11174( 2) - 04/23/07 11:29 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 11174 Version: 2 Check-in Time: 23-Apr-2007 15:29:13 STScI Edit Number: 0 Title A Spitzer/X-ray candidate cluster at z>2: NICMOS imaging ------------------------------------------------------------------------------------ Type Cycle Parallel Pointing Tolerance GO 16 ------------------------------------------------------------------------------------ Investigators Contact? PI: Dr. Emanuele Daddi Commissariat a l'Energie Atomique (CEA) CoI: Prof. Alvio Renzini Osservatorio Astronomico di Padova N CoI: Prof. Nobuo Arimoto National Astronomical Observatory of Japan N (NAOJ) CoI: Dr. Marcella Brusa Max-Planck-Institut fur extraterrestrische N Physik CoI: Dr. Ranga-Ram Chary California Institute of Technology N CoI: Prof. Andrea Cimatti Universita di Bologna N CoI: Dr. Alexis Finoguenov University of Maryland N CoI: Dr. Xu Kong University of Science and Technology of N China CoI: Dr. Masato Onodera Yonsei University, Korea N ------------------------------------------------------------------------------------ Abstract We propose deep H-band imaging with NICMOS of a remarkable z>2 cluster of galaxy candidate. Over a 1000 arcmin^2 field imaged with Spitzer's IRAC and MIPS we have discovered a compact (<30'' diameter) concentration of extremely red galaxies with a factor of >40 overdensity over the adjacent field. Among these galaxies for which we can derive meaningful photometric redshifts, 17 are consistent with zphot=2-2.5, making very likely that the concentrationis is a real cluster at such high redshift. This is further supported by a 3.5 sigma detection of extended X-Ray emission on Newton-XMM data, by a likely color-magnitude sequence of red galaxies, and by the presence of a giant galaxy consistent with a BCG at the cluster redshift. While spectroscopic confirmation of the cluster might result prohibitive with current facilities, HST high resolution imaging will allow us to gain crucial information for the study and scientific exploitation of this hot gas hosting, record high-z cluster of galaxies. The HST high resolution observations will allow us to unveil the rest frame optical morphologies of the galaxies and confirm the presence of ellipticals in the structure, detect and characterize the color-magnitude relation, measure their effective radii and construct their Kormendy relation for the passively evolving subsample, improve the photometric redshift estimates to confirm the real cluster nature of the structure, estimate stellar masses and check for possible deviations from the local mass-size relation, search for mergers and AGNs, and establish a cluster benchmark for cluster-field comparisons at this highest redshift. ------------------------------------------------------------------------------------ 11174( 2) - 04/23/07 11:29 - [ 2] Observations Description ------------------------ Our goal is to obtain high resolution and high S/N imaging of the $z>2$ cluster member candidates in the structure. Given the extremely red SEDs of the sources, the most efficient mean by far is observing in the near-IR with NICMOS in the F160W band. This also allows to obtain data at optical rest-frame wavelengths (between B and V bands rest frame for $z\sim2$--2.5). The angular size of the galaxy overdensity is about 30$''$, which can be easily covered with a single pointing with the NICMOS3 camera. With a FWHM of about 0.2$''$, corresponding to about 1.7 kpc (proper size) at $z=2$--2.5, this will suffice to distinguish disks and irregular (i.e. dusty or merging) galaxies from spheroids and to constrain sizes to a limit of $\simlt1$ kpc. This size limit is comparable to the size of the smallest field $z>1.4$ passive ellipticals (Daddi et al. 2005). The IRAC brightest galaxy in the structure (candidate BCG) has $H=22.2$ AB, derived from the best fit SED (Fig.~\ref{fig:x}). The cluster member candidates are up to 3.5 magnitudes fainter in IRAC than the BCG (see Fig~\ref{fig:1}). Conservatively assuming they are as red as the BCG in $(H- m_{3.6\mu m})$ color, we need to reach $H=25$ AB in order to secure high quality imaging of most cluster members (14/17 to this limit). We have used the NICMOS exposure time calculator for estimating the required integration time to reach $S/N>10$ detection of a $H=25$ source. We consider a 1$''$ diameter aperture and assume that at least 70\% of the flux falls withis the aperture. We consider 2 sub exposures of 1300s per orbit (52 minutes visibility). We find that in total 7 orbits are necessary to reach the required S/N ratio. We will split the observations in a 4-orbit visit plus a 3-orbit visit. Each visit will perform a NIC-SPIRAL-DITH pattern with 2" (10 pixel) spacing (plus 1/2 pixel or 1/3 pixel extra shift for PSF sampling). Real Time Justification ----------------------- Calibration Justification ------------------------- Additional Comments ------------------- ------------------------------------------------------------------------------------ 11174( 2) - 04/23/07 11:29 - [ 3] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 DADDIF-GAL- CLUSTER OF GALAXIES, RA=14H49M14.4000S +/- 0.1", J2000 V = 28.0 CLUS HIGH REDSHIFT CLUSTER DEC=+08D56'18.40" +/- 0.1" J=23 AB brightest sources Reference Frame: ICRS Comments: The 30" diameter area of interest contain 10--20 targets with faint IR magnitudes, between AB 23 and 26 11174( 2) - 04/23/07 11:29 - [ 4] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type NIC-SPIRAL-DITH Pattern_Purpose DITHER Number_Of_Points 8 Point_Spacing 2.06666 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 0.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type NIC-SPIRAL-DITH Pattern_Purpose DITHER Number_Of_Points 6 Point_Spacing 2.1 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 0.0 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 11174( 2) - 04/23/07 11:29 - [ 5] Visit: 01 Visit Priority: Visit Requirements: 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 DADDIF-GAL- NIC3 MULTIAC NIC3 F160W NSAMP=22,SAMP-SEQ=SPARS64 1 DEF PATTERN 1 1 CLUS CUM ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 1 none none none 1 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 2 none none none 1 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 3 none none none 2 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 4 none none none 2 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 5 none none none 3 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 6 none none none 3 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 7 none none none 4 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 8 none none none 4 N/A CUM 11174( 2) - 04/23/07 11:29 - [ 6] Visit: 02 Visit Priority: Visit Requirements: 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| | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 DADDIF-GAL- NIC3 MULTIAC NIC3 F160W SAMP-SEQ=SPARS64,NSAMP=22 1 DEF POS TARG -6.06666, 0; CLUS CUM PATTERN 2 1 ------------------------------------------------------------------------------------------------------------------------------------ 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 | ------------------------------------------------------------------------------------------------------------------------------------ DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 1 none none none 1 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 2 none none none 1 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 3 none none none 2 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 4 none none none 2 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 5 none none none 3 N/A CUM DADDIF-GAL-CLUS 1 NIC3 MULTIAC NIC3 F160W 6 none none none 3 N/A CUM 11174( 2) - 04/23/07 11:29 - [ 7] Summary Form for Proposal 11174 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures NIC3 ------------------------------------------------------------------------------------------------------------------------------------ Configurations NIC3 ------------------------------------------------------------------------------------------------------------------------------------ Opmodes MULTIACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters NSAMP=22 SAMP-SEQ=SPARS64 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1; POS TARG -6.06666, 0; PATTERN 2 1; ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F160W ------------------------------------------------------------------------------------------------------------------------------------ Target Names DADDIF-GAL-CLUS ------------------------------------------------------------------------------------------------------------------------------------