----- Attempting Submission 1 (Mon Jun 30 22:57:00 GMT 2008) ----- Assigned ID: 87 ----- Attempting Submission 1 (Wed Mar 05 20:03:42 GMT 2008) ----- Phase I Proposal 87 (M81.apt) successfully submitted. Resolving the Smallest Galaxies with ACS An order of magnitude more dwarf galaxies are expected to inhabit the Local Group, based on currently accepted galaxy formation models, than have been observed. This discrepancy has been noted in environments ranging from the field to rich clusters, with evidence emerging that lower density regions contain fewer dwarfs per giant than higher density regions, in further contrast to model predictions. However, there is no complete census of the faintest dwarf galaxies in any environment. The discovery of the smallest and faintest dwarfs is hampered by the limitations in detecting such compact or low surface brightness galaxies, and this is compounded by the great difficulty in determining accurate distances to, or ascertaining group membership for, such faint objects. The M81 group provides a powerful means for establishing membership for faint galaxies in a low density region. With a distance modulus of 27.8, the tip of the red giant branch (TRGB) appears at I ~ 24, just within the reach of ground based surveys. We have completed a 65 square degree survey in the region around M81 with the CFHT/MegaCam. Half of our survey was completed before Cycle 16 and we were awarded time with WFPC2 to observe 15 new candidate dwarf galaxy group members in F606W and F814W bands in order to construct color-magnitude diagrams from which to measure accurate TRGB distances and determine star formation and metallicity histories. The data obtained show that 8 - 9 of these objects are galaxies at the same distance as M81. In completing our survey, we have discovered an additional 8 candidate galaxies we propose to image with ACS in order to measure TRGB distances and establish membership. We also wish to re-observe our smallest candidate group member and a tidal dwarf candidate with deeper observations made possible with ACS. Once membership has been established for this second set of candidates, we will have a complete census of the dwarf galaxy population in the M81 group to M_r ~ -10, allowing us to obtain a firm measurement of the luminosity function faint-end slope, and, combined with previous HST data, to provide a complete inventory of the age and abundance properties for the collapsed core of the M81 group.
We propose to obtain imaging observations in F606W and F814W (broad V and I) filters in order to construct a color-magnitude diagram appropriate for measuring TRGB distances. We will use the ACS for its combined superior field of view, sensitivity, and spatial resolution over WFC3 in the wavelength range 6000-8000\AA. Johnson-Cousins V and I-band filters are traditionally used to obtain TRGB distances. The F814W filter transforms well to Cousins I while the broad F606W filter provides acceptable transformation to Johnson V and is chosen over the F555W for its greater throughput. Using the ETC for imaging point sources, we find that we can reach 27.5 mag in F606W in a total of 1250s with 2 exposures to achieve a minimum S/N of 5. Assuming (V-I)_{TRGB} ~ 1.0, we expect to reach 26.5 mag in F814W in 1200s to a S/N ~ 5. At the expected location of the tip of the red giant branch (I_{tip} ~ 23.8), the S/N with these exposure times will be greater than 30. We have previous experience observing M81 dwarf galaxies with HST/ACS. Using the ACS with F606W and F814W filters observed together in a single orbit (exposure times 1200s and 900s respectively) our CMDs reach the limit of I=27. We expect to reach more than 2.5 magnitudes below the tip, assuring a firm detection of the TRGB. From a comparison of the CMD in Figs 2 and 3, it is seen that data from ACS is vastly superior to data from WFPC2. For 3 gyro mode, we expect orbit visibility of 59 minutes for each of our targets. Accounting for guide star acquisition (6min) and instrument overheads (4min + 3 x 2.5min), this will allow for observations of 1200s in F814W and 1250s in F606W. Therefore, each target can be observed within a single orbit. For 10 target candidates, we request 10 orbits. Parallel observations will be made of blank fields with WFC3/IR using the F105W and F160W filters. If there are free floating RGB stars between galaxies in the M81 group, they will be detected in these exposures. Known interactions between the large galaxies M81 - M82 - NGC3077, which have produced HI tidal bridges and potential tidal dwarfs in this dynamically young group, lead to the expectation of the existence of intragroup stars. These parallel observations will test whether a large free floating population exists. RESOLVED STELLAR POPULATIONS 12 false 0.0 0.0 false false false false false SUPPORTED GALAXY DWARF SPHEROIDAL J2000 09 44 22.5000 +69 12 40.00 J2000 GALAXY DWARF SPHEROIDAL J2000 09 59 33.1000 +68 39 25.00 J2000 GALAXY DWARF SPHEROIDAL J2000 09 39 15.9000 +71 18 42.00 J2000 GALAXY DWARF SPHEROIDAL J2000 09 44 34.4000 +71 28 57.00 J2000 GALAXY DWARF SPHEROIDAL J2000 10 12 48.4000 +64 06 27.00 J2000 GALAXY DWARF SPHEROIDAL J2000 10 13 11.7000 +68 43 45.00 J2000 GALAXY DWARF SPHEROIDAL J2000 10 15 6.9000 +69 02 15.00 J2000 GALAXY DWARF SPHEROIDAL J2000 10 19 52.9000 +69 11 19.00 J2000 GALAXY DWARF SPHEROIDAL J2000 10 20 25.0000 +69 11 50.00 J2000 GALAXY DWARF SPHEROIDAL J2000 00 00 0.0000 +00 00 0.00 J2000 ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W ACS/WFC Imaging No No F606W ACS/WFC Imaging No No F814W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W WFC3/IR Imaging No No F105W WFC3/IR Imaging No No F160W POS-TARG DITHER 3.011 LINE false false 2 85.28 ACS-WFC-DITHER-LINE 1 false The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v01.xml (Tic-Visit :proposal-id 11584 :visit-id "01" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:35:37.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3271 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3614 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v02.xml (Tic-Visit :proposal-id 11584 :visit-id "02" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:15:42.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3271 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3614 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v03.xml (Tic-Visit :proposal-id 11584 :visit-id "03" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:49:17.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "03" :obset-id "03" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "03" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3311 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v04.xml (Tic-Visit :proposal-id 11584 :visit-id "04" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:48:41.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "04" :obset-id "04" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "04" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3311 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3658 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v05.xml (Tic-Visit :proposal-id 11584 :visit-id "05" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:21:32.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "05" :obset-id "05" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "05" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3198 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3531 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v06.xml (Tic-Visit :proposal-id 11584 :visit-id "06" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:24:05.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "06" :obset-id "06" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "06" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3271 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3614 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v07.xml (Tic-Visit :proposal-id 11584 :visit-id "07" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:25:27.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "07" :obset-id "07" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "07" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3271 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3614 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v08.xml (Tic-Visit :proposal-id 11584 :visit-id "08" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:26:16.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "08" :obset-id "08" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "08" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3271 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3614 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /home/opik/kchib/Dwarfs/observing/HST2/OP-cache/M81-v09.xml (Tic-Visit :proposal-id 11584 :visit-id "09" :proposal-version -1 :trans-version "20080515" :date "17-Jun-2008 12:27:30.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "09" :obset-id "09" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "09" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3271 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3614 :pcs-gap 0 ) true 1 0 The scheduling data was generated by CASM 17.2. CASM was run in Phase II mode. /tmp/OPVisit63777.xml (Tic-Visit :proposal-id 11584 :visit-id "10" :proposal-version -1 :trans-version "20080515" :date "30-Jun-2008 11:58:06.0" :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 1763616 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 11584 :visit-id "10" :obset-id "10" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 11584 :visit-id "10" :orbit-number 1 :pcs-time 333 :si-vis-utilization 3120 :al-overhead-at-end 0 :internal-dur-at-end 846 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3453 :pcs-gap 0 ) true 1 0