For G160M observations, please consult Chapter 9 of the COS Instrument Handbook to estimate overheads and the number of exposures per orbit, and consequently the correct lifetime position. Use of LP4 with G160M requires justification in the "Special Requirements" section of the Phase I PDF. Use of the default LP6 with G160M requires no justification. Proposals can be submitted with the warning present.0Assigned ID: 5116
----- Attempting Submission 1 (Sun Mar 24 16:29:29 GMT 2024) -----
HST Phase I Proposal 5116 successfully submitted.
Receipt: # 5116-1
----- Attempting Submission 2 (Tue Mar 26 06:54:57 GMT 2024) -----G160M warning.0----- Attempting Submission 1 (Mon Aug 12 19:21:56 GMT 2024) -----Imaging a Giant Intragroup Filament associated with a Damped Lyman-alpha SystemStreams of gas in dark matter halos are critical to galaxy evolution, as they bring matter into halos (accretion) and carry matter out (outflows), while "intergalactic transfer" from satellites and group members can be important for building up the gas mass of galaxies. Such streams may be responsible for a significant number of the metal-enriched QSO absorption lines used to study circumgalactic gas. We propose to study a giant (~100 kpc) intragroup filament identified through its association with a z=0.31 damped Lyman-alpha (DLA) system. The filament overlaps the background AGN and shares kinematics with the DLA gas. Thus this structure gives us the opportunity to directly image the gas giving rise to a damped absorber. We will obtain ACS/SBC imaging to study the spatial distribution and intensity of Lyman-alpha emission from this filament+DLA, constructing a synthetic narrow band filter through difference imaging in two ACS longpass filters. This will allow us for the first time to image the *gas* of a DLA and assess the processes that form and energize it. We will obtain a COS FUV spectrum of the background AGN to precisely measure the metallicity of the gas, search for H2 absorption associated with this very high column density system, and probe its physical properties (density, temperature, ionization). This filament is one of the few opportunities we have to image intergalactic gas prior to the next generation of UV telescopes and is a unique opportunity to compare absorption and emission line observations of a DLA.Overview
This program aims to study a giant (~100 kpc) intragroup filament identified through its association with a z=0.31 damped Lyman-alpha (DLA) system identified toward the AGN PKS1127-145 on the basis of HST UV spectroscopy. The filament overlaps the background AGN and shares kinematics with the DLA gas. Thus this structure gives us the opportunity to directly image the gas giving rise to a damped absorber. We will obtain ACS/SBC imaging to study the spatial distribution and intensity of Lyman-alpha emission from this filament+DLA, constructing a synthetic narrow band filter through difference imaging in two ACS longpass filters (F150LP, F165LP). This will allow us for the first time to image the *gas* of a DLA and assess the processes that form and energize it. We also will obtain a COS FUV spectrum of the background AGN to precisely measure the metallicity of the gas, search for H2 absorption associated with this very high column density system, and probe its physical properties (density, temperature, ionization). Previous FOS/G160L spectroscopy suggests the DLA has a column density log N(HI) = 21.7, but the absorption profile suggests a lower column could be appropriate. The COS/G160M data collected by this program will firmly determine the HI column density.
Imaging instrumental configuration: pseudo-filters to isolate emission lines
Following the technique pioneered by Hayes+ (2005, 2016) we aim to isolate diffuse emission in Ly-alpha 1215 from the z = 0.31 filament associated with a group seen in the field of the AGN PKS1127-145. The Ly-alpha line will be redshifted to ~1590 Ang. We will observe the field in the F150LP and F165LP filters of the ACS/SBC, covering an area 145 x 165 kpc at z = 0.31. We will isolate Ly-alpha using image subtraction in the two longpass filters to create a synthetic narrowband filter: F155NBsyn = F150LP - F165LP. This approach takes advantage of the shared red wings of the longpass filters, which allow the accurate removal of continuum and redder line emission from the bluest filter used. This approach has successfully been demonstrated in several previous cycles through programs 13656, 14079, 15298, 15655, and 16231 in Cycles 22-28. Unlike many of these previous programs, we are imaging pure nebular emission with no continuum.
Imaging observing approach
We request that the visits are scheduled so that SBC has been switched off for at least 24 hours prior to reduce the dark current. For the same reason, we also request that each 2-orbit visit be spaced from the next visit by at least 24 hours, with the SBC turned off in between. The typical visibility of PKS1127-145 52 minutes. In a 2-orbit visit, overheads total ~10.5 min and ~8 min in orbits 1 and 2. This leaves ~2.5 ks in each orbit for exposure. In each visit we will execute a square 4-point box dither pattern (with half-pixel shifts) to subsample the PSF.
To address potential large-scale gradients in the flatfielding, etc., each visit will be made on a 3x3 grid with points offset by 2.5 arcsec using the POS TARG functionality (using only 5 of the 9 grid positions). The pointing center of this pattern is offset from the AGN. This ensures that different observatory orientations will all include the full extent of the filament within the SBC field of view.
COS FUV Spectroscopy
For the COS G160M spectroscopy, we use ACQ/IMAGING Mirror A for the acquisition. We note the following warning from the ETC: "Partial overlap between instrument throughput band and target spectrum." We observe that where the throughput is >0, there is overlapping wavelength coverage between the target spectrum and throughput band.
We target the AGN PKS 1127-145 with 3 orbits of COS/G160M/1533 FUV spectroscopy, which will provide coverage of the restframe wavelengths 1022-1154 Ang and 1167-1300 Ang. We aim for SNR~4 at Ly-alpha, which is sufficient to measure the damping wings extremely accurately and to detect S II 1250/1253/1259 and N I 1200 absorption. This same setup provides SNR~6 near Ly-beta, sufficient to measure O VI 1032/1037, O I 1039, and the large number of H2 lines. This will be adequate to detect or place strong limits on these important lines. Due to the low S/N < 20 (SNR~3-7), we use a different FP-POS per orbit (FP-POS=2, 3, 4 for orbits 1, 2, and 3, respectively) to maximize the exposure time.
According to the bright object tool in the APT, exposure 1 of visit 06 has a health warning with the COS NUV imaging ACQ. The warning is triggered assuming the target is an O5V star, which it is not. Based on the GALEX FOV of this target, there is no UV bright object nearby. Therefore, our observations should not pose a bright limit threat to COS.The PI Howk and CoI Lehner have over 2 decades of experience analyzing UV spectra and have used COS spectra for more than a decade to study the CGM of galaxies, from Local Group galaxies (Milky Way, Magellanic Clouds, M31) to z<1 galaxies. Both have been PI on over 20 GO and archival HST programs.
CoI Hayes is an expert in the use of the ACS/SBC for imaging diffuse emission and pioneered the "synthetic filter" approach for studying O VI and Lyman-alpha emission.
CoIs Peroux and Kulkarni both have decades of experience analyzing the galaxies associated with QSO absorption line systems. This includes collecting ALMA and MUSE data for the target of this proposal.
The broader team represents the MUSE-ALMA haloes collaboration and includes researchers at a broad range of career stages. All lend significant expertise and creativity to the project and will be involved in the interpretation.Intergalactic Medium and the Circumgalactic MediumGalaxies6falsetruefalsefalsefalsefalsefalseSUPPORTEDGALAXYLYMAN ALPHA CLOUDQSOSPIRALThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000GALAXYLYMAN ALPHA CLOUDQSOQUASARNOThis object was generated by the targetselector and retrieved from the SIMBAD database.J2000J2000F(1595) = 1.15e-15 erg/s/cm2/AngACS/SBCImagingNoNoF150LPACS/SBCImagingNoNoF165LPWFC3/UVISImagingNoNoF621MWFC3/UVISImagingNoNoF475WCOS/FUVSpectroscopicNoNoG160M1533POS-TARGDITHER0.894773LINE0.587116falsefalse64.478514420.151333BOX2falseThe scheduling data was generated by CASM 32.1.1.CASM was run in Phase II mode.To minimize the dark current, please schedule after the SBC has been switched off for 24 hours. Similarly, consecutive visits should be spaced by at least 24 hours, with the SBC switched off in between1770815482000334.5305934489297(Tic-Visit
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