arXiv subjects

H. Aussel

Publications and source records attributed to H. Aussel.

At least 145 records · Page 8Linked to original sources

arXiv2016

The COSMOS2015 Catalog: Exploring the 1<z<6 Universe with half a million galaxies

We present the COSMOS2015 catalog which contains precise photometric redshifts and stellar masses for more than half a million objects over the 2deg$^{2}$ COSMOS field. Including new $YJHK_{\rm s}$ images from the UltraVISTA-DR2 survey, $Y$-band from Subaru/Hyper-Suprime-Cam and infrared data from the Spitzer Large Area Survey with the Hyper-Suprime-Cam Spitzer legacy program, this near-infrared-selected catalog is highly optimized for the study of galaxy evolution and environments in the early Universe. To maximise catalog completeness for bluer objects and at higher redshifts, objects have been detected on a $χ^{2}$ sum of the $YJHK_{\rm s}$ and $z^{++}$ images. The catalog contains $\sim 6\times 10^5$ objects in the 1.5 deg$^{2}$ UltraVISTA-DR2 region, and $\sim 1.5\times 10^5$ objects are detected in the "ultra-deep stripes" (0.62 deg$^{2}$) at $K_{\rm s}\leq 24.7$ (3$σ$, 3", AB magnitude). Through a comparison with the zCOSMOS-bright spectroscopic redshifts, we measure a photometric redshift precision of $σ_{Δz/(1+z_s)}$ = 0.007 and a catastrophic failure fraction of $η=0.5$%. At $3<z<6$, using the unique database of spectroscopic redshifts in COSMOS, we find $σ_{Δz/(1+z_s)}$ = 0.021 and $η=13.2\% $. The deepest regions reach a 90\% completeness limit of 10$^{10}M_\odot$ to $z=4$. Detailed comparisons of the color distributions, number counts, and clustering show excellent agreement with the literature in the same mass ranges. COSMOS2015 represents a unique, publicly available, valuable resource with which to investigate the evolution of galaxies within their environment back to the earliest stages of the history of the Universe. The COSMOS2015 catalog is distributed via anonymous ftp (ftp://ftp.iap.fr/pub/from_users/hjmcc/COSMOS2015/) and through the usual astronomical archive systems (CDS, ESO Phase 3, IRSA).

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arXiv2016

ISM Masses and Star Formation at z = 1 to 6 ALMA Observations of Dust Continuum in 180 Galaxies in COSMOS

ALMA Cycle 2 observations of the long wavelength dust emission in 180 star-forming (SF) galaxies are used to investigate the evolution of ISM masses at z = 1 to 6.4. The ISM masses exhibit strong increases from z = 0 to $\rm $ = 1.15 and further to $\rm $ = 2.2 and 4.8, particularly amongst galaxies above the SF galaxy main sequence (MS). The galaxies with highest SFRs at $\rm $ = 2.2 and 4.8 have gas masses 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. For the full sample of galaxies, we find a single, very simple SF law: $\rm SFR \propto M_{\rm ISM}^{0.9}$, i.e. a `linear' dependence on the ISM mass -- on and above the MS. Thus, the galaxies above the MS are converting their larger ISM masses into stars on a timescale similar to those on the MS. At z $> 1$, the entire population of star-forming galaxies has $\sim$5 - 10$\times$ shorter gas depletion times ($\sim0.2$ Gyr) than galaxies at low redshift. These {\bf shorter depletion times are due to a different, dominant mode of SF in the early universe} -- dynamically driven by compressive, high dispersion gas motions and/or galaxy interactions. The dispersive gas motions are a natural consequence of the extraordinarily high gas accretion rates which must occur to maintain the prodigious SF.

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arXiv2015

Prospects for high-z cluster detections with Planck, based on a follow-up of 28 candidates using MegaCam@CFHT

The Planck catalogue of SZ sources limits itself to a significance threshold of 4.5 to ensure a low contamination rate by false cluster candidates. This means that only the most massive clusters at redshift z>0.5, and in particular z>0.7, are expected to enter into the catalogue, with a large number of systems in that redshift regime being expected around and just below that threshold. In this paper, we follow-up a sample of SZ sources from the Planck SZ catalogues from 2013 and 2015. In the latter maps, we consider detections around and at lower significance than the threshold adopted by the Planck Collaboration. To keep the contamination rate low, our 28 candidates are chosen to have significant WISE detections, in combination with non-detections in SDSS/DSS, which effectively selects galaxy cluster candidates at redshifts $z\gtrsim0.5$. By taking r- and z-band imaging with MegaCam@CFHT, we bridge the 4000A rest-frame break over a significant redshift range, thus allowing accurate redshift estimates of red-sequence cluster galaxies up to z~0.8. After discussing the possibility that an overdensity of galaxies coincides -by chance- with a Planck SZ detection, we confirm that 16 of the candidates have likely optical counterparts to their SZ signals, 13 (6) of which have an estimated redshift z>0.5 (z>0.7). The richnesses of these systems are generally lower than expected given the halo masses estimated from the Planck maps. However, when we follow a simplistic model to correct for Eddington bias in the SZ halo mass proxy, the richnesses are consistent with a reference mass-richness relation established for clusters detected at higher significance. This illustrates the benefit of an optical follow-up, not only to obtain redshift estimates, but also to provide an independent mass proxy that is not based on the same data the clusters are detected with, and thus not subject to Eddington bias.

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arXiv2015

The HerMES sub-millimetre local and low-redshift luminosity functions

We used wide area surveys over 39 deg$^2$ by the HerMES collaboration, performed with the Herschel Observatory SPIRE multi-wavelength camera, to estimate the low-redshift, $0.02<z<0.5$, monochromatic luminosity functions (LFs) of galaxies at 250, 350 and 500$\,μ$m. SPIRE flux densities were also combined with Spitzer photometry and multi-wavelength archival data to perform a complete SED fitting analysis of SPIRE detected sources to calculate precise k-corrections, as well as the bolometric infrared (8-1000$\,μ$m) luminosity functions and their low-$z$ evolution from a combination of statistical estimators. Integration of the latter prompted us to also compute the local luminosity density (LLD) and the comoving star formation rate density (SFRD) for our sources, and to compare them with theoretical predictions of galaxy formation models. The luminosity functions show significant and rapid luminosity evolution already at low redshifts, $0.02<z<0.2$, with L$_{IR}^* \propto (1+z)^{6.0\pm0.4}$ and $Φ_{IR}^* \propto (1+z)^{-2.1\pm0.4}$, L$_{250}^* \propto (1+z)^{5.3\pm0.2}$ and $Φ_{250}^* \propto (1+z)^{-0.6\pm0.4}$ estimated using the IR bolometric and the 250$\,μ$m LFs respectively. Converting our IR LD estimate into an SFRD assuming a standard Salpeter IMF and including the unobscured contribution based on the UV dust-uncorrected emission from local galaxies, we estimate a SFRD scaling of SFRD$_0+0.08 z$, where SFRD$_0\simeq (1.9\pm 0.03)\times 10^{-2} [\mathrm{M}_\odot\,\mathrm{Mpc}^{-3}]$ is our total SFRD estimate at $z\sim0.02$.

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arXiv2015

Non-linearity and environmental dependence of the star forming galaxies Main Sequence

Using data from four deep fields (COSMOS, AEGIS, ECDFS, and CDFN), we study the correlation between the position of galaxies in the star formation rate (SFR) versus stellar mass plane and local environment at $z<1.1$. To accurately estimate the galaxy SFR, we use the deepest available Spitzer/MIPS 24 and Herschel/PACS datasets. We distinguish group environments ( $M_{halo}\sim$10$^{12.5-14.2}$$M_{\odot}$) based on the available deep X-ray data and lower halo mass environments based on the local galaxy density. We confirm that the Main Sequence (MS) of star forming galaxies is not a linear relation and there is a flattening towards higher stellar masses ( $M_*>10^{10.4-10.6}$ $M_{\odot}$), across all environments. At high redshift ( $0.5<z<1.1$ ), the MS varies little with environment. At low redshift ( $0.15<z<0.5$ ), group galaxies tend to deviate from the mean MS towards the region of quiescence with respect to isolated galaxies and less-dense environments. We find that the flattening of the MS toward low SFR is due to an increased fraction of bulge dominated galaxies at high masses. Instead, the deviation of group galaxies from the MS at low redshift is caused by a large fraction of red disk dominated galaxies which are not present in the lower density environments. Our results suggest that above a mass threshold ( $\sim10^{10.4}-10^{10.6}$$M_{\odot}$ ) stellar mass, morphology and environment act together in driving the evolution of the SF activity towards lower level. The presence of a dominating bulge and the associated quenching processes are already in place beyond $z\sim$1. The environmental effects appear, instead, at lower redshifts and have a long time-scale.

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arXiv2015

The Subaru COSMOS 20: Subaru Optical Imaging of the HST COSMOS Field with 20 Filters

We present both the observations and the data reduction procedures of the Subaru COSMOS 20 project that is an optical imaging survey of the HST COSMOS field, carried out by using Suprime-Cam on the Subaru Telescope with the following 20 optical filters: 6 broad-band (B, g', V, r', i', and z'), 2 narrow-band (NB711 and NB816), and 12 intermediate-band filters (IA427, IA464, IA484, IA505, IA527, IA574, IA624, IA679, IA709, IA738, IA767, and IA827). A part of this project is described in Taniguchi et al. (2007) and Capak et al. (2007) for the six broad-band and one narrow-band (NB816) filter data. In this paper, we present details of the observations and data reduction for remaining 13 filters (the 12 IA filters and NB711). In particular, we describe the accuracy of both photometry and astrometry in all the filter bands. We also present optical properties of the Suprime-Cam IA filter system in Appendix.

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arXiv2015

The composite nature of Dust-Obscured Galaxies (DOGs) at z~2-3 in the COSMOS field: I. A Far-Infrared View

Dust-Obscured galaxies (DOGs) are bright 24 um-selected sources with extreme obscuration at optical wavelengths. They are typically characterized by a rising power-law continuum of hot dust (T_D ~ 200-1000K) in the near-IR indicating that their mid-IR luminosity is dominated by an an active galactic nucleus (AGN). DOGs with a fainter 24 um flux display a stellar bump in the near-IR and their mid-IR luminosity appears to be mainly powered by dusty star formation. Alternatively, it may be that the mid-IR emission arising from AGN activity is dominant but the torus is sufficiently opaque to make the near-IR emission from the AGN negligible with respect to the emission from the host component. In an effort to characterize the astrophysical nature of the processes responsible for the IR emission in DOGs, this paper exploits Herschel data (PACS + SPIRE) on a sample of 95 DOGs within the COSMOS field. We derive a wealth of far-IR properties (e.g., total IR luminosities; mid-to-far IR colors; dust temperatures and masses) based on SED fitting. Of particular interest are the 24 um-bright DOGs (F_24um > 1mJy). They present bluer far-IR/mid-IR colors than the rest of the sample, unveiling the potential presence of an AGN. The AGN contribution to the total 8-1000 um flux increases as a function of the rest-frame 8 um-luminosity irrespective of the redshift. This confirms that faint DOGs (L_8 um< 10^12 L_sun) are dominated by star-formation while brighter DOGs show a larger contribution from an AGN.

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arXiv2015

Comparison of Sunyaev-Zel'dovich measurements from Planck and from the Arcminute Microkelvin Imager for 99 galaxy clusters

We present observations and analysis of a sample of 123 galaxy clusters from the 2013 Planck catalogue of Sunyaev-Zel'dovich sources with the Arcminute Microkelvin Imager (AMI), a ground-based radio interferometer. AMI provides an independent measurement with higher angular resolution, 3 arcmin compared to the Planck beams of 5-10 arcmin. The AMI observations thus provide validation of the cluster detections, improved positional estimates, and a consistency check on the fitted 'size' ($θ_{s}$) and 'flux' ($Y_{\rm tot}$) parameters in the Generalised Navarro, Frenk and White (GNFW) model. We detect 99 of the clusters. We use the AMI positional estimates to check the positional estimates and error-bars produced by the Planck algorithms PowellSnakes and MMF3. We find that $Y_{\rm tot}$ values as measured by AMI are biased downwards with respect to the Planck constraints, especially for high Planck-SNR clusters. We perform simulations to show that this can be explained by deviation from the 'universal' pressure profile shape used to model the clusters. We show that AMI data can constrain the $α$ and $β$ parameters describing the shape of the profile in the GNFW model for individual clusters provided careful attention is paid to the degeneracies between parameters, but one requires information on a wider range of angular scales than are present in AMI data alone to correctly constrain all parameters simultaneously.

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arXiv2015

Evolution of the specific Star Formation Rate Function at z<1.4 - Dissecting the mass-SFR plane in COSMOS and GOODS

The relation between the stellar mass and the star formation rate characterizes how the instantaneous star formation is determined by the galaxy past star formation history and by the growth of the dark matter structures. We deconstruct the M-SFR plane by measuring the specific SFR functions in several stellar mass bins from z=0.2 out to z=1.4. Our analysis is primary based on a MIPS 24$μm$ selected catalogue combining the COSMOS and GOODS surveys. We estimate the SFR by combining mid- and far-infrared data for 20500 galaxies. The sSFR functions are derived in four stellar mass bins within the range 9.5<log(M/Msun)<11.5. First, we demonstrate the importance of taking into account selection effects when studying the M-SFR relation. Secondly, we find a mass-dependent evolution of the median sSFR with redshift varying as $sSFR \propto (1+z)^{b}$, with $b$ increasing from $b=2.88$ to $b=3.78$ between $M=10^{9.75}Msun$ and $M=10^{11.1}Msun$, respectively. At low masses, this evolution is consistent with the cosmological accretion rate and predictions from semi-analytical models (SAM). This agreement breaks down for more massive galaxies showing the need for a more comprehensive description of the star-formation history in massive galaxies. Third, we obtain that the shape of the sSFR function is invariant with time at z<1.4 but depends on the mass. We observe a broadening of the sSFR function ranging from 0.28 dex at $M=10^{9.75}Msun$ to 0.46 dex at $M=10^{11.1}Msun$. Such increase in the scatter of the M-SFR relation suggests an increasing diversity of SFHs as the stellar mass increases. Finally, we find a gradual decline of the sSFR with mass as $log(sSFR) \propto -0.17M$. We discuss the numerous physical processes, as gas exhaustion in hot gas halos or secular evolution, which can gradually reduce the sSFR and increase the SFH diversity.

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arXiv2015

Planck 2013 results. XXIX. The Planck catalogue of Sunyaev-Zeldovich sources: Addendum

We update the all-sky Planck catalogue of 1227 clusters and cluster candidates (PSZ1) published in March 2013, derived from Sunyaev-Zeldovich (SZ) effect detections using the first 15.5 months of Planck satellite observations. Addendum. We deliver an updated version of the PSZ1 catalogue, reporting the further confirmation of 86 Planck-discovered clusters. In total, the PSZ1 now contains 947 confirmed clusters, of which 214 were confirmed as newly discovered clusters through follow-up observations undertaken by the Planck Collaboration. The updated PSZ1 contains redshifts for 913 systems, of which 736 (~80.6%) are spectroscopic, and associated mass estimates derived from the Y_z mass proxy. We also provide a new SZ quality flag, derived from a novel artificial neural network classification of the SZ signal, for the remaining 280 candidates. Based on this assessment, the purity of the updated PSZ1 catalogue is estimated to be 94%. In this release, we provide the full updated catalogue and an additional readme file with further information on the Planck SZ detections.

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arXiv2014

Probing the galaxy-halo connection in UltraVISTA to $z\sim2$

We use percent-level precision photometric redshifts in the UltraVISTA-DR1 near-infrared survey to investigate the changing relationship be- tween galaxy stellar mass and the dark matter haloes hosting them to $z\sim2$. We achieve this by measuring the clustering properties and abundances of a series of volume-limited galaxy samples selected by stellar mass and star-formation activity. We interpret these results in the framework of a phenomenological halo model and numerical simulations. Our measurements span a uniquely large range in stellar mass and redshift and reach below the characteristic stellar mass to $z\sim2$. Our results are: 1. At fixed redshift and scale, clustering amplitude depends monotonically on sample stellar mass threshold; 2. At fixed angular scale, the projected clustering amplitude decreases with redshift but the co-moving correlation length remains constant; 3. Characteristic halo masses and galaxy bias increase with increasing median stellar mass of the sample; 4. The slope of these relationships is modified in lower mass haloes; 5. Concerning the passive galaxy population, characteristic halo masses are consistent with a simply less-abundant version of the full galaxy sample, but at lower redshifts the fraction of satellite galaxies in the passive population is very different from the full galaxy sample; 6. Finally we find that the ratio between the characteristic halo mass and median stellar mass at each redshift bin reaches a peak at ${\log(M_h/M_\odot)}\sim12.2$ and the position of this peak remains constant out to $z\sim2$. The behaviour of the full and passively evolving galaxy samples can be understood qualitatively by considering the slow evolution of the characteristic stellar mass in the redshift range probed by our survey.

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arXiv2014

The role of massive halos in the Star Formation History of the Universe

The most striking feature of the Cosmic Star Formation History (CSFH) of the Universe is a dramatic drop of the star formation (SF) activity, since z~1. In this work we investigate if the very same process of assembly and growth of structures is one of the major drivers of the observed decline. We study the contribution to the CSFH of galaxies in halos of different masses. This is done by studying the total SFR-halo mass-redshift plane from redshift 0 to redshift z~1.6 in a sample of 57 groups and clusters by using the deepest available mid- and far-infrared surveys conducted with Spitzer MIPS and Herschel PACS and SPIRE. Our results show that low mass groups provide a 60-80% contribution to the CSFH at z~1. Such contribution declines faster than the CSFH in the last 8 billion years to less than 10% at z<0.3, where the overall SF activity is sustained by lower mass halos. More massive systems provide only a marginal contribution (<10%) at any epoch. A simplified abundance matching method shows that the large contribution of low mass groups at z~1 is due to a large fraction (>50%) of very massive, highly star forming Main Sequence galaxies. Below z~1 a quenching process must take place in massive halos to cause the observed faster suppression of their SF activity. Such process must be a slow one though, as most of the models implementing a rapid quenching of the SF activity in accreting satellites significantly underpredicts the observed SF level in massive halos at any redshift. Starvation or the transition from cold to hot accretion would provide a quenching timescale of 1 Gyrs more consistent with the observations. Our results suggest a scenario in which, due to the structure formation process, more and more galaxies experience the group environment and, thus, the associated quenching process. This leads to the progressive suppression of their SF activity shaping the CSFH below z~1.

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arXiv2014

The evolution of galaxy star formation activity in massive halos

There is now a large consensus that the current epoch of the Cosmic Star Formation History (CSFH) is dominated by low mass galaxies while the most active phase at 1 ~1, the most IR-luminous galaxies (LIRGs and ULIRGs) are preferentially located in groups, and this is consistent with a reversal of the star-formation rate vs .density anti-correlation observed in the nearby Universe. At these redshifts, group galaxies contribute 60-80% of the CSFH, i.e. much more than at lower redshifts. Below z~1, the comoving number and SFR densities of IR-emitting galaxies in groups decline significantly faster than those of all IR-emitting galaxies. Our results are consistent with a "halo downsizing" scenario and highlight the significant role of "environment" quenching in shaping the CSFH.

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arXiv2014

The evolution of star formation activity in galaxy groups

We study the evolution of the total star formation (SF) activity, total stellar mass and halo occupation distribution in massive halos by using one of the largest X-ray selected sample of galaxy groups with secure spectroscopic identification in the major blank field surveys (ECDFS, CDFN, COSMOS, AEGIS). We provide an accurate measurement of SFR for the bulk of the star-forming galaxies using very deep mid-infrared Spitzer MIPS and far-infrared Herschel PACS observations. For undetected IR sources, we provide a well-calibrated SFR from SED fitting. We observe a clear evolution in the level of SF activity in galaxy groups. The total SF activity in the high redshift groups (0.5<z<1.1) is higher with respect to the low redshift (0.15<z<0.5) sample at any mass by 0.8+/-0.12 dex. A milder difference (0.35+/-0.1 dex) is observed between the low redshift bin and the groups at z~0. We show that the level of SF activity is declining more rapidly in the more massive halos than in the more common lower mass halos. We do not observe any evolution in the halo occupation distribution and total stellar mass- halo mass relations in groups. The picture emerging from our findings suggests that the galaxy population in the most massive systems is evolving faster than galaxies in lower mass halos, consistently with a "halo downsizing" scenario.

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arXiv2014

Regularity underlying complexity: a redshift-independent description of the continuous variation of galaxy-scale molecular gas properties in the mass-star formation rate plane

Star-forming galaxies (SFGs) display a continuous distribution of specific star formation rates (sSFR) which can be approximated by the superposition of two log-normal distributions. The 1st of these encompasses the main sequence (MS) of SFGs, the 2nd one a rarer population of starbursts (SB). We show that the sSFR-distribution of SBs can be regarded as the result of a physical process (plausibly merging) taking the mathematical form of a log-normal boosting kernel and enhancing star formation activity. We explore the utility of splitting the star-forming population into MS and SB galaxies - an approach we term "2-Star Formation Mode" (2-SFM) framework - for understanding their molecular gas properties. Variations of star formation efficiency (SFE) and gas fractions among SFGs take a simple, redshift-independent form, once these quantities are normalized to the value of an average MS galaxy. The change in SFE for galaxies undergoing a starburst event scales supra-linearly with the SFR-increase, as expected for mergers. This implies a continuous distribution of galaxies in the Schmidt-Kennicutt plane that separates more clearly into loci for SBs and normal galaxies than observed in SFR vs. M* space. SBs with the largest deviations (>10-fold) from the MS, like many local ULIRGs, are not average SBs, but even rarer events with progenitors having larger gas fractions than typical MS galaxies. We statistically infer that the gas fractions of typical SBs decrease by a factor of 2 to 3 with respect to their direct MS progenitors, as expected to occur in short-term SFR-boosts during which internal gas reservoirs are drained more quickly than gas is accreted from the cosmic web. We predict variations of the CO-to-H2 conversion factor in the SFR-M* plane and provide evidence that the higher sSFR of distant galaxies is a direct consequence of larger gas fraction in these systems.

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arXiv2014

Science Case and Requirements for the MOSAIC Concept for a Multi-Object Spectrograph for the European Extremely Large Telescope

Over the past 18 months we have revisited the science requirements for a multi-object spectrograph (MOS) for the European Extremely Large Telescope (E-ELT). These efforts span the full range of E-ELT science and include input from a broad cross-section of astronomers across the ESO partner countries. In this contribution we summarise the key cases relating to studies of high-redshift galaxies, galaxy evolution, and stellar populations, with a more expansive presentation of a new case relating to detection of exoplanets in stellar clusters. A general requirement is the need for two observational modes to best exploit the large (>40 sq. arcmin) patrol field of the E-ELT. The first mode ('high multiplex') requires integrated-light (or coarsely resolved) optical/near-IR spectroscopy of >100 objects simultaneously. The second ('high definition'), enabled by wide-field adaptive optics, requires spatially-resolved, near-IR of >10 objects/sub-fields. Within the context of the conceptual study for an ELT-MOS called MOSAIC, we summarise the top-level requirements from each case and introduce the next steps in the design process.

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arXiv2014

Planck 2013 results. I. Overview of products and scientific results

The ESA's Planck satellite, dedicated to studying the early Universe and its subsequent evolution, was launched 14 May 2009 and has been scanning the microwave and submillimetre sky continuously since 12 August 2009. This paper gives an overview of the mission and its performance, the processing, analysis, and characteristics of the data, the scientific results, and the science data products and papers in the release. The science products include maps of the CMB and diffuse extragalactic foregrounds, a catalogue of compact Galactic and extragalactic sources, and a list of sources detected through the SZ effect. The likelihood code used to assess cosmological models against the Planck data and a lensing likelihood are described. Scientific results include robust support for the standard six-parameter LCDM model of cosmology and improved measurements of its parameters, including a highly significant deviation from scale invariance of the primordial power spectrum. The Planck values for these parameters and others derived from them are significantly different from those previously determined. Several large-scale anomalies in the temperature distribution of the CMB, first detected by WMAP, are confirmed with higher confidence. Planck sets new limits on the number and mass of neutrinos, and has measured gravitational lensing of CMB anisotropies at greater than 25 sigma. Planck finds no evidence for non-Gaussianity in the CMB. Planck's results agree well with results from the measurements of baryon acoustic oscillations. Planck finds a lower Hubble constant than found in some more local measures. Some tension is also present between the amplitude of matter fluctuations derived from CMB data and that derived from SZ data. The Planck and WMAP power spectra are offset from each other by an average level of about 2% around the first acoustic peak.

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arXiv2014

Planck 2013 results. XXIX. Planck catalogue of Sunyaev-Zeldovich sources

We describe the all-sky Planck catalogue of clusters and cluster candidates derived from Sunyaev--Zeldovich (SZ) effect detections using the first 15.5 months of Planck satellite observations. The catalogue contains 1227 entries, making it over six times the size of the Planck Early SZ (ESZ) sample and the largest SZ-selected catalogue to date. It contains 861 confirmed clusters, of which 178 have been confirmed as clusters, mostly through follow-up observations, and a further 683 are previously-known clusters. The remaining 366 have the status of cluster candidates, and we divide them into three classes according to the quality of evidence that they are likely to be true clusters. The Planck SZ catalogue is the deepest all-sky cluster catalogue, with redshifts up to about one, and spans the broadest cluster mass range from (0.1 to 1.6) 10^{15}Msun. Confirmation of cluster candidates through comparison with existing surveys or cluster catalogues is extensively described, as is the statistical characterization of the catalogue in terms of completeness and statistical reliability. The outputs of the validation process are provided as additional information. This gives, in particular, an ensemble of 813 cluster redshifts, and for all these Planck clusters we also include a mass estimated from a newly-proposed SZ-mass proxy. A refined measure of the SZ Compton parameter for the clusters with X-ray counter-parts is provided, as is an X-ray flux for all the Planck clusters not previously detected in X-ray surveys.

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