arXiv subjects
Publications and source records attributed to A. Weiss.
Let K/k be a finite Galois extension of number fields with Galois group G, S a large set of primes of K, and E the G-module of S-units of K. Previous work has determined the data which is necessary to determine the stable isomorphism class of E. This paper explains how to build a G-module M from this data which has the property that M is stably isomorphic to the direct sum of E and some free G-module F.
We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO). We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230 GHz VLBI track with baseline lengths of 2800 M$λ$ to 7200 M$λ$ and a finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on all baselines with SNRs of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy. Visibility data suggest an emission region <38 uas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 10^10 K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ~38 uas. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 uas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40 uas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.
We model the intensity of emission lines from the CO molecule, based on hydrodynamic simulations of spirals, mergers, and high-redshift galaxies with very high resolutions (3pc and 10^3 Msun) and detailed models for the phase-space structure of the interstellar gas including shock heating, stellar feedback processes and galactic winds. The simulations are analyzed with a Large Velocity Gradient (LVG) model to compute the local emission in various molecular lines in each resolution element, radiation transfer and opacity effects, and the intensity emerging from galaxies, to generate synthetic spectra for various transitions of the CO molecule. This model reproduces the known properties of CO spectra and CO-to-H2 conversion factors in nearby spirals and starbursting major mergers. The high excitation of CO lines in mergers is dominated by an excess of high-density gas, and the high turbulent velocities and compression that create this dense gas excess result in broad linewidths and low CO intensity-to-H2 mass ratios. When applied to high-redshift gas-rich disks galaxies, the same model predicts that their CO-to-H2 conversion factor is almost as high as in nearby spirals, and much higher than in starbursting mergers. High-redshift disk galaxies contain giant star-forming clumps that host a high-excitation component associated to gas warmed by the spatially-concentrated stellar feedback sources, although CO(1-0) to CO(3-2) emission is overall dominated by low-excitation gas around the densest clumps. These results overall highlight a strong dependence of CO excitation and the CO-to-H2 conversion factor on galaxy type, even at similar star formation rates or densities. The underlying processes are driven by the interstellar medium structure and turbulence and its response to stellar feedback, which depend on global galaxy structure and in turn impact the CO emission properties.
We combine molecular gas masses inferred from CO emission in 500 star forming galaxies (SFGs) between z=0 and 3, from the IRAM-COLDGASS, PHIBSS1/2 and other surveys, with gas masses derived from Herschel far-IR dust measurements in 512 galaxy stacks over the same stellar mass/redshift range. We constrain the scaling relations of molecular gas depletion time scale (tdepl) and gas to stellar mass ratio (Mmolgas/M*) of SFGs near the star formation main-sequence with redshift, specific star formation rate (sSFR) and stellar mass (M*). The CO- and dust-based scaling relations agree remarkably well. This suggests that the CO-H2 mass conversion factor varies little within 0.6dex of the main sequence (sSFR(ms,z,M*)), and less than 0.3dex throughout this redshift range. This study builds on and strengthens the results of earlier work. We find that tdepl scales as (1+z)^-0.3 *(sSFR/sSFR(ms,z,M*))^-0.5, with little dependence on M*. The resulting steep redshift dependence of Mmolgas/M* ~(1+z)^3 mirrors that of the sSFR and probably reflects the gas supply rate. The decreasing gas fractions at high M* are driven by the flattening of the SFR-M* relation. Throughout the redshift range probed a larger sSFR at constant M* is due to a combination of an increasing gas fraction and a decreasing depletion time scale. As a result galaxy integrated samples of the Mmolgas-SFR rate relation exhibit a super-linear slope, which increases with the range of sSFR. With these new relations it is now possible to determine Mmolgas with an accuracy of 0.1dex in relative terms, and 0.2dex including systematic uncertainties.
We present FIR-CO luminosity relations ($\log L_{\rm FIR} = α\log L'_{\rm CO} + β$) for the full CO rotational ladder from J=1-0 to J=13-12 for 62 local (z < 0.1) (Ultra) Luminous Infrared Galaxies (LIRGs) using data from Herschel SPIRE-FTS and ground-based telescopes. We extend our sample to high redshifts (z > 1) by including 35 (sub)-millimeter selected dusty star forming galaxies from the literature with robust CO observations. The addition of luminous starbursts at high redshifts enlarge the range of the FIR-CO luminosity relations towards the high-IR-luminosity end while also significantly increasing the small amount of mid-/high-J CO line data available prior to Herschel. This new data-set (both in terms of IR luminosity and J-ladder) reveals linear FIR-CO luminosity relations ($α\sim 1$) for J=1-0 up to J=5-4, with a nearly constant normalisation ($β\sim 2$). This is expected from the (also) linear FIR-(molecular line) relations found for the dense gas tracer lines (HCN and CS), as long as the dense gas mass fraction does not vary strongly within our (merger/starburst)-dominated sample. However from J=6-5 and up to J=13-12 we find an increasingly sub-linear slope and higher normalization constant with increasing J. We argue that these are caused by a warm (~100K) and dense ($>10^4{\rm cm^{-3}}$) gas component whose thermal state is unlikely to be maintained by star formation powered far-UV radiation fields (and thus is no longer directly tied to the star formation rate). We suggest that mechanical heating (e.g., supernova driven turbulence and shocks), and not cosmic rays, is the more likely source of energy for this component. The global CO spectral line energy distributions (SLEDs), which remain highly excited from J=6-5 up to J=13-12, are found to be a generic feature of the (U)LIRGs in our sample, and further support the presence of this gas component.
NGC1851 is surrounded by a stellar component that extends more than ten times beyond the tidal radius. Although the nature of this stellar structure is not known, it has been suggested to be a sparse halo of stars or associated with a stellar stream. We analyse the nature of this intriguing stellar component surrounding NGC1851 by investigating its radial velocities and chemical composition, in particular in comparison with those of the central cluster analysed in a homogeneous manner. In total we observed 23 stars in the halo with radial velocities consistent with NGC1851, and for 15 of them we infer [Fe/H] abundances. Our results show that: (i) stars dynamically linked to NGC1851 are present at least up to ~2.5 tidal radii, supporting the presence of a halo of stars surrounding the cluster; (ii) apart from the NGC1851 radial velocity-like stars, our observed velocity distribution agrees with that expected from Galactic models, suggesting that no other sub-structure (such as a stream) at different radial velocities is present in our field; (iii) the chemical abundances for the s-process elements Sr and Ba are consistent with the s-normal stars observed in NGC1851; (iv) all halo stars have metallicities, and abundances for the other studied elements Ca, Mg and Cr, consistent with those exhibited by the cluster. The complexity of the whole NGC1851 cluster+halo system may agree with the scenario of a tidally-disrupted dwarf galaxy in which NGC1851 was originally embedded.
We investigate the influence of Asymptotic Giant Branch stars on integrated colours of star clusters of ages between ~100 Myr and a few gigayears, and composition typical for the Magellanic Clouds. We use state-of-the-art stellar evolution models that cover the full thermal pulse phase, and take into account the influence of dusty envelopes on the emerging spectra. We present an alternative approach to the usual isochrone method, and compute integrated fluxes and colours using a Monte Carlo technique that enables us to take into account statistical fluctuations due to the typical small number of cluster stars. We demonstrate how the statistical variations in the number of Asymptotic Giant Branch stars and the temperature and luminosity variations during thermal pulses fundamentally limit the accuracy of the comparison (and calibration, for population synthesis models that require a calibration of the Asymptotic Giant Branch contribution to the total luminosity) with star cluster integrated photometries. When compared to observed integrated colours of individual and stacked clusters in the Magellanic Clouds, our predictions match well most of the observations, when statistical fluctuations are taken into account, although there are discrepancies in narrow age ranges with some (but not all) set of observations.
We present the average rest-frame spectrum of high-redshift dusty, star-forming galaxies from 250-770GHz. This spectrum was constructed by stacking ALMA 3mm spectra of 22 such sources discovered by the South Pole Telescope and spanning z=2.0-5.7. In addition to multiple bright spectral features of 12CO, [CI], and H2O, we also detect several faint transitions of 13CO, HCN, HNC, HCO+, and CN, and use the observed line strengths to characterize the typical properties of the interstellar medium of these high-redshift starburst galaxies. We find that the 13CO brightness in these objects is comparable to that of the only other z>2 star-forming galaxy in which 13CO has been observed. We show that the emission from the high-critical density molecules HCN, HNC, HCO+, and CN is consistent with a warm, dense medium with T_kin ~ 55K and n_H2 >~ 10^5.5 cm^-3. High molecular hydrogen densities are required to reproduce the observed line ratios, and we demonstrate that alternatives to purely collisional excitation are unlikely to be significant for the bulk of these systems. We quantify the average emission from several species with no individually detected transitions, and find emission from the hydride CH and the linear molecule CCH for the first time at high redshift, indicating that these molecules may be powerful probes of interstellar chemistry in high-redshift systems. These observations represent the first constraints on many molecular species with rest-frame transitions from 0.4-1.2mm in star-forming systems at high redshift, and will be invaluable in making effective use of ALMA in full science operations.
We present new CO and C^o line measurements of the compact circumnuclear disk in the center of NGC 128 (Centaurus~A) obtained with the Herschel Space Observatory, as well as SEST, JCMT, and APEX. The Cen A center CO ladder is quite different from those of either star-burst galaxies or AGNs. In addition, the relative intensity of the central Cen A [CI] emission lines is much greate than that in any other galaxy. The CO surface brightness of the compact circumnuclear disk (CND) is significantly higher than that of the much more extended thin disk (ETD) in the same line of sight. Our LVG and PDR/XDR models suggest that much of the CND gas is relatively cool (25 - 80 K) and not very dense (~ 300 cm^{-3}) if the heating is by UV photons, although there is some gas in both the CND and the ETD with a much higher density of ~30 000 cm^{-3}. Finally, there is also high-excitation, high-density phase in the CND (but not in the ETD), either in the form of an extreme PDR but more likely in the form of an XDR. The total gas mass of the Cen A CND is 8.4 x 10^{7} M(sun), uncertain by a factor of two. The CO-H2 conversion factor is 4 x 10^{20} K km/s, also within a factor of two.
We study the properties of the interstellar medium in the interacting system BR1202-0725 at z=4.7 via its [NII] and [CII] fine-structure line emission. This system consists of a QSO, a sub-mm galaxy (SMG), and two Ly-alpha emitters (LAEs). Such a diversity in galaxy properties makes BR1202-0725 a unique laboratory of star formation and galaxy evolution at high redshift. We present ionized nitrogen ([NII] 205 micron) observations of this system, obtained with the IRAM Plateau de Bure Interferometer. We find no [NII] emission at the quasar location, but tentative [NII] line detections associated with the SMG and one of the LAEs. Together with available ionized carbon ([CII] 158 micron) ALMA observations of this system, we find the following: The [CII]/[NII] luminosity ratio is >5.5 for the QSO and the SMG, but it is as low as ~2 in the LAE, suggesting that, in this source, most of the [CII] emission is associated with the ionized medium (HII regions) rather than the neutral one (PDRs). This study demonstrates the importance of combined studies of multiple fine--structure lines in order to pin down the physical properties of the interstellar medium in distant galaxies.
We model the infrared to submillimeter spectral energy distribution of 11 nearby galaxies of the KINGFISH sample using Spitzer and Herschel data and compare model extrapolations at 870um (using different fitting techniques) with LABOCA 870um observations. We investigate how the differences between predictions and observations vary with model assumptions or environment. At global scales, we find that modified blackbody models using realistic cold emissivity indices (beta_c=2 or 1.5) are able to reproduce the 870um observed emission within the uncertainties for most of the sample. Low values (beta_c<1.3) would be required in NGC0337, NGC1512 and NGC7793. At local scales, we observe a systematic 870um excess when using beta_=2.0. The beta_c=1.5 or the Draine and Li (2007) models can reconcile predictions with observations in part of the disks. Some of the remaining excesses occur towards the centres and can be partly or fully accounted for by non-dust contributions such as CO(3-2) or, to a lesser extent, free-free or synchrotron emission. In three non-barred galaxies, the remaining excesses rather occur in the disk outskirts. This could be a sign of a flattening of the submm slope (and decrease of the effective emissivity index) with radius in these objects.
We present a molecular line scan in the Hubble Deep Field North (HDF-N) that covers the entire 3mm window (79-115 GHz) using the IRAM Plateau de Bure Interferometer. Our CO redshift coverage spans z<0.45, 1 2. We reach a CO detection limit that is deep enough to detect essentially all z>1 CO lines reported in the literature so far. We have developed and applied different line searching algorithms, resulting in the discovery of 17 line candidates. We estimate that the rate of false positive line detections is ~2/17. We identify optical/NIR counterparts from the deep ancillary database of the HDF-N for seven of these candidates and investigate their available SEDs. Two secure CO detections in our scan are identified with star-forming galaxies at z=1.784 and at z=2.047. These galaxies have colors consistent with the `BzK' color selection and they show relatively bright CO emission compared with galaxies of similar dust continuum luminosity. We also detect two spectral lines in the submillimeter galaxy HDF850.1 at z=5.183. We consider an additional 9 line candidates as high quality. Our observations also provide a deep 3mm continuum map (1-sigma noise level = 8.6 $μ$Jy/beam). Via a stacking approach, we find that optical/MIR bright galaxies contribute only to <50% of the SFR density at 1<z<3, unless high dust temperatures are invoked. The present study represents a first, fundamental step towards an unbiased census of molecular gas in `normal' galaxies at high-z, a crucial goal of extragalactic astronomy in the ALMA era.
We present direct constraints on the CO luminosity function at high redshift and the resulting cosmic evolution of the molecular gas density, $ρ_{\rm H2}$(z), based on a blind molecular line scan in the Hubble Deep Field North (HDF-N) using the IRAM Plateau de Bure Interferometer. Our line scan of the entire 3mm window (79-115 GHz) covers a cosmic volume of ~7000 Mpc$^3$, and redshift ranges z<0.45, 1.01 2. We use the rich multiwavelength and spectroscopic database of the HDF-N to derive some of the best constraints on CO luminosities in high redshift galaxies to date. We combine the blind CO detections in our molecular line scan (presented in a companion paper) with stacked CO limits from galaxies with available spectroscopic redshifts (slit or mask spectroscopy from Keck and grism spectroscopy from HST) to give first blind constraints on high-z CO luminosity functions and the cosmic evolution of the H2 mass density $ρ_{\rm H2}$(z) out to redshifts z~3. A comparison to empirical predictions of $ρ_{\rm H2}$(z) shows that the securely detected sources in our molecular line scan already provide significant contributions to the predicted $ρ_{\rm H2}$(z) in the redshift bins ~1.5 and ~2.7. Accounting for galaxies with CO luminosities that are not probed by our observations results in cosmic molecular gas densities $ρ_{\rm H2}$(z) that are higher than current predictions. We note however that the current uncertainties (in particular the luminosity limits, number of detections, as well as cosmic volume probed) are significant, a situation that is about to change with the emerging ALMA observatory.
We present Atacama Large Millimeter/submillimeter Array (ALMA) Cycle 0 Band 7 observations of an extremely metal-poor dwarf starburst galaxy in the Local Universe, SBS0335-052 (12+log(O/H)~7.2). With these observations, dust is detected at 870micron (ALMA Band 7), but 87% of the flux in this band is due to free-free emission from the starburst. We have compiled a spectral energy distribution (SED) of SBS0335-052 that spans almost 6 orders of magnitude in wavelength and fit it with a spherical dust shell heated by a single-age stellar population; the best-fit model gives a dust mass of (3.8+/-0.6)x10^4 Msun. We have also constructed a SED including Herschel archival data for IZw18, another low-metallicity dwarf starburst (12+log(O/H)=7.17), and fit it with a similar model to obtain a dust mass of (3.4+/-1.0)x10^2 Msun. Compared with their atomic gas mass, the dust mass of SBS0335-052 far exceeds the prediction of a linear trend of dust-to-gas mass ratio with metallicity, while IZw18 falls far below. We use gas scaling relations to assess a putative missing gas component in both galaxies and find that the missing, possibly molecular, gas in SBS0335-052 is a factor of 6 times higher than the value inferred from the observed HI column density; in IZw18 the missing component is 4 times smaller. Ultimately, despite their similarly low metallicity, the differences in gas and dust column densities in SBS0335-052 and IZw18 suggest that metal abundance does not uniquely define star-formation processes. At some level, self-shielding and the survival of molecules may depend just as much on gas and dust column density as on metallicity. The effects of low metallicity may at least be partially compensated for by large column densities in the interstellar medium.
We study the sub-mm properties of color-selected galaxies via a stacking analysis applied for the first time to interferometric data at sub-mm wavelengths. We base our study on 344 GHz ALMA continuum observations of ~20''-wide fields centered on 86 sub-mm sources detected in the LABOCA Extended Chandra Deep Field South Sub-mm Survey (LESS). We select various classes of galaxies (K-selected, star-forming sBzK galaxies, extremely red objects and distant red galaxies) according to their optical/NIR fluxes. We find clear, >10-sigma detections in the stacked images of all these galaxy classes. We include in our stacking analysis Herschel/SPIRE data to constrain the dust SED of these galaxies. We find that their dust emission is well described by a modified black body with Tdust~30 K and beta=1.6 and IR luminosities of (5-11)x10^{11} Lsun, or implied star formation rates of 75-140 Msun/yr. We compare our results with those of previous studies based on single-dish observations at 870 micron and find that our flux densities are a factor 2-3 higher than previous estimates. The discrepancy is observed also after removing sources individually detected in ALESS maps. We report a similar discrepancy by repeating our analysis on 1.4\,GHz observations of the whole ECDFS. Hence we find tentative evidence that galaxies that are associated in projected and redshift space with sub-mm bright sources are brighter than the average population. Finally, we put our findings in the context of the cosmic star formation rate density as a function of redshift.
We have employed state-of-the-art evolutionary models of low and intermediate-mass AGB stars, and included the effect of circumstellar dust shells on the spectral energy distribution (SED) of AGB stars, to revise the Padua library of isochrones (Bertelli et al. 1994). The major revision involves the thermally pulsing AGB phase, that is now taken from fully evolutionary calculations by Weiss & Ferguson (2009). Two libraries of about 600 AGB dust-enshrouded SEDs each have also been calculated, one for oxygen-rich M-stars and one for carbon-rich C-stars. Each library accounts for different values of input parameters like the optical depth τ, dust composition, and temperature of the inner boundary of the dust shell. These libraries of dusty AGB spectra have been implemented into a large composite library of theoretical stellar spectra, to cover all regions of the Hertzsprung-Russell Diagram (HRD) crossed by the isochrones. With the aid of the above isochrones and libraries of stellar SEDs, we have calculated the spectro-photometric properties (SEDs, magnitudes, and colours) of single-generation stellar populations (SSPs) for six metallicities, more than fifty ages (from 3 Myr to 15 Gyr), and nine choices of the Initial Mass Function. The new isochrones and SSPs have been compared to the colour-magnitude diagrams (CMDs) of field populations in the LMC and SMC, with particular emphasis on AGB stars, and the integrated colours of star clusters in the same galaxies, using data from the SAGE (Surveying the Agents of Galaxy Evolution) catalogues. We have also examined the integrated colours of a small sample of star clusters located in the outskirts of M31. The agreement between theory and observations is generally good. In particular, the new SSPs reproduce the red tails of the AGB star distribution in the CMDs of field stars in the Magellanic Clouds.
We present observations of SPT-S J053816-5030.8, a gravitationally-lensed dusty star forming galaxy (DSFG) at z = 2.7817, first discovered at millimeter wavelengths by the South Pole Telescope. SPT 0538-50 is typical of the brightest sources found by wide-field millimeter-wavelength surveys, being lensed by an intervening galaxy at moderate redshift (in this instance, at z = 0.441). We present a wide array of multi-wavelength spectroscopic and photometric data on SPT 0538-50, including data from ALMA, Herschel PACS and SPIRE, Hubble, Spitzer, VLT, ATCA, APEX, and the SMA. We use high resolution imaging from HST to de-blend SPT 0538-50, separating DSFG emission from that of the foreground lens. Combined with a source model derived from ALMA imaging (which suggests a magnification factor of 21 +/- 4), we derive the intrinsic properties of SPT 0538-50, including the stellar mass, far-IR luminosity, star formation rate, molecular gas mass, and - using molecular line fluxes - the excitation conditions within the ISM. The derived physical properties argue that we are witnessing compact, merger-driven star formation in SPT 0538-50, similar to local starburst galaxies, and unlike that seen in some other DSFGs at this epoch.
We present new [CI](1-0) and 12CO(4-3) Plateau de Bure Interferometer observations of five Sub-Millimeter Galaxies (SMGs) and combine these with all available [CI](1-0) literature detections in SMGs to probe the gas distribution within a sample of 14 systems. We explore the [CI](1-0) properties of the SMG population, particularly investigating the ratio of the [CI](1-0) luminosity to various 12CO transition and far-infrared luminosities. We find that the SMGs with new observations extend the spread of L[CI](1-0)/LFIR to much higher values than found before, with our complete sample providing a good representation of the diverse z>2 SMG population. We compare the line ratios to the outputs of photodissociation region (PDR) models to constrain the average density (n) and radiation field (in terms of the local field value, G0) of the SMGs. We find the SMGs are most comparable to local ULIRGs in G0 and n, however a significant tail of 5 of the 14 SMGs are likely best compared to less compact, local starburst galaxies, providing new evidence that many SMGs have extended star formation distributions and are therefore not simply scaled up versions of local ULIRGs. We explore the limitations of using simple PDR models to understand [CI], which may be concomitant with the bulk H2 mass rather than PDR-distributed. We therefore also assess [CI] as a tracer of H2, finding that for our sample SMGs, the H2 masses derived from [CI] are often consistent with those determined from low excitation 12CO. We conclude that [CI] observations provide a useful tool to probe the bulk gas and gas processes occurring within merging SMGs, however more detailed, resolved observations are required to fully exploit [CI] as a diagnostic.