29 research outputs found
Gas Dynamics and Outflow in the Barred Starburst Galaxy NGC 1808 Revealed with ALMA
NGC 1808 is a nearby barred starburst galaxy with an outflow from the nuclear
region. To study the inflow and outflow processes related to star formation and
dynamical evolution of the galaxy, we have carried out CO ()
mapping observations of the central kpc of NGC 1808 using the
Atacama Large Millimeter/submillimeter Array (ALMA). Four distinct components
of molecular gas are revealed at high spatial resolution of 2\arcsec
( pc): (1) a compact ( pc) circumnuclear disk (CND), (2)
pc ring, (3) gas-rich galactic bar, and (4) spiral arms. Basic
geometric and kinematic parameters are derived for the central 1-kpc region
using tilted-ring modeling. The derived rotation curve reveals multiple mass
components that include (1) a stellar bulge, (2) nuclear bar and molecular CND,
and (3) unresolved massive (\sim10^7~M_\sun) core. Two systemic velocities,
998 km s for the CND and 964 km s for the 500-pc ring, are
revealed, indicating a kinematic offset. The pattern speed of the primary bar,
derived by using a cloud-orbit model, is km s
kpc. Non-circular motions are detected associated with a nuclear
spiral pattern and outflow in the central 1-kpc region. The ratio of the mass
outflow rate to the star formation rate is
in the case of optically thin CO (1-0) emission in the outflow, suggesting low
efficiency of star formation quenching.Comment: Accepted for publication in The Astrophysical Journa
ALMA multiline observations toward the central region of NGC 613
We report ALMA observations of molecular gas and continuum emission in the 90
and 350 GHz bands toward a nearby Seyfert galaxy NGC 613. Radio continuum
emissions were detected at 95 and 350 GHz from both the circum-nuclear disk
(CND) ( pc) and a star-forming ring (250 pc pc), and
the 95 GHz continuum was observed to extend from the center at a position angle
of . The archival 4.9 GHz data and our 95 GHz data
show spectral indices of and along the jets and in the
star-forming ring; these can be produced by synchrotron emission and free-free
emission, respectively. In addition, we detected the emission of CO(3-2),
HCN(1-0), HCN(4-3), HCO(1-0), HCO(4-3), CS(2-1), and CS(7-6) in both
the CND and ring. The rotational temperatures and column densities of molecules
derived from and lines of HCN and HCO and and
of CS in the CND and ring were derived. Furthermore, a non-LTE model revealed
that the kinetic temperature of K in the CND is higher than
K in the ring, utilizing the intensity ratios of HCN,
HCO, and CS. The star-formation efficiency in the CND is almost an order of
magnitude lower than those at the spots in the star-forming ring, while the
dominant activity of the central region is the star formation rather than
active galactic nuclei. We determined that the large velocity dispersion of CO
extending toward the north side of the CND and decomposing into blueshifted and
redshifted features is probably explained by the effect of the radio jets.
These results strongly suggest that the jets heat the gas in the CND, in which
the feedback prevents star formation.Comment: 37 pages, 22 figures, 6tables, Accepted for publication in PAS
Molecular Gas Outflow in the Starburst Galaxy NGC 1482
Galactic winds are essential to regulation of star formation in galaxies. To
study the distribution and dynamics of molecular gas in a wind, we imaged the
nearby starburst galaxy NGC 1482 in CO () at a resolution of
1'' ( pc) using the Atacama Large Millimeter/submillimeter Array.
Molecular gas is detected in a nearly edge-on disk with a radius of 3 kpc and a
biconical outflow emerging from the central 1 kpc starburst and extending to at
least 1.5 kpc perpendicular to the disk. In the outflow, CO gas is distributed
approximately as a cylindrically symmetrical envelope surrounding the warm and
hot ionized gas traced by H and soft X-rays. The velocity, mass outflow
rate, and kinetic energy of the molecular outflow are
,
, and
, respectively.
is comparable to the star formation rate
() and is of the
total energy released by stellar feedback in the past
, which is the dynamical timescale of the outflow. The
results indicate that the wind is starburst driven.Comment: Accepted to Ap
ALMA Observations of Atomic Carbon [C I] () and Low- CO Lines in the Starburst Galaxy NGC 1808
We present [C I] (), CO,
CO, and CO () observations of the central region
(radius 1 kpc) of the starburst galaxy NGC 1808 at 30-50 pc resolution
conducted with Atacama Large Millimeter/submillimeter Array. Radiative transfer
analysis of multiline data indicates warm ( K)
and dense ( cm) molecular gas with
high column density of atomic carbon (
cm) in the circumnuclear disk (central 100 pc). The C I/H abundance
in the central 1 kpc is , consistent with the values in
luminous infrared galaxies. The intensity ratios of [C I]/CO(1-0) and [C
I]/CO(3-2), respectively, decrease and increase with radius in the central 1
kpc, whereas [C I]/CO(2-1) is uniform within statistical errors. The result can
be explained by excitation and optical depth effects, since the effective
critical density of CO (2-1) is comparable to that of [C I]. The distribution
of [C I] is similar to that of CO (2-1), and the ratios of [C I] to
CO (2-1) and CO (2-1) are uniform within in the
central pc starburst disk. The results suggest that [C I]
() luminosity can be used as a
CO-equivalent tracer of molecular gas mass, although caution is needed when
applied in resolved starburst nuclei (e.g., circumnuclear disk), where the [C
I]/CO(1-0) luminosity ratio is enhanced due to high excitation and atomic
carbon abundance. The [C I]/CO(1-0) intensity ratio toward the base of the
starburst-driven outflow is , and the upper limits of the mass
and kinetic energy of the atomic carbon outflow are
and erg, respectively.Comment: Accepted for publication in ApJ (30 pages, 15 figures
Hot Ammonia in the Center of the Seyfert 2 galaxy NGC 3079
We present the results of ammonia observations toward the center of NGC 3079.
The NH3(J, K) = (1, 1) and (2, 2) inversion lines were detected in absorption
with the Tsukuba 32-m telescope, and the NH3(1,1) through (6,6) lines with the
VLA, although the profile of NH3(3,3) was in emission in contrast to the other
transitions. The background continuum source, whose flux density was ~50 mJy,
could not be resolved with the VLA beam of ~< 0."09 x 0."08. All ammonia
absorption lines have two distinct velocity components: one is at the systemic
velocity and the other is blueshifted, and both components are aligned along
the nuclear jets. For the systemic components, the relatively low temperature
gas is extended more than the high temperature gas. The blueshifted NH3(3,3)
emission can be regarded as ammonia masers associated with shocks by strong
winds probably from newly formed massive stars or supernova explosions in dense
clouds in the nuclear megamaser disk. Using para-NH3(1,1), (2,2), (4,4) and
(5,5) lines with VLA, we derived the rotational temperature Trot = 120 +- 12 K
and 157 +- 19 K for the systemic and blueshifted components, respectively. The
total column densities of NH3(0,0)-(6,6), assuming Tex ~Trot, were (8.85+-0.70)
x 10^16 cm^-2 and (4.47+-0.78) x 10^16 cm-2 for the systemic and blueshifted
components, respectively. The fractional abundance of NH3 relative to molecular
hydrogen H2 for the systemic and blueshifted was [NH3]/[H2]=1.3x10^-7 and 6.5 x
10^-8, respectively. We also found the F = 4-4 and F = 5-5 doublet lines of OH
2{Pi}3/2 J = 9/2 in absorption, which could be fitted by two velocity
components, systemic and redshifted components. The rotational temperature of
OH was estimated to be Trot,OH >~ 175 K, tracing hot gas associated with the
interaction of the fast nuclear outflow with dense molecular material around
the nucleus.Comment: 25 pages, 9 figures, Accepted for publication in PAS
ALMA [CI] observations toward the central region of a Seyfert galaxy NGC 613
We report ALMA observations of [CI](), CO, and CO
() toward the central region of a nearby Seyfert galaxy NGC 613. The
very high resolutions of pc) for [CI] and
pc) for CO, and CO resolve the
circum-nuclear disk (CND) and star-forming ring. The distribution of [CI] in
the ring resembles that of the CO emission, although [CI] is prominent in the
CND. This can be caused by the low intensities of the CO isotopes due to the
low optical depths under the high temperature in the CND. We found that the
intensity ratios of [CI] to CO(3-2) () and to
CO(1-0) () are high at several positions around the
edge of the ring. The spectral profiles of CO lines mostly correspond each
other in the spots of the ring and high , but those of [CI] at
spots of high are different from CO. These results indicate
that [CI] at the high traces different gas from that traced by
the CO lines. The [CI] kinematics along the minor axis of NGC 613 could be
interpreted as a bubbly molecular outflow. The outflow rate of molecular gas is
higher than star formation rate in the CND. The flow could be mainly boosted by
the AGN through its radio jets.Comment: 6 pages, 4 figures, 1 supplement material, Accepted for publication
in PASJ Lette
Dense molecular gas in the starburst nucleus of NGC 1808
Dense molecular gas tracers in the central 1 kpc region of the superwind
galaxy NGC 1808 have been imaged by ALMA at a resolution of 1" (~50 pc).
Integrated intensities and line intensity ratios of HCN (1-0), HCN
(1-0), HCO (1-0), HCO (1-0), HOC (1-0), HCO (4-3), CS
(2-1), CH (1-0), and previously detected CO (1-0) and CO (3-2) are
presented. SiO (2-1) and HNCO (4-3) are detected toward the circumnuclear disk
(CND), indicating the presence of shocked dense gas. There is evidence that an
enhanced intensity ratio of HCN(1-0)/HCO(1-0) reflects star formation
activity, possibly in terms of shock heating and electron excitation in the CND
and a star-forming ring at radius ~300 pc. A non-LTE analysis indicates that
the molecular gas traced by HCN, HCN, HCO, and HCO in the
CND is dense (~ cm) and warm (20
K<100 K). The calculations yield a low average gas density of
~ cm for a temperature of
K in the nuclear outflow. Dense gas tracers HCN (1-0),
HCO (1-0), CS (2-1), and CH (1-0) are detected for the first time in
the superwind of NGC 1808, confirming the presence of a velocity gradient in
the outflow direction.Comment: Accepted for publication in Ap
Discovery of H2O Megamasers in Obscured Active Galactic Nuclei
Recently a new method to discover obscured active galactic nuclei (AGNs) by
utilizing X-ray and Infrared data has been developed. We carried out a survey
of H2O maser emission toward ten obscured AGNs with the Nobeyama 45-m
telescope. We newly detected the maser emission with the signal-noise-ratio
(SNR) of above 4 from two AGNs, NGC 1402 and NGC 7738. We also found a
tentative detection with its SNR > 3 in NGC 5037. The detection rate of 20% is
higher than those of previous surveys (usually several percents).Comment: 5 pages, 1 figures, 3 tables, accepted for publication in PAS
Atomic Carbon [CI] Mapping of the Nearby Galaxy M83
Atomic carbon (CI) has been proposed to be a global tracer of the molecular
gas as a substitute for CO, however, its utility remains unproven. To evaluate
the suitability of CI as the tracer, we performed [CI]
(hereinafter [CI](1-0)) mapping observations of the northern part of the nearby
spiral galaxy M83 with the ASTE telescope and compared the distributions of
[CI](1-0) with CO lines (CO(1-0), CO(3-2), and CO(1-0)), HI, and
infrared (IR) emission (70, 160, and 250m). The [CI](1-0) distribution in
the central region is similar to that of the CO lines, whereas [CI](1-0) in the
arm region is distributed outside the CO. We examined the dust temperature,
, and dust mass surface density, , by fitting
the IR continuum-spectrum distribution with a single-temperature modified
blackbody. The distribution of shows a much better
consistency with the integrated intensity of CO(1-0) than with that of
[CI](1-0), indicating that CO(1-0) is a good tracer of the cold molecular gas.
The spatial distribution of the [CI] excitation temperature, , was
examined using the intensity ratio of the two [CI] transitions. An appropriate
at the central, bar, arm, and inter-arm regions yields a constant
[C]/[H] abundance ratio of within a range of 0.1 dex
in all regions. We successfully detected weak [CI](1-0) emission, even in the
inter-arm region, in addition to the central, arm, and bar regions, using
spectral stacking analysis. The stacked intensity of [CI](1-0) is found to be
strongly correlated with . Our results indicate that the atomic
carbon is a photodissociation product of CO, and consequently, compared to
CO(1-0), [CI](1-0) is less reliable in tracing the bulk of "cold" molecular gas
in the galactic disk.Comment: 14 pages, 11 figures, Accepted for publication in PAS
Resolved neutral carbon emission in nearby galaxies: [CI] Lines as Total Molecular Gas Tracers
We present maps of atomic carbon [CI](1-0) and [CI](2-1) at a linear
resolution ~1kpc scale for a sample of one HII, six LINER, three Seyfert and
five starburst galaxies observed with Herschel. We compare spatial
distributions of two [CI] lines with that of CO(1-0) emission, and find that
both [CI] lines distribute similarly to CO(1-0) emission in most galaxies. We
present luminosity ratio maps of L'_[CI](1-0)/L'_CO(1-0),
L'_[CI](2-1)/L'_CO(1-0), L'_[CI](2-1)/L'_[CI](1-0) (hereafter R_[CI]) and
f_70/f_160. L'_[CI](2-1)/L'_CO(1-0), R_[CI] and f_70/f_160 are centrally peaked
in starbursts; whereas remain relatively constant in LINERs, indicating that
star-forming activity can enhance carbon emission, especially for [CI](2-1). We
explore the correlations between the luminosities of CO(1-0) and [CI] lines,
and find that L'_CO(1-0) correlates tightly and almost linearly with both
L'_[CI](1-0) and L'_[CI](2-1), suggesting that [CI] lines, similar as CO(1-0),
can trace total molecular gas in our resolved galaxies on kpc scales. We
investigate the dependence of L'_[CI](1-0)/L'_CO(1-0), L'_[CI](2-1)/L'_CO(1-0)
and [CI] excitation temperature T_ex on dust temperature T_dust, and find
non-correlation, a weak and modest correlation, respectively. The ratio of
L'_[CI](1-0)/L'_CO(1-0) stays smooth distribution in most galaxies, indicating
that the conversion factor of [CI](1-0) luminosity to H_2 mass (X_[CI](1-0))
changes with CO(1-0) conversion factor (\alpha_CO) proportionally. Under
optically thin and LTE assumptions, we derive a galaxy-wide average carbon
excitation temperature T_ex ~ 19.7 \pm 0.5K and an average neutral carbon
abundance X[CI]/X[H_2] ~2.5 \pm 1.0 * 10^{-5} in our resolved sample, which is
comparable to the usually adopted value of 3*10^{-5}, but ~3 times lower than
the carbon abundance in local (U)LIRGs. We conclude that the carbon abundance
varies in different galaxy types.Comment: 15 pages, 5 figures, accepted for publication in Ap