Scientific Category is a required field. Science Keywords: Select from 2 to 5 items. 0 Assigned ID: 1232 ----- Attempting Submission 1 (Thu May 25 11:44:10 GMT 2017) ----- Joint NRAO/HST Made changes to field location in Visit 1 to avoid bright star. 858493871 ----- Attempting Submission 1 (Wed Jul 05 15:39:44 GMT 2017) ----- ----- Attempting Submission 2 (Thu Aug 10 22:00:16 GMT 2017) ----- Neutral Hydrogen in Tidal Tails: Probing the Extremes of Star Formation The morphologically diverse, HI-rich tidal tails of interacting galaxies represent the edges of the complex parameter space that allows massive star clusters to form and survive. In a prior optical study with the Hubble Space Telescope, our group analyzed 25 tidal tails and their star cluster populations, representing a broad continuum of star/clusterforming activity from a template set of interacting galaxy pairs. Of these 25 tails, we have analyzed and published data on 22 of them. However, our remaining systems, AM 1054-325, MCG-03-13-063, and ESO 376-G028, occupy the extremes of cluster formation: two prolifically cluster-forming environments and one devoid of ongoing star and cluster formation. We propose to observe these systems in the neutral hydrogen 21 cm line with the VLA to gauge the effects of the distribution and kinematics of the HI medium on cluster formation, in the relatively unexplored tidal tail environment. We further propose to age date these clusters with joint HST observations, to link cluster age to the local ISM. Combining these observations with our sample's archival VLA/ATCA data will elucidate the connection between star clusters, the conditions in the HI-dominated ISM that produce them, and holistically, the types of galaxy interactions that promote those conditions. Our program involves U/F336W and B/F438W WFC3 imaging of two interacting galaxies, as part of a successful VLA observing program. We are splitting our 4 orbit request into a pair of 2-orbit visits. We are interested in photometry of faint point- and marginally-resolved sources over the entire WFC3 FOV, and we are requesting a 4 point dither pattern for each filter to properly sample the PSF in our final, combined images. We do not need to cover the chip gap, as long as the ORIENT ranges (below) are OK. We need to make sure the chip gap does not cover area where stars clusters were detected in a previous HST program. Our original request was to have 1.5 orbits in U, and 0.5 orbit in B; however, with the need for a 4-dither pattern, and avoiding any observing inefficiencies with <360s exposures, our best possible observing strategy appears to be 1.3 orbits (U), the rest in B. Although we are interested in the highest possible S/N in our observations, we have left a few x 10s left in each orbit to allow for maximum flexibility in scheduling. Should these cuts be unnecessary, we would like to bump up the F338W observation exposure times as much as is possible. Our ORIENT requests are based on the requirement to cover the WFPC2 footprint from previous observations of these galaxies, but we have found we have many months of available scheduling for each object. We are also trying to avoid a bright star near MCG-03-13-063. NOTE added: we have shifted location of this field to avoid the 'dragons breath' from a nearby star. Finally, we also require a post-FLASH for all images due to the relatively short individual exposures in these blue filters. We used the ETC to look at the expected range of background levels in best and worst-case scenarios for our targets, which have ecliptic latitudes of 35-40 degrees (see links to ETC results below). Note we have assumed a 'best' case scenario where we have the lowest possible zodiacal light, and minimal Earthshine. F438W/B 380s exposures http://etc.stsci.edu/etc/results/WFC3UVIS.im.1004584/ MU_V=22.0 Earth=High airglow=no 7.8 e-/pix HIGH http://etc.stsci.edu/etc/results/WFC3UVIS.im.1004585/ MU_V=23.0 Earth=No airglow=no 2.8 e-/pix LOW Need FLASH=9 to get to 12 e-/pixel F336W/U 850s exposures http://etc.stsci.edu/etc/results/WFC3UVIS.im.1004589/ MU_V=23.0 Earth=no airglow=no 3.2 e-/pix LOW http://etc.stsci.edu/etc/results/WFC3UVIS.im.1004590/ MU_V=22.0 Earth=High airglow=high 5.6 e-/pix LOW Again, need FLASH=9 to get to 12 e-/pixel 6 false false false false false false SUPPORTED GALAXY INTERACTING GALAXY TIDAL TAIL This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 GALAXY INTERACTING GALAXY TIDAL TAIL This object was generated by the targetselector and retrieved from the SIMBAD database. J2000 J2000 WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F438W POS-TARG DITHER 0.173 LINE 0.112 false false 81.785 4 23.884 WFC3-UVIS-DITHER-BOX 1 false The scheduling data was generated by CASM 25.2. CASM was run in Phase II mode. /private/var/folders/ny/3pp1x6l94l58lsgpvwnw0hv40000gn/T/OPVisit7587798302997515265.xml U- and B-band observations of MCG-03-13-063 (Tic-Visit :proposal-id 14937 :visit-id "01" :proposal-version -1 :trans-version "20170613" :date "10-Aug-2017 17:55:57.0" :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 2309984 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14937 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14937 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2841 :al-overhead-at-end 122 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3216 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14937 :visit-id "01" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2942 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3216 :pcs-gap 0 ) true 2 0 The scheduling data was generated by CASM 25.2. CASM was run in Phase II mode. /private/var/folders/ny/3pp1x6l94l58lsgpvwnw0hv40000gn/T/OPVisit4867562021463059644.xml U- and B-band observations of AM 1054-325 + ESO 376-G028 (Tic-Visit :proposal-id 14937 :visit-id "02" :proposal-version -1 :trans-version "20170613" :date "10-Aug-2017 17:56:05.0" :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 2309984 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 14937 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 14937 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2856 :al-overhead-at-end 122 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3240 :pcs-gap 0 ) (Tic-Orbit :proposal-id 14937 :visit-id "02" :orbit-number 2 :pcs-time 222 :si-vis-utilization 2947 :al-overhead-at-end 122 :internal-dur-at-end 668 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3240 :pcs-gap 0 ) true 2 0