7,148 research outputs found
Molecular Gas in the Bulge and Ring of NGC 7331
Maps of the J=2-1 12CO emission from the SbII galaxy NGC 7331 show a
low-contrast ring at a radius of about 3.5 kpc. There is no evidence for a
pronounced central hole in the CO distribution as claimed by others. The
molecular ring is just outside the radius of peak emission from warm dust, but
coincides with the peak of colder dust emission. Various 12CO and 13CO
transitions have been observed from three positions including the center, which
was also observed in the 492 GHz transition. The line measurements have been
modelled by emission from a clumpy mixture of low-density molecular gas at
about T(kin) = 10 K and high-density molecular gas at temperatures of 10 K and
20 K. The CO to H2 conversion factor in NGC 7331 is lower than that in the
Milky Way, and lowest in the center of NGC 7331. The total interstellar gas
mass is dominated by molecular hydrogen in the bulge and in the ring, and by
atomic hydrogen outside the ring. Total hydrogen mass densities in the ring are
about twice those in the bulge. Total gas to dynamic mass ratios increase from
1% in the bulge to 3% outside the ring. The bulge molecular gas may have
originated in mass loss from bulge stars, in which case the molecular ring is
probably the consequence of evacuation efficiency decreases at the outer bulge
edge.Comment: 12 pages, 4 figures, A&A in pres
Incompressible fluid inside an astrophysical black hole?
It is argued that under natural hypothesis the Fermions inside a black hole
formed after the collapse of a neutron star could form a non compressible fluid
(well before reaching the Planck scale) leading to some features of integer
Quantum Hall Effect. The relations with black hole entropy are analyzed.
Insights coming from Quantum Hall Effect are used to analyze the coupling with
Einstein equations. Connections with some cosmological scenarios and with
higher dimensional Quantum Hall Effect are shortly pointed out.Comment: 30 pages, 2 figures. Accepted for publication on Physical Review D:
references added, typos corrected, test polishe
HCN versus HCO+ as dense molecular gas mass tracer in Luminous Infrared Galaxies
It has been recently argued that the HCN J=1--0 line emission may not be an
unbiased tracer of dense molecular gas (\rm n\ga 10^4 cm^{-3}) in Luminous
Infrared Galaxies (LIRGs: ) and HCO J=1--0
may constitute a better tracer instead (Graci\'a-Carpio et al. 2006), casting
doubt into earlier claims supporting the former as a good tracer of such gas
(Gao & Solomon 2004; Wu et al. 2006). In this paper new sensitive HCN J=4--3
observations of four such galaxies are presented, revealing a surprisingly wide
excitation range for their dense gas phase that may render the J=1--0
transition from either species a poor proxy of its mass. Moreover the
well-known sensitivity of the HCO abundance on the ionization degree of the
molecular gas (an important issue omitted from the ongoing discussion about the
relative merits of HCN and HCO as dense gas tracers) may severely reduce
the HCO abundance in the star-forming and highly turbulent molecular gas
found in LIRGs, while HCN remains abundant. This may result to the decreasing
HCO/HCN J=1--0 line ratio with increasing IR luminosity found in LIRGs, and
casts doubts on the HCO rather than the HCN as a good dense molecular gas
tracer. Multi-transition observations of both molecules are needed to identify
the best such tracer, its relation to ongoing star formation, and constrain
what may be a considerable range of dense gas properties in such galaxies.Comment: 16 pages, 4 figures, Accepted for publication in the Astrophysical
Journa
A low-mass HI companion of NGC 1569?
High-sensitivity maps of the large-scale structure of atomic hydrogen in the
starburst dwarf galaxy NGC 1569 show evidence for an HI cloud with a mass of
7*10**6 M_sun, at a projected distance of 5 kpc from the parent galaxy. This
cloud may be a condensation in a low-column-density HI halo or a companion
galaxy/HI-cloud. NGC 1569 and its companion are connected by a low surface
brightness HI bridge. At the edge of NGC1569, the HI bridge coincides with
H_alpha arcs, also detected in soft X-rays.Comment: 5 pages, 4 figures, 1 tabl
Detection of Neutral Carbon in the M 31 Dark Cloud D478
Emission from the 492 GHz CI tranition was detected towards the dark cloud
D478 in M31. Using existing 12CO and 13CO measurements, models for the gas
properties of D478 are discussed. The observed CO and C line ratios can be
explained by two-component models (dense cores and tenuous envelopes);
single-density models appear less likely. The models indicate temperatures
T(kin) = 10 K. The beam-averaged C column density is 0.3 - 0.8 times that of
CO, whereas the total carbon to hydrogen ratio N(C)/N(H) = 5-3 times 10**-4.
The resulting CO-to-H2 conversion factor X is about half that of the Solar
Neighbourhood. With temperatures of about 10 K and projected mass densities of
5-10 M(sun)/pc**2 there appears to be no need to invoke the presence of very
cold and very massive clouds. Rather, D478 appears to be comparable to Milky
Way dark cloud complexes such as the Taurus-Auriga dark cloud complex.Comment: 7 Pages, 1 Figure; accepted by A&
Inflation and Factor Shares
We use results from the literature on the determinants of price-cost margins to derive an equation relating labor's share of national income to the inflation rate (as well as to the output gap, the unemployment rate and the capital stock per worker). The equation is tested with a panel of 15 OECD countries. We obtain a robust positive relationship between inflation and the labor share. Our results suggest that disinflation is not distributively neutral, provide empirical support for the distinct concern about price stability shown by trade unions and employers' organizations, and help explaining the negative impact of inflation on growth.Inflation, Functional Distribution of Income, Markups.
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