0Assigned ID: 86
----- Attempting Submission 1 (Tue Apr 02 15:13:15 GMT 2019) -----
HST Phase I Proposal 86 (mgii_apt) successfully submitted.
Receipt: # 86-1
----- Attempting Submission 2 (Fri Apr 05 14:11:39 GMT 2019) -----Resubmission changing the buffer times as recommended by the CS.-1716340352----- Attempting Submission 1 (Wed Jul 10 20:01:05 GMT 2019) -----
HST Phase II Proposal 15865 (mgII_LyC_cy27.apt) successfully submitted.
Receipt: # 15865-1
----- Attempting Submission 2 (Tue Jul 16 14:03:17 GMT 2019) -----
----- Attempting Submission 3 (Thu Oct 03 19:00:29 GMT 2019) -----Mg II Emission: A new Tracer for Lyman Alpha and Lyman ContinuumIn studies of the intergalactic medium (IGM) reionization, the Lyman Alpha (LyA) emission from galaxies is a heavily used diagnostic. This spectral feature is frequently used to infer the IGM neutral hydrogen fraction, and is also thought to predict the emission of hydrogen-ionizing Lyman Continuum (LyC) photons. Nevertheless, LyA is difficult to observe in a neutral IGM, and its evolution in the reionization epoch may be partly due to galaxy evolution. Therefore, we propose a new way forward: emission from the Mg II 2796, 2803 doublet. Recently, Henry et al. (2018) showed that Mg II appears in emission, rather than absorption, in nearby analogs to reionization-epoch galaxies. Since the strength of Mg II correlates tightly with that of LyA in these galaxies, it is plausible that observations of Mg II from z>6 galaxies could provide valuable constraints on reionization. Still, only seven reionization-epoch analogs have observations in LyA, LyC, and Mg II, and this existing sample misses most of the strongest Mg II emitters. Therefore, we propose new COS observations for eight star-forming galaxies with the highest Mg II equivalent widths. These objects may reveal some of the highest LyC escape fractions seen nearby. These observations will quantify how LyC in this sample relates to the intensity of Mg II and LyA emission, as well as the velocity structure of the emission line profiles. Finally, we will carry out new multi-ion radiation transport modeling, in order to obtain stringent constraints on the scattering gas that regulates the escape of LyC, LyA, and Mg II.Sample Selection
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We have identified a sample of 8 Mg II emitters from SDSS-I/eBOSS spectra. In order to select these galaxies, we made the following cuts: (a) we require GALEX NUV detections, with NUV <22 AB. (b) we choose galaxies with H-beta equivalent width > 5 Angstroms to remove passive galaxies, (c) AGN were removed using a cut in the [NII]/Halpha vs [OIII]/Hbeta plot. (d) We require z=0.3 - 0.45, so that the Mg II is covered by the BOSS spectra, while Lyman Alpha falls in the COS G160M bandpass. These cuts defined a sample which we then fit with custom software to measure the Mg II emission lines. (e) Then, we require Mg II emission at SNR > 7, in order to ensure that we are not proposing followup of spurious detections. (f) Finally, we selected 9 galaxies observable in 4 orbits or less (see below) where the Mg II (summed) equivalent width is greater than 10 Angstroms. Among these 9 galaxies, one has COS Lyman Alpha and LyC observations (G140L and G160M) planned in Cycle 26, and another has LyC observations in G140L. Therefore, we will acquire Lyman Alpha observations for 8 galaxies, and LyC for 7.
Observations
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We aim to observe Lyman Alpha at high resolution in the G160M gating, and LyC and the non-ionizing UV continuum at lower resolution in the G140L grating. Our exposure time calculations assume a point source. In order to quantify the Lyman Alpha line wings, we aim for a signal-to-noise of 0.3 per six (spectral) pixel resolution element in G160M. For the LyC, we aim to measure escape fractions of 5% at 5 sigma signifcance by binning over 20 Angstroms. We assume an intrinsic Lyman Break corresponding to 0.75 magnitudes. Fortuitously, the redshifts of our sources place the LyC near the peak of the G140L throughput, resulting in efficient observations. The depths in this program are comparable to the Low Redshift LyC Survey (GO 15626). The sources are observed for 1-4 orbits each, with G140L:G160M exposure time ratios dictated by our exposure time calculations and efficient usage of each orbit. We use all four FP-POS settings. Since our targets are faint, we use the primary science aperture.
Target Acquisition:
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We acquire the sources using NUV imaging. We use ACQ/IMAGE mode with MIRRORA and the Primary Science Aperture. We assume an extended source with half the light falling within a 0.2" radius. NUV magnitudes used in this calculation are taken from GALEX. The target acquisition exposure times range between 65 and 224 seconds.
Bright Object Checks
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We ran the bright object tool on each visit. Visits 1-7 showed no GALEX-detected objects in the COS field-of-regard (the PSA and the annulus where the BOA could fall.) Visit 8 does not contain GALEX data in Aladin or the BOT, even though the field is covered by GALEX. We used Aladin with SDSS, and also the BOT with GSC II, to identify one potential object in the COS field-of-regard. This object is undetected in the GALEX images found on GalexView/MAST.Our proposing team has substantial expertise in observations and modeling of Lyman Alpha and Lyman Continuum (LyC), at both high and low redshifts. Of particular relevance to the proposed study, Dr. Alaina Henry was the first to obtain Lyman Alpha spectra of Green Pea galaxies (Cycle 20, GO 12928, PI Henry). The resulting publication (Henry et al. 2015) lead to a new interest in the Green Pea galaxies as Lyman Continuum leaker candidates; a number of other studies have now confirmed this finding. Additionally, Dr. Henry's MMT observations of Green Pea galaxies (Henry et al. 2018) were the first to show a relation between Mg II and Lyman Alpha. Overall, as first author, she has written six papers over the last eight years regarding Lyman Alpha, outflows, and the mass-metallicity relation of galaxies. She has extensive experience with observing and analyzing absorption and emission line spectra, from COS, WFC3 grism, and a host of ground-based spectrographs.
Professor Claudia Scarlata, Dr. Danielle Berg, Professor Matthew Hayes, Dr. Anne Jaskot, Professor Timothy Heckman, and Professor Sanchayeeta Borthakur are all experts at UV and optical spectroscopy of galaxies, including studies of metal lines and Lyman Alpha. They are leaders in the observations of galaxies that serve as analogs for high-redshift objects. Each of these team members has used COS as PI, publishing several papers based on these data.
In addition we have spectroscopic observational expertise from key team members:
-- Professor Christy Tremonti is an expert at data mining the SDSS, and has co-authored several papers about outflows.
-- Professor Dawn Erb is one of the world's leading experts in rest-frame UV spectroscopy of galaxies at z~2-3. Her many publications have been influential and are highly cited. Her 2012 paper was the first (at least, since the IUE era) to note that Mg II had a nebular component.
-- Dr. Nicolas Bouche is a leader at linking QSO absorption lines to galaxies. He is a member of the MUSE consortium, and supervised the study that published the first pure Mg II emission profiles from galaxies at z~1 (Finley et al. 2017).
-- Dr. Micaela Bagley recently completed her PhD working with Professor Claudia Scarlata, and is a postdoc at UT Austin. She is highly skilled at spectroscopic data analysis.
Also of note, Professor Claudia Scarlata has guaranteed time on the MMT, and Professor Sanchayeeta Borthakur also has institutional access. These facilities are already being used to obtain higher signal-to-noise and higher spectral resolution Mg II profiles on known LyC leakers, as well as low-z LyC leaker candidates that are being observed in Cycle 26 (HST GO 15626; PI Jaskot). Furthermore, Dr. Danielle Berg has made extensive use of the MMT's Blue Channel Spectrograph, and can reduce these data both carefully, and efficiently.
Lastly, our team includes two theorists specializing in Monte Carlo resonant line radiation transport: Dr. Max Gronke and Dr. Thibault Garel. Their expertise and support will make it possible to carry out joint modeling of the Lyman Alpha and Mg II lines. Dr. Garel is currently using the RASCAS code (Michel-Dansac et al. 2019) to jointly model the Lyman Alpha, Si II and Mg II line profiles seen in our MMT and COS data. Dr. Gronke has recently explored different ISM/CGM properties and feedback recipes, and their impact on Lyman Alpha profiles. Together, these models will help us to better understand the physical conditions in the gas that determine the output of Lyman Alpha, LyC, and Mg II.Galaxies and the IGM0falsefalsetruefalsetruefalsefalseSUPPORTEDGALAXYDWARF COMPACTSTARBURSTNOJ2000J2000FUV = 20.6, NUV = 20.2GALAXYDWARF COMPACTSTARBURSTNOJ2000J2000NUV = 20.8GALAXYDWARF COMPACTSTARBURSTNOJ2000J2000FUV = 21.6, NUV = 21.3GALAXYDWARF COMPACTSTARBURSTNOJ2000J2000FUV = 22.3, NUV = 21.3GALAXYDWARF COMPACTSTARBURSTNOJ2000J2000FUV = 21.5, NUV = 21.3GALAXYDWARF COMPACTSTARBURSTNOJ2000J2000NUV = 21.2, FUV = 21.3GALAXYDWARF COMPACTSTARBURSTNOJ2000J2000FUV 21.9, NUV = 21.5GALAXYDWARF COMPACTSTARBURSTNOJ2000J2000FUV = 21.9, NUV = 21.5COS/FUVSpectroscopicNoNoG160M1533COS/FUVSpectroscopicNoNoG160M1623COS/FUVSpectroscopicNoNoG140L800COS/FUVSpectroscopicNoNoG160M1623COS/FUVSpectroscopicNoNoG140L800COS/FUVSpectroscopicNoNoG160M1623COS/FUVSpectroscopicNoNoG140L800COS/FUVSpectroscopicNoNoG160M1600COS/FUVSpectroscopicNoNoG140L800COS/FUVSpectroscopicNoNoG160M1600COS/FUVSpectroscopicNoNoG140L800COS/FUVSpectroscopicNoNoG160M1577COS/FUVSpectroscopicNoNoG140L800COS/FUVSpectroscopicNoNoG160M1600COS/FUVSpectroscopicNoNoG140L800/private/var/folders/t2/c39hm9n15t3bbrhwh0w6hy6h0001t3/T/OPVisit16266868302527897057.xmlThe scheduling data was generated by CASM 27.2.CASM was run in Phase II mode.(Tic-Visit
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