PGC 2824392, PKS B0529-549, MRC 0529-549, PMMM 052927.1-545647, SUMSS J053025-545422
PKS 0529-549 known as MRC 0529-549 and PKS B0529-549, is a radio galaxy located in the constellation Pictor. At the redshift of 2.57, the object is located nearly 10.8 billion light-years away from Earth.[1]
From further observations, PKS 0529-549 has an energetic source of radiation located throughout most of the electromagnetic spectrum. Such HzRGs like PKS 0529-549 are extremely massive, including old stars (up to ~ 1012 M○), hot gas (up to ~ 1012 M○) and molecular gas (up to ~ 1011 M○).[9] Furthermore, galaxies with M⋆ ≳1011 M⊙ at z ≃ 2–3 tend to have star formation rates of order of ~100 M⊙ yr−1. This suggests PKS 0529-549 lies above the mean SFR–M⋆relation, in the so-called star-forming main sequence.[10]
Like most HzRGs, PKS 0529-549 is known to host large reservoirs of interstellar dust and gas.[11] Apart from that, the galaxy is found to exhibit both hot dust emission at 8.0 μm, with a significant internal visual extinction (~1.6 mag), inferred from Spitzer Space Telescope near/mid-IR imaging.[5]
Observations
According to researchers who observed PKS 0529-549 from Atacama Large Millimeter Array in Chile, it contains chlorine [C I] and doubly ionized oxygen [O III] which display regular velocity gradients. However, their systemic velocities and kinematic PAs differ by ~300 km s−1 and ~30°, respectively. The [C I] is consistent with a rotating disc, meaning it is aligned together with both the stellar and dust components, while the [O III] has a possible outflow trace, that is aligned with two active galactic nuclei-driven radio lobes in the host galaxy of PKS 0529–549.
Moreover, the [C I] cube is reproduced through a 3D disc model with Vrot ≃ 310 km s−1 and σV ≲ 30 km s−1, giving Vrot/σV ≳10, comparable to local spiral galaxies.[12][13] This indicates that the [C I] disc of PKS 0529-549 is not particularly turbulent[14] and indeed remarkable considering that PKS 0529-549 has a star formation at the rate of at ~1000 M⊙ yr−1. Not to mention, it hosts a powerful radio-loud active galactic nucleus, with large amount of energy injected into its interstellar medium.[15]
PKS 0529-549 is known to lie on the local baryonic Tully–Fisher relation. This is interesting since it has both estimates of both M⋆ and Mmol, other than Vrot and σV according to researchers who studied the galaxy. The stellar mass of PKS 0529-549 according to them, are estimated to be M⋆/L[3.6] = 0.5 M○/L○ which is similar for all galaxies, as expected from stellar population synthesis models with a Kroupa IMF.[16]
Researchers further measured the rotation velocities along the flat part of the rotation curve (Vflat) in PKS 0529–549. This is probed by deep H I observations by Spitzer Photometry and Accurate Rotation Curves.[17] In the case, Vrot is an intensity-weighted estimate over the semimajor axis, since the [C I] emission is resolved with ~2 beams. Thus, one might wonder whether they are probing Vflat. Local galaxies that have similar masses as PKS 0529-549 normally have rotation curves, peaking at very small radii (R ≲ 1 kpc). These tend to decline by around ~20–30 percent before reaching Vflat.[18] This suggests some massive galaxies like PKS 0529-549 are in place and kinematically relaxed at z ≃ 2.6, when the universe was only ~2.5 billion years old.[14]
