arXiv subjects

Loretta Dunne

Publications and source records attributed to Loretta Dunne.

51 records · Page 3Linked to original sources

arXiv2007

Gas and Dust in the Taffy Galaxies: Ugc12914/15

We present a comprehensive study of the dust and gas properties in the after-head-on-collision UGC12914/15 galaxy system using multi-transition CO data and SCUBA sub-mm continuum images at both 450 and 850$μ$m. CO(3-2) line emission was detected in the disks of UGC 12914 and UGC 12915 as well as in a bridge connecting the two galaxies. Dust emission at 450$μ$m was detected for the first time in the two galactic disks and in the connecting bridge. Using an LVG excitation analysis model we have obtained good estimates of the physical parameters in different regions of this system and the amount of molecular gas was found to be 3-4 times lower than that estimated by other investigators using the standard Galactic CO-to-H2 conversion factor. Comparing with the dust mass derived from the SCUBA data, we found that the gas-to-dust ratio was comparable to the Galactic value in the two galaxy disks but a factor of ~3 higher in the bridge. The physical condition of the molecular gas in the bridge is comparable to that in the diffuse clouds in our Galaxy. Our result is consistent with the scenario that the bridge molecular gas originated from the disk molecular clouds and has been drawn out of the galactic disks due to direct cloud-cloud collision. Our data indicate that the global star formation efficiency (SFE) in UGC 12915 is comparable to that of normal spiral galaxies, and the SFE is 40% lower in UGC 12914 than in UGC 12915. Little star formation activity was found in the bridge except in an HII region adjacent to the disk of UGC 12915.

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arXiv2005

The SCUBA Local Universe Galaxy Survey - III. Dust along the Hubble sequence

We present new results from the SCUBA Local Universe Galaxy Survey (SLUGS), the first large systematic submillimetre survey of the local Universe. Since our initial survey of a sample of 104 IRAS-selected galaxies we have now completed a survey of a sample of 81 optically-selected galaxies, observed with the SCUBA camera on the James Clerk Maxwell Telescope. Since SCUBA is sensitive to the 90% of dust too cold to radiate significantly in the IRAS bands our new sample represents the first unbiased survey of dust in galaxies along the whole length of the Hubble sequence. We find little change in the properties of dust in galaxies along the Hubble sequence and detected 6 out of 11 elliptical galaxies. As in our earlier work on IRAS galaxies we find that the IRAS and submm fluxes are well-fitted by a two-component dust model with dust emissivity index beta=2. The major difference from our earlier work is that we find the ratio of the mass of cold dust to the mass of warm dust is much higher for our optically-selected galaxies and can reach values of ~1000. Comparison of the results for the IRAS- and optically-selected samples shows that there is a population of galaxies containing a large proportion of cold dust that is unrepresented in the IRAS sample. We derive local submm luminosity and dust mass functions, both directly from our optically-selected SLUGS sample, and by extrapolation from the IRAS PSCz survey using the method of Serjeant & Harrison, and find excellent agreement between the two. We find them to be well-fitted by Schechter functions except at the highest luminosities. We find that as a consequence of the omission of cold galaxies from the IRAS sample the luminosity function presented in our earlier work is too low by a factor of 2.

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arXiv2004

The SCUBA Local Universe Galaxy Survey: Results from the Optically-Selected Sample

We present new results from the SCUBA Local Universe Galaxy Survey, the first large statistical submillimetre survey of the local Universe. Following our initial survey of a sample of 104 IRAS-selected galaxies we now present the results of a sample of 80 Optically-selected galaxies. Since SCUBA is sensitive to the large proportion of dust too cold to be detected by IRAS the addition of this Optically-selected sample allows us for the first time to determine the amount of cold dust in galaxies of different Hubble types. We detect 6 ellipticals in the sample and find them to have dust masses in excess of 10^7 solar masses. We derive local submillimetre Luminosity Functions and Dust Mass functions, both directly for the Optically-Selected SLUGS sample and by extrapolation from the IRAS PSCz survey, and find them to be well-fitted by Schechter functions. We find excellent agreement between the two LFs and DMFs and show that, whereas the slope of the IRAS-selected LF at lower luminosities was steeper than -2 (a submm "Olbers' Paradox"), as expected the PSCz-extrapolated LF flattens out at the low luminosity end.

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arXiv2004

The SCUBA Local Universe Galaxy Survey Optically-Selected Sample

We discuss the progress of the SCUBA Local Universe Galaxy Survey (SLUGS), the first large, statistical sub-mm survey of the local universe. Since our original survey of a sample of 104 IRAS-selected galaxies we have recently completed a sample of 78 Optically-Selected galaxies. Since SCUBA is sensitive to the large proportion of dust too cold to be detected by IRAS the addition of this optically-selected sample allows us for the first time to determine the amount of cold dust in galaxies of different Hubble types. We detect 6 ellipticals in the sample and find them to have dust masses in excess of 10^7 solar masses. We derive local sub-mm luminosity functions, both directly for the two samples, and by extrapolation from the IRAS PSCz, and find excellent agreement.

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arXiv2003

The Canada-UK Deep Submillimetre Survey VIII: Source Identifications in the 3-hour field

We present optical, near-infrared and radio observations of the 3-hour field of the Canada-UK Deep Submillimetre Survey. Of the 27 submillimetre sources in the field, nine have secure identifications with either a radio source or a near-IR source. We show that the percentage of sources with secure identifications in the CUDSS is consistent with that found for the bright `8 mJy' submillimetre survey, once allowance is made for the different submillimetre and radio flux limits. Of the 14 secure identifications in the two CUDSS fields, eight are VROs or EROs, five have colours typical of normal galaxies, and one is a radio source which has not yet been detected at optical/near-IR wavelengths. Eleven of the identifications have optical/near-IR structures which are either disturbed or have some peculiarity which suggests that the host galaxy is part of an interacting system. One difference between the CUDSS results and the results from the 8-mJy survey is the large number of low-redshift objects in the CUDSS; we give several arguments why these are genuine low-redshift submillimetre sources rather than being gravitational lenses which are gravitationally amplifying a high-$z$ submillimetre source. We construct a $K-z$ diagram for various classes of high-redshift galaxy and show that the SCUBA galaxies are on average less luminous than classical radio galaxies, but are very similar in both their optical/IR luminosities and their colours to the host galaxies of the radio sources detected in $μ$Jy radio surveys.

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arXiv2003

The Canada-UK Deep Submillimeter Survey VII: Optical and near-infrared identifications for the 14h field

We present the multi-wavelength identifications for 23 sources in the Canada-UK Deep Submillimeter Survey (CUDSS) 14h field. The identifications have been selected on the basis of radio and near-infrared data and we argue that, to our observational limits, both are effective at selecting the correct counterparts of the SCUBA sources. We discuss the properties of these identifications and find that they are very red in near-infrared color, with many classified as Extremely Red Objects, and show disturbed morphologies. Using the entire CUDSS catalogue of 50 sources we use a combination of spectroscopic redshifts (4 objects), 1.4GHz-to-850um flux ratio redshift estimates (10 objects), and redshift lower-limits based on non-detections at 1.4GHz (the rest of the sample) to estimate a lower-limit on the median redshift of the population of z_med > 1.4. Working from simple models and using the properties of the secure identifications, we discuss general and tentative constraints on the redshift distribution and the expected colors and magnitudes of the entire population.

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arXiv2003

The Origin of Cosmic Dust

Large amounts of dust have recently been discovered in high-z galaxies and QSOs. The stellar winds produced by AGB stars are thought to be the main source of dust in galaxies, but they cannot produce that dust on a short enough timescale (<1 Gyr) to explain the results in the high-z galaxies. Supernova explosions of massive stars (TypeII) are also a potential source, with models predicting 0.2-4 Msun of dust from each. As massive stars evolve rapidly, on timescales of a few Myr, these supernovae could be responsible for the high-z dust. Observations of supernova remnants in the Milky Way have previously only revealed 10^-7 - 10^-3 Msun of dust each, which is insufficient to explain the high-z data. Here we report the detection of ~2-4 Msun of cold dust in Cas A. This implies that supernovae are at least as important as stellar winds in producing dust in our Galaxy and would have been the dominant source of dust at high-z.

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arXiv2003

SCUBA Observations of MAMBO Sources

We have observed 23 sources from the MAMBO 1200 micron survey with SCUBA at 850 microns, detecting 19 of the sources. The sources generally have low values for the ratio of 850 micron to 1200 micron flux. Two possible explanations for the low values are either that the sources are at very high redshift or that the global properties of the dust in the MAMBO sources are different from the global properties of dust in low-redshift galaxies. If the former explanation is correct, we estimate that 15 of the MAMBO sources lie at z > 3.

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arXiv2003

CO Molecular Gas in Infrared Luminous Galaxies

We present the first statistical survey of the properties of the 12CO(1-0) and 12CO(3-2) line emission from the nuclei of a nearly complete subsample of 60 infrared (IR) luminous galaxies selected from SCUBA Local Universe Galaxy Survey (SLUGS). This subsample is flux limited at S60 mincron > 5.24 Jy with far-IR (FIR) luminosities mostly at LFIR > 10^10 LSUN. We compare the emission line strengths of 12CO(1-0) and (3-2) transitions at a common resolution of 15". The measured 12CO(3-2) to (1-0) line intensity ratios r31 vary from 0.22 to 1.72 with a mean value of 0.66 for the sources observed, indicating a large spread of the degree of excitation of CO in the sample. These CO data, together with a wide range of data at different wavelengths obtained from the literature, allow us to study the relationship between the CO excitation conditions and the physical properties of gas/dust and star formation in the central regions of galaxies. Our analysis shows that there is a non-linear relation between CO and FIR luminosities, such that their ratio LCO/LFIR decreases linearly with increasing LFIR. This behavior was found to be consistent with the Schmidt Law relating star formation rate to molecular gas content, with an index N = 1.4 +- 0.3. We also find a possible dependence of the degree of CO gas excitation on the efficiency of star forming activity. Using the large velocity gradient (LVG) approximation to model the observed data, we investigate the CO-to-H2 conversion factor X for the SLUGS sample. The results show that the mean value of X for the SLUGS sample is lower by a factor of 10 compared to the conventional value derived for the Galaxy, if we assume the abundance of CO relative to H2, ZCO = 10^-4.

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arXiv2001

The SCUBA Local Universe Galaxy Survey II. 450 micron data - evidence for cold dust in bright IRAS Galaxies

This is the second in a series of papers presenting results from the SCUBA Local Universe Galaxy Survey. In our first paper we provided 850 micron flux densities for 104 galaxies selected from the IRAS Bright Galaxy Sample and we found that the 60, 100 micron (IRAS) and 850 micron (SCUBA) fluxes could be adequately fitted by emission from dust at a single temperature. In this paper we present 450 micron data for the galaxies. With the new data, the spectral energy distributions of the galaxies can no longer be fitted with an isothermal dust model - two temperature components are now required. Using our 450 micron data and fluxes from the literature, we find that the 450/850 micron flux ratio for the galaxies is remarkably constant and this holds from objects in which the star formation rate is similar to our own Galaxy, to ultraluminous infrared galaxies (ULIRGS) such as Arp 220. The only possible explanation for this is if the dust emissivity index for all of the galaxies is ~2 and the cold dust component has a similar temperature in all galaxies (20-21 K). The dust masses estimated using the new temperatures are higher by a factor ~2 than those determined previously using a single temperature. This brings the gas-to-dust ratios of the IRAS galaxies into agreement with those of the Milky Way and other spiral galaxies which have been intensively studied in the submm.

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arXiv2000

The Canada-UK Deep Submillimetre Survey: The Survey of the 14-hour field

We have used SCUBA to survey an area of 50 square arcmin, detecting 19 sources down to a 3sigma sensitivity limit of 3.5 mJy at 850 microns. We have used Monte-Carlo simulations to assess the effect of source confusion and noise on the SCUBA fluxes and positions, finding that the fluxes of sources in the SCUBA surveys are significantly biased upwards and that the fraction of the 850 micron background that has been resolved by SCUBA has been overestimated. The radio/submillmetre flux ratios imply that the dust in these galaxies is being heated by young stars rather than AGN. We have used simple evolution models based on our parallel SCUBA survey of the local universe to address the major questions about the SCUBA sources: (1) what fraction of the star formation at high redshift is hidden by dust? (2) Does the submillimetre luminosity density reach a maximum at some redshift? (3) If the SCUBA sources are proto-ellipticals, when exactly did ellipticals form? However, we show that the observations are not yet good enough for definitive answers to these questions. There are, for example, acceptable models in which 10 times as much high-redshift star formation is hidden by dust as is seen at optical wavelengths, but also acceptable ones in which the amount of hidden star formation is less than that seen optically. There are acceptable models in which very little star formation occurred before a redshift of three (as might be expected in models of hierarchical galaxy formation), but also ones in which 30% of the stars have formed by this redshift. The key to answering these questions are measurements of the dust temperatures and redshifts of the SCUBA sources.

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arXiv1999

Deep sub-mm surveys: High redshift ULIRGs and the formation of the metal-rich spheroids

Deep surveys of the sky at millimeter wavelengths have revealed a population of ultra-luminous infrared galaxies (ULIRGs) at high redshifts. These appear similar to local objects of similar luminosities (such as Arp220) but are much more ``important'' at high redshift than at low reshift, in the sense that they represent a much larger fraction of the total luminous output of the distant Universe than they do locally. In fact the ULIRGs at high redshift are producing a significant fraction (>= 15%) of the total luminous output of the Universe averaged over all wavelengths and all epochs. The high z ULIRGs could plausibly be responsible for producing the metal-rich spheroidal components of galaxies, including the bulges that are the subject of this conference. In this case we would infer from the redshift distribution of the sources that much of this activity is probably happening relatively recently at z <= 2.

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arXiv1999

The Canada-UK Deep Sub-Millimeter Survey II: First identifications, redshifts and implications for galaxy evolution

Identifications are sought for 12 sub-mm sources detected by Eales et al (1998). Six are securely identified, two have probable identifications and four remain unidentified with I_AB > 25. Spectroscopic and estimated photometric redshifts indicate that four of the sources have z < 1, and four have 1 < z < 3, with the remaining four empty field sources probably lying at z > 3. The spectral energy distributions of the identifications are consistent with those of high extinction starbursts such as Arp 220. The far-IR luminosities of the sources at z > 0.5 are of order 3 x 10^12 h_50^-2 L_sun, i.e. slightly larger than that of Arp 220. Based on this small sample, the cumulative bolometric luminosity function shows strong evolution to z ~ 1, but weaker or possibly even negative evolution beyond. The redshift dependence of the far-IR luminosity density does not appear, at this early stage, to be inconsistent with that seen in the ultraviolet luminosity density. Assuming that the energy source in the far-IR is massive stars, the total luminous output from star-formation in the Universe is probably dominated by the far-IR emission. The detected systems have individual star-formation rates (exceeding 300 h_50^-2 M_O yr^-1) that are much higher than seen in the ultraviolet selected samples, and which are sufficient to form substantial stellar populations on dynamical timescales of 10^8 yr. The association with merger-like morphologies and the obvious presence of dust makes it attractive to identify these systems as forming the metal-rich spheroid population, in which case we would infer that much of this activity has occurred relatively recently, at z ~ 2.

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arXiv1998

The Canada-UK Deep Submillimetre Survey: First Submillimetre Images, the Source Counts, and Resolution of the Background

We present the first results of a deep unbiased submillimetre survey carried out at 450 and 850 microns. We detected 12 sources at 850 microns, giving a surface density of sources with 850-micron flux densities > 2.8mJy of of 0.49+-0.16 per square arcmin. The sources constitute 20-30% of the background radiation at 850 microns and thus a significant fraction of the entire background radiation produced by stars. This implies, through the connection between metallicity and background radiation, that a significant fraction of all the stars that have ever been formed were formed in objects like those detected here. The combination of their large contribution to the background radiation and their extreme bolometric luminosities make these objects excellent candidates for being proto-ellipticals. Optical astronomers have recently shown that the UV-luminosity density of the universe increases by a factor of about 10 between z=0 and z=1 and then decreases again at higher redshifts. Using the results of a parallel submillimetre survey of the local universe, we show that both the submillimetre source density and background can be explained if the submillimetre luminosity density evolves in a similar way to the UV-luminosity density. Thus, if these sources are ellipticals in the process of formation, they may be forming at relatively modest redshifts.

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arXiv1998

Deep Sub-millimeter Surveys and the Hidden Phases of Galaxy Formation

Deep surveys in the far-infrared and sub-millimeter wavebands are revealing a new phase of galactic evolution hidden by dust. Observations with SCUBA on the JCMT show that 25% of the COBE/FIRAS background at 850 microns is being produced by high luminosity sources (L ~ 3x10^12 L_sun) at high redshifts 0.5 < z < 3+. These sources have an estimated redshift distribution that is broadly consistent with a global star-formation history that is similar to that inferred from optical observations. The sub-mm galaxies and optically selected galaxies are producing comparable quantities of stars. However, the sub-mm sources are doing so in systems that have luminosities that are an order of magnitude higher, and comoving densities an order of magnitude lower, then the optically selected galaxies. These high luminosity sources are plausibly responsible for producing the spheroidal components of massive galaxies at z ~ 2.

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