Molecular gas at intermediate redshifts

We present Giant Metrewave Radio Telescope (GMRT) observations of OH absorption in B3~1504+377 ($z \sim 0.673$) and PKS 1413+135 ($z \sim 0.247$). OH has now been detected in absorption towards four intermediate redshift systems, viz. the lensing galaxies towards B~0218+357 ($z \sim 0.685$; Kanekar et al. 2001) and 1830-211 ($z \sim 0.886$; Chengalur et al. 1999), in addition to the two systems listed above. All four systems also give rise to well studied millimetre wavelength molecular line absorption from a host of molecules, including HCO$^+$. Comparing our OH data with these millimetre line transitions, we find that the linear correlation between $N_{\rm OH}$ and $N_{\rm HCO^+}$ found in molecular clouds in the Milky Way (Liszt & Lucas 1996) persists out to $z \sim 1$. It has been suggested (Liszt & Lucas 1999) that OH is a good tracer of ${\rm H_2}$, with $N_{\rm H_2}/N_{\rm OH} \approx 10^7$ under a variety of physical conditions. We use this relationship to estimate $N_{\rm H_2}$ in these absorbers. The estimated $N_{\rm H_2}$ is \ga 10^{22} in all four cases and substantially different from estimates based on CO observations.Comment: 4 pages, 3 figures. Accepted for publication in Astronomy and Astrophysics Letter

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

A search for molecules in damped Lyman-alpha absorbers occulting millimetre-loud quasars

We have used the SEST 15-metre and Onsala 20-metre telescopes to perform deep (r.m.s. >~ 30 mJy) integrations of various molecular rotational transitions towards damped Lyman-alpha absorption systems (DLAs) known to occult millimetre-loud quasars. We have observed 6 new systems and improved the existing limits for 11 transitions. These limits may be approaching the sensitivities required to detect new systems and we present a small number of candidate systems which we believe warrant further observation.Comment: 7 pages, 1 PS figure, 4 tables. Accepted by A&

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

Disk Growth in Bulge-Dominated Galaxies: Molecular Gas and Morphological Evolution

Substantial numbers of morphologically regular early-type (elliptical and lenticular) galaxies contain molecular gas, and the quantities of gas are probably sufficient to explain recent estimates of the current level of star formation activity. This gas can also be used as a tracer of the processes that drive the evolution of early-type galaxies. For example, in most cases the gas is forming dynamically cold stellar disks with sizes in the range of hundreds of pc to more than one kpc, although there is typically only 1% of the total stellar mass currently available to form young stars. The numbers are still small, but the molecular kinematics indicate that some of the gas probably originated from internal stellar mass loss while some was acquired from outside. Future studies will help to quantify the role of molecular gas (dissipational processes) in the formation of early-type galaxies and their evolution along the red sequence.Comment: 4 pages. To appear in the proceedings of IAU Symposium 245, "Formation and Evolution of Galaxy Bulges," M. Bureau, E. Athanassoula, and B. Barbuy, ed

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

ALMA Observations of Molecular Absorption in the Gravitational Lens PMN 0134-0931

We report the detection of molecular absorption lines at z=0.7645 towards the radio-loud QSO PMN 0134-0931. The CO J=2-1 and HCO+ J=2-1 lines are seen in absorption along two different lines of sight to lensed images of the background QSO. The lines of sight are separated by ~0.7", corresponding to 5 kpc in the lens plane. PMN 0134-0931 represents one out of only five known molecular absorption line systems at cosmologically significant distances. Moreover, it is also one of three such systems where the absorption occurs in a galaxy acting as a gravitational lens. The absorption lines through the two lines of sight are shifted by 215+/-8 km/s, possibly representing rotational motion in one of the lensing galaxies. The absorption profiles are wide, ~200 km/s, suggesting that the absorption occurs in a highly inclined disk galaxy with a flat rotation curve and a cloud-cloud velocity dispersion ~30 km/s. Gravitational lens models require two equal mass galaxies to account for the observed configuration of lensed images. The presence of two galaxies in close proximity means that they might be interacting and potentially merging and the kinematics of the molecular gas may not reflect ordered rotational motion. The column densities of both CO and HCO+ are normal for diffuse molecular gas towards one of the lensed images, but significantly higher towards the other. Also, the abundance ratio N(CO)/N(HCO+) is 2-3 times higher than in typical diffuse molecular gas. It is plausible that the second line of sight probes denser molecular gas than what is normally the case for absorption.Comment: 17 pages, 4 figures, 4 table