6669( 10) - 04/21/97 12:47 - [ 1] PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID: 6669 Version: 10 Check-in Date: 21-Apr-1997 12:44:11 1.Proposal Title: Imaging of Two Dwarf Galaxies in Tidal Tails ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Cycle STELLAR POPULATIONS GO 6 ------------------------------------------------------------------------------------ 5. Investigators Contact? PI: JOHN HIBBARD INSTITUTE FOR ASTRONOMY CoI: John Hibbard University of Hawaii N ------------------------------------------------------------------------------------ 6. Abstract We propose to image the two nearest dwarf galaxy candidates that are entrained in tidal tails. NGC 3077 is a member of the M81 group, and recent models suggest that it is interacting with, but has not formed from, the HI surrounding M81. In contrast, a dwarf at the SW end of the NGC4038/9 interaction tail appears to have formed out of gas ejected from that merger. The latter process is proposed to be a significant mechanism for the formation of dwarf spheroidal galaxies (cf. Schweizer, 1978; Barnes & Hernquist, 1992). We will determine the ages, luminosity functions, and spatial distributions of OB associations in these systems and also search for older (>1\ Gyr) red AGB stars. We hope to illuminate the star formation history of these dwarfs and constrain how much of their mass (particularly the NGC4038/9 system) has formed after the merger event. We may also shed light on the long term survivability of the 4038/9 dwarf as a stellar system. ------------------------------------------------------------------------------------ 6669( 10) - 04/21/97 12:47 - [ 2] Observations Description ------------------------ Two sets of observations are proposed. (1) ``light" U, B exposures; 1 orbit each for 4038/9. These are used to reach the brightest OB stars and to measure the reddening. Deep V, I exposures will obtain the luminosity function and spatial distribution of the young stars, and will reach deep enough to measure 1 Gyr old AGB stars, should they be present. A galaxy formed entirely from a recent merger should have no stars on the AGB. We consider the deep integration of 4 orbits in each of V (F555W) and I (F814W) for the NGC 4038/9 dwarf. If each orbit is to be CR- split, then no integration is longer than about 1200- 1500 sec. The WFPC2 ETC determines that we should reach V~ 27 with S/N=5 in this time. We expect that with great care, we can reach V=28 with 0.5 mag errors in the 10,000 sec available in 4 orbits (WFPC2 ETC finds S/N=6). This will reach to M_V=- 3.5, about as deep as Wilson's (1991, AJ, 101, 1663) study of OB associations in M33. The presence of red stars at M_I=- 4.5 would prove an old population is present. We must reach I=26.5 to solidly detect these stars (and the WFPC2 ETC estimates S/N = 6.2 after 8000s). For NGC 3077, (m- M)=27.8. In 2 orbits we get ~ 5000 sec in each color due to the efficiency of the CVZ. We estimate that we could reach V~ 28 and I~ 27, which would definitely permit us to detect any older stars present. Note that in both cases it will be possible to identify and to subtract the bluest, youngest stars from these images. One could then construct a color map for the residual light; this kind of work would be impossible with any imaginable ground-based effort. Real Time Justification ----------------------- Hibbard plans to make a deep neutral hydrogen map with the Very Large Array. Deep infrared imaging is also planned for both NGC 3077 and the 4038/9 dwarf, using telescopes on Mauna Kea. The IR maps will be compared with the young star distribution to estimate the ratio of new to old stellar populations. Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ Data Distribution Media: 8MM Blocking Factor: 10 Ship To: PI_Address Ship Via: Email: ------------------------------------------------------------------------------------ 6669( 10) - 04/21/97 12:47 - [ 3] TARGET LIST a) Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 01 NGC4038- GALAXY,INTERACTING RA=12H 1M 25.6S +/- 0.05S,DEC=- J2000 V=+1660 V = 17.3 120130- GALAXY,AMORPHOUS 19D 0' 32" +/- 0.2" B-V = 0.4 190100 IRREGULAR,LSB,STARBURST SURF(V) = 24.0 Comments: Target is a star-forming knot near the end of the SW tidal tail. This may possibly be a dwarf galaxy (Magellanic Irregular) in the process of forming. Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec) 1990 0.0 0.0 0.0 6669( 10) - 04/21/97 12:47 - [ 4] Visit: 01 Visit Requirements: ORIENT 280D TO 280D On Hold Comments: Additional Comments: Position of Target will be tweaked depending on likely. ORIENT of observation. Preferred ORIENT is 180-360D. Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC4038-120 WFPC2 IMAGE PC1-FIX F450W 1 2400 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC4038-120 WFPC2 IMAGE PC1-FIX F336W 1 2600 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC4038-120 WFPC2 IMAGE PC1-FIX F336W 1 2600 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 6669( 10) - 04/21/97 12:47 - [ 5] Visit: 02 Visit Requirements: ORIENT 280D TO 280D On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC4038-120 WFPC2 IMAGE PC1-FIX F555W 1 2400 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC4038-120 WFPC2 IMAGE PC1-FIX F555W 1 2600 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 6 NGC4038-120 WFPC2 IMAGE PC1-FIX F555W 1 2600 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 7 NGC4038-120 WFPC2 IMAGE PC1-FIX F814W 1 2600 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 8 NGC4038-120 WFPC2 IMAGE PC1-FIX F814W 1 2600 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 9 NGC4038-120 WFPC2 IMAGE PC1-FIX F814W 1 2600 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 10 NGC4038-120 WFPC2 IMAGE PC1-FIX F814W 1 2600 S END ORBIT MAX DUR EXPAND 130-190100 ------------------------------------------------------------------------------------------------------------------------------------ 6669( 10) - 04/21/97 12:47 - [ 6] Summary Form for Proposal 6669 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Proposal Category GO ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category STELLAR POPULATIONS ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements ORIENT 280D TO 280D END ORBIT MAX DUR EXPAND ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F450W F336W F555W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC4038-120130-190100 ------------------------------------------------------------------------------------------------------------------------------------