arXiv subjects

Frank Bertoldi

Publications and source records attributed to Frank Bertoldi.

At least 73 records · Page 4Linked to original sources

arXiv2016

ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Infrared Excess of UV-selected z=2-10 galaxies as a function of UV-continuum Slope and Stellar Mass

We make use of deep 1.2mm-continuum observations (12.7microJy/beam RMS) of a 1 arcmin^2 region in the Hubble Ultra Deep Field to probe dust-enshrouded star formation from 330 Lyman-break galaxies spanning the redshift range z=2-10 (to ~2-3 Msol/yr at 1sigma over the entire range). Given the depth and area of ASPECS, we would expect to tentatively detect 35 galaxies extrapolating the Meurer z~0 IRX-beta relation to z>~2 (assuming T_d~35 K). However, only 6 tentative detections are found at z>~2 in ASPECS, with just three at >3sigma. Subdividing z=2-10 galaxies according to stellar mass, UV luminosity, and UV-continuum slope and stacking the results, we only find a significant detection in the most massive (>10^9.75 Msol) subsample, with an infrared excess (IRX=L_{IR}/L_{UV}) consistent with previous z~2 results. However, the infrared excess we measure from our large selection of sub-L* (<10^9.75 Msol) galaxies is 0.11(-0.42)(+0.32) and 0.14(-0.14)(+0.15) at z=2-3 and z=4-10, respectively, lying below even an SMC IRX-beta relation (95% confidence). These results demonstrate the relevance of stellar mass for predicting the IR luminosity of z>~2 galaxies. We furthermore find that the evolution of the IRX-stellar mass relationship depends on the evolution of the dust temperature. If the dust temperature increases monotonically with redshift (as (1+z)^0.32) such that T_d~44-50 K at z>=4, current results are suggestive of little evolution in this relationship to z~6. We use these results to revisit recent estimates of the z>~3 SFR density. One less obvious implication is in interpreting the high Halpha EWs seen in z~5 galaxies: our results imply that star-forming galaxies produce Lyman-continuum photons at twice the efficiency (per unit UV luminosity) as implied in conventional models. Star-forming galaxies can then reionize the Universe, even if the escape fraction is <10%.

astro-ph.GA↗

arXiv2016

ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: Survey Description

We present the rationale for and the observational description of ASPECS: The ALMA SPECtroscopic Survey in the Hubble Ultra-Deep Field (UDF), the cosmological deep field that has the deepest multi-wavelength data available. Our overarching goal is to obtain an unbiased census of molecular gas and dust continuum emission in high-redshift (z$>$0.5) galaxies. The $\sim$1$'$ region covered within the UDF was chosen to overlap with the deepest available imaging from HST. Our ALMA observations consist of full frequency scans in band 3 (84-115 GHz) and band 6 (212-272 GHz) at approximately uniform line sensitivity ($L'_{\rm CO}\sim$2$\times$10$^{9}$ K km/s pc$^2$), and continuum noise levels of 3.8 $μ$Jy beam$^{-1}$ and 12.7 $μ$Jy beam$^{-1}$, respectively. The molecular surveys cover the different rotational transitions of the CO molecule, leading to essentially full redshift coverage. The [CII] emission line is also covered at redshifts $6.0<z<8.0$. We present a customized algorithm to identify line candidates in the molecular line scans, and quantify our ability to recover artificial sources from our data. Based on whether multiple CO lines are detected, and whether optical spectroscopic redshifts as well as optical counterparts exist, we constrain the most likely line identification. We report 10 (11) CO line candidates in the 3mm (1mm) band, and our statistical analysis shows that $<$4 of these (in each band) are likely spurious. Less than 1/3 of the total CO flux in the low-J CO line candidates are from sources that are not associated with an optical/NIR counterpart. We also present continuum maps of both the band 3 and band 6 observations. The data presented here form the basis of a number of dedicated studies that are presented in subsequent papers.

astro-ph.GA↗

arXiv2016

The European ALMA Regional Centre Network: A Geographically Distributed User Support Model

In recent years there has been a paradigm shift from centralised to geographically distributed resources. Individual entities are no longer able to host or afford the necessary expertise in-house, and, as a consequence, society increasingly relies on widespread collaborations. Although such collaborations are now the norm for scientific projects, more technical structures providing support to a distributed scientific community without direct financial or other material benefits are scarce. The network of European ALMA Regional Centre (ARC) nodes is an example of such an internationally distributed user support network. It is an organised effort to provide the European ALMA user community with uniform expert support to enable optimal usage and scientific output of the ALMA facility. The network model for the European ARC nodes is described in terms of its organisation, communication strategies and user support.

astro-ph.IM↗

arXiv2015

Imaging the cold molecular gas in SDSS J1148 + 5251 at z = 6.4

We present Karl G. Jansky Very Large Array (VLA) observations of the CO ($J = 2 \rightarrow 1$) line emission towards the $z = 6.419$ quasar SDSS J$114816.64+525150.3$ (J$1148+5251$). The molecular gas is found to be marginally resolved with a major axis of $0.9"$ (consistent with previous size measurements of the CO ($J = 7 \rightarrow 6$) emission). We observe tentative evidence for extended line emission towards the south west on a scale of ~$1.4"$, but this is only detected at $3.3σ$ significance and should be confirmed. The position of the molecular emission region is in excellent agreement with previous detections of low frequency radio continuum emission as well as [C ii] line and thermal dust continuum emission. These CO ($J = 2 \rightarrow 1$) observations provide an anchor for the low excitation part of the molecular line SED. We find no evidence for extended low excitation component, neither in the spectral line energy distribution nor the image. We fit a single kinetic gas temperature model of 50 K. We revisit the gas and dynamical masses in light of this new detection of a low order transition of CO, and confirm previous findings that there is no extended reservoir of cold molecular gas in J$1148+5251$, and that the source departs substantially from the low $z$ relationship between black hole mass and bulge mass. Hence, the characteristics of J$1148+5251$ at $z = 6.419$ are very similar to $z$~$2$ quasars, in the lack of a diffuse cold gas reservoir and kpc-size compactness of the star forming region.

astro-ph.GA↗

arXiv2015

An ALMA survey of Sub-millimeter Galaxies in the Extended Chandra Deep Field South: Physical properties derived from ultraviolet-to-radio modelling

[abridged] The ALESS survey has followed-up a sample of 122 sub-millimeter sources in the Extended Chandra Deep Field South at 870um with ALMA, allowing to pinpoint the positions of sub-millimeter galaxies (SMGs) to 0.3'' and to find their precise counterparts at different wavelengths. This enabled the first compilation of the multi-wavelength spectral energy distributions (SEDs) of a statistically reliable survey of SMGs. In this paper, we present a new calibration of the MAGPHYS modelling code that is optimized to fit these UV-to-radio SEDs of z>1 star-forming galaxies using an energy balance technique to connect the emission from stellar populations, dust attenuation and dust emission in a physically consistent way. We derive statistically and physically robust estimates of the photometric redshifts and physical parameters for the ALESS SMGs. We find that they have a median stellar mass $M_\ast=(8.9\pm0.1)\times10^{10} M_\odot$, SFR$=280\pm70 M_\odot$/yr, overall V-band dust attenuation $A_V=1.9\pm0.2$ mag, dust mass $M_\rm{dust}=(5.6\pm1.0)\times10^8 M_\odot$, and average dust temperature Tdust~40 K. The average intrinsic SED of the ALESS SMGs resembles that of local ULIRGs in the IR range, but the stellar emission of our average SMG is brighter and bluer, indicating lower dust attenuation, possibly because they are more extended. We explore how the average SEDs vary with different parameters, and we provide a new set of SMG templates. To put the ALESS SMGs into context, we compare their stellar masses and SFRs with those of less actively star-forming galaxies at the same redshifts. At z~2, about half of the SMGs lie above the star-forming main sequence, while half are at the high-mass end of the sequence. At higher redshifts (z~3.5), the SMGs tend to have higher SFR and Mstar, but the fraction of SMGs that lie significantly above the main sequence decreases to less than a third.

astro-ph.GA↗

arXiv2015

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

We used the PdBI to map a sample of 15 SMGs in the COSMOS field at the wavelength of 1.3 mm. The target SMGs were originally discovered in the JCMT/AzTEC 1.1 mm continuum survey at S/N=4-4.5. This paper presents, for the first time, interferometric millimetre-wavelength observations of these sources. The angular resolution of our observations, 1.8", allowed us to accurately determine the positions of the target SMGs. Using a detection threshold of S/N>4.5 regardless of multiwavelength counterpart association, and 4<S/N<=4.5 if a multiwavelength counterpart within 1.5" is also present, the total number of detections in our survey is 22. Three of our detected SMGs (AzTEC21, 27, and 28; which corresponds to 20%) are marginally resolved at our angular resolution, and these sources are found to have elongated or clumpy morphologies and/or multiple components. Using optical to NIR photometric redshifts, available spectroscopic redshifts, and redshifts estimated from the radio-to-submm spectral index we infer a median redshift of $\tilde{z}=3.20\pm0.25$ for our sample. To study the overall multiplicity and redshift distribution of flux-limited samples of SMGs we combined these sources with the 15 brightest AzTEC SMGs detected at 1.1 mm, AzTEC1-15, and studied previously. This constitutes a complete, flux- and S/N-limited 1.1-mm selected sample. We find that the median redshift for the 15 brightest AzTEC SMGs ($\tilde{z}=3.05\pm0.44$) is consistent with that for AzTEC16-30. This conforms to recent observational findings that SMGs do not exhibit any significant trend between the redshift and (sub)mm flux density. For the combined AzTEC1-30 sample we derive a median redshift of $\tilde{z}=3.17\pm0.27$, consistent with previous results based on mm-selected samples. We further infer that within the combined AzTEC1-30 sample $\sim25\pm9\%$ of sources separate into multiple components.

astro-ph.GA↗

arXiv2015

Evidence for a pressure discontinuity at the position of the Coma relic from Planck Sunyaev-Zel'dovich effect data

Radio relics are Mpc-scale diffuse synchrotron sources found in galaxy cluster outskirts. They are believed to be associated with large-scale shocks propagating through the intra-cluster medium, although the connection between radio relics and the cluster merger shocks is not yet proven conclusively. We present a first tentative detection of a pressure jump in the well-known relic of the Coma cluster through Sunyaev-Zel'dovich (SZ) effect imaging.The SZE data are extracted from the first public all-sky data release of Planck and we use high-frequency radio data at 2.3 GHz to constrain the shock-front geometry. The SZE data provide evidence for a pressure discontinuity, consistent with the relic position, without requiring any additional prior on the shock-front location. The derived Mach number M = 2.9 (+0.8/-0.6) is consistent with X-ray and radio results. A high-pressure "filament" without any pressure discontinuity is disfavoured by X-ray measurements and a "sub-cluster" model based on the infalling group NGC 4839 can be ruled out considering the published mass estimates for this group. These results signify a first attempt towards directly measuring the pressure discontinuity for a radio relic and the first SZ-detected shock feature observed near the virial radius of a galaxy cluster.

astro-ph.CO↗

arXiv2014

Evolution of the dust emission of massive galaxies up to z=4 and constraints on their dominant mode of star formation

We aim to measure the average dust and molecular gas content of massive star-forming galaxies ($\rm > 3 \times 10^{10}\,M_\odot$) up to z=4 in the COSMOS field to determine if the intense star formation observed at high redshift is induced by major mergers or caused by large gas reservoirs. Firstly, we measured the evolution of the average spectral energy distributions as a function of redshift using a stacking analysis of Spitzer, Herschel, LABOCA, and AzTEC data for two samples of galaxies: normal star-forming objects and strong starbursts, as defined by their distance to the main sequence. We found that the mean intensity of the radiation field $< U >$ heating the dust (strongly correlated with dust temperature) increases with increasing redshift up to z$\sim$4 in main-sequence galaxies. We can reproduce this evolution with simple models that account for the decrease of the gas metallicity with redshift. No evolution of $< U >$ with redshift is found in strong starbursts. We then deduced the evolution of the molecular gas fraction (defined here as $\rm M_{\rm mol}/(M_{\rm mol}+M_\star)$) with redshift and found a similar, steeply increasing trend for both samples. At z$\sim$4, this fraction reaches $\sim$60%. The average position of the main-sequence galaxies is on the locus of the local, normal star-forming disks in the integrated Schmidt-Kennicutt diagram (star formation rate versus mass of molecular gas), suggesting that the bulk of the star formation up to z=4 is dominated by secular processes.

astro-ph.GA↗

arXiv2014

Confirming the Quiescent Galaxy Population out to $z=3$: A Stacking Analysis of Mid-, Far-Infrared and Radio Data

We present stringent constraints on the average mid-, far-infrared and radio emissions of $\sim$14200 quiescent galaxies (QGs), identified out to $z=3$ in the COSMOS field via their rest-frame NUV$-$r and r$-$J colors, and with stellar masses $M_{\star}=10^{9.8-12.2} \,M_{\odot} $. Stacking in deep Spitzer (MIPS $24\,μ$m), Herschel (PACS and SPIRE), and VLA (1.4 GHz) maps reveals extremely low dust-obscured star formation rates for QGs (SFR $<0.1-3\,M_{\odot}$yr$^{-1}$ at $z \leqslant 2$ and $<6-18\,M_{\odot}$yr$^{-1}$ at $z > 2$), consistent with the low unobscured SFRs ($<0.01-1.2\,M_{\odot}$yr$^{-1}$) inferred from modeling their ultraviolet-to-near-infrared photometry. The average SFRs of QGs are $>10\times$ below those of star-forming galaxies (SFGs) within the $M_{\star}$- and $z$-ranges considered. The stacked 1.4 GHz signals (S/N $> 5$) are, if attributed solely to star formation, in excess of the total (obscured plus unobscured) SFR limits, suggestive of a widespread presence of low-luminosity active galactic nuclei (AGN) among QGs. Our results reaffirm the existence of a significant population QGs out to $z = 3$, thus corroborating the need for powerful quenching mechanism(s) to terminate star formation in galaxies at earlier epochs.

astro-ph.GA↗

arXiv2014

ALMA Imaging of Gas and Dust in a Galaxy Protocluster at Redshift 5.3: [CII] Emission in "Typical" Galaxies and Dusty Starbursts ~1 Billion Years after the Big Bang

We report interferometric imaging of [CII] and OH emission toward the center of the galaxy protocluster associated with the z=5.3 submillimeter galaxy (SMG) AzTEC-3, using the Atacama Large (sub)Millimeter Array (ALMA). We detect strong [CII], OH, and rest-frame 157.7 um continuum emission toward the SMG. The [CII] emission is distributed over a scale of 3.9 kpc, implying a dynamical mass of 9.7 x 10^10 Msun, and a star formation rate (SFR) surface density of Sigma_SFR = 530 Msun/yr/kpc2. This suggests that AzTEC-3 forms stars at Sigma_SFR approaching the Eddington limit for radiation pressure supported disks. We find that the OH emission is slightly blueshifted relative to the [CII] line, which may indicate a molecular outflow associated with the peak phase of the starburst. We also detect and dynamically resolve [CII] emission over a scale of 7.5 kpc toward a triplet of Lyman-break galaxies with moderate UV-based SFRs in the protocluster at ~95kpc projected distance from the SMG. These galaxies are not detected in the continuum, suggesting far-infrared SFRs of <18-54 Msun/yr, consistent with a UV-based estimate of 22 Msun/yr. The spectral energy distribution of these galaxies is inconsistent with nearby spiral and starburst galaxies, but resembles those of dwarf galaxies. This is consistent with expectations for young starbursts without significant older stellar populations. This suggests that these galaxies are significantly metal-enriched, but not heavily dust-obscured, "normal" star-forming galaxies at z>5, showing that ALMA can detect the interstellar medium in "typical" galaxies in the very early universe.

astro-ph.GA↗

arXiv2014

ALMA Observation of 158 micron [CII] Line and Dust Continuum of a z=7 Normally Star-forming Galaxy in the Epoch of Reionization

We present ALMA observations of the [CII] line and far-infrared (FIR) continuum of a normally star-forming galaxy in the reionization epoch, the z=6.96 Ly-alpha emitter (LAE) IOK-1. Probing to sensitivities of sigma_line = 240 micro-Jy/beam (40 km/s channel) and sigma_cont = 21 micro-Jy/beam, we found the galaxy undetected in both [CII] and continuum. Comparison of UV - FIR spectral energy distribution (SED) of IOK-1, including our ALMA limit, with those of several types of local galaxies (including the effects of the cosmic microwave background, CMB, on the FIR continuum) suggests that IOK-1 is similar to local dwarf/irregular galaxies in SED shape rather than highly dusty/obscured galaxies. Moreover, our 3 sigma FIR continuum limit, corrected for CMB effects, implies intrinsic dust mass M_dust < 6.4 x 10^7 M_sun, FIR luminosity L_FIR < 3.7 x 10^{10} L_sun (42.5 - 122.5 micron), total IR luminosity L_IR < 5.7 x 10^{10} L_sun (8 - 1000 micron) and dust-obscured star formation rate (SFR) < 10 M_sun/yr, if we assume that IOK-1 has a dust temperature and emissivity index typical of local dwarf galaxies. This SFR is 2.4 times lower than one estimated from the UV continuum, suggesting that < 29% of the star formation is obscured by dust. Meanwhile, our 3 sigma [CII] flux limit translates into [CII] luminosity, L_[CII] < 3.4 x 10^7 L_sun. Locations of IOK-1 and previously observed LAEs on the L_[CII] vs. SFR and L_[CII]/L_FIR vs. L_FIR diagrams imply that LAEs in the reionization epoch have significantly lower gas and dust enrichment than AGN-powered systems and starbursts at similar/lower redshifts, as well as local star-forming galaxies.

astro-ph.GA↗

arXiv2014

An ALMA Survey of Submillimeter Galaxies in the Extended Chandra Deep Field South: The Redshift Distribution and Evolution of Submillimeter Galaxies

We present the first photometric redshift distribution for a large unbiased sample of 870um selected submillimeter galaxies (SMGs) with robust identifications based on observations with the Atacama Large Millimeter Array (ALMA). In our analysis we consider 96 SMGs in the Extended Chandra Deep Field South, 77 of which have 4-19 band, optical-near-infrared, photometry. We model the Spectral Energy Distributions (SEDs) for these 77 SMGs, deriving a median photometric redshift of z=2.3+/-0.1. The remaining 19 SMGs have insufficient optical or near-infrared photometry to derive photometric redshifts, but a stacking analysis of IRAC and Herschel observations confirms they are not spurious. Assuming these sources have an absolute H-band magnitude distribution comparable to that of a complete sample of z~1-2 SMGs, we demonstrate that the undetected SMGs lie at higher redshifts, raising the median redshift for SMGs to z=2.5+/-0.2. More critically we show that the proportion of galaxies undergoing an SMG phase at z>3 is 35+/-5% of the total population. We derive a median stellar mass for SMGs of Mstar=(8+/-1)x10^10Mo, but caution that there are significant systematic uncertainties in our stellar mass estimate, up to x5 for individual sources. We compare our sample of SMGs to a volume-limited, morphologically classified sample of ellipticals in the local Universe. Assuming the star formation activity in SMGs has a timescale of ~100Myr we show that their descendants at z~0 would have a space density and M_H distribution which are in good agreement with those of local ellipticals. In addition the inferred mass-weighted ages of the local ellipticals broadly agree with the look-back times of the SMG events. Taken together, these results are consistent with a simple model that identifies SMGs as events that form most of the stars seen in the majority of luminous elliptical galaxies at the present day.

astro-ph.CO↗

arXiv2014

Pinpointing the Molecular Gas within a Lyman Alpha Blob at z ~ 2.7

We present IRAM PdBI observations of the CO(3-2) and CO(5-4) line transitions from a Ly-alpha blob at z~2.7 in order to investigate the gas kinematics, determine the location of the dominant energy source, and study the physical conditions of the molecular gas. CO line and dust continuum emission are detected at the location of a strong MIPS source that is offset by ~1.5" from the Ly-alpha peak. Neither of these emission components is resolved with the 1.7" beam, showing that the gas and dust are confined to within ~7kpc from this galaxy. No millimeter source is found at the location of the Ly-alpha peak, ruling out a central compact source of star formation as the power source for the Ly-alpha emission. Combined with a spatially-resolved spectrum of Ly-alpha and HeII, we constrain the kinematics of the extended gas using the CO emission as a tracer of the systemic redshift. Near the MIPS source, the Ly-alpha profile is symmetric and its line center agrees with that of CO line, implying that there are no significant bulk flows and that the photo-ionization from the MIPS source might be the dominant source of the Ly-alpha emission. In the region near the Ly-alpha peak, the gas is slowly receding (~100km/s) with respect to the MIPS source, thus making the hyper-/superwind hypothesis unlikely. We find a sub-thermal line ratio between two CO transitions, I_CO(5-4)/I_CO(3-2)=0.97+/-0.21. This line ratio is lower than the average values found in high-z SMGs and QSOs, but consistent with the value found in the Galactic center, suggesting that there is a large reservoir of low-density molecular gas that is spread over the MIPS source and its vicinity.

astro-ph.GA↗

arXiv2014

Search for [CII] emission in z=6.5-11 star-forming galaxies

We present the search for the [CII] emission line in three $z>6.5$ Lyman-alpha emitters (LAEs) and one J-Dropout galaxy using the Combined Array for Research in Millimeter-wave Astronomy (CARMA) and the Plateau de Bure Interferometer (PdBI). We observed three bright $z\sim6.5-7$ LAEs discovered in the SUBARU deep field (SDF) and the Multiple Imaged lensed $z\sim 11$ galaxy candidate found behind the galaxy cluster MACSJ0647.7+7015. For the LAEs IOK-1 ($z=6.965$), SDF J132415.7+273058 ($z=6.541$) and SDF J132408.3+271543 ($z=6.554$) we find upper limits for the [CII] line luminosity of $<2.05$, $<4.52$ and $<10.56\times10^{8}{\rm L}_{\odot}$ respectively. We find upper limits to the FIR luminosity of the galaxies using a spectral energy distribution template of the local galaxy NGC 6946 and taking into account the effects of the Cosmic Microwave Background on the mm observations. For IOK-1, SDF J132415.7+273058 and SDF J132408.3+271543 we find upper limits for the FIR luminosity of $<2.33$, $3.79$ and $7.72\times10^{11}{\rm L}_{\odot}$ respectively. For the lensed galaxy MACS0647-JD, one of the highest redshift galaxy candidate to date with $z_{\rm ph}=10.7^{+0.6}_{-0.4}$ we put an upper limit in the [CII] emission of $<1.36\times10^{8}\times(μ/15)^{-1}{\rm L}_{\odot}$ and an upper limit in the FIR luminosity of $<6.1\times10^{10}\times(μ/15)^{-1}{\rm L}_{\odot}$ (where $μ$ is the magnification factor). We explore the different conditions relevant for the search for [CII] emission in high redshift galaxies as well as the difficulties for future observations with ALMA and CCAT.

astro-ph.GA↗

arXiv2013

Star Formation and Gas Kinematics of Quasar Host Galaxies at z~6: New insights from ALMA

We present ALMA observations of the [C II] 158 micron fine structure line and dust continuum emission from the host galaxies of five redshift 6 quasars. We also report complementary observations of 250 GHz dust continuum and CO (6-5) line emission from the z=6.00 quasar SDSS J231038.88+185519.7. The ALMA observations were carried out in the extended array at 0.7" resolution. We have detected the line and dust continuum in all five objects. The derived [C II] line luminosities are 1.6x10^{9} to 8.8x10^{9} Lsun and the [C II]-to-FIR luminosity ratios are 3.0-5.6x10^{-4}, which is comparable to the values found in other high-redshift quasar-starburst systems and local ultra-luminous infrared galaxies. The sources are marginally resolved and the intrinsic source sizes (major axis FWHM) are constrained to be 0.3" to 0.6" (i.e., 1.7 to 3.5 kpc) for the [C II] line emission and 0.2" to 0.4" (i.e., 1.2 to 2.3 kpc) for the continuum. These measurements indicate that there is vigorous star formation over the central few kpc in the quasar host galaxies. The ALMA observations also constrain the dynamical properties of the atomic gas in the starburst nuclei. The intensity-weighted velocity maps of three sources show clear velocity gradients. Such velocity gradients are consistent with a rotating, gravitationally bound gas component, although they are not uniquely interpreted as such. Under the simplifying assumption of rotation, the implied dynamical masses within the [C II]-emitting regions are of order 10^{10} to 10^{11} Msun. Given these estimates, the mass ratios between the SMBHs and the spheroidal bulge are an order of magnitude higher than the mean value found in local spheroidal galaxies, which is in agreement with results from previous CO observations of high redshift quasars.

astro-ph.CO↗

arXiv2013

An ALMA survey of submillimetre galaxies in the Extended Chandra Deep Field South: High resolution 870um source counts

We report the first counts of faint submillimetre galaxies (SMG) in the 870-um band derived from arcsecond resolution observations with the Atacama Large Millimeter Array (ALMA). We have used ALMA to map a sample of 122 870-um-selected submillimetre sources drawn from the (0.5x0.5)deg^2 LABOCA Extended Chandra Deep Field South Submillimetre Survey (LESS). These ALMA maps have an average depth of sigma(870um)~0.4mJy, some ~3x deeper than the original LABOCA survey and critically the angular resolution is more than an order of magnitude higher, FWHM of ~1.5" compared to ~19" for the LABOCA discovery map. This combination of sensitivity and resolution allows us to precisely pin-point the SMGs contributing to the submillimetre sources from the LABOCA map, free from the effects of confusion. We show that our ALMA-derived SMG counts broadly agree with the submillimetre source counts from previous, lower-resolution single-dish surveys, demonstrating that the bulk of the submillimetre sources are not caused by blending of unresolved SMGs. The difficulty which well-constrained theoretical models have in reproducing the high-surface densities of SMGs, thus remains. However, our observations do show that all of the very brightest sources in the LESS sample, S(870um)>12mJy, comprise emission from multiple, fainter SMGs, each with 870-um fluxes of <9mJy. This implies a natural limit to the star-formation rate in SMGs of <10^3 M_Sun/yr, which in turn suggests that the space densities of z>1 galaxies with gas masses in excess of ~5x10^10 M_Sun is <10^-5 Mpc^-3. We also discuss the influence of this blending on the identification and characterisation of the SMG counterparts to these bright submillimetre sources and suggest that it may be responsible for previous claims that they lie at higher redshifts than fainter SMGs.

astro-ph.CO↗

arXiv2013

Empirical predictions for (sub-)millimeter line and continuum deep fields

[abridged] Modern (sub-)millimeter/radio interferometers will enable us to measure the dust and molecular gas emission from galaxies that have luminosities lower than the Milky Way, out to high redshifts and with unprecedented spatial resolution and sensitivity. This will provide new constraints on the star formation properties and gas reservoir in galaxies throughout cosmic times through dedicated deep field campaigns targeting the CO/[CII] lines and dust continuum emission. In this paper, we present empirical predictions for such (sub-)millimeter line and continuum deep fields. We base these predictions on the deepest available optical/near-infrared ACS and NICMOS data on the Hubble Ultra Deep Field. Using a physically-motivated spectral energy distribution model, we fit the observed optical/near-infrared emission of 13,099 galaxies with redshifts up to z=5, and obtain median likelihood estimates of their stellar mass, star formation rate, dust attenuation and dust luminosity. We derive statistical constraints on the dust emission in the infrared and (sub-)millimeter which are consistent with the observed optical/near-infrared emission in terms of energy balance. This allows us to estimate, for each galaxy, the (sub-)millimeter continuum flux densities in several ALMA, PdBI/NOEMA and JVLA bands. Using empirical relations between the observed CO/[CII] line luminosities and the infrared luminosity, we infer the flux of the CO(1-0) and [CII] lines from the estimated infrared luminosity of each galaxy in our sample. We then predict the fluxes of higher CO transition lines CO(2-1) to CO(7-6) bracketing two extreme gas excitation scenarios. We use our predictions to discuss possible deep field strategies with ALMA. The predictions presented in this study will serve as a direct benchmark for future deep field campaigns in the (sub-)millimeter regime.

astro-ph.CO↗

arXiv2012

Star Formation in Quasar Host Galaxies at Redshift 6: Millimeter Surveys and New Insights from ALMA

We have been carrying out a systematic survey of the star formation and ISM properties in the host galaxies of z~6 quasars. Our 250 GHz observations, together with available data from the literature, yield a sample of 14 z~6 quasars that are bright in millimeter dust continuum emission with estimated FIR luminosities of a few 10^12 to 10^13 Lsun. Most of these millimeter-detected z~6 quasars have also been detected in molecular CO line emission, indicating molecular gas masses on order of 10^10 Msun. We have searched for [C II] 158 micron fine structure line emission toward four of the millimeter bright z~6 quasars with ALMA and all of them have been detected. All these results suggest massive star formation at rates of about 600 to 2000 Msun/yr over the central few kpc region of these quasar host galaxies.

astro-ph.CO↗