MRC 0316-257 is classified as a high redshift radio galaxy.[2][3] It is found to be hosted inside a massive star-forming galaxy containing large reservoirs of gas and interstellar dust.[4][5] Such host galaxies like MRC 0316-257 are believed to be progenitors of massive elliptical galaxies that are present in the local universe, given most powerful radio galaxies are hosted in ellipticals that are considered large.[6][7] Its 1.5-Jy radio source was listed in the 408-MHz Molonglo Reference Catalogue which was optically identified with a galaxy at z= 3.13[8] with a typical radio luminosity and radio loudness of L5 = 1043 - 1044 ergs −1 and log R = 3–4.[9]
MRC 0316-257 protocluster
MRC 0316-257 is situated in the center of a massive protocluster.[10][11] The cluster has a larger size compared than 3.3x3.3 Mpc^2, which its mass structure is estimated to be > 3-6x10^14 M_sun. This makes it a progenitor of the cluster of galaxies similar like the Virgo cluster.[12]
Two Lyα emitting companions located at z = 3.1378 +/- 0.0028 and z = 3.1351 +/- 0.0028, are found in the MRC 0316-257 protocluster according to research conducted by Le Fevre et al. (1996).[13] The first galaxy is 0.3 h ^{-1}50 Mpc from MRC 0316–257, which is then resolved with an intrinsic size of 11.6 +/- 1.1 h ^{-1}50 kpc, and a Ly alpha in emission with rest WLy alpha = 55 +/- 14 A. The galaxy has an extremely blue V - I color indicating it as a protogalaxy in the midst of forming the first stars in a low-dust medium. The second is at least 1.3 h ^{-1}50 Mpc. The galaxy is marginally resolved, which in addition to Ly alpha in emission, there is C IV in emission with its broad component indicating the contribution from the active galactic nucleus.[13]
The protocluster has a comoving density. These galaxies have V < 23.8 and Ly alpha flux greater than 10-16 ergs cm-2 s-1 within the vicinity of MRC 0316–257. They have ~2.5 x 10-3 h 350 Mpc-3, making them significantly higher than the expected background density of field galaxies, suggesting as a rich cluster.[13]
Through spectroscopy of 40 candidate emitters, 33 emission-line galaxies are discovered. 31 are Ly-alpha emitters with similar redshifts of MRC 0316–257, while the remaining two turned out to be [OII] emitters, with widths between the range of 120–800 km/s, with a median of 260 km/s. They are asymmetric, with apparent absorption troughs blueward of the profile peaks, indicative of absorption along the line of sight of an HI mass of at least 2x10^2 - 5x10^4 M_sun and are found to be faint, blue and small and consistent with young star forming galaxies considered as dust free.[12]
The volume density of Ly-alpha emitting galaxies in the field around MRC 0316-257 have a factor of 3.3+0.5-0.4. This are larger compared with the density of field Ly-alpha emitters at that redshift with a velocity distribution of 1510 km/s, smaller than the width of the narrow-band filter (FWHM ~ 3500 km/s). The velocity distribution is at the peak of 200 km/s, which is within the redshift, thus confirming Ly-alpha emitter galaxies as members of a protocluster at z~3.13.[12]
^ abcVenemans, B. P.; Rottgering, H. J. A.; Miley, G. K.; Kurk, J. D.; De Breuck, C.; Overzier, R. A.; van Breugel, W. J. M.; Carilli, C. L.; Ford, H.; Heckman, T.; Pentericci, L.; McCarthy, P. (March 2005). "Properties of Ly-alpha emitters around the radio galaxy MRC 0316-257". Astronomy & Astrophysics. 431 (3): 793–812. arXiv:astro-ph/0501259. doi:10.1051/0004-6361:20042038. ISSN0004-6361.
