We report a remarkable over-density of high-redshift submillimetre galaxies (SMG), 4-7 times the background, around a statistically complete sample of twelve 250-micron selected galaxies at z=0.35, ...which were targeted by ALMA in a study of gas tracers. This over-density is consistent with the effect of lensing by the halos hosting the target z=0.35 galaxies. The angular cross-correlation in this sample is consistent with statistical measures of this effect made using larger sub-mm samples. The magnitude of the over-density as a function of radial separation is consistent with intermediate scale lensing by halos of order 7x 10^{13} M_o, which should host one or possibly two bright galaxies and several smaller satellites. This is supported by observational evidence of interaction with satellites in four out of the six fields with SMG, and membership of a spectroscopically defined group for a fifth. We also investigate the impact of these SMG on the reported Herschel fluxes of the z=0.35 galaxies, as they produce significant contamination in the 350 and 500-micron Herschel bands. The higher than random incidence of these boosting events implies a significantly larger bias in the sub-mm colours of Herschel sources associated with z<0.7 galaxies than has previously been assumed, with f_boost = 1.13, 1.26, 1.44 at 250, 350 and 500-microns. This could have implications for studies of spectral energy distributions, source counts and luminosity functions based on Herschel samples at z=0.2-0.7.
This thesis presents new results from the SCUBA Local Universe Galaxy Survey (SLUGS) the optically-selected sample. SLUGS is the first large systematic submillimetre survey of the local Universe, and ...was carried out 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 this new sample, taken from the Center for Astrophysics (CfA) optical redshift survey (Huchra et al. 1983) and hence selected on the basis of optical emission alone, represents the first unbiased survey of dust in galaxies along the whole length of the Hubble sequence. There is little change found in the properties of dust in galaxies along the Hubble sequence, except a marginally significant trend for early-type galaxies to be less luminous submillimetre sources than late-types. Nevertheless, 6 out of 11 elliptical galaxies were detected, although some of the emission may possibly be synchrotron rather than dust emission. The IRAS and submillimetre fluxes are found to be well-fitted by a two-component dust model with dust emissivity index fi=2. The ratio of the mass of cold dust to the mass of warm dust is found to be much higher for the optically-selected galaxies than found for the previous IRAS-selected SLUGS sample (Dunne et al. 2000 Dunne & Eales 2001), 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. Local submillimetre luminosity and dust mass functions are derived, both directly from the optically-selected SLUGS sample, and by extrapolation from the IRAS PSCz survey using the method of Serjeant & Harrison (2005) (by extrapolating the spectral energy distributions of the IRAS PSCz survey galaxies out to 850 /zm we probe a wider range of luminosities than probed directly by the SLUGS samples), and excellent agreement is found between the two. They are found to be well-fitted by Schechter functions except at the highest luminosities. As a consequence of the omission of cold galaxies from the IRAS sample the previous //i45-selected luminosity function is found to be too low by a factor of 2, reducing the amount of cosmic evolution required between the low-z and high-z universe. Finally, the results of the OS SLUGS are used to assess the reliability of the Carilli & Yun (1999, 2000a) radio-submillimetre redshift estimator technique, for the first time using a sample of 'normal' local galaxies.
This thesis presents new results from the SCUBA Local Universe Galaxy Survey (SLUGS) the optically-selected sample. SLUGS is the first large systematic submillimetre survey of the local Universe, and ...was carried out 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 this new sample, taken from the Center for Astrophysics (CfA) optical redshift survey (Huchra et al. 1983) and hence selected on the basis of optical emission alone, represents the first unbiased survey of dust in galaxies along the whole length of the Hubble sequence. There is little change found in the properties of dust in galaxies along the Hubble sequence, except a marginally significant trend for early-type galaxies to be less luminous submillimetre sources than late-types. Nevertheless, 6 out of 11 elliptical galaxies were detected, although some of the emission may possibly be synchrotron rather than dust emission. The IRAS and submillimetre fluxes are found to be well-fitted by a two-component dust model with dust emissivity index fi=2. The ratio of the mass of cold dust to the mass of warm dust is found to be much higher for the optically-selected galaxies than found for the previous IRAS-selected SLUGS sample (Dunne et al. 2000 Dunne & Eales 2001), 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. Local submillimetre luminosity and dust mass functions are derived, both directly from the optically-selected SLUGS sample, and by extrapolation from the IRAS PSCz survey using the method of Serjeant & Harrison (2005) (by extrapolating the spectral energy distributions of the IRAS PSCz survey galaxies out to 850 /zm we probe a wider range of luminosities than probed directly by the SLUGS samples), and excellent agreement is found between the two. They are found to be well-fitted by Schechter functions except at the highest luminosities. As a consequence of the omission of cold galaxies from the IRAS sample the previous //i45-selected luminosity function is found to be too low by a factor of 2, reducing the amount of cosmic evolution required between the low-z and high-z universe. Finally, the results of the OS SLUGS are used to assess the reliability of the Carilli & Yun (1999, 2000a) radio-submillimetre redshift estimator technique, for the first time using a sample of 'normal' local galaxies.
ALMA observations of the long wavelength dust continuum are used to estimate the gas masses in a sample of 708 star-forming (SF) galaxies at z = 0.3 to 4.5. We determine the dependence of gas masses ...and star formation efficiencies (SFE=SFR per unit gass mass). We find that 70 percent of the increase in SFRs of the MS is due to the increased gas masses at earlier epochs while 30 percent is due to increased efficiency of SF. For galaxies above the MS this is reversed with 70 percent of the increased SFR relative to the MS being due to elevated SFEs. Thus, the major evolution of star formation activity at early epochs is driven by increased gas masses, while the starburst activity taking galaxies above the MS is due to enhanced triggering of star formation (likely due to galactic merging). The interstellar gas peaks at z = 2 and dominates the stellar mass down to z = 1.2. Accretion rates needed to maintain continuity of the MS evolution exceed 100 Msun per yr at z > 2. The galactic gas contents are likely the driving determinant for both the rise in SF and AGN activity from z = 5 to their peak at z = 2 and subsequent fall to lower z. We suggest that for self-gravitating clouds with supersonic turbulence, cloud collisions and the filamentary structure of the clouds regulate the star formation activity.
High resolution (1'' \(\times\) 2'') ALMA CO(2-1) observations of the ram pressure stripped galaxy NGC 4402 in the Virgo cluster show some of the clearest evidence yet for the impacts of ram pressure ...on the molecular ISM of a galaxy. The eastern side of the galaxy at \(r \sim 4.5\) kpc, upon which ram pressure is incident, has a large (width \(\sim\)1 kpc, height \(\sim\)1 kpc above the disk midplane) extraplanar plume of molecular gas and dust. Molecular gas in the plume region shows distinct non-circular motions in the direction of the ram pressure; the kinematic offset of up to 60 km s\(^{-1}\) is consistent with acceleration by ram pressure. We also detect a small amount of gas in clouds below the plume that are spatially and kinematically distinct from the surrounding medium, and appear to be decoupled from the stripped ISM. We propose that diffuse molecular gas is directly stripped but GMC density gas is not directly stripped, and so decouples from lower density stripped gas. However, GMCs become effectively stripped on short timescales. We also find morphological and kinematic signatures of ram pressure compression of molecular gas in a region of intense star formation on the leading side at \(r \sim 3.5\) kpc. We propose that the compressed and stripped zones represent different evolutionary stages of the ram pressure interaction, and that feedback from star formation in the compressed zone facilitates the effective stripping of GMCs by making the gas cycle rapidly to a lower density diffuse state.
We present new sub-arcsecond-resolution Karl G. Jansky Very Large Array (VLA) imaging at 10 GHz of 155 ultra-luminous (\(L_{\rm bol}\sim10^{11.7-14.2} L_\odot\)) and heavily obscured quasars with ...redshifts \(z \sim0.4-3\). The sample was selected to have extremely red mid-infrared (MIR)-optical color ratios based on data from Wide-Field Infrared Survey Explorer (WISE) along with a detection of bright, unresolved radio emission from the NRAO VLA Sky Survey (NVSS) or Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) Survey. Our high-resolution VLA observations have revealed that the majority of the sources in our sample (93 out of 155) are compact on angular scales \(<0.2^{\prime \prime}\) (\(\leq 1.7\) kpc at \(z \sim2\)). The radio luminosities, linear extents, and lobe pressures of our sources are similar to young radio active galactic nuclei (AGN; e.g., Gigahertz Peaked Spectrum, GPS, and Compact Steep Spectrum, CSS, sources), but their space density is considerably lower. Application of a simple adiabatic lobe expansion model suggests relatively young dynamical ages (\(\sim10^{4-7}\) years), relatively high ambient ISM densities (\(\sim1-10^4\) cm\(^{-3}\)), and modest lobe expansion speeds (\(\sim30-10,000\) km s\(^{-1}\)). Thus, we find our sources to be consistent with a population of newly triggered, young jets caught in a unique evolutionary stage in which they still reside within the dense gas reservoirs of their hosts. Based on their radio luminosity function and dynamical ages, we estimate only \(\sim20\%\) of classical large scale FRI/II radio galaxies could have evolved directly from these objects. We speculate that the WISE-NVSS sources might first become GPS or CSS sources, of which some might ultimately evolve into larger radio galaxies.
We combine data from ALMA and MUSE to study the resolved (~300 pc scale) star formation relation (star formation rate vs. molecular gas surface density) in cluster galaxies. Our sample consists of 9 ...Fornax cluster galaxies, including spirals, ellipticals, and dwarfs, covering a stellar mass range of ~10^8.8 - 10^11 M_Sun. CO(1-0) and extinction corrected Halpha were used as tracers for the molecular gas mass and star formation rate, respectively. We compare our results with Kennicutt (1998) and Bigiel et al. (2008). Furthermore, we create depletion time maps to reveal small-scale variations in individual galaxies. We explore these further in FCC290, using the 'uncertainty principle for star formation' (Kruijssen & Longmore, 2014a) to estimate molecular cloud lifetimes, which we find to be short (<10 Myr) in this galaxy. Galaxy-averaged depletion times are compared with other parameters such as stellar mass and cluster-centric distance. We find that the star formation relation in the Fornax cluster is close to those from Kennicutt (1998) and Bigiel et al. (2008}), but overlaps mostly with the shortest depletion times predicted by Bigiel et al. (2008). This slight decrease in depletion time is mostly driven by dwarf galaxies with disturbed molecular gas reservoirs close to the virial radius. In FCC90, a dwarf galaxy with a molecular gas tail, we find that depletion times are a factor >~10 higher in its tail than in its stellar body.
We present the first results of the ALMA Fornax Cluster Survey (AlFoCS): a complete ALMA survey of all members of the Fornax galaxy cluster that were detected in HI or in the far infrared with ...Herschel. The sample consists of a wide variety of galaxy types, ranging from giant ellipticals to spiral galaxies and dwarfs, located in all (projected) areas of the cluster. It spans a mass range of 10^(~8.5 - 11) M_Sun. The CO(1-0) line was targeted as a tracer for the cold molecular gas, along with the associated 3 mm continuum. CO was detected in 15 of the 30 galaxies observed. All 8 detected galaxies with stellar masses below 3x10^9 M_Sun have disturbed molecular gas reservoirs, only 6 galaxies are regular/undisturbed. This implies that Fornax is still a very active environment, having a significant impact on its members. Both detections and non-detections occur at all projected locations in the cluster. Based on visual inspection, and the detection of molecular gas tails in alignment with the direction of the cluster centre, in some cases ram pressure stripping is a possible candidate for disturbing the molecular gas morphologies and kinematics. Derived gas fractions in almost all galaxies are lower than expected for field objects with the same mass, especially for the galaxies with disturbed molecular gas, with differences of sometimes more than an order of magnitude. The detection of these disturbed molecular gas reservoirs reveals the importance of the cluster environment for even the tightly bound molecular gas phase.
In a radio interferometer, the determination of geometrical antenna positions relies on accurate calibration of the dry and wet delay of the atmosphere above each antenna. For the Atacama Large ...Millimeter/Submillimeter Array (ALMA), which has baseline lengths up to 16 kilometers, the geography of the site forces the height above mean sea level of the more distant antenna pads to be significantly lower than the central array. Thus, both the ground level meteorological values and the total water column can be quite different between antennas in the extended configurations. During 2015, a network of six additional weather stations was installed to monitor pressure, temperature, relative humidity and wind velocity, in order to test whether inclusion of these parameters could improve the repeatability of antenna position determinations in these configurations. We present an analysis of the data obtained during the ALMA Long Baseline Campaign of Oct. through Nov. 2015. The repeatability of antenna position measurements typically degrades as a function of antenna distance. Also, the scatter is more than three times worse in the vertical direction than in the local tangent plane, suggesting that a systematic effect is limiting the measurements. So far we have explored correcting the delay model for deviations from hydrostatic equilibrium in the measured air pressure and separating the partial pressure of water from the total pressure using water vapor radiometer (WVR) data. Correcting for these combined effects still does not provide a good match to the residual position errors in the vertical direction. One hypothesis is that the current model of water vapor may be too simple to fully remove the day-to-day variations in the wet delay. We describe possible avenues of improvement, including measuring and applying more accurate values of the sky coupling efficiency of the WVRs.
