The first blazar observed at z>6 (2002.05178v2)

Abstract: We present the discovery of PSO J030947.49+271757.31, the radio brightest (23.7 mJy at 1.4 GHz) active galactic nucleus (AGN) at z>6.0. It was selected by cross-matching the NRAO VLA Sky Survey and the Panoramic Survey Telescope and Rapid Response System PS1 databases and its high-z nature was confirmed by a dedicated spectroscopic observation at the Large Binocular Telescope. A pointed Neil Gehrels $Swift$ Observatory XRT observation allowed us to measure a flux of $\sim$3.4$\times$10$^{-14}$ erg s$^{-1}$ cm$^{-2}$ in the [0.5-10] keV energy band, which also makes this object the X-ray brightest AGN ever observed at z>6.0. Its flat radio spectrum ($\alpha_{\nu r}$<0.5), very high radio loudness (R>10$^3$), and strong X-ray emission, compared to the optical, support the hypothesis of the blazar nature of this source. %i.e. a radio-loud (RL) AGN with the relativistic jet pointed toward us. Assuming that this is the only blazar at this redshift in the surveyed area of sky, we derive a space density of blazars at z$\sim$6 and with M${1450 \mbox{\AA}}$ < -25.1 of 5.5$^{+11.2}{-4.6}$$\times$10$^{-3}$ Gpc$^{-3}$. From this number, and assuming a reasonable value of the bulk velocity of the jet ($\Gamma$=10), we can also infer a space density of the entire radio-loud AGN population at z$\sim$6 with the same optical/UV absolute magnitude of 1.10$^{+2.53}_{-0.91}$ Gpc$^{-3}$. Larger samples of blazars will be necessary to better constrain these estimates.

• The paper identifies PSO J0309+27, the first blazar at z>6, through multiwavelength surveys and spectroscopic confirmation.
• It reveals exceptional radio brightness at 1.4 GHz and strong X-ray emission, solidifying its blazar classification.
• The study estimates the space density of high-redshift blazars, offering key insights into early AGN evolution and mass accretion processes.

The Discovery and Analysis of a High-Redshift Blazar: PSO J0309+27

The paper presents an astrophysical paper focused on PSO J030947.49+271757.31, identified as the first blazar observed at a redshift greater than six. The paper elaborates on its discovery, multiwavelength properties, and subsequent analysis using various observational data. Blazars are a subclass of active galactic nuclei (AGN) that are radio-loud and have relativistic jets directed towards the observer, often resulting in significant brightness due to Doppler boosting.

Key Findings

• Identification of PSO J0309+27: PSO J0309+27 was identified as a potential high-redshift blazar through the cross-correlation of the NRAO VLA Sky Survey and Pan-STARRS PS1 databases. Spectroscopic observations using the Large Binocular Telescope confirmed its redshift at z = 6.10.
• Radio, Optical, and X-ray Characteristics: At 1.4 GHz, it recorded a radio brightness of 23.7 mJy, making it the brightest known AGN in the radio domain at this redshift. Its radio spectral index is 0.44, illustrating a flat spectrum typical of blazars. The X-ray observations with the Neil Gehrels Swift Observatory showed it to be the brightest X-ray AGN at this redshift.
• Blazar Classification: The significant radio loudness, measured with an R value higher than 2500, in conjunction with its flat radio spectrum and predominance of X-ray emission over optical light, strongly suggests PSO J0309+27 is a blazar.
• Space Density Estimation: Assuming that PSO J0309+27 is the only blazar of its kind observed in the surveyed area, the paper provides a space density estimate for blazars and the broader radio-loud AGN population at z ~ 6. The inferred space density of blazars with M$_{\rm 1450 \AA}$ < -25.1 is 5.5$^{+11.2}_{-4.6}$\times$10$^{-3}$Gpc$^{-3}$$, which when adjusted for the bulk Lorentz factor ($$\Gamma = 10$) suggests a larger space density for the entirety of radio-loud AGNs.

Implications and Future Research

The observation of PSO J0309+27 provides substantial insights into the early universe's high-energy astrophysical processes, particularly those linked with supermassive black holes and the evolution of AGNs. The existence of such a blazar at a significant cosmological distance suggests the presence of highly efficient mass accretion processes into central black holes early in cosmic history.

Further investigation is necessary to better constrain the population estimates for high-redshift blazars and radio-loud AGNs. Upcoming surveys and advancements in telescope technology, particularly radio all-sky surveys and next-generation observatories like the Vera C. Rubin Observatory, will potentially identify additional blazars at such high redshifts. The expectation is that around 15-20 blazars could be found, allowing a more precise measurement of the space density of the radio-loud AGN population at these extreme distances and the end of the re-ionization epoch.

Conclusion

This paper successfully identifies and characterizes PSO J0309+27, advancing our understanding of blazars' role in the high-redshift universe. By documenting its multiwavelength properties and exploring its significance in AGN evolutionary models, this research prompts further inquiry into the early universe's AGN activities, serving as a foundation for future astronomical observations and theoretical models.