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Register a new userDiscovery of CO absorption at z=0.05 in G0248+430
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Absorption lines in front of distant quasars are quite rare in the millimeter domain. They can however bring a very useful and complementary information to emission lines. We report here the detection with NOEMA of CO(1-0) and CN(1-0) lines in absorption, and confirmation of CO emission in the quasar/galaxy pair Q0248+430/G0248+430. The system G0248+430 corresponds to two merging galaxies (a Seyfert and a LINER) at z=0.0519 with a tidal tail just on the line of sight to the background quasar Q0248+430 at z = 1.313. Optical (CaII, NaI), HI-21cm and OH-1667 MHz absorption lines associated with the tidal tail of the foreground system have previously been detected toward the quasar, while four CO lines at different rotation J levels have been detected in emission from the foreground galaxies. New HI 21-cm line observations with the upgraded GMRT array are presented. We discuss the molecular content of the merging galaxies, and the physical conditions in the absorbing interstellar medium of the tidal tail.
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We have carried out follow-up spectroscopy on three overdense regions of $g$- and $r$-dropout galaxies in the Canada-France-Hawaii Telescope Legacy Survey Deep Fields, finding two new protoclusters at $z=4.898$, 3.721 and a possible protocluster at $z=3.834$. The $z=3.721$ protocluster overlaps with a previously identified protocluster at $z=3.675$. The redshift separation between these two protoclusters is $Delta z=0.05$, which is slightly larger than the size of typical protoclusters. Therefore, if they are not the progenitors of a $>10^{15},mathrm{M_odot}$ halo, they would grow into closely-located independent halos like a supercluster. The other protocluster at $z=4.898$ is also surrounded by smaller galaxy groups. These systems including protoclusters and neighboring groups are regarded as the early phase of superclusters. We quantify the spatial distribution of member galaxies of the protoclusters at $z=3.675$ and 3.721 by fitting triaxial ellipsoids, finding a tentative difference: one has a pancake-like shape while the other is filamentary. This could indicate that these two protoclusters are in different stages of formation. We investigate the relation between redshift and the velocity dispersion of protoclusters, including other protoclusters from the literature, in order to compare their dynamical states. Although there is no significant systematic trend in the velocity dispersions of protoclusters with redshift, the distribution is skewed to higher velocity dispersion over the redshift range of $z=2mathrm{-}6$. This could be interpreted as two phases of cluster formation, one dominated by the steady accretion of galaxies, and the other by the merging between group-size halos, perhaps depending on the surrounding large-scale environments.
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