1st submission of 11691 Phase II ----- Attempting Submission 1 (Tue Jul 01 20:04:25 GMT 2008) ----- First submission. Assigned ID: 184 ----- Attempting Submission 1 (Thu Mar 06 20:05:37 GMT 2008) ----- Phase I Proposal 184 (iagcs.apt) successfully submitted. Using Massive Star Clusters in Merger Remnants To Provide Reference Colors of Intermediate-Age Stellar Populations Much current research in cosmology and galaxy formation relies on an accurate interpretation of colors of galaxies in terms of their evolutionary state, i.e., in terms of ages and metallicities. One particularly important topic is the ability to identify early-type galaxies at "intermediate" ages (~ 500 Myr - 5 Gyr), i.e., the period between the end of star formation and ~ half the age of the universe. Currently, integrated-light studies must rely on population synthesis models which rest upon spectral libraries of stars in the solar neighborhood. These models have a difficult time correctly incorporating short-lived evolutionary phases such as thermally pulsing AGB stars, which produce up to 80% of the flux in the near-IR in this age range. Furthermore, intermediate-age star clusters in the Local Group do not represent proper templates against which to calibrate population synthesis models in this age range, because their masses are too low to render the effect of stochastic fluctuations due to the number of bright RGB and AGB stars negligible. As a consequence, current population synthesis models have trouble reconciling the evolutionary state of high-redshift galaxies from optical versus near-IR colors. We propose a simple and effective solution to this issue, namely obtaining high-quality EMPIRICAL colors of massive globular clusters in galaxy merger remnants which span this important age range. These colors should serve as relevant references, both to identify intermediate-age objects in the local and distant universe and as calibrators for population synthesis modellers.
The Wide Field Camera 3 is used with the broad-band filters F336W, F438W, F110W, and F160W for four target galaxies, all of which are established remnants of dissipative galaxy mergers. To allow us to address all goals of this project as mentioned in the Scientific Justification, we obtain the following data. (i) For all target merger remnants, we need to to reach S/N = 15 for GCs 3 mag fainter than the brightest GC in those galaxies in all filters. (ii) For the intermediate-age merger remnants NGC 1316 and NGC 3610, we have an additional need to reach S/N = 15 for globular clusters (GCs) at the calculated turnover magnitude of the LF of ‘old’ GCs (M_V = -7.3) in the F160W filter only. This will yield F110W-F160W color indices with an accuracy that is adequate to constrain the age distribution of GCs in the ‘red’ peak. To evaluate the necessary exposure times as a function of the surface brightness of the diffuse light of the host galaxy, we wrote a custom exposure time calculator (ETC) based on count rates given by the STScI ETCs, but including the ability to take into account a given background surface brightness (due to diffuse light from the host galaxy). Sub-exposures in each filter are positioned so as to allow cosmic-ray removal and dithering. The WFC3 UVIS subexposures are positioned several tens of pixels apart from one another in order to mitigate the potentially negative effects of the 'droplets' that were recently identified during WFC3 ground testing. For the near-IR imaging, we use logarithmically spaced MULTIACCUM read sequences to avoid saturated pixels near the galaxy centers and to yield high S/N ratios for both faint and bright GCs superposed onto the rapidly changing background (i.e., the diffuse light of the host galaxies). (a) We will utilize ACS/WFC in parallel to the WFC3 observations (using the F555W and F814W filters of ACS) in order to measure the V-I colors of globular clusters in the target galaxies over a range of galactocentric distances. These colors provide important constraints on the metallicities and ages of the globular clusters, and the parallel ACS/WFC data will extend these over a much greater range of radii than previously observed for any merger remnant galaxy. (b) We will have the observations of NGC 3610 conducted during CVZ orbits. This will constitute a very efficient use of HST, and seems to be well possible: Its declination (DEC ~ +59 degrees) allows a total of 7 two-day CVZ opportunities per year according to APT version 17.2.1. UNRESOLVED STELLAR POPULATIONS AND GALAXY STRUCTURE 12 false 0.0 0.0 false false false false false SUPPORTED GALAXY INTERACTING GALAXY Converted GSC-I coordinates to GSC-II reference frame using http://gsss.stsci.edu/webservices/GSCconvert/WebForm.aspx J2000 11 51 7.1300 +55 04 41.60 J2000 GALAXY INTERACTING GALAXY Converted GSC-I coordinates to GSC-II reference frame using http://gsss.stsci.edu/webservices/GSCconvert/WebForm.aspx J2000 22 20 44.7800 -24 40 41.80 J2000 GALAXY ELLIPTICAL Converted GSC-I coordinates to GSC-II reference frame using http://gsss.stsci.edu/webservices/GSCconvert/WebForm.aspx J2000 03 22 41.5200 -37 12 33.50 J2000 GALAXY ELLIPTICAL Converted GSC-I coordinates to GSC-II reference frame using http://gsss.stsci.edu/webservices/GSCconvert/WebForm.aspx J2000 11 18 25.4100 +58 47 10.70 J2000 WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F336W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F336W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W WFC3/UVIS Imaging No No F336W WFC3/IR Imaging No No F110W WFC3/IR Imaging No No F160W ACS/WFC Imaging No No F555W ACS/WFC Imaging No No F814W POS-TARG DITHER 2.4 2-exposure dither over chip gap of WFC3/UVIS LINE false false 2 85.754 WFC3-UVIS-DITHER-LINE 1 false POS-TARG DITHER 0.572 LINE 0.365 false false 74.653 4 18.528 WFC3-IR-DITHER-BOX-MIN 4 false The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /private/tmp/OPVisit18775.xml NGC 3921 visit (Tic-Visit :proposal-id 11691 :visit-id "01" :proposal-version -1 :trans-version "20080624" :date "01-Jul-2008 15:49:56.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 5864480 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11691 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11691 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3159 :al-overhead-at-end 40 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3517 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11691 :visit-id "01" :orbit-number 2 :pcs-time 195 :si-vis-utilization 3294 :al-overhead-at-end 0 :internal-dur-at-end 641 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3517 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11691 :visit-id "01" :orbit-number 3 :pcs-time 195 :si-vis-utilization 3269 :al-overhead-at-end 0 :internal-dur-at-end 1055 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3517 :pcs-gap 0 ) true 3 0 POS TARG 0,0 Parallel to F438W line pattern, step 1 Parallel to F336W line pattern POS TARG'ed over chip gap Parallel to F438W line pattern, step 2 3rd F336W exposure, 100 pix. away from 1st (stepping over any Droplets) 1st F110W exp, POS TARG 0,0 2nd F110W exp, same pos as 1st 3rd F110W exp, offset by 3.3, 3.3 pix from 1st 4th F110W exp, POS TARG 6.7, 6.7 pix from 1st F160W exp's at pos targ 0,12 F160W exp,'s, offset by 3.3, 3.3 pix from 1st F160W exp's, offset by 6.7, 6.7 pix from 1st The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /private/tmp/OPVisit18776.xml NGC 7252 visit (Tic-Visit :proposal-id 11691 :visit-id "02" :proposal-version -1 :trans-version "20080624" :date "01-Jul-2008 15:50:15.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 6005312 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11691 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11691 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2914 :al-overhead-at-end 80 :internal-dur-at-end 702 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3258 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11691 :visit-id "02" :orbit-number 2 :pcs-time 195 :si-vis-utilization 3024 :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 3258 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11691 :visit-id "02" :orbit-number 3 :pcs-time 195 :si-vis-utilization 3037 :al-overhead-at-end 91 :internal-dur-at-end 703 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3258 :pcs-gap 0 ) true 3 0 1st short F110W exp, POS TARG 0,0 2nd short F110W exp, POS TARG 4.0, 1.5 pix from 1st 3rd short F110W exp, POS TARG 2.5, 4.0 pix from 1st Nominal position Parallel to F336W line pattern POS TARG 4.5, 1.5 pixels * 20 (i.e., ~100 pix step, to mitigate effects of droplets) Parallel to F336W line pattern POS TARG 2.5, 4.0 pixels * 20 (to mitigate effects of droplets) Parallel to F336W line pattern F160W exp's with IR pattern (4 posns) 4th short F160W exp, POS TARG -1.5, 2.5 pix from 1st Longer F110W exp, BOX pattern POS TARG -4.0, 1.5 pix * 20 (to mitigate effects of droplets) Parallel to 4th F336W exp. The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /private/tmp/OPVisit18779.xml NGC 1316 visit. ORIENT ranges to avoid very bright stars or galaxy NGC 1317 in parallel ACS images (Tic-Visit :proposal-id 11691 :visit-id "03" :proposal-version -1 :trans-version "20080624" :date "01-Jul-2008 15:52:26.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 5935664 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11691 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11691 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2959 :al-overhead-at-end 70 :internal-dur-at-end 702 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11691 :visit-id "03" :orbit-number 2 :pcs-time 195 :si-vis-utilization 3024 :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 3310 :pcs-gap 0 ) (Tic-Orbit :proposal-id 11691 :visit-id "03" :orbit-number 3 :pcs-time 195 :si-vis-utilization 3084 :al-overhead-at-end 101 :internal-dur-at-end 703 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3310 :pcs-gap 0 ) true 3 0 1st short F110W exp, POS TARG 0,0 2nd short F110W exp, POS TARG 4.0, 1.5 pix 3rd short F110W exp, POS TARG 2.5, 4.0 pix Nominal position Parallel to F336W exp #1 POS TARG 4.5, 1.5 pixels * 20 (to mitigate effects of droplets) Parallel to F336W exp #2 POS TARG 4.5, 60.25 pixels (across chip gap) Parallel to F336W exp #3 F160W exp's with IR pattern (4 posns) 4th short F160W exp, POS TARG -1.5, 2.5 pix Longer F110W exp, BOX pattern POS TARG 3.778, 3.56 (2nd across chip gap, ~100 pix away from 1st to mitigate effects of droplets) Parallel to F336W exp #4 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /private/tmp/OPVisit18778.xml NGC 3610 visit. ORIENT ranges to avoid very bright stars falling in parallel ACS images. (Tic-Visit :proposal-id 11691 :visit-id "04" :proposal-version -1 :trans-version "20080624" :date "01-Jul-2008 15:50:50.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 6063216 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11691 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :cvz T :proposal-id 11691 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 10063 :al-overhead-at-end 70 :internal-dur-at-end 1019 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 0 :low-sky "N" :pcs-visibility 0 :pcs-gap 0 ) true 2 0 Longer F110W exp, BOX pattern 5th F110W exp, POS TARG -4.5, -1.5 pix F160W exp's with BOX pattern (4 posns) Parallel to F160W BOX pattern 5th F160W exp, POS TARG -4.0, -1.5 pix Parallel to F160W position #5 Nominal position Parallel to F336W #1 POS TARG 4.5, 1.5 pixels * 20 (to mitigate effects of droplets) Parallel to F336W exp #2 POS TARG 4.5, 60.25 pix (jumping chip gap) Parallel to F336W exp #3 POS TARG 3.778, 3.56 (2nd exp across chip gap, ~100 pix away from 1st to mitigate effects of droplets) Parallel to 4th F336W exp.