PFS Expected Performance
The sensitivity information below is as of Jul. 2024, and may change in the future.
Basic Information
| Arm | Wavelength range | Throughput(1) | Resolving Power | Continuum sensitivity(2) | Emission line sensitivity(3) | |||
|---|---|---|---|---|---|---|---|---|
| [AB mag] | [10-17 erg/s/cm2] | |||||||
| [nm] | mean(4) | representative(5) | mean(4) | representative(5) | ||||
| Blue | 380 - 450 | 10% | ∼2500 | 21.8 | 21.9 (@415nm) | 4.6 | 4.3 (@415nm) | |
| 450 - 550 | 18% | 22.3 | 22.3 (@505nm) | 2.1 | 2.1 (@505nm) | |||
| 550 - 650 | 21% | 22.1 | 22.2 (@605nm) | 1.9 | 1.7 (@605nm) | |||
| Red | Low Res. | 630 - 750 | 27% | ∼3000 | 22.3 | 22.5 (@680nm) | 1.5 | 1.2 (@680nm) |
| 750 - 850 | 26% | 22.1 | 22.4 (@796nm) | 1.5 | 1.1 (@796nm) | |||
| 850 - 970 | 23% | 21.7 | 22.1 (@912nm) | 1.7 | 1.2 (@912nm) | |||
| Mid. Res. | 710 - 775 | 25% | ∼5500 | 21.7 | 21.9 (@741nm) | 1.5 | 1.3 (@741nm) | |
| 775 - 825 | 24% | 21.6 | 21.9 (@796nm) | 1.5 | 1.2 (@796nm) | |||
| 825 - 885 | 22% | 21.5 | 21.8 (@856nm) | 1.5 | 1.3 (@856nm) | |||
| NIR | 940 - 1050 | 21% | ∼4500 | 21.2 | 21.8 (@993nm) | 2.2 | 1.4 (@993nm) | |
| 1050 - 1150 | 19% | 21.1 | 21.5 (@1100nm) | 1.9 | 1.5 (@1100nm) | |||
| 1150 - 1260 | 14% | 20.8 | 21.2 (@1208nm) | 2.2 | 1.7 (@1208nm) | |||
Note: These estimates are based on the PFS exposure time calculated developed by C. Hirata arXiv:1204.5151 under the following assumptions:
- FWHM=0.8 arcsec seeing condition (the fraction of incoming flux to fiber aperture is ∼62% at the field center and ∼54% at the edge if the fiber is perfectly aligned with a stellar object)
- Observation at a zenith angle of 35 deg.
- Observation at a dark night
- Observation near the field edge (0.45 deg. from the center)
- No Galactic dust extinction
- Recent sky model provided by Jim Gunn
- Systematic sky subtraction error of 1%
- Diffused stray light on the detector originating from 2% of incoming sky flux
- Dark current [e-/pix/s] of 0.0002 (blue), 0.0001 (red), and 0.01 (NIR)
- Read-out noise [e-RMS/pix] of 4.0 (blue and red) and 4.0 (NIR)
(1) The total throughput including primary mirror reflectivity, WFC transmission, and PFS instrument. See here. The fiber aperture effect is not included because it depends on seeing condition and object type. The vignetting effect, ∼94% at the field center and ∼71% at the field edge, is not included either because it depends on the field position. The continuum and emission-line sensitivity information, however, are calculated taking these factors into consideration.
(2) Continuum sensitivity in case of a point source, to achieve S/N=5 for 1-hour on-source exposure (4×900 sec.), after 3 pixel binning.
(3) Emission-line sensitivity in case of an extended rouce (r_eff=0.3 arcsec.), to achieve S/N=5 for 1-hour on-source exposure (4×900 sec.). Here, the line width is assumed to be σ=70 km/s.
(4) The average limiting magnitude and line flux in the wavelength range. This value may be affected by the sky emission line.
(5) The representative value at the wavelength where the spectrum is not affected by the sky emission line.
Fig. 1. S/N expected for continuum (left) and emission line (right) in case of the total on-source integration time of 1 hour. Flat continuum of 22.5 AB mag of a point source and line flux of 1 × 10-17 erg/s/cm2 of an extended source are assumed. For the red arm, only the low resolution result is shown.
Fig. 2. Limiting magnitude for continuum of a point source (left) and limiting flux of a single emission line of an extended source (right) to achieve S/N=5 in case of the total on-source exposure time of 1 hour. The gray horizontal bar indicates the average value while the open circle shows the representative value in the specific wavelength range. For the red arm, only the low resolution result is shown.
Fig. 3. A similar plot to Fig. 2, but for the medium resolution mode.
Moonlight Effects
[Note: this study was done with an older version of ETC.] Moonlight effects on the limiting magnitude are presented below. Using the PFS exposure calculator (see above), the limiting magnitude requried for S/N=5 in case of 900-sec exposure time is compared among three cases: Night skys with new moon, half moon, and full moon. The assumptions in the calculation are the same as the above, except for the systematic sky subtraction error (no error is assumed here).
Fig.4. Comparison of the limiting magnitude (S/N=5 with a 900-sec exposure) for continuum at 415 nm (left), 796 nm (middle), and 1100 nm (right), as a function of the separation angle between the object and the moon. The difference in the magnitude from the dark night case (i.e. new moon) is plotted. At a separation angle lower than 60 deg., calculations were performed for various combinations of the zenith angles of the moon and the object keeping the separation angle constant, and the variation among the individual results is indicated by the vertical stretch of the plot at a given separation angle. In the red arm, the effects in the MR mode are also plotted with a small horizontal shift.
Fig.5. The same as Fig. 4, but for a emission line with sigma=70 km/s. The ratio of the limiting flux to a dark night is plotted.