arXiv subjects

F. Bertoldi

Publications and source records attributed to F. Bertoldi.

At least 109 records · Page 6Linked to original sources

arXiv2010

The VLA-COSMOS Survey. IV. Deep Data and Joint Catalog

In the context of the VLA-COSMOS Deep project additional VLA A array observations at 1.4 GHz were obtained for the central degree of the COSMOS field and combined with the existing data from the VLA-COSMOS Large project. A newly constructed Deep mosaic with a resolution of 2.5" was used to search for sources down to 4 sigma with 1 sigma ~ 12 microJy/beam in the central 50'x50'. This new catalog is combined with the catalog from the Large project (obtained at 1.5"x1.4" resolution) to construct a new Joint catalog. All sources listed in the new Joint catalog have peak flux densities of >5 sigma at 1.5" and/or 2.5" resolution to account for the fact that a significant fraction of sources at these low flux levels are expected to be slighty resolved at 1.5" resolution. All properties listed in the Joint catalog such as peak flux density, integrated flux density and source size are determined in the 2.5" resolution Deep image. In addition, the Joint catalog contains 43 newly identified multi-component sources.

astro-ph.CO↗

arXiv2010

Ionization near-zones associated with quasars at z ~ 6

We analyze the size evolution of HII regions around 27 quasars between z=5.7 to 6.4 ('quasar near-zones' or NZ). We include more sources than previous studies, and we use more accurate redshifts for the host galaxies, with 8 CO molecular line redshifts and 9 MgII redshifts. We confirm the trend for an increase in NZ size with decreasing redshift, with the luminosity normalized proper size evolving as: R_{NZ,corrected} = (7.4 \pm 0.3) - (8.0 \pm 1.1) \times (z-6) Mpc. While derivation of the absolute neutral fraction remains difficult with this technique, the evolution of the NZ sizes suggests a decrease in the neutral fraction of intergalactic hydrogen by a factor ~ 9.4 from z=6.4 to 5.7, in its simplest interpretation. Alternatively, recent numerical simulations suggest that this rapid increase in near-zone size from z=6.4 to 5.7 is due to the rapid increase in the background photo-ionization rate at the end of the percolation or overlap phase, when the average mean free path of ionizing photons increases dramatically. In either case, the results are consistent with the idea that z ~ 6 to 7 corresponds to the tail end of cosmic reionization. The scatter in the normalized NZ sizes is larger than expected simply from measurement errors, and likely reflects intrinsic differences in the quasars or their environments. We find that the near-zone sizes increase with quasar UV luminosity, as expected for photo-ionization dominated by quasar radiation.

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arXiv2010

High-resolution CO and radio imaging of z~2 ULIRGs: extended CO structures, and implications for the universal star formation law

We present high spatial resolution (0.4", ~3.5 kpc) PdBI interferometric data on three ultra-luminous infrared galaxies (ULIRGs) at z~2: two submillimetre galaxies and one submillimetre faint star forming radio galaxy. The three galaxies have been ro- bustly detected in CO rotational transitions, either 12CO(J=4-3) or 12CO(J=3-2), allowing their sizes and gas masses to be accurately constrained. These are the highest spatial resolution observations observed to date (by a factor of ~2) for intermediate-excitation CO emission in z~2 ULIRGs. The galaxies appear extended over several resolution elements, having a mean radius of 3.7 kpc. High-resolution (0.3") combined MERLIN-VLA observations of their radio continua allow an analysis of the star formation behaviour of these galaxies, on comparable spatial scales to that of the CO observations. This 'matched beam' approach sheds light on the spatial distribution of both molecular gas and star formation, and we can therefore calculate accurate star formation rates and gas surface densities: this allows us to place the three systems in the context of a Kennicutt-Schmidt (KS)-style star formation law. We find a difference in size between the CO and radio emission regions, and as such we suggest that using the spatial extent of the CO emission region to estimate the surface density of star formation may lead to error. This size difference also causes the star formation efficiencies within systems to vary by up to a factor of 5. We also find, with our new accurate sizes, that SMGs lie significantly above the KS relation, indicating that stars are formed more efficiently in these extreme systems than in other high-z star forming galaxies.

astro-ph.CO↗

arXiv2009

Multi-frequency imaging of the galaxy cluster Abell 2163 using the Sunyaev-Zel'dovich Effect

We used the APEX-SZ and LABOCA bolometer cameras on the APEX telescope to map the decrement of the Sunyaev-Zeldovich effect at 150 GHz and the increment at 345 GHz toward the galaxy cluster Abell 2163. The SZE images were used to model the radial density and temperature distribution of the ICM, and to derive the gas mass fraction in the cluster under the assumption of hydrostatic equilibrium. We used the isothermal beta model to fit the SZE decrement/increment radial profiles. We performed a simple, non-parametric de-projection of the radial density and temperature profiles, in conjunction with XMM-Newton X-ray data, under the simplifying assumption of spherical symmetry. We combined the peak SZE signals derived in this paper with published SZE measurements of this cluster to derive the cluster line-of-sight bulk velocity and the central Comptonization, using priors on the ICM temperature. We find that the best-fit isothermal model to the SZE data is consistent with the ICM properties implied by the X-ray data, particularly inside the central 1 Mpc radius. Although the assumptions of hydrostatic equilibrium and spherical symmetry may not be optimal for this complex system, the results obtained under these assumptions are consistent with X-ray and weak-lensing measurements. This shows the applicability of the simple joint SZE and X-ray de-projection technique described in this paper for clusters with a wide range of dynamical states. (Abridged)

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arXiv2009

The Herschel ATLAS

The Herschel ATLAS is the largest open-time key project that will be carried out on the Herschel Space Observatory. It will survey 510 square degrees of the extragalactic sky, four times larger than all the other Herschel surveys combined, in five far-infrared and submillimetre bands. We describe the survey, the complementary multi-wavelength datasets that will be combined with the Herschel data, and the six major science programmes we are undertaking. Using new models based on a previous submillimetre survey of galaxies, we present predictions of the properties of the ATLAS sources in other wavebands.

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arXiv2009

The LABOCA Survey of the Extended Chandra Deep Field South

We present a sensitive 870 micron survey of the Extended Chandra Deep Field South (ECDFS) using LABOCA on the APEX telescope. The LABOCA ECDFS Submillimetre Survey (LESS) covers the full 30' x 30' field size of the ECDFS and has a uniform noise level of 1.2 mJy/beam. LESS is thus the largest contiguous deep submillimetre survey undertaken to date. The noise properties of our map show clear evidence that we are beginning to be affected by confusion noise. We present a catalog of 126 SMGs detected with a significance level above 3.7 sigma. The ECDFS exhibits a deficit of bright SMGs relative to previously studied blank fields but not of normal star-forming galaxies that dominate the extragalactic background light (EBL). This is in line with the underdensities observed for optically defined high redshift source populations in the ECDFS (BzKs, DRGs,optically bright AGN and massive K-band selected galaxies). The differential source counts in the full field are well described by a power law with a slope of alpha=-3.2, comparable to the results from other fields. We show that the shape of the source counts is not uniform across the field. The integrated 870 micron flux densities of our source-count models account for >65% of the estimated EBL from COBE measurements. We have investigated the clustering of SMGs in the ECDFS by means of a two-point correlation function and find evidence for strong clustering on angular scales <1'. Assuming a power law dependence for the correlation function and a typical redshift distribution for the SMGs we derive a spatial correlation length of r_0=13+/-6 h^-1 Mpc.

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arXiv2009

A Search for Neutral Carbon towards two z=4.05 Submillimetre Galaxies, GN20 and GN20.2

Using the IRAM Plateau-de-Bure Interferometer (PdBI) we have searched for the upper fine structure line of neutral carbon (CI(2->1), nu_rest = 809 GHz) and 12CO(J=7->6) (nu_rest=806GHz) towards the submillimetre galaxies (SMGs) GN20 (SMM J123711.9+622212, z = 4.055) and GN20.2 (SMM J123708.8+622202, z = 4.051). The far-infrared (FIR) continuum is detected at 8sigma significance in GN20, with a flux density of S_1.8mm = 1.9+-0.2mJy, while no continuum is detected in GN20.2. Both sources are statistically undetected in both CI and CO(7-6) lines; we derive line luminosity limits for both CI and CO of L'<~2x10^10K km s^-1 pc^2. Assuming carbon excitation temperatures of T_ex = 30K (the galaxies' measured dust temperatures), we infer CI mass limits of M_CI < 5.4x10^6 Msun (GN20) and M_CI < 6.8x10^6 Msun (GN20.2). The derived CI abundance limits are <1.8x10^-5 for GN20 and <3.8x10^-5 for GN20.2 implying that the systems have Milky Way level neutral carbon enrichment (X[CI]/X[H2]) or lower, similar to high-redshift carbon-detected systems (at 5x10^-5) but about 50 times less than the neutral carbon enrichment of local starburst galaxies. Observations of GN20 and GN20.2 in high-resolution MERLIN+VLA radio maps of GOODS-N are used to further constrain the sizes and locations of active regions. We conclude that the physical gas properties of young rapidly evolving systems like GN20 and GN20.2 are likely significantly different than starburst/ULIRG environments in the local Universe yet similar to z~2 SMGs. Unless gravitationally amplified examples can be found, observations of galaxies like GN20 will require the order of magnitude increase in sensitivity of the Atacama Large Millimetre Array (ALMA) to constrain their CI and high-J CO content, despite the fact that they are the brightest systems at z~4.

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arXiv2009

Constraints on the High-l Power Spectrum of Millimeter-wave Anisotropies from APEX-SZ

We present measurements of the angular power spectrum of millimeter wave anisotropies with the APEX-SZ instrument. APEX-SZ has mapped 0.8 square degrees of sky at a frequency of 150 GHz with an angular resolution of 1'. These new measurements significantly improve the constraints on anisotropy power at 150 GHz over the range of angular multipoles 3000 < l < 10,000, limiting the total astronomical signal in a flat band power to be less than 105 microK^2 at 95% CL. We expect both submillimeter-bright, dusty galaxies and to a lesser extent secondary CMB anisotropies from the Sunyaev-Zel'dovich effect (SZE) to significantly contribute to the observed power. Subtracting the SZE power spectrum expected for sigma_8=0.8 and masking bright sources, the best fit value for the remaining power is C_l = 1.1^{+0.9}_{-0.8} x 10^{-5} micro K^2 (1.7^{+1.4}_{-1.3} Jy^2 sr^{-1}). This agrees well with model predictions for power due to submillimeter-bright, dusty galaxies. Comparing this power to the power detected by BLAST at 600 GHz, we find the frequency dependence of the source fluxes to be S_nu ~ nu^{2.6^{+0.4}_{-0.2}} if both experiments measure the same population of sources. Simultaneously fitting for the amplitude of the SZE power spectrum and a Poisson distributed point source population, we place an upper limit on the matter fluctuation amplitude of sigma_8 < 1.18 at 95% confidence.

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arXiv2009

Search for Cold Debris Disks around M-dwarfs. II

Although 70 % of the stars in the Galaxy are M-dwarfs, thermal emission searches for cold debris disks have been conducted mostly for A-type and solar-type stars. We report on new lambda=1.2 mm continuum observations of thirty M-dwarfs, using the MAMBO-2 bolometer array camera at the IRAM 30m telescope. For a statistical analysis, we combine these data with our prior SCUBA and MAMBO-2 observations of 20 other M-dwarfs. Our total sample divides in M-dwarfs in moving groups, with relatively young ages, and in nearby M-dwarfs with unknown ages. Only one cold debris disk (GJ842.2) was detected significantly. We compare the implied disk abundance constraints with those found in two comparable submillimeter surveys of 10 to 190 Myr old A- and FGK-type stars. For the 19 youngest (ages less than 200 Myr) M-dwarfs in our sample, we derive a cold disk fraction of 5.3^{+10.5}_{-5.0} %, compared to 15 +/-11.5 % for FGK-stars and 22^{+33}_{-20} % for A-stars. Hence, for this age group, there is an apparent trend of fewer cold disks for later stellar types, i.e., lower star masses. Although its statistical significance is marginal, this trend is strengthened by the deeper sensitivity of observations in the M-dwarf sample. We derive a cold disk fraction of < 10 % for the older (likely a few Gyr) M-dwarfs in our sample. Finally, although inconclusively related to a debris disk, we present the complex millimeter structure found around the position of the M1.5 dwarf GJ526 in our sample.

astro-ph.GA↗

arXiv2009

Sunyaev-Zel'dovich Effect Observations of the Bullet Cluster (1E 0657-56) with APEX-SZ

We present observations of the Sunyaev-Zel'dovich effect (SZE) in the Bullet cluster (1E 0657--56) using the APEX-SZ instrument at 150 GHz with a resolution of 1 arcmin. The main results are maps of the SZE in this massive, merging galaxy cluster. The cluster is detected with 23 sigma significance within the central 1 arcmin radius of the source position. The SZE map has a broadly similar morphology to that in existing X-ray maps of this system, and we find no evidence for significant contamination of the SZE emission by radio or IR sources. In order to make simple quantitative comparisons with cluster gas models derived from X-ray observations, we fit our data to an isothermal elliptical beta model, despite the inadequacy of such a model for this complex merging system. With an X-ray derived prior on the power-law index, beta = 1.04 +0.16 -0.10, we find a core radius r_c =142 +/- 18 arcsec, an axial ratio of 0.889 +/- 0.072, and a central temperature decrement of -771 +/- 71 micro-K_CMB, including a +/-5.5% flux calibration uncertainty. Combining the APEX-SZ map with a map of projected electron surface density from Chandra X-ray observations, we determine the mass-weighted temperature of the cluster gas to be T_mg=10.8 +/- 0.9 keV, significantly lower than some previously reported X-ray spectroscopic temperatures. Under the assumption of an isothermal cluster gas distribution in hydrostatic equilibrium, we compute the gas mass fraction for prolate and oblate spheroidal geometries and find it to be consistent with previous results from X-ray and weak lensing observations. This work is the first result from the APEX-SZ experiment, and represents the first reported scientific result from observations with a large array of multiplexed superconducting transition-edge sensor bolometers.

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arXiv2009

Photometric monitoring of the young star Par 1724 in Orion

We report new photometric observations of the 200000 year old naked weak-line run-away T Tauri star Par 1724, located north of the Trapezium cluster in Orion. We observed in the broad band filters B, V, R, and I using the 90cm Dutch telescope on La Silla, the 80cm Wendelstein telescope, and a 25cm telescope of the University Observatory Jena in Grossschwabhausen near Jena. The photometric data in V and R are consistent with a 5.7 day rotation period due to spots, as observed before between 1960ies and 2000. Also, for the first time, we present evidence for a long-term 9 or 17.5 year cycle in photometric data (V band) of such a young star, a cycle similar to that to of the Sun and other active stars.

astro-ph.SR↗

arXiv2009

A LABOCA survey of the Extended Chandra Deep Field South - submillimeter properties of near-IR selected galaxies

Using the 330hr ESO-MPG 870-micron survey of the Extended Chandra Deep Field South (ECDF-S) obtained with the Large Apex BOlometer CAmera (LABOCA) on the Atacama Pathfinder EXperiment (APEX), we have carried out a stacking analysis at submillimeter (submm) wavelengths of a sample of 8266 near-infra-red (near-IR) selected (K_vega <= 20) galaxies, including 893 BzK galaxies, 1253 extremely red objects (EROs) and 737 distant red galaxies (DRGs), selected from the Multi-wavelength Survey by Yale-Chile (MUSYC). We measure average 870-micron fluxes of 0.20+-0.01mJy (20.0sigma), 0.45+-0.04mJy (11.3sigma), 0.42+-0.03mJy (14.0sigma), and 0.41+-0.04mJy (10.3sigma) for the K_vega <= 20, BzK, ERO and DRG samples, respectively. For the BzK, ERO and DRG subsamples, which overlap to some degree and are like to be at z ~ 1-2, this implies an average far-IR luminosity of ~2-6x10^{11} Lsolar and star formation rate of ~40-100Msolar. Splitting the BzK galaxies up into star-forming (sBzK) and passive (pBzK) galaxies, the former is significantly detected (0.48+-0.04mJy, 12.0sigma) while the latter is only marginally detected (0.27+-0.10mJy, 2.7sigma), thus confirming that the sBzK/pBzK criteria do isolate obscured, star forming and truly passive galaxies. The K_vega <= 20 galaxies are found to contribute with 6.6+-0.3Jy deg^{-2} (~15%) to the 870-micron extragalactic background light (EBL). sBzK and pBzK galaxies contribute 1.7+-0.2Jy deg^{-2} (~4%) and 0.2+-0.1 Jy deg^{-2} (< 0.5%) to the EBL. [Abridged]

astro-ph.CO↗

arXiv2009

The Large APEX Bolometer Camera LABOCA

The Large APEX Bolometer Camera, LABOCA, has been commissioned for operation as a new facility instrument t the Atacama Pathfinder Experiment 12m submillimeter telescope. This new 295-bolometer total power camera, operating in the 870 micron atmospheric window, combined with the high efficiency of APEX and the excellent atmospheric transmission at the site, offers unprecedented capability in mapping submillimeter continuum emission for a wide range of astronomical purposes.

astro-ph.IM↗

arXiv2009

Imaging the cool gas, dust, star formation, and AGN in the first galaxies

When, and how, did the first galaxies and supermassive black holes (SMBH) form, and how did they reionization the Universe? First galaxy formation and cosmic reionization are among the last frontiers in studies of cosmic structure formation. We delineate the detailed astrophysical probes of early galaxy and SMBH formation afforded by observations at centimeter through submillimeter wavelengths. These observations include studies of the molecular gas (= the fuel for star formation in galaxies), atomic fine structure lines (= the dominant ISM gas coolant), thermal dust continuum emission (= an ideal star formation rate estimator), and radio continuum emission from star formation and relativistic jets. High resolution spectroscopic imaging can be used to study galaxy dynamics and star formation on sub-kpc scales. These cm and mm observations are the necessary compliment to near-IR observations, which probe the stars and ionized gas, and X-ray observations, which reveal the AGN. Together, a suite of revolutionary observatories planned for the next decade from centimeter to X-ray wavelengths will provide the requisite panchromatic view of the complex processes involved in the formation of the first generation of galaxies and SMBHs, and cosmic reionization.

astro-ph.CO↗

arXiv2009

A Kiloparsec-Scale Hyper-Starburst in a Quasar Host Less than 1 Gigayear after the Big Bang

The host galaxy of the quasar SDSS J114816.64+525150.3 (at redshift z=6.42, when the Universe was <1 billion years old) has an infrared luminosity of 2.2x10^13 L_sun, presumably significantly powered by a massive burst of star formation. In local examples of extremely luminous galaxies such as Arp220, the burst of star formation is concentrated in the relatively small central region of <100pc radius. It is unknown on which scales stars are forming in active galaxies in the early Universe, which are likely undergoing their initial burst of star formation. We do know that at some early point structures comparable to the spheroidal bulge of the Milky Way must have formed. Here we report a spatially resolved image of [CII] emission of the host galaxy of J114816.64+525150.3 that demonstrates that its star forming gas is distributed over a radius of ~750pc around the centre. The surface density of the star formation rate averaged over this region is ~1000 M_sun/yr/kpc^2. This surface density is comparable to the peak in Arp220, though ~2 orders of magnitudes larger in area. This vigorous star forming event will likely give rise to a massive spheroidal component in this system.

astro-ph.GA↗

arXiv2008

A Sensitive Search For [NII] Emission in a z=6.4 Quasar Host Galaxy

We present a sensitive search for the ^3P_1->^3P_0 ground state fine structure line at 205 microns of ionized nitrogen ([NII]) in one of the highest redshift quasars (J1148+5251 at z=6.42) using the IRAM 30m telescope. The line is not detected at a (3 sigma) depth of 0.47 Jy km s^-1, corresponding to a [NII] luminosity limit of L_[NII] < 4.0x10^8 L_sun and a L_[NII]/L$_FIR ratio of <2x10^-5. In parallel, we have observed the CO(J=6-5) line in J1148+5251, which is detected at a flux level consistent with earlier interferometric observations. Using our earlier measurements of the [CII] 158 micron line strength, we derive an upper limit for the [NII]/[CII] line luminosity ratio of ~1/10 in J1148+5251. Our upper limit for the [CII]/[NII] ratio is similar to the value found for our Galaxy and M82 (the only extragalactic system where the [NII] line has been detected to date). Given the non-detection of the [NII] line we can only speculate whether or not high-z detections are within reach of currently operating observatories. However, [NII] and other fine strucure lines will play a critical role in characterizing the interstellar medium at the highest redshifts (z>7) using the Atacama Large Millimeter/submillimeter Array (ALMA), for which the highly excited rotational transitions of CO will be shifted outside the accessible (sub-)millimeter bands.

astro-ph↗

arXiv2008

A strong optical flare before the rising afterglow of GRB 080129

We report on GROND observations of a 40 sec duration (rest-frame) optical flare from GRB 080129 at redshift 4.349. The rise- and decay time follow a power law with indices +12 and -8, respectively, inconsistent with a reverse shock and a factor 10$^5$ faster than variability caused by ISM interaction. While optical flares have been seen in the past (e.g. GRB 990123, 041219B, 060111B and 080319B), for the first time, our observations not only resolve the optical flare into sub-components, but also provide a spectral energy distribution from the optical to the near-infrared once every minute. The delay of the flare relative to the GRB, its spectral energy distribution as well as the ratio of pulse widths suggest it to arise from residual collisions in GRB outflows \cite{liw08}.If this interpretation is correct and can be supported by more detailed modelling or observation in further GRBs, the delay measurement provides an independent, determination of the Lorentz factor of the outflow.

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arXiv2008

Molecular Gas in a Submillimeter Galaxy at z=4.5: Evidence for a Major Merger at 1 Billion Years after the Big Bang

We report the detection of CO molecular line emission in the z=4.5 millimeter-detected galaxy COSMOS_J100054+023436 (hereafter: J100+0234) using the IRAM Plateau de Bure interferometer (PdBI) and NRAO's Very Large Array (VLA). The CO(4-3) line as observed with PdBI has a full line width of ~1000 km/s, an integrated line flux of 0.66 Jy km/s, and a CO luminosity of 3.2e10 L_sun. Comparison to the 3.3sigma detection of the CO(2-1) line emission with the VLA suggests that the molecular gas is likely thermalized to the J=4-3 transition level. The corresponding molecular gas mass is 2.6e10 M_sun assuming an ULIRG-like conversion factor. From the spatial offset of the red- and blue-shifted line peaks and the line width a dynamical mass of 1.1e11 M_sun is estimated assuming a merging scenario. The molecular gas distribution coincides with the rest-frame optical and radio position of the object while being offset by 0.5'' from the previously detected Ly$α$ emission. J1000+0234 exhibits very typical properties for lower redshift (z~2) sub-millimeter galaxies (SMGs) and thus is very likely one of the long sought after high redshift (z>4) objects of this population. The large CO(4-3) line width taken together with its highly disturbed rest-frame UV geometry suggest an ongoing major merger about a billion years after the Big Bang. Given its large star formation rate (SFR) of >1000 M_sun/yr and molecular gas content this object could be the precursor of a 'red-and-dead' elliptical observed at a redshift of z=2.

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