Illustrated aXeSIM examples

In this chapter we show some examples for aXeSIM simulations. In a step-by-step approach, we present the simulation input, the aXeSIM task executed and display the simulation results. In order to illustrate all possibilities of aXeSIM, we start with very simple examples and finish with rather complex simulations that expose all options in aXeSIM.

Working with aXeSIM frequently requires modifying or creating ASCII tables in the SEXtractor catalogue format. The python module AstroAsciiData (distributed at: http://www.stecf.org/software/PYTHONtools/astroasciidata/) is very convenient to do this interactively or within small python scripts.

Example 1

Simulation details

instrument:	WFC3/IR G102
# of objects:	1
object spectrum:	defined by one magnitude value
object brightness:	defined by one magnitude value
flux normalization:	not required
object shape	Gaussian
default extraction	YES

Directories and files before the simulation

example_1>ls -R
.:
CONF  DATA  OUTPUT  OUTSIM

./CONF:
wfc3_abscal_IRg102_0th_sens.fits  wfc3_abscal_IRg102_2nd_sens.fits
wfc3_abscal_IRg102_1st_sens.fits  WFC3.IR.G102.TV2_sim.conf

./DATA:
example_1_MOT.dat

./OUTPUT:

./OUTSIM:
example_1>setenv AXE_IMAGE_PATH ./DATA
example_1>setenv AXE_OUTPUT_PATH ./OUTPUT
example_1>setenv AXE_CONFIG_PATH ./CONF
example_1>setenv AXE_OUTSIM_PATH ./OUTSIM

The Model Object Table example_1_MOT.dat

# 1 NUMBER
# 2 X_IMAGE
# 3 Y_IMAGE
# 4 A_IMAGE
# 5 B_IMAGE
# 6 THETA_IMAGE
# 7 MAG_F1248W
  1  512.0  512.0  2.0  1.0 30.5 19.5

The simulation command

--> simdata incat='example_1_MOT.dat' config='WFC3.IR.G102.TV2_sim.conf' extraction='YES'

Figure 3.1: The results of the first simulation: the simulated slitless image in the left panel left panel and the default-extracted spectrum (solid, red line) in comparison to the input ``spectrum" (dashed, blue line) in the right panel.

Directories and files after the simulation

example_1>ls -R
.:
CONF  DATA  OUTPUT  OUTSIM

./CONF:
wfc3_abscal_IRg102_0th_sens.fits  wfc3_abscal_IRg102_2nd_sens.fits  WFC3.IR.G102.TV2_sim.conf.simul
wfc3_abscal_IRg102_1st_sens.fits  WFC3.IR.G102.TV2_sim.conf

./DATA:
example_1_MOT.dat

./OUTPUT:

./OUTSIM:
example_1_MOT_slitless_2.SPC.fits  example_1_MOT_slitless_2.STP.fits  example_1_MOT_slitless.fits

7#7

The simulation results

As already mentioned in Sect. 1.2, aXeSIM collects all output in the directory AXE_OUTSIM_PATH, which is ./OUTSIM in this example. This result comprises in detail:

• the simulated slitless image example_1_MOT_slitless.fits
• the extracted spectrum example_1_MOT_slitless_2.SPC.fits
• the stamp file example_1_MOT_slitless_2.STP.fits

Figure 3.1 displays the main results of the example, the simulated slitless image (left) and the extracted spectrum (right). The blue line marks the ``input spectrum'', which is a flat spectrum at the value 8#8 corresponding to the given AB-magnitude ( 9#9).

Some annotations

• The dispersed image in Fig. 3.1 shows, besides the central first order,also the zeroth order (left) and second order(right) slitless spectrum.
• The extracted spectrum appears to differ in flux level from the input spectrum (solid and dashed lines in Fig. 3.1). The quantitative difference is explained by the finite extraction width (which corresponds to the aXe parameter 10#10).
• An observant reader may have noticed that, after performing the example simulation, there is, next to the configuration file WFC3.IR.G102.TV2_sim.conf, a file with the similar name WFC3.IR.G102.TV2_sim.conf.simul. aXeSIM has created and used in the simulations this variant of the original configuration file. The new configuration file contains a keyword for the telescope area (necessary for generating direct images), which has the HST collecting area as default. Moreover the new configuration file always marks the extensions 1, 2 and 3 as science-, error- and dq-extension. As a consequence, aXeSIM simulates only images with one science extension, and for simulating ACS/WFC and WFC3/UVIS grism images the two chips must be treated separately. Concerning the essential quantities, the descriptions of trace and dispersion of the various orders, there is no difference between the original and the new configuration file, and both can be used to extract spectra from the simulated slitless images (the original one may need to be corrected to address the correct image extension).
• A close inspection of the Model Object Table reveals that during the simulation some additional columns were appended. For internal reasons these added columns are necessary for running aXeSIM. However these modifications to the Model Object Table never change essential simulation input given by the user, and repeating a simulation with the modified table will yield the identical simulated images.

Example 2

Simulation details

instrument:	WFC3/IR G102
# of objects:	1
object spectrum:	spectral energy distribution defined by several magnitude values
object brightness:	defined by several magnitude values
flux normalization:	not required
object shape	template image
default extraction	YES
direct image	YES, filter: wfc3_ir_f105w_tpass_m01.dat

Directories and files before the simulation

~>ls -R
.:
CONF  DATA  OUTPUT  OUTSIM  SIMDATA  template_images.lis

./CONF:
wfc3_abscal_IRg102_0th_sens.fits  wfc3_abscal_IRg102_2nd_sens.fits
wfc3_abscal_IRg102_1st_sens.fits  WFC3.IR.G102.TV2_sim.conf

./DATA:
example_2_MOT.dat

./OUTPUT:

./OUTSIM:

./SIMDATA:
spiral_1.fits            wfc3_ir_f105w_tpass_m01.dat
WFC3_IR_1400nm_psf.fits  WFC3_UVIS_350nm_psf.fits
WFC3_IR_950nm_psf.fits

~>setenv AXE_IMAGE_PATH ./DATA
~>setenv AXE_OUTPUT_PATH ./OUTPUT
~>setenv AXE_CONFIG_PATH ./CONF
~>setenv AXE_SIMDATA_PATH ./SIMDATA
~>setenv AXE_OUTSIM_PATH ./OUTSIM

The Model Object Table example_2_MOT.dat

# 1  NUMBER
# 2  X_IMAGE
# 3  Y_IMAGE
# 4  A_IMAGE
# 5  B_IMAGE
# 6  THETA_IMAGE
# 7  MAG_F432W
# 8  MAG_F592W
# 9  MAG_F769W
# 10 MAG_F906W
# 11 MAG_F1123W
# 12 MAG_F1603W
# 13 MODIMAGE
  269  312.0  512.0  8.0  8.0  90.0  22.984  22.163  21.890  21.807  22.027  21.788 4

The Image Template List template_images.lis

~> more template_images.lis
WFC3_IR_1400nm_psf.fits
WFC3_IR_950nm_psf.fits
WFC3_UVIS_350nm_psf.fits
spiral_1.fits

The simulation command

--> simdata incat='example_2_MOT.dat' config='WFC3.IR.G102.TV2_sim.conf'
inlist_ima='template_images.lis' tpass_direct='wfc3_ir_f105w_tpass_m01.dat'

Figure 3.2: The results of the second simulation: the direct image (left) and the slitless image (right). Both images are displayed with a logarithmic lookup table to enhance the contrast.

Directories and files after the simulation

~> ls -R
.:
CONF  DATA  gaga.txt  OUTPUT  OUTSIM  SIMDATA  template_images.lis

./CONF:
wfc3_abscal_IRg102_0th_sens.fits  WFC3.IR.G102.TV2_sim.conf
wfc3_abscal_IRg102_1st_sens.fits  WFC3.IR.G102.TV2_sim.conf.simul
wfc3_abscal_IRg102_2nd_sens.fits

./DATA:
example_2_MOT.dat  template_images.fits

./OUTPUT:

./OUTSIM:
example_2_MOT_direct.fits          example_2_MOT_slitless.fits
example_2_MOT_slitless_2.SPC.fits  template_images.fits
example_2_MOT_slitless_2.STP.fits

./SIMDATA:
spiral_1.fits            wfc3_ir_f105w_tpass_m01.dat
WFC3_IR_1400nm_psf.fits  wfc3_ir_f105w_tpass_m01.fits
WFC3_IR_950nm_psf.fits   WFC3_UVIS_350nm_psf.fits

Figure 3.3: Left panel: Comparison between the default extracted spectrum (red, solid line) and the input spectrum (dashed, blue line), a spectral energy distribution defined by the AB-magnitude values. Right panel: The image template.

The simulation results

In the Model Object Table, the column MODIMAGE contains the value 4, thus pointing to the fourth entry in the Image Template List. This entry, named spiral_1.fits, is then used as the image template when simulating the direct and dispersed image. The spiral structure of the template image is clearly visible in Figure 3.2, which shows the direct image and the dispersed image on the left and right side, respectively.

In total, the results comprise:

• the simulated slitless image example_2_MOT_slitless.fits
• the simulated direct image example_2_MOT_direct.fits
• the extracted spectrum example_1_MOT_slitless_2.SPC.fits
• the stamp file example_1_MOT_slitless_2.STP.fits
• the Model Images template_images.fits

The Model Images template_images.fits is a multi-extension fits image which contains all template images listed in template_images.lis and replicates user input. aXeSIM needs the template images in this compact form and generates this file, hence it is considered as part of the result.

Figure 3.3 shows a comparison of the input spectrum and the default extracted spectrum in the left panel and the image template in the right panel. The input spectral energy distribution is defined by the AB-magnitudes and a linear interpolation in between the values.

Some annotations

• The simulated object and brightness was taken from the NICMOS UDF catalogue published in [7]. The UDF was observed in the ACS filters F425W, F606W, F775W, F814W, F850LP and the NICMOS filters F110W and F160W. However in the column names we have used the pivot wavelength of the filter and not the less accurate filter name to give the characteristic wavelength of the filter.
• The total passband (see Sect. 5.3 for a definition) of the direct image was given as the ASCII table wfc3_ir_f105w_tpass_m01.dat and transformed to the equivalent fits file wfc3_ir_f105w_tpass_m01.fits in aXeSIM.
• The default extraction of aXeSIM uses, like aXe, the columns A_IMAGE and B_IMAGE in the object table to determine the extraction width. For the definitely extended object in the image template (see Fig. 3.3) the tentative value 8.0 was given. An independent SExtractor run on the direct image would deliver the correct value. The Gauss parameters (A_IMAGE, B_IMAGE and THETA_IMAGE) are not used when making the simulated images, since the object shape is defined with a template image.
• There are a number of reasons why the default extracted spectrum does not completely coincide with the input spectrum in Fig. 3.3. As in the first example, there is a wiggle on the long wavelength end due to the object extent and the drop in sensitivity. Also when using image templates, care must be taken to put the sources into the centre of the template. aXeSIM puts the centre of the template image at the nominal position given in the Model Object Table, and the default extraction also uses this position for the extraction. An off-center template source results in a wavelength shift between the simulation and the extraction, which can translate into a flux difference between the simulated and the extracted spectrum. Running SExtractor on the direct image and using the catalogue in an aXe spectral extraction would avoid this problem

Example 3

Simulation details

instrument:	WFC3/IR G102
# of objects:	6
object spectrum:	high resolution spectra at different redshift
object brightness:	defined at 11#11
flux normalization:	in 12#12
object shape	template image
default extraction	YES
direct image	YES, filter: wfc3_ir_f110w_tpass_m01.dat

Directories and files before the simulation

example_3> ls -R
.:
CONF  DATA  OUTPUT  OUTSIM  SIMDATA  template_images.lis  template_spectra.lis

./CONF:
wfc3_abscal_IRg102_0th_sens.fits  WFC3.IR.G102.TV2_sim.conf
wfc3_abscal_IRg102_1st_sens.fits
wfc3_abscal_IRg102_2nd_sens.fits

./DATA:
example_3_MOT.dat

./OUTPUT:

./OUTSIM:

./SIMDATA:
s0_template.fits      WFC3_IR_1400nm_big_psf.fits  wfc3_ir_f105w_tpass_m01.dat
starb1_template.fits  WFC3_IR_1400nm_psf.fits      wfc3_ir_f110w_tpass_m01.dat
starb2_template.fits  WFC3_IR_950nm_big_psf.fits   WFC3_UVIS_350nm_psf.fits
starb3_template.fits  WFC3_IR_950nm_psf.fits

example_3>setenv AXE_IMAGE_PATH ./DATA
example_3>setenv AXE_OUTPUT_PATH ./OUTPUT
example_3>setenv AXE_CONFIG_PATH ./CONF
example_3>setenv AXE_OUTSIM_PATH ./OUTSIM
example_3>setenv AXE_SIMDATA_PATH ./SIMDATA

The Model Object Table example_3_MOT.dat

# 1  NUMBER
# 2  X_IMAGE
# 3  Y_IMAGE
# 4  A_IMAGE
# 5  B_IMAGE
# 6  THETA_IMAGE
# 7  MAG_F1155W
# 8  SPECTEMP
# 9  Z
# 10 MODIMAGE
    1  500.0  100.0  1.5  1.5  90.0  20.0     3  0.5     3
    2  500.0  120.0  1.5  1.5  90.0  20.0     3  0.7     3
    3  500.0  140.0  1.5  1.5  90.0  20.0     3  0.9     3
    4  500.0  160.0  1.5  1.5  90.0  20.0     3  1.1     3
    5  500.0  180.0  1.5  1.5  90.0  20.0     3  1.3     3
    6  500.0  200.0  1.5  1.5  90.0  20.0     3  1.5     3

The Image Template List template_images.lis

~> more template_images.lis
WFC3_IR_1400nm_big_psf.fits
WFC3_IR_1400nm_psf.fits
WFC3_IR_950nm_big_psf.fits
WFC3_IR_950nm_psf.fits
WFC3_UVIS_350nm_psf.fits

The Spectrum Template List template_spectra.lis

~> more template_spectra.lis
s0_template.fits
starb1_template.fits
starb2_template.fits
starb3_template.fits

13#13

The simulation command

--> simdata incat='example_3_MOT.dat' config='WFC3.IR.G102.TV2_sim.conf'
utput_root='StarBurst' inlist_spec='template_spectra.lis' tpass_flux='1040,1060'
inlist_ima='template_images.lis' exptime_disp=2000.0 bck_flux_disp=1.0
tpass_direct='wfc3_ir_f110w_tpass_m01.dat' exptime_dir=100.0 bck_flux_dir=0.5

Directories and files after the simulation

~> ls -R
.:
CONF  DATA  OUTPUT  OUTSIM  SIMDATA  template_images.lis  template_spectra.lis

./CONF:
wfc3_abscal_IRg102_0th_sens.fits  WFC3.IR.G102.TV2_sim.conf
wfc3_abscal_IRg102_1st_sens.fits  WFC3.IR.G102.TV2_sim.conf.simul
wfc3_abscal_IRg102_2nd_sens.fits

./DATA:
example_3_MOT.dat  StarBurst_images.fits  StarBurst_spectra.fits

./OUTPUT:

./OUTSIM:
StarBurst_direct.fits  StarBurst_slitless_2.SPC.fits  StarBurst_slitless.fits
StarBurst_images.fits  StarBurst_slitless_2.STP.fits  StarBurst_spectra.fits

./SIMDATA:
s0_template.fits      WFC3_IR_1400nm_big_psf.fits  wfc3_ir_f105w_tpass_m01.dat
starb1_template.fits  WFC3_IR_1400nm_psf.fits      wfc3_ir_f110w_tpass_m01.dat
starb2_template.fits  WFC3_IR_950nm_big_psf.fits   wfc3_ir_f110w_tpass_m01.fits
starb3_template.fits  WFC3_IR_950nm_psf.fits       WFC3_UVIS_350nm_psf.fits

Figure 3.4: The results of the third simulation: the direct image (left) and the slitless image (right). Only a cutout image of 1#1 pix and 2#2pix around the simulated objects is shown for the direct and slitless image, respectively.

The simulation results

The six objects simulated in this example all use the same model image, which is a WFC/IR PSF at 14#14. All objects are based on the identical high resolution spectral template starb2_template.fits, however the template is shifted to different redshift values prior to simulating the images.

Figure 3.4 shows the direct image and the slitless image in the left and right panel, respectively. As the redshift increases from bottom to top, the emission lines are shifted to longer wavelengths (to the right).

In total, the results comprise:

• the direct image StarBurst_direct.fits
• the slitless image StarBurst_slitless.fits
• the Model Images StarBurst_images.fits
• the Model Spectra StarBurst_spectra.fits
• the default extracted spectra StarBurst_slitless_2.SPC.fits
• the stamp images StarBurst_slitless_2.STP.fits

All results start with the string given in the simdata parameter output_root. Before simulating the direct and slitless images, the template spectra are shifted in redshift and in flux. These spectra are stored in the Model Spectra file StarBurst_spectra.fits. The column MODSPEC, which simdata appends to the Model Object Table, contains for each object the corresponding extension in the Model Spectra file.

Figure 3.5 shows a comparison between the default extracted spectra from StarBurst_slitless_2.SPC.fits and their corresponding extension in StarBurst_spectra.fits for all objects in this example. The blue, dashed line marks the template, and the red, solid line the extracted spectrum. The green point marks the wavelength and normalization flux value, the black bar indicates the wavelength interval used for the flux normalization.

Figure 3.5: Comparison between the default extracted spectrum (red, solid line) and the simulated spectrum (dashed, blue line). The green point marks the flux normalization value, and the black bar the wavelength interval for the flux normalization.

Some annotations

• Since exposure time values were specified for the slitless and the direct image, these images contain noise according to a simple noise model which takes into account photon noise (from sources and sky background) and readout noise (given in the configuration file). In addition, this noise model is used to generate the error extension of the slitless and direct images. The noise is clearly visible in the background of Fig. 3.4 and the continuum of the extracted spectra in Fig. 3.5.
• Background levels specified in the simdata parameters (bck_flux_disp and bck_flux_disp) are added to the simulated images. However the default spectral extraction is done on a temporary slitless image that had the background removed. Hence the default extraction in aXeSIM is always perfect concerning the sky background removal.
• When executing the task simdata with a long list of parameters as in this example, it is good practice not enter the command line directly but to work with a small PyRAF or cl script that contains the entire command.
• Due to the narrow passband chosen for flux normalization, the continuum levels of the simulated objects vary significantly. At the redshift of object #4, the average flux in normalization passband is very high due to the strong emission line (see Fig. 3.5). This results in a large normalization factor and a lower continuum level of this source (see object traces in Fig. 3.4) as compared to the other objects.

Example 4

Simulation details

instrument:	WFC3/IR G141
# of objects:	14
object spectrum:	high resolution spectra and spectral energy distributions
object brightness:	defined at 11#11
flux normalization:	filter: wfc3_ir_f105w_tpass_m01.dat
object shape	template images and Gaussian shapes
default extraction	YES
direct image	YES, filter: wfc3_ir_f105w_tpass_m01.dat

Directories and files before the simulation

example_4>ls -R
.:
CONF  DATA  OUTPUT  OUTSIM  SIMDATA  template_images.lis  template_spectra.lis

./CONF:
wfc3_abscal_IRg141_0th_sens.fits  wfc3_abscal_IRg141_3rd_sens.fits
wfc3_abscal_IRg141_1st_sens.fits  WFC3.IR.G141.TV2_sim.conf
wfc3_abscal_IRg141_2nd_sens.fits

./DATA:
example_4_MOT.dat

./OUTPUT:

./OUTSIM:
ObjMix_direct.fits  ObjMix_slitless_2.SPC.fits  ObjMix_slitless.fits
ObjMix_images.fits  ObjMix_slitless_2.STP.fits  ObjMix_spectra.fits

./SIMDATA:
Mann_E.dat            starb3_template.fits         WFC3_IR_950nm_psf.fits
Mann_S0.dat           WFC3_IR_1400nm_big_psf.fits  wfc3_ir_f105w_tpass_m01.dat
starb1_template.fits  WFC3_IR_1400nm_psf.fits      wfc3_ir_f110w_tpass_m01.dat
starb2_template.fits  WFC3_IR_950nm_big_psf.fits   WFC3_UVIS_350nm_psf.fits

example_4>setenv AXE_IMAGE_PATH ./DATA
example_4>setenv AXE_OUTPUT_PATH ./OUTPUT
example_4>setenv AXE_CONFIG_PATH ./CONF
example_4>setenv AXE_OUTSIM_PATH ./OUTSIM
example_4>setenv AXE_SIMDATA_PATH ./SIMDATA

The Model Object Table example_2_MOT.dat after a simdata run

Unlike the previous examples, we have listed here the Model Object Table as it looks after the execution of simdata. During the simulations, the columns #11-#16 were appended. No original table entry in #1-#10 was modified.

# 1  NUMBER
# 2  X_IMAGE
# 3  Y_IMAGE
# 4  A_IMAGE
# 5  B_IMAGE
# 6  THETA_IMAGE
# 7  MAG_F1155W
# 8  SPECTEMP
# 9  Z
# 10 MODIMAGE
# 11 MODSPEC
# 12 A_WORLD
# 13 B_WORLD
# 14 THETA_WORLD
# 15 X_WORLD
# 16 Y_WORLD
    1  450.0  170.0  1.6  1.3  270.0  21.0     0  0.0     0     0  1.600000e+00  1.300000e+00  2.700000e+02  5.320378e+01 -2.778795e+01
    2  460.0  110.0  1.5  1.2  45.0  21.0     0  0.0     0     0  1.500000e+00  1.200000e+00  4.500000e+01  5.320448e+01 -2.778852e+01
    3  450.0  130.0  1.9  1.5 -70.0  21.0     5  2.0     3     1  1.900000e+00  1.500000e+00 -7.000000e+01  5.320431e+01 -2.778826e+01
    4  450.0  80.0  1.5  1.5  90.0  21.0     0  0.0     0     0  1.500000e+00  1.500000e+00  9.000000e+01  5.320497e+01 -2.778865e+01
    5  500.0  95.0  1.5  1.5  90.0  20.0     3  0.5     1     2  1.500000e+00  1.500000e+00  9.000000e+01  5.320429e+01 -2.778908e+01
    6  500.0  120.0  1.5  1.5  90.0  20.0     0  0.7     1     0  1.500000e+00  1.500000e+00  9.000000e+01  5.320396e+01 -2.778888e+01
    7  650.0  105.0  2.5  1.5   0.0  21.5     0  0.0     0     0  2.500000e+00  1.500000e+00  0.000000e+00  5.320272e+01 -2.779064e+01
    8  350.0  150.0  1.5  1.0  90.0  21.5     0  0.0     0     0  1.500000e+00  1.000000e+00  9.000000e+01  5.320500e+01 -2.778701e+01
    9  550.0  220.0  1.5  1.5  10.0  21.5     0  0.0     0     0  1.500000e+00  1.500000e+00  1.000000e+01  5.320217e+01 -2.778866e+01
   10  50.0  105.0  1.5  1.5  135.0  21.5     0  0.0     0     0  1.500000e+00  1.500000e+00  1.350000e+02  5.320847e+01 -2.778407e+01
   11  510.0  140.0  1.5  1.5  90.0  20.0     2  0.9     1     3  1.500000e+00  1.500000e+00  9.000000e+01  5.320360e+01 -2.778884e+01
   12  490.0  160.0  1.5  1.5  90.0  20.0     5  2.1     1     4  1.500000e+00  1.500000e+00  9.000000e+01  5.320353e+01 -2.778846e+01
   13  570.0  177.0  1.5  1.5  90.0  20.0     4  1.3     0     5  1.500000e+00  1.500000e+00  9.000000e+01  5.320254e+01 -2.778921e+01
   14  400.0  212.0  1.5  1.5  90.0  20.0     1  1.5     1     6  1.500000e+00  1.500000e+00  9.000000e+01  5.320371e+01 -2.778707e+01

Figure 3.6: The image results of the fourth simulation: the slitless image (left) and the direct image. Only coutouts of 3#3pix and 4#4pix centered on the objects are shown.

The Image Template List template_images.lis

-> more template_images.lis
WFC3_IR_1400nm_big_psf.fits
WFC3_IR_1400nm_psf.fits
WFC3_IR_950nm_big_psf.fits
WFC3_IR_950nm_psf.fits
WFC3_UVIS_350nm_psf.fits

The Spectrum Template List template_spectra.lis

-> more template_spectra.lis
Mann_S0.dat
starb1_template.fits
starb2_template.fits
starb3_template.fits
Mann_E.dat

The simulation command

--> simdata incat='example_4_MOT.dat' config='WFC3.IR.G141.TV2_sim.conf' output_root='ObjMix'
inlist_spec='template_spectra.lis' tpass_flux='wfc3_ir_f110w_tpass_m01.dat'
inlist_ima='template_images.lis' exptime_disp=2000.0 bck_flux_disp=1.4
tpass_direct='wfc3_ir_f105w_tpass_m01.dat' exptime_dir=100.0 bck_flux_dir=0.7

Directories and files after the simulation

example_4>ls -R
.:
CONF  DATA  OUTPUT  OUTSIM  SIMDATA  template_images.lis  template_spectra.lis

./CONF:
wfc3_abscal_IRg141_0th_sens.fits  wfc3_abscal_IRg141_3rd_sens.fits
wfc3_abscal_IRg141_1st_sens.fits  WFC3.IR.G141.TV2_sim.conf
wfc3_abscal_IRg141_2nd_sens.fits  WFC3.IR.G141.TV2_sim.conf.simul

./DATA:
example_4_MOT.dat  ObjMix_images.fits  ObjMix_spectra.fits

./OUTPUT:

./OUTSIM:
ObjMix_direct.fits  ObjMix_slitless_2.SPC.fits  ObjMix_slitless.fits
ObjMix_images.fits  ObjMix_slitless_2.STP.fits  ObjMix_spectra.fits

./SIMDATA:
Mann_E.dat            WFC3_IR_1400nm_big_psf.fits  wfc3_ir_f105w_tpass_m01.fits
Mann_S0.dat           WFC3_IR_1400nm_psf.fits      wfc3_ir_f110w_tpass_m01.dat
starb1_template.fits  WFC3_IR_950nm_big_psf.fits   WFC3_UVIS_350nm_psf.fits
starb2_template.fits  WFC3_IR_950nm_psf.fits
starb3_template.fits  wfc3_ir_f105w_tpass_m01.dat

Figure 3.7: Comparison between the default extracted spectra (red, solid line) and the simulated spectrum (dashed, blue line) for selected objects.

The simulation results

Technically, this example only shows cases which had been already presented in the previous examples. The main issue here is to illustrate a mix of object definitions with various complexity.

The simplest object characterization using Gaussian shapes and a spectral energy distribution using at least one AB-magnitude value is always possible (see objects #1, #2, #7-10) and achieved by entering ``0'' in the columns SPECTEMP and MODIMAGE. Beyound that it is possible to mix these simple objects with objects that have a template image (#6) with (e.g. #3, #5, #11) or without (#13) a high resolution template spectrum.

A simulation as shown here represents a typical mix of some primary targets together with many other, rather poorly defined surrounding objects.

In total, the results comprise:

• the direct image ObjMix_direct.fits
• the slitless image ObjMix_slitless.fits
• the Model Images ObjMix_images.fits
• the Model Spectra ObjMix_spectra.fits
• the default extracted spectra ObjMix_slitless_2.SPC.fits
• the stamp images ObjMix_slitless_2.STP.fits

Some annotations

• The spectral templates can be given as fits tables and ASCII lists. Even a mix of these two formats as in this example is accepted.
• To see which extension in the Model Spectra ObjMix_spectra.fits corresponds to which simulated and extracted object, check the Model Object Table (here example_2_MOT.dat) after the simulations. The column MODSPEC (here #11) contains the corresponding extension number of the object in ObjMix_spectra.fits. When e.g. simulating object #3, the already redshifted and flux scaled extension 1 of example_2_MOT.dat was used as input spectrum. The panel for Object #5 in Fig. 3.7 was done plotting ObjMix_slitless_2.SPC.fits[beam_5A] over ObjMix_spectra.fits[2]. 15#15 in this column means no spectral template, hence a spectral energy distribution is used as spectral input.
• Fig. 3.7, object #5 is an example of the extrapolation (constant in 16#16) of a spectrum beyond the defined range shown with the blue, dotted line.
• For some objects in Fig. 3.7 the extracted flux seems to exceed the input spectra. As Fig. 3.6 shows, contamination (the mutual overlap of spectra) could be an issue here.
• Using the passband of an existing filter is natural if observational data in this filter already exists and the simulation is perhaps even based on an according SExtractor catalogue. Defining a boxcar passband as in Example 3.3 is more appropriate for purely synthetic data, or in cases where the spectral template does not completely cover the intended normalization passband (see box on page ).