0Assigned ID: 1211
----- Attempting Submission 1 (Tue Sep 29 21:36:38 GMT 2020) -----
----- Attempting Submission 2 (Wed Oct 07 14:01:43 GMT 2020) -----This Phase II is to re-observe an orbit due to issues with the initial data acquisition.293447730----- Attempting Submission 1 (Tue Nov 24 16:01:23 GMT 2020) -----
----- Attempting Submission 2 (Thu May 06 21:41:58 GMT 2021) -----I was unable to run the orbit and visit planners because some of the observations have already been acquired
(which prevented the planner tools from working in the APT).Measuring the Distance to SN Ia Host NGC 4457The local measurement of the Hubble constant, H0, is now in tension with measurements from the distant universe by 4.4 sigma. The local H0 value is based on using Type Ia Supernovae (SNe Ia) as standard candles, calibrated from a small sample (<20) of nearby galaxies and limited by the (in)frequency of SN Ia events. One of the biggest improvements we can make in measuring H0 locally is to increase the number of calibrating systems.
A new SN Ia event has just occurred in the nearby galaxy NGC 4457, estimated to be at ~17 Mpc based on the light-curve. The host galaxy is close enough that a precision distance can be made using the tip of the red giant branch (TRGB) method. We propose ACS+WFC3 imaging of the resolved stars in the galaxy to precisely measure the distance and calibrate the SN Ia luminosity. A statistical sample of galaxies with SNe Ia and independent distance measurements is the ultimate goal for improving the local H0 measurement and such a sample is only built galaxy-by-galaxy when a nearby SN Ia occurs. In this context, NGC 4457 is a high priority target for a precision TRGB distance measurement.
In addition, the host-galaxy NGC 4457 is a more massive galaxy with little recent star formation. These properties are unique among SNe Ia calibrating systems but common in galaxies in the Hubble flow. SNe Ia in massive hosts standardize to a luminosity up to 10% brighter than those in lower mass hosts, a potential source of systematic uncertainty in the SN Ia distance scale. The new TRGB distance will provide an independent distance to a SN Ia in a galaxy with such properties and enable a comparison with SN Ia luminosity offsets estimated from galaxy redshifts.The primary goal of this proposal is to measure the tip of the red giant branch (TRGB) distance to the galaxy NGC 4457 using optical imaging from the ACS camera of the halo stars and an additional halo field from WFC3 UVIS imaging. Orbit allocation = 6 (3 per filter) orbits which includes 6 primary ACS orbits and 6 coordinated parallel WFC3 orbits.
All visits are broken into 2 orbits. ACS/WFC exposure times are split between the F606W filter and the F814W. The coordinated parallel observations are to be obtained with the WFC UVIS camera with exposure times split between the F606W and F814W filters.
Small ditherings are performed between orbits in order to remove hot pixels, smooth the detector response, and provide some sub-pixel sampling of the PSF. We don't intend to cover the interchip gap. Ditherings are performed using POS-TARG and follow the 3-point pattern no. 13 with shifts of 2-5 pix in the x and y direction. After the first 3 orbits have completed a full dither patter, we shift the field by ~10 pixels in the x direction and repeat the 3-point pattern no. 13.
The first visit is requested with specific orient ranges. The orientation ranges have been chosen such that the primary observations are of a field in the halo of NGC 4457 while the coordinated parallels images cover an additional halo field of the target galaxy. Subsequent visits are requested to be obtained with the same ORIENT as the first visit in order to maximize the sky area covered at full depth and ensure precise alignments of the observations.PI Kristen McQuinn and Co-Is Evan Skillman, Andrew Dolphin have deep experience as a team measuring the TRGB distances to nearby galaxies using imaging of resolved stellar populations (McQuinn et al. 2013, 2014, 2016a,b, 2017, 2019). Andrew Dolphin was involved with the calibration of the TRGB in the HST filters and developed the Maximum Likelihood code to identify the TRGB using photometry and consideration of the incompleteness of the data measured by artificial star tests. Co-PI Max Newman has experience working with HST data to measure the TRGB distances as part of PID 15907. Co-I Saurabh Jha has deep experience studying Type Ia Supernovae as it relates to measuring and calibrating light-curves. Our team has the skills needed to perform a careful measurement of the distance to NGC 4457 in a timely and efficient manner.Large Scale Structure of the Universe3falsetruefalsefalsefalsefalsefalseSUPPORTEDEXT-STARK III-INOThis object was generated by the targetselector and retrieved from the NED database.J2000J2000ACS/WFCImagingNoNoF814WACS/WFCImagingNoNoF606WWFC3/UVISImagingNoNoF606WWFC3/UVISImagingNoNoF814WHst Same orient constraint links visits (01 02 03)The scheduling data was generated by CASM 28.2.CASM was run in Phase II mode.1618412677000114.57137999999998(Tic-Visit
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