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 electromagnetic 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 imaging survey data in Red, Green, and Blue color channels, with their respective intensities at each pixel, resulting in a false-colored image. Conventionally in RAD@home Collaboratory, 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-RGB image has an exception allowed for green channel only.
The two widely used RAD-RGB images in our analysis are:
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 angular radius of the image, and what sort of images you would like to make.
Here is a brief description of each label provided in the form:
Your name will be displayed on the image enabling mentors, professors, fellow students to be able to recognize your work. Credit is important!
The object name or the sky coordinates of the object ( R.A. Dec. FK5 (J2000) system). Ex: "14 09 48.86 -03 02 32.6", M87, NGC1243, without quotes.
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. Default value is 0.12 degree. Note: 1 degree=60 arc minutes and 1 arc minute=60 arc second.
This dropdown gives you a choice of the composite images you want to create.
This option returns four images. Read the top header of each RGB-contour image carefully.
You are ready to make your RAD-RGB images! Just press the query 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 -- try to explain the multi-wavelength colour and structure you see in these RGB-contour images -- every pixel there has a story. All the best for that! Note not to copy-paste statements from the internet about that galaxy but try to explain the image you produced. You can read Wikipedia article on Galaxy and radio galaxy.
Once you are good at this analysis (through #DailyGalaxyRGBC in our Facebook group or #NIUgalaxyRGBCanalysis through a RAD@home Astronomy Workshop Google Form) you can also try advanced levels of analysis as follows.
This option returns two images.
This dropdown currently offers access to the NVAS image archive (WARNING). 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. Directly clicking that NVAS image link will lead to opening a large-size binary file on your web-browser, incapable of displaying the image. You may require to rename the file with a suffix .fits to open it in SAO ds9 FITS viewer.
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 pixel values as spectral flux density (unit of the pixel value in radio images is Jansky per beam). These values contain signal or real bright sources in the sky along with background noise data or the empty part. Each sky survey has a typical/average Sensitivity level in their images which depends on the size of the telescope, exposure time, band width etc etc.. Sources significantly fainter (lower pixel values) than this Sensitivity can not be called detected/seen, and with pixel values significantly brighter than that Sensitivity can be bright enough to be considered as a real object in the sky. We need to quantify that Sensitivity or noise in the sky. Regions with pixel values above three times the root mean square (RMS) value or above 3-sigma are usually taken as detection of the radio source signal and can be studied further as real cosmic objects. It's absolutely essential for radio images and if a source is not seen with contours with 3 sigma or above, it is considered unreliable. There is one-to-one mapping of GMRT-TGSS contours and Red pixels in ROR-RGB images and similarly for NVSS contours. Interestingly, the contour maps help present a 4th image along with three channels of Red-Green-Blue (RGB) image. Understanding contour images is a must for RAD@home citizen scientists as we focus on discoveries that can be made with GMRT telescope, pride of India, using TGSS images and through the project GOOD-RAC@GMRT. We also prepare the nation for the Mega Science project Square Kilometre Array Observatory.
Table with technical 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 | GMRT 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 Refer to our Publications on RAD-RGB image analysis:
"RAD@home RGB-maker web-tool for citizen science research in multi-wavelength study of AGNs with radio jets" Avinash Kumar, Avinash Ck., Arundhati Purohit & Ananda Hota; Proceedings of the International Astronomical Union, Cambridge University Press, September, 2023 DOI: https://doi.org/10.1017/S1743921323000674
Hota et al. 2016 https://ui.adsabs.harvard.edu/abs/2016JApA...37...41H/abstract
Hota et al. 2014 https://ui.adsabs.harvard.edu/abs/2014ASInC..13..141H/abstract
Please check the RAD-RGB Acknowledgment at the bottom of the page for further details : RAD-RGB Maker Tool Acknowledgement