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Register a new userThe 300-pc Scale ALMA View of [CI] $^3P_1$-$^3P_0$, CO $J$=1-0, and 609 $mu$m Dust Continuum in A Luminous Infrared Galaxy
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We present high-quality ALMA Band 8 observations of the [CI] $^3P_1$-$^3P_0$ line and 609 $mu$m dust continuum emission toward the nearby luminous infrared galaxy (LIRG) IRAS F18293-3413, as well as matched resolution (300-pc scale) Band 3 CO $J=$1-0 data, which allow us to assess the use of the [CI] $^3P_1$-$^3P_0$ line as a total gas mass estimator. We find that the [CI] line basically traces structures detected in CO (and dust), and a mean (median) [CI]/CO luminosity ($L_{rm [CI]}$/$L_{rm CO}$) ratio of 0.17 (0.16) with a scatter of 0.04. However, a pixel-by-pixel comparison revealed that there is a radial $L_{rm [CI]}$/$L_{rm CO}$ gradient and a superlinear $L_{rm CO}$ vs. $L_{rm [CI]}$ relation (slope = 1.54 $pm$ 0.02) at this spatial scale, which can be explained by radial excitation and/or line opacity gradients. Based on the molecular gas masses converted from the dust continuum emission, we found that the CO-to-H$_2$ and [CI]-to-H$_2$ conversion factors are relatively flat across the molecular gas disk with a median value of 3.5$^{+1.9}_{-1.3}$ and 20.7$^{+9.2}_{-4.9}$ $M_{odot}$ (K km s$^{-1}$ pc$^2$)$^{-1}$, respectively. A non-LTE calculation yields that typical molecular gas properties seen in nearby (U)LIRGs ($n_{rm H_2}$ = 10$^{3-4}$ cm$^{-3}$, $T_{rm kin}$ $sim$ 50 K, and $X_{rm CI}$ = (0.8-2.3) $times$ 10$^{-5}$) can naturally reproduce the derived [CI]-to-H$_2$ conversion factor. However, we caution that a careful treatment of the physical gas properties is required in order to measure H$_2$ gas mass distributions in galaxies using a single [CI] line. Otherwise, a single [CI] line is not a good molecular gas estimator in a spatially resolved manner.
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We present the results of surveying [CI] $^3P_1-^3P_0$, $^{12}$CO $J=4-3$, and 630 $mu$m dust continuum emission for 36 nearby ultra/luminous infrared galaxies (U/LIRGs) using the Band 8 receiver mounted on the Atacama Compact Array (ACA) of the Atacama Large Millimeter/submillimeter Array. We describe the survey, observations, data reduction, and results; the main results are as follows. (i) We confirmed that [CI] $^3P_1-^3P_0$ has a linear relationship with both the $^{12}$CO $J=4-3$and 630 $mu$m continuum. (ii) In NGC 6052 and NGC 7679, $^{12}$CO $J=4-3$ was detected but [CI] $^3P_1-^3P_0$ was not detected with a [CI] $^3P_1-^3P_0$/ $^{12}$CO $J=4-3$ ratio of $lesssim0.08$. Two possible scenarios of weak [CI] $^3P_1-^3P_0$ emission are C$^0$-poor/CO-rich environments or an environment with an extremely large [CI] $^3P_1-^3P_0$ missing flux. (iii) There is no clear evidence showing that galaxy mergers, AGNs, and dust temperatures control the ratios of [CI] $^3P_1-^3P_0$/ $^{12}$CO $J=4-3$ and $L_{rm [CI](1-0)}/L_{rm 630mu m}$. (iv) We compare our nearby U/LIRGs with high-z galaxies, such as galaxies on the star formation main sequence (MS) at z$sim1$ and submillimeter galaxies (SMGs) at $z=2-4$. We found that the mean value for the [CII] $^3P_1$--$^3P_0$/ $^{12}$CO $J=4-3$ ratio of U/LIRGs is similar to that of SMGs but smaller than that of galaxies on the MS.
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]$(^3P_1-^3P_0)$ (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 $^{13}$CO(1-0)), HI, and infrared (IR) emission (70, 160, and 250$ mu$m). 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, $T_{rm dust}$, and dust mass surface density, $Sigma_{rm dust}$, by fitting the IR continuum-spectrum distribution with a single-temperature modified blackbody. The distribution of $Sigma_{rm dust}$ 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, $T_{rm ex}$, was examined using the intensity ratio of the two [CI] transitions. An appropriate $T_{rm ex}$ at the central, bar, arm, and inter-arm regions yields a constant [C]/[H$_2$] abundance ratio of $sim7 times 10^{-5}$ 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 $T_{rm dust}$. 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.
We present new ALMA observations and physical properties of a Lyman Break Galaxy at z=7.15. Our target, B14-65666, has a bright ultra-violet (UV) absolute magnitude, $M_{rm UV}approx-22.4$, and has been spectroscopically identified in Ly$alpha$ with a small rest-frame equivalent width of $approx4$ AA. Previous HST image has shown that the target is comprised of two spatially separated clumps in the rest-frame UV. With ALMA, we have newly detected spatially resolved [OIII] 88 $mu$m, [CII] 158 $mu$m, and their underlying dust continuum emission. In the whole system of B14-65666, the [OIII] and [CII] lines have consistent redshifts of $7.1520pm0.0003$, and the [OIII] luminosity, $(34.4pm4.1)times10^{8}L_{rm odot}$, is about three times higher than the [CII] luminosity, $(11.0pm1.4)times10^{8}L_{rm odot}$. With our two continuum flux densities, the dust temperature is constrained to be $T_{rm d}approx50-60$ K under the assumption of the dust emissivity index of $beta_{rm d}=2.0-1.5$, leading to a large total infrared luminosity of $L_{rm TIR}approx1times10^{12}L_{rm odot}$. Owing to our high spatial resolution data, we show that the [OIII] and [CII] emission can be spatially decomposed into two clumps associated with the two rest-frame UV clumps whose spectra are kinematically separated by $approx200$ km s$^{-1}$. We also find these two clumps have comparable UV, infrared, [OIII], and [CII] luminosities. Based on these results, we argue that B14-65666 is a starburst galaxy induced by a major-merger. The merger interpretation is also supported by the large specific star-formation rate (defined as the star-formation rate per unit stellar mass), sSFR$=260^{+119}_{-57}$ Gyr$^{-1}$, inferred from our SED fitting. Probably, a strong UV radiation field caused by intense star formation contributes to its high dust temperature and the [OIII]-to-[CII] luminosity ratio.
We report an observational study of the giant molecular cloud (GMC) associated with the Galactic infrared ring-like structure N35 and two nearby HII regions G024.392+00.072 (HII region A) and G024.510-00.060 (HII region B), using the new CO J=1-0 data obtained as a part of the FOREST Unbiased Galactic Plane Imaging survey with the Nobeyama 45-m telescope (FUGIN) project at a spatial resolution of 21. Our CO data revealed that the GMC, with a total molecular mass of 2.1x10^6Mo, has two velocity components over ~10-15km/s. The majority of molecular gas in the GMC is included in the lower-velocity component (LVC) at ~110-114km/s, while the higher-velocity components (HVCs) at ~118-126km/s consist of three smaller molecular clouds which are located near the three HII regions. The LVC and HVCs show spatially complementary distributions along the line-of-sight, despite large velocity separations of ~5-15km/s, and are connected in velocity by the CO emission with intermediate intensities. By comparing the observations with simulations, we discuss a scenario where collisions of the three HVCs with LVC at velocities of ~10-15km/s can provide an interpretation of these two observational signatures. The intermediate velocity features between the LVC and HVCs can be understood as broad bridge features, which indicate the turbulent motion of the gas at the collision interfaces, while the spatially complementary distributions represent the cavities created in the LVC by the HVCs through the collisions. Our model indicates that the three HII regions were formed after the onset of the collisions, and it is therefore suggested that the high-mass star formation in the GMC was triggered by the collisions.
We present a supermassive black hole (SMBH) mass measurement in the Seyfert 1 galaxy NGC7469 using Atacama Large Millimeter/submillimeter Array (ALMA) observations of the atomic-${rm [CI]}$(1-0) and molecular-$^{12}$CO(1-0) emission lines at the spatial resolution of $approx0.3$ (or $approx$ 100 pc). These emissions reveal that NGC7469 hosts a circumnuclear gas disc (CND) with a ring-like structure and a two-arm/bi-symmetric spiral pattern within it, surrounded by a starbursting ring. The CND has a relatively low $sigma/Vapprox0.35$ ($rsim0.5$) and $sim0.19$ ($r>0.5$), suggesting that the gas is dynamically settled and suitable for dynamically deriving the mass of its central source. As is expected from X-ray dominated region (XDR) effects that dramatically increase an atomic carbon abundance by dissociating CO molecules, we suggest that the atomic [CI](1-0) emission is a better probe of SMBH masses than CO emission in AGNs. Our dynamical model using the ${rm [CI]}$(1-0) kinematics yields a $M_{rm BH}=1.78^{+2.69}_{-1.10}times10^7$M$_odot$ and $M/L_{rm F547M}=2.25^{+0.40}_{-0.43}$ (M$_odot$/L$_odot$). The model using the CO(1-0) kinematics also gives a consistent $M_{rm BH}$ with a larger uncertainty, up to an order of magnitude, i.e. $M_{rm BH}=1.60^{+11.52}_{-1.45}times10^7$M$_odot$. This newly dynamical $M_{rm BH}$ is $approx$ 2 times higher than the mass determined from the reverberation mapped (RM) method using emissions arising in the unresolved broad-line region (BLR). Given this new $M_{rm BH}$, we are able to constrain the specific RM dimensionless scaling factor of $f=7.2^{+4.2}_{-3.4}$ for the AGN BLR in NGC7469. The gas within the unresolved BLR thus has a Keplerian virial velocity component and the inclination of $iapprox11.0^circ$$_{-2.5}^{+2.2}$, confirming its face-on orientation in a Seyfert 1 AGN by assuming a geometrically thin BLR model.
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