Millimetre/submillimetre-wave emission line searches for high-redshift galaxies

The redshifted spectral line radiation emitted from both atomic fine-structure and molecular rotational transitions in the interstellar medium (ISM) of high-redshift galaxies can be detected in the centimetre, millimetre and submillimetre wavebands. Here we predict the counts of galaxies detectable in an array of molecular and atomic lines. This calculation requires a reasonable knowledge of both the surface density of these galaxies on the sky, and the physical conditions in their ISM. The surface density is constrained using the results of submillimetre-wave continuum surveys. Follow-up OVRO Millimeter Array observations of two of the galaxies detected in the dust continuum have provided direct measurements of CO rotational line emission at redshifts of 2.56 and 2.81. Based on these direct high-redshift observations and on models of the ISM that are constrained by observations of low-redshift ultraluminous infrared galaxies, we predict the surface density of line-emitting galaxies as a function of line flux density and observing frequency. We incorporate the sensitivities and mapping speeds of existing and future millimetre/submillimetre-wave telescopes and spectrographs, and so assess the prospects for blank-field surveys to detect this line emission from gas-rich high-redshift galaxies.Comment: 13 pages, 12 figures, to appear in MNRAS. Final proof versio

Molecular hydrogen in the galaxy and galactic gamma rays

Recent surveys of 2.6 mm CO emission and 100 MeV gamma-radiation in the galactic plane reveal a striking correlation suggesting that both emissions may be primarily proportional to the line-of-sight column density of H2 in the inner galaxy. Both the gamma ray and CO data suggest a prominent ring or arm consisting of cool clouds of H2 at a galactocentric distance of approximately 5 kpc with a mean density of approximately 4 atoms/cu cm. The importance of H2 in understanding galactic gamma ray observations is also reflected in the correlation of galactic latitude distribution of gamma rays and dense dust clouds. A detailed calculation of the gamma ray flux distribution in the 0 deg to 180 deg range using the CO data to obtain the average distribution of molecular clouds in the galaxy shows that most of the enhancement in the inner galaxy is due to pion-decay radiation and the 5 kpc ring plays a major role. Detailed agreement with the gamma ray data is obtained with the additional inclusion of contributions from bremsstrahlung and Compton radiation of secondary electrons and Compton radiation from the intense radiation field near the galactic center

First Interferometric Observations of Molecular Gas in a Polar Ring: The Helix Galaxy NGC 2685

We have detected four Giant Molecular cloud Associations (GMAs) (sizes < 6.6'' ~ 430 pc) in the western and eastern region of the polar ring in NGC2685 (the Helix galaxy) using the Owens Valley Radio Observatory (OVRO) millimeter interferometer. Emission from molecular gas is found close to the brightest Halpha and HI peaks in the polar ring and is confirmed by new IRAM 30m single dish observations. The CO and HI line velocities are very similar, providing additional kinematic confirmation that the CO emission emerges from the polar ring. For the first time, the total molecular mass within a polar ring is determined (M_H2~(8-11)x10^6 M_sol, using the standard Galactic conversion factor). We detect about M_H2~4.4x10^6 M_sol in the nuclear region with the single dish. Our upper limit derived from the interferometric data is lower (M_H2<0.7x10^6 M_sol) suggesting that the molecular gas is distributed in an extended (< 1.3 kpc) diffuse disk. These new values are an order of magnitude lower than in previous reports. The total amount of molecular gas and the atomic gas content of the polar ring are consistent with formation due to accretion of a small gas-rich object, such as a dwarf irregular. The properties of the NGC2685 system suggest that the polar ring and the host galaxy have been in a stable configuration for a considerable time (few Gyr). The second (outer) HI ring within the disk of NGC2685 is very likely at the outer Lindblad resonance (OLR) of the ~ 11 kpc long stellar bar.Comment: 8 pages, 4 figures, accepted by ApJ Letter

How Barred is the NIR Nearby Universe? An analysis using 2MASS

We determine a firm lower limit to the bar fraction of 0.58 in the nearby universe using J+H+Ks-band images for 134 spirals from 2MASS. With a mean deprojected semi-major axis of 5.1 kpc, and a mean deprojected ellipticity of 0.45 this local bar sample lays the ground work for studies on bar formation and evolution at high redshift.Comment: In the proceedings "Penetrating Bars through Masks of Cosmic Dust: The Hubble Tuning Fork strikes a New Note

CO (J=3-2) Emission in the Radio Galaxy 53W002 at z=2.394

We report a sensitive search for redshifted CO (3-2) emission from the weak radio galaxy 53W002 at z=2.394. Maps at resolutions of 3 arcsec and 235km/s show a significant emission peak within 0.5 arcsec of the optical and radio continuum peaks. The measured narrow band flux is approximately ten times the extrapolated cm-wavelength non-thermal radio continuum expected at 101.9 GHz and exhibits a spectral profile implying a 540 km/s width (FWHM) at a systemic redshift z=2.394 for CO (3-2). This emission has a total integrated flux of 1.51(+/-0.2) Jy km/s, approximately four times weaker than that previously seen in the lensed systems FSC10214+4724 and the Cloverleaf QSO. For a Galactic CO-to-H2 conversion ratio, the implied molecular gas mass is 7.4x10^10 solar masses (H=75 km/s/Mpc and q=0.5). The CO emission is elongated at P.A.=120 degrees with a deconvolved major axis radius of 15 kpc (2.8 arcsec). This extension is along a similar direction to that seen in the cm-wave radio continuum and the optical but approximately three times larger. A velocity gradient is seen along the major axis, and if this structure is a (forming) disk, the implied dynamical mass is 9-22x10^10 solar masses at radii less than or equal to 15 kpc, assuming inclination i=0 degrees (edge-on). The magnitude of these masses and the similarity of the high gas-mass fraction are consistent with the host galaxy of 53W002 being a young galactic system, but the metallicity (probably greater than or equal to 0.1 solar in order to produce the CO lines) implies significant heavy element production prior to z=2.4. This constitutes the first high redshift molecular gas which is detected in emission where there is probably no gravitational magnification

Is the Cygnus Loop two supernova remnants?

The Cygnus Loop is classified as a middle-aged supernova remnant (SNR) located below the Galactic equator (l=74, b=-8.6) and 770 pc away from us. Its large size and little confusion with Galactic emission makes it an ideal test ground for evolutionary and structural theories of SNRs. New radio continuum mapping of the Cygnus Loop at 2695 MHz with the Effelsberg 100-m telescope provides indications that the Cygnus Loop consists of two separate SNRs. Combining this result with data from the literature we argue that a secondary SNR exists in the south with a recently detected neutron star close to its center. Two interacting SNRs seem to be the best explanation to account for the Cygnus Loop observations at all wavelengths.Comment: 4 pages, 2 figures, Astron. Astrophys., accepte

Dynamically Driven Evolution of the Interstellar Medium in M51

We report the highest-fidelity observations of the spiral galaxy M51 in CO emission, revealing the evolution of giant molecular clouds (GMCs) vis-a-vis the large-scale galactic structure and dynamics. The most massive GMCs (so-called GMAs) are first assembled and then broken up as the gas flow through the spiral arms. The GMAs and their H2 molecules are not fully dissociated into atomic gas as predicted in stellar feedback scenarios, but are fragmented into smaller GMCs upon leaving the spiral arms. The remnants of GMAs are detected as the chains of GMCs that emerge from the spiral arms into interarm regions. The kinematic shear within the spiral arms is sufficient to unbind the GMAs against self-gravity. We conclude that the evolution of GMCs is driven by large-scale galactic dynamics --their coagulation into GMAs is due to spiral arm streaming motions upon entering the arms, followed by fragmentation due to shear as they leave the arms on the downstream side. In M51, the majority of the gas remains molecular from arm entry through the inter-arm region and into the next spiral arm passage.Comment: 6 pages, including 3 figures. Accepted, ApJ

HI observations of luminous infrared galaxy mergers

A total of 19 luminous infrared galaxy mergers, with L_IR~2 10^11 L_sun for H_0=75 km/s/Mpc, have been observed in the HI line at Nancay and four of them were observed at Arecibo as well. Of these 19, ten had not been observed before. Six were clearly detected, one of which for the first time. The objective was to statistically sample the \HI gas mass in luminous infrared mergers along a starburst merger sequence where the molecular CO gas content is already known.Comment: 11 pages, accepted for Astron. Astrophys., 22/12/200

Molecular Clouds in the Galactic Center Region: Carbon Monoxide Observations at 2.6 Millimeters

A preliminary CO emission line survey covering a strip at b = -2' from ℓ = 359°.7 to ℓ = 2°.8 is presented which shows a continuous band of emission connecting the region between Sgr A and Sgr B. A high-resolution map of the Sgr A cloud near the galactic center shows that there are at least two clouds centered within 3' of each other with a velocity difference of 35 km s^(-1). Measurement of the ^(13)C^(16)O and ^12)C^(18)O emission indicates isotopic abundances similar to those of the solar system