arXiv subjects

E. Ibar

Publications and source records attributed to E. Ibar.

At least 73 records · Page 4Linked to original sources

arXiv2017

The SCUBA-2 Cosmology Legacy Survey: the nature of bright submm galaxies from 2 deg2 of 850-um imaging

We present physical properties [redshifts (z), star-formation rates (SFRs) and stellar masses (Mstar)] of bright (S850>4mJy) submm galaxies in the ~2deg2 COSMOS and UDS fields selected with SCUBA-2/JCMT. We complete the galaxy identification process for all (~2000) S/N>3.5 850-um sources, but focus our scientific analysis on a high-quality sub-sample of 651 S/N>4 sources with complete multi-wavelength coverage including 1.1-mm imaging. We check the reliability of our identifications, and the robustness of the SCUBA-2 fluxes by revisiting the recent ALMA follow-up of 29 sources in our sample. Considering >4mJy ALMA sources, our identification method has a completeness of ~86 per cent with a reliability of ~92 per cent, and only ~15-20 per cent of sources are significantly affected by multiplicity (when a secondary component contributes >1/3 of the primary source flux). The impact of source blending on the 850-um source counts as determined with SCUBA-2 is modest; scaling the single-dish fluxes by ~0.9 reproduces the ALMA source counts. For our final SCUBA-2 sample we find median z=2.40+0.10-0.04, SFR=287+-6Moyr-1, and log(Mstar/Mo)=11.12+-0.02 (the latter for 349/651 sources with optical identifications). These properties clearly locate bright submm galaxies on the high-mass end of the 'main sequence' of star-forming galaxies out to z~6, suggesting that major mergers are not a dominant driver of the high-redshift submm-selected population. Their number densities are also consistent with the evolving galaxy stellar mass function. Hence, the submm galaxy population is as expected, albeit reproducing the evolution of the main sequence of star-forming galaxies remains a challenge for theoretical models/simulations.

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arXiv2017

Witnessing the birth of the red sequence: the physical scale and morphology of dust emission in hyper-luminous starbursts in the early Universe

We present high-spatial-resolution ($\sim 0.12''$ or $\approx 800 \, {\rm pc}$ at $z = 4.5$) ALMA $870\,μ$m dust continuum observations of a sample of 44 ultrared dusty star-forming galaxies (DSFGs) selected from the H-ATLAS and HerMES far-infrared surveys because of their red colors from 250 to 500 $μ$m: $S_{500} / S_{250} > 1.5$ and $S_{500} / S_{350} > 1.0$. With photometric redshifts in the range $z \sim 4$-6, our sample includes the most luminous starbursting systems in the early Universe known so far, with total obscured star-formation rates (SFRs) of up to $\sim 4,500 \, M_\odot \, {\rm yr}^{-1}$, as well as a population of lensed, less intrinsically luminous sources. The lower limit on the number of ultrared DSFGs at 870 $μ$m (with flux densities measured from the ALMA maps and thus not affected by source confusion) derived in this work is in reasonable agreement with models of galaxy evolution, whereas there have been reports of conflicts at 500 $μ$m (where flux densities are derived from SPIRE). Ultrared DSFGs have a variety of morphologies (from relatively extended disks with smooth radial profiles, to compact sources, both isolated and interacting) and an average size, $θ_{\rm FWHM}$, of $1.46 \pm 0.41\, {\rm kpc}$, considerably smaller than the values reported in previous work for less-luminous DSFGs at lower redshifts. The size and the estimated gas-depletion times of our sources are compatible with their being the progenitors of the most massive, compact, red-and-dead galaxies at $z \sim 2$-3, and ultimately of local ultra-massive elliptical galaxies or massive galaxy clusters. We are witnessing the birth of the high-mass tail of the red sequence of galaxies.

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arXiv2017

The ALMA Frontier Fields Survey - II. Multiwavelength Photometric analysis of 1.1mm continuum sources in Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223

[abridged] The Hubble and Spitzer Space Telescope surveys of the Frontier Fields (FF) provide extremely deep images around six massive, strong-lensing clusters of galaxies. The ALMA FF survey aims to cover the same fields at 1.1mm, with maps reaching (unlensed) sensitivities of $<$70$μ$Jy, in order to explore the properties of background dusty star-forming galaxies. We report on the multi-wavelength photometric analysis of all 12 significantly detected ($>$5$σ$) sources in the first three FF clusters observed by ALMA, based on data from Hubble and Spitzer, the VLT and Herschel. We measure the total photometry in all available bands and determine the photometric redshifts and the physical properties of the counterparts via SED-fitting. In particular, we carefully estimate the FIR photometry using 1.1mm priors to limit the misidentification of blended FIR counterparts, which strongly affect some flux estimates in previous FIR catalogs. We identify robust near-infrared (NIR) counterparts for all 11 sources with K$_s$ detection, the majority of which are quite red, with eight having $F814W-K_s\gtrsim 4$ and five having $F160W-[4.5]\gtrsim3$. From the FIR point of view, all our objects have $z_{phot}$$\sim$1--3, whereas based on the optical SED one object prefers a high-$z$ solution ($z\geq\ $7). Five objects among our sample have spectroscopic redshifts from the GLASS survey for which we can reproduce their SEDs with existing templates. This verification confirms the validity of our photometric redshift methodology. The mean redshift of our sample is $z_{phot}$=1.99$\pm$0.27. All 1.1mm selected objects are massive (10.0$<\log[M_{\star}(M_{\odot})]<$ 11.5), with high star formation rates ($<\log[SFR(M_{\odot}/yr)]> \approx$1.6) and high dust contents (8.1 $<\log[M_{dust} (M_{\odot})]<$8.8), consistent with previous ALMA surveys.

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arXiv2017

VALES: I. The molecular gas content in star-forming dusty H-ATLAS galaxies up to z=0.35

We present an extragalactic survey using observations from the Atacama Large Millimeter/submillimeter Array (ALMA) to characterise galaxy populations up to $z=0.35$: the Valparaíso ALMA Line Emission Survey (VALES). We use ALMA Band-3 CO(1--0) observations to study the molecular gas content in a sample of 67 dusty normal star-forming galaxies selected from the $Herschel$ Astrophysical Terahertz Large Area Survey ($H$-ATLAS). We have spectrally detected 49 galaxies at $>5σ$ significance and 12 others are seen at low significance in stacked spectra. CO luminosities are in the range of $(0.03-1.31)\times10^{10}$ K km s$^{-1}$ pc$^2$, equivalent to $\log({\rm M_{gas}/M_{\odot}}) =8.9-10.9$ assuming an $α_{\rm CO}$=4.6(K km s$^{-1}$ pc$^{2}$)$^{-1}$, which perfectly complements the parameter space previously explored with local and high-z normal galaxies. We compute the optical to CO size ratio for 21 galaxies resolved by ALMA at $\sim 3$."$5$ resolution (6.5 kpc), finding that the molecular gas is on average $\sim$ 0.6 times more compact than the stellar component. We obtain a global Schmidt-Kennicutt relation, given by $\log [Σ_{\rm SFR}/({\rm M_{\odot} yr^{-1}kpc^{-2}})]=(1.26 \pm 0.02) \times \log [Σ_{\rm M_{H2}}/({\rm M_{\odot}\,pc^{-2}})]-(3.6 \pm 0.2)$. We find a significant fraction of galaxies lying at `intermediate efficiencies' between a long-standing mode of star-formation activity and a starburst, specially at $\rm L_{IR}=10^{11-12} L_{\odot}$. Combining our observations with data taken from the literature, we propose that star formation efficiencies can be parameterised by $\log [{\rm SFR/M_{H2}}]=0.19 \times {\rm (\log {L_{IR}}-11.45)}-8.26-0.41 \times \arctan[-4.84 (\log {\rm L_{IR}}-11.45) ]$. Within the redshift range we explore ($z<0.35$), we identify a rapid increase of the gas content as a function of redshift.

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arXiv2017

Molecular Gas, Dust and Star Formation in Galaxies: II. Dust properties and scalings in \sim\ 1600 nearby galaxies

We aim to characterize the relationship between dust properties. We also aim to provide equations to estimate accurate dust properties from limited observational datasets. We assemble a sample of 1,630 nearby (z<0.1) galaxies-over a large range of Mstar, SFR - with multi-wavelength observations available from wise, iras, planck and/or SCUBA. The characterization of dust emission comes from SED fitting using Draine & Li dust models, which we parametrize using two components (warm and cold ). The subsample of these galaxies with global measurements of CO and/or HI are used to explore the molecular and/or atomic gas content of the galaxies. The total Lir, Mdust and dust temperature of the cold component (Tc) form a plane that we refer to as the dust plane. A galaxy's sSFR drives its position on the dust plane: starburst galaxies show higher Lir, Mdust and Tc compared to Main Sequence and passive galaxies. Starburst galaxies also show higher specific Mdust (Mdust/Mstar) and specific Mgas (Mgas/Mstar). The Mdust is more closely correlated with the total Mgas (atomic plus molecular) than with the individual components. Our multi wavelength data allows us to define several equations to estimate Lir, Mdust and Tc from one or two monochromatic luminosities in the infrared and/or sub-millimeter. We estimate the dust mass and infrared luminosity from a single monochromatic luminosity within the R-J tail of the dust emission, with errors of 0.12 and 0.20dex, respectively. These errors are reduced to 0.05 and 0.10 dex, respectively, if the Tc is used. The Mdust is correlated with the total Mism (Mism \propto Mdust^0.7). For galaxies with Mstar 8.5<log(Mstar/Msun) < 11.9, the conversion factor α_850mum shows a large scatter (rms=0.29dex). The SF mode of a galaxy shows a correlation with both the Mgass and Mdust: high Mdust/Mstar galaxies are gas-rich and show the highest SFRs.

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arXiv2017

The SCUBA-2 Cosmology Legacy Survey: Multi-wavelength Properties of ALMA-identified Submillimeter Galaxies in UKIDSS-UDS

We present a multi-wavelength analysis of 52 sub-millimeter galaxies (SMGs), identified using ALMA 870$μ$m continuum imaging in a pilot program to precisely locate bright SCUBA2-selected sub-mm sources in the UKIDSS Ultra Deep Survey (UDS) field. Using the available deep (especially near-infrared), panoramic imaging of the UDS field at optical-to-radio wavelengths we characterize key properties of the SMG population. The median photometric redshift of the bright ALMA/SCUBA-2 UDS (AS2UDS) SMGs that are detected in a sufficient number of wavebands to derive a robust photometric redshift is $z$=2.65$\pm$0.13. However, similar to previous studies, 27% of the SMGs are too faint at optical-to-near-infrared wavelengths to derive a reliable photometric redshift. Assuming that these SMGs lie at z$\gtrsim$3 raises the median redshift of the full sample to $z$=2.9$\pm$0.2. A subset of 23, unlensed, bright AS2UDS SMGs have sizes measured from resolved imaging of their rest-frame far-infrared emission. We show that the extent and luminosity of the far-infrared emission are consistent with the dust emission arising from regions that are optically thick, on average, at a wavelength of $λ_0$$\ge$75$μ$m (1-$σ$ dispersion of 55-90$μ$m). Using the dust masses derived from our optically-thick spectral energy distribution models we determine that these galaxies have a median hydrogen column density of $N_{H}$=9.8$_{-0.7}^{+1.4}$$\times$10$^{23}$cm$^{-2}$, or a corresponding median $V$-band obscuration of $A_\mathrm{v}$=540$^{+80}_{-40}$mag, averaged along the line of sight to the source of their restframe $\sim$200$μ$m emission. We discuss the implications of this extreme attenuation by dust for the multiwavelength study of dusty starbursts and reddening-sensitive tracers of star formation.

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arXiv2017

VALES: III. The calibration between the dust continuum and interstellar gas content of star-forming galaxies

We present the calibration between the dust continuum luminosity and interstellar gas content obtained from the Valparaíso ALMA Line Emission Survey (VALES) sample of 67 main-sequence star-forming galaxies at 0.02<$z$<0.35. We use CO(1-0) observations from the Atacama Large Millimetre/submillimetre Array (ALMA) to trace the molecular gas mass, $M_{\mathrm{H}_{2}}$, and estimate the rest-frame monochromatic luminosity at 850 $μ$m, $L_{ν_{850}}$, by extrapolating the dust continuum from MAGPHYS modelling of the far-ultraviolet to submillimetre spectral energy distribution sampled by the Galaxy And Mass Assembly (GAMA) survey. Adopting $α_{\rm CO}$ = 6.5 (K km s$^{-1}$ pc$^{2}$)$^{-1}$, the average ratio of $L_{ν_{850}}/M_{\mathrm{H}_{2}}$ = (6.4$\pm$1.4)$\times10^{19}$ erg s$^{-1}$ Hz$^{-1}$ $\mathrm{M}_{\odot}^{-1}$, in excellent agreement with literature values. We obtain a linear fit of $\log_{10}$ ($M_{\mathrm{H}_{2}}/\mathrm{M}_{\odot}$) = (0.92$\pm$0.02) $\log_{10}$ ($L_{ν_{850}}$/erg s$^{-1}$ Hz$^{-1}$)-(17.31$\pm$0.59). We provide relations between $L_{ν_{850}}$, $M_{\mathrm{H}_{2}}$ and $M_{\mathrm{ISM}}$ when combining the VALES and literature samples, and adopting a Galactic $α_{\rm CO}$ value.

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arXiv2016

A deep ALMA image of the Hubble Ultra Deep Field

We present the results of the first, deep ALMA imaging covering the full 4.5 sq arcmin of the Hubble Ultra Deep Field (HUDF) as previously imaged with WFC3/IR on HST. Using a mosaic of 45 pointings, we have obtained a homogeneous 1.3mm image of the HUDF, achieving an rms sensitivity of 35 microJy, at a resolution of 0.7 arcsec. From an initial list of ~50 >3.5sigma peaks, a rigorous analysis confirms 16 sources with flux densities S(1.3) > 120 microJy. All of these have secure galaxy counterparts with robust redshifts ( = 2.15), and 12 are also detected at 6GHz in new deep JVLA imaging. Due to the wealth of supporting data in this unique field, the physical properties of the ALMA sources are well constrained, including their stellar masses (M*) and UV+FIR star-formation rates (SFR). Our results show that stellar mass is the best predictor of SFR in the high-z Universe; indeed at z > 2 our ALMA sample contains 7 of the 9 galaxies in the HUDF with M* > 2 x 10^10 Msun and we detect only one galaxy at z > 3.5, reflecting the rapid drop-off of high-mass galaxies with increasing redshift. The detections, coupled with stacking, allow us to probe the redshift/mass distribution of the 1.3-mm background down to S(1.3) ~ 10 micro-Jy. We find strong evidence for a steep `main sequence' for star-forming galaxies at z ~ 2, with SFR \propto M* and a mean specific SFR = 2.2 /Gyr. Moreover, we find that ~85% of total star formation at z ~ 2 is enshrouded in dust, with ~65% of all star formation at this epoch occurring in high-mass galaxies (M* > 2 x 10^10 Msun), for which the average obscured:unobscured SF ratio is ~200. Finally, we combine our new ALMA results with the existing HST data to revisit the cosmic evolution of star-formation rate density; we find that this peaks at z ~ 2.5, and that the star-forming Universe transits from primarily unobscured to primarily obscured thereafter at z ~ 4.

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arXiv2016

SINFONI-HiZELS: The dynamics, merger rates & metallicity gradients of `typical' star-forming galaxies at $z$ = 0.8-2.2

We present adaptive optics (AO) assisted SINFONI integral field unit (IFU) spectroscopy of eleven H$α$ emitting galaxies selected from the High-Z Emission Line Survey (HiZELS). We obtain spatially resolved dynamics on ~kpc-scales of star-forming galaxies (stellar mass M$_\star$ = 10$^{9.5-10.5}$ M$_\odot$ and star formation rate SFR = 2-30 M$_\odot$ yr$^{-1}$) near the peak of the cosmic star-formation rate history. Combining these observations with our previous SINFONI-HiZELS campaign, we construct a sample of twenty homogeneously selected galaxies with IFU AO-aided observations -- the `SHiZELS' survey, with roughly equal number of galaxies per redshift slice, at $z$ = 0.8, 1.47, and 2.23. We measure the dynamics and identify the major kinematic axis by modelling their velocity fields to extract rotational curves and infer their inclination-corrected rotational velocities. We explore the stellar mass Tully-Fisher relationship, finding that galaxies with higher velocity dispersions tend to deviate from this relation. Using kinemetry analyses we find that galaxy interactions might be the dominant mechanism controlling the star-formation activity at $z$ = 2.23 but they become gradually less important down to $z$ = 0.8. Metallicity gradients derived from the [NII]/H$α$ emission line ratio show a median negative gradient for the SHiZELS survey of $Δ$log(O/H)/$Δ$R = -0.026$\pm$0.008 dex kpc$^{-1}$. We find that metal-rich galaxies tend to show negative gradients, whereas metal-poor galaxies tend to exhibit positive metallicity gradients. This result suggests that the accretion of pristine gas in the periphery of galaxies plays an important role in replenishing the gas in `typical' star-forming galaxies.

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arXiv2016

VALES: II. The physical conditions of interstellar gas in normal star-forming galaxies up to z=0.2 revealed by ALMA

We use new Band-3 CO(1-0) observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) to study the physical conditions in the interstellar gas of a sample of 27 dusty main-sequence star-forming galaxies at 0.03<$z$<0.2 present in the Valparaíso ALMA Line Emission Survey (VALES). The sample is drawn from far-IR bright galaxies over $\sim$160 deg$^{2}$ in the Herschel Astrophysical Terahertz Large Area Survey (HATLAS), which is covered by Herschel [CII] 158 $μ$m spectroscopy and far-infrared (FIR) photometry. The [CII] and CO lines are both detected at >5$σ$ in 26 sources. We find an average [CII] to CO(1-0) luminosity ratio of 3500$\pm$1200 for our sample that is consistent with previous studies. Using the [CII], CO and FIR measurements as diagnostics of the physical conditions of the interstellar medium, we compare these observations to the predictions of a photodissociation region (PDR) model to determine the gas density, surface temperature, pressure, and the strength of the incident far-ultraviolet (FUV) radiation field, $G_{0}$, normalised to the Habing Field. The majority of our sample exhibit hydrogen densities of 4 < $\log n/\mathrm{cm}^{3}$ < 5.5 and experience an incident FUV radiation field with strengths of 2 < $\log G_0$ < 3 when adopting standard adjustments. A comparison to galaxy samples at different redshifts indicates that the average strength of the FUV radiation field appears constant up to redshift $z\sim$6.4, yet the neutral gas density increases with redshift by a factor of $\sim$100, that persists regardless of various adjustments to our observable quantities. This evolution could provide an explanation for the observed evolution of the star formation rate density with cosmic time, yet could arise from a combination of observational biases when using different suites of emission lines as diagnostic tracers of PDR gas.

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arXiv2016

The space density of luminous dusty star-forming galaxies at $z>4$: SCUBA-2 and LABOCA imaging of ultrared galaxies from $Herschel$-ATLAS

Until recently, only a handful of dusty, star-forming galaxies (DSFGs) were known at $z>4$, most of them significantly amplified by gravitational lensing. Here, we have increased the number of such DSFGs substantially, selecting galaxies from the uniquely wide 250-, 350- and 500-$μ$m Herschel-ATLAS imaging survey on the basis of their extremely red far-infrared colors and faint 350- and 500-$μ$m flux densities - ergo they are expected to be largely unlensed, luminous, rare and very distant. The addition of ground-based continuum photometry at longer wavelengths from the JCMT and APEX allows us to identify the dust peak in their SEDs, better constraining their redshifts. We select the SED templates best able to determine photometric redshifts using a sample of 69 high-redshift, lensed DSFGs, then perform checks to assess the impact of the CMB on our technique, and to quantify the systematic uncertainty associated with our photometric redshifts, $σ=0.14\,(1+z)$, using a sample of 25 galaxies with spectroscopic redshifts, each consistent with our color selection. For Herschel-selected ultrared galaxies with typical colors of $S_{500}/S_{250}\sim 2.2$ and $S_{500}/S_{350}\sim 1.3$ and flux densities, $S_{500}\sim 50\,$mJy, we determine a median redshift, $\hat{z}_{\rm phot}=3.66$, an interquartile redshift range, 3.30$-$4.27, with a median rest-frame 8$-$1000-$μ$m luminosity, $\hat{L}_{\rm IR}$, of $1.3\times 10^{13}\,$L$_\odot$. A third lie at $z>4$, suggesting a space density, $ρ_{z>4}$, of $\approx 6 \times 10^{-7}\,$Mpc$^{-3}$. Our sample contains the most luminous known star-forming galaxies, and the most over-dense cluster of starbursting proto-ellipticals yet found.

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arXiv2016

ATCA detections of massive molecular gas reservoirs in dusty, high-z radio galaxies

Observations using the 7 mm receiver system on the Australia Telescope Compact Array have revealed large reservoirs of molecular gas in two high-redshift radio galaxies: HATLAS J090426.9+015448 (z = 2.37) and HATLAS J140930.4+003803 (z = 2.04). Optically the targets are very faint, and spectroscopy classifies them as narrow-line radio galaxies. In addition to harbouring an active galactic nucleus the targets share many characteristics of sub-mm galaxies. Far-infrared data from Herschel-ATLAS suggest high levels of dust (>10^9 M_solar) and a correspondingly large amount of obscured star formation (~1000 M_solar / yr). The molecular gas is traced via the J = 1-0 transition of 12CO, its luminosity implying total H_2 masses of (1.7 +/- 0.3) x 10^11 and (9.5 +/- 2.4) x 10^10 (alpha_CO/0.8) M_solar in HATLAS J090426.9+015448 and HATLAS J140930.4+003803 respectively. Both galaxies exhibit molecular line emission over a broad (~1000 km/s) velocity range, and feature double-peaked profiles. We interpret this as evidence of either a large rotating disk or an on-going merger. Gas depletion timescales are ~100 Myr. The 1.4 GHz radio luminosities of our targets place them close to the break in the luminosity function. As such they represent `typical' z > 2 radio sources, responsible for the bulk of the energy emitted at radio wavelengths from accretion-powered sources at high redshift, and yet they rank amongst the most massive systems in terms of molecular gas and dust content. We also detect 115 GHz rest-frame continuum emission, indicating a very steep high-radio-frequency spectrum, possibly classifying the targets as compact steep spectrum objects.

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arXiv2016

The ALMA Frontier Fields survey I: 1.1 mm continuum detections in Abell 2744, MACSJ0416.1-2403 and MACSJ1149.5+2223

Dusty star-forming galaxies are among the most prodigious systems at high redshift (z>1), characterized by high star formation rates and huge dust reservoirs. The bright end of this population has been well characterized in recent years, but considerable uncertainties remain for fainter dusty star-forming galaxies, which are responsible for the bulk of star formation at high redshift and thus play a key role in galaxy growth and evolution. In this first paper of our series, we describe our methods for finding high redshift faint dusty galaxies using millimeter observations with ALMA. We obtained ALMA 1.1 mm mosaic images for three strong-lensing galaxy clusters from the Frontier Fields survey. The 2'x2' mosaics overlap with the deep HST WFC3/IR footprints and encompass the high magnification regions of each cluster. The combination of extremely high ALMA sensitivity and the magnification power of these clusters allows us to systematically probe the sub-mJy population of dusty star-forming galaxies over a large surveyed area. We present a description of the reduction and analysis of the ALMA continuum observations for the galaxy clusters Abell 2744 (z=0.308), MACSJ0416.1-2403 (z=0.396) and MACSJ1149.5+2223 (z=0.543), for which we reach observed rms sensitivities of 55, 59 and 71 $μ$Jy beam$^{-1}$ respectively. We detect 12 dusty star-forming galaxies at S/N>5.0 across the three clusters, all of them presenting coincidence with NIR detected counterparts in the HST images. None of the sources fall close to the lensing caustics, thus they are not strongly lensed. The observed 1.1 mm flux densities for the total sample of galaxies range from 0.41 to 2.82 mJy, with observed effective radii spanning <0.05" to 0.37"$\pm$0.21". The lensing-corrected sizes of the detected sources appear to be in the same range as those measured in brighter samples, albeit with possibly larger dispersion.

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arXiv2016

ALMA spectroscopic survey in the Hubble Ultra Deep Field: Continuum number counts, resolved 1.2-mm extragalactic background, and properties of the faintest dusty star forming galaxies

We present an analysis of a deep (1$σ$=13 $μ$Jy) cosmological 1.2-mm continuum map based on ASPECS, the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field. In the 1 arcmin$^2$ covered by ASPECS we detect nine sources at $>3.5σ$ significance at 1.2-mm. Our ALMA--selected sample has a median redshift of $z=1.6\pm0.4$, with only one galaxy detected at z$>$2 within the survey area. This value is significantly lower than that found in millimeter samples selected at a higher flux density cut-off and similar frequencies. Most galaxies have specific star formation rates similar to that of main sequence galaxies at the same epoch, and we find median values of stellar mass and star formation rates of $4.0\times10^{10}\ M_\odot$ and $\sim40~M_\odot$ yr$^{-1}$, respectively. Using the dust emission as a tracer for the ISM mass, we derive depletion times that are typically longer than 300 Myr, and we find molecular gas fractions ranging from $\sim$0.1 to 1.0. As noted by previous studies, these values are lower than using CO--based ISM estimates by a factor $\sim$2. The 1\,mm number counts (corrected for fidelity and completeness) are in agreement with previous studies that were typically restricted to brighter sources. With our individual detections only, we recover $55\pm4\%$ of the extragalactic background light (EBL) at 1.2 mm measured by the Planck satellite, and we recover $80\pm7\%$ of this EBL if we include the bright end of the number counts and additional detections from stacking. The stacked contribution is dominated by galaxies at $z\sim1-2$, with stellar masses of (1-3)$\times$10$^{10}$ M$_\odot$. For the first time, we are able to characterize the population of galaxies that dominate the EBL at 1.2 mm.

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arXiv2016

ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Search for [CII] line and dust emission in 6<z<8 galaxies

We present a search for [CII] line and dust continuum emission from optical dropout galaxies at $z>6$ using ASPECS, our ALMA Spectroscopic Survey in the Hubble Ultra-Deep Field (UDF). Our observations, which cover the frequency range $212-272$ GHz, encompass approximately the range $6 $4.5 $σ$, two of which correspond to blind detections with no optical counterparts. At this significance level, our statistical analysis shows that about 60\% of our candidates are expected to be spurious. For one of our blindly selected [CII] line candidates, we tentatively detect the CO(6-5) line in our parallel 3-mm line scan. None of the line candidates are individually detected in the 1.2 mm continuum. A stack of all [CII] candidates results in a tentative detection with $S_{1.2mm}=14\pm5μ$Jy. This implies a dust-obscured star formation rate (SFR) of $(3\pm1)$ M$_\odot$ yr$^{-1}$. We find that the two highest--SFR objects have candidate [CII] lines with luminosities that are consistent with the low-redshift $L_{\rm [CII]}$ vs. SFR relation. The other candidates have significantly higher [CII] luminosities than expected from their UV--based SFR. At the current sensitivity it is unclear whether the majority of these sources are intrinsically bright [CII] emitters, or spurious sources. If only one of our line candidates was real (a scenario greatly favored by our statistical analysis), we find a source density for [CII] emitters at $6<z<8$ that is significantly higher than predicted by current models and some extrapolations from galaxies in the local universe.

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arXiv2016

HerMES: A search for high-redshift dusty galaxies in the HerMES Large Mode Survey - Catalogue, number counts and early results

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 $5 σ$ 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 have obtained spectroscopic redshift measurements for two of our sources using the Atacama Large Millimeter/submillimeter Array (ALMA). The redshifts z = 5.1 and z = 3.8 confirm that with our selection method we can indeed find high-redshift dusty star-forming galaxies.

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arXiv2016

GAMA/H-ATLAS: Common star-formation rate indicators and their dependence on galaxy physical parameters

We compare common star-formation rate (SFR) indicators in the local Universe in the GAMA equatorial fields (around 160 sq. deg.), using ultraviolet (UV) photometry from GALEX, far-infrared (FIR) and sub-millimetre (sub-mm) photometry from H-ATLAS, and Halpha spectroscopy from the GAMA survey. With a high-quality sample of 745 galaxies (median redshift 0.08), we consider three SFR tracers: UV luminosity corrected for dust attenuation using the UV spectral slope beta (SFRUV,corr), Halpha line luminosity corrected for dust using the Balmer decrement (BD) (SFRHalpha,corr), and the combination of UV and IR emission (SFRUV+IR). We demonstrate that SFRUV,corr can be reconciled with the other two tracers after applying attenuation corrections by calibrating IRX (i.e. the IR to UV luminosity ratio) and attenuation in the Halpha (derived from BD) against beta. However, beta on its own is very unlikely to be a reliable attenuation indicator. We find that attenuation correction factors depend on parameters such as stellar mass, z and dust temperature (Tdust), but not on Halpha equivalent width (EW) or Sersic index. Due to the large scatter in the IRX vs beta correlation, when compared to SFRUV+IR, the beta-corrected SFRUV,corr exhibits systematic deviations as a function of IRX, BD and Tdust.

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arXiv2016

The Herschel-ATLAS Data Release 1 Paper I: Maps, Catalogues and Number Counts

We present the first major data release of the largest single key-project in area carried out in open time with the Herschel Space Observatory. The Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS) is a survey of 600 deg^2 in five photometric bands - 100, 160, 250, 350 and 500 um - with the PACS and SPIRE cameras. In this paper and a companion paper (Bourne et al. 2016) we present the survey of three fields on the celestial equator, covering a total area of 161.6 deg^2 and previously observed in the Galaxy and Mass Assembly (GAMA) spectroscopic survey. This paper describes the Herschel images and catalogues of the sources detected on the SPIRE 250 um images. The 1-sigma noise for source detection, including both confusion and instrumental noise, is 7.4, 9.4 and 10.2 mJy at 250, 350 and 500 um. Our catalogue includes 120230 sources in total, with 113995, 46209 and 11011 sources detected at >4-sigma at 250, 350 and 500 um. The catalogue contains detections at >3-sigma at 100 and 160 um for 4650 and 5685 sources, and the typical noise at these wavelengths is 44 and 49 mJy. We include estimates of the completeness of the survey and of the effects of flux bias and also describe a novel method for determining the true source counts. The H-ATLAS source counts are very similar to the source counts from the deeper HerMES survey at 250 and 350 um, with a small difference at 500 um. Appendix A provides a quick start in using the released datasets, including instructions and cautions on how to use them.

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