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PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only
ID: 6100
Version: 7
Check-in Date: 09-Apr-1996
10:50:05
1.Proposal Title:
Measuring the Characteristic Size of Lyman-Alpha Forest Clouds
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2. Scientific Category 3. Proposal For 4. Cycle
Quasars GO 5
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5. Investigators
Contact?
PI: Craig Foltz Multiple Mirror Telescope Observatory
CoI: Chris Impey Steward Observatory N
CoI: Nadine Dinshaw Steward Observatory Y
CoI: Ray Weymann Observatories of the Carnegie Institution N
of Washington
CoI: Simon Morris Dominion Astrophysical Observatory N
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6. Abstract
We are obtaining FOS UV spectra (GO Program 5320) of three pairs of quasars with
projected separations less than two arcminutes in order to constrain the sizes of
Lyman-Alpha forest clouds. We anticipated that these observations would yield
improved upper limits of ~ 100 kpc and so were surprised when the spectra of the
first pair, Q0107-025 A,B (z = 0.956, 0.952, separation 1.44 arcmin), showed a large
number of absorption lines common to both spectra. Assuming that these are Lyman-
Alpha forest lines, the directly-measured lower limit on the sizes of the clouds at
0.32 <= z <= 0.90 is between 300 and 450 kpc (H_0=80, q_0=0.5). This is an order of
magnitude larger than the best published lower limit. Furthermore, the rms velocity
difference between the absorption lines along the two lines of sight is only about
100 km/sec. These results challenge all current theoretical models for the
absorbers. Perhaps even more exciting is the fact the there is a third bright
quasar, LBQS 0107-0232 (z=0.728, B_J=18.4), lying a few arcminutes away from the
pair (separations 2.00 and 2.93 arcmin from Q0107-025 A,B), which will allow us to
sample scales from 300 kpc to nearly 1 Mpc. We are requesting time to make FOS
observations of these three quasars in order to: (1) extend the wavelength coverage
of the observations of Q0107-025A,B to contain the Lyman alpha emission line and (2)
obtain spectra of the Lyman-Alpha forest in LBQS 0107-0232.
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Observations Description
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Spectroscopic observations of the three quasars fall into two categories:
First, FOS/RD observations of LBQS 0107-0232 with G190H. The difference in B_J
magnitude between Q0107-0232 and Q0107-025A is well-known from the LBQS plates
to be 0.3 +/- 0.1 mag (barring variability). The exposure time was then
calculated from the S/N realized in the GO 5320 observations of Q0107-025A,
using this magnitude difference and assuming that both quasars have the same
spectral slope. The latter assumption is more-or-less consistent with the
optical data; if anything, Q0107-0232 is somewhat bluer than Q0107-025A. Our
calculations indicate that 420 minutes of integration (11 orbits) will give S/N
approximately equal to that of the Q0107-025A,B spectra obtained in GO 5320.
The predicted count rates are a factor of 15 above the dark rate, which we have
therefore assumed to be negligible in estimating the exposure time. Second,
FOS/RD observations of all Q0107-025 A,B will be taken with G270H to extend the
wavelength coverage to contain the Lyman alpha emission lines in each quasar.
This will also complete our spectral coverage on these two objects from 1200 to
5500 Angstrom. Count rates for these observations were estimated from Figure
1.2.3 in the FOS Manual by extrapolating the GO program 5320 fluxes to longer
wavelength (the spectra are essentially flat in F_Lambda). In one orbit we
would expect to achieve a S/N of about 16 (per diode) at the short wavelength
end of the spectrum of Q0107-025A (the fainter of the pair), inadequate for our
purposes. In two orbits we will realize a S/N greater than 25 (per diode) at
all wavelengths in the range 2200 - 3100 Angstrom. Therefore, we will use two
orbits on each of the two quasars Q0107-025A,B for these data. We are very
concerned about the accuracy of the wavelength calibration since it limits the
accuracy of measurements of velocity differences between the three lines of
sight. We therefore specify that a wavelength calibration exposure be taken
upon each visit to a target and after a grating change. Furthermore, we request
that the same guide star be used for both of the G270H observations.
Spectroscopic observations covering the range from 3150 to 5500 Angstrom at a
resolution of 1 Angstrom have been collected at the Multiple Mirror Telescope.
These will overlap the G270H spectra of Q0107-025 A&B at their blue ends and
extend to longward of the Mg II Lambda2798 emission line, thereby completing
the coverage from shortward of Lyman Alpha emission to longward of Mg II.
Coupled with the G270H spectra, these should allow us to identify any metal-
line absorption systems which could have members which are mis-identified as
Lyman Alpha forest lines. More importantly, the G270H data will allow us to
identify absorption lines in the Lyman alpha emission line, which could be
effected by the ionizing flux from the quasars (the proximity effect).
Real Time Justification
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Calibration Justification
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The success of this proposal relies on whether the absorption features in one
quasar can be unambiguously identified as common (or not) to those in the other
quasar in the pair. This demands accurate zero-point calibration of the
wavelength scale. According to Papers I and II of the HST Quasar Absorption
Line Key Project, the rms scatter in the zero point is about 0.5 Angstrom (60-
80 km/sec) in the G190H and G270H gratings. The offsets can be determined from
the Galactic absorption lines, however in calibrating the G190H spectra only
the AlII 1670 line is suitable and is not always well detected. Therefore, one
wavelength calibration frame following an exposure of LBQS 0107-0232 with the
G190H is requested. We will not need a calibration frame for every exposure
because the relative zero-point shifts between exposures of a given quasar can
be calculated by cross-correlating the individual exposures of the same quasar.
Note that the GO 5320 observations achieved an uncertainty in the difference in
wavelengths between the members of a common pair of about 40 km/sec because the
observations of the two quasars used the same guide star, thereby minimizing
the uncertainty in the relative positioning of the two quasars in the
spectrograph aperture. We request that the same procedure be used for the G270H
observations of Q0107-025 A,B, i.e. the same guide stars should be used for
both observations.
Additional Comments
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Data Distribution
Media: 8MM
Blocking Factor: 10
Ship To: PI_Address
Ship Via: UPS
Email: ,
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TARGET LIST a) Fixed Targets
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Tar| Target | Target | Target |Coord | Radial | Flux data
No | Name | Description | Position |Eqnx | Vel. |
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1 Q0107-025A Galaxy, Lyman Alpha RA = 01H 10M 13.16S +/- 1S, DEC J2000 Z=0.956 V = 18.2
Cloud = -02D 19' 54.2" +/- 1", PLATE-
ID = 00WM
Comments: COMPONENT A OF QUASAR PAIR Q0107-025A,B
Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec)
1982.886 0.0 0.0 0.0
2 Q0107-025B Galaxy, Lyman Alpha RA = 01H 10M 16.28S +/- 1S, DEC J2000 Z=0.952 V = 17.4
Cloud = -02D 18' 52.4" +/- 1", PLATE-
ID = 00WM
Comments: COMPONENT B OF QUASAR PAIR Q0107-025A,B
Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec)
1982.886 0.0 0.0 0.0
3 Q0107-0232 Galaxy, Lyman Alpha RA = 01H 10M 14.47S +/- 1S, DEC J2000 Z=0.728 V = 18.5
Cloud = -02D 16' 58.9" +/- 1"
Epoch of Position RA proper motion (seconds of time/yr) DEC Proper Motion (arcsec/yr) Annual Parallax (arcsec)
1982.886 0.0 0.0 0.0
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Visit: 01
Visit Requirements: <none>
On Hold Comments: <none>
Additional Comments: USE SAME GUIDE STARS FOR TARGETS 1 AND 2 AND FOR ALL EXPOSURES IN THIS
VISIT
Exposures
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Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special
Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements
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1 Q0107-025A FOS/RD ACQ/BIN 4.3 MIRROR 1 62.6S ONBOARD ACQ FOR 2-5
ARY
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2 Q0107-025A FOS/RD ACCUM 1.0 G270H 2223- 1 26M
3278
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3 Q0107-025A FOS/RD ACCUM 1.0 G270H 2223- 1 40M
3278
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4 Q0107-025A FOS/RD ACCUM 1.0 G270H 2223- 1 40M
3278
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5 Q0107-025A FOS/RD ACCUM 1.0 G270H 2223- 1 40M
3278
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6 Q0107-025B FOS/RD ACQ/BIN 4.3 MIRROR 1 32.7S ONBOARD ACQ FOR 7-9
ARY
Comments: USE SAME GUIDE STARS AS FOR TARGET 1
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7 Q0107-025B FOS/RD ACCUM 1.0 G270H 2223- 1 28M
3278
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8 Q0107-025B FOS/RD ACCUM 1.0 G270H 2223- 1 40M
3278
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9 Q0107-025B FOS/RD ACCUM 1.0 G270H 2223- 1 40M
3278
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Visit: 02
Visit Requirements: <none>
On Hold Comments: <none>
Additional Comments: USE SAME GUIDE STARS FOR ALL EXPOSURES IN THIS VISIT; KEEP TELESCOPE
POSITION AND ORIENTATION THE SAME FOR ALL EXPOSURES IN THIS VISIT
Exposures
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Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special
Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements
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10 Q0107-0232 FOS/RD ACQ/BIN 4.3 MIRROR 1 100.6S ONBOARD ACQ FOR 11,13,15,17,19,21,23,25
ARY
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11 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590- 1 24M
2312
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12 Q0107-0232 WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 15M PAR WITH 11
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13 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590- 1 37M
2312
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14 Q0107-0232 WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 15M PAR WITH 13
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15 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590- 1 37M
2312
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16 Q0107-0232 WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 15M PAR WITH 15
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17 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590- 1 37M
2312
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18 Q0107-0232 WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 15M PAR WITH 17
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19 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590- 1 37M
2312
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20 Q0107-0232 WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 15M PAR WITH 19
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21 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590- 1 37M
2312
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22 Q0107-0232 WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 15M PAR WITH 21
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23 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590- 1 37M
2312
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24 Q0107-0232 WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 15M PAR WITH 23
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25 Q0107-0232 FOS/RD ACCUM 1.0 G190H 1590- 1 37M
2312
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26 Q0107-0232 WFPC2 IMAGE WFALL F606W CR-SPLIT=NO 1 15M PAR WITH 25
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Exposures
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Exposure| Target |Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special
Number | Name |Config| Mode |or FOV |Element |Waveln.| Parameters |Exp| | Requirements
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27 WAVE FOS/RD ACCUM 1.0 G190H 1590- 1 DEF
2312
Comments: DO NOT CHANGE GRATING POSITION BETWEEN
EXPOSURES
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Summary Form for Proposal 6100
Item Used in this proposal
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Configurations FOS/RD WFPC2
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Opmodes ACQ/BINARY ACCUM IMAGE
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Optional Parameters CR-SPLIT=NO
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Proposal Category GO
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Scientific Category Quasars
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Special Requirements ONBOARD ACQ FOR 2-5 ONBOARD ACQ FOR 7-9 ONBOARD ACQ FOR 11,13,15,17,19,21,23,25 PAR WITH 11 PAR
WITH 13 PAR WITH 15 PAR WITH 17 PAR WITH 19 PAR WITH 21 PAR WITH 23 PAR WITH 25
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Spectral Elements MIRROR G270H G190H F606W
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Target Names Q0107-025A Q0107-025B Q0107-0232 WAVE
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