Hopefully final version.-1559539662Assigned ID: 4912
----- Attempting Submission 1 (Wed Nov 15 16:57:20 GMT 2023) -----
HST Phase I Proposal 4912 successfully submitted.
Receipt: # 4912-1
----- Attempting Submission 2 (Wed Nov 15 22:33:04 GMT 2023) -----ORBITAL VISIBILITY OVERRUN
ORBITAL VISIBILITY OVERRUNRe-submission after Visit 01 failed due to gyro issues.
Visit 01 was duplicated and renamed to Vist 51.
Re-submission on 2024-05-28.
Re-submission on 2024-06-18, adapting for reduced gyro mode-413470368----- Attempting Submission 1 (Fri Feb 09 16:22:16 GMT 2024) -----
HST Phase II Proposal 17601 successfully submitted.
Receipt: # 17601-1
----- Attempting Submission 2 (Fri Feb 09 16:27:45 GMT 2024) -----
----- Attempting Submission 3 (Tue May 28 16:12:44 GMT 2024) -----
----- Attempting Submission 4 (Tue Jun 18 17:26:59 GMT 2024) -----Visit planner: maybe cannot be run for Visit 01, which is failed and uneditable?
2 errors: I assume orbital overruns in Visit 01, which is uneditable and was tailored to normal operation, not RGMThe first changing-multiplicity lensed quasar: a probe of sub-parsec quasar structure at Cosmic NoonA standard scheme for quasar structure has been built up over the last 60 years, comprising a supermassive black hole, accretion disk, torus, and broad and narrow line regions. Constraining these regions' kinematics and geometry remains difficult, particularly at high redshift, where all studies are unresolved. A recent discovery of a quadruply imaged lensed quasar has opened up an unprecedented and exciting probe of the subparsec-scale geometry of a quasar at z=2.7. The system shows 4 point sources in the optical (to 0.93 microns), yet only two point sources in recent JWST-MIRI imaging (5.6 microns), and follow-up ERIS-NIX Ks imaging (2.1 microns). This is entirely unexpected since lensing is achromatic, but could be explained by the source lying within a parsec of the region that splits the 4- and 2-image regimes. However, there are still several unanswered questions. How is the rest-frame UV of the accretion disk imaged four times, yet its optical emission is not? How can parts of the broad line region be imaged four times, yet the torus, thought to be larger, is not. High-resolution optical imaging is necessary to answer these questions: HST multi-band imaging will resolve the close optical image pair, and constrain a precise mass model from the lensed host galaxy arcs. Such a model will map the various optical quasar components back to the source at sub-parsec resolution, and fully exploit the existing JWST-MIRI, MUSE and ERIS datasets. Finally we will constrain the disappearance of the image pair to a narrow wavelength range, disambiguating several plausible explanations, e.g., an asymmetric torus, a second UV continuum source, or alternative dark matter models.We propose to use HST's Wide Field Camera 3 (WFC3) for deep, high-resolution imaging in the optical and near-infrared.
We plan observations in three filters to provide a comprehensive view and understanding of the system.
Specifically, we describe the reason for each filter below:
- F475X: this band will provide the first ever view of image A, confirming our suspicion
that this is a nearby merging pair. The bright Lya emission in the host galaxy would
fall within this filter, providing an Einstein ring to constrain the lens model and map
the host galaxy Lya emission,
- F814W: a second optical filter where we know the images exist will allow comparison
to F475X, and detect any astrometric change and thus a possible second spatially
separated source of UV continuum emission. Furthermore, the host galaxy will again
be lensed into a bright arc of about 21 i-mag/arcsec2 (F814W), and can be revealed with
high SNR,
- F160W: this filter covers a yet completely uncharted wavelength range, that of the
disappearing image. If the images are seen, we can again compare the point source
pair's astrometry to the optical positions and confirm the presence of any spatially
separated rest-frame optical emission region. If the images are not seen, this will put
strong constraints on the non-AGN continuum emitter and its position.
These filter/instrument combinations match closely those of previous lensed quasar proposals
(e.g., proposals 14254, 15320, and 17199), and would add to a homogeneous dataset for future
studies of collections of quadruply imaged lensed quasars.
Dithering pattern and exposure times: In F475X and F814W, we care about sampling the
PSF as well as possible, and centroiding/separating two nearby PSFs to within milliarsecond
precision. We choose to perform 4 dithers in each band, consisting of two short and two long
exposures to avoid saturating the bright quasar images, with a total exposure time of 1600s.
Given previous WFC3-UVIS exposure times on lensed quasars of similar brightness, such an
astrometric precision can be achieved.
With the WFC3/IR detector we will use a four-point dither pattern, with the standard
multiple-readout sampling (MULTIACCUM mode). We will use STEP50 exposure sequences
which will provide 6-8 samples in the brightest regions of the quasar images and will allow
parallel buffer dumps to minimize overheads. Persistence will occur at the locations of
the quasar images, and we will therefore ensure that our dithering pattern does not place
our target on affected pixels. This configuration will efficiently reject cosmic rays and hot
pixels, improve the sampling of the PSF of the drizzled images, and properly sample the full
dynamical range of these high-contrast data. While the SNR in the arc will be high (up to
20 per pixel), we do not know the brightness of the close image pair (or even if they will exist
at the wavelength of F160W). A total exposure time of 2200s will allow for the detection of
very faint PSFs (22.2 Vega-mag, 5 sigma point source), and allow for a sufficient dynamic range
to expose both the bright quasar images (B and C) and the host galaxy/faint PSF pair.Dr Lemon is an expert on lensed quasar discovery and characterisation, analysis of optical and infrared imaging
and spectra, and gravitational lens modeling with a focus on understanding quasar populations. Prof. Nierenberg
is an expert on using lensed quasars to constrain dark matter substructure, in particular using flux ratio
anomalies from various datasets, with particularly relevant expertise on fitting spectra with physically motivated
multi-component models consisting of continuum, broad and narrow emission lines, and torus components.
Prof. Anguita and Dr Sluse have unique expertise on microlensing in lensed quasars, with a focus on using it as
a tool to understand the source quasar structure, and Dr Sluse has extensive expertise with the analysis of IFU
datasets, including MUSE. Dr Jackson is an expert on discovery annd analysis of various datasets of lensed
quasars, including optical, infrared, and radio data. Prof. Courbin is the world leading expert on measuring time
delays in lensed quasars, and using them as a probe of quasar structure. Mr Dux is an expert on gravitational
lens modeling, and has already focused on modeling various other datasets for this system.Supermassive Black Holes and Active GalaxiesGalaxies3falsefalsefalsefalsefalsetruefalsefalseSUPPORTEDGALAXYGRAVITATIONAL LENSQSOQUASARJ2000J2000WFC3/UVISImagingNoNoF475WWFC3/UVISImagingNoNoF814WWFC3/IRImagingNoNoF160WPOS-TARGDITHER1.56LINEfalsefalse441.788WFC3-IR-DITHER-LINE2falseThe scheduling data was generated by CASM 32.1.CASM was run in Phase II mode./tmp/OPVisit7493768579138452831.xml1715370305000253.07161547572366(Tic-Visit
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