HST WFC3/Grism Observations of the Candidate Ultra-High-Redshift Radio Galaxy GLEAM J0917-0012

Abstract

We present Hubble Space Telescope Wide Field Camera 3 photometric and grism observations of the candidate ultra-high-redshift (z>7) radio galaxy, GLEAM J0917-0012. This radio source was selected due to the curvature in its 70-230 MHz, low-frequency Murchison Widefield Array radio spectrum and its faintness in K-band. Follow-up spectroscopic observations of this source with the VLA and ALMA were inconclusive as to its redshift. Our F105W and F0986M imaging observations detect the host of GLEAM J0917-0012 and a companion galaxy, ~one arcsec away. The G102 grism observations reveal a single weak line in each of the spectra of the host and the companion. To help identify these lines we utilised several photometric redshift techniques including template fitting to the grism spectra, fitting the UV-to-radio photometry with galaxy templates plus a synchrotron model, fitting of the UV-to-near-infrared photometry with EAZY, and fitting the radio data alone with RAiSERed. For the host of GLEAM J0917-0012 we find a line at 1.12 micron and the UV-to-radio spectral energy distribution fitting favours solutions at z~2 or z~8. While this fitting shows a weak preference for the lower redshift solution, the models from the higher redshift solution are more consistent with the strength of the spectral line. The redshift constraint by RAiSERed of z>6.5 also supports the interpretation that this line could be Lyman-alpha at z=8.21; however EAZY favours the z~2 solution. We discuss the implications of both solutions. For the companion galaxy we find a line at 0.98 micron and the spectral energy distribution fitting favours solutions at z<3 implying that the line could be the [OII]3727 doublet at z=1.63 (although the EAZY solution is z~2.6+/-0.5). Further observations are still required to unambiguously determine the redshift of this intriguing candidate ultra-high-redshift radio galaxy (abridged).

18 pages, 7 figures, 6 tables, accepted for publication in PASA

References in corpus (20)

• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• EAZY: A Fast, Public Photometric Redshift Code
• Distant Radio Galaxies and their Environments
• Dust in the reionization era: ALMA observations of a $z$=8.38 Galaxy
• Extragalactic Peaked-Spectrum Radio Sources at Low Frequencies
• The Energetics and Lifetimes of Local Radio Active Galactic Nuclei
• Relativistic jet feedback II: Relationship to gigahertz peak spectrum and compact steep spectrum radio galaxies
• Rapidly growing black holes and host galaxies in the distant Universe from the Herschel Radio Galaxy Evolution Project
• The discovery of a highly accreting, radio-loud quasar at z=6.82
• Probing Cosmic Dawn : Ages and Star Formation Histories of Candidate $z\ge$9 Galaxies
• RAiSE III: 3C radio AGN energetics and composition
• RAiSE II: resolved spectral evolution in radio AGN
• The Herschel-ATLAS Data Release 2, Paper I. Submillimeter and Far-infrared Images of the South and North Galactic Poles: The Largest Herschel Survey of the Extragalactic Sky
• Pégase.3: A code for modeling the UV-to-IR/submm spectral and chemical evolution of galaxies with dust
• Galaxy And Mass Assembly (GAMA): The inferred mass--metallicity relation from z=0 to 3.5 via forensic SED fitting
• The many lives of active galactic nuclei-II: The formation and evolution of radio jets and their impact on galaxy evolution
• Radio Detection of VIK J2318$-$3113, the Most Distant Radio-Loud Quasar ($z$=6.44)
• A discovery of young radio sources in the cores of giant radio galaxies selected at hard X-rays
• Phase Shift of Planetary Waves and Wave--Jet Resonance on Tidally Locked Planets
• RAiSERed: radio continuum redshifts for lobed AGNs

Cited by in corpus (1)

• The Long and the Short of It: The Benefits and Leverage of Ultraviolet-Radio Galaxy Fitting