Lyman-alpha Observations of a z=8.45 Powerful Radio Galaxy

Second submission 1931607640 Assigned ID: 1948 ----- Attempting Submission 1 (Fri Apr 09 15:04:21 GMT 2021) ----- HST Phase I Proposal 1948 successfully submitted. Receipt: # 1948-1 ----- Attempting Submission 2 (Fri Apr 09 23:38:47 GMT 2021) ----- This pattern is not used in this proposal. SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE SAME POS MAY NOT BE APPROPRIATE F140W pre-imaging has been updated to NSAMP-10 and SPARS10 based upon advice from Mireia Montes Quiles. An extra 1min on source time per-orbit has been gained! 1702578963 ----- Attempting Submission 1 (Fri Jul 23 08:36:52 GMT 2021) ----- ----- Attempting Submission 2 (Tue Oct 05 01:58:58 GMT 2021) ----- These are explained in the submission comments. The same position errors are only for pre-imaging grism pairs with each pair separated by a large dither. Lyman-alpha Observations of a z=8.45 Powerful Radio Galaxy Powerful radio galaxies have been unique probes of the distant Universe for many decades. This proposal requests WFC3 G141 grism with F140W pre-imaging observations to confirm an emission line observed at 1.15 microns. A high continuum flux longward of this line (seen with the G141 grism and broad-band photometry) would confirm that this line is Lyman-alpha and hence this radio galaxy at z=8.45. This detection would be the most distant super-massive black hole (SMBH) and active galactic nucleus (AGN) known. At this redshift the radio galaxy would lie at the centre of a highly ionised Stromgren sphere with contributions to the ionising flux from the accretion onto the SMBH, inverse Compton emission from the jets, and star-formation. As well as reaffirming the redshift of the host and challenging models of black hole formation, these observations will potentially reveal the complex interaction of this radio-loud AGN with its local environment. Furthermore, confirmation of the existence of a luminous radio galaxy within the Epoch of Reionisation would allow studies of neutral hydrogen from absorption of the 21 cm line. Due to the transmission of the Earth's atmosphere at 1.15 microns, this observation would take >40 times longer if conducted from the ground (eight times longer if the spectrum is binned to the resolution of the G141 grism). The aim of this proposal is to confirm the redshift of a candidate ultra-high redshift radio galaxy. Previous G102 observations suggest a line at 1.15um which may be Lyman-alpha. SED modelling supports this assertion. These G141 observations aim to (a) confirm this line and (b) confirm the interpretation that this line is Lyman-alpha (by detecting continuum and other lines longward of it). Our proposal consists of four orbits of G141 imaging with the F140W band as pre-imaging. As well as being ideal for the G141 grism, the F140W band supports the imaging we obtained previously with F098M and F105W. The four orbits are split into two orientations to provide redudancy and each orientation restricted to prevent contamination of the sprectrum by an adjacent target. These observations should not be impacted by a gyro failure (other than their schedulability). There are no time restraints. This team has considerable experience in the study of distant radio galaxies, with core members having published 40 papers together. The team includes members who have studied high redshift radio galaxies across the electromagnetic spectrum including in the radio (100 MHz to 100 GHz), the far-infrared with ALMA and Herschel, the mid-infrared with Spitzer, the near-infrared from the ground and with HST, the optical from the ground and with HST, and in the X-ray. In particular, the team includes several members who have worked on and led publications using HST grism observations of high redshift radio galaxies and their environments. Hence, the team is well placed to rapidly exploit these observations once the data are obtained. Supermassive Black Holes and Active Galaxies 6 false false false false false false false false SUPPORTED GALAXY HIGH REDSHIFT GALAXY RADIO GALAXY Redshift unknown, possible z~8 J2000 J2000 F105W = 0.60+/-0.02 uJy WFC3/IR Spectroscopic No No G141 WFC3/IR Imaging No No F160W POS-TARG DITHER 4.004 LINE 2.555 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1

false

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