C. Feruglio

DEEP SPITZER 24 μm COSMOS IMAGING. I. THE EVOLUTION OF LUMINOUS DUSTY GALAXIES—CONFRONTING THE MODELS

We present the first results obtained from the identification of ~30,000 sources in the Spitzer/24 μm observations of the COSMOS field at S_(24 μm) ≳ 80 μJy. Using accurate photometric redshifts (σ_ z ~ 0.12 at z ~ 2 for 24 μm sources with i ^+ ≳ 25 mag AB) and simple extrapolations of the number counts at faint fluxes, we resolve with unprecedented detail the buildup of the mid-infrared background across cosmic ages. We find that ~50% and ~80% of the 24 μm background intensity originate from galaxies at z ≳ 1 and z ≳ 2, respectively, supporting the scenario where highly obscured sources at very high redshifts (z ≳ 2) contribute only marginally to the cosmic infrared background. Assuming flux-limited selections at optical wavelengths, we also find that the fraction of i ^+-band sources with 24 μm detection strongly increases up to z ~ 2 as a consequence of the rapid evolution that star-forming galaxies have undergone with look-back time. Nonetheless, this rising trend shows a clear break at z ~ 1.3, probably due to k-correction effects implied by the complexity of spectral energy distributions in the mid-infrared. Finally, we compare our results with the predictions from different models of galaxy formation. We note that semianalytical formalisms currently fail to reproduce the redshift distributions observed at 24 μm. Furthermore, the simulated galaxies at S _(24 μm) > 80 μJy exhibit R–K colors much bluer than observed and the predicted K-band fluxes are systematically underestimated at z ≳ 0.5. Unless these discrepancies mainly result from an incorrect treatment of extinction in the models they may reflect an underestimate of the predicted density of high-redshift massive sources with strong ongoing star formation, which would point to more fundamental processes and/or parameters (e.g., initial mass function, critical density to form stars, feedback,...) that are still not fully controlled in the simulations. The most recent backward evolution scenarios reproduce reasonably well the flux/redshift distribution of 24 μm sources up to z ~ 3, although none of them is able to exactly match our results at all redshifts.

Millimeter imaging of submillimeter galaxies in the COSMOS field: redshift distribution

We present new IRAM Plateau de Bure interferometer (PdBI) 1.3 mm continuum observations at similar to 1.5 ` resolution of 28 submillimeter galaxies (SMGs), previously discovered with the 870 mu m bolometer LABOCA at the APEX telescope from the central 0.7 deg(2) of the COSMOS field. Nineteen out of the 28 LABOCA sources were detected with PdBI at a greater than or similar to 3 sigma level of approximate to 1.4 mJy/beam. A combined analysis of this new sample with existing interferometrically identified SMGs in the COSMOS field yields the following results: i) greater than or similar to 15%, and possibly up to similar to 40% of single-dish detected SMGs consist of multiple sources; ii) statistical analysis of multi-wavelength counterparts to single-dish SMGs shows that only similar to 50% have real radio or IR counterparts; iii) similar to 18% of interferometric SMGs have either no multi-wavelength counterpart or only a radio-counterpart; and iv) similar to 50-70% of z greater than or similar to 3 SMGs have no radio counterparts (down to an rms of 7-12 mu Jy at 1.4 GHz). Using the exact interferometric positions to identify the multi-wavelength counterparts allows us to determine accurate photometric redshifts for these sources. The redshift distributions of the combined and the individual 1.1 mm and 870 mu m selected samples shows a higher mean and a broader width than those derived in previous studies. This study finds that on average brighter and/or mm-selected SMGs are located at higher redshifts, consistent with previous studies. The mean redshift for the 1.1 mm selected sample ((z) over bar = 3.1 +/- 0.4) is tentatively higher than that for the 870 mu m selected sample ((z) over bar = 2.6 +/- 0.4). Based on our nearly complete sample of AzTEC 1.1 mm SMGs in a 0.15 deg(2) area, we infer a higher surface density of z greater than or similar to 4 SMGs than predicted by current cosmological models. In summary, our findings imply that interferometric identifications at (sub-) millimeter wavelengths are crucial to build statistically complete and unbiased samples of SMGs.

NGC 6240: extended CO structures and their association with shocked gas

We present deep CO(1–0) observations of NGC 6240 performed with the IRAM Plateau de Bure Interferometer (PdBI). NGC 6240 is the prototypical example of a major galaxy merger in progress, caught at an early stage, with an extended, strongly-disturbed butterfly-like morphology and a heavily obscured active nucleus in the core of each progenitor galaxy. The CO line shows a skewed profile with very broad and asymmetric wings detected out to velocities of −600 km s −1 and +800 km s −1 with respect to the systemic velocity. The PdBI maps reveal two prominent structures of blueshifted CO emission. One extends eastward, i.e. approximately perpendicular to the line connecting the galactic nuclei, on scales of ∼7 kpc, and it shows velocities up to −400 km s −1 . The other extends southwestward out to ∼7 kpc from the nuclear region, and has a velocity of −100 km s −1 with respect to the systemic one. Interestingly, redshifted emission with velocities 400 to 800 km s −1 is detected around the two nuclei, extending in the east-west direction, and partly overlapping with the eastern blueshifted structure, although tracing a more compact region of size ∼1.7 kpc. The overlap between the southwestern CO blob and the dust lanes seen in HST images, which are interpreted as tidal tails, indicates that the molecular gas is deeply affected by galaxy interactions. The eastern blueshifted CO emission is cospatial with an Hα filament that is associated with strong H2 and soft X-ray emission. The analysis of Chandra X-ray data provides strong evidence of shocked gas at the position of the Hα emission. Its association with outflowing molecular gas supports a scenario where the molecular gas is compressed into a shock wave that propagates eastward from the nuclei. If this is an outflow, the active galactic nuclei are very likely the driving force.

A HIGHER EFFICIENCY OF CONVERTING GAS TO STARS PUSHES GALAXIES AT z ∼ 1.6 WELL ABOVE THE STAR-FORMING MAIN SEQUENCE

Local starbursts have a higher efficiency of converting gas into stars, as compared to typical star-forming galaxies at a given stellar mass, possibly indicative of different modes of star formation. With the peak epoch of galaxy formation occurring at z > 1, it remains to be established whether such an efficient mode of star formation is occurring at high redshift. To address this issue, we measure the molecular gas content of seven high-redshift (z ˜ 1.6) starburst galaxies with the Atacama Large Millimeter/submillimeter Array and IRAM/Plateau de Bure Interferometer. Our targets are selected from the sample of Herschel far-infrared-detected galaxies having star formation rates (˜300-800 M⊙ yr-1) elevated (≳4×) above the star-forming main sequence (MS) and included in the FMOS-COSMOS near-infrared spectroscopic survey of star-forming galaxies at z ˜ 1.6 with Subaru. We detect CO emission in all cases at high levels of significance, indicative of high gas fractions (˜30%-50%). Even more compelling, we firmly establish with a clean and systematic selection that starbursts, identified as MS outliers, at high redshift generally have a lower ratio of CO to total infrared luminosity as compared to typical MS star-forming galaxies, although with a smaller offset than expected based on past studies of local starbursts. We put forward a hypothesis that there exists a continuous increase in star formation efficiency with elevation from the MS with galaxy mergers as a possible physical driver. Along with a heightened star formation efficiency, our high-redshift sample is similar in other respects to local starbursts, such as being metal rich and having a higher ionization state of the interstellar medium.

(Sub)millimetre interferometric imaging of a sample of COSMOS/AzTEC submillimetre galaxies. I. Multiwavelength identifications and redshift distribution

We used the Plateau de Bure Interferometer (PdBI) to map a sample of 15 submillimetre galaxies (SMGs) in the COSMOS field at the wavelength of 1.3 mm. The target SMGs were originally discovered in the James Clerk Maxwell Telescope (JCMT)/AzTEC 1.1 mm continuum survey at S/N_(1.1 mm) = 4−4.5. This paper presents, for the first time, interferometric millimetre-wavelength observations of these sources. The angular resolution of our observations, ~1.8, allowed us to accurately determine the positions of the target SMGs. Using a detection threshold of S/N_(1.3 mm)> 4.5 regardless of multiwavelength counterpart association, and 4 <S/N_(1.3 mm) ≤ 4.5 if a multiwavelength counterpart within 1.5 is also present, the total number of detections in our survey is 22. The most significant PdBI detection of S/N_(1.3 mm) = 10.3 is towards AzTEC19. Three of our detected SMGs (AzTEC21, 27, and 28; which corresponds to 20%) are marginally resolved at our angular resolution, and these sources are found to have elongated or clumpy morphologies and/or multiple components. Using optical to near-infrared photometric redshifts, available spectroscopic redshifts, and redshifts estimated from the radio-to-submm spectral index we infer a median redshift of z = 3.20 ± 0.25 for our sample. To study the overall multiplicity and redshift distribution of flux-limited samples of SMGs we combined these sources with the 15 brightest JCMT/AzTEC SMGs detected at 1.1 mm, AzTEC1−15, and studied previously. This constitutes a complete, flux- and S/N-limited 1.1-mm selected sample. We find that the median redshift for the 15 brightest JCMT/AzTEC SMGs (z = 3.05 ± 0.44) is consistent with that for AzTEC16−30. This conforms to recent observational findings that SMGs do not exhibit any significant trend between the redshift and (sub)mm flux density. For the combined AzTEC1−30 sample we derive a median redshift of z = 3.17 ± 0.27, consistent with previous results based on mm-selected samples. We further infer that within the combined AzTEC1−30 sample ~25 ± 9% of sources separate into multiple components.

High resolution mapping of CO(1–0) in NGC 6240

We present high spatial resolution CO(1-0) mapping of the luminous infrared galaxy NGC6240 obtained with the IRAM - Plateau de Bure Interferometer. This source is a well-known early-stage merging system hosting two AGN. We find a broad CO(1-0) line profile, with maximum velocity 800 km/s and FWZI=1400 km/s, and displaying several kinematic components, revealing the complexity of the gas dynamics in this system. We detect a blueshifted CO emission with velocity in the range -200 and -500 km/s, peaked around the southern AGN, at the same position where the H2 outflow is located, and with a mass loss rate of ~500 Msun/yr. We interpret this blueshifted component as a outflow, originating from the southern nucleus. The spatial and spectral match strongly suggests that the CO outflow is connected to the H2 superwind located around the southern nucleus, and to the large scale CO outflow, with similar velocities, extended on scales of 10 kpc. The large mass loading factor (dM/dt /SFR ~ 10) of the molecular gas suggests that the outflow is likely driven by both SNa winds and the radiation of the southern AGN. We discovered a nuclear, redshifted CO emission peaking in the mid point of the two nuclei, as it is the case for the CO emission at the systemic velocity. The large velocity dispersion, which reaches its maximum (~500 Km/s) in the mid point between the two nuclei, suggests that the gas might be highly turbulent in this region, although the presence of an unresolved rotation component cannot be ruled out.

Gas reservoir of a hyper-luminous quasar at z = 2.6

Context. Understanding the relationship between the formation and evolution of galaxies and their central super-massive black holes (SMBH) is one of the main topics in extragalactic astrophysics. Links and feedback may reciprocally affect both black hole and galaxy growth.Aims. Observations of the CO line at the main epoch of galaxy and SMBH assembly (z = 2−4) are crucial to investigating the gas mass, star formation, and accretion onto SMBHs, and the effect of AGN feedback. Potential correlations between AGN and host galaxy properties can be highlighted by observing extreme objects.Methods. We targeted CO(3–2) in ULAS J1539+0557, a hyper-luminous quasar (Lbol > 1048 erg/s) at z = 2.658, selected through its unusual red colour in the UKIDSS Large Area Survey (ULAS).Results. We find a molecular gas mass of 4.1 ± 0.8 × 1010 M⊙, by adopting a conversion factor α = 0.8 M⊙ K-1 km s-1 pc2, and a gas fraction of ~0.4−0.1, depending mostly on the assumed source inclination. We also find a robust lower limit to the star-formation rate (SFR = 250−1600 M⊙/yr) and star-formation efficiency (SFE = 25−350 L⊙/(Ku2009kmu2009s-1u2009pc2) by comparing the observed optical-near-infrared spectral energy distribution with AGN and galaxy templates. The black hole gas consumption timescale, M(H2) /Ṁacc, is ~160 Myr, similar to or higher than the gas consumption timescale.Conclusions. The gas content and the star formation efficiency are similar to those of other high-luminosity, highly obscured quasars, and at the lower end of the star-formation efficiency of unobscured quasars, in line with predictions from AGN-galaxy co-evolutionary scenarios. Further measurements of the (sub)mm continuum in this and similar sources are mandatory to obtain a robust observational picture of the AGN evolutionary sequence.

The ESO-Spitzer Imaging extragalactic Survey (ESIS)II. VIMOS I, z wide field imaging of ELAIS-S1 and selection of distant massive galaxies

Context. The ESO-Spitzer Imaging extragalactic Survey (ESIS) is the optical follow up of the Spitzer Wide-area Infra-Red Extragalactic survey (SWIRE) in the ELAIS-S1 region of the sky. n nAims. In the era of observational cosmology, the main efforts are focused on the study of galaxy evolution and its environmental dependence. Wide area, multiwavelength, extragalactic surveys are needed in order to probe sufficiently large volumes, minimize cosmic variance and find significant numbers of rare objects. n nMethods. We present VIMOS I and z band imaging belonging to the ESIS survey. A total of ~4 deg^2 was targeted in I and ~1 deg^2 in z. Accurate data processing includes removal of fringing, and mosaicking of the complex observing pattern. Completeness levels and photometric uncertainties are estimated through simulations. The multi-wavelength data available in the area are exploited to identify high-redshift galaxies, using the IR-peak technique. nResults. More than 300 000 galaxies have been detected in the I band and ~50 000 in the z band. Object coordinates are defined within an uncertainty of ~0.2 arcsec rms, with respect to GSC 2.2. We reach a 90% average completeness at 23.1 and 22.5 mag (Vega) in the I and z bands, respectively. On the basis of IRAC colors, we identify galaxies having the 1.6

ALMA suggests outflows in z ∼ 5.5 galaxies

mu

The WISSH quasars project IV. Broad line region versus kiloparsec-scale winds

m stellar peak shifted to z = 1-3. The new I, z band data provide reliable constraints to help avoid low-redshift interlopers and reinforce this selection. Roughly 1000 galaxies between z = 2-3 are identified over the ESIS ~4 deg^2, at the SWIRE 5.8