| PKS 2126-158 | |
|---|---|
 PKS 2126-158 seen onDESI Legacy Surveys | |
| Observation data (J2000.0epoch) | |
| Constellation | Capricornus |
| Right ascension | 21h 29m 12.176s |
| Declination | -15d 38m 41.04s |
| Redshift | 3.268000 |
| Heliocentric radial velocity | 979,722km/s |
| Distance | 11.5Gly (light travel time distance) |
| Apparent magnitude (V) | 0.216 |
| Apparent magnitude (B) | 0.286 |
| Surface brightness | 16.1 |
| Characteristics | |
| Type | LPQ;GPS, FRSQ |
| Other designations | |
| 2MASS J212912.18-1538410, OX -146, PKS 2126-15,PGC 4681153,IRCF J212912.1-153841, 2E 4479, SWIFT J2129.1-1538, PMN J2129-1538,NVSS J212912-153841 | |
PKS 2126-158 (referred to QSO B2126-158), also known asPKS 2126-15, is aquasar located inCapricornus. It has aredshift of 3.268000, which corresponds to thedistance of 11.5 billionlight years.[1] It is classified as agigahertz peaked-spectrum quasar (GPS)[2] with a flat-spectrumradio source[3] and ablazar, a type ofactive galaxy shooting anastrophysical jet towardsEarth.
First identified byastronomers in 1977 who were studying an optical follow-up of flat-spectrum sources from theParkes 2700MHzsurveys,[4] and subsequently by the Imaging Proportional Counter by theEinstein Observatory in 1981,[5] PKS 2126-158 was only the fifth radio quasar withz > 3 to have its redshift measured. It is found to have anemission-line redshift of 3.270 + or - 0.004 and a richabsorption spectrum shortward ofLy-alpha.[6]
PKS 2126−158 is a notable bright object emittingradio signals ofS2.7 GHz= 1.17 Jy,optical withnear-infrared rays ofV= 16.92,H= 14.89[7] andX-ray (F0.1−2.4 keV= 2 × 10−12 erg s-1 cm −2)frequencies.[8] Such fluxes, combined with the high redshift, meant PKS 2126-158 is one of the mostluminous quasars known.
Notably, an optical/near-infraredspectrum showed PKS 2126−158 has a bluepower-law shape for longerwavelengths compared toV bands where the Lyα line falls.[7] The flux drops off at shorter wavelengths due to its absorption by the interveninggas of the Lyman α forest.[9]
PKS 2126-158 is the brightest quasar observed through X-rays at redshift of z > 3 and second brightest object, after PKS 2149-306 located at z > 2.[10] For this reason, PKS 2126-158 has been observed in greater details at X-ray frequencies since the firstEinstein detection, which researchers discovered there is a strong energy[11] which was contributed by thephotoelectricabsorption along the path, in addition to the Galactic 21 cmcolumn density of 4.85 × 1020 cm−2 observed by Elvis et al. (1989).[12]
Throughspectral analysis observation from theEXOSATdatabase, PKS 2126-158 is found to be flat spectrum source (α = 0.3+/-0.15) given its power law and fixed absorption model fits within itsspectrum. In this database, the soft (0.1-2 keV) and hard (2-10 keV) X- rayluminosities of this quasar are found to be (0.7 +/- 0.1)10^48^erg s^-1^ and (2.3+/-0.3)10^48^ erg s^-1^ respectively. Although, there is no soft excess and low energy absorption have been detected, thethermal bremsstrahlung model is found to fit with the spectrum of PKS 2126 - 158, with arest-frametemperature of 6.4_-4_^+40^keV. This makes it the most luminous quasar detected in (30 keV) hard X-rays.[13]
A more detailed observation conducted byBeppoSAX during May 28 to May 29, 1999, found, compared to previous observations by ROSAT andASCA, the 2-10 keV and 0.1-2.5 keV fluxes were twice the factor higher. Moreover, it is also 40% higher compared to two recent observations byChandra X-ray Observatory andXMM-Newton. As compared to the causaltimescale associated with an emission region of ~10Schwarzschild radii around few black holes, the shortest detected rest frame variability timescale is few months. Apart from it, the source that is detected, contains signal to noise ratio right up to ~50 keV and 215 keV rest frame.[10]
These observations confirms the presence of a lowenergy absorption unrelated from thecontinuum model adopted, at a highconfidence level. Despite its limitedspectral resolution done by the BeppoSAX low energy concentrator system (LECS) and the medium energy concentrator system (MECS),[14] it is quite possible to putconstraints on different absorption and continuum models. For the absorber however, it is not easy to estimated its redshift. Furthermore, strong and complex metal line systems aligned with PKS 2126-158 were found at z = 0.6631 and at 2.64 < z < 2.82. This could be associated with the X-ray absorption.[10]
Further observations of PKS 2126-158 according to researchers, have found the presence of 113absorption lines in its spectrum, between the wavelength range from 4153 and 6807 A. Two sets of absorptionredshiftsystems consisting of 14 lines at z = 2.6381 and 16 lines at z = 2.7685 are established, together with a possible four line system at z = 2.3938. As for theions in the z = 2.7685 system, a columndensity is conducted, suggesting the absence of a 1533-A excitedfine-structure line of Si II (J = 3/2) but the presence of 1335-A excited fine-structure line of C II (J = 3/2). An inspected examination of many unidentified lines shortward of L-alpha emission, finds that no more than three L-alpha and beta pairs are seen in the spectrum. From thecross-correlation analysis indicates there single L-alpha lines makes up 90% of the unidentified lines.[15]
Thesupermassive black hole in PKS 2126-158 has an estimatedmass of 10 billionsolar masses,[16][17] which researchers found out through using thebolometric light technique.[18] This makes PKS 2126–158 to have one of the mostmassive black holes.
Through measuring redshifts of differentgalaxies fromGemini South in multi-objectspectroscopy mode around PKS 2126–158, five confirmed members fromgroup of galaxies are found atz~ 0.66, similarvelocities to metal-line absorption system seen in the quasar's spectrum. Four more fainter galaxies can be seen nearby and possibly associated with the group. There are a further three galaxies are close in redshift but have larger separations. While not related to the group, they are certainly part of the samelarge-scale structure.[9]
