13821( 3) - 14-Oct-2014 12:38:55 - [ 1] HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 13821 Version: 3 Check-in Time: 14-Oct-2014 12:38:55 STScI Edit Number: 0 Title H-alpha Filaments and Feedback in NGC4696 at the centre of the Centaurus cluster ------------------------------------------------------------------------------------ Type Cycle GO 22 ------------------------------------------------------------------------------------ Investigators Contact? PI: Prof. Andrew C. Fabian University of Cambridge Y CoI: Dr. Carolin S. Crawford University of Cambridge N CoI: Dr. Roderick M. Johnstone University of Cambridge Y CoI: Dr. Jeremy S Sanders Max-Planck-Institut fur extraterrestrische N Physik CoI: Prof. John S. Gallagher III University of Wisconsin - Madison N CoI: Prof. Ellen Zweibel University of Wisconsin - Madison N CoI: Dr. Christopher J. Conselice University of Nottingham N CoI: Dr. Gary J. Ferland University of Kentucky N CoI: Dr. Nina Hatch University of Nottingham N CoI: Dr. Rebecca E. A. Canning Stanford University N CoI: Dr. Christopher S. Reynolds University of Maryland N CoI: Dr. Philippe Salome Observatoire de Paris N CoI: Dr. Stephen Alexander Walker University of Cambridge Y CoI: Dr. Helen R Russell University of Cambridge N CoI: Ms. Electra Panagoulia University of Cambridge N ------------------------------------------------------------------------------------ Abstract One third of Brightest Cluster Galaxies (BCG) have strong optical emission lines originating in an extensive filamentary nebula. The prototype is the spectacular nebula around NGC1275 in the Perseus cluster which we are have imaged in H-alpha and [NII] with HST, spatially resolving the filamentary structure. Here we propose deep observations of the nebula in NGC4696, the BCG in the Centaurus cluster. NGC4696, at approximately half the distance of NGC1275 is the nearest BCG nebula with molecular filaments, thus affording the highest linear spatial resolution in this type of source. These observations will test the magnetic support model for the filaments by resolving and measuring the width of the filaments, and test the particle heating model for the excitation of the filaments through measurement of their surface brightness distribution and morphology. The relation of the filaments to the dust lanes, and the complex Faraday Rotation maps of this source will provide further diagnostics not available in NGC1275. The results will have a wide relevance to similar nebulae found around distant radio galaxies and young galaxies. ------------------------------------------------------------------------------------ Observations Description ------------------------ 13821( 3) - 14-Oct-2014 12:38:55 - [ 2] We propose to image the BCG (NGC~4696) in the Centaurus cluster in H$\alpha$+[NII] with WFC3/UVIS and the F665N narrow band filter. HST is required for this project in order to obtain the high spatial resolution. WFC3 has a comprehensive filter set well matched for the H$\alpha$ imaging. NGC~4696 ground-based imaging (Crawford et al 2005), with seeing of about one arcsec, shows a bright extended filament 22 arcsec to the South East of the nucleus with an (observed) H$\alpha$ surface brightness of $\sim 1\times10^{-16}$~erg~s$^{-1}$~cm$^{-2}$~arcsec$^{-2}$ (the value quoted in the paper is $1.4\times10^{-16}$~erg~s$^{-1}$~cm$^{-2}$~arcsec$^{-2}$ after correction for Galactic reddening by a factor of 33\%). In this proposal we aim to construct a good map with a signal-to-noise ratio of ~10 per 2$\times$2 pixel resolution element down to one third of this surface brightness. Our NGC~1275 HST data (Fig.~1b, c) show detailed structures down to 0.1-0.2 arcsec scales, indicating that the intrinsic surface brightness is much higher than observed in the ground-based data. Assuming the filaments have a spatial size of 0.3 arcsec would imply that their surface brightness is $\sim$10 times higher than observed in the ground-based optical data. We note also that in NGC~4696 the NII$\lambda6584$ line is twice a bright as H$\alpha$, and that this will also be transmitted by our selected narrow-band filter. We model the extended emission (using the WFC3 ETC) as arising from two emission lines (H$\alpha$ and [NII]$\lambda 6584$) of surface brightness 3 and 6 $\times 10^{-16}$~erg~s$^{-1}$~cm$^{-2}$~arcsec$^{-2}$ (a line width of 200 km/s is used) plus an underlying elliptical galaxy continuum. The normalization for the galaxy taken from the work of Schombert (1987) shows that the surface brightness of NGC4696 is 21 Vmag arcsec$^{-2}$ at a radial distance of 28 arcsec from the nucleus, appropriate to the fainter outermost filaments. However, more modern references suggest R~21 at this radius (Penereiro et al 1994; Sparks et al 1989). For the simulation we use a Galactic extinction value normalized to E(B-V)=0.12mag, standard background values and choose a 4-point box dither pattern for the full orbit exposures and a 3-point line dither pattern for the half-orbit exposures. The APT indicates that after overheads there is time for ~2700s of on-source exposure on NGC~4696 in a single orbit after spacecraft and instrument overheads are taken into account. We require an off-band image in a line-free spectral region to enable the galaxy continuum to be subtracted. This can be obtained efficiently using the F814W filter for NGC~4696. A further image, taken in a bluer continuum band, will allow dust 13821( 3) - 14-Oct-2014 12:38:55 - [ 3] extinction maps to be made and any young star clusters to be seen. The F467M filter is ideal, as it transmits a relatively blue and, crucially, emission-line free part of the spectrum with good system throughput. In Table 1 we provide a summary of the target, its properties, selected filters, exposure times and the expected signal-to-noise ratio based on ETC calculations. A major contributor to background counts (and hence noise) in the emission line image (F665N) is the underlying galaxy. This is included in the ETC calculation with the surface brightness given in column 6. We assumed each full orbit to be split into four exposures by a 4-point box dither and calculated signal-to-noise ratios for a 2x2 pixel (0.08x0.08 arcsec) spatial region. Half-orbit exposures use the 3-point line dither. Although the underlying galaxy emission gives sufficient counts to ensure good charge transfer near the centre of the galaxy, near the outermost visible filaments, this is not the case. We therefore choose to post-flash the chip to ensure a minimum of 12e- even far away from the galaxy to enable possible detection of very remote filaments. The required post-flash was included in the ETC calculations. A total 10.5 orbits will give us a signal-to-noise ratio of 8.6 in the narrow-band F665N filter in a 2$\times$2 pixel resolution element. A further 0.5 orbit in the broad-band F814W filter will give a signal-to-noise ratio of 25.9 (in the same spatial region), sufficient to subtract the underlying galaxy without significantly degrading the signal-to-noise ratio of the narrow-band observations. Two orbits of exposure taken with the F467M filter will allow a signal-to-noise ratio of 8.3 to be reached. \begin{table} \centerline{Table 1. Proposed observations} \begin{tabular}{lccccccccc} \hline Target& Redshift & Band & Line SB & E$_{B-V}$ & Gal & Inst & Filter & Exp & S/N\\ \hline NGC~4696 & 0.00987& H$\alpha$+[NII] & 3, 6e-16 & 0.12 & $\mu_R$=21.0 & WFC3 & F665N &10.5 & 8.6 \\ NGC~4696 & 0.00987& Red cont & - & 0.12 & $\mu_V$=21.0 & WFC3 & F814W &0.5 & 25.9 \\ NGC~4696 & 0.00987& Blue cont & - & 0.12 & $\mu_R$=21.0 & WFC3 & F467M &2.0 & 8.3 \\ \hline \end{tabular} %\caption[]{Targets and proposed observations.} Column 4 gives the line surface brightnesses in erg~s$^{-1}$~cm$^{-2}$~arcsec$^{-2}$ of H$\alpha$ and [NII]$\lambda 6584$. Column 6 gives the galaxy continuum surface brightness in mags arcsec$^{-2}$. Column 9 gives the exposure time in orbits to reach the signal-to-noise ratio given in column 10 13821( 3) - 14-Oct-2014 12:38:55 - [ 4] in a 2x2 pixel spatial region. \label{tab:calratio} \end{table} ------------------------------------------------------------------------------------ 13821( 3) - 14-Oct-2014 12:38:55 - [ 5] TARGET LIST Fixed Targets ------------------------------------------------------------------------------------------------------------------------------------ Tar| Target | Target | Target |Coord | Radial | Flux data No | Name | Description | Position |Eqnx | Vel. | ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-4696 GALAXY, ELLIPTICAL RA=12H48M49.2700S +/- 0.1", J2000 Z = V = 21.0 DEC=-41D18'39.01" +/- 0.1" 0.00987 Reference Frame: ICRS ------------------------------------------------------------------------------------------------------------------------------------ 13821( 3) - 14-Oct-2014 12:38:55 - [ 6] Patterns ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 1 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-BOX Pattern_Purpose DITHER Number_Of_Points 4 Point_Spacing 0.173 Line_Spacing 0.112 Coordinate_Frame POS-TARG Pattern_Orient 23.884 Angle_Between_Sides 81.785 Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ Pattern_Number: 2 Primary_Pattern Secondary_Pattern Pattern_Type WFC3-UVIS-DITHER-LINE-3PT Pattern_Purpose DITHER Number_Of_Points 3 Point_Spacing 0.135 Line_Spacing Coordinate_Frame POS-TARG Pattern_Orient 46.84 Angle_Between_Sides Center_Pattern NO ------------------------------------------------------------------------------------------------------------------------------------ 13821( 3) - 14-Oct-2014 12:38:55 - [ 7] Visit: 01 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 643 S PATTERN 1 1 S (2572 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 671 S PATTERN 1 2 S (2684 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 671 S PATTERN 1 3 S (2684 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 671 S PATTERN 1 4 S (2684 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 671 S PATTERN 1 5 S (2684 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 1 N/A S NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 1 N/A S NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 1 N/A S NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 1 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 2 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 2 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 2 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 2 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 3 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 3 N/A S 13821( 3) - 14-Oct-2014 12:38:55 - [ 8] 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-4696 3 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 3 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 3 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 4 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 4 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 4 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 4 N/A S NGC-4696 5 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 5 N/A S NGC-4696 5 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 5 N/A S NGC-4696 5 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 5 N/A S NGC-4696 5 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 5 N/A S 13821( 3) - 14-Oct-2014 12:38:55 - [ 9] Visit: 02 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=11 1 378 S PATTERN 2 1 S (1134 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-4696 WFC3/UVI ACCUM UVIS1 F814W 1 385 S PATTERN 2 2 S (1155 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-4696 WFC3/UVI ACCUM UVIS1 F467M FLASH=8 1 671 S PATTERN 1 3 S (2684 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-4696 WFC3/UVI ACCUM UVIS1 F467M FLASH=8 1 671 S PATTERN 1 4 S (2684 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 1 N/A S NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 1 N/A S NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 1 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F814W 1 none none none 1 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F814W 2 none none none 1 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F814W 3 none none none 1 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F467M 1 none none none 2 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F467M 2 none none none 2 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F467M 3 none none none 2 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F467M 4 none none none 2 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F467M 1 none none none 3 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F467M 2 none none none 3 N/A S 13821( 3) - 14-Oct-2014 12:38:55 - [ 10] 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-4696 4 WFC3/UVI ACCUM UVIS1 F467M 3 none none none 3 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F467M 4 none none none 3 N/A S 13821( 3) - 14-Oct-2014 12:38:55 - [ 11] Visit: 03 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| (Total) | Requirements ------------------------------------------------------------------------------------------------------------------------------------ 1 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 643 S PATTERN 1 1 S (2572 S) ------------------------------------------------------------------------------------------------------------------------------------ 2 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 671 S PATTERN 1 2 S (2684 S) ------------------------------------------------------------------------------------------------------------------------------------ 3 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 671 S PATTERN 1 3 S (2684 S) ------------------------------------------------------------------------------------------------------------------------------------ 4 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 671 S PATTERN 1 4 S (2684 S) ------------------------------------------------------------------------------------------------------------------------------------ 5 NGC-4696 WFC3/UVI ACCUM UVIS1 F665N FLASH=9 1 671 S PATTERN 1 5 S (2684 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 1 N/A S NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 1 N/A S NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 1 N/A S NGC-4696 1 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 1 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 2 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 2 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 2 N/A S NGC-4696 2 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 2 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 3 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 3 N/A S 13821( 3) - 14-Oct-2014 12:38:55 - [ 12] 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 | ------------------------------------------------------------------------------------------------------------------------------------ NGC-4696 3 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 3 N/A S NGC-4696 3 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 3 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 4 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 4 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 4 N/A S NGC-4696 4 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 4 N/A S NGC-4696 5 WFC3/UVI ACCUM UVIS1 F665N 1 none none none 5 N/A S NGC-4696 5 WFC3/UVI ACCUM UVIS1 F665N 2 none none none 5 N/A S NGC-4696 5 WFC3/UVI ACCUM UVIS1 F665N 3 none none none 5 N/A S NGC-4696 5 WFC3/UVI ACCUM UVIS1 F665N 4 none none none 5 N/A S 13821( 3) - 14-Oct-2014 12:38:55 - [ 13] Summary Form for Proposal 13821 Item Used in this proposal ------------------------------------------------------------------------------------------------------------------------------------ Apertures UVIS1 ------------------------------------------------------------------------------------------------------------------------------------ Configurations WFC3/UVIS ------------------------------------------------------------------------------------------------------------------------------------ Opmodes ACCUM ------------------------------------------------------------------------------------------------------------------------------------ Optional Parameters FLASH=11, FLASH=8, FLASH=9 ------------------------------------------------------------------------------------------------------------------------------------ Special Requirements PATTERN 1 1, PATTERN 1 2, PATTERN 1 3, PATTERN 1 4, PATTERN 1 5, PATTERN 2 1, PATTERN 2 2 ------------------------------------------------------------------------------------------------------------------------------------ Spectral Elements F467M, F665N, F814W ------------------------------------------------------------------------------------------------------------------------------------ Target Names NGC-4696 ------------------------------------------------------------------------------------------------------------------------------------