| 1. |
- Curran, S.J., et al.
(författare)
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On the absence of molecular absorption in high-redshift millimetre-band searches
- 2011
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 416:3, s. 2143-2153
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Tidskriftsartikel (refereegranskat)abstract
- We have undertaken a search for millimetre-waveband absorption (through the CO and HCO(+) rotational transitions) in the host galaxies of reddened radio sources (z = 0.405-1.802). Despite the colour selection (optical-near-infrared colours of V - K greater than or similar to 5 in all but one source), no absorption was found in any of the eight quasars for which the background continuum flux was detected. On the basis of the previous (mostly intervening) H(2) and OH detections, the limits reached here and in some previous surveys should be deep enough to detect molecular absorption according to their V - K colours. However, our survey makes the assumption that the reddening is associated with dust close to the emission redshift of the quasar and that the narrow millimetre component of this emission is intercepted by the compact molecular cores. By using the known millimetre absorbers to define the colour depth and comparing this with the ultraviolet luminosities of the sources, we find that, even if these assumptions are valid, only 12 of the 40 objects (mainly from this work) are potentially detectable. This is assuming an excitation temperature of T(x) = 10 K at z = 0, with the number decreasing with increasing temperatures (to zero detectable at T(x) greater than or similar to 100 K).
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| 2. |
- Curran, S.J., et al.
(författare)
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Redshifted H I and OH absorption in radio galaxies and quasars
- 2011
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Ingår i: Monthly Notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 413:2, s. 1165-1173
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Tidskriftsartikel (refereegranskat)abstract
- From a survey for the redshifted H i 21-cm and OH 18-cm absorption in the hosts of a sample of radio galaxies and quasars, we detect H i in three of the 10 and OH in none of the 14 sources for which useful data were obtained. As expected from our recent result, all of the 21-cm detections occur in sources with ultraviolet (UV) continuum luminosities of L(UV) 1023 W Hz-1. Our 21-cm detections in combination with those previously published give a total of eight (associated and intervening) H i-absorbing sources searched and undetected in OH. Using the detected 21-cm line strengths to normalize the limits, we find that only two of these eight sources may have been searched sufficiently deeply in OH, even though these are marginal.
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| 3. |
- Gratier, P., et al.
(författare)
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Molecular and atomic gas in the Local Group galaxy M 33
- 2010
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 522:1
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Tidskriftsartikel (refereegranskat)abstract
- We present high-resolution large-scale observations of the molecular and atomic gas in the Local Group galaxy M 33. The observations were carried out using the HEterodyne Receiver Array (HERA) at the 30 m IRAM telescope in the CO(2-1) line, achieving a resolution of 12 '' x 2.6 km s(-1), enabling individual giant molecular clouds (GMCs) to be resolved. The observed region is 650 square arcminutes mainly along the major axis and out to a radius of 8.5 kpc, and covers entirely the 2' x 40' radial strip observed with the HIFI and PACS Spectrometers as part of the HERM33ES Herschel key program. The achieved sensitivity in main-beam temperature is 20-50 mK at 2.6 km s(-1) velocity resolution. The CO(2-1) luminosity of the observed region is 1.7 +/- 0.1 x 10(7) K km s(-1) pc(2) and is estimated to be 2.8 +/- 0.3 x 10(7) K km s(-1) pc(2) for the entire galaxy, corresponding to H-2 masses of 1.9 x 10(8) M-circle dot and 3.3 x 10(8) M-circle dot respectively (including He), calculated with N(H-2)/ICO(1-0) twice the Galactic value due to the half-solar metallicity of M 33. The HI 21 cm VLA archive observations were reduced, and the mosaic was imaged and cleaned using the multi-scale task in the CASA software package, yielding a series of datacubes with resolutions ranging from 5 '' to 25 ''. The HI mass within a radius of 8.5 kpc is estimated to be 1.4 x 10(9) M-circle dot. The azimuthally averaged CO surface brightness decreases exponentially with a scale length of 1.9 +/- 0.1 kpc whereas the atomic gas surface density is constant at Sigma(HI) = 6 +/- 2 M-circle dot pc(-2) deprojected to face-on. For an N(H-2)/ICO(1-0) conversion factor twice that of the Milky Way, the central kiloparsec H-2 surface density is Sigma(H2) = 8.5 +/- 0.2 M-circle dot pc(-2). The star formation rate per unit molecular gas (SF efficiency, the rate of transformation of molecular gas into stars), as traced by the ratio of CO to H-alpha and FIR brightness, is constant with radius. The SFE, with a N(H-2)/ICO(1-0) factor twice galactic, appears 2-4 times greater than for large spiral galaxies. A morphological comparison of molecular and atomic gas with tracers of star formation is presented showing good agreement between these maps both in terms of peaks and holes. A few exceptions are noted. Several spectra, including those of a molecular cloud situated more than 8 kpc from the galaxy center, are presented.
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| 4. |
- Muller, Sebastien, 1976, et al.
(författare)
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An ALMA Early Science survey of molecular absorption lines toward PKS 1830-211 Analysis of the absorption profiles
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 566
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Tidskriftsartikel (refereegranskat)abstract
- We present the first results of an ALMA spectral survey of strong absorption lines for common interstellar species in the z = 0.89 molecular absorber toward the lensed blazar PKS 1830-211. The dataset brings essential information on the structure and composition of the absorbing gas in the foreground galaxy. In particular, we find absorption over large velocity intervals (greater than or similar to 100 km s(-1)) toward both lensed images of the blazar. This suggests either that the galaxy inclination is intermediate and that we sample velocity gradients or streaming motions in the disk plane, that the molecular gas has a large vertical distribution or extraplanar components, or that the absorber is not a simple spiral galaxy but might be a merger system. The number of detected species is now reaching a total of 42 different species plus 14 different rare isotopologues toward the SW image, and 14 species toward the NE line-of-sight. The abundances of CH, H2O, HCO+, HCN, and NH3 relative to H-2 are found to be comparable to those in the Galactic diffuse medium. Of all the lines detected so far toward PKS 1830-211, the ground-state line of ortho-water has the deepest absorption. We argue that ground-state lines of water have the best potential for detecting diffuse molecular gas in absorption at high redshift.
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