Science Keywords: Select from 2 to 5 items. Science Keywords is a required field. Please specify your scheduling constraints or 'No Constraints' on all Observation forms. 0 Assigned ID: 1044 ----- Attempting Submission 1 (Fri Aug 09 11:33:57 GMT 2019) ----- HST Phase I Proposal 1044 (Blanton.apt) successfully submitted. Receipt: # 1044-1 Joint Chandra/HST 0 ----- Attempting Submission 1 (Tue Jan 28 18:44:47 GMT 2020) ----- ----- Attempting Submission 2 (Wed Jan 29 20:34:55 GMT 2020) ----- Bent, double-lobed radio sources associated with AGN are frequently found in clusters of galaxies. The hosts of these radio sources are typically giant elliptical or cD galaxies. Occasionally, the bent radio sources are hosted by optically luminous quasars. Our Spitzer IR observations of 646 bent radio sources have revealed approximately 200 new, distant clusters. These objects comprise the Clusters Occupied by Bent Radio AGN (COBRA) survey. Here, we propose joint Chandra and HST observations of a COBRA cluster associated with a quasar with a spectroscopically measured redshift of 1.82. This cluster is one of very few known at z > 1.5 and can provide insight into AGN feedback and the formation of structure at high-z. We propose to observe our candidate z = 1.8 cluster with the Hubble Space Telescope using the WFC3 and the G141 grism. HST infrared grism observations have been instrumental, particularly in the last few years, in confirming several of the highest redshift clusters known and in measuring star formation rates in cluster member galaxies (Stanford et al. 2012, Zeimann et al. 2012, Gobat et al. 2013, Newman et al. 2014, Noirot et al. 2016). Our main observational goals are to spectroscopically confirm our target as a cluster by measuring redshifts for several cluster members, measure a mass independent of an X-ray-derived mass using the velocity dispersion of member galaxies, and measure star formation rates in individual galaxies. We propose to use the WFC3 with the G141 grism to accomplish our goals. Ground-based spectroscopic observations of cluster galaxies at this redshift are very difficult given the faintness of the galaxies and the Earth's atmospheric lines in the spectral region of interest. The field of view of the WFC3 of 136 x 123 arcsec will cover a region of approximately 1 x 1 Mpc at the redshift of our source which is a sufficiently large region to detect many cluster member galaxies. Given the wavelength coverage of the WFC3 with the G141 grism of 1.08 - 1.70 um, our observations will cover the spectral regions that include the Hbeta 486.1 nm and [OIII] 495.9/500.7 nm lines as well as the 400 nm break. We have used the online WFC3 + G141 exposure time calculator (ETC) to estimate an exposure time necessary for robust signal-to-noise ratios for cluster galaxies to a limit of an L* galaxy at the redshift of our cluster. We assume an L* galaxy with an SDSS i-band AB magnitude (mi = 25.6) appropriate to the redshift of our source assuming a Salpeter initial mass function and a Bruzual & Charlot stellar population model with a formation redshift of z = 3 (calculated using EzGal, Mancone & Gonzalez 2012). We assume an elliptical galaxy spectrum and an extended source with an effective radius of re approximately 0.3 arcsec. We then convert our total magnitude to surface brightness to use with the ETC and use a measurement box of 5 x 1 pixels. We find for an exposure of 2000 sec, we are able to achieve a SNR > 5 at 1.3 um and SNR > 8 at 1.5 um for our target galaxy limit. Slitless grism observations require direct images before and after the grism exposures to set the wavelength zeropoint. Additionally, slitless grism observations can result in overlap of sources. We will therefore choose two different ORIENT settings. Successful measurements have been made for similar objects using this method (Zeiman et al. 2012, Stanford et al. 2012, Noirot et al. 2016). Given a grism exposure of 2000 sec (33 min.) and allowing 6 min. for target acquisition, 1 min. for instrumental overhead and 5 min. for two images through the F160W filter (before and after each grism observation), we require 45 min. for our target. We will observe the target at two separate orientations to help reduce sources lost due to overlap. This can be achieved in 2 orbits. None Required Cosmology Galaxies and the IGM 6 false false false false false false false SUPPORTED CLUSTER OF GALAXIES HIGH REDSHIFT CLUSTER J2000 J2000 WFC3/IR Spectroscopic No No G141 POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false 1580236721374 The scheduling data was generated by CASM 28.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15994 :visit-id "01" :proposal-version -1 :trans-version "20191203" :date "28-Jan-2020 13:38:41.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1323072 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15994 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15994 :visit-id "01" :orbit-number 1 :pcs-time 241 :si-vis-utilization 2892 :al-overhead-at-end 0 :internal-dur-at-end 595 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 1 0 1580236596805 The scheduling data was generated by CASM 28.0. CASM was run in Phase II mode. (Tic-Visit :proposal-id 15994 :visit-id "02" :proposal-version -1 :trans-version "20191203" :date "28-Jan-2020 13:36:36.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 1 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1323072 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15994 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15994 :visit-id "02" :orbit-number 1 :pcs-time 241 :si-vis-utilization 2892 :al-overhead-at-end 0 :internal-dur-at-end 595 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3180 :pcs-gap 0 ) true 1 0