A study of NGC1068 using TOPCAT for data retrieval (developed by E. Hatziminaoglou)
NGC1068 is a very well studied prototype Seyfert 2 galaxy. The available data cover the entire wavelength range from the X-rays to the far-infrared.
This is a zero-level science case, whose purpose is to familiarise the user with some basic functionalities of the various tools.
- launch the latest versions of TOPCAT (v3.7), Aladin (v7.015a) and SPLAT-VO (3.9.0) and make sure the all "see" each-other (i.e. the icons of Aladin and SPLAT-VO should appear at the bottom right of the TOPCAT window in the field "Clients"; the small antenna at the bottom right of Aladin should be emitting; if the tools have not connected to the SAMP hub, launch the internal hub of TOPCAT or SPLAT-VO)
- search for images of NGC 1068 in the Chandra, HST and 2MASS archives: in the TOPCAT menu, click on VO and select SIA query (SIA stands for Simple Image Access)
- to query all relevant resources simultaneously, type in the keywords field "Chandra HST 2MASS" (without the double quotes) and set the keyword selection to "Or", so that all resources including any of the above keywords in any of the selected Matched Fields are returned; hit "Submit Query"; (tip: you can keep the SIA Query window open by clicking on the pin, on the upper left corner of the window);
- OR query the registry using a single keyword at a time a repeat the prodecude for each resource;
- from the returned list of resources, try the following resources:
- Chandra X-ray Observatory Data Archive
- HST preview images
- 2MASS Large Galaxy Atlas
- note that you can only select one resource at a time;
- in the lower part of the window, fill in the Object Name (NGC1068) and press "Resolve"; this will use the Simbad resolver to get back the coordinates for the galaxy; set the Angular Size into something reasonable (i.e. a few arcsec); press "OK"
- repeat the procedure for each selected resource
- click on each of the loaded catalogues under "Table List" in the main TOPCAT window and then View and select Table Data, or just click on ; try to locate the column that points to the URL of the image files
- to view the table metadata, click on and to view the column names and description, click on
- TOPCAT only shows the finding in the form of tables; we will now visualise the images. In order to do that select a table and next to "Activation Action" on the main TOPCAT window, click on "no action"; select "View URL as image"; in the field "Image Location column" select the column that points to the URL of the image files; and in "Image Viewer" select "Aladin"; then click "OK"
click on any entry of any of the catalogues: the images will be automatically shown on the main Aladin window; to change its name from SAMP to a name of your choice, select "properties" and change the name that appears in the PlaneID field;
- use the "pixel" button (3rd from the bottom) to adjust the image contrast or to change the colour map
- repeat the prodedure with images from the other services
- explore Aladin
- you can view more than one image using the multiview capability of Aladin by selecting any of the options at the bottom of the viewing window: ; you can view 2, 4, 9 or 16, images simultaneously
- once you have loaded three or more images in Aladin, create an RBG image of NGC1068, using a Chandra image as blue, an HST image as green and a 2MASS image as red: from the main menu select Image and then RGB image builder, pick the red, green and blue images from the list of loaded images and "CREATE"
- activate the Simbad automatic pointer in the Tool menu; place the cursor on any of the objects in any of the images and see if these objects have entries in the Simbad database
- look for information on NGC1068 coming from various catalogues: in the "Server Selector" window that opens by File -> Open ...; click on "allVO", tick out the "Images" and "Spectra" and edit the "Detailed list" of Catalogue servers; select a few (e.g. SuperCOSMOS catalogue, 2MASS-PSC, GALEX) and fire the query in a radius of a few arcmin around NGC1068
- select any of the catalogues that have been returned and "Submit"; the objects in the catalogue will appear on top of all the images. If the symbols are too small or the colour is not adequate, highligh the catalogue plane on the Aladin main window and clock on "prop" (2nd button from the bottom) to change the symbols and/or colour
- draw a region on an image including a number of sources from the catalogue; all the selected sources will now appear in a tabular form at the very bottom of the Aladin main window
- right click on the catalogue plane and "Broadcast" it to TOPCAT
- back in TOPCAT, create an RA, Dec scatter plot; on the Aladin window place the cursor on any of the objects of that same catalogue; see how the same object is highligted in the TOPCAT RA, Dec plot
- for any of the catalogues listed under "Table List" in the main TOPCAT window, perform a coordinate transform: in the "Table Columns" window click on , define the System, Units, RA and Dec for the Input coordinates as well as the equivalent information for the Output coordinates and "OK"; the new RA, Dec columns will be appended to the selected table (last two columns)
- we will now look for spectra of NGC1068;
- click on VO and select SSA Query (SSA stands for Simple Spectral Access); repeat the procedure by filtering the registry with keywords and look for spectra in a radius of a few arcsec; try the following SSAs:
- on the catalogues that will come back from the SSA queries, locate the URL that point to the SSA query URL; in "Activation Action" select "View URL as Spectrum", set the "Spectrum Location column", point the "Spectrum Viewer" to "splat" and then click "OK"
- clicking on any of the entries in any catalogue, will send the spectrum to SPLAT-VO for visualisation; the list of spectra will appear under "Global list of spectra" on the main SPLAT-VO window; select one or more and click on or to see each one of them in its own window or all together, if you want to see a full spectra energy distribution of the source
- using SPLAT-VO look for more spectra of NGC1068: Search SSAP servers (), put the name of the object (NGC1068) and "lookup", then "GO"; the spectra will appear in lists under "Query results", one tab per server; you can chose to download (i.e. list in the main SPLAT-VO window) or directly display either a selection or all the spectra found (we suggest you only download and visualise a few spectra)
- if at any given moment information is not exchanged between the various applications, click on the SAMP control button of TOPCAT and check for error messages