination | −20° 53′ 55.94″ |
| Distance | 7.88 |
| Apparent magnitude (V) | 17.35 (g) |
| Characteristics | |
| Type | dwarf galaxy |
| Apparent size (V) | 0.5 x 0.5 arcmin |
| Half-light radius (physical) | 176±14 pc |
| Other designations | |
| LGC2024 dw1322m2053 | |
Hedgehog is less massive than the other extremely isolated dwarfs KKs3 and KKR25. It shows no sign of recent star formation and has an old stellar population.[1]
Hedgehog is most likely to originate from the Cen A group, given their proximity. However, its distance to Cen A might be too far compared with simulations. Given its current distance of 1.7 Mpc from Cen A, Hedgehog’s travel time, assuming an ejection velocity of v ≈260±60kms−1 (Müller et al. 2022), would be 4–6 Gyr. If Hedgehog was quenched within 1–2 Gyr after it had the pericenter passage in the Cen A group, the estimated travel time agrees quite well with the inferred age of Hedgehog’s stellar population (≈ 5–7 Gyr). However, it is important to note that the inferred age of Hedgehog is still quite uncertain due to the age metallicity degeneracy. Additionally, if a major merger of Cen A occurred around 2 Gyr ago, it would complicate this timing argument.[1]
Hedgehog’s mass is close to the upper limit, where reionization can effectively quench star formation. Recent simulations demonstrate that field dwarfs with 105−6 solar masses can be quenched by reionization but can also be rejuvenated later. To remain quiescent, it is possible that Hedgehog has a slightly lower halo mass, as indicated by its small half light radius, or experienced a stronger UV background due to the inhomogeneous nature of reionization.[1]
