14701( 2) - 19-Jul-2016 14:12:08 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 14701 Version: 2 Check-in Time: 19-Jul-2016 14:12:08 STScI Edit Number: 0 Title Is galaxy formation different during the epoch of reionization? Confirmation of the brightest ever candidate at redshift z>8 ------------------------------------------------------------------------------------ Type Cycle GO 24 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Michele Trenti University of Melbourne Y CoI: Prof. Tommaso L. Treu University of California - Los Angeles N CoI: Ms. Stephanie R Bernard University of Melbourne N CoI: Ms. Charlotte Mason University of California - Los Angeles N ------------------------------------------------------------------------------------ Abstract How bright can galaxies be during the epoch of reionization? Recent Hubble observations challenged prior expectations and led to the identification of two surprisingly luminous galaxies with spectroscopic confirmation within 600 Myr from the Big Bang: A source with m_AB=25.3 at z=8.7 and another with m_AB=26.0 at z=11.1. Such galaxies hint a tension with the assumption of a luminosity function (LF) with a Schechter (exponential) profile at the bright end, otherwise well established after reionization is complete. A clear excess of L>L* galaxies, if confirmed, would be a strong indication of a different physics of galaxy formation at play during the epoch of reionization. Leveraging upon the large-area pure-parallel BoRG survey, we identified a yet more luminous galaxy candidate at z>8, a source with m_AB=24.5, corresponding to M_AB=-22.8, almost ten times brighter than the Milky Way! The F105W dropout is detected at very high S/N in the IR, has no optical flux and a compact size (r_e=0."17) leading to a most likely redshift of z~8.4. However, a secondary peak in the redshift distribution is present at z~1.8 (p~10%). To exclude this solution and confirm the high-z nature of BoRG_0116+1425, we propose observations in the medium-band F098M filter. If the galaxy is an interloper, it will have m_AB~26.4 in F098M, while it will be undetected if at z>7.8. Since a Schechter-like LF predicts less than 0.002 galaxies as bright as BoRG_0116+1425 in the survey area, this single orbit proposal has the potential to unequivocally establish departure from a Schechter LF at confidence greater than 99.8%, supporting theoretical predictions of decreasing efficiency of AGN feedback at high-z ------------------------------------------------------------------------------------ Observations Description ------------------------ The observation consists of one 1-orbit visit of F098M imaging (4 exposures). We selected 4 13-NSAMP SPARS50 exposures to fill the orbit, using a 4-point minimum box with optimal half-pixel sampling in both x and y. Timing requirements are requested to coordinate ground-based follow-up observations of targets selected by these HST observations using the MOSFIRE spectrograph on Keck. ------------------------------------------------------------------------------------ 14701( 2) - 19-Jul-2016 14:12:08 - [ 2] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 BORG0116+142 GALAXY, HIGH REDSHIFT RA=01H16M12.2566S, J2000 24.5 in F160W 5 GALAXY DEC=+14D24'38.77" Reference Frame: ICRS Comments: Dropout coordinates are: 01 16 8.3280 +14 24 9.36 Field of view has been centered to increase overlap with original BoRG field ------------------------------------------------------------------------------------------------------------------------------------ 14701( 2) - 19-Jul-2016 14:12:08 - [ 3] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-IR-DITHER-BOX-MIN Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.572 Line_Spacing 0.365 Coordinate_Frame POS-TARG Pattern_Orient 18.528 Angle_Between_Sides 74.653 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 14701( 2) - 19-Jul-2016 14:12:08 - [ 4] Visit: 01 Visit Requirements: ORIENT 63D TO 70 D; ORIENT 152D TO 165 D; ORIENT 234D TO 262 D; BEFORE 25-FEB-2017:00:00:00 On Hold Comments: Additional Comments: Exposures ------------------------------------------------------------------------------------------------------------------------------------ Exp | Target | Instr | Oper. | Aper |Spectral|Central| Optional |Num| Time | Special Num | Name | Config | Mode | or FOV |Element |Waveln.| Parameters |Exp| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 BORG0116+14 WFC3/IR MULTIAC IR F098M NSAMP=14, SAMP-SEQ=SPARS50 1 DEF PATTERN 1 1 25 CUM (2611.753 S) ------------------------------------------------------------------------------------------------------------------------------------ Sub Exposures ------------------------------------------------------------------------------------------------------------------------------------ Target | Exp |Instr | Oper. | Aper |Spectral|Cent.|Primary |Secondary |Iteration |CR-SPLIT |Orbit |Duration Name | Num |Config | Mode | or FOV |Element |Wave.|Pattern Pos |Pattern Pos |Num |Num |Number | ------------------------------------------------------------------------------------------------------------------------------------ BORG0116+1425 1 WFC3/IR MULTIAC IR F098M 1 none none none 1 N/A CUM BORG0116+1425 1 WFC3/IR MULTIAC IR F098M 2 none none none 1 N/A CUM BORG0116+1425 1 WFC3/IR MULTIAC IR F098M 3 none none none 1 N/A CUM BORG0116+1425 1 WFC3/IR MULTIAC IR F098M 4 none none none 1 N/A CUM 14701( 2) - 19-Jul-2016 14:12:08 - [ 5] Summary Form for Proposal 14701 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures IR ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/IR ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=14, SAMP-SEQ=SPARS50 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements BEFORE 25-FEB-2017:00:00:00, ORIENT 152D TO 165 D, ORIENT 234D TO 262 D, ORIENT 63D TO 70 D, PATTERN 1 1 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F098M ------------------------------------------------------------------------------------------------------------------------------------ Target Names BORG0116+1425 ------------------------------------------------------------------------------------------------------------------------------------