PKS 0529−549

PKS 0529−549 is one of the high redshift radio galaxies (HzRGs) found.^[2][3][4] Detected from high-resolution 12-mm and 3-cm images, obtained by the Australia Telescope Compact Array, the galaxy is found to have a Type-II active galactic nucleus (AGN) showing two radio lobes. With a rest-frame of -9600 rad m-2, the eastern radio lobe holds a record for the highest Faraday rotation measure to date, signifying a strong magnetic field or either a dense circumgalactic medium.^[5]

The host galaxy for PKS 0529−549 is a starburst galaxy^[6] in the final stages of merging with another galaxy.^[7] The result of this galaxy merger would be progenitor of an elliptical galaxy, in which causes increasing luminosity due to high star formation in its regions.^[8] Signs of star formation included a plethora of absorption line features detected through using the deep X-shooter spectrum, stellar photospheric and wind features indicating presence of OB-type stars as well as both emission lines and low-ionization absorption features.^[7]

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]

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 V_rot ≃ 310 km s⁻¹ and σ_V ≲ 30 km s⁻¹⁠, giving V_rot/σ_V ≳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 M_mol, other than V_rot and σ_V 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 (V_flat) in PKS 0529−549. This is probed by deep H I observations by Spitzer Photometry and Accurate Rotation Curves.^[17] In the case, V_rot 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 V_flat. 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 V_flat.^[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]