Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSpatially-resolved Dense Molecular Gas Excitation in the Nearby LIRG VV 114
64
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present high-resolution observations (0.2-1.5) of multiple dense gas tracers, HCN and HCO$^+$ ($J$ = 1-0, 3-2, and 4-3), HNC ($J$ = 1-0), and CS ($J$ = 7-6) lines, toward the nearby luminous infrared galaxy VV 114 with the Atacama Large Millimeter/submillimeter Array. All lines are robustly detected at the central gaseous filamentary structure including the eastern nucleus and the Overlap region, the collision interface of the progenitors. We found that there is no correlation between star formation efficiency and dense gas fraction, indicating that the amount of dense gas does not simply control star formation in VV 114. We predict the presence of more turbulent and diffuse molecular gas clouds around the Overlap region compared to those at the nuclear region assuming a turbulence-regulated star formation model. The intracloud turbulence at the Overlap region might be excited by galaxy-merger-induced shocks, which also explains the enhancement of gas-phase CH$_3$OH abundance previously found there. We also present spatially resolved spectral line energy distributions of HCN and HCO$^+$ for the first time, and derive excitation parameters by assuming optically-thin and local thermodynamic equilibrium (LTE) conditions. The LTE model revealed that warmer, HCO$^+$-poorer molecular gas medium is dominated around the eastern nucleus, harboring an AGN. The HCN abundance is remarkably flat ($sim$3.5 $times$ 10$^{-9}$) independently of the various environments within the filament of VV 114 (i.e., AGN, star formation, and shock).
rate research
Read More
We present the results of our ALMA HCN J=3-2 and HCO+ J=3-2 line observations of a uniformly selected sample (>25) of nearby ultraluminous infrared galaxies (ULIRGs) at z < 0.15. The emission of these dense molecular gas tracers and continuum are spatially resolved in the majority of observed ULIRGs for the first time with achieved synthesized beam sizes of ~0.2 arcsec or ~500 pc. In most ULIRGs, the HCN-to-HCO+ J=3-2 flux ratios in the nuclear regions within the beam size are systematically higher than those in the spatially extended regions. The elevated nuclear HCN J=3-2 emission could be related to (a) luminous buried active galactic nuclei, (b) the high molecular gas density and temperature in ULIRGs nuclei, and/or (c) mechanical heating by spatially compact nuclear outflows. A small fraction of the observed ULIRGs display higher HCN-to-HCO+ J=3-2 flux ratios in localized off-nuclear regions than those of the nuclei, which may be due to mechanical heating by spatially extended outflows. The observed nearby ULIRGs are generally rich in dense (>10^5 cm^-3) molecular gas, with an estimated mass of >10^9 Msun within the nuclear (a few kpc) regions, and dense gas can dominate the total molecular mass there. We find a low detection rate (<20%) regarding the possible signature of a vibrationally excited (v2=1f) HCN J=3-2 emission line in the vicinity of the bright HCO+ J=3-2 line that may be due, in part, to the large molecular line widths of ULIRGs.
Aims. We present new IRAM Plateau de Bure Interferometer observations of Arp 220 in HCN, HCO$^{+}$, HN$^{13}$C J=1-0, C$_{2}$H N=1-0, SiO J = 2-1, HNCO J$_{k,k}$ = 5$_{0,4}$ - 4$_{0,4}$, CH$_{3}$CN(6-5), CS J=2-1 and 5-4 and $^{13}$CO J=1-0 and 2-1 and of NGC 6240 in HCN, HCO$^{+}$ J = 1-0 and C$_{2}$H N = 1-0. In addition, we present Atacama Large Millimeter/submillmeter Array science verification observations of Arp 220 in CS J = 4-3 and CH$_{3}$CN(10-9). Various lines are used to analyse the physical conditions of the molecular gas including the [$^{12}$CO]/[$^{13}$CO] and [$^{12}$CO]/[C$^{18}$O] abundance ratios. These observations will be made available to the public. Methods. We create brightness temperature line ratio maps to present the different physical conditions across Arp 220 and NGC 6240. In addition, we use the radiative transfer code RADEX and a Monte Carlo Markov Chain likelihood code to model the $^{12}$CO, $^{13}$CO and C$^{18}$O lines of Arp 220 at ~2 (~700 pc) scales, where the $^{12}$CO and C$^{18}$O measurements were obtained from literature. Results. Line ratios of optically thick lines such as $^{12}$CO show smoothly varying ratios while the line ratios of optically thin lines such as $^{13}$CO show a east-west gradient across Arp 220. The HCN/HCO$^{+}$ line ratio differs between Arp 220 and NGC 6240, where Arp 220 has line ratios above 2 and NGC 6240 below 1. The radiative transfer analysis solution is consistent with a warm (~40 K), moderately dense (~10$^{3.4}$ cm$^{-3}$) molecular gas component averaged over the two nuclei. We find [$^{12}$CO]/[$^{13}$CO] and [$^{12}$CO]/[C$^{18}$O] abundance ratios of ~90 for both. The abundance enhancement of C$^{18}$O can be explained by stellar nucleosynthesis enrichment of the interstellar medium.
Among more than 200 quasars known at $zgtrsim6$, only one object, J0100+2802 (z=6.327), was found hosting a $>10^{10}M_odot$ super-massive black hole (SMBH). In order to investigate the host galaxy properties of J0100+2802, we performed multi-band ALMA observations, aiming at mapping the dust continuum, [CII] and CO(6-5) emission lines with sub-kiloparsec scale resolution, as well as detecting high-J CO lines in CO(11-10), CO(10-9), and CO(7-6). The galaxy size is measured to be $R_{rm major}=3.6pm0.2$ kpc from the high resolution continuum observations. No ordered motion on kilo-parsec scales was found in both [CII] and CO(6-5) emissions. The velocity dispersion is measured to be 161$pm$7 km s$^{-1}$, $sim$3 times smaller than that estimated from the local M-$sigma$ relation. In addition, we found that the CO emission is more concentrate (a factor of 1.8$pm$0.4) than the [CII] emission. Together with CO(2-1) detected by VLA, we measured the CO Spectral Line Energy Distribution (SLED), which is best fit by a two-components model, including a cool component at $sim24$ K with a density of $n_{rm (H_2)}$=10$^{4.5}$ cm$^{-3}$, and a warm component at $sim224$ K with a density of $n_{rm (H_2)}$=10$^{3.6}$ cm$^{-3}$. We also fitted the dust continuum with a graybody model, which indicates that it has either a high dust emissivity $betagtrsim2$ or a hot dust temperature $T_{rm dust}gtrsim60$ K, or a combination of both factors. The highly excited CO emission and hot dust temperature suggest that the powerful AGN in J0100+2802 could contribute to the gas and dust heating although future observations are needed to confirm this.
We present a first look at the local LIRG, IRAS04296+2923. This barred spiral, overlooked because of its location in the Galactic plane, is among the half dozen closest LIRGs. More IR-luminous than either M82 or the Antennae, it may be the best local example of a nuclear starburst caused by bar-mediated secular evolution. We present Palomar J and Pa beta images, VLA maps from 20-1.3cm, a Keck LWS image at 11.7mic and OVRO CO(1-0) and ^13CO(1-0), and 2.7 mm continuum images. The J-band image shows a symmetric barred spiral. Two bright, compact mid-IR/radio sources in the nucleus comprise a starburst that is equivalent to 10^5 O7 stars, probably a pair of young super star clusters separated by 30pc. The nuclear starburst is forming stars at the rate of ~12Msun/yr, half of the total star formation rate for the galaxy of ~25Msun/yr. IRAS04296 is bright in CO, and among the most gas-rich galaxies in the local universe. The CO luminosity of the inner half kpc is equivalent to that of the entire Milky Way. While the most intense CO emission extends over a 15(2 kpc) region, the nuclear starburst is confined to ~1-2(150-250 pc) of the dynamical center. From ^13CO, we find that the CO conversion factor in the nucleus is higher than the Galactic value by a factor 3-4, typical of gas-rich spiral nuclei. The nuclear star formation efficiency is M_gas/SFR^nuc = 2.7x10^-8 yr^-1, corresponding to gas consumption timescale, tau_SF^nuc~4x10^7 yrs. The star formation efficiency is ten times lower in the disk, tau_SF^disk~3.3x10^8 yrs. The low absolute star formation efficiency in the disk implies that the molecular gas is not completely consumed before it drifts into the nucleus, and is capable of fueling a sustained nuclear starburst. IRAS04296 is beginning a 100Myr period as a LIRG, during which it will turn much of its 6x10^9Msun of molecular gas into a nuclear cluster of stars. (abridged)
We performed 12CO(1-0), 13CO(1-0), and HCN(1-0) single-dish observations (beam size ~14-18) toward nearby starburst and non-starburst galaxies using the Nobeyama 45 m telescope. The 13CO(1-0) and HCN(1-0) emissions were detected from all the seven starburst galaxies, with the intensities of both lines being similar (i.e., the ratios are around unity). On the other hand, for case of the non-starburst galaxies, the 13CO(1-0) emission was detected from all three galaxies, while the HCN(1-0) emission was weakly or not detected in past observations. This result indicates that the HCN/13CO intensity ratios are significantly larger (~1.15+-0.32) in the starburst galaxy samples than the non-starburst galaxy samples (<0.31+-0.14). The large-velocity-gradient model suggests that the molecular gas in the starburst galaxies have warmer and denser conditions than that in the non-starburst galaxies, and the photon-dominated-region model suggests that the denser molecular gas is irradiated by stronger interstellar radiation field in the starburst galaxies than that in the non-starburst galaxies. In addition, HCN/13CO in our sample galaxies exhibit strong correlations with the IRAS 25 micron flux ratios. It is a well established fact that there exists a strong correlation between dense molecular gas and star formation activities, but our results suggest that molecular gas temperature is also an important parameter.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
