Page 1 PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only ID 5302 Report Date: 18-Jul-95:17:07 Version: ********** Check-in Date: ********** 1.Proposal Title: THE SIZE AND MORPHOLOGY OF NORMAL GALAXIES AT Z~3 ------------------------------------------------------------------------------------ 2. Scientific Category 3. Proposal For 4. Proposal Type 5. Continuation ID GALAXIES & CLUSTERS GO Sub Category DISTANT GALAXIES ------------------------------------------------------------------------------------ 6. Principal Investigator Institution Country Telephone Palle Moller 3470 410 338 1018 ------------------------------------------------------------------------------------ 7. Abstract Using the ESO 3.6m and the ESO-NTT, in Dec. 1991 we discovered three candidate sources of Ly-alpha emission associated with a damped Ly-alpha absorber at z(abs)=2.81, along the line of sight to the quasar Q0528-250. The first two candidates have been confirmed by spectroscopy. This is the first detection, confirmed by both imaging and spectroscopy, of a damped Ly-alpha galaxy. The absorber lies near the quasar z(em)=2.77, and possibly the far side of the cloud is photoionised by it. In this case we should see the circumference of the absorber as a ring of Ly-alpha emission. Indeed the nearest of the three sources may be a section where the ring is bright. However ground-based observations cannot distinguish between several possible explanations for the three sources. For example they could be regions of star formation in a single large (100 kpc) spiral disk, or three galaxies in a compact group. or merging subunits of a proto-galaxy. High- resolution HST Ly-alpha and continuum images of this system would greatly clarify these issues, for we would be able to resolve the three sources, and possibly detect the sought-for ring. Such detailed information on a young galaxy, proto-galaxy, or cluster, would go a long way to answering some fundamental questions on the origin of galaxies: What do galaxies at high redshift z~3 look like\? How large were they, and were they still being assembled then\? ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ 9. Est obs time (hours) pri: 16.00 par: 0 10. Num targs pri: 1 par: 0 ------------------------------------------------------------------------------------ 11. Instruments requested: WF/PC ------------------------------------------------------------------------------------ ------------------------------------------------------------------------------------ Page 2 I. GENERAL FORM Proposal 5302 PI: Palle Moller Proposal Title: THE SIZE AND MORPHOLOGY OF NORMAL GALAXIES AT Z~3 ------------------------------------------------------------------------------------ 1. Proposers: Proposers Institution Country ESA ------------------------------------------------------------------------------------ Palle Moller 3470 X Stephen J Warren 8058 X ------------------------------------------------------------------------------------ 3. Description of proposed observations. This proposal is only concerned with deep imaging (WFPC2) of one single field. We shall obtain exposures through the b (F467M), the wide B (F450W), and the wide I (F814W) filters (10, 3, and 3 hours total exposure time respectively). These observations should be fairly simple to execute. There are, however, a few little important details which have to be taken proper into account, so let me go through them here. The primary objective of these observations is to go as deep as possible. Calculating the sky-noise, dark-noise, and read-out-noise from the WFPC2 handbook, it is seen that in a single orbit the sky-noise is negligible for the b-images which are hence dominated by read-out-noise with a minor dark-noise contribution, the sky-noise is equal to the dark-noise for the B-images which are also read-out-noise dominated but with some sky-noise/dark-noise contribution, the sky-noise is only just dominating the I images but with a strong read-out- noise contribution. 1. To make certain that we obtain the highest possible signal to noise (S/N), it is therefore important to make all exposures as long as possible. Hence exposures should be of roughly one orbit length. 2. If one can believe the sky-levels given in the handbook, only the I images would benefit from dark time assignment, not the b nor the B images. We would hence appreciate dark-time for the I images if possible. 3. It is important NOT to destroy the good data which have accumulated on the CCD during the major part of an orbit, by making the exposure too long and hence possibly add a major sky background in the last few minutes (close to Earth limb). I don't know if this is a real problem at all, but if it is then it is an important thing to worry about for this project. Hence, rather cut a few minutes at each end of the orbit if you are not certain about the sky level at this point. 4. Our field contains a fairly bright (V=17.7, B=18.5) quasar only 1.5 arcsec away from our primary target, as well as many bright (as bright as V=11) stars. Many of these objects will strongly saturate, and bleed along the columns. We also expect that many will cause bright diffraction spikes at angles of 45 deg with respect to the columns. It is important that neither a bleeding column, nor a diffraction spike will interfere with the extremely faint objects we are aiming to study. This places some limits on the allowed position angle, but depending on how we place our objects on the CCDs. The specifications we have given for the observations below represents one possible way of combining these constrains. If these specifications are for some reason impractical to implement, an other combination can be found. 5. We shall be obtaining a total of twenty 1800 second exposures through the b filter. Since these will be the less saturated images, we would prefer to have a set of b images done first, to verify that the pointing and position angle used do indeed live up to the above requirements. If they do not it could be unimportant for the b images, but be totally destructive for the I images. Page 3 ------------------------------------------------------------------------------------ 4. Justification of need for HST observations. We need the high-resolution of HST to settle the question of the morphology of the Sources S1, S2, and S3 found in our deep ground based images. Also we need the small point spread function of HST to be able to get broad band images of the object of primary interest, S1, which is too close to the quasar to be observed from ground. Detailed simulations and S/N calculations have been carried out to calculate the optimal exposure times in the 3 bands needed to obtain all our goals. Morphology of the Lyman alpha emission regions. -------------------------- --------------------- To be able to distinguish between different possible morphologies of the line emission from S1, we need 10 hours of integration time. Since the b band is not as narrow as our ground based narrow band filter, we expect that some underlying continuum may be present in the b image. To subtract the continuum contribution we shall use a properly scaled B image. Calculating the total noise in the final combined images from the sky-noise, dark-noise, and read-out-noise as given in the WFPC2 handbook, we find that subtracting a scaled 3 hour B image adds about 10% extra noise to the narrow band image, which is acceptable. A much shorter B exposure would severely degrade the S/N of the final emission line image. Also, since exposures should not be split, three hours exposure time will still provide us with sufficient images to be able to perform an efficient cosmic rejection, which is critical for this programme. Equivalent widths of Lyman alpha emission lines. -------------------------------- ---------------- To measure the equivalent width of the emission lines of the three sources, we also need a high S/N broad band detection of the continuum. For sources S2 and S3 we have ground based detections of B=26.4. S1 cannot be measured from ground. Aiming at determining the equivalent widths for sources of B=26.4, and of size one arc sec square (100 pixels), we shall detect 989 photons in three hours, with a total rms of 227 e-, hence a 4.4 sigma detection. For the narrow band image we get a 5.1 sigma detection, and hence the final error on the equivalent width is fairly evenly distributed between the two but with the major contribution coming from the B image. To exactly optimise the exposure time in B to provide smallest error for given total exposure time, B should be a bit longer than 3 hours. Broad band morphology and spectral shape of sources. -------------- -------------------------------------- To reveal the broad band morphology it is most efficient to obtain images in I where we expect the objects to be brighter, and where the CCDs are most efficient. Assuming again here an object extending over 1 arc sec square (100 pixels), and assuming its spectrum to be flat (f-nu = konst, I=25.9), we get a total detection of 8.1 sigma. This is a slightly better S/N than for both the b and the B images, and this should give us information about broad band morphology. When combined with the B image, we obtain the spectral shape of all three sources. ------------------------------------------------------------------------------------ 5. Description of special scheduling requirements. As argued above (QUESTION: 3), dark time would improve S/N for our I band images. ------------------------------------------------------------------------------------ 11. Address Information Name: Palle Moller Category: PI Institution: 3470 Address: 3700 San Martin Drive City: Baltimore State: MD Zip Code: 21218 Country: USA Telephone: 410 338 1018 Telex (or e-mail): moller@stsci.edu ------------------------------------------------------------------------------------ Page 4 Name: Category: CON Institution: Address: City: State: Zip Code: Country: Telephone: Telex (or e-mail): ------------------------------------------------------------------------------------ TARGET LIST a) Fixed Targets ID = 5302 [ 5] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial |Acqui|FLX| Flux data No | Name | Description | Position |Eqnx | Vel. |Prblm|REF| | | | | | | | | ------------------------------------------------------------------------------------------------------------------------------------ 1 PKS0528-250 E,314,318,321,322,325 RA = 5H 28M 5.16S +/- 0.1S, 1950 Z = 1 F-LINE(1216) = 7.4 +/- 0.6 E-17 DEC = -25D 5' 44.8" +/- 2.811 1 SIZE = 1 +/- 1 0.2", ------------------------------------------------------------------------------------------------------------------------------------ EXPOSURE LOGSHEET ID = 5302 [ 6] ------------------------------------------------------------------------------------------------------------------------------------ 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 |10 | 11 | 12 |13 |14| 15 ------------------------------------------------------------------------------------------------------------------------------------ Line | Seq | Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | S/N |Flx|Pr| Special Number | Name | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| |Rel. Time|Ref| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 DEFINE PKS0528-250 WFPC2 IMAGE WF3-FIX # CR-SPLIT=NO 1 1900S 1 CYCLE 4 EXPO ORIENT 75D +/- 10D POS TARG +13.6, +5.7 SEQ 1.0-4.0 NO GAP ------------------------------------------------------------------------------------------------------------------------------------ 2 DEFINE PKS0528-250 WFPC2 IMAGE WF3-FIX # CR-SPLIT=NO 1 2200S 1 CYCLE 4 EXPO SAME POS FOR 2 AS 1 ------------------------------------------------------------------------------------------------------------------------------------ 3 DEFINE PKS0528-250 WFPC2 IMAGE WF3-FIX # CR-SPLIT=NO 2 2200S 1 CYCLE 4 EXPO POS TARG +13.15, +5.25 SAME ORIENT FOR 2.0-4.0 AS 1.0 Comments: THIS FIELD CONTAINS MANY BRIGHT (UP TO V=11) STARS. THE CHOSEN ORIENT AND POS TARG REPRESENTS ONE POSSIBLE WAY OF ADDRESSING THIS. IF THESE SPECS ARE HARD TO IMPLEMENT, OTHER ALLOWABLE SPECIFICATIONS CAN BE FOUND. ------------------------------------------------------------------------------------------------------------------------------------ 4 DEFINE PKS0528-250 WFPC2 IMAGE WF3-FIX # CR-SPLIT=NO 2 2200S 1 CYCLE 4 EXPO POS TARG +13.15, +5.7 Comments: THIS FIELD CONTAINS MANY BRIGHT (UP TO V=11) STARS. THE CHOSEN ORIENT AND POS TARG REPRESENTS ONE POSSIBLE WAY OF ADDRESSING THIS. IF THESE SPECS ARE HARD TO IMPLEMENT, OTHER ALLOWABLE SPECIFICATIONS CAN BE FOUND. ------------------------------------------------------------------------------------------------------------------------------------ 10 USE F467M EXPO ------------------------------------------------------------------------------------------------------------------------------------ 20 USE F467M EXPO ------------------------------------------------------------------------------------------------------------------------------------ 30 USE F467M EXPO ------------------------------------------------------------------------------------------------------------------------------------ 40 USE F450W EXPO ------------------------------------------------------------------------------------------------------------------------------------ 50 USE F814W EXPO ------------------------------------------------------------------------------------------------------------------------------------ Summary Form for Proposal 5302 [ 7] Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFPC2 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes IMAGE ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters CR-SPLIT=NO ------------------------------------------------------------------------------------------------------------------------------------ Proposal for GO ------------------------------------------------------------------------------------------------------------------------------------ S/C Hours 16.00 ------------------------------------------------------------------------------------------------------------------------------------ Scientific Category GALAXIES & CLUSTERS ------------------------------------------------------------------------------------------------------------------------------------ Scientific Sub-category DISTANT GALAXIES ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements CYCLE 4; ORIENT 75D +/- 10D; POS TARG +13.6,+5.7; SEQ 1.0-4.0 NO GAP SAME POS FOR 2 AS 1 POS TARG +13.15,+5.25; SAME ORIENT FOR 2.0-4.0 AS 1.0 POS TARG +13.15,+5.7 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements # F467M F450W F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names PKS0528-250 ------------------------------------------------------------------------------------------------------------------------------------