by Nitpicker » Wed Mar 27, 2019 12:02 am
The HST image of Arp 194, recorded in Jan 2009, must have been one of the last to be recorded with the WFPC2 camera, which was removed in May 2009, and replaced with the WFC3 camera.
The 2002 paper than Ann provided a link to, and the 2016 paper in the "because of" link in the APOD caption, are both clear in their assertions that the southern galaxy "recently" passed through the northern galaxy (of two close components). Both these papers were based on detailed spectral observations using large, ground-based telescopes.
I am not sure of the basis for the alternative assertion, that the southern galaxy is more distant and unrelated to the bridge between the northern and southern components. The only basis I have read was something along the lines of "the higher resolution of the Hubble image shows the bridge to be clearly in front of the southern galaxy". This seems like a weak basis to form an alternative assertion. I don't profess to be very good at interpreting images of galaxies, but it is certainly not obvious to me that the bridge is "clearly" in front of the southern galaxy in this APOD, to the point that they are only a chance alignment.
The HST image of Arp 194, recorded in Jan 2009, must have been one of the last to be recorded with the WFPC2 camera, which was removed in May 2009, and replaced with the WFC3 camera.
The 2002 paper than Ann provided a link to, and the 2016 paper in the "because of" link in the APOD caption, are both clear in their assertions that the southern galaxy "recently" passed through the northern galaxy (of two close components). Both these papers were based on detailed spectral observations using large, ground-based telescopes.
I am not sure of the basis for the alternative assertion, that the southern galaxy is more distant and unrelated to the bridge between the northern and southern components. The only basis I have read was something along the lines of "the higher resolution of the Hubble image shows the bridge to be clearly in front of the southern galaxy". This seems like a weak basis to form an alternative assertion. I don't profess to be very good at interpreting images of galaxies, but it is certainly not obvious to me that the bridge is "clearly" in front of the southern galaxy in this APOD, to the point that they are only a chance alignment.