288 research outputs found
The complex molecular absorption line system at z=0.886 towards PKS1830-211
New millimeter wave observations of the molecular absorption line system in
the gravitational lens to PKS1830-211 at z=0.88582 is presented.
Self-calibrated interferometer data shows unequivocally that the previously
detected absorption component is associated with the gravitationally lensed
south-west image of the background source. A second absorption line of
HCO+(2-1) at z=0.88582 is detected. This component is shifted in velocity by
-147 km/s relative to the main absorption line, and is shown to be associated
with the north-east image. These two absorption lines are used to constrain the
mass of the lensing galaxy. Upper limits to absorption and emission lines from
the possible absorption system at z=0.1927, seen in 21cm HI by Lovell et al,
are reported.Comment: 16 pages, 7 figures, Accepted for publication in Ap
Distribution of the molecular absorption in front of the quasar B0218+357
The line of sight to the quasar B0218+357, one of the most studied lensed
systems, intercepts a z=0.68 spiral galaxy, which splits its image into two
main components A and B, separated by ca. 0.3'', and gives rise to molecular
absorption. Although the main absorption component has been shown to arise in
front of image A, it is not established whether some absorption from other
velocity components is also occuring in front of image B. To tackle this
question, we have observed the HCO+(2-1) absorption line during the
commissioning phase of the new very extended configuration of the Plateau de
Bure Interferometer, in order to trace the position of the absorption as a
function of frequency. Visibility fitting of the self-calibrated data allowed
us to achieve position accuracy between ~12 and 80 mas per velocity component.
Our results clearly demonstrate that all the different velocity components of
the HCO+(2-1) absorption arise in front of the south-west image A of the
quasar. We estimate a flux ratio fA/fB = 4.2 (-1.0;+1.8 at 106 GHz.Comment: accepted for publication in A&A Letter special issue for the new
extended configuration of the Plateau de Bure Interferomete
Do the fundamental constants change with time ?
Comparisons between the redshifts of spectral lines from
cosmologically-distant galaxies can be used to probe temporal changes in
low-energy fundamental constants like the fine structure constant and the
proton-electron mass ratio. In this article, I review the results from, and the
advantages and disadvantages of, the best techniques using this approach,
before focussing on a new method, based on conjugate satellite OH lines, that
appears to be less affected by systematic effects and hence holds much promise
for the future.Comment: 15 pages, 3 figures. This is an electronic version of an invited
review article for Mod. Phys. Lett. A, published as [Mod. Phys. Lett. A, Vol.
23, No. 32, 2008, pp. 2711] (copyright World Scientific Publishing Company;
http://www.worldscientific.com/
A search for high redshift molecular absorption lines toward millimetre-loud, optically faint quasars
We describe initial results of a search for redshifted molecular absorption
toward four millimetre-loud, optically faint quasars. A wide frequency
bandwidth of up to 23 GHz per quasar was scanned using the Swedish-ESO
Sub-millimetre Telescope at La Silla. Using a search list of commonly detected
molecules, we obtained nearly complete redshift coverage up to z_abs=5. The
sensitivity of our data is adequate to have revealed absorption systems with
characteristics similar to those seen in the four known redshifted
millimetre-band absorption systems, but none were found. Our frequency-scan
technique nevertheless demonstrates the value of wide-band correlator
instruments for searches such as these. We suggest that a somewhat larger
sample of similar observations should lead to the discovery of new
millimetre-band absorption systems.Comment: 8 pages, 7 EPS figures, 3 tables, accepted by MNRA
Molecular gas and dust in NGC4550: A galaxy with two counterrotating stellar disks
We report the detection of 1 10^7 M_sun of molecular gas in the central region of the S0/E7 galaxy NGC4550, inferred from observations of CO(1-0) emission. Dust is detected in HST WFPC2 images and found to be asymmetrically distributed around the nucleus, only extending to a galactocentric distance of 7'' (600 pc). The shape of the CO emission profile is consistent with a molecular gas distribution following the dust. The distribution of the dust and gas in the center could be the result of an m=1 instability, which is the fastest growing unstable mode in counterrotating stellar disks. On a global scale the molecular gas in NGC4550 is stable against gravitational collapse but nevertheless star formation appears to be ongoing with normal star formation efficiency and gas consumption time scales. The stellar velocity dispersion in NGC4550 resembles that of elliptical galaxies. It is therefore likely that a hot X-ray emitting plasma limits the lifetime of the molecular gas, that must arise from a recent (<1 Gyr) accretion event
Constraining the variation of fundamental constants using 18cm OH lines
We describe a new technique to estimate variations in the fundamental
constants using 18cm OH absorption lines. This has the advantage that all lines
arise in the same species, allowing a clean comparison between the measured
redshifts. In conjunction with one additional transition (for example, an
HCO line), it is possible to simultaneously measure changes in ,
and . At present, only the 1665 MHz and 1667 MHz lines
have been detected at cosmological distances; we use these line redshifts in
conjunction with those of HI 21cm and mm-wave molecular absorption in a
gravitational lens at to constrain changes in the above three
parameters over the redshift range . While the constraints
are relatively weak ( 1 part in ), this is the first
simultaneous constraint on the variation of all three parameters. We also
demonstrate that either one (or more) of , and must vary with
cosmological time or there must be systematic velocity offsets between the OH,
HCO and HI absorbing clouds.Comment: 5 pages, no figures. Accepted for publication in Phys. Rev. Let
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