The study of high redshift cluster galaxies near the epoch at which they form their stars provides the most diagnostic power on models of galaxy formation, which make strong predictions for galaxy evolution in these high density environments. This motivates the study of cluster galaxies at redshifts > 1.5, where most of the stars in cluster galaxies form, and the clusters assemble. Here we propose a detailed study of galaxy evolution in one galaxy cluster at z=1.62 using HST/ACS and WFC3 imagining, and WFC3 spectroscopy. This galaxy cluster was identified solely as an overdensity of Spitzer/IRAC sources with red IRAC colors, with little bias toward optically red or blue galaxies. The cluster has only 12 spectroscopic redshifts, mostly for active and star-forming galaxies, and measuring redshifts for most of the passive galaxies is beyond the capabilities of ground-based telescopes. The scientific goals of this proposal are (1) to measure spectroscopic redshifts of the red, passive galaxies to J(AB)=22.8 mag (~J* + 1 mag) in this cluster with the WFC3 grism in order to confirm cluster members and map the cluster in redshift space, (2) to measure the strength of the 4000 Angstrom/Balmer break from the grism spectra, providing valuable information on the galaxy stellar population ages and masses, (3) to measure the spatially resolved structures and faint, H(AB)=26 mag, subcomponents in these galaxies, constraining their assembly and formation histories, and (4) to use these observations to make comparisons to expectations from theoretical galaxy formation models.

Observing Description for HST Cycle 19 Proposal 12590 PI: Casey Papovich (papovich@physics.tamu.edu) We will observe the galaxy cluster IRC 0218A at z=1.6 with -10 orbits of WFC3 G102 grism spectroscopy - 1 orbit of WFC3 F105W imaging - 2/3 orbit of WFC3 F125W imaging - 4/3 orbit of WFC3 F160W imaging - 2 orbits of ACS WFC F475W imaging - 2 orbits of ACS WFC F814W imaging. ** WFC3 G102 Grism observations: (Visits 1-5) While working on the Phase II with our Technical Contact, we discovered that there are no pointings with 2 suitable guide stars for optimal field pointing. For any combination of 2 guide stars, the cluster galaxies fall near the edge of the WFC3 FOV, and the allowable ORIENT angles cause the light dispersed by the grism to fall off the chip. After much trial and error, we adopted a strategy using only a single guide star. We therefore have broken the 10 grism orbits into 5 separate visits of 2 orbits each. Also, because we are aware that some rotation is expected during an orbit using only 1 guide star, we are adopting the following strategy during each 2 orbit visit: Orbit 1: direct (A) - grism (A) - grism (B) - direct (B) Orbit 2: direct (C) - grism (C) - grism (D) -direct (D) where ABCD are four different 1/2-integer pixel positions. We adopt the same dither positions as the standard WFC3-IR-DITHER-BOX pattern, but give the offsets explicitly so that we can effectively spread the dithers over two orbits. By placing a direct image at the beginning and end of each orbit we can track any rotation. We have constrained Visit 1 (the first grism visit) to occur well in advance of Visits 2-5 (the other grism visits) so that we can verify that this plan produces good data before committing to Visits 2-5. Using 1 guide star allows for a large range of ORIENT, and we constrain Visits 1-5 to each be separated by 10 deg in ORIENT. This will mitigate any collisions between spectra traces. ** WFC3 Imaging: (Visits 6, 9) The F105W imaging is offset slightly from the cluster center coordinates. This is to include as many cluster members as possible. To include as many cluster members as possible, we have added an ORIENT constraint designed for optical field coverage (this includes a small associated group of galaxies to the NE of the cluster core). For the F125W and F160W imaging, we have centered the field to minimze the overlap with existing WFC3 imaging from the CANDELS observations in this field. (CANDELS imaged with F125W and F160W and we avoid duplication.) There is a small overlap to include imaging of a cluster member that falls on the "death star" of the CANDELS WFC3 imaging. We have added an ORIENT constraint to minimze overlap with the existing CANDELS imaging. The constraint is ORIENT=40-50 deg. The DITHER pattern we have adopted for the WFC3 F125W and F160W imaging is identical to that of CANDELS. CANDELS was constrained by the need for 1/2-integer pixel shifts in the primary WFC3 images and ACS parallels. While we have no ACS constraint (no parallels) we adopt the same dither pattern to allow for uniform F125W and F160W mosaic with CANDELS with a very similar PSF, etc. For the F105W imaging, we adopt the standard WFC3-IR-DITHER-BOX. We have checked that temporal variations in the sky background have a negligible impact on object S/N for our different observing windows. Therefore, we have no constrain owing to changes in background. ** ACS Imaging: (Visits 7, 8) For the F475W and F814W images, we adopt a dither pattern to fill in the chip gap and include fraction pixel shifts. This uses the 2 pt DITHER-LINE pattern as the primary (to fill in the chip gap) and the DITHER-BOX as a subpattern, to take 4 pt dither at each position of the DITHER-LINE pattern. Because we take 2 x 4 ACS exposures we are not using CRSPLIT (=no). We have manually entered the "ACTUAL-DURATION" to each ACS exposure to fill in the visibility window for the orbit. (If the actual duration of the visibility window changes, we will manually change the ACTUAL DURACTIONS". To maximize the field overlap we have included a constraint that both images be taken with the same ORIENT, though the actual ORIENT is not constained. The ACS imaging is centered at a point to maximize overlap with the WFC3 imaging (both from here and the CANDELS data). ------------------------------------------------------------ UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE 12 false 0.0 0.0 false false false false SUPPORTED CLUSTER OF GALAXIES HIGH REDSHIFT CLUSTER CLG0218.3-0510 J2000 J2000 Redshift z=1.62, J(AB)=21-26 CLUSTER OF GALAXIES HIGH REDSHIFT CLUSTER CLG0218.3-0510 J2000 J2000 Redshift z=1.62, J(AB)=21-26 CLUSTER OF GALAXIES HIGH REDSHIFT CLUSTER CLG0218.3-0510 J2000 J2000 Redshift z=1.62, J(AB)=21-26 CLUSTER OF GALAXIES HIGH REDSHIFT CLUSTER J2000 Redshift z=1.62, J(AB)=21-26 WFC3/IR Spectroscopic No No G102 WFC3/IR Imaging No No F140W WFC3/IR Spectroscopic No No G102 WFC3/IR Imaging No No F140W WFC3/IR Imaging No No F105W ACS/WFC Imaging No No F475W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F125W WFC3/IR Imaging No No F160W POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 1 false POS-TARG DITHER DITHER 4 3.011 ACS-WFC-DITHER-BOX false 69.05 false 0.187 0.265 2 85.28 POS-TARG ACS-WFC-DITHER-LINE 20.67 4 true Timing link suitability includes constraints ([02 After 01 by 10.0 to 100.0 days] [03 After 01 by 10.0 to 100.0 days] [04 After 01 by 10.0 to 100.0 days] [05 After 01 by 10.0 to 100.0 days]) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. We were unable to achieve two suitable guide stars for high-priority galaxies, such that they would lie on the WFC3 detector and have the light dispersed from the grism falling on the detector. We are using a single guide star for all grism observations. This star allows us to use the optimal pointing and gives a range of U3=48-90 deg. We have split our grism observations into 5 visits of 2 orbits each. Each visit is separated in ORIENT by 8-10 deg. (Tic-Visit :proposal-id 12590 :visit-id "01" :proposal-version -1 :trans-version "20110811" :date "20-Sep-2011 22:59:52.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1479728 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12590 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12590 :visit-id "01" :orbit-number 1 :pcs-time 241 :si-vis-utilization 2749 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12590 :visit-id "01" :orbit-number 2 :pcs-time 176 :si-vis-utilization 2849 :al-overhead-at-end 0 :internal-dur-at-end 635 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 2 0 Timing link suitability includes constraints ([02 After 01 by 10.0 to 100.0 days]) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. We were unable to achieve two suitable guide stars for high-priority galaxies, such that they would lie on the WFC3 detector and have the light dispersed from the grism falling on the detector. We are using a single guide star for all grism observations. This star allows us to use the optimal pointing and gives a range of U3=48-90 deg. We have split our grism observations into 5 visits of 2 orbits each. Each visit is separated in ORIENT by 8-10 deg. (Tic-Visit :proposal-id 12590 :visit-id "02" :proposal-version -1 :trans-version "20110811" :date "20-Sep-2011 22:59:53.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1479728 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12590 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12590 :visit-id "02" :orbit-number 1 :pcs-time 241 :si-vis-utilization 2749 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12590 :visit-id "02" :orbit-number 2 :pcs-time 176 :si-vis-utilization 2849 :al-overhead-at-end 0 :internal-dur-at-end 635 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 2 0 Timing link suitability includes constraints ([03 After 01 by 10.0 to 100.0 days]) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. We were unable to achieve two suitable guide stars for high-priority galaxies, such that they would lie on the WFC3 detector and have the light dispersed from the grism falling on the detector. We are using a single guide star for all grism observations. This star allows us to use the optimal pointing and gives a range of U3=48-90 deg. We have split our grism observations into 5 visits of 2 orbits each. Each visit is separated in ORIENT by 8-10 deg. (Tic-Visit :proposal-id 12590 :visit-id "03" :proposal-version -1 :trans-version "20110811" :date "20-Sep-2011 22:59:55.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1479728 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12590 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12590 :visit-id "03" :orbit-number 1 :pcs-time 241 :si-vis-utilization 2749 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12590 :visit-id "03" :orbit-number 2 :pcs-time 176 :si-vis-utilization 2849 :al-overhead-at-end 0 :internal-dur-at-end 635 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 2 0 Timing link suitability includes constraints ([04 After 01 by 10.0 to 100.0 days]) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. We were unable to achieve two suitable guide stars for high-priority galaxies, such that they would lie on the WFC3 detector and have the light dispersed from the grism falling on the detector. We are using a single guide star for all grism observations. This star allows us to use the optimal pointing and gives a range of U3=48-90 deg. We have split our grism observations into 5 visits of 2 orbits each. Each visit is separated in ORIENT by 8-10 deg. (Tic-Visit :proposal-id 12590 :visit-id "04" :proposal-version -1 :trans-version "20110811" :date "20-Sep-2011 22:59:56.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1479728 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12590 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12590 :visit-id "04" :orbit-number 1 :pcs-time 241 :si-vis-utilization 2749 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12590 :visit-id "04" :orbit-number 2 :pcs-time 176 :si-vis-utilization 2849 :al-overhead-at-end 0 :internal-dur-at-end 635 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 2 0 Timing link suitability includes constraints ([05 After 01 by 10.0 to 100.0 days]) The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. We were unable to achieve two suitable guide stars for high-priority galaxies, such that they would lie on the WFC3 detector and have the light dispersed from the grism falling on the detector. We are using a single guide star for all grism observations. This star allows us to use the optimal pointing and gives a range of U3=48-90 deg. We have split our grism observations into 5 visits of 2 orbits each. Each visit is separated in ORIENT by 8-10 deg. (Tic-Visit :proposal-id 12590 :visit-id "05" :proposal-version -1 :trans-version "20110811" :date "20-Sep-2011 22:59:58.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "30" :si-bright-earth-limb-angle 20.0 :data-volume 1479728 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12590 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12590 :visit-id "05" :orbit-number 1 :pcs-time 241 :si-vis-utilization 2749 :al-overhead-at-end 0 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12590 :visit-id "05" :orbit-number 2 :pcs-time 176 :si-vis-utilization 2849 :al-overhead-at-end 0 :internal-dur-at-end 635 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. (Tic-Visit :proposal-id 12590 :visit-id "06" :proposal-version -1 :trans-version "20110811" :date "20-Sep-2011 22:59:59.0" :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 1462368 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12590 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12590 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2900 :al-overhead-at-end 0 :internal-dur-at-end 540 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) false 1 0 The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. We have manually entered the "Actual Duration" into each ACS exposure to fill in the orbit. (Tic-Visit :proposal-id 12590 :visit-id "07" :proposal-version -1 :trans-version "20110811" :date "20-Sep-2011 23:00:01.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12590 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12590 :visit-id "07" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2641 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12590 :visit-id "07" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2559 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 2 0 We have used the "auto-adjust" to fill out the orbit. We would like to use as much exposure time as possible. The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. We have manually entered the "Actual Duration" into each ACS exposure to fill in the orbit. (Tic-Visit :proposal-id 12590 :visit-id "08" :proposal-version -1 :trans-version "20110811" :date "20-Sep-2011 23:00:03.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "27" :si-bright-earth-limb-angle 20.0 :data-volume 2273792 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 12590 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 12590 :visit-id "08" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2781 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) (Tic-Orbit :proposal-id 12590 :visit-id "08" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2699 :al-overhead-at-end 0 :internal-dur-at-end 349 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3242 :pcs-gap 0 ) true 2 0 We have used the "auto-adjust" to fill out the orbit. We would like to use as much exposure time as possible. The scheduling data was generated by CASM 19.3. CASM was run in Phase II mode. We have forced the ORIENT of this visit to match the existing CANDELS data. This places the new pointing adjacent to the existing WFC3 imaging with minimal overlap. 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