6,698 research outputs found
A third HI 21-cm absorption system in the sight-line of MG J0414+0534: A redshift for Object X?
We report the detection of a third HI 21-cm absorber in the sight-line
towards the z=2.64 quasar MG J0414+0534 (4C +05.19). In addition to the
absorption at the host redshift and in the z=0.96 gravitational lens, we find,
through a decimetre-wave spectral scan towards this source, strong absorption
at z=0.38. We believe this may be associated with "Object X", an additional
feature apparent in the field of the lensing galaxy and lensed images, on the
basis of its close proximity to the quasar images and the possible detection of
the [OIII] doublet in a published optical spectrum. If real, the strength of
the [OIII] emission would suggest the presence of an active galactic nucleus,
or a gas-rich galaxy undergoing rapid star formation, either of which is
consistent with the strong outflows apparent in the 21-cm spectrum. Although
this is the strongest intervening 21-cm absorber yet found, simultaneous
observations failed to detect any of the 18-cm OH lines at the 21-cm redshift.
This suggests that, as for the lensing galaxy, this is not the primary location
of the intervening material responsible for the very red colour of MG
J0414+0534.Comment: 5 pages, accepted by MNRAS Letter
Exciton-photon coupling in a ZnSe based microcavity fabricated using epitaxial liftoff
We report the observation of strong exciton-photon coupling in a ZnSe based
microcavity fabricated using epitaxial liftoff. Molecular beam epitaxial grown
ZnSe/ZnCdSe quantum wells with a one wavelength optical length
at the exciton emission were transferred to a SiO/TaO mirror with a
reflectance of 96% to form finesse matched microcavities. Analysis of our angle
resolved transmission spectra reveals key features of the strong coupling
regime: anticrossing with a normal mode splitting of at ;
composite evolution of the lower and upper polaritons; and narrowing of the
lower polariton linewidth near resonance. The heavy hole exciton oscillator
strength per quantum well is also deduced to be .Comment: 3 pages, 3 figure
A fourth HI 21-cm absorption system in the sight-line of MG J0414+0534: a record for intervening absorbers
We report the detection of a strong HI 21-cm absorption system at z=0.5344,
as well as a candidate system at z=0.3389, in the sight-line towards the z=2.64
quasar MG J0414+0534. This, in addition to the absorption at the host redshift
and the other two intervening absorbers, takes the total to four (possibly
five). The previous maximum number of 21-cm absorbers detected along a single
sight-line is two and so we suspect that this number of gas-rich absorbers is
in some way related to the very red colour of the background source. Despite
this, no molecular gas (through OH absorption) has yet been detected at any of
the 21-cm redshifts, although, from the population of 21-cm absorbers as a
whole, there is evidence for a weak correlation between the atomic line
strength and the optical--near-infrared colour. In either case, the fact that
so many gas-rich galaxies (likely to be damped Lyman-alpha absorption systems)
have been found along a single sight-line towards a highly obscured source may
have far reaching implications for the population of faint galaxies not
detected in optical surveys, a possibility which could be addressed through
future wide-field absorption line surveys with the Square Kilometre Array.Comment: Accepted by ApJ Letter
Recommended from our members
Mapping solar irradiance within Schrödinger Basin for future robotic sample return missions
The US National Research Council (NRC) identified eight scientific concepts and thirty-five prioritized investigations to be addressed with continued lunar exploration. These objectives are broadly consistent with those identified throughout the international community. the majority of these objectives require sample return from the Moon. Schrödinger basin has been highlighted as a particularly attractive location to find suitable samples
HI and OH absorption in the lensing galaxy of MG J0414+0534
We report the detection of \HI 21-cm absorption in the early-type
lensing galaxy towards MG J0414+0534 with the Green Bank Telescope. The
absorption, with total , is resolved into two strong components, probably due to the two
strongest lens components, which are separated by 0.4\arcsec. Unlike the other
three lenses which have been detected in \HI, J0414+0534 does not exhibit
strong OH absorption, giving a OH/\HI column density ratio of N_{\rm
OH}/N_{\rm HI}\lapp10^{-6} (for K, K and
). This underabundance of molecular gas may indicate
that the extreme optical--near-IR colour () along the line-of-sight
is not due to the lens. We therefore suggest that despite the strong upper
limits on molecular absorption at the quasar redshift, as traced by millimetre
lines, the extinction occurs primarily in the quasar host galaxy.Comment: Accepted by MNRAS Letters, 5 (and a bit) pages, 5 figure
Developmental patterning of rod and cone photoreceptors in embryonic zebrafish
Cone photoreceptors in the zebrafish retina are arranged in a crystalline lattice, with each spectral subtype at a specific position in the array: rod photoreceptors are inserted around the cones. Patterning events and developmental mechanisms that lead to the formation of the cone mosaic are not known. To begin investigating this issue, we examined the initial stages of opsin expression in zebrafish embryos by in situ hybridization with goldfish opsin cRNA probes to determine how and when the cone mosaic pattern arises. We found both differences and similarities in the spatiotemporal patterns of rod and cone development, which suggest the following: (1) Expression of opsin message (including rod opsin, blue and red cone opsins) was initiated at 50–52 hours postfertilization by a few photoreceptors which were consistently found in a ventral patch of retina located nasal to the choroid fissure. (2) The cone mosaic pattern was generated by a crystallization-like process initiated in the precocial ventral patch and secondarily in nasal retina, which then swept like a wave into dorsotemporal retina. (3) The pattern of differentiation of rods in the ventronasal patch differed substantially from that in the remainder of the retina, suggesting that these precocial rods might differ from typical rods. (4) Developmental maturation of rods in zebrafish, as reflected by expression of opsin, may be accelerated compared to cones, which are thought to become postmitotic before rods. These data are consistent with a model in which lateral inductive interactions among differentiating photoreceptors lead to patterning of the array. © 1995 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/50066/1/903590403_ftp.pd
- …