Integrated CO Line Research Articles

Molecular Gas Heating, Star Formation Rate Relations, and AGN Feedback in Infrared-Luminous Galaxy Mergers

We examine the origin of molecular gas heating in a sample of 42 infrared-luminous galaxies at z<0.3 by combining two sets of archival data: first, integrated CO line luminosities in the 1–0 and 5–4 through 13–12 transitions; second, results from radiative transfer modelling that decompose their bolometric emission into starburst, AGN, and host galaxy components. We find that the CO 1–0 and 5–4 through 9–8 lines primarily arise via radiative heating in the starburst and the host galaxy. In contrast, the CO 10–9 through 13–12 lines may arise primarily in the starburst and AGN, with an increasing contribution from mechanical heating and shocks. For the sample as a whole, we find no evidence that AGN luminosity affects the heating of molecular gas by star formation. However, for starbursts with low initial optical depths, a more luminous AGN may reduce the efficiency of starburst heating of the CO 5–4 and above lines, consistent with negative AGN feedback.

Towards a resolved Kennicutt-Schmidt law at high redshift

Massive galaxies in the distant Universe form stars at much higher rates than today. Although direct resolution of the star forming regions of these galaxies is still a challenge, recent molecular gas observations at the IRAM Plateau de Bure interferometer enable us to study the star formation efficiency on subgalactic scales around redshift z = 1.2. We present a method for obtaining the gas and star formation rate (SFR) surface densities of ensembles of clumps composing galaxies at this redshift, even though the corresponding scales are not resolved. This method is based on identifying these structures in position-velocity diagrams corresponding to slices within the galaxies. We use unique IRAM observations of the CO(3-2) rotational line and DEEP2 spectra of four massive star forming distant galaxies - EGS13003805, EGS13004291, EGS12007881, and EGS13019128 in the AEGIS terminology - to determine the gas and SFR surface densities of the identifiable ensembles of clumps that constitute them. The integrated CO line luminosity is assumed to be directly proportional to the total gas mass, and the SFR is deduced from the [OII] line. We identify the ensembles of clumps with the angular resolution available in both CO and [OII] spectroscopy; i.e., 1-1.5". SFR and gas surface densities are averaged in areas of this size, which is also the thickness of the DEEP2 slits and of the extracted IRAM slices, and we derive a spatially resolved Kennicutt-Schmidt (KS) relation on a scale of ~8 kpc. The data generally indicates an average depletion time of 1.9 Gyr, but with significant variations from point to point within the galaxies.

The open cluster NGC 6823 and possible triggered star formation associated with SNR G59.5+0.1

We investigate the environment in the vicinity of the supernova remnant (SNR) G59.5+0.1 and identify all young stellar objects (YSOs) around the SNR, to derive the physical properties, obtain insight into the star-formation history, and further see whether SNR G59.5+0.1 can trigger star formation in this region. We have performed the submillimeter/millimeter observations in CO lines toward the southeast of SNR G59.5+0.1 with the KOSMA 3m Telescope. High integrated CO line intensity ratio R(CO 3-2/CO 2-1) is identified as one good signature of SNR-MCs (molecular clouds) interacting system. To investigate the impact of SNR G59.5+0.1 on the process of star formation, we used GLIMPSE I Catalog to select YSOs (including class I and class II sources). CO emission in an arc-like shape and mid-infrared 8.28 um emission are well coincident with SNR G59.5+0.1, which has the total mass of 1.1*10^{4}Msun and fully cover open cluster NGC 6823. Three molecular clumps were identified in the CO molecular arc, each clump shows the broad line wing emission, indicating that there are three outflows motion. The integrated CO line intensity ratio (R(CO 3-2/CO 2-1) for the whole molecular arc is between 0.48 and 1.57. The maximum value is 1.57, which is much higher than previous measurements of individual Galactic MCs. The CO molecular arc has a line intensity ratio gradient. SNR G59.5+0.1 is in adiabatic expansion phase. The age of the SNR is 8.6*10^{4} yr. Based on GLIMPSE I Catalog 625 young stellar objects (YSOs) candidates (including 176 class I sources and 449 class II sources) are selected. The timescales for class 0, class I and class II sources are <10^{4} yr, ~10^{5} yr, and ~10^{6} yr, respectively. The number of YSOs are significantly enhanced in the interacting regions, indicating the presence of some recently formed stars.

Submillimeter/millimeter observations of the molecular clouds associated with Tycho's supernova remnant

We have carried out CO J = 2 − 1 and CO J = 3 − 2 observations toward Tycho's supernova remnant (SNR) using the KOSMA 3m-telescope. From these observations, we identified three molecular clouds (MCs) around the SNR. The small cloud in the southwest was discovered for the first time. In the north and east, two MCs (Cloud A and Cloud B) adjacent in space display a bow-shaped morphology, and have broad emission lines, which provide some direct evidences of the SNR-MCs interaction. The MCs are revealed at −69∼ −59 km s−1, coincident with Tycho's SNR. The MCs associated with Tycho's SNR have a mass of ∼ 2.13 × 103 M⊙. Position-velocity diagrams show the two clouds to be adjacent in velocity, which means cloud-cloud collision could occur in this region. The maximum value (0.66 ± 0.10) of the integrated CO line intensity ratio (ICO J=3−2/ICO J=2−1) for the three MCs agrees well with the previous measurement of individual Galactic MCs, implying that the SNR shock drove into the MCs. The two MCs have a line intensity ratio gradient. The distribution of the ratio appears to indicate that the shock propagates from the southwest to the northeast.

STAR FORMATION ASSOCIATED WITH THE SUPERNOVA REMNANT IC443

We have performed the submillimeter and millimeter observations in CO lines toward supernova remnant (SNR) IC443. CO molecular shell is well coincident with the partial shell of the SNR detected in radio continuum observations. The broad emission lines and three 1720-MHz OH masers were detected in CO molecular shell. The present observations have provided further evidence in support of the interaction between the SNR and the adjoining molecular clouds (MCs). The total mass of the MCs is 9.26*10^{3} sun masses. The integrated CO line intensity ratio I(CO(3-2))/I(CO(2-1)) for the whole molecular cloud is between 0.79 and 3.40. The average value is 1.58, which is much higher than previous measurements of individual Galactic MCs. Higher line ratios imply that shocks have driven into the MCs. We conclude that high I(CO(3-2))/I(CO(2-1)) is identified as one good signature of SNR-MCs interacting system. Based on $IRAS$ Point Source Catalog and 2MASS near-infrared database, 12 protostellar objects and 1666 young stellar objects (YSOs) candidates (including 154 CTTSs and 419 HAeBe stars) are selected. In the interacting regions, the significant enhancement of the number of protostellar objects and YSOs indicates the presence of some recently formed stars. After comparing the characteristic timescales of star formation with the age of IC443, we conclude that the protostellar objects and YSOs candidates are not triggered by IC443. For the age of stellar winds shell, we have performed calculation on the basis of stellar winds shell expansion model. The results and analysis suggest that the formation of these stars may be triggered by the stellar winds of IC443 progenitor.

Massive molecular outflows associated with UCHII/HII regions

Received date ; Accepted date Abstract. Aims: We searched for the molecular outflows from fifteen mole cular clouds associated with ultra-compact and compact HII (UCHII/HII) regions and discussed possible gas heating mechanism. Methods: Mapping observations of CO J = 3− 2 and J = 2− 1 lines were carried out with the KOSMA 3m-Telescope towards the 15 HII regions/molecular cloud complexes. Results: Ten molecular outflows were identified o ut of the fifteen HII region /molecular cloud complexes. The higher outflow detection rate (67%) suggested that such outflows are as common in high mass star forming regions as those in low mass star forming regions, which is consistent with the results o f other authors. The observations also showed that the outflo w might occur in the HII region. The integrated CO line intensity ratios (RICO(3−2)/ICO(2−1) ) were determined from the core component of the spectra as well as from both the blue and red wings. Maximum line intensity ratios from the wings and core components appeared to be related to the mid-infrared sources imaged by Midcourse Space Experiment (MSX). The relationship between the maximum line intensity ratios and MSX sources indicates that the molecular gas could be heated by the emission of dust associated with massive stars. Based on maser observations reported in the literature, we found that H 2O masers were only detected in seven regions. The H2O masers in these regions are located near the MSX sources and within the maximum line intensity ratio regions, suggesting that H 2O masers occur in relatively warm environments.

A CO survey of gravitationally lensed quasars with the IRAM interferometer

We present the results of a CO survey of gravitationally lensed quasars, conducted with the Plateau de Bure Interferometer over the last three years. Among the 18 objects surveyed, one was detected in CO line emission, while six were detected in the continuum at 3mm and three in the continuum at 1mm. The low CO detection rate may at least in part be due to uncertainties in the redshifts derived from quasar broad emission lines. The detected CO source, the z=3.2 radio quiet quasar MG0751+2716, is quite strong in the CO(4-3) line and in the millimeter/submillimeter continuum, the latter being emission from cool dust. The integrated CO line flux is 5.96 +- 0.45 Jy.km/s, and the total molecular gas mass is estimated to be in the range M(H_2) = 1.6-3.1 X 10^9 solar masses.

CO Emission in the Radio-loud Quasar 3C 48

view Abstract Citations (51) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CO Emission in the Radio-loud Quasar 3C 48 Scoville, N. Z. ; Padin, S. ; Sanders, D. B. ; Soifer, B. T. ; Yun, M. S. Abstract We have used the Owens Valley Millimeter Array to conduct a sensitive search for CO (1 - 0) emission in the radio-loud quasar 3C 48. An emission feature is detected (4σ) at the redshift of the narrow optical emission lines (z = 0.3695). The width of this feature is ~250 km s^-1^(FWHM) similar to that expected for a galactic disk, and the integrated CO line flux implies an H_2_ mass of 7 x 10^10^ M_sun_ (assuming the same CO to H_2_ conversion factor found for giant molecular clouds in the Milky Way). This H_2_ mass is ~30 times that for the Galaxy, and about twice that estimated for ultraluminous IRAS galaxies such as Arp 220 and the UV-excess quasar Mrk 1014. These data support previous suggestions that 3C 48 may have formed from the recent merger of gas-rich galaxies and that the extended nebulosity surrounding the quasar is largely due to a population of young stars which could have been formed from the gas detected here. Publication: The Astrophysical Journal Pub Date: October 1993 DOI: 10.1086/187036 Bibcode: 1993ApJ...415L..75S Keywords: GALAXIES: ACTIVE; ISM: MOLECULES; GALAXIES: INTERACTIONS; GALAXIES: QUASARS: GENERAL; GALAXIES: QUASARS: INDIVIDUAL ALPHANUMERIC: 3C 48; GALAXIES: STARBURST full text sources ADS | data products SIMBAD (5) NED (1)

A dense molecular ring surrounding the nonthermal Galactic center radio shell G359.1 - 0.5

A new 12 CO survey of the Galactic center region reveals a nearly continuous ring of molecular gas that is centered on and concentric with the nonthermal radio continuum shell G359.1-0.5. The molecular feature has high radial velocities, between -60 and -190 km/s, indicating that it is likely to be located at the distance of the Galactic center; its diameter is then about 75 pc. The mass of the ring, based on its integrated CO line emission, is about 2.5 x 10 6 M ⊙

The properties of individual giant molecular clouds in M33

view Abstract Citations (127) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Properties of Individual Giant Molecular Clouds in M33 Wilson, Christine D. ; Scoville, Nick Abstract Nineteen fields have been observed in the nearby spiral galaxy M33 with the Owens Valley Millimeter-Wave Interferometer at 7"-8" (30 pc) resolution detecting a total of 38 individual molecular clouds. The velocity widths, diameters, peak brightness temperatures, and masses of the clouds are very similar to those of Galactic giant molecular clouds (GMCs). The velocity widths and diameters of the M33 clouds are related by V_FWHM_ = (1.2^+1.3^_-0.6_)D^0.5+/-0.2^_pc_, which agrees within the errors with the velocity-diameter relation obtained for Galactic GMCs. The masses derived from the virial theorem and those derived from the integrated CO line fluxes agree to within 10% in the mean for this sample, implying that in this region of M33 the value of the conversion factor from CO flux to H_2_ column density, α, is similar to that of our own Galaxy. This is the first direct confirmation that the Galactic value of α is appropriate in an external galaxy. The clouds within 200 pc of the nucleus have elevated CO brightness temperatures, possibly due to an increased ultraviolet radiation field. The mass spectrum of clouds is consistent with that derived in the Galaxy for M = (0.8-4) x 10^5^ M_sun_ but shows a total lack of clouds with masses greater than 4 x 10^5^ M_sun_. Comparison of the flux detected with the interferometer with single-dish data indicates that roughly 50% of the molecular gas resides in structures less massive than 0.8 x 10^5^ M_sun_, in contrast to the Galaxy, where only 15% of the H_2_ mass is in these smaller structures. A simple model is proposed to explain the high-mass cutoff as arising from the competing processes of cloud growth through accretion and cloud destruction due to star formation. Publication: The Astrophysical Journal Pub Date: November 1990 DOI: 10.1086/169356 Bibcode: 1990ApJ...363..435W Keywords: Molecular Clouds; Spiral Galaxies; Galactic Structure; Interstellar Matter; Mass Spectra; Molecular Gases; Astrophysics; GALAXIES: INDIVIDUAL MESSIER NUMBER: M33; GALAXIES: INTERSTELLAR MATTER; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (40) NED (1)

High-energy gamma rays and the large-scale distribution of gas and cosmic rays

The COS-B gamma-ray survey is compared with 12CO and HI surveys in a region containing the Orion complex and in the outer Galaxy. The observed gamma-ray intensities in the Orion region (100 MeV&lt;E&lt;5 GeV) can be ascribed to the interaction of uniformly distributed cosmic rays with the interstellar gas. Calibration of the ratio between H2 column-density and integrated CO line intensity resulted in the value: (3.0±0.7)x102 0 molecules cm-2K -1km -1s. In the outer Galaxy HI column-density maps in three galacto-centric distance ranges are used in combination with COS-B gamma-ray data to determine the radial distribution of the gamma-ray emissivity. A steep negative gradient of the emissivity for the 70 MeV-150 MeV range and an approximately constant (within ~20%) emissivity for the 300 MeV-5 GeV range is found. The result is interpreted as a strong decrease in the cosmic-ray electron density and a near constancy of the nuclear component.

The galactic distribution of cosmic-ray particles

COS-B gamma-ray observations are compared with large-scale HI and CO surveys in different regions of the sky to derive information on the cosmic-ray density distribution throughout the Galaxy and/or a calibration of the ratio between H 2 column density and integrated CO line intensity [ N(H 2) W co ] . In the region of the large complex of interstellar clouds in Orion and Monoceros the observed gamma-ray emission can be explained in terms of interactions between cosmic rays distributed uniformly with the local density in this region, and the interstellar gas. In the outer galaxy a steep negative gradient of the emissivity for the 70–150 MeV energy range is found, interpreted as a steep gradient in the cosmic-ray electron density. The emissivity for the 300–5000 MeV range is found to be approximately constant (within 20%) and equal to the local value out to large (∼20 kpc) galacto-centric distances, interpreted as a near constancy of the nuclear component. Results sofar available for the inner galaxy indicate that this trend, a stronger gradient in the electron distribution compared to that of the nuclei, can be extrapolated into the Galaxy. Calibration of the ratio N(H 2) W co in the Orion, Monoceros region and in the first galactic quadrant give consistent values in the range (2.5–3) 10 20 molecules cm −2 K −1 km −1 s. The galactic centre region is found to be an anomaly: (i) the density of cosmic-ray nuclei with energies of ∼1 GeV is anomalously small relative to the local value, or (ii) perhaps these cosmic rays do not efficiently penetrate the molecular clouds in the central region of the Galaxy (contrary to the case of Orion) or (iii) the N(H 2) W co ratio is anomalously low.

Gamma-rays from atomic and molecular gas in the first galactic quadrant

view Abstract Citations (126) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gamma-rays from atomic and molecular gas in the first galactic quadrant Lebrun, F. ; Bennett, K. ; Bignami, G. F. ; Bloemen, J. B. G. M. ; Buccheri, R. ; Caraveo, P. A. ; Gottwald, M. ; Hermsen, W. ; Kanbach, G. ; Mayer-Hasselwander, H. A. ; Montmerle, T. ; Paul, J. A. ; Sacco, B. ; Strong, A. W. ; Wills, R. D. ; Dame, T. M. ; Cohen R. S. ; Thaddeus, P. Abstract The fully sampled Columbia 1 deg CO survey and the Berkeley H I survey are compared with the COS B gamma-ray survey. As a first step, the study is limited to the high-energy gamma-rays (E greater than 300 MeV). It is found that a simple model, in which uniformly distributed cosmic rays interact with the interstellar gas, as traced by H I and CO, can account for almost all the observed gamma-rays. Furthermore, if the contribution from point sources to the gamma-ray flux is significant, these sources must have a galactic distribution similar to that of CO. The analysis permits calibration of the ratio between H2 column density and integrated CO line intensity: N(H2)/W(CO) = (1-3) 10 to the 20th molecules per sq cm k km per s. Publication: The Astrophysical Journal Pub Date: November 1983 DOI: 10.1086/161440 Bibcode: 1983ApJ...274..231L Keywords: Carbon Monoxide; Galactic Radiation; Gamma Rays; Hydrogen Atoms; Interstellar Gas; Astronomical Maps; Milky Way Galaxy; Millimeter Waves; Radiant Flux Density; Radio Sources (Astronomy); Space Radiation full text sources ADS | Related Materials (1) Erratum: 1984ApJ...282..359L