Comment Re:Only one line detection? (Score 5, Interesting) 39
I agree that only one line is suspicious. But the spectral energy distribution --- its optical and infrared colors --- argue pretty convincingly for its idenitification as a high-redshift galaxy (at least for me, as someone who's worked in this subject).
Moreover, the authors argue in the paper that the object sits on the appropriate gravitational-lensing caustic for a redshift 9-10 object. I.e., if the galaxy in question---Abell 1835 IR1916 --- sits on at the right place relative to the foreground galaxy cluster (Abell 1835), the General Theory of Relativity says that the mass of the cluster should magnify the galaxy by 25 to 100x in brightness (one of the authors, J.-P. Kneib, is a world expert on gravitational lensing).
Lastly, if the galaxy was at, say, z=2.7, and thus much closer---but consistent with the colors if the galaxy was full of dust---the line would have to be the forbidden doublet of singly-ionized oxygen at 372.62 and 372.89 nm. But this doublet would have been easily resolved by the high resolution of ISAAC, the infrared spectrograph on the VLT used by the authors, but not seen.
BTW, probably not a quasar --- the IR (restframe UV) colors are too blue compared to the Sloan z=6 clusters.
The thing that bothers me, though, is the the shape of the Ly-alpha line --- it's asymmetric in the wrong way (too sharp on the red side, too gaussian on the blue side) compared to the z=3 galaxies.
Still need a lot more data, though --- both deeper NIR spectra to look for the continuum and mid-IR images (perhaps from the VLT, or Spitzer Space Telescope, or eventually the James Webb Space Telescope) to confirm the restframe optical colors.
Cheers,
Scott
Moreover, the authors argue in the paper that the object sits on the appropriate gravitational-lensing caustic for a redshift 9-10 object. I.e., if the galaxy in question---Abell 1835 IR1916 --- sits on at the right place relative to the foreground galaxy cluster (Abell 1835), the General Theory of Relativity says that the mass of the cluster should magnify the galaxy by 25 to 100x in brightness (one of the authors, J.-P. Kneib, is a world expert on gravitational lensing).
Lastly, if the galaxy was at, say, z=2.7, and thus much closer---but consistent with the colors if the galaxy was full of dust---the line would have to be the forbidden doublet of singly-ionized oxygen at 372.62 and 372.89 nm. But this doublet would have been easily resolved by the high resolution of ISAAC, the infrared spectrograph on the VLT used by the authors, but not seen.
BTW, probably not a quasar --- the IR (restframe UV) colors are too blue compared to the Sloan z=6 clusters.
The thing that bothers me, though, is the the shape of the Ly-alpha line --- it's asymmetric in the wrong way (too sharp on the red side, too gaussian on the blue side) compared to the z=3 galaxies.
Still need a lot more data, though --- both deeper NIR spectra to look for the continuum and mid-IR images (perhaps from the VLT, or Spitzer Space Telescope, or eventually the James Webb Space Telescope) to confirm the restframe optical colors.
Cheers,
Scott
