R. J. Ivison

European Southern Observatory, Arching, Bavaria, Germany

Are you R. J. Ivison?

Claim your profile

Publications (773)3215.69 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a list of candidate gravitationally lensed dusty star-forming galaxies (DSFGs) from the HerMES Large Mode Survey (HeLMS) and the Herschel Stripe 82 Survey (HerS). Together, these partially overlapping surveys cover 372 deg^2 on the sky. After removing local spiral galaxies and known radio-loud blazars, our candidate list of lensed DSFGs is composed of 77 sources with 500 micron flux densities (S_500) greater than 100 mJy. Such sources are likely dusty starburst galaxies that are selected as bright sub-millimeter galaxies (SMGs). We expect a large fraction of this list to be strongly lensed, with a small fraction made up of bright SMG-SMG mergers that appear as hyper-luminous infrared galaxies (HyLIRGs). Thirteen of the 77 candidates have spectroscopic redshifts from CO spectroscopy with ground-based interferometers, putting them at z>1 and well above the redshift of the foreground lensing galaxies. The surface density of our sample of 0.21 +/- 0.03 deg^-2. We also find nine radio-bright blazars that are also bright in the sub-mm with S_500 > 100 mJy. We present follow-up imaging of a few of the candidates that confirm their lensing nature. The sample presented here is an ideal tool for higher resolution imaging and spectroscopic observations to understand detailed properties of starburst phenomena in distant galaxies. The appendix also contains 250, 350 and 500\,$\mu$m flux densities of spiral galaxies and radio blazars with S_500 > 100 mJy in the HeLMS and HerS regions.
    No preview · Article · Jan 2016
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present multiwavelength identifications for the counterparts of 1088 submillimeter sources detected at 850$\mu$m in the SCUBA-2 Cosmology Legacy Survey study of the UKIDSS-UDS field. By utilising an ALMA pilot study on a subset of our bright SCUBA-2 sample as a training set, along with the deep optical-near-infrared data available in this field, we develop a novel technique, Optical-IR Triple Color (OIRTC), using $z-K$, $K-[3.6]$, $[3.6]-[4.5]$ colors to select the candidate submillimeter galaxy (SMG) counterparts. By combining radio identification and the OIRTC technique, we find counterpart candidates for 80% of the Class = 1 $\geq4\,\sigma$ SCUBA-2 sample, defined as those that are covered by both radio and OIR imaging and the base sample for our scientific analyses. Based on the ALMA training set, we expect the accuracy of these identifications to be $82\pm20$%, with a completeness of $69\pm16$%, essentially as accurate as the traditional $p$-value technique but with higher completeness. We find that the fraction of SCUBA-2 sources having candidate counterparts is lower for fainter 850$\mu$m sources, and we argue that for follow-up observations sensitive to SMGs with $S_{850}\gtrsim 1$ mJy across the whole ALMA beam, the fraction with multiple counterparts is likely to be $>40$% for SCUBA-2 sources at $S_{850} \gtrsim 4$ mJy. We find that the photometric redshift distribution for the SMGs is well fit by a lognormal distribution, with a median redshift of $z=2.3\pm0.1$. After accounting for the sources without any radio and/or OIRTC counterpart, we estimate the median redshift to be $z=2.6\pm0.1$ for SMGs with $S_{850} >1$ mJy. We also use this new large sample to study the clustering of SMGs and the the far-infrared properties of the unidentified submillimeter sources by stacking their Herschel SPIRE far-infrared emission.
    No preview · Article · Jan 2016 · The Astrophysical Journal
  • [Show abstract] [Hide abstract]
    ABSTRACT: Selecting sources with rising flux densities towards longer wavelengths from Herschel/SPIRE maps is an efficient way to produce a catalogue rich in high-redshift (z > 4) dusty star-forming galaxies. The effectiveness of this approach has already been confirmed by spectroscopic follow-up observations, but the previously available catalogues made this way are limited by small survey areas. Here we apply a map-based search method to 274 deg$^2$ of the HerMES Large Mode Survey (HeLMS) and create a catalogue of 477 objects with SPIRE flux densities $S_{500} > S_{350} >S_{250}$ and a 5 \sigma cut-off $S_{500}$ > 52 mJy. From this catalogue we determine that the total number of these "red" sources is at least an order of magnitude higher than predicted by galaxy evolution models. These results are in agreement with previous findings in smaller HerMES fields; however, due to our significantly larger sample size we are also able to investigate the shape of the red source counts for the first time. We examine the 500 $\mu$m differential number counts of these sources, and we find that the resulting "red" counts are very steep and suggest strong evolution in the properties of this population. We have obtained spectroscopic redshift measurements for two of our sources using the Atacama Large Millimeter/submillimeter Array (ALMA). One source is at z = 5.126 and the redshift for the other object is z $\gtrsim$ 3.8, confirming that with our selection method we can indeed find high-redshift dusty star-forming galaxies.
    No preview · Article · Jan 2016
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have conducted 1.1 mm ALMA observations of a contiguous $105'' \times 50''$ or 1.5 arcmin$^2$ window in the SXDF-UDS-CANDELS. We achieved a 5$\sigma$ sensitivity of 0.28 mJy, providing a flat sensus of dusty star-forming galaxies with $L_{\rm IR} \sim6\times10^{11}$ $L_\odot$ (for $T_{\rm dust}$ =40K) up to $z\sim10$ thanks to the negative K-correction at this wavelength. We detected 5 brightest sources (S/N$>$6) and 18 low-significance sources (5$>$S/N$>$4; these may contain spurious detections, though). One of the 5 brightest ALMA sources ($S_{\rm 1.1mm} = 0.84 \pm 0.09$ mJy) is extremely faint in the WFC3 and VLT/HAWK-I images, demonstrating that a contiguous ALMA imaging survey is able to uncover a faint dust-obscured population that is invisible in deep optical/near-infrared surveys. We found a possible [CII]-line emitter at $z=5.955$ or a low-$z$ CO emitting galaxy within the field, which may allow us to constrain the [CII] and/or the CO luminosity functions across the history of the universe.
    No preview · Article · Jan 2016
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We used wide-area surveys over 39 deg2 by the HerMES (Herschel Multi-tiered Extragalactic Survey) collaboration, performed with the Herschel Observatory SPIRE multiwavelength camera, to estimate the low-redshift, 0.02 < z < 0.5, monochromatic luminosity functions (LFs) of galaxies at 250, 350 and 500 μm. Within this redshift interval, we detected 7087 sources in five independent sky areas, ∼40 per cent of which have spectroscopic redshifts, while for the remaining objects photometric redshifts were used. The SPIRE LFs in different fields did not show any field-to-field variations beyond the small differences to be expected from cosmic variance. SPIRE flux densities were also combined with Spitzer photometry and multiwavelength archival data to perform a complete spectral energy distribution fitting analysis of SPIRE detected sources to calculate precise k-corrections, as well as the bolometric infrared (IR; 8–1000 μm) LFs and their low-z evolution from a combination of statistical estimators. Integration of the latter prompted us to also compute the local luminosity density and the comoving star formation rate density (SFRD) for our sources, and to compare them with theoretical predictions of galaxy formation models. The LFs show significant and rapid luminosity evolution already at low redshifts, 0.02 < z < 0.2, with L$_{\text{IR}}^{\ast } \propto (1+z)^{6.0\pm 0.4}$ and $\Phi _{\text{IR}}^{\ast } \propto (1+z)^{-2.1\pm 0.4}$, L$_{250}^{\ast } \propto (1+z)^{5.3\pm 0.2}$ and $\Phi _{250}^{\ast } \propto (1+z)^{-0.6\pm 0.4}$ estimated using the IR bolometric and the 250 μm LFs, respectively. Converting our IR LD estimate into an SFRD assuming a standard Salpeter initial mass function and including the unobscured contribution based on the UV dust-uncorrected emission from local galaxies, we estimate an SFRD scaling of SFRD0 + 0.08z, where SFRD0 ≃ (1.9 ± 0.03) × 10−2 [M⊙ Mpc−3] is our total SFRD estimate at z ∼ 0.02.
    Preview · Article · Nov 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: ALMA Cycle 2 observations of the long wavelength dust emission in 145 star-forming galaxies are used to probe the evolution of star-forming ISM. We also develop the physical basis and empirical calibration (with 72 low-z and z ~ 2 galaxies) for using the dust continuum as a quantitative probe of interstellar medium (ISM) masses. The galaxies with highest star formation rates (SFRs) at = 2.2 and 4.4 have gas masses up to 100 times that of the Milky Way and gas mass fractions reaching 50 to 80%, i.e. gas masses 1 - 4 times their stellar masses. We find a single high-z star formation law: SFR = 35 M_ mol^0.89 x (1+z)_{z=2}^0.95 x (sSFR)_{MS}^0.23 \msun yr^-1 -- an approximately linear dependence on the ISM mass and an increased star formation efficiency per unit gas mass at higher redshift. Galaxies above the Main Sequence (MS) have larger gas masses but are converting their ISM into stars on a timescale only slightly shorter than those on the MS -- thus these 'starbursts' are largely the result of having greatly increased gas masses rather than and increased efficiency for converting gas to stars. At z $> 1$, the entire population of star-forming galaxies has $\sim$ 2 - 5 times shorter gas depletion times than low-z galaxies. These shorter depletion times indicate a different mode of star formation in the early universe -- most likely dynamically driven by compressive, high-dispersion gas motions -- a natural consequence of the high gas accretion rates.
    Preview · Article · Nov 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We report the results of $1^{\prime}.5 \times3^{\prime}$ mapping at 1.1~mm with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the central region of the $z=3.09$ SSA22 protocluster. By combining our source catalog with archival spectroscopic redshifts, we find that eight submillimeter galaxies (SMGs) with flux densities, $S_{\rm 1.1~mm}=0.7-6.4$~mJy ($L_{\rm IR}\sim10^{12.1}-10^{13.1}L_\odot$) are at $z=3.08-3.10$. Not only are these SMGs members of the protocluster but they in fact reside within the node at the junction of the 50 Mpc-scale filamentary three-dimensional structure traced by Lyman-$\alpha$ emitters (LAEs) in this field. The eight SMGs account for a star formation rate density (SFRD) $\sim$10 $M_\odot$ yr$^{-1}$ Mpc$^{-3}$ in the node, which is two orders of magnitudes higher than the global SFRD at this redshift. We find that four of the eight SMGs host a X-ray luminous active galactic nuclei (AGN). Our results suggest that the vigorous star formation activity and the growth of super massive black holes (SMBHs) occurred simultaneously in the densest regions at $z\sim3$, which may correspond to the most active historical phase of the massive galaxy population found in the core of the clusters in the present universe. Two SMGs are associated with Lyman-$\alpha$ blobs (LABs), implying that the two populations coexist in high density environments for a few cases.
    Full-text · Article · Oct 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Next-Generation Very Large Array (ngVLA) will be critical for understanding how galaxies are built and evolve at the earliest epochs. The sensitivity and frequency coverage will allow for the detection of cold gas and dust in `normal' distant galaxies, including the low-J transitions of molecular gas tracers such as CO, HNC, and HCO+; synchrotron and free-free continuum emission; and even the exciting possibility of thermal dust emission at the highest (z~7) redshifts. In particular, by enabling the total molecular gas reservoirs to be traced to unprecedented sensitivities across a huge range of epochs simultaneously -- something no other radio or submillimeter facility will be capable of -- the detection of the crucial low-J transitions of CO in a diverse body of galaxies will be the cornerstone of ngVLA's contribution to high-redshift galaxy evolution science. The ultra-wide bandwidths will allow a complete sampling of radio SEDs, as well as the detection of emission lines necessary for spectroscopic confirmation of elusive dusty starbursts. The ngVLA will also deliver unique contributions to our understanding of cosmic magnetism and to science accessible through microwave polarimetry. Finally, the superb angular resolution will move the field beyond detection experiments and allow detailed studies of the morphology and dynamics of these systems, including dynamical modeling of disks/mergers, determining the properties of outflows, measuring black hole masses from gas disks, and resolving multiple AGN nuclei. We explore the contribution of a ngVLA to these areas and more, as well as synergies with current and upcoming facilities including ALMA, SKA, large single-dish submillimeter observatories, GMT/TMT, and JWST.
    Preview · Article · Oct 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a pilot study of the z=2.923 radio galaxy MRC0943-242, where we for the first time combine information from ALMA and MUSE data cubes. Even with modest integration times, we disentangle an AGN and a starburst dominated set of components. These data reveal a highly complex morphology, as the AGN, starburst, and molecular gas components show up as widely separated sources in dust continuum, optical continuum and CO line emission observations. CO(1-0) and CO(8-7) line emission suggest that there is a molecular gas reservoir offset from both the dust and the optical continuum that is located ~90kpc from the AGN. The UV line emission has a complex structure in emission and absorption. The line emission is mostly due to i) a large scale ionisation cone energised by the AGN, ii) a Ly-alpha emitting bridge of gas between the radio galaxy and a heavily star-forming set of components. Strangely, the ionisation cone has no Ly-alpha emission. We find this is due to an optically thick layer of neutral gas with unity covering fraction spread out over a region of at least ~100kpc from the AGN. Other, less thick absorption components are associated with Ly-alpha emitting gas within a few tens of kpc from the radio galaxy and are connected by a bridge of emission. We speculate that this linear structure of dust, Ly-alpha and CO emission, and the redshifted absorption seen in the circum-nuclear region may represent an accretion flow feeding gas into this massive AGN host galaxy.
    No preview · Article · Oct 2015 · Astronomy and Astrophysics
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Dragonfly Galaxy (MRC0152-209), at redshift z~2, is one of the most vigorously star-forming radio galaxies in the Universe. What triggered its activity? We present ALMA Cycle 2 observations of cold molecular CO(6-5) gas and dust, which reveal that this is likely a gas-rich triple merger. It consists of a close double nucleus (separation ~4 kpc) and a weak CO-emitter at ~10 kpc distance, all of which have counterparts in HST/NICMOS imagery. The hyper-luminous starburst and powerful radio-AGN were triggered at this precoalescent stage of the merger. The CO(6-5) traces dense molecular gas in the central region, and complements existing CO(1-0) data, which revealed more widespread tidal debris of cold gas. We also find ~10$^{10}$ M(sun) of molecular gas with enhanced excitation at the highest velocities. At least 20-50% of this high-excitation, high-velocity gas shows kinematics that suggests it is being displaced and redistributed within the merger, although with line-of-sight velocities of |v| < 500 km/s, this gas will probably not escape the system. The processes that drive the redistribution of cold gas are likely related to either the gravitational interaction between two kpc-scale discs, or starburst/AGN-driven outflows. We estimate that the rate at which the molecular gas is redistributed is at least ~1200 +- 500 M(sun)/yr, and could perhaps even approach the star formation rate of ~3000 +- 800 M(sun)/yr. The fact that the gas depletion and gas redistribution timescales are similar implies that dynamical processes can be important in the evolution of massive high-z galaxies.
    Preview · Article · Oct 2015 · Astronomy and Astrophysics
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present far-infrared and submillimeter maps from the Herschel Space Observatory and the James Clerk Maxwell Telescope of the debris disk host star AU Microscopii. Disk emission is detected at 70, 160, 250, 350, 450, 500 and 850 micron. The disk is resolved at 70, 160 and 450 micron. In addition to the planetesimal belt, we detect thermal emission from AU Mic's halo for the first time. In contrast to the scattered light images, no asymmetries are evident in the disk. The fractional luminosity of the disk is $3.9 \times 10^{-4}$ and its mm-grain dust mass is 0.01 MEarth (+/- 20%). We create a simple spatial model that reconciles the disk SED as a blackbody of 53 +/- 2 K (a composite of 39 and 50 K components) and the presence of small (non-blackbody) grains which populate the extended halo. The best fit model is consistent with the "birth ring" model explored in earlier works, i.e., an edge-on dust belt extending from 8.8-40 AU, but with an additional halo component with an $r^{-1.5}$ surface density profile extending to the limits of sensitivity (140 AU). We confirm that AU Mic does not exert enough radiation force to blow out grains. For stellar mass loss rates of 10-100x solar, compact (zero porosity) grains can only be removed if they are very small, consistently with previous work, if the porosity is 0.9, then grains approaching 0.1 micron can be removed via corpuscular forces (i.e., the stellar wind).
    No preview · Article · Sep 2015 · The Astrophysical Journal
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present first results from the SXDF-ALMA 1.5 arcmin^2 deep survey at 1.1 mm using Atacama Large Millimeter Array (ALMA). The map reaches a 1sigma depth of 55 uJy/beam and covers 12 Halpha-selected star-forming galaxies at z = 2.19 or z=2.53. We have detected continuum emission from three of our Halpha-selected sample, including one compact star-forming galaxy with high stellar surface density, NB2315-07. They are all red in the rest-frame optical and have stellar masses of log (M*/Msun)>10.9 whereas the other blue, main-sequence galaxies with log(M*/Msun)=10.0-10.8 are exceedingly faint, <290 uJy (2sigma upper limit). We also find the 1.1 mm-brightest galaxy, NB2315-02, to be associated with a compact (R_e=0.7+-0.1 kpc), dusty star-forming component. Given high gas fraction (44^{+20}_{-8}% or 37^{+25}_{-3}%) and high star formation rate surface density (126^{+27}_{-30} Msun yr^{-1}kpc^{-2}), the concentrated starburst can within less than 50^{+12}_{-11} Myr build up a stellar surface density matching that of massive compact galaxies at z~2, provided at least 19+-3% of the total gas is converted into stars in the galaxy centre. On the other hand, NB2315-07, which already has such a high stellar surface density core, shows a gas fraction (23+-8%) and is located in the lower envelope of the star formation main-sequence. This compact less star-forming galaxy is likely to be in an intermediate phase between compact dusty star-forming and quiescent galaxies.
    Preview · Article · Aug 2015
  • Source
    I. Oteo · M. A. Zwaan · R. J. Ivison · I. Smail · A. D. Biggs
    [Show abstract] [Hide abstract]
    ABSTRACT: We have exploited ALMA calibration observations to carry out a novel, wide and deep submm survey, ALMACAL. These calibration data comprise a large number of observations of calibrator fields in a variety of frequency bands and array configurations. Gathering together data acquired during multiple visits to many ALMA calibrators, it is possible to reach noise levels which allow the detection of faint dusty, star-forming galaxies (DSFGs) over a significant area. In this paper we outline our survey strategy and report the first results. We have analysed data for 69 calibrators, reaching depths of $\sim 25 \, {\rm \mu Jy \, beam^{-1}}$ at sub-arcsec resolution. Adopting a conservative approach based on $\geq 5 \sigma$ detections, we have found eight and 11 DSFGs in ALMA bands 6 and 7, respectively, with flux densities $S_{\rm 1.2 mm} \geq 0.2 \, {\rm mJy}$. The faintest galaxies would have been missed by even the deepest \emph{Herschel} surveys. Our cumulative number counts have been determined independently at 870 $\mu$m and 1.2 mm, from a sparse sampling of the astronomical sky, and are thus relatively free of cosmic variance. The counts are lower than reported previously by a factor of at least $2\times$. Future analyses will yield large, secure samples of DSFGs, with redshifts determined via detection of submm spectral lines. Uniquely, our strategy then allows morphological studies of very faint DSFGs - representative of more normal star-forming galaxies than conventional submm galaxies (SMGs) - in fields where self-calibration is feasible, yielding milliarcsecond spatial resolution.
    Full-text · Article · Aug 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: We report contributions to cosmic infrared background (CIB) intensities originating from known galaxies and their faint companions at submillimeter wavelengths. Using the publicly available UltraVISTA catalog and maps at 250, 350, and 500 μm from the Herschel Multi-tiered Extragalactic Survey, we perform a novel measurement that exploits the fact that uncataloged sources may bias stacked flux densities-particularly if the resolution of the image is poor-and intentionally smooth the images before stacking and summing intensities. By smoothing the maps we are capturing the contribution of faint (undetected in KS ∼ 23.4) sources that are physically associated, or correlated, with the detected sources. We find that the cumulative CIB increases with increased smoothing, reaching 9.82 ± 0.78, 5.77 ± 0.43 and 2.32 ± 0.19 nWm-2 sr-1 at 250, 350, and 500 μm at 300 arcsec FWHM. This corresponds to a fraction of the fiducial CIB of 0.94 ± 0.23, 1.07 ± 0.31, and 0.97 ± 0.26 at 250, 350, and 500 μm, where the uncertainties are dominated by those of the absolute CIB. We then propose, with a simple model combining parametric descriptions for stacked flux densities and stellar mass functions, that emission from galaxies with log(M/M⊙) > 8.5 can account for most of the measured total intensities and argue against contributions from extended, diffuse emission. Finally, we discuss prospects for future survey instruments to improve the estimates of the absolute CIB levels, and observe any potentially remaining emission at z > 4. © 2015. The American Astronomical Society. All rights reserved.
    No preview · Article · Aug 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a complete census of all 263 Herschel-detected sources within the HST Frontier Fields (HFF), a deep multi-filter HST programme covering six massive lensing clusters. We provide a robust legacy catalogue of Herschel fluxes, primarily based on imaging from the Herschel Lensing Survey (HLS) and PEP/HerMES Key Programmes. Photometry is derived via a simultaneous PSF-fit using priors from archival Spitzer imaging. We optimally combine Herschel, Spitzer and WISE infrared (IR) photometry with data from HST, VLA and ground-based observatories, identifying optical counterparts to gain source redshifts. Hence for each Herschel-detected source we also present magnification factor (mu), intrinsic IR luminosity and characteristic dust temperature, providing a comprehensive view of dust-obscured star formation within the HFF. We demonstrate the utility of our catalogues through an exploratory overview of HST morphologies for the IR-bright population. In particular we briefly describe the highest redshift (z>2.5) and most magnified (mu>4) sources in the gravitationally lensed background.
    Full-text · Article · Aug 2015
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a detailed multiwavelength study (from rest-frame ultraviolet to far-infrared) of narrow-band selected, star-forming (SF) Hα emitters (HAEs) at z ∼ 2.23 taken from the High-Redshift(Z) Emission Line Survey (HiZELS). We find that HAEs have similar properties and colours derived from spectral energy distributions as sBzK galaxies, and probe a well-defined portion of the SF population at z ∼ 2. This is not true for Lyα emitters (LAEs), which are strongly biased towards blue, less massive galaxies (missing a significant percentage of the SF population). Combining our Hα observations with matched, existing Lyα data, we determine that the Lyα escape fraction (fesc) is low (only ∼4.5 per cent of HAEs show Lyα emission) and decreases with increasing dust attenuation, ultraviolet continuum slope, stellar mass and star formation rate (SFR). This suggests that Lyα preferentially escapes from blue galaxies with low dust attenuation. However, a small population of red and massive LAEs is also present, in agreement with previous works and indicating that dust and Lyα are not mutually exclusive. Using different and completely independent measures of the total SFR, we show that the Hα emission is an excellent tracer of star formation at z ∼ 2 with deviations typically lower than 0.3 dex for individual galaxies. We find that the slope and zero-point of the HAE main sequence at z ∼ 2 strongly depend on the dust-correction method used to recover the SFR, although they are consistent with previous works when similar assumptions are made.
    No preview · Article · Jul 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We examine the relationship between star formation and active galactic nuclei (AGN) activity by constructing matched samples of local (0 < z < 0.6) radio-loud and radio-quiet AGN in the Herschel-Astrophysical Terahertz Large Area Survey fields. Radio-loud AGN are classified as high-excitation and low-excitation radio galaxies using their emission lines and WISE 22-μm luminosity. AGN accretion and jet powers in these active galaxies are traced by [O iii] emission-line and radio luminosity, respectively. Star formation rates (SFRs) and specific star formation rates (SSFRs) were derived using Herschel 250-μm luminosity and stellar mass measurements from the Sloan Digital Sky Survey–Max Planck Institute for Astrophysics-John Hopkins University catalogue. In the past, star formation studies of AGN have mostly focused on high-redshift sources to observe the thermal dust emission that peaks in the far-infrared, which limited the samples to powerful objects. However, with Herschel we can expand this to low redshifts. Our stacking analyses show that SFRs and SSFRs of both radio-loud and radio-quiet AGN increase with increasing AGN power but that radio-loud AGN tend to have lower SFR. Additionally, radio-quiet AGN are found to have approximately an order of magnitude higher SSFRs than radio-loud AGN for a given level of AGN power. The difference between the star formation properties of radio-loud and -quiet AGN is also seen in samples matched in stellar mass.
    Full-text · Article · Jul 2015 · Monthly Notices of the Royal Astronomical Society
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Using results from the Herschel Astrophysical Terrahertz Large-Area Survey (H-ATLAS) and the Galaxy and Mass Assembly (GAMA) project, we show that, for galaxy masses above ≃ 108 M⊙, 51 per cent of the stellar mass-density in the local Universe is in early-type galaxies (ETGs; Sérsic n > 2.5) while 89 per cent of the rate of production of stellar mass-density is occurring in late-type galaxies (LTGs; Sérsic n < 2.5). From this zero-redshift benchmark, we have used a calorimetric technique to quantify the importance of the morphological transformation of galaxies over the history of the Universe. The extragalactic background radiation contains all the energy generated by nuclear fusion in stars since the big bang. By resolving this background radiation into individual galaxies using the deepest far-infrared survey with the Herschel Space Observatory and a deep near-infrared/optical survey with the Hubble Space Telescope (HST), and using measurements of the Sérsic index of these galaxies derived from the HST images, we estimate that ≃83 per cent of the stellar mass-density formed over the history of the Universe occurred in LTGs. The difference between this value and the fraction of the stellar mass-density that is in LTGs today implies there must have been a major transformation of LTGs into ETGs after the formation of most of the stars.
    Full-text · Article · Jun 2015 · Monthly Notices of the Royal Astronomical Society
  • [Show abstract] [Hide abstract]
    ABSTRACT: We exploit long baseline ALMA submillimeter observations of the lensed star-forming galaxy SDP 81 at z = 3.042 to investigate the properties of the interstellar medium (ISM) on scales of 50-100 pc. The kinematics of the 12CO gas within this system are well described by a rotationally supported disk with an inclination-corrected rotation speed, = 320 ± 20 km s−1, and a dynamical mass of = (3.5 ± 1.0)× 1010 within a radius of 1.5 kpc. The disk is gas-rich and unstable, with a Toomre parameter, Q = 0.30 ± 0.10, and so into star-forming regions with Jeans length 130 pc. We identify five star-forming regions within the ISM on these scales and show that their scaling relations between luminosity, line widths, and sizes are significantly offset from those typical of molecular clouds in local galaxies (Larson's relations). These offsets are likely to be caused by the high external hydrostatic pressure for the ISM, /× 107 K cm−3, which is ~104× higher than the typical ISM pressure in the Milky Way. The physical conditions of the star-forming ISM and giant molecular clouds appear to be similar to those found in the densest environments in the local universe, such as those in the Galactic center.
    No preview · Article · Jun 2015
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present a detailed multi-wavelength study (from rest-frame UV to far-IR) of narrow-band (NB) selected, star-forming (SF) H$\alpha$ emitters (HAEs) at $z \sim 2.23$ taken from the High Redshift(Z) Emission Line Survey (HiZELS). We find that HAEs have similar SED-derived properties and colors to $sBzK$ galaxies and probe a well-defined portion of the SF population at $z \sim 2$. This is not true for Ly$\alpha$ emitters (LAEs), which are strongly biased towards blue, less massive galaxies (missing a significant percentage of the SF population). Combining our H$\alpha$ observations with matched, existing Ly$\alpha$ data we determine that the Ly$\alpha$ escape fraction ($f_{\rm esc}$) is low (only $\sim$ 4.5\% of HAEs show Ly$\alpha$ emission) and decreases with increasing dust attenuation, UV continuum slope, stellar mass, and star formation rate (SFR). This suggests that Ly$\alpha$ preferentially escapes from blue galaxies with low dust attenuation. However, a small population of red and massive LAEs is also present in agreement with previous works. This indicates that dust and Ly$\alpha$ are not mutually exclusive. Using different and completely independent measures of the total SFR we show that the H$\alpha$ emission is an excellent tracer of star formation at $z \sim 2$ with deviations typically lower than 0.3 dex for individual galaxies. We find that the slope and zero-point of the HAE main-sequence (MS) at $z \sim 2$ strongly depend on the dust correction method used to recover SFR, although they are consistent with previous works when similar assumptions are made.
    Full-text · Article · Jun 2015

Publication Stats

25k Citations
3,215.69 Total Impact Points

Institutions

  • 2015
    • European Southern Observatory
      Arching, Bavaria, Germany
    • University of Victoria
      Victoria, British Columbia, Canada
  • 1997-2015
    • The University of Edinburgh
      • • Institute for Astronomy (IfA)
      • • School of Physics and Astronomy
      Edinburgh, Scotland, United Kingdom
  • 2011-2014
    • Cardiff University
      • School of Physics and Astronomy
      Cardiff, Wales, United Kingdom
    • University of Hertfordshire
      Hatfield, England, United Kingdom
  • 1996-2014
    • The Royal Observatory, Edinburgh
      Edinburgh, Scotland, United Kingdom
  • 2009-2013
    • California Institute of Technology
      • Spitzer Science Center
      Pasadena, California, United States
    • University of Cambridge
      • Institute of Astronomy
      Cambridge, England, United Kingdom
  • 2007-2013
    • Scottish Universities Physics Alliance
      Glasgow, Scotland, United Kingdom
  • 2012
    • University of Colorado at Boulder
      • Center for Astrophysics and Space Astronomy
      Boulder, Colorado, United States
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany
  • 2011-2012
    • Imperial College London
      • Department of Physics
      Londinium, England, United Kingdom
  • 2008
    • Harvard-Smithsonian Center for Astrophysics
      • Smithsonian Astrophysical Observatory
      Cambridge, Massachusetts, United States
    • Durham University
      • Institute for Computational Cosmology "ICC"
      Durham, England, United Kingdom
  • 1998-2008
    • University College London
      • Department of Physics and Astronomy
      London, ENG, United Kingdom
  • 2006
    • University of Sydney
      • School of Physics
      Sydney, New South Wales, Australia
  • 1991-2005
    • The University of Manchester
      • School of Physics and Astronomy
      Manchester, England, United Kingdom
  • 2001
    • Massachusetts Institute of Technology
      • Kavli Institute for Astrophysics and Space Research
      Cambridge, Massachusetts, United States
  • 1995
    • University of Toronto
      Toronto, Ontario, Canada
  • 1993
    • University of Central Lancashire
      Preston, England, United Kingdom