Introduction

• Generate (and display) a photometric Spectral Energy Distribution (SED)
• Study the multi-wavelength (radio, optical, X-ray) emission from the lobes and the cluster
• Identify red objects in the field
• Study the properties of individual galaxies in the cluster

The science case is based on the VOTECH Science Framework Document. The reader is referred to this document for more details on the underlying scientific drivers.

In order to effectively follow this workflow, some knowledge of basic functionalities of VO tools such as Aladin, topcat, and VOSpec may be helpful. Please, refer to the EURO-VO recipes user manual for more information.

Set-up

1. launch AstroScope from the AstroGrid Workbench
   
   The AstroGrid Workbench main panel.

2. launch topcat
3. register topcat in the PLASTIC hub, through: Interop/Register with PLASTIC

Data Selection

1. Search on Position or Object Name=3C295, Search Radius=0.01, Catalogues=Yes, Images=No, Spectra=No
   
   The results of a query in AstroScope on 3C295.

2. For each of the following catalogues:
   • Green Bank 6-cm (GB6) Radio
   • Two Micron All Sky Survey (2MASS) [0.001 deg]
   • SDSS Data Release 5 (DR5) [0.001 deg]
   • RASS ROSAT All Sky Survey
   • Chandra Xassist Source List
   • Integral Reference Catalogue
   do the following:
   • select the closest catalogue entry to the (resolved) nominal position of 3C295, as indicated by the distance estimator in AstroScope
     
     The SDSS catalogue entries associated to 3C295 in AstroScope.

   • send the catalogue entry to PLASTIC, by clicking with the right mouse button on the asterisk (*) box and choosing to Topcat
     
     The main topcat window. The SDSS catalogue entries corresponding to 3C295 have been sent ("broadcasted") to topcat through the PLASTIC hub.

   • save each catalogue as VOTable (tabledata)
   The search radius can be the default [0.01 deg], except for SDSS and 2MASS (see values in square brackets above), to avoid that too many entries appear.

Data manipulation

1. Photometric measurements in the selected catalogue come in different formats and units. Some manipulation is required before the SED can be displayed.
   • magnitudes need to be converted in fluxes. Generate a new flux density column it in the following way:
     • by applying the formula: Flux = F_0 * pow(10,-2.5/m) for 2MASS magnitudes, where m is the magnitude in band H, J, K, and F_O is the flux density for 0 magnitude
     • by applying the intrinsic AB magnitude to flux conversion function in TOPCAT for SDSS
       
       The topcat panel, allowing to define a new synthetic column in a table. The intrinsic function to convert from magnitude to fluxes is being used.

     • by dividing the flux by a median bandpass wavelength for the X-ray photometric points
   • one needs to generate explicitly a new column with the "frequency/wavelength" value:
     • GB6 -> 5E+09 (Hz)
     • 2MASS (J) -> 1.235E-06 (m)
     • 2MASS (H) -> 1.662E-06 (m)
     • 2MASS (K) -> 2.159E-06 (m)
     • SDSS (u) -> 3551 (Å)
     • SDSS (g) -> 4686 (Å)
     • SDSS (r) -> 6165 (Å)
     • SDSS (i) -> 7481 (Å)
     • SDSS (z) -> 8931 (Å)
     • RASS -> 2.42E17 (Hz)
     • Chandra -> 3.63E17 (Hz)
   • one needs to generate one VOTable for each photometric point one wants to display in VOSpec. This can be conveniently done by highlighting only the "frequency/wavelength" column through the topcat Table Columns panel, and saving the file.
     
     The topcat window listing all the columns in a catalogue (SDSS in the example). By selecting a sub-set of columns in this panel (using the tick boxes under the Visible column) one can create a smaller version of the original file.

SED display

1. The photometric SED can be displayed in VOSpec by reading each of the files produced in the previous step. Before the photometric point is actually displayed, a panel asks for the column where the X- and Y-axis are defined, and their units.
   
   3C295 photometric SED displayed by VOSpec.

Images display

1. launch Aladin [automatically PLASTICized]
2. launch the MERLINImager from the AstroGrid Workbench Task Launcher
   
   AstroGrid Workbench Task Launcher panel.
   
   MERLINImager selection panel.

3. generate three images:
   • small field-of-view 5GHz image (Freq=4850, Ftol=350, Image Size=5, Resolution = 0.1)
   • small field-of-view 1.4GHz image (Freq=1400, Ftol=30, Image Size=5, Resolution = 0.1)
   • large field-of-view 1.4GHz image (Freq=1400, Ftol=30, Image Size=200, Resolution = 0.25)
   
   MERLINImager input parameters selection panel.

4. send them to Aladin via MERLINImages -> to Aladin
   
   Radio images produced by the MERLINImager broadcasted to Aladin.

5. search in the Aladin All VO the available images for 3C295, and select the following ones:
   • Chandra (1.2'x1.2')
   • HST (F555W)
   • HST (F702W)
6. perform an astrometric correction of the HST image, by:
   • run the option Tools .../Image astrometric re-calibration with the following parameters:
     • Coordinates (J2000): 14 11 20.6 +52 12 09 (e.g., the nominal coordinates of the radio galaxy in NED)
     • Corresp. pos. (x,y): the pixel coordinates of the closest source in the HST image
7. generate an RGB image of the small field-of-view radio images and the F702W/HST image through the rgb Aladin function
   RGB composite image of MERLIN (red, green) and HST (blue) images of 3C295, without (left) and with (right) astrometric correction. The pink cross indicates the nominal position of the radio active nucleus.

8. generate contours of the Chandra image (~20, more thickly spaced towards the X-ray centroid) and superpose them to the large field-of-view radio image
   
   Merlin (greyscale) and Chandra/ACIS (contours) images of the 3C295 nucleus.

Identification of extreme red sources

1. load the following catalogues in Aladin (from the Vizier menu):
   • II/276 (SDSS photometric catalogue)
   • II/246 (2MASS)
   • 2MASS All-Sky Extended Source Catalogue
   
   List of VIZIER catalogues including an entry for 3C295 (from the all VO panel in Aladin

2. Cross-match the SDSS and the 2MASS catalogue (Tools/Catalogue cross ...)
   
   Catalogue cross-match panel in Aladin

3. Broadcast the correlation catalogue to topcat [tip: use the menu activated by the small antenna icon at the right bottom of the Aladin window]
4. Create the following additional columns in topcat:
   • J-K
   • r-g
   • i-z
5. Plot J_K vs. r-g
6. Configure the plot axis (Plot/Configure axis) to show the quadrant where both colors are >0.5 (see, e.g., Davoodi et al., 2006, MNRAS, 371, 1113)
   
   topcat J-K versus r-g plot, where only the sources for which both colors are >0.5 are shown.

7. Select (Subsets/Draw subset region) the source with the highest but one IR color
8. Broadcast 1-source sub-table back to Aladin (Interop/Send table to ...)
9. load r and g SDSS images from the all VO Aladin panel. The red source nicely coincide with a galaxy in the SDSS [tip: in order to see the faint diffuse emission, one need to modify the contrast through the "pixel" button in Aladin. A logarithmic scale is advisable].
10. Enjoy the results
    
    Multipanel Aladin view, showing all the images used in this workflow.

Color selection via a pre-canned workflow: Colour Cutter

1. Select Data Analysis/Science Workflows in the AstroGrid Workbench
   
   Science Workflows launcher in the AstroGrid Workbench.

2. After log-in, select Colour Cutter in the workflow selection panel
3. Define the proper parameters in the Task Editor user interface:
   • Sky Region -> 212.83, 52.20, 1.0
   • IR coluor limit -> j_m, k_m, 1.0
   • Optical catalogue -> SDSS DR-5
   • Optical colour limit -> g,r,0.5
   
   Colour Cutter input parameter set-up.

4. send the output catalogue to Aladin via [right mouse button] merged_output -> to Aladin