MRC 0406-244

MRC 0406-244 also known as TN J0408-2418, is a radio galaxy producing an astrophysical jet, located in the constellation of Eridanus. At its redshift of 2.44, it is roughly ten billion light years from Earth.

Characteristics
MRC 0406-244 is one of the most powerful radio galaxies known date-to-date;  it was studied extensively by the MRC/1 Jy radio source survey. MRC 0406-244 is also classified a Seyfert type 2 galaxy, with a complex morphology featuring several components, including a point source with an extended nebular and continuum emission. Moreover, it contains an ultra-deep spectrum radio source (USS).

Host galaxy

The host galaxy of MRC 0406-244 is a dusty obscured massive early-type galaxy with a star formation of (M⋆ ~ 1011 M⊙). The galaxy also has a stellar disc, within the range of 3.5 to 8.2 kpc which is similar to coeval star-forming galaxies, which is found to be smooth.

Galaxy merger

From recent Hubble Space Telescope (HST) images, researchers have found several bright clumps with figure-of-eight shapes elongated along the radio jet axis of MRC 0406–244. Further images reveal there is a spatially resolved continuum. It is associated with its southeastern component that is aligned with the radio axis, with a complex morphology, including a double nucleus and tidal tail features. This suggests of a tidal origin, meaning a recent galaxy merger has taken place. It is believed that galaxy merger plays a dominant role in which its supermassive black hole is fueled. Signs show the black hole inside the center of MRC 0406–244, is growing at an exponential rate of hundreds to thousands of solar masses per year, so as the luminosity, turning it into a quasar.

Observation of MRC 0406-244
According from HST and ground-based multiwavelength observations of MRC 0406–244, researchers found there are two distinct components, aligned with its radio source axis. One of them has the red optical-to-IR and blue ultraviolet colors, making it a characteristic of radio galaxies, while the other is red in all colors. From the Lyα image, a nebula in MRC 0406-244 is found to be 3  × 5  extent, confined to the range of azimuth angles with respect to the nucleus of 60° to either side. Another component is also found extending northwest with similar morphology seen in the HST images.

Researchers also found the long axis of the Lyman-alpha emission that is 130° east of north in MRC 0406–244, aligns with the radio source. They found out, the total Ly flux is 1.2 × 10−14 ergs s−1 cm−2, equivalent to a luminosity of 1 × 1045 ergs s−1. 1 40% of this flux is within the 25 × 35 area that is measured in the spectrum. The peak surface brightness of the Ly emission is found to be 9.0 × 10−16 ergs s−1 cm−2 arcsec−2, and emission is detected down to a level of 1.5 × 10−16 ergs s−1 cm−2 arcsec−2.

Radio Properties
A triple radio source found in MRC 0406–244, is amongst the most power radio sources known according to researchers. They noted that the radio source reaches up to luminosity of 1.2 × 1036 ergs s−1 Hz−1 at 1 GHz and radiating at 6.3 × 1045 ergs s−1 between 100 MHz and 100 GHz. This extends over 84 kpc between the hot spots of MRC 0406–244, which found to be steep and strongly curved. The spectral index of the radio source changes from 1.21 at 1 GHz to 1.49 at 16 GHz in the rest frame to flux densities at several frequencies between 408 MHz and 8.44 GHz. This radio core contains a spectral index of 0.80 ± 0.18 (between 4.7 and 8.4 GHz, observed) that contributes the total emission at 15 GHz at 2%.

The two radio lobes in MRC 0406-244 are notable for their degree of asymmetry. Given the asymmetries in arm length and the spectral indices in powerful sources, they are both related both intrinsic asymmetries and light travel-time differences. From the correlation between emission-line and radio asymmetries in other 3CR radio galaxies, this suggests dominance of environmental effects, which cosmic dust plays a main role in correlation of optical and radio asymmetries.

Gas and dust beyond MRC 0406-244
Further observations from researchers found, that nebular and continuum ultraviolet light extends up to 25 kpc from the nucleus of the galaxy. This is six times more than the length of the minor axis in the direction of the radio jets. Both extended components are shown to contribute to the alignment effect given their distribution is biconical along the jet axis. The dust at similarly large radii is known to exist, given the diffuse blue continuum is dust-scattered from active galactic nucleus light or from dust-reddened young stars. The dust must had probably originated in the galaxy, hence the outflow of both metal-rich gas and dust is important for enriching the intracluster medium.

The nebular gas can be driven out from MRC 0406–244 in two ways. One, either through expanding starburst bubbles. Two, by overpressurized cocoons of material that is surrounding the expanding radio jets. The dust grains are likely destroyed when interacting with powerful radio jets, so they instead transported by radiation pressure or supernovae induced winds.

Dust in the intergalactic medium has theorized for a long time, but detected only recently. From the study published by Ménard et al. (2010), it is suggested half of the cosmic dust lies within galaxies, whilst the other half is expelled to the intergalactic medium. The extended light in MRC 0406−244 allows researchers, a rare opportunity to observe the dust in the midst of leaving the galaxy. As the host galaxy of MRC 0406−244 does not have different characteristics compared to other massive star-forming galaxies, it is possible that many highly star-forming galaxies lying at a similar redshift also expels out similar amounts of dust in bipolar outflows. The dust remains invisible unless it gets illuminated through sufficiently bright active galactic nuclei or through feedback driven star formations. If such dusty outflows in MRC 0406-244 is common, then researchers are expected to see ultraviolet-bright emission along the minor axis of stacked images of starbursting active galactic nuclei.