6674( 4) - 07/24/96 16:23 - [ 1]
PROPOSAL FOR HUBBLE SPACE TELESCOPE OBSERVATIONS ST ScI Use Only
ID: 6674
Version: 4
Check-in Date: 24-Jul-1996
16:17:34
1.Proposal Title:
Fine Structure in the Nuclear Superbubble of NGC 3079
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2. Scientific Category 3. Proposal For 4. Cycle
GALAXIES & CLUSTERS GO 6
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5. Investigators
Contact?
PI: GERALD CECIL UNIVERSITY OF NORTH CAROLINA
CoI: Sylvain Veilleux University of Maryland, College Park N
CoI: Alex Filippenko University of California, Berkeley N
CoI: Joss Bland-Hawthorn Anglo-Australian Observatory N
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6. Abstract
The nearby (17 Mpc), nearly edge-on spiral galaxy NGC 3079 contains the most
energetic known example of a windblown superbubble. The bubble has ionized mass
10^7/n_e Msun and kinetic energy 2x^56/n_e ergs (for average electron density n_e),
a compact apex at the nucleus, and protrudes 1 kpc (12") above the disk plane. It is
the visually emitting part of a larger superwind-driven complex that comprises radio
loops and spatially extended thermal x-ray emission. Our Fabry -Perot
spectrophotometry has mapped Doppler velocity gradients of >1150kms across the
superbubble, and we infer that space velocities increase radially from the nucleus.
The boundary just resolves in 1" seeing. However, the emission-line profiles here
range over 350 kms, indicating unresolved (turbulent?) kinematic substructure. An
HST WFPC2 image is required to resolve fluctuations in surface brightness across the
superbubble. These will improve constraints on the gaseous volume filling factor,
and establish if the input kinetic energy comes solely from the starburst (small
filling factor) or if the AGN must also contribute. If the AGN dominates, the
superbubble will join the NLR of NGC 1068 as the most spatially extended structures
thought to have been blown by an accretion-disk wind. The proposed image of this
superbubble will provide insight into the simultaneity of AGN/starbursts, jet
formation and collimation, winds in broad- absorption line quasars, and the extended
x-ray halos of galaxies.
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Observations Description
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Our FP spectrophotometry shows that F658N will pass all H Alpha except for the
most blueshifted gas at the very top of the bubble, and all N II blueward of
the galaxy's systemic velocity. The fluxes passed in each line are similar, and
total 10^-13 erg s^-1 cm^-2. The flux ratio [N II]/H Alpha doesn't vary much
across the bubble (e.g. Fig. 4 of Veilleux Etal 1994), so we can separate the
two lines and more tightly constrain variations in filling factors Epsilon. We
have used our data to locate regions (by their kinematics) where background
emission from H II regions farther out in the disk of NGC 3079 is faint
compared to the bubble shell. For planning, we estimate exposures near the
bubble center because we wish to minimize the column length of the emitting
gas, to get the tightest possible constraint. We approximate the superbubble as
a circular shell of diameter 12", and assume that half of its total flux comes
from the edge-brightened ring (Veilleux Etal 1994) of 1/3 the total area. We
begin with 2 x 400s ( e.g. 800s ) F814W images to accurately subtract off the
galaxy starlight. In the worst but unlikely case, where the gas is uniformly
distributed across the boundary of the superbubble in the WF2 image, the
average flux on each pixel near the center will be 0.12 photons s^-1 for an
unobstructed telescope area of 45239 cm^2. The conversion efficiency from
unobstructed photons to detected electrons is 0.12 for F658N. Because we are
already taking multiple exposures, to minimize total readout noise we will not
CR-SPLIT exposures through F658N. Assuming a dark rate of 0.003 e^- s^-1 (-
88degrees C on WF2), we reach S/N = 8 in each WF2 pixel after 4 orbits
(exposures of 1500 s + 3*3000 s). (The sky contributes ~110 electrons.) This
S/N ratio suffices to establish an accurate mean surface bightness, and will be
increased substantially in the clumped gas that we expect to map. Dark current
is minimized by imaging the superbubble on WF2. The individual exposures will
be dithered to improve sampling. NOTE: F814W was changed from F791W in
consultation between CS and PI.
Real Time Justification
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Calibration Justification
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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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6674( 4) - 07/24/96 16:23 - [ 3]
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 NGC3079 GALAXY, Spiral, Radio RA=10H 01M 58.46S +/- 0.2S, 2000 V=+1128 V = 9.7
Galaxy, Starburst DEC=+55D 41' 02.3" +/- 1", PLATE
-ID=01RP
6674( 4) - 07/24/96 16:23 - [ 4]
Visit: 01
Visit Requirements: ORIENT 297D TO 318D
On Hold Comments: <none>
Additional Comments: There is a bright star in PC1 quadrant which may cause scattered light to
fall onto the PC, but this is OK.
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 NGC3079 WFPC2 IMAGE WF2 F814W CR-SPLIT=NO 1 400 S POS TARG 0,0
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2 NGC3079 WFPC2 IMAGE WF2 F814W CR-SPLIT=NO 1 400 S POS TARG 0.25,0.25
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3 NGC3079 WFPC2 IMAGE WF2 F658N CR-SPLIT=NO 1 1700 S POS TARG 0,0 EXPAND
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4 NGC3079 WFPC2 IMAGE WF2 F658N CR-SPLIT=NO 1 1400 S POS TARG 0.25,0.25
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5 NGC3079 WFPC2 IMAGE WF2 F658N CR-SPLIT=NO 1 1500 S POS TARG 0,0 EXPAND
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6 NGC3079 WFPC2 IMAGE WF2 F658N CR-SPLIT=NO 1 2900 S POS TARG 0.25,0.25 EXPAND
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6674( 4) - 07/24/96 16:23 - [ 5]
Summary Form for Proposal 6674
Item Used in this proposal
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Configurations WFPC2
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Opmodes IMAGE
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Optional Parameters CR-SPLIT=NO
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Proposal Category GO
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Scientific Category GALAXIES & CLUSTERS
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Special Requirements ORIENT 297D TO 318D POS TARG 0,0 POS TARG 0.25,0.25 POS TARG 0,0 EXPAND POS TARG 0.25,0.25 EXPAND
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Spectral Elements F814W F658N
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Target Names NGC3079
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