Observations Of CO Emission Research Articles

ALMA Observations of CO Emission from Luminous Lyman-break Galaxies at z = 6.0293–6.2037

We present our new Atacama Large Millimeter/submillimeter Array (ALMA) observations targeting CO(6–5) emission from three luminous Lyman-break galaxies (LBGs) at z spec = 6.0293–6.2037 found in the Subaru/Hyper Suprime-Cam survey, whose [O iii] 88 μm and [C ii] 158 μm emissions have been detected with ALMA. We find a marginal detection of the CO(6–5) line from one of our LBGs, J0235–0532, at the ≃4σ significance level and obtain upper limits for the other two LBGs, J1211–0118 and J0217–0208. Our z = 6 luminous LBGs are consistent with the previously found correlation between the CO luminosity and the infrared luminosity. The unique ensemble of the multiple far-infrared emission lines and underlying continuum fed to a photodissociation region model reveals that J0235–0532 has a relatively high density of hydrogen nuclei n H that is comparable to those of low-z (U)LIRGs, quasars, and Galactic star-forming regions with high n H values, while the other two LBGs have lower n H consistent with local star-forming galaxies. By carefully taking account of various uncertainties, we obtain constraints on total gas mass and gas surface density from their CO luminosity measurements. We find that J0235–0532 is located below the Kennicutt–Schmidt (KS) relation, comparable to the z = 5.7 LBG, HZ10, previously detected with CO(2–1). Combined with previous results for dusty starbursts at similar redshifts, the KS relation at z = 5–6 is on average consistent with the local one.

NOEMA Observations of CO Emission in Arp 142 and Arp 238

Abstract Previous studies have shown significant differences in the enhancement of the star formation rate (SFR) and star formation efficiency (SFE = SFR/M mol) between spiral–spiral and spiral–elliptical mergers. In order to shed light on the physical mechanism of these differences, we present NOEMA observations of the molecular gas distribution and kinematics (linear resolutions of ∼2 kpc) in two representative close major-merger star-forming pairs: the spiral–elliptical pair Arp 142 and the spiral–spiral pair Arp 238. The CO in Arp 142 is widely distributed over a highly distorted disk without any nuclear concentration, and an off-center ringlike structure is discovered in channel maps. The SFE varies significantly within Arp 142, with a starburst region (region 1) near the eastern tip of the distorted disk showing an SFE ∼ 0.3 dex above the mean of the control sample of isolated galaxies and the SFE of the main disk (region 4) 0.43 dex lower than the mean of the control sample. In contrast, the CO emission in Arp 238 is detected only in two compact sources at the galactic centers. Compared to the control sample, Arp 238-E shows an SFE enhancement of more than 1 dex, whereas Arp 238-W has an enhancement of ∼0.7 dex. We suggest that the extended CO distribution and large SFE variation in Arp 142 are due to an expanding large-scale ring triggered by a recent high-speed head-on collision between the spiral galaxy and the elliptical galaxy, and the compact CO sources with high SFEs in Arp 238 are associated with nuclear starbursts induced by gravitational tidal torques in a low-speed coplanar interaction.

The filamentary structures in the CO emission toward the Milky Way disk

We present a statistical study of the filamentary structure orientation in the CO emission observations obtained in the Milky Way Imaging Scroll Painting survey in the range 25.°8 < l < 49.°7, |b| ≤ 1.°25, and −100 < vLSR < 135 km s−1. We found that most of the filamentary structures in the 12CO and 13CO emission do not show a global preferential orientation either parallel or perpendicular to the Galactic plane. However, we found ranges in Galactic longitude and radial velocity where the 12CO and 13CO filamentary structures are parallel to the Galactic plane. These preferential orientations are different from those found for the HI emission. We consider this an indication that the molecular structures do not simply inherit these properties from parental atomic clouds. Instead, they are shaped by local physical conditions, such as stellar feedback, magnetic fields, and Galactic spiral shocks.

A black-hole mass measurement from molecular gas kinematics in NGC4526

The masses of the supermassive black holes found in galaxy bulges are correlated with a multitude of galaxy properties, leading to suggestions that galaxies and black holes may evolve together. The number of reliably measured black-hole masses is small, and the number of methods for measuring them is limited, holding back attempts to understand this co-evolution. Directly measuring black-hole masses is currently possible with stellar kinematics (in early-type galaxies), ionized-gas kinematics (in some spiral and early-type galaxies) and in rare objects that have central maser emission. Here we report that by modelling the effect of a black hole on the kinematics of molecular gas it is possible to fit interferometric observations of CO emission and thereby accurately estimate black-hole masses. We study the dynamics of the gas in the early-type galaxy NGC 4526, and obtain a best fit that requires the presence of a central dark object of 4.5(+4.2)(-3.1) × 10(8) solar masses (3σ confidence limit). With the next-generation millimetre-wavelength interferometers these observations could be reproduced in galaxies out to 75 megaparsecs in less than 5 hours of observing time. The use of molecular gas as a kinematic tracer should thus allow one to estimate black-hole masses in hundreds of galaxies in the local Universe, many more than are accessible with current techniques.

Distances of Galactic supernova remnants

AbstractSupernova remnants (SNRs) play a key role in understanding supernovae explosion mechanisms, exploring the likely sources of Galactic cosmic rays and the chemical enrichment of interstellar medium (ISM). Reliable distance determinations to Galactic SNRs are key to obtain their basic parameters, such as size, age, explosion energy, which helps us to study their environment and interstellar medium. We review the methods to determine the distances to SNRs and highlight the kinematic distance measurement by Hi absorption and CO emission observations.

Unexpectedly large mass loss during the thermal pulse cycle of the red giant star R Sculptoris

The asymptotic-giant-branch star R Sculptoris is surrounded by a detached shell of dust and gas. The shell originates from a thermal pulse during which the star underwent a brief period of increased mass loss. It has hitherto been impossible to constrain observationally the timescales and mass-loss properties during and after a thermal pulse--parameters that determine the lifetime of the asymptotic giant branch and the amount of elements returned by the star. Here we report observations of CO emission from the circumstellar envelope and shell around R Sculptoris with an angular resolution of 1.3″. What was previously thought to be only a thin, spherical shell with a clumpy structure is revealed to also contain a spiral structure. Spiral structures associated with circumstellar envelopes have been previously seen, leading to the conclusion that the systems must be binaries. Combining the observational data with hydrodynamic simulations, we conclude that R Sculptoris is a binary system that underwent a thermal pulse about 1,800 years ago, lasting approximately 200 years. About 3 × 10(-3) solar masses of material were ejected at a velocity of 14.3 km s(-1) and at a rate around 30 times higher than the pre-pulse mass-loss rate. This shows that about three times more mass was returned to the interstellar medium during and immediately after the pulse than previously thought.

ASPITZERSURVEY OF MID-INFRARED MOLECULAR EMISSION FROM PROTOPLANETARY DISKS. II. CORRELATIONS AND LOCAL THERMAL EQUILIBRIUM MODELS

We present an analysis of Spitzer-IRS observations of H2O, OH, HCN, C2H2, and CO2 emission, and Keck-NIRSPEC observations of CO emission, from a diverse sample of T Tauri and Herbig Ae/Be circumstellar disks. We find that detections and strengths of most mid-IR molecular emission features are correlated with each other, suggesting a common origin and similar excitation conditions. We note that the line detection efficiency is anti-correlated with the 13/30 um SED spectral slope, which is a measure of the degree of grain settling in the disk atmosphere. We also note a correlation between detection efficiency and H-alpha equivalent width, and tentatively with accretion rate, suggesting that accretional heating contributes to line excitation. If detected, H2O line fluxes are correlated with the mid-IR continuum flux, and other co-varying system parameters, such as L_star. However, significant sample variation, especially in molecular line ratios, remains. LTE models of the H2O emission show that line strength is primarily related to the best-fit emitting area, and this accounts for most source-to-source variation in H2O emitted flux. Best-fit temperatures and column densities cover only a small range of parameter space, near 10^{18} cm-2 and 450 K for all sources, suggesting a high abundance of H2O in many planet-forming regions. Other molecules have a range of excitation temperatures from ~500-1500 K, also consistent with an origin in planet-forming regions. We find molecular ratios relative to water of ~10^{-3} for all molecules, with the exception of CO, for which n(CO)/n(H2O)~1. However, LTE fitting caveats and differences in the way thermo-chemical modeling results are reported make comparisons with such models difficult, and highlight the need for additional observations coupled with the use of line-generating radiative transfer codes.

Odin observations of water in molecular outflows and shocks

Aims. We investigate the ortho-water abundance in outflows and shocks in order to improve our knowledge of shock chemistry and of the physics behind molecular outflows. Methods. We have used the Odin space observatory to observe the H2O(110-101) line. We obtain strip maps and single pointings of 13 outflows and two supernova remnants where we report detections for eight sources. We have used RADEX to compute the beam averaged abundances of o-H2O relative to H2. In the case of non-detection, we derive upper limits on the abundance. Results. Observations of CO emission from the literature show that the volume density of H2 can vary to a large extent, a parameter that puts severe uncertainties on the derived abundances. Our analysis shows a wide range of abundances reflecting the degree to which shock chemistry is affecting the formation and destruction of water. We also compare our results with recent results from the SWAS team. Conclusions. Elevated abundances of ortho-water are found in several sources. The abundance reaches values as high as what would be expected from a theoretical C-type shock where all oxygen, not in the form of CO, is converted to water. However, the high abundances we derive could also be due to the low densities (derived from CO observations) that we assume. The water emission may in reality stem from high density regions much smaller than the Odin beam. We do not find any relationship between the abundance and the mass loss rate. On the other hand, there is a relation between the derived water abundance and the observed maximum outflow velocity.

The Dust Envelope of the Preplanetary Nebula IRAS 19475+3119

We present the spectral energy distribution (SED) of the preplanetary nebula, IRAS 19475+3119 (hereafter I 19475), from the optical to the far-infrared. We identify emission features due to crystalline silicates in the ISO SWS spectra of the star. We have fitted the SED of I 19475 using a one-dimensional radiative transfer code and find that a shell with inner and outer radii of 8.8 × 1016 and 4.4 × 1017 cm and dust temperatures ranging from about 94 to 46 K provides the best fit. The mass of this shell is 1[34 cm2 g-1/κ(100 μm)] (δ/200) M☉, where κ(100 μm) is the 100 μm dust mass absorption coefficient (per unit dust mass) and δ is the gas-to-dust ratio. In agreement with results from optical imaging and millimeter-wave observations of CO emission of I 19475, our model fits support an r-3 density law for its dust shell, with important implications for the interaction process between the fast collimated post-AGB winds and the dense AGB envelopes that results in the observed shapes of PPNs and PNs. We find that the observed JCMT flux at submillimeter wavelengths (850 μm) is a factor ~2 larger than our model flux, suggesting the presence of large dust grains in the dust shell of I 19475 that are not accounted for by our adopted standard MRN grain size distribution.

Sub-arcsecond imaging of the radio continuum and neutral hydrogen in the Medusa merger

We present sub-arcsecond, Multi-Element Radio Linked Interferometer (MERLIN) observations of the decimetre radio continuum structure and neutral hydrogen (HI) absorption from the nuclear region of the starburst galaxy NGC 4194 (the Medusa Merger). The continuum structure of the central kiloparsec of the Medusa has been imaged, revealing a pair of compact radio components surrounded by more diffuse, weak radio emission. Using the constraints provided by these observations and those within the literature we conclude that the majority of this radio emission is related to the ongoing star-formation in this merger system. With these observations we also trace deep HI absorption across the detected radio continuum structure. The absorbing HI gas structure exhibits large variations in column densities. The largest column densities are found toward the south of the nuclear radio continuum, co-spatial with both a nuclear dust lane and peaks in $^{12}$CO (1->0) emission. The dynamics of the HI absorption, which are consistent with lower resolution $^{12}$CO emission observations, trace a shallow north-south velocity gradient of ~320km/s/kpc. This gradient is interpreted as part of a rotating gas structure within the nuclear region. The HI and CO velocity structure, in conjunction with the observed gas column densities and distribution, is further discussed in the context of the fuelling and gas physics of the ongoing starburst within the centre of this merger.

A high-resolution radio study of neutral gas in the starburst galaxy NGC 520

We present subarcsec angular resolution observations of the neutral gas in the nearby starburst galaxy NGC 520. The central kpc region of NGC 520 contains an area of significantly enhanced star formation. The radio continuum structure of this region resolves into ∼10 continuum components. By comparing the flux densities of the brightest of these components at 1.4 GHz with published 15-GHz data we infer that these components detected at 1.4 and 1.6 GHz are related to the starburst and are most likely to be collections of several supernova remnants within the beam. None of these components is consistent with emission from an active galactic nuclei. Both neutral hydrogen (HI) and hydroxyl (OH) absorption lines are observed against the continuum emission, along with a weak OH maser feature probably related to the star formation activity in this galaxy. Strong H i absorption (N H ∼ 10 2 2 atoms cm - 2 ) traces a velocity gradient of 0.5 km s - 1 pc - 1 across the central kpc of NGC 520. The HI absorption velocity structure is consistent with the velocity gradients observed in both the OH absorption and in CO emission observations. The neutral gas velocity structure observed within the central kpc of NGC 520 is attributed to a kpc-scale ring or disc. It is also noted that the velocity gradients observed for these neutral gas components appear to differ with the velocity gradients observed from optical ionized emission lines. This apparent disagreement is discussed and attributed to the extinction of the optical emission from the actual centre of this source hence implying that optical ionized emission lines are only detected from regions with significantly different radii to those sampled by the observations presented here.

Carbon monoxide emission as a precise tracer of molecular gas in the Andromeda galaxy

Stars are known to form in clouds of cold molecular hydrogen, which are relatively poorly understood despite being one of the main components of the interstellar medium. The problem is that H2 is invisible in the cold interstellar medium, so its distribution and motion must be inferred from observations of minor constituents of the clouds, such as carbon monoxide and dust. Most of our present knowledge comes from observations of CO emission, but there is much debate on whether this is an effective tracer of H2: it might miss a large fraction of the molecular gas1. It is difficult to address this question on the basis of observations within the Milky Way alone, whose edge-on orientation makes it hard to discern the distant cloud structures. We have therefore surveyed the CO emission of the molecular clouds of M31 (the Andromeda galaxy), the nearest spiral galaxy to the Milky Way, and investigated the extent to which it follows the extinction of starlight by dust. We find a remarkably tight association between the CO emission and the dust, from which we conclude that CO does indeed trace all of the molecular gas.

Are Flocculent Spirals Devoid of Density Waves? Gas Morphology and Kinematics in NGC 5055

We present interferometric observations of CO and H I in the prototypical flocculent spiral NGC 5055, which has recently been shown to exhibit weak, two-arm spiral structure in the near-infrared. The morphology and kinematics described by VLA observations of H I emission and FCRAO and Berkeley-Illinois-Maryland Association (BIMA) Array observations of CO emission provide evidence for the presence of low-amplitude density waves in NGC 5055. The distribution of CO and H I emission suggests enhanced gas surface densities along the NIR spiral arms, and structures similar to the giant molecular associations found in the grand design spirals M51 and M100 are detected. An analysis of H I and Hα velocity fields shows the kinematic signature of streaming motions similar in magnitude to those of M100 in both tracers. The lesser degree of organization along the spiral arms of NGC 5055 may be due to the lower overall gas surface density, which in the arms of NGC 5055 is a factor of 2 lower than in M100 and a factor of 6 lower than in M51; an analysis of gravitational instability shows the gas in the arms is only marginally unstable and the interarm gas is marginally stable. The limited extent of the spiral arm pattern is consistent with an isolated density wave with a relatively high pattern speed; other possible formation mechanisms are also discussed.

Molecular Clouds in the Dwarf Elliptical Galaxy NGC 205

We present observations of CO emission in NGC 205 (a dwarf elliptical companion of M31) obtained with the Berkeley-Illinois-Maryland Association (BIMA) array and the IRAM 30 m telescope. We compare the CO results to VLA observations of the H I emission at the same spatial resolution. On scales of 90 pc, the atomic gas and dust have very similar distributions, and the atomic and molecular gas have similar kinematics. A12CO (2-1)/(1-0) brightness temperature ratio of 0.9 is derived for one molecular cloud in NGC 205. This cloud is resolved by the 40 pc × 20 pc beam of the BIMA array; the cloud is elongated and shows a velocity gradient along its major axis. CO line widths are comparable to those in the Galaxy and the Small Magellanic Cloud (SMC) for clouds of the same size, which suggests that the molecular clouds in NGC 205 have similar virial masses to those in the Galaxy and the SMC.

Morphology of Dust Lanes in Bars

AbstractGiven that dust and molecular gas tend to concentrate at the locations of either shocks or orbit crowding, the study of the dust morphology of barred spirals can give insight into the kinematics of the galaxies. In order to do this, we present a sample of barred galaxies for which we have obtained near infrared and optical photometry and BIMA interferometer observations of CO emission. We obtain the dust extinction and relative scale height of the dust and stars using a radiative transfer model to interpret the photometry. We find that the scale height of the stars compared to the dust is generally larger in the central regions compared to further out in the bar dust lanes. The morphology of the dust extinction regions closely resembles the distribution of CO emission. An analysis of a larger sample of galaxies with IR data indicates that dust column densities appear larger in the nuclear regions than in the bar dust lanes. The sample also shows that the distribution of dust is not symmetrical along the bar with one side of the bar usually having a larger column density of dust than the other side.

Molecular Outflows

The development of millimeter and submillimeter spectroscopy has allowed astronomers to probe the cold, dense component of the interstellar medium. This medium, primarily composed of gas in molecular form, is gravitationally bound into relatively distinct clouds that are sites of star formation within our Galaxy. The most ubiquitous tracers of these molecular clouds are the rotational transitions of carbon monoxide. Observations of CO emission have been commonly used to estimate the size, temperature, mass, and density of molecular clouds; in addition, the spectral line profiles can be used to study the internal dynamics of these clouds. Although the sound speed within molecular clouds is only about 0.2 km s−1, observed CO line widths are more typically 1 to 5 km s−1. Thus, the internal dynamics of molecular clouds are characterized by supersonic gas motions whose nature is poorly understood.

The small molecular cloud toward HD 169454

view Abstract Citations (33) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Small Molecular Cloud toward HD 169454 Jannuzi, Buell T. ; Black, John H. ; Lada, Charles J. ; van Dishoeck, Ewine F. Abstract Optical absorption line observations of the B1 supergiant HD 169454 reveal the presence of an intervening translucent interstellar cloud. Millimeter wavelength observations of CO emission show that the absorption lines can be attributed to a well-defined cloud approximately 18 by 22 min in extent at the same radial velocity as the C2 and CN absorption lines. The map of the CO emission shows three large condensations and evidence of unresolved structure on smaller scales. Various procedures for determining the cloud mass are compared. The estimated mass is 7-14 M solar masses if the cloud lies at the distance (D about 125 pc) of an extended atomic cloud at the same radial velocity, and is 250-500 M solar masses if the kinematic distance (D about 750 pc) is adopted. The dynamical state of the cloud is examined. The composition and structure of the cloud are discussed with reference to detailed theoretical models and the properties of other interstellar clouds. Publication: The Astrophysical Journal Pub Date: September 1988 DOI: 10.1086/166707 Bibcode: 1988ApJ...332..995J Keywords: Absorption Spectra; B Stars; Interstellar Gas; Line Spectra; Molecular Clouds; Supergiant Stars; Carbon Monoxide; Cn Emission; Millimeter Waves; Radial Velocity; Astrophysics; INTERSTELLAR: MOLECULES; STARS: INDIVIDUAL HENRY DRAPER NUMBER: HD 169454 full text sources ADS | data products SIMBAD (1)

Star formation in giant molecular associations synchronized by a spiral density wave

Observations of CO emission from the prototypical spiral galaxy M51 reveal density wave streaming motions in molecular gas coincident with the dust lanes. This is strong evidence that spiral density waves assemble pre-existing molecular clouds into giant associations and trigger the collapse of suitably primed clouds, leading to the formation of stars.

Molecular spiral structure in M51

view Abstract Citations (56) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Molecular Spiral Structure in M51 Lo, K. Y. ; Ball, R. ; Masson, C. R. ; Phillips, T. G. ; Scott, S. ; Woody, D. P. Abstract Observations of CO emission at 7 arcsec resolution from the central 2 arcmin x 1 arcmin of M51 show directly that molecular gas, probably complexes of relatively warm giant molecular clouds, is strongly confined to spiral arms outlined by prominent dust lanes and radio continuum ridges. Molecular clouds must also populate fairly uniformly the interarm regions. The arm-to-interarm N(H2) ratio, averaged over 300 pc, is at least three. These observations suggest that in the inner region of M51 molecular clouds coalesce to form bigger complexes in the presence of a spiral gravitational potential, and that such complexes are redispersed into molecular clouds upon leaving the arms. The spiral arm molecular cloud complexes last at most 50 million yr, the arm crossing time, and molecular clouds probably last as long as the interarm crossing time which is at most 100 million yr at 45 arcsec (2.2 kpc) from the center. Publication: The Astrophysical Journal Pub Date: June 1987 DOI: 10.1086/184913 Bibcode: 1987ApJ...317L..63L Keywords: Carbon Monoxide; Galactic Structure; Molecular Clouds; Spiral Galaxies; Astronomical Maps; Coalescing; Galactic Nuclei; Interferometry; Interstellar Gas; Astrophysics; GALAXIES: STRUCTURE; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (1) NED (1)

High-resolution observations of CO from the bipolar nebula CRL 2688

The results of high spatial resolution mapping observations of CO emission from the bipolar nebula CRL 2688 are reported. The CO spectrum toward the center shows line wings with a full width of 85 km/s. On the blueshifted wing, a narrow and deep absorption feature is seen at a velocity shifted by 20 km/s from the systemic velocity. A central compact core elongated perpendicularly to the bipolar axis and blueshifted high-velocity emission distributed along the optical lobes suggest the presence of an expanding disk of molecular gas and fast stellar wind as the acceleration agent. The absorption feature suggests that an expanding cold absorbing envelope surrounds the relatively warm molecular envelope. The absorbing envelope has an excitation temperature lower than about 5 K and an optical depth larger than 1.2 in the CO(J = 1-0) line, and it is expanding at 20 km/s. The size of this envelope is larger than about 0.6 pc and its mass is larger than 0.016-0.044 solar mass. 16 references.