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Aims. We present the X-ray imaging and spectral analysis of the diffuse emission around the radio galaxy J1140-2629 (the Spiderweb galaxy) at z = 2.16 and of its nuclear emission, based on a deep (700 ks) Chandra observation. Methods. We obtained a robust characterization of the unresolved nuclear emission, and carefully computed the contamination in the surrounding regions due to the wings of the instrument point spread function. Then, we quantified the extended emission within a radius of 12 arcsec. We used the Jansky Very Large Array radio image to identify the regions overlapping the jets, and performed X-ray spectral analysis separately in the jet regions and in the complementary area. Results. We find that the Spiderweb galaxy hosts a mildly absorbed quasar, showing a modest yet significant spectral and flux variability on a timescale of ∼1 year (observed frame). We find that the emission in the jet regions is well described by a power law with a spectral index of Γ ∼ 2 − 2.5, and it is consistent with inverse-Compton upscattering of the cosmic microwave background photons by the relativistic electrons. We also find a roughly symmetric, diffuse emission within a radius of ∼100 kpc centered on the Spiderweb galaxy. This emission, which is not associated with the jets, is significantly softer and consistent with thermal bremsstrahlung from a hot intracluster medium (ICM) with a temperature of kT = 2.0−0.4+0.7 k T = 2. 0 − 0.4 + 0.7 $ kT = 2.0_{-0.4}^{+0.7} $ keV, and a metallicity of Z <  1.6 Z⊙ at 1σ c.l. The average electron density within 100 kpc is ne = (1.51  ±  0.24 ± 0.14) × 10−2 cm−3, corresponding to an upper limit for the total ICM mass of ≤(1.76  ±  0.30  ±  0.17) × 1012 M⊙ (where error bars are 1σ statistical and systematic, respectively). The rest-frame luminosity L0.5 − 10 keV = (2.0 ± 0.5) × 1044 erg s−1 is about a factor of 2 higher than the extrapolated L − T relation for massive clusters, but still consistent within the scatter. If we apply hydrostatic equilibrium to the ICM, we measure a total gravitational mass M(<100 kpc) = (1.5−0.3+0.5) × 1013 M⊙ M (< 100 kpc) = (1. 5 − 0.3 + 0.5) × 10 13 M ⊙ $ M({ and, extrapolating at larger radii, we estimate a total mass M500 = (3.2−0.6+1.1) × 1013 M⊙ M 500 = (3. 2 − 0.6 + 1.1) × 10 13 M ⊙ $ M_{500} = (3.2^{+1.1}_{-0.6})\times 10^{13}\, M_\odot $ within a radius of r500 = (220 ± 30) kpc. Conclusions. We conclude that the Spiderweb protocluster shows significant diffuse emission within a radius of 12 arcsec, whose major contribution is provided by inverse-Compton scattering associated with the radio jets. Outside the jet regions, we also identified thermal emission within a radius of ∼100 kpc, revealing the presence of hot, diffuse baryons that may represent the embryonic virialized halo of the forming cluster. [ABSTRACT FROM AUTHOR]

Using the IRAM NOrthern Extended Millimeter Array (NOEMA), we conducted a program to measure redshifts for 13 bright galaxies detected in the Herschel Astrophysical Large Area Survey with S 500 μm ≥ 80 mJy. We report reliable spectroscopic redshifts for 12 individual sources, which are derived from scans of the 3 and 2mm bands, covering up to 31 GHz in each band, and are based on the detection of at least two emission lines. The spectroscopic redshifts are in the range 2:08 < z < 4:05 with a median value of z = 2.9 ± 0.6. The sources are unresolved or barely resolved on scales of 10 kpc. In one field, two galaxies with different redshifts were detected. In two cases the sources are found to be binary galaxies with projected distances of ~140 kpc. The linewidths of the sources are large, with a mean value for the full width at half maximum of 700 ± 300 km s-1 and a median of 800 km s-1. We analyze the nature of the sources with currently available ancillary data to determine if they are lensed or hyper-luminous (LFIR > 1013 L) galaxies. We also present a reanalysis of the spectral energy distributions including the continuum flux densities measured at 3 and 2mm to derive the overall properties of the sources. Future prospects based on these efficient measurements of redshifts of high-z galaxies using NOEMA are outlined, including a comprehensive survey of all the brightest Herschel galaxies. [ABSTRACT FROM AUTHOR]

By using data from the Atacama Large Millimeter/submillimeter Array and near-infrared (NIR) integral field spectrographs, including both Spectrograph for INtegral Field Observations in the Near Infrared and K-band Multi Object Spectrograph on the Very Large Telescope, we investigate the two-dimensional distributions of H and rest-frame far-infrared (FIR) continuum in six submillimeter galaxies (SMGs) at z ~ 2. At a similar spatial resolution (~0: 005 FWHM; ~4.5 kpc at z = 2), we find that the half-light radius of Hα is significantly larger than that of the FIR continuum in half of the sample, and on average Hα is a median factor of 2:0 ± 0:4 larger. Having explored various ways to correct for the attenuation, we find that the attenuation-corrected Hα-based star-formation rates (SFRs) are systematically lower than the infrared (IR)-based SFRs by at least a median factor of 3 ± 1, which cannot be explained by the diαerence in half-light radius alone. In addition, we find that in 40% of cases the total V-band attenuation (AV) derived from energy balance modeling of the full ultraviolet (UV)-to-FIR spectral energy distributions (SEDs) is significantly higher than what is derived from SED modeling using only the UV-to-NIR part of the SEDs, and the discrepancy appears to increase with increasing total infrared luminosity. Finally, in considering all of our findings along with the studies in the literature, we postulate that the dust distributions in SMGs, and possibly also in less IR luminous z ~ 2 massive star-forming galaxies, can be decomposed into the following three main components: the diαuse dust heated by older stellar populations, the more obscured and extended young star-forming Hii regions, and the heavily obscured central regions that have a low filling factor but dominate the infrared luminosity in which the majority of attenuation cannot be probed via UV-to-NIR emissions. [ABSTRACT FROM AUTHOR]

We investigate the CO excitation of normal (near-IR selected BzK) star-forming (SF) disk galaxies at z = 1.5 using IRAM Plateau de Bure observations of the CO[2-1], CO[3-2], and CO[5-4] transitions for four galaxies, including VLA observations of CO[1-0] for three of them, with the aim of constraining the average state of H2 gas. By exploiting previous knowledge of the velocity range, spatial extent, and size of the CO emission, we measure reliable line fluxes with a signal-to-noise ratio >4-7 for individual transitions. While the average CO spectral line energy distribution (SLED) has a subthermal excitation similar to the Milky Way (MW) up to CO[3-2], we show that the average CO[5-4] emission is four times stronger than assuming MW excitation. This demonstrates that there is an additional component of more excited, denser, and possibly warmer molecular gas. The ratio of CO[5-4] to lower-J CO emission is lower than in local (ultra-)luminous infrared galaxies (ULIRGs) and high-redshift starbursting submillimeter galaxies, however, and appears to be closely correlated with the average intensity of the radiation field (U) and with the star formation surface density, but not with the star formation efficiency. The luminosity of the CO[5-4] transition is found to be linearly correlated with the bolometric infrared luminosity over four orders of magnitudes. For this transition, z = 1.5 BzK galaxies follow the same linear trend as local spirals and (U)LIRGs and high-redshift star-bursting submillimeter galaxies. The CO[5-4] luminosity is thus empirically related to the dense gas and might be a more convenient way to probe it than standard high-density tracers that are much fainter than CO. We see excitation variations among our sample galaxies that can be linked to their evolutionary state and clumpiness in optical rest-frame images. In one galaxy we see spatially resolved excitation variations, where the more highly excited part of the galaxy corresponds to the location of massive SF clumps. This provides support to models that suggest that giant clumps are the main source of the high-excitation CO emission in high-redshift disk-like galaxies. [ABSTRACT FROM AUTHOR]

We present APEX LABOCA 870 μm observations of the field around the high-redshift radio galaxy MRC1138-262 at z = 2.16. We detect 16 submillimeter galaxies (SMGs) in this ∼140 arcmin2 bolometer map with flux densities in the range 3-11 mJy. The raw number counts indicate a density of SMGs that is up to four times that of blank field surveys. Based on an exquisite multiwave-length database, including VLA 1.4 GHz radio and infrared observations, we investigate whether these sources are members of the protocluster structure at z ≈ 2.2. Using Herschel PACS and SPIRE and Spitzer MIPS photometry, we derive reliable far-infrared (FIR) photometric redshifts for all sources. Follow-up VLT ISAAC and SINFONI NIR spectra confirm that four of these SMGs have redshifts of z ≈ 2.2.We also present evidence that another SMG in this field, detected earlier at 850 μm, has a counterpart that exhibits Hα and CO(1-0) emission at z = 2.15. Including the radio galaxy and two SMGs with FIR photometric redshifts at z = 2.2, we conclude that at least eight submm sources are part of the protocluster at z = 2.16 associated with the radio galaxy MRC1138-262. We measure a star formation rate density SFRD ∼1500 M☉ yr-1 Mpc-3, four magnitudes higher than the global SFRD of blank fields at this redshift. Strikingly, these eight sources are concentrated within a region of 2Mpc (the typical size of clusters in the local universe) and are distributed within the filaments traced by the HAEs at z ≈ 2.2. This concentration of massive, dusty starbursts is not centered on the submillimeter-bright radio galaxy which could support the infalling of these sources into the cluster center. Approximately half (6/11) of the SMGs that are covered by the Hα imaging data are associated with HAEs, demonstrating the potential of tracing SMG counterparts with this population. To summarize, our results demonstrate that submillimeter observations may enable us to study (proto)clusters of massive, dusty starbursts. [ABSTRACT FROM AUTHOR]

We measure the dust and gas content of the three submillimeter galaxies (SMGs) in the GN20 proto-cluster at z = 4.05 using new IRAM Plateau de Bure interferometer (PdBI) CO(4-3) and 1.2-3.3 mm continuum observations. All these three SMGs are heavily dust obscured, with UV-based star formation rate (SFR) estimates significantly smaller than the ones derived from the bolometric infrared (IR), consistent with the spatial offsets revealed by HST and CO imaging. Based also on evaluations of the specific SFR, CO-to-H2 conversion factor and gas depletion timescale, we classify all the three galaxies as starbursts (SBs), although with a lower confidence for GN20.2b that might be a later stage merging event. We place our measurements in the context of the evolutionary properties of main sequence (MS) and SB galaxies. ULIRGs have 3-5 times larger L' CO/Mdust and Mdust/M* ratios than z = 0 MS galaxies, but by z ∼ 2 the difference appears to be blurred, probably due to differential metallicity evolution. SB galaxies appear to slowly evolve in their L' CO/Mdust and Mdust/M* ratios all the way to z > 6 (consistent with rapid enrichment of SB events), while MS galaxies rapidly increase in Mdust/M* from z = 0 to 2 (due to gas fraction increase, compensated by a decrease of metallicities). While no IR/submm continuum detection is available for indisputably normal massive galaxies at z > 2.5, we show that if metallicity indeed decrease rapidly for these systems at z > 3 as claimed in the literature, we should expect a strong decrease of their Mdust/M*, consistent with recent PdBI and ALMA upper limits.We conclude that the Mdust/M* ratio could be a powerful tool for distinguishing starbursts from normal galaxies at z > 4. [ABSTRACT FROM AUTHOR]

Deep Herschel PACS/SPIRE imaging and 12CO(2−1) line luminosities from the IRAM Plateau de Bure Interferometer are combined for a sample of 17 galaxies at z > 1 from the GOODS-N field. The sample includes galaxies both on and above the main sequence (MS) traced by star-forming galaxies in the SFR-M∗ plane. The far-infrared data are used to derive dust masses, Mdust, following the Draine & Li (2007, ApJ, 657, 810) models. Combined with an empirical prescription for the dependence of the gas-to-dust ratio on metallicity (δGDR(μ0)), the CO luminosities and Mdust values are used to derive for each galaxy the CO-to-H2 conversion factor, αCO. Like in the local Universe, the value of αCO is a factor of ~5 smaller in starbursts compared to normal star-forming galaxies (SFGs). We additionally uncover a relation between αCO and dust temperature (Tdust; αCO decreasing with increasing Tdust) as obtained from modified blackbody fits to the far-infrared data. While the absolute normalization of the αCO(Tdust) relation is uncertain, the global trend is robust against possible systematic biases in the determination of Mdust, δGDR(μ0) or metallicity. Although we cannot formally distinguish between a step and a smooth evolution of αCO with the dust temperature, we can unambiguously conclude that in galaxies of near-solar metallicity, a critical value of Tdust = 30 K can be used to determine whether the appropriate αCO is closer to the "starburst" value (1.0 Mʘ (K km s-1 pc2)-1, when Tdust > 30 K) or closer to the Galactic value (4.35 Mʘ (K km s-1 pc2)-1, when Tdust < 30 K). This indicator has the great advantage of being less subjective than visual morphological classifications of mergers/SFGs, which can be difficult at high z because of the clumpy nature of SFGs. Using Tdust to select the appropriate αCO is also more indicative of ISM conditions than a fixed LIR criterion. In the absence of far-infrared data, the offset of a galaxy from the star formation main sequence (i.e., Δlog (SSFR)MS = log [SSFR(galaxy)/SSFRMS(M∗,z)]) can be used to identify galaxies requiring the use of an αCO conversion factor lower than the Galactic value (i.e., when Δlog (SSFR)MS ≳ 0.3 dex). [ABSTRACT FROM AUTHOR]

Deep Herschel PACS/SPIRE imaging and 12CO(2-1) line luminosities from the IRAM Plateau de Bure Interferometer are combined for a sample of 17 galaxies at z > 1 from the GOODS-N field. The sample includes galaxies both on and above the main sequence (MS) traced by star-forming galaxies in the SFR-M⋆ plane. The far-infrared data are used to derive dust masses, Mdust, following the Draine & Li (2007, ApJ, 657, 810) models. Combined with an empirical prescription for the dependence of the gas-to-dust ratio on metallicity (δGDR(μ0)), the CO luminosities and Mdust values are used to derive for each galaxy the CO-to-H2 conversion factor, αCO. Like in the local Universe, the value of αCO is a factor of ∼5 smaller in starbursts compared to normal star-forming galaxies (SFGs).We additionally uncover a relation between αCO and dust temperature (Tdust; αCO decreasing with increasing Tdust) as obtained from modified blackbody fits to the far-infrared data. While the absolute normalization of the αCO(Tdust) relation is uncertain, the global trend is robust against possible systematic biases in the determination of Mdust, δGDR(μ0) or metallicity. Although we cannot formally distinguish between a step and a smooth evolution of αCO with the dust temperature, we can unambiguously conclude that in galaxies of near-solar metallicity, a critical value of Tdust = 30 K can be used to determine whether the appropriate αCO is closer to the "starburst" value (1.0 M☉ (K km s-1 pc2)-1, when Tdust > 30K) or closer to the Galactic value (4.35 M☉ (K km s-1 pc2)-1, when Tdust < 30 K). This indicator has the great advantage of being less subjective than visual morphological classifications of mergers/SFGs, which can be difficult at high z because of the clumpy nature of SFGs. Using Tdust to select the appropriate αCO is also more indicative of ISM conditions than a fixed LIR criterion. In the absence of far-infrared data, the offset of a galaxy from the star formation main sequence (i.e., Δlog (SSFR)MS = log[SSFR(galaxy)/SSFRMS(M⋆, z)]) can be used to identify galaxies requiring the use of an αCO conversion factor lower than the Galactic value (i.e., when Δlog (SSFR)MS ≳ 0.3 dex). [ABSTRACT FROM AUTHOR]

We study a sample of 61 submillimetre galaxies (SMGs) selected from ground-based surveys, with known spectroscopic redshifts and observed with the Herschel Space Observatory as part of the PACS Evolutionary Probe (PEP) and the Herschel Multi-tiered Extragalactic Survey (HerMES) guaranteed time key programmes. Our study makes use of the broad far-infrared and submillimetre wavelength coverage (100-600 μm) only made possible by the combination of observations from the PACS and SPIRE instruments aboard the Herschel Space Observatory. Using a power-law temperature distribution model to derive infrared luminosities and dust temperatures, we measure a dust emissivity spectral index for SMGs of β = 2.0 ± 0.2. Our results unambiguously unveil the diversity of the SMG population. Some SMGs exhibit extreme infrared luminosities of ~1013L ☉and relatively warm dust components, while others are fainter (a few times 1012 L☉) and are biased towards cold dust temperatures. Although at z ~ 2 classical SMGs (>5 mJy at 850 μm) have large infrared luminosities (~1013 L☉), objects only selected on their submm flux densities (without any redshift informations) probe a large range in dust temperatures and infrared luminosities. The extreme infrared luminosities of some SMGs (LIR ≲ 1012.7 L☉, 26/61 systems) imply star formation rates (SFRs) of >500 M☉ yr-1 (assuming a Chabrier IMF and no dominant AGN contribution to the FIR luminosity). Such high SFRs are difficult to reconcile with a secular mode of star formation, and may instead correspond to a merger-driven stage in the evolution of these galaxies. Another observational argument in favour of this scenario is the presence of dust temperatures warmer than that of SMGs of lower luminosities (~40 K as opposed to ~25 K), consistent with observations of local ultraluminous infrared galaxies triggered by major mergers and with results from hydrodynamic simulations of major mergers combined with radiative transfer calculations. Moreover, we find that luminous SMGs are systematically offset from normal star-forming galaxies in the stellar mass-SFR plane, suggesting that they are undergoing starburst events with short duty cycles, compatible with the major merger scenario. On the other hand, a significant fraction of the low infrared luminosity SMGs have cold dust temperatures, are located close to the main sequence of star formation, and therefore might be evolving through a secular mode of star formation. However, the properties of this latter population, especially their dust temperature, should be treated with caution because at these luminosities SMGs are not a representative sample of the entire star-forming galaxy population. [ABSTRACT FROM AUTHOR]