Discovery of a radio galaxy at z = 5.72

Saxena, A.; Marinello, Murilo; Overzier, Roderik; Best, P. N.; Röttgering, H. J. A.; Duncan, K. J.; Prandoni, I.; Pentericci, L.; Magliocchetti, M.; Paris, D.; Cusano, F.; Marchi, F.; Intema, H. T.; Miley, G. K.

doi:10.1093/mnras/sty1996

Cited by 70 publications

(81 citation statements)

References 88 publications

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“…The spectroscopic redshift distribution peaks at 2 < z < 3, with the total range of redshifts between 0.52 < z < 5.72. This includes the recent discovery of the highest redshift radio galaxy discovered at z = 5.72, which was reported separately in Saxena et al (2018b). The detection of a fair amount of z > 2 radio galaxies, through USS selection combined with optical faintness and compact radio sizes, is holds promise for similar studies in the future with even deeper radio surveys, such as the LOFAR Two-meter Sky Survey (Shimwell et al 2017(Shimwell et al , 2019.…”

Section: Redshift Distributionmentioning

confidence: 91%

“…The highest redshift radio galaxy, TGSS J1530+1049 at z = 5.72, which was part of our sample and was presented in Saxena et al (2018b) is one of the lowest stellar mass radio galaxy from our sample. It is important to remember, however, that the overall lower stellar masses of galaxies in our sample are obtained under the assumptions that go into the stellar population modelling mentioned earlier.…”

Section: Stellar Massesmentioning

confidence: 99%

“…The median size of our faint radio sources is 22 kpc and the median size of the literature HzRGs is 42 kpc. It is important to remember that Saxena et al (2018b) introduced an angular size restriction (< 10 ) while selecting faint HzRG candidates, which would preferentially select compact radio sources across all redshifts.…”

Section: Linear Sizesmentioning

confidence: 99%

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The nature of faint radio galaxies at high redshifts

Saxena

Röttgering

Duncan

et al. 2019

Monthly Notices of the Royal Astronomical Society

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We present spectra and near-infrared images of a sample of faint radio sources initially selected as promising high-redshift radio galaxy (HzRG) candidates. We have determined redshifts for a total of 13 radio galaxies with redshifts ranging from 0.52 ≤ z ≤ 5.72. Our sample probes radio luminosities that are almost an order of magnitude fainter than previous large samples at the highest redshifts. We use near-infrared photometry for a subsample of these galaxies to calculate stellar masses using simple stellar population models, and find stellar masses to be in the range 10 10.8 − 10 11.7 M . We then compare our faint radio galaxies with brighter radio galaxies at z ≥ 2 from the literature. We find that fainter radio galaxies have lower Lyα luminosities and narrower full width at half maxima compared to the bright ones, implying photoionisation by weaker AGN. We also rule out the presence of strong shocks in faint HzRGs. The stellar masses determined for faint HzRGs are lower than what has been observed for brighter ones. We find that faint HzRG population in the redshift range 2 − 4 forms a bridge between star-forming and narrow-line AGN, whereas the ones at z > 4 are dominated by star-formation, and may be building up their stellar mass through cold accretion of gas. Finally, we show that the overall redshift evolution of radio sizes at z > 2 is fully compatible with increased inverse Compton scattering losses at high redshifts.

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Section: Redshift Distributionmentioning

confidence: 91%

Section: Stellar Massesmentioning

confidence: 99%

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The nature of faint radio galaxies at high redshifts

Saxena

Röttgering

Duncan

et al. 2019

Monthly Notices of the Royal Astronomical Society

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“…The radio power calculated from the VLA flux density (∼ 10 28 W Hz −1 , Saxena et al 2018) and the projected source size derived from our EVN data place J1530+1049 among the medium-sized symmetric objects (MSOs). These are young counterparts of radio galaxies in the evolutionary diagram of An & Baan (2012).…”

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confidence: 98%

High-resolution Radio Image of a Candidate Radio Galaxy at z = 5.72

et al. 2018

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Saxena et al. (2018) reported the discovery of a possible radio galaxy at a redshift of z = 5.72, based on the detection of a single Lyα emission line. If it is indeed a radio galaxy, this would be the most distant known object of this type. The authors collected a sample of ultra-steep spectrum sources, with the spectral index α < −1.3 (S ∼ ν α , where ν is the frequency and S is the flux density measured between 150 MHz and 1.4 GHz) and with compact radio morphologies using the TIFR GMRT Sky Survey Alternative Data Release (Intema et al. 2017), the Faint Images of the Radio Sky at Twenty-Centimeters (Becker et al. 1995) and the 1.4-GHz NRAO VLA Sky Survey (Condon et al. 1998). Only sources which were not detected in various optical (SDSS DR12, Alam et al. 2015; PAN-STARRS1, Chambers et al. 2016) and infrared surveys (AllWISE, Wright et al. 2010; UKIDSS, Lawrence et al. 2007) were further imaged with the Karl G. Jansky Very Large Array (VLA) at 1.4 GHz in its most extended A configuration. TGSS1530 (hereafter J1530+1049) was one of their brightest sources detected with a flux density of S = 7.5 ± 0.1 mJy. It was unresolved in the VLA-A observation and its spectral index is −1.4 ± 0.1.We observed J1530+1049 with the European Very Long Baseline Interferometry (VLBI) Network (EVN) at 1.7 GHz on 2018 Sep 19. The following radio telescopes provided data: a single antenna of the Westerbork Synthesis Radio Telescope (the Netherlands), Effelsberg (Germany), Medicina (Italy), Onsala (Sweden), Tianma (China), Toruń (Poland), Hartebeesthoek (South Africa), and Sardinia (Italy). Eight 16-MHz wide intermediate frequency channels were used in left and right circular polarizations. The observation was conducted in phase-reference mode (Beasley & Conway 1995). The target and the phase-reference calibrator (J1525+1107, its coordinates are known within an accuracy of 0.2 mas 1 ) were observed alternately to facilitate the detection of the faint target and its precise relative astrometry. On-source time was 1.3 h. For the details of data reduction we refer to Gabányi et al. (2018). We detected two faint radio features in J1530+1049 with a separation of ∼ 400 mas (Fig. 1), corresponding to ∼ 2.5 kpc at z = 5.72 (assuming a flat ΛCDM cosmological model with H 0 = 70 km s −1 Mpc −1 , Ω m = 0.27). The position of the brighter northern feature is right ascension 15 h 30 m 49. s 8903 and declination +10 • 49 31. 175 with 1 mas estimated accuracy. The sum of the flux densities of the two components is 1.7 ± 0.2 mJy. Even taking into account its steep spectrum, the EVN observations recovered only a fraction of the flux density extrapolated from the VLA value. While this can be related to variability since the radio observations were not simultaneous, it is more probable that the missing flux density is in sub-arcsec structure compact on the VLA scale but resolved out by the EVN.The radio power calculated from the VLA flux density (∼ 10 28 W Hz −1 , Saxena et al. 2018) and the projected source size derived from our EVN data place J1530+1...

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“…They are expected to evolve to present day massive central cluster galaxies and are often found at the center of (proto)clusters (see Miley & De Breuck (2008) for a review). Recently, even a radio galaxy at z = 5.72 close to the presumed end of the epoch of reionization has been found by Saxena et al (2018). Thus studies of these species allow us to investigate the early formation of massive structures in the young Universe.…”

Section: Introductionmentioning

confidence: 98%

3C 294 revisited: Deep Large Binocular Telescope AO NIR images and optical spectroscopy

Heidt

Quirrenbach

Hoyer

et al. 2019

A&A

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Context. High redshift radio galaxies are among the most massive galaxies at their redshift, are often found at the center of protoclusters of galaxies, and are expected to evolve into the present day massive central cluster galaxies. Thus they are a useful tool to explore structure formation in the young Universe. Aims. 3C 294 is a powerful FR II type radio galaxy at z = 1.786. Past studies have identified a clumpy structure, possibly indicative of a merging system, as well as tentative evidence that 3C 294 hosts a dual active galactic nucleus (AGN). Due to its proximity to a bright star, it has been subject to various adaptive optics imaging studies. Methods. In order to distinguish between the various scenarios for 3C 294, we performed deep, high-resolution adaptive optics near-infrared imaging and optical spectroscopy of 3C 294 with the Large Binocular Telescope. Results. We resolve the 3C 294 system into three distinct components separated by a few tenths of an arcsecond on our images. One is compact, the other two are extended, and all appear to be non-stellar. The nature of each component is unclear. The two extended components could be a galaxy with an internal absorption feature, a galaxy merger, or two galaxies at different redshifts. We can now uniquely associate the radio source of 3C 294 with one of the extended components. Based on our spectroscopy, we determined a redshift of z = 1.784±0.001, which is similar to the one previously cited. In addition we found a previously unreported emission line at λ6749.4 Å in our spectra. It is not clear that it originates from 3C 294. It could be the Ne [IV] doublet λ2424/2426 Å at z = 1.783, or belong to the compact component at a redshift of z ∼ 4.56. We thus cannot unambiguously determine whether 3C 294 hosts a dual AGN or a projected pair of AGNs.

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Discovery of a radio galaxy at z = 5.72

Cited by 70 publications

References 88 publications

The nature of faint radio galaxies at high redshifts

The nature of faint radio galaxies at high redshifts

High-resolution Radio Image of a Candidate Radio Galaxy at z = 5.72

3C 294 revisited: Deep Large Binocular Telescope AO NIR images and optical spectroscopy

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