We present C i , 12CO, 13CO, and C18O ( ) observations of the central region (radius 1 kpc) of the starburst galaxy NGC 1808 at 30-50 pc resolution conducted with the Atacama Large ...Millimeter/submillimeter Array. Radiative transfer analysis of multiline data indicates warm ( K) and dense ( cm−3) molecular gas with high column density of atomic carbon ( cm−2) in the circumnuclear disk (central 100 pc). The C i/H2 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 13CO (2-1), and the ratios of C i to 13CO (2-1) and C18O (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 owing 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 , respectively.
Galactic winds are essential to the regulation of star formation in galaxies. To study the distribution and dynamics of molecular gas in wind, we imaged the nearby starburst galaxy NGC 1482 in CO (J ...= 1 → 0) at a resolution of 1″ ( 100 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 Ew is ∼1% 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.
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), H13CN (1-0), HCO+ (1-0), H13CO+ (1-0), HOC+ (1-0), HCO+ (4-3), CS (2-1), C2H (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-local thermodynamic equilibrium analysis indicates that the molecular gas traced by HCN, H13CN, HCO+, and H13CO+ in the CND is dense ( ) and warm (20 K Tk 100 K). The calculations yield a low average gas density of for a temperature of in the nuclear outflow. Dense gas tracers HCN (1-0), HCO+ (1-0), CS (2-1), and C2H (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.
ALMA imaging of the cold molecular medium in the nearby starburst galaxy NGC 1808 is presented. The observations reveal the distribution of molecular gas, traced by 12CO (1-0) and 12CO (3-2), and ...continuum (93 and 350 GHz) across the central 1 kpc starburst region at a high resolution of . A molecular gas torus (radius ∼ 30 pc) is discovered in the circumnuclear disk (CND; central 100 pc), with a high CO (3-2)/CO (1-0) ratio of ∼1, surrounded by massive (106- ) clouds with high star formation efficiency ( yr−1), molecular spiral arms, and a 500 pc pseudo-ring. The CND harbors a continuum core and molecular gas exhibiting peculiar motion. The new data confirm the line splitting along the minor galactic axis, interpreted as a nuclear gas outflow with average velocity ∼180 km s−1, and show evidence of a velocity gradient of km s−1 pc−1 along the axis. In addition, supershells expanding from the 500 pc ring with maximum velocities of ∼75 km s−1 are revealed. The distribution and CO luminosities of molecular clouds in the central 1 kpc starburst region indicate an evolutionary sequence, from gas accretion onto the 500 pc ring from the large-scale bar to enhanced star formation in the ring, and outflow as feedback.
We present maps of atomic carbon C i( ) and C i( ) emission (hereafter C i (1−0) and C i (2−1), respectively) at a linear resolution ∼1 kpc scale for a sample of one H ii, six LINER, three Seyfert, ...and five starburst galaxies observed with the Herschel Space Observatory. We compare spatial distributions of two C i lines with that of CO (hereafter CO (1−0)) emission, and find that both C i lines distribute similarly to CO (1−0) emission in most galaxies. We present luminosity ratio maps of / , / , (hereafter ) and 70-to-160 m far-infrared color of f70/f160. / , and are centrally peaked in starbursts; whereas they remain relatively constant in LINERs, indicating that star-forming activity can enhance carbon emission, especially for C i (2−1). We explore the correlations between the luminosities of CO (1−0) and C i lines, and find that correlates tightly and almost linearly with both and , suggesting that C i lines, similar to CO (1−0), can trace total molecular gas in H ii, LINER, Seyfert, and starburst galaxies on kpc scales. We investigate the dependence of / , / and C i excitation temperature, Tex, on dust temperature, Tdust, and find noncorrelation and a weak and modest correlation, respectively. The ratio of / stays a smooth distribution in most galaxies, indicating that the conversion factor of C i (1−0) luminosity to H2 mass ( ) changes with CO (1−0) conversion factor ( ) proportionally. Under optically thin and local thermodynamical equilibrium assumptions, we derive a galaxy-wide average carbon excitation temperature of , and an average neutral carbon abundance of 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 (ultra)luminous infrared galaxies. We conclude that the carbon abundance varies in different galaxy types.
Abstract
We report ALMA observations of C i(3P1 − 3P0), 13CO, and C18O(J = 1–0) toward the central region of a nearby Seyfert galaxy NGC 613. The very high resolutions of ...0${^{\prime\prime}_{.}}$26 × 0${^{\prime\prime}_{.}}$23 (=22 × 20 pc) for C i and 0${^{\prime\prime}_{.}}$42 × 0${^{\prime\prime}_{.}}$35 (=36 × 30 pc) for 13CO, and C18O resolve the circumnuclear disk (CND) and star-forming ring. The distribution of C i in the ring resembles that of the CO emission, although C i is prominent in the CND. This can be caused by the low intensities of the CO isotopes due to the low optical depths under the high temperature in the CND. We found that the intensity ratios of C i to 12CO(3–2) ($R_{\rm C\,{\small I}/CO}$) and to 13CO(1–0) ($R_{\rm C\,{\small I}/^{13}CO}$) 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 $R_{\rm C\,{\small I}/CO}$, but those of C i at spots of high $R_{\rm C\,{\small I}/CO}$ are different from those of CO. These results indicate that C i at the high $R_{\rm C\,{\small I}/CO}$ traces different gas from that traced by the CO lines. The C i 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 active galactic nucleus through its radio jets.
Abstract
Molecular outflows are expected to play a key role in galaxy evolution at high redshift. To study the impact of outflows on star formation at the epoch of reionization, we performed ...sensitive Atacama Large Millimeter/submillimeter Array observations of OH 119
μ
m toward J2054-0005, a luminous quasar at
z
= 6.04. The OH line is detected and exhibits a P-Cygni profile that can be fitted with a broad blueshifted absorption component, providing unambiguous evidence of an outflow, and an emission component at near-systemic velocity. The mean and terminal outflow velocities are estimated to be
v
out
≈ 670 and 1500 km s
−1
, respectively, making the molecular outflow in this quasar one of the fastest at the epoch of reionization. The OH line is marginally spatially resolved for the first time in a quasar at
z
> 6, revealing that the outflow extends over the central 2 kpc region. The mass outflow rate is comparable to the star formation rate (
M
̇
out
/
SFR
∼
2
), indicating rapid (∼10
7
yr) quenching of star formation. The mass outflow rate in a sample of star-forming galaxies and quasars at 4 <
z
< 6.4 exhibits a positive correlation with the total infrared luminosity, although the scatter is large. Owing to the high outflow velocity, a large fraction (up to ∼50%) of the outflowing molecular gas may be able to escape from the host galaxy into the intergalactic medium.
Abstract
We report Atacama Large Millimeter/submillimeter Array Band 3 observations of CO(6−5), CO(7−6), and C
i
(2−1) in B14-65666 (“Big Three Dragons”), one of the brightest Lyman-break galaxies at
...z
> 7 in the rest-frame ultraviolet continuum, far-infrared continuum, and emission lines of O
iii
88
μ
m and C
ii
158
μ
m. CO(6−5), CO(7−6), and C
i
(2−1), whose 3
σ
upper limits on the luminosities are approximately 40 times fainter than the C
ii
luminosity, are all not detected. The
L
C
II
/
L
CO(6–5)
and
L
C
II
/
L
CO(7–6)
ratios are higher than the typical ratios obtained in dusty star-forming galaxies or quasar host galaxies at similar redshifts, and they may suggest a lower gas density in the photodissociated region in B14-65666. By using the (1) C
ii
luminosity, (2) dust mass-to-gas mass ratio, and (3) a dynamical mass estimate, we find that the molecular gas mass (
M
mol
) is (0.05–11) × 10
10
M
⊙
. This value is consistent with the upper limit inferred from the nondetection of mid-
J
CO and C
i
(2−1). Despite the large uncertainty in
M
mol
, we estimate a molecular gas-to-stellar mass ratio (
μ
gas
) of 0.65–140 and a gas depletion time (
τ
dep
) of 2.5–550 Myr; these values are broadly consistent with those of other high-redshift galaxies. B14-65666 could be an ancestor of a passive galaxy at
z
≳ 4 if no gas is fueled from outside the galaxy.
Abstract
Atomic carbon (C i) 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 C i as the ...tracer, we performed C i(3P1–3P0) hereinafter C i(1–0) mapping observations of the northern part of the nearby spiral galaxy M 83 with the Atacama Submillimeter Telescope Experiment (ASTE) telescope and compared the distributions of C i(1–0) with CO lines CO(1–0), CO(3–2), and 13CO(1–0), H i, and infrared (IR) emission (70, 160, and 250 μm). The C i(1–0) distribution in the central region is similar to that of the CO lines, whereas C i(1–0) in the arm region is distributed outside the CO. We examined the dust temperature, Tdust, and dust mass surface density, Σdust, by fitting the IR continuum-spectrum distribution with a single-temperature modified blackbody. The distribution of Σdust shows a much better consistency with the integrated intensity of CO(1–0) than with that of C i(1–0), indicating that CO(1–0) is a good tracer of the cold molecular gas. The spatial distribution of the C i excitation temperature, Tex, was examined using the intensity ratio of the two C i transitions. An appropriate Tex at the central, bar, arm, and inter-arm regions yields a constant C$/$H2 abundance ratio of ∼7 × 10−5 within a range of 0.1 dex in all regions. We successfully detected weak C i(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 C i(1–0) is found to be strongly correlated with Tdust. Our results indicate that the atomic carbon is a photodissociation product of CO, and consequently, compared to CO(1–0), C i(1–0) is less reliable in tracing the bulk of “cold” molecular gas in the galactic disk.
Abstract
The barred spiral galaxy NGC 613 has a star-forming ring in the center, and near-infrared observations have previously shown that the star formation activity on the eastern and western sides ...of the ring is asymmetric. We examined the dynamics and physical state of the molecular gas in the ring using high-resolution (∼15 pc) 12CO(1–0), 12CO(3–2), and 13CO(1–0) observations with ALMA. Using a dendrogram, we identified 111 molecular clouds in the bar and ring, and found that the virial parameter (αvir) gradually decreases (αvir < 2) toward the confluence of the northern bar and eastern ring, while the virial parameter is large (αvir > 2) around the corresponding confluence in the western side of the ring. A non-LTE analysis using RADEX showed that the temperature and density of the molecular gas increase downstream of the eastern point of confluence, whereas they change irregularly on the western side. The star formation efficiency is (1.7 ± 0.2) × 10−8 yr−1 in the eastern side of the ring, which is substantially higher than the (0.9 ± 0.3) × 10−8 yr−1 for the western side of the ring. Position–velocity diagrams show that the relative velocity of the gas between the bar and the ring is ∼70 km s−1 in the east, while it reaches ∼170 km s−1 in the west. We suggest that the star formation activity in the central region of NGC 613 depends strongly on the relative velocity of the gas between the bar and the ring.
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![ALMA [C i ] observations t...](http://api.summon.serialssolutions.com/2.0.0/image/issn/XR4PS5YY4K/0004-6264_2053-051X/small "ALMA [C i ] observations toward the central region of Seyfert galaxy NGC 613")