David Elbaz

The intense starburst HDF 850.1 in a galaxy overdensity at z ≈ 5.2 in the Hubble Deep Field

The Hubble Deep Field provides one of the deepest multiwavelength views of the distant Universe and has led to the detection of thousands of galaxies seen throughout cosmic time. An early map of the Hubble Deep Field at a wavelength of 850u2009micrometres, which is sensitive to dust emission powered by star formation, revealed the brightest source in the field, dubbed HDFu2009850.1 (ref. 2). For more than a decade, and despite significant efforts, no counterpart was found at shorter wavelengths, and it was not possible to determine its redshift, size or mass. Here we report a redshift of z = 5.183 for HDFu2009850.1, from a millimetre-wave molecular line scan. This places HDFu2009850.1 in a galaxy overdensity at zu2009≈u20095.2, corresponding to a cosmic age of only 1.1u2009billion years after the Big Bang. This redshift is significantly higher than earlier estimates and higher than those of most of the hundreds of submillimetre-bright galaxies identified so far. The source has a star-formation rate of 850 solar masses per year and is spatially resolved on scales of 5 kiloparsecs, with an implied dynamical mass of about 1.3u2009×u20091011 solar masses, a significant fraction of which is present in the form of molecular gas. Despite our accurate determination of redshift and position, a counterpart emitting starlight remains elusive.

The suppression of star formation by powerful active galactic nuclei.

The old, red stars that constitute the bulges of galaxies, and the massive black holes at their centres, are the relics of a period in cosmic history when galaxies formed stars at remarkable rates and active galactic nuclei (AGN) shone brightly as a result of accretion onto black holes. It is widely suspected, but unproved, that the tight correlation between the mass of the black hole and the mass of the stellar bulge results from the AGN quenching the surrounding star formation as it approaches its peak luminosity. X-rays trace emission from AGN unambiguously, whereas powerful star-forming galaxies are usually dust-obscured and are brightest at infrared and submillimetre wavelengths. Here we report submillimetre and X-ray observations that show that rapid star formation was common in the host galaxies of AGN when the Universe was 2–6 billion years old, but that the most vigorous star formation is not observed around black holes above an X-ray luminosity of 1044 ergs per second. This suppression of star formation in the host galaxy of a powerful AGN is a key prediction of models in which the AGN drives an outflow, expelling the interstellar medium of its host and transforming the galaxy’s properties in a brief period of cosmic time.

Submillimetre galaxies reside in dark matter haloes with masses greater than 3 × 10 11 solar masses

The extragalactic background light at far-infrared wavelengths comes from optically faint, dusty, star-forming galaxies in the Universe with star formation rates of a few hundred solar masses per year. These faint, submillimetre galaxies are challenging to study individually because of the relatively poor spatial resolution of far-infrared telescopes. Instead, their average properties can be studied using statistics such as the angular power spectrum of the background intensity variations. A previous attempt at measuring this power spectrum resulted in the suggestion that the clustering amplitude is below the level computed with a simple ansatz based on a halo model. Here we report excess clustering over the linear prediction at arcminute angular scales in the power spectrum of brightness fluctuations at 250, 350 and 500u2009μm. From this excess, we find that submillimetre galaxies are located in dark matter haloes with a minimum mass, Mmin, such that log10[Mmin/M⊙] = at 350u2009μm, where M⊙ is the solar mass. This minimum dark matter halo mass corresponds to the most efficient mass scale for star formation in the Universe, and is lower than that predicted by semi-analytical models for galaxy formation.

The Herschel Multi-tiered Extragalactic Survey: SPIRE–mm photometric redshifts

We investigate the potential of submmmm and submmmmradio photometric redshifts using a sample of mm-selected sources as seen at 250, 350 and 500 mu m by the SPIRE instrument on Herschel. From a sample of 63 previously identified mm sources with reliable radio identifications in the Great Observatories Origins Deep Survey North and Lockman Hole North fields, 46 (73 per cent) are found to have detections in at least one SPIRE band. We explore the observed submm/mm colour evolution with redshift, finding that the colours of mm sources are adequately described by a modified blackbody with constant optical depth tau=(/nu0)beta, where beta=+1.8 and nu 0=c/100 mu m. We find a tight correlation between dust temperature and IR luminosity. Using a single model of the dust temperature and IR luminosity relation, we derive photometric redshift estimates for the 46 SPIRE-detected mm sources. Testing against the 22 sources with known spectroscopic or good quality optical/near-IR photometric redshifts, we find submm/mm photometric redshifts offer a redshift accuracy of vertical bar Delta z vertical bar/(1+z)= 0.16 (textlessvertical bar Delta z vertical bar textgreater=0.51). Including constraints from the radiofar-IR correlation, the accuracy is improved to vertical bar Delta z vertical bar/(1+z)=0.15 (textlessvertical bar Delta z vertical bar textgreater=0.45). We estimate the redshift distribution of mm-selected sources finding a significant excess at z textgreater 3 when compared to similar to 850 mu m selected samples.

Herschel deep far-infrared counts through Abell 2218 cluster-lens

Gravitational lensing by massive galaxy clusters allows study of the population of intrinsically faint infrared galaxies that lie below the sensitivity and confusion limits of current infrared and submillimeter telescopes. We present ultra-deep PACS 100 and 160 μm observations toward the cluster lens Abell 2218 to penetrate the Herschel confusion limit. We derive source counts down to a flux density of 1 mJy at 100 μm and 2 mJy at 160 μm, aided by strong gravitational lensing. At these levels, source densities are 20 and 10 beams/source in the two bands, approaching source density confusion at 160 μm. The slope of the counts below the turnover of the Euclidean-normalized differential curve is constrained in both bands and is consistent with most of the recent backwards evolutionary models. By integrating number counts over the flux range accessed by Abell 2218 lensing (0.94−35 mJy at 100 μ ma nd 1.47−35 mJy at 160 μm), we retrieve a cosmic infrared background surface brightness of ∼8.0 and ∼9.9 nW m −2 sr −1 , in the respective bands. These values correspond to 55 ± 24% and 77 ± 31% of DIRBE direct measurements. Combining Abell 2218 results with wider/shallower fields, these figures increase to 62 ± 25% and 88 ± 32% CIB total fractions, resolved at 100 and 160 μm, disregarding the high uncertainties of DIRBE absolute values.

The VANDELS ESO public spectroscopic survey

VANDELS is a uniquely deep spectroscopic survey of high-redshift galaxies with the VIMOS spectrograph on ESO’s Very Large Telescope (VLT). The survey has obtained ultradeep optical (0.48 < λ < 1.0 nμ n nm) spectroscopy of ≃2100 galaxies within the redshift interval 1.0 ≤ z ≤ 7.0, over a total area of ≃0.2 deg2 centred on the CANDELS Ultra Deep Survey and Chandra Deep Field South fields. Based on accurate photometric redshift pre-selection, 85u2009peru2009cent of the galaxies targeted by VANDELS were selected to be at z ≥ 3. Exploiting the red sensitivity of the refurbished VIMOS spectrograph, the fundamental aim of the survey is to provide the high-signal-to-noise ratio spectra necessary to measure key physical properties such as stellar population ages, masses, metallicities, and outflow velocities from detailed absorption-line studies. Using integration times calculated to produce an approximately constant signal-to-noise ratio (20 < tint< 80 h), the VANDELS survey targeted: (a) bright star-forming galaxies at 2.4 ≤ z ≤ 5.5, (b) massive quiescent galaxies at 1.0 ≤ z ≤ 2.5, (c) fainter star-forming galaxies at 3.0 ≤ z ≤ 7.0, and (d) X-ray/Spitzer-selected active galactic nuclei and Herschel-detected galaxies. By targeting two extragalactic survey fields with superb multiwavelength imaging data, VANDELS will produce a unique legacy data set for exploring the physics underpinning high-redshift galaxy evolution. In this paper, we provide an overview of the VANDELS survey designed to support the science exploitation of the first ESO public data release, focusing on the scientific motivation, survey design, and target selection.

Molecular gas, dust, and star formation in galaxies: I. Dust properties and scalings in ~ 1600 nearby galaxies

Context. Dust and its emission is increasingly being used to constrain the evolutionary stage of a galaxy. A comprehensive characterization of dust, best achieved in nearby bright galaxies, is thus a highly useful resource. Aims. We aim to characterize the relationship between dust properties (mass, luminosity, and temperature) and their relationships with galaxy-wide properties (stellar, atomic, and molecular gas mass, and star formation mode). We also aim to provide equations to accurately estimate dust properties from limited observational datasets. Methods. We assemble a sample of 1630 nearby ( z M ∗ ), star formation rates (SFR) and specific star formation rates ( sSFR = SFR / M ∗ ) – for which comprehensive and uniform multi-wavelength observations are available from WISE, IRAS, Planck , and/or SCUBA. The characterization of dust emission comes from spectral energy distribution (SED) fitting using Draine & Li (2007, ApJ, 657, 810) dust models, which we parametrize using two components (warm at 45–70 K and cold at 18–31 K). 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. Results. The total infrared luminosity ( L IR ), dust mass ( M dust ), and dust temperature of the cold component ( T cold ) form a plane that we refer to as the dust plane . A galaxy’s sSFR drives its position on the dust plane: starburst (high sSFR) galaxies show higher L IR , M dust , and T cold compared to main sequence (typical sSFR) and passive galaxies (low sSFR). Starburst galaxies also show higher specific dust masses ( M dust / M ∗ ) and specific gas masses ( M gas / M ∗ ). We confirm earlier findings of an anti-correlation between the dust to stellar mass ratio and M ∗ . We also find different anti-correlations depending on sSFR; the anti-correlation becomes stronger as the sSFR increases, with the spread due to different cold dust temperatures. The dust mass is more closely correlated with the total gas mass (atomic plus molecular) than with the individual atomic and molecular gas masses. Our comprehensive multiwavelength data allows us to define several equations to accurately estimate L IR , M dust , and T cold from one or two monochromatic luminosities in the infrared and/or sub-millimeter. Conclusions. It is possible to estimate the dust mass and infrared luminosity from a single monochromatic luminosity within the Rayleigh-Jeans tail of the dust emission, with errors of 0.12 and 0.20 dex, respectively. These errors are reduced to 0.05 and 0.10 dex, respectively, if the dust temperature of the cold component is used. The dust mass is better correlated with the total ISM mass ( M ISM u2009∝ M dust 0.7 ). For galaxies with stellar masses 8.5 M ∗ / M ⊙ ) μ m and the total ISM mass ( α 850 μ m ) shows a large scatter (rms = 0.29 dex) and a weak correlation with the L IR . The star formation mode of a galaxy shows a correlation with both the gas mass and dust mass: the dustiest (high M dust / M ∗ ) galaxies are gas-rich and show the highest SFRs.

Lyman break and ultraviolet-selected galaxies at z similar to 1-II. PACS 100 mu m/160 mu m FIR detections

We report the PACS-100um/160um detections of a sample of 42 GALEX-selected and FIR-detected Lyman break galaxies (LBGs) at z ~ 1 located in the COSMOS field and analyze their ultra-violet (UV) to far-infrared (FIR) properties. The detection of these LBGs in the FIR indicates that they have a dust content high enough so that its emission can be directly detected. According to a spectral energy distribution (SED) fitting with stellar population templates to their UV-to-near-IR observed photometry, PACS-detected LBGs tend to be bigger, more massive, dustier, redder in the UV continuum, and UV-brighter than PACS-undetected LBGs. PACS-detected LBGs at z ~ 1 are mostly disk-like galaxies and are located over the green-valley and red sequence of the color-magnitude diagram of galaxies at their redshift. By using their UV and IR emission, we find that PACS-detected LBGs tend to be less dusty and have slightly higher total star-formation rates (SFRs) than other PACS-detected UV-selected galaxies within their same redshift range. As a consequence of the selection effect due to the depth of the FIR observations employed, all our PACS-detected LBGs are LIRGs. However, none of them are in the ULIRG regime, where the FIR observations are complete. The finding of ULIRGs-LBGs at higher redshifts suggests an evolution of the FIR emission of LBGs with cosmic time. In an IRX-

A Deep-Wide Far-Infrared Survey of Cosmological Star Formation and AGN Activity

beta

On the missing heavily obscured AGN population

diagram, PACS-detected LBGs at z ~ 1 tend to be located around the relation for local starburst similarly to other UV-selected PACS-detected galaxies at their same redshift. Consequently, the dust-correction factors obtained with their UV continuum slope allow to determine their total SFR, unlike at higher redshifts. However, the dust attenuation derived from UV to NIR SED fitting overestimates the total SFR for most of our PACS-detected LBGs in age-dependent way: the overestimation factor is higher in younger galaxies.