105 research outputs found
Deep CO Observations and the CO-to-H_2 Conversion Factor in DDO 154, a Low Metallicity Dwarf Irregular Galaxy
We present a deep spectroscopic search for CO emission in the dwarf irregular
galaxy DDO154, which has an Oxygen abundance of only 1/20 the solar value. The
observations were conducted in order to constrain the CO-to-
conversion factor at low metallicity. No CO was detected, however, despite
being one of the sensitive observations done towards galaxies of this type. We
succeed in putting a strong lower limit on the conversion factor, at least 10
times the Galactic value. Our result supports previous studies which argue for
a high conversion factor at low metallicity.Comment: 11 pages, 4 figures. Accepted for publication in PAS
Constraint on the inflow/outflow rates in star-forming galaxies at z~1.4 from molecular gas observations
We constrain the rate of gas inflow into and outflow from a main-sequence
star-forming galaxy at z~1.4 by fitting a simple analytic model for the
chemical evolution in a galaxy to the observational data of the stellar mass,
metallicity, and molecular gas mass fraction. The molecular gas mass is derived
from CO observations with a metallicity-dependent CO-to-H2 conversion factor,
and the gas metallicity is derived from the H{\alpha} and [NII]{\lambda} 6584
emission line ratio. Using a stacking analysis of CO integrated intensity maps
and the emission lines of H{\alpha} and [NII], the relation between stellar
mass, metallicity, and gas mass fraction is derived. We constrain the inflow
and outflow rates with least-chi-square fitting of a simple analytic chemical
evolution model to the observational data. The best-fit inflow and outflow
rates are ~1.7 and ~0.4 in units of star-formation rate, respectively. The
inflow rate is roughly comparable to the sum of the star-formation rate and
outflow rate, which supports the equilibrium model for galaxy evolution; i.e.,
all inflow gas is consumed by star formation and outflow.Comment: 5 pages, 2 figures, Accepted for publication in the Ap
Evolutionary phases of gas-rich galaxies in a galaxy cluster at z=1.46
We report a survey of molecular gas in galaxies in the XMMXCS J2215.9-1738
cluster at . We have detected emission lines from 17 galaxies within a
radius of from the cluster center, in Band 3 data of the Atacama
Large Millimeter/submillimeter Array (ALMA) with a coverage of 93 -- 95 GHz in
frequency and 2.33 arcmin in spatial direction. The lines are all
identified as CO =2--1 emission lines from cluster members at by
their redshifts and the colors of their optical and near-infrared (NIR)
counterparts. The line luminosities reach down to K km s pc. The spatial distribution of
galaxies with a detection of CO(2--1) suggests that they disappear from the
very center of the cluster. The phase-space diagram showing relative velocity
versus cluster-centric distance indicates that the gas-rich galaxies have
entered the cluster more recently than the gas-poor star-forming galaxies and
passive galaxies located in the virialized region of this cluster. The results
imply that the galaxies have experienced ram-pressure stripping and/or
strangulation during the course of infall towards the cluster center and then
the molecular gas in the galaxies at the cluster center is depleted by star
formation.Comment: 7 pages, 4 figures, 1 table, accepted for publication in the ApJ
Letter
Molecular Gas Properties in the Host Galaxy of GRB 080207
We present the results of CO(1–0) and CO(4–3) observations of the host galaxy of a long-duration gamma-ray burst GRB 080207 at z = 2.0858 by using the Karl G. Jansky Very Large Array and the Atacama Large Millimeter/submillimeter Array. The host is detected in CO(1–0) and CO(4–3), becoming the first case for a gamma-ray burst (GRB) host with more than two CO transitions detected combined with CO(2–1) and CO(3–2) in the literature. Adopting a metallicity-dependent CO-to-H2 conversion factor, we derive a molecular gas mass of M gas = 8.7 × 1010 M ⊙, which places the host in a sequence of normal star-forming galaxies in an M gas–star formation rate (SFR) plane. A modified blackbody fit to the far-infrared–millimeter photometry results in a dust temperature of 37 K and a dust mass of M dust = 1.5 × 108 M ⊙. The spatially resolved CO(4–3) observations allow us to examine the kinematics of the host. The CO velocity field shows a clear rotation and is reproduced by a rotation-dominated disk model with a rotation velocity of 350 km s‑1 and a half-light radius of 2.4 kpc. The CO spectral line energy distribution derived from the four CO transitions is similar to that of starburst galaxies, suggesting a high excitation condition. Comparison of molecular gas properties between the host and normal (main-sequence) galaxies at similar redshifts shows that they share common properties such as gas mass fraction, gas depletion timescale, gas-to-dust ratio, location in the M gas–SFR (or surface density) relation, and kinematics, suggesting that long-duration GRBs can occur in normal star-forming environments at z ∼ 2
Characterizing CO Emitters in the SSA22-AzTEC26 Field
We report the physical characterization of four CO emitters detected near the
bright submillimeter galaxy (SMG) SSA22-AzTEC26. We analyze the data from
Atacama Large Millimeter/submillileter Array band 3, 4, and 7 observations of
the SSA22-AzTEC26 field. In addition to the targeted SMG, we detect four line
emitters with a signal-to-noise ratio in the cube smoothed with 300 km
s FWHM Gaussian filter. All four sources have NIR counterparts within
1\arcsec. We perform UV-to-FIR spectral energy distribution modeling to
derive the photometric redshifts and physical properties. Based on the
photometric redshifts, we reveal that two of them are CO(2-1) at redshifts of
1.113 and 1.146 and one is CO(3-2) at . The three sources are massive
galaxies with a stellar mass , but have different
levels of star formation. Two lie within the scatter of the main sequence (MS)
of star-forming galaxies at , and the most massive galaxy lies
significantly below the MS. However, all three sources have a gas fraction
within the scatter of the MS scaling relation. This shows that a blind CO line
search can detect massive galaxies with low specific star formation rates that
still host large gas reservoirs and that it also complements targeted surveys,
suggesting later gas acquisition and the need for other mechanisms in addition
to gas consumption to suppress star formation.Comment: accepted for publication in the Astrophysical Journa
- …