Spectroscopy with PACS M82 PACS line imaging from the SHINING team (Contursi et al First Results workshop talk) Phil Appleton and Dario Fadda for the PACS Team

Important Resources NHSC Proposal Planning Page – NHSC HELPDESK – links to AOT Release notes for each spectrometer mode—very useful. – links to HSpot and Observer Manuals – links to other calibration documents NHSC Proposal Planning Page – NHSC HELPDESK – links to AOT Release notes for each spectrometer mode—very useful. – links to HSpot and Observer Manuals – links to other calibration documents

Line Spectroscopy Chop/Nodding (Phil Appleton will discuss) – Chop rapidly between two sky position – Targeted “Line” scans or broad “Range/SED” spectroscopy available – Single Pointed or mapping on scale < 4 arcmins Unchopped scans with “off” position (Dario Fadda will discuss) – Allows for targets that cannot be chopped – Line-scans or Range/SED Spectroscopy – Single pointed or mapping on any scale

Chop/Nod Cycle Each line is visited with one up and down scan per repetition Example above shows three lines in simple NodA/Nod B pattern Simple LINE SCAN– GRATING SCANS OVER TARGETED LINE ONLY

Range Scan User can specify the range of the scan Useful for known broad or multiple lines Special version is SED mode where Blue/Red or Green Red bands scanned Range Scan is only mode that allows exploitation of extended second order (see next slide) Range scans can provide broader coverage if there are multiple features User can control the scan range

Order Selection and Line/AOR 1 st is always selected2nd 3rd You can only select in any one AOR either the 2 nd or 3 rd order paired with 1 st order You can only select in any one AOR either the 2 nd or 3 rd order paired with 1 st order You can observe the same line 10 times (10 repetitions) or 5 different lines x 2 repetitions, or as many repetition-lines not exceeding 10 total per AOR. To repeat the whole sequence you can add more cycles. Note that calibration block is run at beginning or AOR. You can observe the same line 10 times (10 repetitions) or 5 different lines x 2 repetitions, or as many repetition-lines not exceeding 10 total per AOR. To repeat the whole sequence you can add more cycles. Note that calibration block is run at beginning or AOR. Either “Blue/RED” or “Green/RED” You can select multiple lines per AOR—for each line scanned you will get “for free” an observation in the blue or red band (e. g. If request 2 nd /1 st ordermodes and you observe [CII]158  m, you wlll “simultaneously” get “blue” observation at 158/2 = 79  m You can select multiple lines per AOR—for each line scanned you will get “for free” an observation in the blue or red band (e. g. If request 2 nd /1 st ordermodes and you observe [CII]158  m, you wlll “simultaneously” get “blue” observation at 158/2 = 79  m Accessible in range/SED mode

For True Point Source Know your position well! Place target at center array and use “Pointed Mode”. Be careful of any avoidance angle constraints (visualize in HSpot) Be aware of distortions (rotation) in footprint of NODA and NOD B –only fully aligned at center of field

Chopped distortion on Large Throw (1, 3, 6 arcmin throw separations) If you suspect your source is not a point-source or you are very unsure of its position to 1-2”, probably best NOT to use POINTED mode, but a fully sample mapping mode. If you suspect your source is not a point-source or you are very unsure of its position to 1-2”, probably best NOT to use POINTED mode, but a fully sample mapping mode. Only the central few pixels are properly aligned for largest (LARGE) chopped throw. Best to use small or medium throw if possible.

Mapping Slightly Extended Sources Chop-Nod Observations First select target Choose which “blue” order? 3 rd +1 st or 2 nd +1 st Note that if you have target lines in all three orders you will need 2 separate AORs Choose a line (manual or from list) –don’t forget to check the box at right! Enter continuum and line flux—saturation will trigger different capacitance—warning in Pacs time est. message Select the Observational Mode Set up the mapping parameters – raster step sizes (follow guidelines of the release ) herschel.esac.esa.int/AOTsReleaseStatus.shtml ) herschel.esac.esa.int/AOTsReleaseStatus.shtml First select target Choose which “blue” order? 3 rd +1 st or 2 nd +1 st Note that if you have target lines in all three orders you will need 2 separate AORs Choose a line (manual or from list) –don’t forget to check the box at right! Enter continuum and line flux—saturation will trigger different capacitance—warning in Pacs time est. message Select the Observational Mode Set up the mapping parameters – raster step sizes (follow guidelines of the release ) herschel.esac.esa.int/AOTsReleaseStatus.shtml ) herschel.esac.esa.int/AOTsReleaseStatus.shtml

Time estimation and S/N calculation” Also warnings for saturation a b c = a+b+c On slew IF ENTERED FLUX TOO LARGE: HSPOT WILL REQUEST A NEW GAIN BY CHANGING CAPACITANCE USUALLY FOR VERY HIGH FLUX > 10^4 Jy! (See PACS Observer Manual) IF ENTERED FLUX TOO LARGE: HSPOT WILL REQUEST A NEW GAIN BY CHANGING CAPACITANCE USUALLY FOR VERY HIGH FLUX > 10^4 Jy! (See PACS Observer Manual)

Cycles versus Repetitions versus complete AOR? One line observation involves a complete up and down scan with the grating—this is called a repetition. 2 repetitions= 2 complete up and down scans If you have one weak line (say [NII]205  m) and one strong one [CII]158  m, you can increase the number of repetitions on the [NII] line at the expense of the brighter line. e. g. 9 reps [NII], and say 1 rep for [CII]. If you need more time on both lines you can then increase the number of cycles. (complete sets of repetitions). A cycle does NOT lead to a repeat of the calibration block. If you request a new AOR you will allows get a new cal block. One line observation involves a complete up and down scan with the grating—this is called a repetition. 2 repetitions= 2 complete up and down scans If you have one weak line (say [NII]205  m) and one strong one [CII]158  m, you can increase the number of repetitions on the [NII] line at the expense of the brighter line. e. g. 9 reps [NII], and say 1 rep for [CII]. If you need more time on both lines you can then increase the number of cycles. (complete sets of repetitions). A cycle does NOT lead to a repeat of the calibration block. If you request a new AOR you will allows get a new cal block.

Repetition v Cycles: large-chop HSpot v5.0.2 (from obs estimate button) C/N Single pointing mode 1 line, 2 repetitons Total time = 952s (on source*=688s, cal=129s) C/N Single pointing 1 line, 2 cycles Total time = 985s (on source 688s) Extra inst. overhead of 33s! C/N Single pointing 1 line, 1 rep, 2 AORs Total time = 2 x 586 (on 688s; cal=2 x 129) = 1172s but you get 2 cal blocks..very inefficient.. C/N Single pointing mode 1 line, 2 repetitons Total time = 952s (on source*=688s, cal=129s) C/N Single pointing 1 line, 2 cycles Total time = 985s (on source 688s) Extra inst. overhead of 33s! C/N Single pointing 1 line, 1 rep, 2 AORs Total time = 2 x 586 (on 688s; cal=2 x 129) = 1172s but you get 2 cal blocks..very inefficient.. * Note HSpot reports “On source” time including the time chopped off! Repetitions have less overhead than cycles.

Some considerations with Chop-Nod Is your source point-like, slightly extended or very extended, or HUGE? (If huge use unchopped scan mode) Choose an appropriate chopper throw small=±0.5 medium =±1.5 large =±3 arcmins Choose the right mapping strategy for your object (Pointed = point source, large-scale map or small map use correct raster step size) Nyquist spatial sampling is best achieved in instrument coordinates rather than sky coordinates. Coverage can be less uniform in sky coordinates because of potential telescope pointing drifts If you want to ratio two lines, best include in same AOR to ensure pixels fall on same place on sky

Example Dither Pattern (large source)

Worked Examples: (AOR Design one or more AOR which provides minimal coverage along major axis of NGC 4565 Map along the major axis of the galaxy NGC 4565 in [OI]63um line with 5 x 2 raster map-covering with 38 x 38 tile size” redshift z = (CHOP-NOD)—left below right below—an unchopped scan—see DARIO Worked Examples: (AOR Design one or more AOR which provides minimal coverage along major axis of NGC 4565 Map along the major axis of the galaxy NGC 4565 in [OI]63um line with 5 x 2 raster map-covering with 38 x 38 tile size” redshift z = (CHOP-NOD)—left below right below—an unchopped scan—see DARIO Chop-nod mapping is limited to instrument plane (chops along z axis). Limited ability to map a feature without multiple AORs = 4.1hrs 3 x (38 x 38” 5 x 2 raster) one line Chop-nod mapping is limited to instrument plane (chops along z axis). Limited ability to map a feature without multiple AORs = 4.1hrs 3 x (38 x 38” 5 x 2 raster) one line Unchopped grating scan in RA/Dec Coords. 38 x 38 “ 20 x 2 raster at orientation = 135 degrees = 3.7 hrs clock time Unchopped grating scan in RA/Dec Coords. 38 x 38 “ 20 x 2 raster at orientation = 135 degrees = 3.7 hrs clock time detector cords z y Unchopped scan can be programmed in sky coords Off position