arXiv subjects

F. Bertoldi

Publications and source records attributed to F. Bertoldi.

At least 127 records · Page 7Linked to original sources

arXiv2008

MAMBO 1.2mm observations of luminous starbursts at z~2 in the SWIRE fields

We report on--off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected star-forming galaxies from the SWIRE survey. The sources are selected on the basis of bright 24um fluxes (f_24um>0.4mJy) and of stellar dominated near-infrared spectral energy distributions in order to favor z~2 starburst galaxies. The average 1.2mm flux for the whole sample is 1.5+/-0.2 mJy. Our analysis focuses on 29 sources in the Lockman Hole field where the average 1.2mm flux (1.9+/-0.3 mJy) is higher than in other fields (1.1+/-0.2 mJy). The analysis of the sources multi-wavelength spectral energy distributions indicates that they are starburst galaxies with far-infrared luminosities ~10^12-10^13.3 Lsun, and stellar masses of ~0.2-6 x10^11 M_sun. Compared to sub-millimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among those with the largest 24um/millimeter flux ratios. The origin of such large ratios is investigated by comparing the average mid-infrared spectra and the stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources and of SMGs. The mid-infrared spectra exhibit strong PAH features, and a warm dust continuum. The warm dust continuum contributes to ~34% of the mid-infrared emission, and is likely associated with an AGN component. This constribution is consistent with what is found in SMGs. The large 24um/1.2mm flux ratios are thus not due to AGN emission, but rather to enhanced PAH emission compared to SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust temperatures than typically observed in SMGs. Our selection favors warm ultra-luminous infrared sources at high-z, a class of objects that is rarely found in SMG samples. Our sample is the largest Spitzer-selected sample detected at millimeter wavelengths currently available.

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arXiv2008

Thermal Emission from Warm Dust in the Most Distant Quasars

We report new continuum observations of fourteen z~6 quasars at 250 GHz and fourteen quasars at 1.4 GHz. We summarize all recent millimeter and radio observations of the sample of the thirty-three quasars known with 5.71<=z<=6.43, and present a study of the rest frame far-infrared (FIR) properties of this sample. These quasars were observed with the Max Plank Millimeter Bolometer Array (MAMBO) at 250 GHz with mJy sensitivity, and 30% of them were detected. We also recover the average 250 GHz flux density of the MAMBO undetected sources at 4 sigma, by stacking the on-source measurements. The derived mean radio-to-UV spectral energy distributions (SEDs) of the full sample and the 250 GHz non-detections show no significant difference from that of lower-redshift optical quasars. Obvious FIR excesses are seen in the individual SEDs of the strong 250 GHz detections, with FIR-to-radio emission ratios consistent with that of typical star forming galaxies. Most 250 GHz-detected sources follow the L_{FIR}--L_{bol} relationship derived from a sample of local IR luminous quasars (L_{IR}>10^{12}L_{\odot}), while the average L_{FIR}/L_{bol} ratio of the non-detections is consistent with that of the optically-selected PG quasars. The MAMBO detections also tend to have weaker Lyαemission than the non-detected sources. We discuss possible FIR dust heating sources, and critically assess the possibility of active star formation in the host galaxies of the z~6 quasars. The average star formation rate of the MAMBO non-detections is likely to be less than a few hundred M_{\odot} yr^{-1}, but in the strong detections, the host galaxy star formation is probably at a rate of \gtrsim10^{3} M_{\odot} yr^{-1}, which dominates the FIR dust heating.

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arXiv2008

Interferometric CO Observations of submillimeter-faint, radio-selected starburst galaxies at z~2

High-redshift, dust-obscured galaxies -- selected to be luminous in the radio but relatively faint at 850um -- appear to represent a different population from the ultra-luminous submillimeter- (submm-) bright population. They may be star-forming galaxies with hotter dust temperatures or they may have lower far-infrared luminosities and larger contributions from obscured active galactic nuclei (AGN). Here we present observations of three z~2 examples of this population, which we term submm-faint radio galaxies (SFRGs) in CO(3-2) using the IRAM Plateau de Bure Interferometer to study their gas and dynamical properties. We estimate the molecular gas mass in each of the three SFRGs (8.3x10^{9} M_odot, <5.6x10^{9} M_odot and 15.4x10^{9} M_odot, respectively) and, in the case of RG163655, a dynamical mass by measurement of the width of the CO(3-2) line (8x10^{10} csc^2i M_odot). While these gas masses are substantial, on average they are 4x lower than submm-selected galaxies (SMGs). Radio-inferred star formation rates ( =970 M_odot\yr) suggest much higher star-formation efficiencies than are found for SMGs, and shorter gas depletion time scales (~11 Myr), much shorter than the time required to form their current stellar masses (~160 Myr; ~10^{11} M_odot). By contrast, SFRs may be overestimated by factors of a few, bringing the efficiencies in line with those typically measured for other ultraluminous star-forming galaxies and suggesting SFRGs are more like ultraviolet- (UV-)selected star-forming galaxies with enhanced radio emission. A tentative detection of \rga at 350um suggests hotter dust temperatures -- and thus similar gas-to-dust mass fractions -- as the SMGs. We conclude that SFRGs' radio luminosities are larger than would naturally scale from local ULIRGs given their gas masses or gas fractions.

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arXiv2008

A 1200-micron MAMBO survey of the GOODS-N field: a significant population of submillimetre drop-out galaxies

We present a 1200-micron image of the Great Observatories Origin Deep Survey North (GOODS-N) field, obtained with the Max Planck Millimeter Bolometer array (MAMBO) on the IRAM 30-m telescope. The survey covers a contiguous area of 287 square arcmin to a near-uniform noise level of ~0.7mJy/beam. After Bayesian flux deboosting, a total of 30 sources are recovered (>=3.5sigma). An optimal combination of our 1200-micron data and an existing 850-micron image from the Submillimetre Common-User Bolometer Array (SCUBA) yielded 33 sources (>=4sigma). We combine our GOODS-N sample with those obtained in the Lockman Hole and ELAIS-N2 fields (Scott et al. 2002; Greve et al. 2004) in order to explore the degree of overlap between 1200-micron- and 850-micron-selected galaxies (hereafter SMGs), finding no significant difference between their 850-micron to 1200-micron flux density distributions. However, a noise-weighted stacking analysis yields a significant detection of the 1200-micron-blank SCUBA sources, whereas no significant 850-micron signal is found for the 850-micron-blank MAMBO sources. The hypothesis that the 850/1200-micron flux density distribution of SCUBA sources is also representative of the MAMBO population is rejected at the ~4sigma level, via Monte Carlo simulations. Therefore, although the populations overlap, galaxies selected at 850 and 1200micron are different, and there is compelling evidence for a significant 1200-micron-detected population which is not recovered at 850micron. These are submm drop-outs (SDOs), with S_850/S_1200 = 0.7-1.7, requiring very cold dust or unusual spectral energy distributions (T_d ~ 10K; beta ~ 1), unless SDOs reside beyond the redshift range observed for radio-identified SMGs, i.e. at z > 4.

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arXiv2008

Submillimeter Line Emission from LMC N159W: a Dense, Clumpy PDR in a Low Metallicity Environment

Star formation at earlier cosmological times takes place in an interstellar medium with low metallicity. The Large Magellanic Cloud (LMC) is ideally suited to study star formation in such an environment. The physical and chemical state of the ISM in a star forming environment can be constrained by observations of submm and FIR spectral lines of the main carbon carrying species, CO, CI and CII, which originate in the surface layers of molecular clouds illuminated by the UV radiation of the newly formed, young stars. We present high-angular resolution sub-millimeter observations in the N159W region in the LMC obtained with the NANTEN2 telescope of the 12CO J = 4-3, J = 7-6, and 13CO J = 4-3 rotational and [CI] 3P1-3P0 and 3P2-3P1 fine-structure transitions. The 13CO J =4-3 and [CI] 3P2-3P1 transitions are detected for the first time in the LMC. We derive the physical and chemical properties of the low-metallicity molecular gas using an escape probability code and a self-consistent solution of the chemistry and thermal balance of the gas in the framework of a clumpy cloud PDR model. The separate excitation analysis of the submm CO lines and the carbon fine structure lines shows that the emitting gas in the N159W region has temperatures of about 80 K and densities of about 10^4 cm^-3. The estimated C to CO abundance ratio close to unity is substantially higher than in dense massive star-forming regions in the Milky Way. The analysis of all observed lines together, including the [CII] line intensity reported in the literature, in the context of a clumpy cloud PDR model constrains the UV intensity to about χ~220 and an average density of the clump ensemble of about 10^5 cm^-3, thus confirming the presence of high density material in the LMC N159W region.

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arXiv2008

Submillimeter Galaxies at z~2: Evidence for Major Mergers & Constraints on Lifetimes, IMF and CO-H2 Conversion Factor

We report sub-arcsecond resolution IRAM PdBI millimeter CO interferometry of four z~2 submillimeter galaxies (SMGs), and sensitive CO (3-2) flux limits toward three z~2 UV-/optically selected star forming galaxies. The new data reveal for the first time spatially resolved CO gas kinematics in the observed SMGs. Two of the SMGs show double or multiple morphologies, with complex, disturbed gas motions. The other two SMGs exhibit CO velocity gradients of ~500 km/s across 0.2 arcsec (1.6 kpc) diameter regions, suggesting that the star forming gas is in compact, rotating disks. Our data provide compelling evidence that these SMGs represent extreme, short-lived 'maximum' star forming events in highly dissipative mergers of gas rich galaxies. The resulting high mass surface and volume densities of SMGs are similar to those of compact quiescent galaxies in the same redshift range, and much higher than those in local spheroids. From the ratio of the comoving volume densities of SMGs and quiescent galaxies in the same mass and redshift ranges, and from the comparison of gas exhaustion time scales and stellar ages, we estimate that the SMG phase duration is about 100 Myrs. Our analysis of SMGs and optically/UV selected high redshift star forming galaxies supports a 'universal' Chabrier IMF as being valid over the star forming history of these galaxies. We find that the 12CO luminosity to total gas mass conversion factors at z~2-3 are probably similar to those assumed at z~0. The implied gas fractions in our sample galaxies range from 20 to 50%.

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arXiv2007

12CO 4-3 and [CI] 1-0 at the centers of NGC 4945 and Circinus

Studying molecular gas in the central regions of the star burst galaxies NGC4945 and Circinus enables us to characterize the physical conditions and compare them to previous local and high-z studies. We estimate temperature, molecular density and column densities of CO and atomic carbon. Using model predictions we give a range of estimated CO/C abundance ratios. Using the new NANTEN2 4m sub-millimeter telescope in Pampa La Bola, Chile, we observed for the first time CO 4-3 and [CI] 3P1-3 P0 at the centers of both galaxies at linear scale of 682 pc and 732 pc respectively. We compute the cooling curves of 12CO and 13CO using radiative transfer models and estimate the physical conditions of CO and [CI]. The centers of NGC4945 and Circinus are very [CI] bright objects, exhibiting [CI] 3P1 - 3 P0 luminosities of 91 and 67Kkms-1kpc2, respectively. The [CI] 3P1-3 P0/CO 4-3 ratio of integrated intensities are large at 1.2 in NGC4945 and 2.8 in Circinus. Combining previous CO J= 1-0, 2-1 and 3-2 and 13CO J= 1-0, 2-1 studies with our new observations, the radiative transfer calculations give a range of densities, n(H2) = 10^3-3*104^cm-3, and a wide range of kinetic temperatures, Tkin = 20 - 100K, depending on the density. Future CO J= 7-6 and [CI] 2-1 observations will be important to resolve the ambiguity in the physical conditions and confirm the model predictions.

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arXiv2007

Clumpy photon-dominated regions in Carina. I. [CI] and mid-J CO lines in two 4'x4' fields

The Carina region is an excellent astrophysical laboratory for studying the feedback mechanisms of newly born, very massive stars within their natal giant molecular clouds (GMCs) at only 2.35 kpc distance. We use a clumpy PDR model to analyse the observed intensities of atomic carbon and CO and to derive the excitation conditions of the gas. The NANTEN2-4m submillimeter telescope was used to map the [CI] 3P1-3P0, 3P2-3P1 and CO 4-3, 7-6 lines in two 4'x4' regions of Carina where molecular material interfaces with radiation from the massive star clusters. One region is the northern molecular cloud near the compact OB cluster Tr14, and the second region is in the molecular cloud south of etaCar and Tr16. These data were combined with 13CO SEST spectra, HIRES/IRAS 60um and 100um maps of the FIR continuum, and maps of 8um IRAC/Spitzer and MSX emission. We used the HIRES far-infrared dust data to create a map of the FUV field heating the gas. The northern region shows an FUV field of a few 1000 in Draine units while the field of the southern region is about a factor 10 weaker. We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the 38" beam (0.43pc), which follow canonical power-law mass and mass-size distributions. We find that an average local clump density of 2x10**5 cm-3 is needed to reproduce the observed line emission at two selected interface positions. Stationary, clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.

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arXiv2007

Wide-field mid-infrared and millimetre imaging of the high-redshift radio galaxy, 4C41.17

We present deep 350- and 1200-micron imaging of the region around 4C41.17 -- one of the most distant (z = 3.792) and luminous known radio galaxies -- obtained with the Submillimeter High Angular Resolution Camera (SHARC-II) and the Max Planck Millimeter Bolometer Array (MAMBO). The radio galaxy is robustly detected at 350- and 1200-micron, as are two nearby 850-micron-selected galaxies; a third 850-micron source is detected at 350-micron and coincides with a ~ 2-sigma feature in the 1200-micron map. Further away from the radio galaxy an additional nine sources are detected at 1200-micron, bringing the total number of detected (sub)millimeter selected galaxies (SMGs) in this field to 14. Using radio images from the Very Large Array (VLA) and Spitzer mid-infrared (mid-IR) data, we find statistically robust radio and/or 24-micron counterparts to eight of the 14 SMGs in the field around 4C41.17. Follow-up spectroscopy with Keck/LRIS has yielded redshifts for three of the eight robustly identified SMGs, placing them in the redshift range 0.5 < z < 2.7, i.e. well below that of 4C41.17. We infer photometric redshifts for a further four sources using their 1.6-micron (rest-frame) stellar feature as probed by the IRAC bands; only one of them is likely to be at the same redshift as 4C41.17. Thus at least four, and as many as seven, of the SMGs within the 4C41.17 field are physically unrelated to the radio galaxy. With the redshift information at hand we are able to constrain the observed over-densities of SMGs within radial bins stretching to R=50 and 100" (~ 0.4 and ~ 0.8Mpc at z ~ 3.8) from the radio galaxy to ~ 5x and ~ 2x that of the field, dropping off to the background value at R=150". [Abridged]

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arXiv2007

Molecular gas in QSO host galaxies at z>5

We present observations with the IRAM Plateau de Bure Interferometer of three QSOs at z>5 aimed at detecting molecular gas in their host galaxies as traced by CO transitions. CO (5-4) is detected in SDSSJ033829.31+002156.3 at z=5.0267, placing it amongst the most distant sources detected in CO. The CO emission is unresolved with a beam size of ~1", implying that the molecular gas is contained within a compact region, less than ~3kpc in radius. We infer an upper limit on the dynamical mass of the CO emitting region of ~3x10^10 Msun/sin(i)^2. The comparison with the Black Hole mass inferred from near-IR data suggests that the BH-to-bulge mass ratio in this galaxy is significantly higher than in local galaxies. From the CO luminosity we infer a mass reservoir of molecular gas as high as M(H2)=2.4x10^10 Msun, implying that the molecular gas accounts for a significant fraction of the dynamical mass. When compared to the star formation rate derived from the far-IR luminosity, we infer a very short gas exhaustion timescale (~10^7 yrs), comparable to the dynamical timescale. CO is not detected in the other two QSOs (SDSSJ083643.85+005453.3 and SDSSJ163033.90+401209.6) and upper limits are given for their molecular gas content. When combined with CO observations of other type 1 AGNs, spanning a wide redshift range (0 5) the CO luminosity appears to saturate. We discuss the implications of these findings in terms of black hole-galaxy co-evolution.

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arXiv2007

Detection of $1.6\times 10^{10}$ M$_\odot$ of molecular gas in the host galaxy of the $z=5.77$ SDSS quasar J0927+2001

We have detected emission by the CO 5-4 and 6-5 rotational transitions at $z = 5.7722\pm 0.0006$ from the host galaxy of the SDSS quasar J0927+2001 using the Plateau de Bure interferometer. The peak line flux density for the CO 5-4 line is $0.72 \pm 0.09$ mJy, with a line FWHM = $610 \pm 110$ km s$^{-1}$. The implied molecular gas mass is $(1.6 \pm 0.3) \times 10^{10}$ M$_\odot$. We also detect the 90 GHz continuum at $0.12 \pm 0.03$ mJy, consistent with a 47K dust spectrum extrapolated from higher frequencies. J0927+2001 is the second example of a huge molecular gas reservoir within the host galaxy of a quasar within 1 Gyr of the big bang. Observations of J0927+2001 are consistent with a massive starburst coeval with a bright quasar phase in the galaxy, suggesting the rapid formation of both a super-massive black hole through accretion, and the stellar host spheroid, at a time close to the end of cosmic reionization.

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arXiv2007

Studying the first galaxies with ALMA

We discuss observations of the first galaxies, within cosmic reionization, at centimeter and millimeter wavelengths. We present a summary of current observations of the host galaxies of the most distant QSOs ($z \sim 6$). These observations reveal the gas, dust, and star formation in the host galaxies on kpc-scales. These data imply an enriched ISM in the QSO host galaxies within 1 Gyr of the big bang, and are consistent with models of coeval supermassive black hole and spheroidal galaxy formation in major mergers at high redshift. Current instruments are limited to studying truly pathologic objects at these redshifts, meaning hyper-luminous infrared galaxies ($L_{FIR} \sim 10^{13}$ L$_\odot$). ALMA will provide the one to two orders of magnitude improvement in millimeter astronomy required to study normal star forming galaxies (ie. Ly-$α$ emitters) at $z \sim 6$. ALMA will reveal, at sub-kpc spatial resolution, the thermal gas and dust -- the fundamental fuel for star formation -- in galaxies into cosmic reionization.

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arXiv2006

Radio and millimeter properties of $z \sim 5.7$ Ly$α$ emitters in the COSMOS field: limits on radio AGN, submm galaxies, and dust obscuration

We present observations at 1.4 and 250 GHz of the $z\sim 5.7$ Ly$α$ emitters (LAE) in the COSMOS field found by Murayama et al.. At 1.4 GHz there are 99 LAEs in the lower noise regions of the radio field. We do not detect any individual source down to 3$σ$ limits of $\sim 30μ$Jy beam$^{-1}$ at 1.4 GHz, nor do we detect a source in a stacking analysis, to a 2$σ$ limit of $2.5μ$Jy beam$^{-1}$. At 250 GHz we do not detect any of the 10 LAEs that are located within the central regions of the COSMOS field covered by MAMBO ($20' \times 20'$) to a typical 2$σ$ limit of $S_{250} < 2$mJy. The radio data imply that there are no low luminosity radio AGN with $L_{1.4} > 6\times 10^{24}$ W Hz$^{-1}$ in the LAE sample. The radio and millimeter observations also rule out any highly obscured, extreme starbursts in the sample, ie. any galaxies with massive star formation rates $> 1500$ M$_\odot$ year$^{-1}$ in the full sample (based on the radio data), or 500 M$_\odot$ year$^{-1}$ for the 10% of the LAE sample that fall in the central MAMBO field. The stacking analysis implies an upper limit to the mean massive star formation rate of $\sim 100$ M$_\odot$ year$^{-1}$.

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arXiv2006

The VLA-COSMOS Survey: II. Source Catalog of the Large Project

The VLA-COSMOS large project is described and its scientific objective is discussed. We present a catalog of ~ 3,600 radio sources found in the 2deg^2 COSMOS field at 1.4 GHz. The observations in the VLA A and C configuration resulted in a resolution of 1.5''x1.4'' and a mean rms noise of ~ 10.5(15) uJy/beam in the central 1(2)deg^2. 80 radio sources are clearly extended consisting of multiple components, and most of them appear to be double-lobed radio galaxies. The astrometry of the catalog has been thoroughly tested and the uncertainty in the relative and absolute astrometry are 130mas and <55mas, respectively.

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arXiv2006

The Effect of Noise in Dust Emission Maps on the Derivation of Column Density, Temperature and Emissivity Spectral Index

We have mapped the central 10'x10' of the dense core TMC-1C at 450, 850 and 1200 microns using SCUBA on the James Clerk Maxwell Telescope and MAMBO on the IRAM 30m telescope. We show that although one can, in principle, use images at these wavelengths to map the emissivity spectral index, temperature and column density independently, noise and calibration errors would have to be less than 2% to accurately derive these three quantities from a set of three emission maps. Because our data are not this free of errors, we use our emission maps to fit the dust temperature and column density assuming a constant value of the emissivity spectral index and explore the effects of noise on the derived physical parameters. We find that the derived extinction values for TMC-1C are large for a starless core (80 mag Av), and the derived temperatures are low (6 K) in the densest regions of the core, using our derived value of beta = 1.8.

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arXiv2006

Search for Cold Debris Disks around M-dwarfs

Debris disks are believed to be related to planetesimals left over around stars after planet formation has ceased. The frequency of debris disks around M-dwarfs which account for 70% of the stars in the Galaxy is unknown while constrains have already been found for A- to K-type stars. We have searched for cold debris disks around 32 field M-dwarfs by conducting observations at lambda = 850 microns with the SCUBA bolometerarray camera at the JCMT and at lambda = 1.2mm with the MAMBO array at the IRAM 30-m telescopes. This is the first survey of a large sample of M-dwarfs conducted to provide statistical constraints on debris disks around this type of stars. We have detected a new debris disk around the M0.5 dwarf GJ842.2 at lambda = 850 microns, providing evidence for cold dust at large distance from this star (~ 300AU). By combining the results of our survey with the ones of Liu et al. (2004), we estimate for the first time the detection rate of cold debris disks around field M-dwarfs with ages between 20 and 200 Myr. This detection rate is 13^{+6}_{-8} % and is consistent with the detection rate of cold debris disks (9 - 23 %) around A- to K-type main sequence stars of the same age. This is an indication that cold disks may be equally prevalent across stellar spectral types.

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arXiv2006

High resolution CO imaging of high redshift QSO host galaxies

We review recent high-resolution CO observations of distant QSOs obtained at the Very Large Array. The aim of these observations is to resolve the molecular gas distribution in these extreme objects both spatially and in velocity space. They provide unique information regarding the small-scale distribution, the extent, and the brightness temperatures of the molecular gas in these early systems. E.g., the structure and dynamics of the molecular gas may reveal whether or not mergers can be the cause of the ongoing starburst activity. The observations also allow for a first estimate of the dynamical gas mass. Currently, only the VLA is able to obtain resolutions in CO of up to 0.15" which is needed to resolve typical galactic structures of sizes ~1 kpc. We present new high-resolution VLA imaging of high-z QSOs (BRI 1335-0417, APM 08279+5255 and J1148+5251). These observations pave the road to future ALMA observations where resolutions of order 0.1'' will be obtained routinely.

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arXiv2006

Radio and millimeter observations of z~2 luminous QSOs

We present Very Large Array observations at 1.4 and 5 GHz of a sample of 16 quasi-stellar objects (QSOs) at z = 1.78 to 2.71. Half of the chosen quasars are bright at mm wavelengths (250 or 350 GHz) while the other half were not detected at mm wavelengths; the former QSOs were detected at 1.4 GHz, in most cases at high significance (S/N > ~7), but only three of the latter sources were detected at radio frequencies, and only at lower significance (S/N ~ 3). The data are consistent with a correlation between the mm and radio fluxes indicating a physical connection between the mechanisms responsible for the radio and mm emission. However, this conclusion is based on data which includes many upper limits, and deeper observations are clearly needed to verify this correlation. All eight mm detected QSOs are detected in the radio continuum, with radio flux densities consistent with the radio-to-FIR correlation for low z star forming galaxies. However, four of these have flatter spectral indices than is typical for star forming galaxies (i.e. greater than -0.5) suggesting that radiation from the central AGN dominates the observed radio emission. All the sources detected at 1.4 GHz are spatially unresolved, with the size limits typically < 1'' = 6 kpc. High star formation rate galaxies at low redshift are typically nuclear starbursts, with sizes < 1 kpc. Hence, the current radio size limits are insufficient to constrain the emission model (AGN or starburst).

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