Institut de Radio Astronomie
Millimétrique, 300 rue de la Piscine, 38406 St Martin d'Hères,
France Appeared in: EAS Publications Series, Vol. 19, 167
, Neri R., Gurwell M. A.
IRAM, 300 rue de la Piscine, Domaine Universitaire,
Saint Martin d'Hères, France,
Harvard-Smithsonian Center for Astrophysics,
60 Garden Street, Cambridge, MA 02138 Appeared in: ApJS 164, 552
, Walter F., Carilli C. L., Weiss A.
,
Bertoldi F.
, Menten K. M., Knudsen K. K., Cox P.
Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany,
National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801,
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany,
Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, D-53121 Bonn, Germany,
Institut de Radioastronomie Millimétrique, 300 rue de la Piscine,
Domaine Universitaire, F-38406 Saint Martin d'Hères, France 
emission toward the
Cloverleaf quasar (
) through observations with the Very Large
Array. This is the first detection of ionized molecular gas emission
at high redshift (
). HCO
emission is a star formation indicator
similar to HCN, tracing dense molecular hydrogen gas [
cm
] within star-forming molecular clouds. We derive a
lensing-corrected HCO line luminosity of
K
km s
pc
. Combining our new results with CO and HCN
measurements from the literature, we find an HCO/CO luminosity ratio
of 0.08 and an HCO/HCN luminosity ratio of 0.8. These ratios fall
within the scatter of the same relationships found for low-z
star-forming galaxies. However, an HCO/HCN luminosity ratio close to
unity would not be expected for the Cloverleaf if the recently
suggested relation between this ratio and the far-infrared luminosity
were to hold. We conclude that a ratio between HCO and HCN luminosity
close to 1 is likely due to the fact that the emission from both lines
is optically thick and thermalized and emerges from dense regions of
similar volume. The CO, HCN, and HCO luminosities suggest that the
Cloverleaf is a composite active galactic nucleus-starburst system, in
agreement with the previous finding that about 20% of the total
infrared luminosity in this system results from dust heated by star
formation rather than heating by the active nucleus. We conclude that
HCO is potentially a good tracer for dense molecular gas at high
redshift.
Appeared in: ApJ 645, L13
; Neininger, N.
, Guélin M., Ungerechts H., Lucas R.; Berkhuijsen E. M., Beck R., Wielebinski R.
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany,
Radioastronomisches Institut der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St. Martin d' Hères, France,
Instituto de Radioastronomía Milimétrica, Avenida Divina Pastora 7, 18012 Granada, Spain
Aims. We study the distribution of the molecular gas in the Andromeda
galaxy (M 31) and compare this with the distributions of the atomic
gas and the emission from cold dust at
m.
Methods. We obtained a new 
CO(
)-line survey of the
Andromeda galaxy with the highest resolution to date (
, or 85
pc along the major axis), observed On-the-Fly with the IRAM 30-m
telescope. We fully sampled an area of
with a
velocity resolution of 2.6 km s. In several selected regions we
also observed the CO(2-1)-line. Results.Emission from the
CO(1-0) line was detected from galactocentric radius 
kpc to
kpc with a maximum in intensity at 
kpc. The molecular gas
traced by the (velocity-integrated) (1-0)-line intensity is
concentrated in narrow arm-like filaments, which often coincide with
the dark dust lanes visible at optical wavelengths. Between R=4 kpc
and R=12 kpc the brightest CO filaments define a two-armed spiral
pattern that is described well by two logarithmic spirals with a pitch
angle of 
. The arm-interarm brightness ratio averaged
over a length of 15 kpc along the western arms reaches about 20
compared to 4 for H I at an angular resolution of
. For a
constant conversion factor 
, the molecular fraction of the
neutral gas is enhanced in the spiral arms and decreases radially from
0.6 on the inner arms to 0.3 on the arms at 
kpc. The
apparent gas-to-dust ratios
and
increase by a factor of 20 between the centre and
kpc, whereas the ratio
only increases
by a factor of 4.
Conclusions. Either the atomic and total gas-to-dust ratios increase by
a factor of 20 or the dust becomes colder towards larger radii. A
strong variation of with radius seems unlikely. The observed
gradients affect the cross-correlations between gas and dust. In the
radial range 
kpc total gas and cold dust are well correlated;
molecular gas correlates better with cold dust than atomic gas. The
mass of the molecular gas in M 31 within a radius of 18 kpc is
at the adopted distance of 780 kpc. This is
7% of the total neutral gas mass in M 31.
Appeared in: A&A 453, 459
, Pineau Des Forêts G.
, Hily-Blant P., Schilke P.
LERMA/LRA, CNRS - UMR 8112, École Normale Supérieure,
24 rue Lhomond, 75005 Paris, France,
IAS, CNRS - UMR 8617, Université Paris-Sud, 91405 Orsay, France,
LUTH, CNRS - UMR 8102, Observatoire de Paris, 92195 Meudon, France,
IRAM, 300 rue de la Piscine, 38406 St. Martin d'Hères, France,
MPIfR, Auf den Hügel 69, 53121 Bonn, Germany
Methods: We observed HCO(1-0) lines and the two lowest rotational transitions of CO and 
CO with an exceptional signal-to-noise ratio in the translucent environment of low-mass dense cores, where turbulence dissipation is expected to take place. Some of the observed positions belong to a new kind of small-scale structure identified in CO(1-0) maps of these environments as the locus of non-Gaussian velocity shears in the statistics of their turbulent velocity field, i.e. singular regions generated by the intermittent dissipation of turbulence.
Results: We report the detection of broad HCO(1-0) lines (10 mK
K). We achieve the interpretation of ten HCO velocity
components by conducting it in conjunction with that of the associated
optically thin CO emission. The derived HCO column densities span a
broad range, 
N(HCO
cm
/km s,
and the inferred HCO abundances,
HCO
, are more than one order of magnitude above those produced by
steady-state chemistry in gas that is weakly shielded from UV photons,
even at large densities. We compare our results with predictions of
non-equilibrium chemistry, swiftly triggered in bursts of turbulence
dissipation and followed by a slow thermal and chemical relaxation
phase, assumed to be isobaric. The set of values derived from
observations, i.e. large HCO abundances, temperatures in the range of
100-200 K, and densities in the range 
cm, unambiguously
belongs to the relaxation phase. In contrast, the kinematic properties
of the gas suggest that the observed HCO line emission results from a
space-time average in the beam of the whole cycle followed by the gas
and that the chemical enrichment is made at the expense of the
non-thermal energy. Last, we show that the "warm chemistry" signature
(i.e. large abundances of HCO, CH, H
O, and OH) acquired by the
gas within a few hundred years, which is the duration of the impulsive
chemical enrichment, is kept over more than a thousand years. During
the relaxation phase, the HO/OH abundance ratio stays close to the
value measured in diffuse gas by the SWAS satellite, while the OH/HCO
ratio increases by more than one order of magnitude.
Appeared in: A&A 452, 511
, Michel Guelin,
Michael Dumke, Robert Lucas, Françoise Combes
ASIAA, P.O. Box 23-141, Taipei, 106 Taiwan,
IRAM, 300 rue de la Piscine, 38406 St Martin d'Hères, France,
ESO, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile,
LERMA, 61 av. de l'Observatoire, F-75014 Paris, France 
O/
O and 
N/
N ratios are
low, as one would expect from an object too young to let low mass
stars play a major role in the regeneration of the gas.
Accepted for publication in A&A