The Planck and Herschel missions are currently measuring the far-infrared to millimeter emission of dust, which combined with existing IR data, will for the first time provide the full spectral energy distribution (SED) of the galactic interstellar medium dust emission, from the mid-IR to the mm range, with an unprecedented sensitivity and down to spatial scales ~30”. Such a global SED will allow a systematic study of the dust evolution processes (e.g. grain growth or fragmentation) that directly affect the SED because they redistribute the dust mass among the observed grain sizes. The dust SED is also affected by variations of the radiation field intensity. Here we present a versatile numerical tool, DustEM, that predicts the emission and extinction of dust grains given their size distribution and their optical and thermal properties. In order to model dust evolution, DustEM has been designed to deal with a variety of grain types, structures and size distributions and to be able to easily include new dust physics. We use DustEM to model the dust SED and extinction in the diffuse interstellar medium at high-galactic latitude (DHGL), a natural reference SED that will allow us to study dust evolution. We present a coherent set of observations for the DHGL SED, which has been obtained by correlating the IR and HI-21 cm data. The dust components in our DHGL model are (i) polycyclic aromatic hydrocarbons; (ii) amorphous carbon and (iii) amorphous silicates. We use amorphous carbon dust, rather than graphite, because it better explains the observed high abundances of gas-phase carbon in shocked regions of the interstellar medium. Using the DustEM model, we illustrate how, in the optically thin limit, the IRAS/Planck HFI (and likewise Spitzer/Herschel for smaller spatial scales) photometric band ratios of the dust SED can disentangle the influence of the exciting radiation field intensity and constrain the abundance of small grains (a ⪉ 10 nm) relative to the larger grains. We also discuss the contributions of the different grain populations to the IRAS, Planck (and similarly to Herschel) channels. Such information is required to enable a study of the evolution of dust as well as to systematically extract the dust thermal emission from CMB data and to analyze the emission in the Planck polarized channels. The DustEM code described in this paper is publically available.

Jauzac, M.; Dole, H.; Le Floc'h, E.; Aussel, H.; Caputi, K.; Ilbert, O.; Salvato, M.; Bavouzet, N.; Beelen, A.; Béthermin, M.; Kneib, J.-P.; Lagache, G.; Puget, J.-L. 2011, A&A 525, 52

The cosmic far-infrared background buildup since redshift 2 at 70 and 160 microns in the COSMOS and GOODS fields

Context. The cosmic far-infrared background (CIB) at wavelengths around 160 μm corresponds to the peak intensity of the whole extragalactic background light, which is being measured with increasing accuracy. However, the build up of the CIB emission as a function of redshift is still not well known.

Aims: Our goal is to measure the CIB history at 70 μm and 160 μm at different redshifts, and provide constraints for infrared galaxy evolution models.

Methods: We used deep Spitzer 24 μm catalogs complete to about 80 μJy with spectroscopic and photometric redshift identifications, derived using the GOODS and COSMOS deep infrared surveys covering 2 square degrees total. After cleaning the Spitzer/MIPS 70 μm and 160 μm maps of detected sources, we stacked the far-IR images at the positions of the 24 μm sources in different redshift bins. We measured the contribution of each stacked source to the total 70 and 160 μm light, and compared with model predictions and far-IR measurements obtained for Herschel/PACS data of smaller fields.

Results: We detect components of the 70 and 160 μm backgrounds in different redshift bins up to z ~ 2. The contribution to the CIB reaches a maximum at 0.3 ≤ z ≤ 0.9 at 160 μm (and z ≤ 0.5 at 70 μm). A total of 81% (74%) of the 70 (160) μm background was emitted at z < 1. We estimate that the AGN contribution to the far-IR CIB is less than about 10% at z < 1.5. We provide a comprehensive view of the CIB buildup at 24, 70, 100 and 160 μm.

Conclusions: We find that IR galaxy models predicting a major contribution to the CIB from sources at z < 1 agree with our measurements, while our results exclude other models that predict a peak of the background at higher redshifts. The consistency of our results with those obtained by the direct study of Herschel far-IR data at 160 μm confirms that the stacking analysis method is a valid approach to estimate the components of the far-IR background using prior information about resolved mid-IR sources.

Nesvadba, N. P. H.; De Breuck, C.; Lehnert, M. D.; Best, P. N.; Binette, L.; Proga, D.  2011, A&A 525, 43

The black holes of radio galaxies during the ``Quasar Era'': masses, accretion rates, and evolutionary stage

We present an analysis of the AGN broad-line regions of 6 powerful radio galaxies at z ~ 2 (HzRGs), which is part of a study of a sample of 50 HzRGs with rest-frame optical imaging spectroscopy obtained at the VLT. In 6 galaxies we detect luminous (L(Hα) = few × 10⁴⁴ erg s^-1), spatially unresolved, broad (FWHM ≥ 10 000 km s^-1) Hα line emission from the nucleus (HαBLRs), consistent with broad-line regions of supermassive black holes with masses of few × 10⁹ M_ȯ and accretion luminosities of a few percent of the Eddington luminosity. In two galaxies we also detect HβBLRs, suggesting relatively low extinction of A_V ~ 1 mag, which agrees with constraints from X-ray observations. Overall, we find HαBLRs in ~20% of the galaxies where Hα is observed. By relating black hole and bulge mass, we find a possible offset towards higher black-hole masses of at most ˜0.6 dex relative to nearby galaxies at a given host mass, although each individual galaxy is within the scatter of the local relationship. If not entirely from systematic effects, this would then suggest that the masses of the host galaxies have increased by at most a factor ≈4 since z ˜ 2 2 relative to the black-hole masses, perhaps through accretion of satellite galaxies or because of a time lag between star formation in the host galaxy and AGN fueling. We also compare the radiative and mechanical energy output (from jets) of our targets with predictions of recent models of “synthesis” or “grand unified” AGN feedback, which postulate that AGN with similar radiative and mechanical energy output rates to those found in our HzRGs may be nearing the end of their period of active growth. We discuss evidence that they may reach this stage at the same time as their host galaxies.

In recent decades, a number of molecules and diverse dust features have been identified by astronomical observations in various environments. Most of the dust that determines the physical and chemical characteristics of the interstellar medium is formed in the outflows of asymptotic giant branch stars and is further processed when these objects become planetary nebulae. We studied the environment of Tc 1, a peculiar planetary nebula whose infrared spectrum shows emission from cold and neutral C₆₀ and C₇₀. The two molecules amount to a few percent of the available cosmic carbon in this region. This finding indicates that if the conditions are right, fullerenes can and do form efficiently in space.


J. Grain, A. Barrau, T. Cailleteau, J. Mielczarek, 2010, Phys. Rev. D82 123520

Observing the big bounce with tensor modes in the cosmic microwave background: phenomenology and fundamental LQC paramaters

Cosmological models where the standard big bang is replaced by a bounce have been studied for decades. The situation has, however, dramatically changed in the past years for two reasons: first, because new ways to probe the early Universe have emerged, in particular, thanks to the cosmic microwave background, and second, because some well grounded theories -especially loop quantum cosmology- unambiguously predict a bounce, at least for homogeneous models. In this article, we investigate into the details the phenomenological parameters that could be constrained or measured by next-generation B-mode cosmic micorwave background experiments. We point out that an important observational window could be opened. We then show that those constraints can be converted into very meaningful limits on the fundamental loop quantum cosmology parameters. This establishes the early Universe as an invaluable quantum gravity laboratory.


Ogle, Patrick; Boulanger, Francois; Guillard, Pierre; Evans, Daniel A.; Antonucci, Robert; Appleton, P. N.; Nesvadba, Nicole; Leipski, Christian, 2010, ApJ, 724, 1193

Jet-powered Molecular Hydrogen Emission from Radio Galaxies

H₂ pure-rotational emission lines are detected from warm (100-1500 K) molecular gas in 17/55 (31% of) radio galaxies at redshift z < 0.22 observed with the Spitzer IR Spectrograph. The summed H₂ 0-0 S(0)-S(3) line luminosities are L(H₂) = 7 × 10³⁸-2 × 10⁴² erg s^-1, yielding warm H₂ masses up to 2 × 10¹⁰ M _sun. These radio galaxies, of both FR radio morphological types, help to firmly establish the new class of radio-selected molecular hydrogen emission galaxies (radio MOHEGs). MOHEGs have extremely large H₂ to 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission ratios: L(H₂)/L(PAH7.7) = 0.04-4, up to a factor 300 greater than the median value for normal star-forming galaxies. In spite of large H₂ masses, MOHEGs appear to be inefficient at forming stars, perhaps because the molecular gas is kinematically unsettled and turbulent. Low-luminosity mid-IR continuum emission together with low-ionization emission line spectra indicates low-luminosity active galactic nuclei (AGNs) in all but three radio MOHEGs. The AGN X-ray emission measured with Chandra is not luminous enough to power the H₂ emission from MOHEGs. Nearly all radio MOHEGs belong to clusters or close pairs, including four cool-core clusters (Perseus, Hydra, A2052, and A2199). We suggest that the H₂ in radio MOHEGs is delivered in galaxy collisions or cooling flows, then heated by radio-jet feedback in the form of kinetic energy dissipation by shocks or cosmic rays.

Béthermin, M.; Dole, H.; Cousin, M.; Bavouzet, N., 2010, A&A, 516, 43

Submillimeter number counts at 250 μm, 350 μm and 500 μm in BLAST data

Context. The instrument BLAST (Balloon-borne Large-Aperture Submillimeter Telescope) performed the first deep and wide extragalactic survey at 250, 350 and 500 μm. The extragalactic number counts at these wavelengths are important constraints for modeling the evolution of infrared galaxies.

Aims: We estimate the extragalactic number counts in the BLAST data, which allow a comparison with the results of the P(D) analysis of Patanchon et al. (2009).

Methods: We use three methods to identify the submillimeter sources. 1) Blind extraction using an algorithm when the observed field is confusion-limited and another one when the observed field is instrumental-noise-limited. The photometry is computed with a new simple and quick point spread function (PSF) fitting routine (FASTPHOT). We use Monte-Carlo simulations (addition of artificial sources) to characterize the efficiency of this extraction, and correct the flux boosting and the Eddington bias. 2) Extraction using a prior. We use the Spitzer 24 μm galaxies as a prior to probe slightly fainter submillimeter flux densities. 3) A stacking analysis of the Spitzer 24 μm galaxies in the BLAST data to probe the peak of the differential submillimeter counts.

Results: With the blind extraction, we reach 97 mJy, 83 mJy and 76 mJy at 250 μm, 350 μm and 500 μm respectively with a 95% completeness. With the prior extraction, we reach 76 mJy, 63 mJy, 49 mJy at 250 μm, 350 μm and 500 μm respectively. With the stacking analysis, we reach 6.2 mJy, 5.2 mJy and 3.5 mJy at 250 μm, 350 μm and 500 μm respectively. The differential submillimeter number counts are derived, and start showing a turnover at flux densities decreasing with increasing wavelength.

Conclusions: There is a very good agreement with the P(D) analysis of Patanchon et al. (2009). At bright fluxes (>100 mJy), the Lagache et al. (2004) and Le Borgne et al. (2009) models slightly overestimate the observed counts, but the data agree very well near the peak of the differential number counts. Models predict that the galaxy populations probed at the peak are likely z ~ 1.8 ultra-luminous infrared galaxies.

Béthermin, M.; Dole, H.; Beelen, A.; Aussel, H., 2010, A&A, 512, 78

Spitzer deep and wide legacy mid- and far-infrared number counts and lower limits of cosmic infrared background

Aims: We aim to place stronger lower limits on the cosmic infrared background (CIB) brightness at 24 μm, 70 μm and 160 μm and measure the extragalactic number counts at these wavelengths in a homogeneous way from various surveys.

Methods: Using Spitzer legacy data over 53.6 deg² of various depths, we build catalogs with the same extraction method at each wavelength. Completeness and photometric accuracy are estimated with Monte-Carlo simulations. Number count uncertainties are estimated with a counts-in-cells moment method to take galaxy clustering into account. Furthermore, we use a stacking analysis to estimate number counts of sources not detected at 70 μm and 160 μm. This method is validated by simulations. The integration of the number counts gives new CIB lower limits.

Results: Number counts reach 35 μJy, 3.5 mJy and 40 mJy at 24 μm, 70 μm, and 160 μm, respectively. We reach deeper flux densities of 0.38 mJy at 70, and 3.1 at 160 μm with a stacking analysis. We confirm the number count turnover at 24 μm and 70 μm, and observe it for the first time at 160 μm at about 20 mJy, together with a power-law behavior below 10 mJy. These mid- and far-infrared counts: 1) are homogeneously built by combining fields of different depths and sizes, providing a legacy over about three orders of magnitude in flux density; 2) are the deepest to date at 70 μm and 160 μm; 3) agree with previously published results in the common measured flux density range; 4) globally agree with the Lagache et al. (2004) model, except at 160 μm, where the model slightly overestimates the counts around 20 and 200 mJy.

Conclusions: These counts are integrated to estimate new CIB firm lower limits of 2.29_-0.09^+0.09 nW m^-2 sr^-1, 5.4_-0.4^+0.4 nW m^-2 sr^-1, and 8.9_-1.1^+1.1 nW m^-2 sr^-1 at 24 μm, 70 μm, and 160 μm, respectively, and extrapolated to give new estimates of the CIB due to galaxies of 2.86_-0.16^+0.19 nW m^-2 sr^-1, 6.6_-0.6^+0.7 nW m^-2 sr^-1, and 14.6_-2.9^+7.1 nW m^-2 sr^-1, respectively. Products (point spread function, counts, CIB contributions, software) are publicly available for download at http://www.ias.u-psud.fr/irgalaxies/">http://www.ias.u-psud.fr/irgalaxies/

Lehnert, M. D.; Nesvadba, N. P. H.; Cuby, J.-G.; Swinbank, A. M.; Morris, S.; Clément, B.; Evans, C. J.; Bremer, M. N.; Basa, S., Nature, 467, 940

Spectroscopic confirmation of a galaxy at redshift z = 8.6

Galaxies had their most significant impact on the Universe when they assembled their first generations of stars. Energetic photons emitted by young, massive stars in primeval galaxies ionized the intergalactic medium surrounding their host galaxies, cleared sightlines along which the light of the young galaxies could escape, and fundamentally altered the physical state of the intergalactic gas in the Universe continuously until the present day. Observations of the cosmic microwave background, and of galaxies and quasars at the highest redshifts, suggest that the Universe was reionized through a complex process that was completed about a billion years after the Big Bang, by redshift z~6. Detecting ionizing Lyman-α photons from increasingly distant galaxies places important constraints on the timing, location and nature of the sources responsible for reionization. Here we report the detection of Lyα photons emitted less than 600million years after the Big Bang. UDFy-38135539 (ref. 5) is at a redshift of z = 8.5549+/-0.0002, which is greater than those of the previously known most distant objects, at z = 8.2 (refs 6 and 7) and z = 6.96 (ref. 8). We find that this single source is unlikely to provide enough photons to ionize the volume necessary for the emission line to escape, requiring a significant contribution from other, probably fainter galaxies nearby.

Glenn, J.; Conley, A.; Béthermin, M.; Altieri, B.; Amblard, A.; Arumugam, V.; Aussel, H.; Babbedge, T.; Blain, A.; Bock, J.; Boselli, A.; Buat, V.; Castro-Rodríguez, N.; Cava, A.; Chanial, P.; Clements, D. L.; Conversi, L.; Cooray, A.; Dowell, C. D.; Dwek, E.; Eales, S.; Elbaz, D.; Ellsworth-Bowers, T. P.; Fox, M.; Franceschini, A.; Gear, W.; Griffin, M.; Halpern, M.; Hatziminaoglou, E.; Ibar, E.; Isaak, K.; Ivison, R. J.; Lagache, G.; Laurent, G.; Levenson, L.; Lu, N.; Madden, S.; Maffei, B.; Mainetti, G.; Marchetti, L.; Marsden, G.; Nguyen, H. T.; O'Halloran, B.; Oliver, S. J.; Omont, A.; Page, M. J.; Panuzzo, P.; Papageorgiou, A.; Pearson, C. P.; Pérez-Fournon, I.; Pohlen, M.; Rigopoulou, D.; Rizzo, D.; Roseboom, I. G.; Rowan-Robinson, M.; Portal, M. Sánchez; Schulz, B.; Scott, Douglas; Seymour, N.; Shupe, D. L.; Smith, A. J.; Stevens, J. A.; Symeonidis, M.; Trichas, M.; Tugwell, K. E.; Vaccari, M.; Valtchanov, I.; Vieira, J. D.; Vigroux, L.; Wang, L.; Ward, R.; Wright, G.; Xu, C. K.; Zemcov, M., 2010, MNRAS, 409, 109G

HerMES: deep galaxy number counts from a P(D) fluctuation analysis of SPIRE Science Demonstration Phase observations,

Dusty, star-forming galaxies contribute to a bright, currently unresolved cosmic far-infrared background. Deep Herschel-Spectral and Photometric Imaging Receiver (SPIRE) images designed to detect and characterize the galaxies that comprise this background are highly confused, such that the bulk lies below the classical confusion limit. We analyse three fields from the Herschel Multi-tiered Extragalactic Survey (HerMES) programme in all three SPIRE bands (250, 350 and 500 μm) parametrized galaxy number count models are derived to a depth of ~2mJybeam^-1, approximately four times the depth of previous analyses at these wavelengths, using a probability of deflection [P(D)] approach for comparison to theoretical number count models. Our fits account for 64, 60 and 43 per cent of the far-infrared background in the three bands. The number counts are consistent with those based on individually detected SPIRE sources, but generally inconsistent with most galaxy number count models, which generically overpredict the number of bright galaxies and are not as steep as the P(D)-derived number counts. Clear evidence is found for a break in the slope of the differential number counts at low flux densities. Systematic effects in the P(D) analysis are explored. We find that the effects of clustering have a small impact on the data, and the largest identified systematic error arises from uncertainties in the SPIRE beam.

F. Stivoli, J. Grain, S. M. Leach, M. Tristram, C. Baccigalupi, R. Stompor,  2010, MNRAS 408 2319

Maximum likelihood, parametric component separation and CMB B-mode detection in suborbital experiments

We investigate the performance of the parametric Maximum Likelihood component separation method in the context of the CMB B-mode signal detection and its characterization by small-scale CMB suborbital experiments. We consider high-resolution (FWHM=8') balloon-borne and ground-based observatories mapping low dust-contrast sky areas of 400 and 1000 square degrees, in three frequency channels, 150, 250, 410 GHz, and 90, 150, 220 GHz, with sensitivity of order 1 to 10 micro-K per beam-size pixel. These are chosen to be representative of some of the proposed, next-generation, bolometric experiments. We study the residual foreground contributions left in the recovered CMB maps in the pixel and harmonic domain and discuss their impact on a determination of the tensor-to-scalar ratio, r. In particular, we find that the residuals derived from the simulated data of the considered balloon-borne observatories are sufficiently low not to be relevant for the B-mode science. However, the ground-based observatories are in need of some external information to permit satisfactory cleaning. We find that if such information is indeed available in the latter case, both the ground-based and balloon-borne experiments can detect the values of r as low as ~0.04 at 95% confidence level. The contribution of the foreground residuals to these limits is found to be then subdominant and these are driven by the statistical uncertainty due to CMB, including E-to-B leakage, and noise. We emphasize that reaching such levels will require a sufficient control of the level of systematic effects present in the data.


Nesvadba, N. P. H.; Boulanger, F.; Salomé, P.; Guillard, P.; Lehnert, M. D.; Ogle, P.; Appleton, P.; Falgarone, E.; Pineau Des Forets, G.

Energetics of the molecular gas in the H₂ luminous radio galaxy 3C 326: Evidence for negative AGN feedback

We present a detailed analysis of the gas conditions in the H₂ luminous radio galaxy 3C 326 N at z ~ 0.1, which has a low star-formation rate (SFR ~ 0.07 M_ȯ yr^-1) in spite of a gas surface density similar to those in starburst galaxies. Its star-formation efficiency is likely a factor ~10-50 lower than those of ordinary star-forming galaxies. Combining new IRAM CO emission-line interferometry with existing Spitzer mid-infrared spectroscopy, we find that the luminosity ratio of CO and pure rotational H₂ line emission is factors 10-100 lower than what is usually found. This suggests that most of the molecular gas is warm. The Na D absorption-line profile of 3C 326 N in the optical suggests an outflow with a terminal velocity of ~-1800 km s^-1 and a mass outflow rate of 30-40 M_ȯ yr^-1, which cannot be explained by star formation. The mechanical power implied by the wind, of order 10⁴³ erg s^-1, is comparable to the bolometric luminosity of the emission lines of ionized and molecular gas. To explain these observations, we propose a scenario where a small fraction of the mechanical energy of the radio jet is deposited in the interstellar medium of 3C 326 N, which powers the outflow, and the line emission through a mass, momentum and energy exchange between the different gas phases of the ISM. Dissipation times are of order 10^7-8 yrs, similar or greater than the typical jet lifetime. Small ratios of CO and PAH surface brightnesses in another 7 H₂¹¹ M_ȯ

luminous radio galaxies suggest that a similar form of AGN feedback could be lowering star-formation efficiencies in these galaxies in a similar way. The local demographics of radio-loud AGN suggests that secular gas cooling in massive early-type galaxies of ≥10 could generally be regulated through a fundamentally similar form of “maintenance-phase” AGN feedback.




mise à jour le 07 janvier 2011