177,144 research outputs found
Full-disc CO(1-0) mapping across nearby galaxies of the EMPIRE survey and the CO-to-H conversion factor
Carbon monoxide (CO) provides crucial information about the molecular gas
properties of galaxies. While CO has been targeted extensively,
isotopologues such as CO have the advantage of being less optically
thick and observations have recently become accessible across full galaxy
discs. We present a comprehensive new dataset of CO(1-0) observations
with the IRAM 30-m telescope of the full discs of 9 nearby spiral galaxies from
the EMPIRE survey at a spatial resolution of 1.5kpc. CO(1-0) is
mapped out to and detected at high signal-to-noise throughout our
maps. We analyse the CO(1-0)-to-CO(1-0) ratio () as a
function of galactocentric radius and other parameters such as the
CO(2-1)-to-CO(1-0) intensity ratio, the 70-to-160m flux
density ratio, the star-formation rate surface density, the star-formation
efficiency, and the CO-to-H conversion factor. We find that varies by
a factor of 2 at most within and amongst galaxies, with a median value of 11
and larger variations in the galaxy centres than in the discs. We argue that
optical depth effects, most likely due to changes in the mixture of
diffuse/dense gas, are favored explanations for the observed variations,
while abundance changes may also be at play. We calculate a spatially-resolved
CO(1-0)-to-H conversion factor and find an average value of
cm (K.km/s) over our sample with a standard
deviation of a factor of 2. We find that CO(1-0) does not appear to be a
good predictor of the bulk molecular gas mass in normal galaxy discs due to the
presence of a large diffuse phase, but it may be a better tracer of the mass
than CO(1-0) in the galaxy centres where the fraction of dense gas is
larger.Comment: accepted for publication in MNRA
Extended Cold Molecular Gas Reservoirs in z~3.4 Submillimeter Galaxies
We report the detection of spatially resolved CO(1-0) emission in the z~3.4
submillimeter galaxies (SMGs) SMM J09431+4700 and SMM J13120+4242, using the
Expanded Very Large Array (EVLA). SMM J09431+4700 is resolved into the two
previously reported millimeter sources H6 and H7, separated by ~30kpc in
projection. We derive CO(1-0) line luminosities of L'(CO 1-0) = (2.49+/-0.86)
and (5.82+/-1.22) x 10^10 K km/s pc^2 for H6 and H7, and L'(CO 1-0) =
(23.4+/-4.1) x 10^10 K km/s pc^2 for SMM J13120+4242. These are ~1.5-4.5x
higher than what is expected from simple excitation modeling of higher-J CO
lines, suggesting the presence of copious amounts of low-excitation gas. This
is supported by the finding that the CO(1-0) line in SMM J13120+4242, the
system with lowest CO excitation, appears to have a broader profile and more
extended spatial structure than seen in higher-J CO lines (which is less
prominently seen in SMM J09431+4700). Based on L'(CO 1-0) and excitation
modeling, we find M_gas = 2.0-4.3 and 4.7-12.7 x 10^10 Msun for H6 and H7, and
M_gas = 18.7-69.4 x 10^10 Msun for SMM J13120+4242. The observed CO(1-0)
properties are consistent with the picture that SMM J09431+4700 represents an
early-stage, gas-rich major merger, and that SMM J13120+4242 represents such a
system in an advanced stage. This study thus highlights the importance of
spatially and dynamically resolved CO(1-0) observations of SMGs to further
understand the gas physics that drive star formation in these distant galaxies,
which becomes possible only now that the EVLA rises to its full capabilities.Comment: 6 pages, 4 figures, to appear in ApJL (EVLA Special Issue; accepted
May 19, 2011
CO(1-0) in z>2 Quasar Host Galaxies: No Evidence for Extended Molecular Gas Reservoirs
We report the detection of CO(1-0) emission in the strongly lensed
high-redshift quasars IRAS F10214+4724 (z=2.286), the Cloverleaf (z=2.558), RX
J0911+0551 (z=2.796), SMM J04135+10277 (z=2.846), and MG 0751+2716 (z=3.200),
using the Expanded Very Large Array and the Green Bank Telescope. We report
lensing-corrected CO(1-0) line luminosities of L'(CO) = 0.34-18.4 x 10^10 K
km/s pc^2 and total molecular gas masses of M(H2) = 0.27-14.7 x 10^10 Msun for
the sources in our sample. Based on CO line ratios relative to previously
reported observations in J>=3 rotational transitions and line excitation
modeling, we find that the CO(1-0) line strengths in our targets are consistent
with single, highly-excited gas components with constant brightness temperature
up to mid-J levels. We thus do not find any evidence for luminous extended, low
excitation, low surface brightness molecular gas components. These properties
are comparable to those found in z>4 quasars with existing CO(1-0)
observations. These findings stand in contrast to recent CO(1-0) observations
of z~2-4 submillimeter galaxies (SMGs), which have lower CO excitation and show
evidence for multiple excitation components, including some low-excitation gas.
These findings are consistent with the picture that gas-rich quasars and SMGs
represent different stages in the early evolution of massive galaxies.Comment: 6 pages, 4 figures, 1 table, to appear in ApJL (EVLA Special Issue;
accepted June 10, 2011
The Molecular Gas Reservoirs of Galaxies: A comparison of CO(1-0) and dust-based molecular gas masses
We test the use of long-wavelength dust continuum emission as a molecular gas
tracer at high redshift, via a unique sample of 12, z~2 galaxies with
observations of both the dust continuum and CO(1-0) line emission (obtained
with the Atacama Large Millimeter Array and Karl G. Jansky Very Large Array,
respectively). Our work is motivated by recent, high redshift studies that
measure molecular gas masses (\ensuremath{\rm{M}_{\rm{mol}}}) via a calibration
of the rest-frame m luminosity () against the
CO(1-0)-derived \ensuremath{\rm{M}_{\rm{mol}}}\ of star-forming galaxies. We
hereby test whether this method is valid for the types of high-redshift,
star-forming galaxies to which it has been applied. We recover a clear
correlation between the rest-frame m luminosity, inferred from the
single-band, long-wavelength flux, and the CO(1-0) line luminosity, consistent
with the samples used to perform the m calibration. The molecular gas
masses, derived from , agree to within a factor of
two with those derived from CO(1-0). We show that this factor of two
uncertainty can arise from the values of the dust emissivity index and
temperature that need to be assumed in order to extrapolate from the observed
frequency to the rest-frame at 850. The extrapolation to
850 therefore has a smaller effect on the accuracy of \Mmol\
derived via single-band dust-continuum observations than the assumed
CO(1-0)-to-\ensuremath{\rm{M}_{\rm{mol}}}\ conversion factor. We therefore
conclude that single-band observations of long-wavelength dust emission can be
used to reliably constrain the molecular gas masses of massive, star-forming
galaxies at
Study of pharmaceutical industrial problems
The growth of a human colon carcinoma cell line (SK-CO-1) and its production of carcinoembryonic antigen (CEA) in monolayer culture and on single layers of glass beads in unit gravity were evaluated. The limitations of using a microsphere-cell growth system in unit gravity were identified and how these may be overcome in space was considered. The project had the following tasks: (1) growth of cultured human colon carcinoma cells on a monolayer and CEA production; (2) evaluation of CEA production and release by SK-CO-1 cells grown on glass beads; (3) evaluation of other microcarriers for growing SK-CO-1 cells and determination of the minimum amount of culture medium needed for cell growth; and (4) growth of SK-CO-1 cells on collagen monolayers and CEA production
Beneath the Baselines: Detecting Molecular Emission from Submillimeter Galaxies with the GBT
We report the first detection of a submillimeter galaxy (SMG) in CO(1 →0) emission using the GBT. We identify a line with Δv_(FWHM) ~1000 kms^(−1) in the 1 cm spectrum of SMM J13120+4242 at z = 3.408, which is significantly greater than the width of the previously detected CO(4→3) line. If the observed CO(1→0) line profile arises from a single object and not several merging objects, the CO(4 →3)/CO(1→0) brightness temperature ratio of ~0.26 suggests n(H_2) > 10^3 cm^(−3) and the presence of sub-thermally excited gas. The 10σ integrated line flux implies a cold molecular gas mass M(H2) ~10^(11)M_⊙, comparable to the dynamical mass estimate and four times larger than the H_2 mass found from the CO(4 →3) line. While our observations confirm that this SMG is massive and highly gas-rich, they also suggest that J_(upper) > 3 transitions of CO may not accurately trace cold, diffuse molecular gas in SMGs
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