SXDF308: challenging the Case-B assumption in Extreme Emission Line Galaxies

0 Assigned ID: 1702 ----- Attempting Submission 1 (Thu Mar 22 02:57:56 GMT 2018) ----- ORBITAL VISIBILITY OVERRUN ORBITAL VISIBILITY OVERRUN 0 ----- Attempting Submission 1 (Wed May 30 14:19:46 GMT 2018) ----- Your proposal could not be saved. Submission aborted. ----- Attempting Submission 2 (Tue Dec 18 14:35:29 GMT 2018) ----- These two warnings are on a previously executed visit. --M. Leveille SXDF308: challenging the Case-B assumption in Extreme Emission Line Galaxies We propose a comprehensive study of SXDF308, a compact, low-mass galaxy with extreme emission lines. The emission line spectrum of this objects shares many similarities with those of the most metal poor galaxies currently known (e.g., Skillman+2013) as well as with the Green Peas, the only galaxy population with confirmed substantial escape of Lyman Continuum ionizing radiation (Vanzella+2016, Izotov+2018, Jaskot+2018). However, critically, the Balmer decrement (Halpha/Hbeta) measured from ground-based spectroscopy suggests that the common Case B assumption often invoked to interpret emission line spectra may not be valid in this object. A low Halpha/Hbeta ratio may in fact be a common feature of extreme emission line galaxies: 32 out of 41 Green Pea galaxies in the Yang+(2017) sample have Halpha/Hbeta ratio smaller than Case-B. If the Case B assumption does not apply to EELGs, then that most of the intrinsic physical properties determined for these galaxies are severely incorrect! Here we request 3 orbits with COS-G140L and 2 orbits with WFC3-UVIS, with the goal of fully characterize: 1) the spatial distribution of the ionized gas and stars using the high resolution optical and UV WFCS/UVIS imaging, along with 2) the physical properties of the HII regions and the nature of the ionizing sources using COS FUV spectroscopy and thus, 3) confirm the validity and impact of the fundamental assumptions associated in the inference of physical properties of these galaxies. This project will obtain two orbits of WFC3+UVIS multiband imaging of SXDF308. We will image the target in the F275W, F336W, F438W broad band filters and in the F547M, F621M, F689M and F763M medium band filters. To reduce overhead and minimize CTE effects we use the UVIS-C512C-SUB aperture for imaging. We add a POST-FLASH flux to each exposure, to ensure a minimum charge packet of 12 electrons (http://www.stsci.edu/hst/wfc3/ins_performance/CTE). The POST-FLASH was computed using the ETC. We will also observe the target for three orbits, with COS-G140L. We have added a time constraint to the COS visit, to observe it after the WFC3-UVIS visit has been executed. Once the UVIS observations are conducted we will immediately obtain the images from MAST, process them, and make the size and flux measurements in the F275W, to opitmize the exposure time of the COS acquisition image. We'll use ACQ/IMAGE for target acquisition, and then do four exposures of spectroscopy in the G140L grating with CENWAVE=1280. We'll use FP-POS = ALL to best remove fixed pattern noise. Galaxies and the IGM Stellar Populations 3 false false true false false false false SUPPORTED ISM HII REGION NO J2000 J2000 COS/FUV Spectroscopic No No G140L 1280 WFC3/UVIS Imaging No No F275W WFC3/UVIS Imaging No No F336W WFC3/UVIS Imaging No No F410M WFC3/UVIS Imaging No No F467M WFC3/UVIS Imaging No No F547M WFC3/UVIS Imaging No No F621M WFC3/UVIS Imaging No No F689M WFC3/UVIS Imaging No No F763M POS-TARG DITHER 0.135 LINE false false 3 46.84 WFC3-UVIS-DITHER-LINE-3PT 1

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1545143636567 The scheduling data was generated by CASM 26.2.2. CASM was run in Phase II mode. /Users/mleveille/Desktop/OP-cache/15470-v01.xml 1544543122000 66.09552140765939 (Tic-Visit :proposal-id 15470 :visit-id "01" :proposal-version -1 :trans-version "20181130" :date "18-Dec-2018 09:33:55.0" :trans-errors '(:WARNINGS 2 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 2 :saa-model "29" :si-bright-earth-limb-angle 20.0 :data-volume 96112 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15470 :visit-id "01" :obset-id "01" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15470 :visit-id "01" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2869 :al-overhead-at-end 47 :internal-dur-at-end 0 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15470 :visit-id "01" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2980 :al-overhead-at-end 45 :internal-dur-at-end 142 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 2 2 The ETC link shows how we determined the POST-FLASH value: we assumed a source with a magnitude of 40, to ensure only background flux was present. The ETC link shows how we determined the POST-FLASH value: we assumed a source with a magnitude of 40, to ensure only background flux was present. The ETC link shows how we determined the POST-FLASH value: we assumed a source with a magnitude of 40, to ensure only background flux was present. 1545143468300 The scheduling data was generated by CASM 26.2.2. CASM was run in Phase II mode. /Users/mleveille/Desktop/OP-cache/15470-v02.xml (Tic-Visit :proposal-id 15470 :visit-id "02" :proposal-version -1 :trans-version "20181130" :date "18-Dec-2018 09:31:07.0" :trans-errors '(:WARNINGS 0 :ERRORS 0 :HEALTH-AND-SAFETY 0 :FATAL-ERRORS 0 :CONTINUABLE-FATALS 0) :number-of-orbits 3 :saa-model "31" :si-bright-earth-limb-angle 20.0 :data-volume 61104 :tdrss-contact-duration 0 :coron NIL ) (Tic-Obset :proposal-id 15470 :visit-id "02" :obset-id "02" :pcs-mode "FGS" ) (Tic-Orbit :proposal-id 15470 :visit-id "02" :orbit-number 1 :pcs-time 333 :si-vis-utilization 2806 :al-overhead-at-end 0 :internal-dur-at-end 38 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15470 :visit-id "02" :orbit-number 2 :pcs-time 302 :si-vis-utilization 2839 :al-overhead-at-end 0 :internal-dur-at-end 38 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) (Tic-Orbit :proposal-id 15470 :visit-id "02" :orbit-number 3 :pcs-time 302 :si-vis-utilization 2840 :al-overhead-at-end 0 :internal-dur-at-end 341 :dark-offset NIL :dark-utilization 0 :max-dark-utilization 1920 :low-sky "N" :pcs-visibility 3142 :pcs-gap 0 ) true 3 0