What are IOU ROR and RGB images?

RAD-RGB images are false-colored images of astronomical objects.

The astronomical study involves a multi-wavelength analysis of the object from the radio part of the spectrum to x-rays. Astronomers access these data from various archival data services which are sky survey data on a particular wavelength taken by a particular telescope. No telescope can observe in all bands of electromagnetic spectrum. Different telescope images have different sensitivity, resolution (angular/frequency) and many other parameters. Each RGB image is a combination of these survey data in Red, Green, and Blue color channels, with their respective intensities at each pixel, resulting in a false-colored image. Conventionally in [email protected], the surveys are selected so that the order of wavelength of each data and colour of the channels are in same order i.e survey data in the red channel has a wavelength higher than that in green and green has a wavelength greater than that in blue. This is followed in optical and IOU RGB images and ROR image has an exception allowed for green channel.

The two widely used RAD-RGB images in our analysis are:

• Optical RGB
  This image is close to our natur

• IOU-RGB

  These are Infrared - Optical - Ultraviolet, RAD-RGB images i.e the red channel has IR data (WISE 22), the green channel has data at the Optical visible wavelength (DSS2 R) and the blue channel has UV data (Galex NUV). So, an IOU-RGB image is not a real colour image but multi-wavelength image, one visible and two invisible to human eye. 

• ROR RGB

  These are Radio-Optical-Radio RAD-RGB images i.e the red channel has radio data of higher wavelength (TGSS ADR1), the green channel has optical data (DSS2 R) and the blue channel has radio data of lower wavelength (VLA NVSS) at each pixel.
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How to use the RAD-RGB Maker Tool:

RAD-RGB Maker Tool is a very simple to use tool. All you need is the name of the astronomical object of interest or its coordinates, the radius of the image search scope, and what sort of images you would like to make.

Here is a brief description of each label provided in the form:

• Name (Optional)

  Your name will be displayed on the image enabling mentors, professors, fellow students to be able to recognize your work. Credit is important!

• Position (Required)

  The object name or the coordinates of the object in the FK5 (J2000) system. Ex: "14 09 48.86 -03 02 32.6", M87, NGC1243, without quotes.

• Radius (Required)

  The size of the image in degrees, this size will be used for the field of view in the resultant image. For reference, in the night sky, the moon is about 0.52 degrees across.

• Images

  This dropdown gives you a choice of the composite images you want to create.

  IOU ROR Optical

  This option returns four images.

  • There are two ROR (Radio (TGSS ADR1) - Optical (DSS2Red) - Radio (NVSS)) images. One with TGSS Contours and another with NVSS Contours.

  • The third image is an IOU (Infrared (WISE 22) - Optical (DSS2 Red) - Ultraviolet (Galex Near UV)) with TGSS Contours.

  • The final RGB image is an optical image with (DSS2IR - DSS2Red - DSS2Blue) with TGGSS Contours.

  Composite Contours on DSS2R

  This option returns two images.

  • The first is a ROR Image with TGSS contours. The various symbol seen on the image is the catalog data of the respective survey.

  • The second image is a composite image with DSS2Red background and contours of various radio surveys like TGSS, NVSS, and VLA First (if available).

• Archives

  This dropdown currently offers access to the NVAS image archive. Selecting this option will return the top 5 results from NVAS (if exists). These can be downloaded as .imfits files (open with DS9) by using save as an option when right-clicked.

• Query

  You are now finally ready to make your RAD-RGB image! Just press the button, give it a few seconds, and you will have taken your first step in the RGB image analysis. The next and most important step in the analysis. All the best for that!

Contour Map

contour maps are lines which joins the pixels with same pixel-value of a given image or lines of equal intensity.  

Radio survey data contains a range of values as spectral flux density (Jy). These values contain signal or real bright sources in the sky along with background noise data or the empty part.  Each sky survey provides a RMS (Root Mean Squared or 1-sigma) value or an accepted signal (3-5 sigma) value for the sky region. Three times the RMS value or a region above 3-sigma is taken as detection of the radio source signal and can be studied further. The contour map helps represent a 4th image along with three channels Red-Green-Blue (RGB) image. Its absolutely essential for radio images and if a source is not seen with contours with 3 sigma or above, it is considered unreliable. 

Table with details of a few radio surveys :

Frequency	Survey	3 sigma Detection	Resolution
-	-	Jy/beam	(arcsec)
1.4 GHz	VLA FIRST	0.0005 Jy	5 x 5
1.4 GHz	VLA NVSS	0.0015 Jy	45 x 45
150 MHz	TGSS ADR1	0.015 Jy	25 x 25
74 MHz	VLSSr	0.3 Jy	75 x 75
325 MHz	WENSS	0.018 Jy	54 x 54
843 MHz	SUMSS	0.010 Jy	45 x 45

Please check the RAD-RGB acknowledgment at the bottom of the page for further details : RAD-RGB Maker Tool Acknowledgement