Neutral Hydrogen Mass Research Articles

A Dark Hydrogen Cloud in the Virgo Cluster

VIRGOHI 21 is an H I source detected in the Virgo Cluster survey of Davies et al. that has a neutral hydrogen mass of 108 M and a velocity width of ?V20 = 220 km s-1. From the Tully-Fisher relation, a galaxy with this velocity width would be expected to be 12 mag or brighter; however, deep CCD imaging has failed to turn up a counterpart down to a surface brightness level of 27.5 B mag arcsec-2. The H I observations show that it is extended over at least 16 kpc, which, if the system is bound, gives it a minimum dynamical mass of ~1011 M and a mass-to-light ratio of Mdyn/LB > 500 M/L. If it is tidal debris, then the putative parents have vanished; the remaining viable explanation is that VIRGOHI 21 is a dark halo that does not contain the expected bright galaxy. This object was found because of the low column density limit of our survey, a limit much lower than that achieved by all sky H I surveys such as those carried out at Parkes and Jodrell Bank. Further such sensitive surveys might turn up a significant number of the dark matter halos predicted by galaxy formation models.

Damped Lyman-α Absorbers in Cosmological SPH Simulations: the “Metallicity Problem”

We study the distribution of star formation rate (SFR) and metallicity of damped Lyman-α absorbers (DLAs) using cosmological smoothed particle hydrodynamics (SPH) simulations of the Λ cold dark matter (CDM) model. Our simulations include a phenomenological model for feedback by galactic winds which allows us to examine the effect of galactic outflows on the distribution of SFR and metallicity of DLAs. For models with strong galactic winds, we obtain good agreement with recent observations with respect to total neutral hydrogen mass density, NHI column-density distribution, abundance of DLAs, and for the distribution of SFR in DLAs. However, we also find that the median metallicity of simulated DLAs is higher than the values typically observed by nearly an order of magnitude. This discrepancy with observations could be due to shortcomings in the treatment of the supernova feedback or the multiphase structure of the gas in our current simulations. Recent observations by Wolfe et al. (2003a,b) seem to point to the same problem; i.e. the observed DLA metallicities are much lower than those expected from the (either observed or simulated) DLA star formation rates, a puzzle that has been known as the “missing metals”-problem for the globally averaged quantities.

Predictions for the SKA from hierarchical galaxy formation models

There is now overwhelming evidence to suggest that structure in the Universe formed hierarchically. The development of collapsed structures in the dark matter due to gravitational instability has been studied extensively using numerical simulations and analytic techniques. Modelling the baryonic component of the Universe is much more challenging. The process of galaxy formation and evolution can be followed in the context of hierarchical structure formation using the technique of semi-analytical modelling. Due to our lack of knowledge of the pertinent physics, some parts of the model are more uncertain than others, one clear example being the parameterization of the timescale for star formation. The SKA will help to remove this ambiguity by testing predictions for the evolution of the distribution of star formation rates and the neutral hydrogen mass function. Here we give examples of such predictions for two models which differ in how the star formation timescale in galaxies scales with redshift. We use the GALFORM semi-analytical model to compute the evolution of the neutral hydrogen mass function with redshift. The star formation histories generated by the GALFORM model are combined with the spectro-photometric code GRASIL to generate spectral energy distributions for model galaxies that extend beyond the optical to sub-millimetre and radio wavelengths. We use this hybrid code to make predictions for the number counts of radio sources whose radio emission is driven by star formation.

The First Sample of Sub-Damped Lyα Systems and their Chemical Properties

We took advantage of the ESO UVES/VLT archive of quasar spectra to build a homogeneous sample of ‘sub-DLAs’, absorption line systems with HI column densities between 1019 and 2×1020 cm−2. According to Péroux et al. (2002), these systems should contain a major fraction of the neutral hydrogen mass at z > 3.5 and may thus play an important role at high redshift. Twelve sub-DLAs have been identified. We performed a detailed chemical analysis, and addressed the issues of photoionization corrections. We obtained the first sub-DLA chemical abundance data base ideal for the study of a number of interesting properties of these systems. The implication of sub-DLAs in the cosmic metallicity evolution was our main concern. We also undertook a detailed comparison of the sub-DLA chemical properties with the well studied DLAs to see whether the sub-DLAs are associated with a different class of objects.

Starbursts and Extra-planar Hα from SINGG

The NOAO Survey for Ionization in Neutral Gas Galaxies (SINGG) is the largest star formation survey of an H I selected sample. Since the selection is made without regard to optical morphology, it is not biased toward or against “interesting” types of galaxies; thus SINGG is an ideal sample for studying galaxy demographics. Of a sample of 90 extra-galactic sources observed in photometric conditions, all are detected in Hα. This indicates that dormant galaxies, those containing an appreciable ISM but no star formation, are at best rare. We have made first pass morphological surveys for starbursts, as judged by Hα surface brightness, and outflows as judged by extra-planar Hα. We find that about 15% of the sources contain starbursts, with little dependence on the neutral hydrogen mass MHI. Nearly one half of a sample ~ 35 edge-on galaxies show evidence for extra-planar Hα having a scale size of 0.5 Kpc or larger, while nearly one quarter have extra-planar Hα features 1.0 Kpc in size or larger. There is a hint that high MHI systems preferentially have displaced outflows (chimneys, or fountains) while central outflows (galactic winds) preferentially occur in low MHI systems. However, a larger sample (e.g. the full SINGG survey) is needed to confirm this trend.

The evolution of ΩH iand the epoch of formation of damped Lyman α absorbers

We present a study of the evolution of the column density distribution, f(N, z), and total neutral hydrogen mass in high column density quasar absorbers using candidates from a recent high-redshift survey for damped Lyman α (DLA) and Lyman-limit system (LLS) absorbers. The observed number of LLS [N(H_i) >1.6 × 10^(17) atom cm^(−2)] is used to constrain f(N, z) below the classical DLA definition of 2 × 10^(20) atom cm^(−2). The evolution of the number density of LLS is consistent with our previous work but steeper than previously published work of other authors. At z= 5, the number density of Lyman-limit systems per unit redshift is ∼5, implying that these systems are a major source of ultraviolet (UV) opacity in the high-redshift Universe. The joint LLS–DLA analysis shows unambiguously that f(N, z) deviates significantly from a single power law and that a Γ-law distribution of the form f(N,z) = (f_*/N_*)(N/N_*)^(−β)exp(−N/N_*) provides a better description of the observations. These results are used to determine the amount of neutral gas contained in DLAs and in systems with lower column density. Whilst in the redshift range 2–3.5, ∼90 per cent of the neutral H i mass is in DLAs, we find that at z > 3.5 this fraction drops to only 55 per cent and that the remaining ‘missing’ mass fraction of the neutral gas lies in sub-DLAs with N(H i) 10^(19)–2 × 10^(20) atom cm^(−2). The characteristic column density, N_*, changes from 1.6 × 10^(21) atom cm^(−2) at z 3.5, supporting a picture where at z > 3.5, we are directly observing the formation of high column density neutral hydrogen DLA systems from lower column density units. Moreover, since current metallicity studies of DLA systems focus on the higher column density systems they may be giving a biased or incomplete view of global galactic chemical evolution at z > 3. After correcting the observed mass in H i for the ‘missing’ neutral gas the comoving mass density now shows no evidence for a decrease above z= 2.

Abundance of damped Lyman α absorbers in cosmological smoothed particle hydrodynamics simulations

We use cosmological smoothed particle hydrodynamics (SPH) simulations of the A cold dark matter (CDM) model to study the abundance of damped Lyman a absorbers (DLAs) in the redshift range z = 0-4.5. We compute the cumulative DLA abundance by using the relation between the DLA cross-section and the total halo mass inferred from the simulations. Our approach includes standard radiative cooling and heating with a uniform ultraviolet background, star formation, supernova feedback and a phenomenological model for feedback by galactic winds. The latter allows us to examine, in particular, the effect of galactic outflows on the abundance of DLAs. We employ the 'conservative entropy' formulation of SPH developed by Springel & Hernquist, which mitigates against the systematic overcooling that affected earlier simulations. In addition, we utilize a series of simulations of varying box-size and particle number to isolate the impact of numerical resolution on our results. We show that the DLA abundance was overestimated in previous studies for three reasons: (i) the overcooling of gas occurring with non-conservative formulations of SPH, (ii) a lack of numerical resolution and (iii) an inadequate treatment of feedback. Our new results for the total neutral hydrogen mass density, DLA abundance and column density distribution function all agree reasonably well with observational estimates at redshift z = 3, indicating that DLAs arise naturally from radiatively cooled gas in dark matter haloes that form in a ACDM universe. Our simulations suggest a moderate decrease in DLA abundance by roughly a factor of 2 from z = 4.5 to 3, consistent with observations. A significant decline in abundance from z = 3 to 1, followed by weak evolution from z = 1 to 0, is also indicated, but our low-redshift results need to be interpreted with caution because they are based on coarser simulations than those employed at high redshift. Our highest resolution simulation also suggests that the halo massscale below which DLAs do not exist is slightly above 10 8 h -1 M ○. at z = 3-4, somewhat lower than previously estimated.

A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies

The Wisconsin Hα Mapper has been used to set the first deep upper limits on the intensity of diffuse Hα emission from warm ionized gas in the Draco and Ursa Minor dwarf spheroidal galaxies (dSphs). Assuming a velocity dispersion of 15 km s-1 for the ionized gas, we set limits of IHα ≤ 0.024 R and IHα ≤ 0.021 R for the Draco and Ursa Minor dSphs, respectively, averaged over our 1° circular beam. Adopting a simple model for the ionized interstellar medium, these limits translate to upper bounds on the mass of ionized gas of 10% of the stellar mass, or ~10 times the upper limits for the mass of neutral hydrogen. Note that the Draco and Ursa Minor dSphs could contain substantial amounts of interstellar gas, equivalent to all of the gas injected by dying stars since the end of their main star-forming episodes 8 Gyr in the past, without violating these limits on the mass of ionized gas.

High and Low Surface Brightness Galaxies in the Local Universe. IV. Optical and 21 Centimeter Spectroscopy

We present flux-calibrated spectra in the range 3500 to 8000 A for the nuclear regions of 250 galaxies and H I 21 cm line profiles for 238 galaxies selected from the catalog of low surface brightness galaxies identified in Automated Plate Measuring Facility (APM) scans of UK Schmidt Telescope survey plates. For the optical spectra, common nebular absorption- and emission-line equivalent widths and emission-line fluxes were measured with typical errors of about 20%. H I mass and velocity widths were measured from the 21 cm line emission, with 15% accuracy. Galaxies in this study span over 6 mag in surface brightness. Only about 20% of these galaxies show spectroscopic evidence of active galactic nuclei. Derived quantities such as synthetic colors, metallicity, star formation rate, the ratio of neutral hydrogen mass to blue light, and gas mass fraction are presented in a companion paper.

A High-Resolution H [CSC]i[/CSC] Study of the Interstellar Medium Local to HD 193793

A 2° field centered at the optical position of the Wolf-Rayet (WR) star HD 193793 (≡ WR 140) was surveyed in the H I 21 cm line and in the 1420 MHz radio continuum, using the Dominion Radio Astrophysical Observatory interferometer. The aim of this observations was to look for evidence of an interaction between the WR star and its local interstellar medium (ISM). Our H I data displays a large oval minimum at a velocity of Vsys -12 km s-1, close to the optical position of HD 193793. We believe this H I void was created by WR 140 and its massive companion (HD 193793 is a member of a well-known binary system). The major axis of the H I void is ~11.5 pc and its axial ratio, the ratio of major to minor axis, is ~1.4. This structure is observable over a velocity range of around 11 km s-1. The H I minimum appears surrounded by a clumpy shell of H I in emission that has a total mass of neutral hydrogen of MHI ~ 1300 solar masses. The kinematical distance corresponding to a local standard of rest velocity of -12 km s-1 is approximately 5.4 kpc, which disagrees with the distance of HD 193793, namely, around 1 kpc. Therefore, it is concluded that the H I bubble was blown in an ISM having nonnegligible peculiar motions. Hipparcos proper-motion measurements indicate that HD 193793 has a tangential velocity of 28 ± 3 km s-1 along the major axis of one of the H I minima detected in the interior of the main H I cavity. To reconcile this motion with the physical size of the H I structure blown by the winds of the binary system, it is concluded that such tangential velocity was acquired by the system a short while ago, namely, ~1.3 × 105 yr. Maps from the IRAS database show a large-scale IR feature, with good spatial correlation with the H I shell surrounding the main H I void. We believe the emission from the IR shell arises from dust grains heated by the energetic stellar continuum photons emitted by the stellar objects.

The Space Density of Primordial Gas Clouds near Galaxies and Groups and their Relation to Galactic High-Velocity Clouds

The Arecibo H i Strip Survey probed the halos of approximately 300 cataloged galaxies and the environments of approximately 14 groups with sensitivity to neutral hydrogen masses >/=107 M middle dot in circle. The survey detected no objects with properties resembling the high-velocity clouds (HVCs) associated with the Milky Way or Local Group. If the HVCs were typically MHi=107.5 M middle dot in circle objects distributed throughout groups and galaxy halos at distances of approximately 1 Mpc, the survey should have made approximately 70 HVC detections in groups and approximately 250 detections around galaxies. The null detection implies that HVCs are deployed at typical distances of </=200 kpc from the galaxies or group barycenters. If the clouds are in virial equilibrium, their average dark matter fraction must be 98% or higher.

High-Velocity H I in the Spiral Galaxy NGC 5668

The nature and origin of the high-velocity clouds (HVCs) of neutral hydrogen in our Galaxy are not well understood, in part because of the uncertain distances to the clouds. As a result it is difficult to measure the mass of neutral hydrogen in the HVCs in the Galaxy, but further insight into the nature of HVCs can be obtained by finding and studying such gas in other galaxies. The Sc-galaxy NGC 5668 was found to have high-velocity wings beyond the double-horned 21 cm profile in observations performed with the Arecibo 305 m telescope; these wings are the expected signature of HVCs in a disk galaxy. In this paper, Very Large Array observations of NGC 5668 are presented that confirm the high- velocity H I wings detected with the Arecibo telescope. About 60% of the material in the high-velocity wings is distinct in position-velocity diagrams, located primarily outside the optical disk of the galaxy, and may be infalling material comparable to the Magellanic Stream in our own Galaxy. The total mass of this kinematically distinct neutral hydrogen is 4 x 10^8^ M_sun_. A natural source for the rest of the wing material is halo gas produced by a galactic fountain. Such a fountain would be driven by supernovae and energetic stellar winds from massive stars in OB associations that would also transfer kinetic energy to the neutral hydrogen disk. This would result in a larger H I velocity dispersion within the optical disk than outside of it, as is suggested by these observations.

Low Surface Brightness Galaxies in the Local Universe. I. The Catalog

Data are presented for 693 galaxies identified in a large new survey for low surface brightness galaxies in the nearby universe (z less than or similar to 0.1). The survey covers 786 square degrees centered on the equator, and it extends significantly the surface brightness range of galaxy surveys in which there are a substantial number of galaxies with redshifts. The data are derived from the Automated Plate Measuring machine scans of survey plates from the UK Schmidt Telescope and from follow-up observations at radio and optical wavelengths. Accurate positions, total B magnitudes, surface brightness parameters, and angular sizes are tabulated for each galaxy. Radial velocities, optical luminosities, and neutral hydrogen masses are listed for a subset of the sample. Finding charts are also presented for those objects having a large enough angular size that the scans from survey plates provide some morphological information. The selection function and the luminosity function that can be derived from the survey are discussed in two companion papers.

Neutral hydrogen profiles of cluster galaxies

Neutral hydrogen profiles of 67 galaxies in seven nearby clusters have been obtained with the Arecibo telescope. The neutral hydrogen masses of these galaxies range from 2 x 10(exp 8) to 2 x 10(exp 10) M. There is no evidence for significant neutral hydrogen deficiency in any of these clusters.

A VLA search for neutral hydrogen in cooling flow clusters

view Abstract Citations (33) References (45) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A VLA Search for Neutral Hydrogen in Cooling Flow Clusters Dwarakanath, K. S. ; van Gorkom, J. H. ; Owen, F. N. Abstract We present a VLA search for neutral hydrogen in three clusters, which are considered to be prime examples of so-called cooling flow clusters: Virgo (Virgo A), Abell 2199 (3C 338), and Abell 780 (Hydra A). We looked for H I in absorption against the central radio sources with a velocity coverage ~2600 km s^-1^ and with a velocity resolution ~87 km s^-1^. We do not detect a spatially extended distribution of cold clouds. Our 3σ optical depth limits are 0.0005 over a typical velocity range of 500 km s^-1^, Assuming the currently popular cooling flow scenarios in which the distribution of the cold gas can be characterized by a core radius of ~100 kpc, our results place an upper limit of 1.2 x 10^10^ M_sun_ to the mass of neutral hydrogen in such a flow for an assumed spin temperature of 100 K. This limit is a factor of 30 below what is expected from the Einstein Solid State Spectrometer observations of cooling flow clusters and is 1-2 orders of magnitude below what is expected from the cooling flow models. The expected large amount of H I is unlikely to exist in these clusters even as optically thick clouds unless their spin temperature is less than 10 K and/or their covering factor is much less than 1. We discuss some physical conditions in which the expected large amounts of H I could have escaped detection. We do, however, find H I absorption against the core of Hydra A. This line is narrow (~50 km s^-1^) and is not seen against the extended radio lobes. The properties of this absorption system are similar to those seen in some other cooling flow clusters and in isolated radio galaxies. We also detect a spiral galaxy in A 2199 with a total mass of 1.8 x 10^9^ M_sun_. Despite this detection of what might be a small H I cloud near the systemic velocity of the core of Hydra A, we do place stringent limits on the existence of such clouds anywhere within the primary beam. The upper limit to H I emission from such clouds ranges from 10^7^ to 10^9^ M_sun_. Publication: The Astrophysical Journal Pub Date: September 1994 DOI: 10.1086/174586 Bibcode: 1994ApJ...432..469D Keywords: Cooling Flows (Astrophysics); Galactic Clusters; H Lines; Hydrogen; Intergalactic Media; Radio Sources (Astronomy); Velocity Distribution; X Ray Absorption; Brightness Distribution; Very Large Array (Vla); X Ray Astronomy; Astrophysics; GALAXIES: COOLING FLOWS; GALAXIES: CLUSTERS: INDIVIDUAL NAME: ABELL 780; GALAXIES: CLUSTERS: INDIVIDUAL NAME: ABELL 2199; GALAXIES: CLUSTERS: INDIVIDUAL NAME: VIRGO A; GALAXIES: CLUSTERS OF; GALAXIES: INTERGALACTIC MEDIUM; RADIO LINES: GENERAL full text sources ADS | data products SIMBAD (6) NED (6)

An H I survey of high-velocity clouds in nearby disk galaxies

We observed 14 nearly face-on disk galaxies with the Arecibo 305 m telescope and found the double-horned H I profiles to have high-velocity wings in 10 of these galaxies. Such wings can be caused by high-velocity clouds, similar to those observed in our own Galaxy. Disk galaxy models were constructed that include both high-velocity clouds (modeled as a component of galactic gas with a velocity dispersion of either 30 or 50 km/s) and warped H I disks. We find that the high-velocity wings can be reproduced by models with high-velocity clouds but not by models with warps that are similar to those observed in other galaxies. If these wings are due to high-velocity clouds, then the mass of neutral hydrogen in high-velocity clouds for the 10 galaxies ranges from 6 X 10(exp 7) solar mass to 4 x 10(exp 9) solar mass, which corresponds to 4% - 14% of the total H I in these galaxies. The galaxies with no detected high-velocity wings are also those with the lowest far-infrared fluxes as measured by Infrared Astronomy Satellite (IRAS), which is consistent with the galactic fountain model in which the young stellar population (responsible for most of the far-infrared emission produces supernovae which then provide the kinetic energy of the high-velocity clouds.

Detection of CO J = 2 goes to 1 emission from the polar rings of NGC 2685 and NGC 4650A

view Abstract Citations (24) References (15) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Detection of CO J = 2 1 Emission from the Polar Rings of NGC 2685 and NGC 4650A Watson, Dan M. ; Guptill, Matthew T. ; Buchholz, Leah M. Abstract We report the detection of the J = 2 - 1(230 GHz) line of carbon monoxide in the polar rings of the galaxies NGC 2685 and NGC 4650A, and we use the results in a simple analysis of the composition of the neutral interstellar medium therein. Only 17%-35% of the gas mass of the NGC 4650A ring is provided by molecular clouds, perhaps consistent with the conventional picture of the origin of polar rings in the capture of a dwarf galaxy or tidal mass transfer from a spiral galaxy. The polar ring of NGC 2685, however, is quite rich in molecular matter, with an H_2_ mass greater than the neutral atomic hydrogen mass. Such a composition may be difficult to explain with the picture that applies to NGC 4650A. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/187153 Bibcode: 1994ApJ...420L..21W Keywords: Carbon Monoxide; Dwarf Galaxies; Hydrogen; Molecular Clouds; Radio Astronomy; Radio Spectra; Ring Galaxies; Spiral Galaxies; Transition; Infrared Astronomy Satellite; Interstellar Gas; Radio Telescopes; Spectrometers; Astronomy; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 4650A; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 2685; GALAXIES: ISM full text sources ADS | data products SIMBAD (2) NED (2)

A neutral hydrogen survey of polar-ring galaxies, 1: Green Bank observations of the northern sample

We present the results of a neutral hydrogen survey conducted with the Green Bank 140-foot radio telescope of 47 northern objects in the polar-ring galaxy atlas of Whitmore \etal (1990). We detected 39 of these above our detection limit of 1.7 \hbox{Jy\CDOT\KMS}; the average measured flux of 21 Jy\CDOT\KMS corresponds to an average neutral hydrogen mass of $\rm 5.3 \times 10^9$ \MSUN for a Hubble constant of $\rm H_0 = 75$ \KMS Mpc$^{-1}$. For the polar-ring galaxies in our sample that have also been observed with radio arrays, we find that the 21\AMIN (FWHM) Green Bank beam often includes much more flux than found by the synthesis instruments for the polar rings alone; some of these galaxies are known to have gas-rich companions. We compare the neutral hydrogen content of the sample to the blue luminosity and IRAS fluxes. The \HI-to-blue- light ratios of the confirmed and probable polar rings are around unity in solar units, indicating that polar ring galaxies (or their environments) are as gas-rich as typical irregular galaxies. For their blue luminosity, the confirmed polar rings are underluminous in the far-infrared, as compared with the rest of the sample. They are also FIR-underluminous for their \HI masses, which suggests that most of the gas in the ring may be in stable orbits, rather than flowing inward to trigger star formation in the central galaxy. The more disordered class of `related objects,' which includes a number of obvious mergers, is highly luminous in the far-infrared.

Further analysis of a 'Complete Sample' in the Virgo Supercluster of galaxies

In the context of the Local (Virgo-centred) Supercluster of galaxies, a statistical study is made of the radio-derived properties for the 165 spiral and irregular galaxies in the recently published Complete Sample by Fitt & Alexander. I find a trend for a larger neutral hydrogen mass in spiral galaxies located farther from the plane of the Local Supercluster (or smaller H I mass in spiral galaxies closer to the Local Supercluster plane). A previously known result, of a deficiency of H I mass in spiral galaxies located radially close to the centre of the Virgo cluster, is seen again in the Complete Sample. Contrary to some theoretical predictions, the magnetic field strength in spiral galaxies does not seem to be well correlated with the star-formation efficiency or the neutral hydrogen mass

Molecular gas content of the primaeval galaxy IRAS 10214+4724

THE faint IRAS source 10214 + 4724, identified1 with a distant galaxy at redshift z = 2.286, is one of the most intrinsically luminous objects in the Universe, with L≈1014 L⊙ (whereL⊙ is the solar luminosity). The remarkable detection of emission from neutral CO (ref. 2) leads, by comparison with similar detections in nearby galaxies, to an estimate of 2–6 x 1011M⊙ for the mass of neutral molecular hydrogen in this galaxy. This is 30–90 times less than the estimate given in ref. 2, but still comparable to the total mass (gas, dust and stars) of a large spiral galaxy. This gas mass is consistent with the dynamical mass of the galaxy inferred from the CO emission line-width. The CO line luminosity is twenty times larger than is seen in nearby (z 3xl011 M⊙) galaxies3–5. Although it is extremely gas-rich, with a higher CO luminosity than any other galaxy, the infrared to CO luminosity ratio of 10214 + 4724 is twice that of most infrared-luminous galaxies, and ∼30 times higher than that of normal spirals. Its infrared colours and high infrared/CO luminosity ratio indicate that 10214 + 4724 is similar to nearby ultra-luminous galaxies5 that are known to be merging. This galaxy is a primaeval molecular galaxy with the mass of a large spiral, but with most of the mass in molecular gas rather than stars.