The Comoving Infrared Luminosity Density: Domination of Cold Galaxies across 0<z<1

In this paper we examine the contribution of galaxies with different infrared (IR) spectral energy distributions (SEDs) to the comoving infrared luminosity density, a proxy for the comoving star formation rate (SFR) density. We characterise galaxies as having either a cold or hot IR SED depending upon whether the rest-frame wavelength of their peak IR energy output is above or below 90um. Our work is based on a far-IR selected sample both in the local Universe and at high redshift, the former consisting of IRAS 60um-selected galaxies at z<0.07 and the latter of Spitzer 70um selected galaxies across 0.1<z<1. We find that the total IR luminosity densities for each redshift/luminosity bin agree well with results derived from other deep mid/far-IR surveys. At z<0.07 we observe the previously known results: that moderate luminosity galaxies (L_IR<10^11 Lsun) dominate the total luminosity density and that the fraction of cold galaxies decreases with increasing luminosity, becoming negligible at the highest luminosities. Conversely, above z=0.1 we find that luminous IR galaxies (L_IR>10^11 Lsun), the majority of which are cold, dominate the IR luminosity density. We therefore infer that cold galaxies dominate the IR luminosity density across the whole 0<z<1 range, hence appear to be the main driver behind the increase in SFR density up to z~1 whereas local luminous galaxies are not, on the whole, representative of the high redshift population.Comment: 5 pages, 3 figures, accepted for publication in MNRA

OH spectral evolution of oxygen-rich late-type stars

We investigated the main-line spectral evolution with shell thickness of oxygen rich AGB stars. The study is based on a sample of 30 sources distributed along the IRAS colour-colour diagram. The sources were chosen to trace the Miras with thick shells and the whole range of OH/IR stars. The Miras exhibit a 1665 MHz emission strength comparable to that at 1667 MHz. Even though the Miras of the study have quite thick shells, their spectral characteristics in both main lines attest to a strong heterogeneity in their OH shell with, in particular, the presence of significant turbulence and acceleration. The expansion velocity has been found to be about the same at 1665 and 1667 MHz, taking into account a possible velocity turbulence of 1-2km/s at the location of the main-line maser emission. An increase in the intensity ratio 1667/1665 with shell thickness has been found. A plausible explanation for such a phenomenon is that competitive gain in favour of the 1667 MHz line increases when the shell is getting thicker. There is an evolution in the spectral profile shape with the appearance of a substantial inter-peak signal when the shell is getting thicker. Also, inter-peak components are found and can be as strong as the external standard peaks when the shell is very thick. This trend for an increase of the signal in between the two main peaks is thought to be the result of an increase of the saturation with shell thickness. All sources but two - a Mira and an OH/IR star from the lower part of the colour-colour diagram - are weakly polarized. The strong polarization observed for those two particular objects is thought to be the result of perturbations in their shells.Comment: 19 pages, 12 figures, accepted for publication in A&

Selection of ULIRGs in Infrared and Submm Surveys

We examine the selection characteristics of infrared and sub-mm surveys with IRAS, Spitzer, BLAST, Herschel and SCUBA and identify the range of dust temperatures these surveys are sensitive to, for galaxies in the ULIRG luminosity range (12<log(LIR)<13), between z=0 and z=4. We find that the extent of the redshift range over which surveys are unbiased is a function of the wavelength of selection, flux density limit and ULIRG luminosity. Short wavelength (<200{\mu}m) surveys with IRAS, Spitzer/MIPS and Herschel/PACS are sensitive to all SED types in a large temperature interval (17-87K), over a substantial fraction of their accessible redshift range. On the other hand, long wavelength (>200{\mu}m) surveys with BLAST, Herschel/ SPIRE and SCUBA are significantly more sensitive to cold ULIRGs, disfavouring warmer SEDs even at low redshifts. We evaluate observations in the context of survey selection effects, finding that the lack of cold ULIRGs in the local (z<0.1) Universe is not a consequence of selection and that the range of ULIRG temperatures seen locally is only a subset of a much larger range which exists at high redshift. We demonstrate that the local luminosity-temperature (L-T) relation, which indicates that more luminous sources are also hotter, is not applicable in the distant Universe when extrapolated to the ULIRG regime, because the scatter in observed temperatures is too large. Finally, we show that the difference between the ULIRG temperature distributions locally and at high redshift is not the result of galaxies becoming colder due to an L-T relation which evolves as a function of redshift. Instead, they are consistent with a picture where the evolution of the infrared luminosity function is temperature dependent, i.e. cold galaxies evolve at a faster rate than their warm counterparts.Comment: 11 pages, 6 figures, accepted for publication in MNRA

The influence of slope and peatland vegetation type on riverine dissolved organic carbon and water colour at different scales

Peatlands are important sources of fluvial carbon. Previous research has shown that riverine dissolved organic carbon (DOC) concentrations are largely controlled by soil type. However, there has been little work to establish the controls of riverine DOC within blanket peatlands that have not undergone major disturbance from drainage or burning. A total of 119 peatland catchments were sampled for riverine DOC and water colour across three drainage basins during six repeated sampling campaigns. The topographic characteristics of each catchment were determined from digital elevation models. The dominant vegetation cover was mapped using 0.5 m resolution colour infrared aerial images, with ground-truthed validation revealing 82 % accuracy. Forward and backward stepwise regression modelling showed that mean slope was a strong (and negative) determinant of DOC and water colour in blanket peatland river waters. There was a weak role for plant functional type in determining DOC and water colour. At the basin scale, there were major differences between the models depending on the basin. The dominance of topographic predictors of DOC found in our study, combined with a weaker role of vegetation type, paves the way for developing improved planning tools for water companies operating in peatland catchments. Using topographic data and aerial imagery it will be possible to predict which tributaries will typically yield lower DOC concentrations and which are therefore more suitable and cost-effective as raw water intakes

Identification of two bright z>3 submillimeter galaxy candidates in the COSMOS field

We present high-resolution interferometric Submillimeter Array (SMA) imaging at 890 microns (~2" resolution) of two millimeter selected galaxies -- MMJ100015+021549 and MMJ100047+021021 -- discovered with the Max-Planck Millimeter Bolometer (MAMBO) on the IRAM 30 m telescope and also detected with Bolocam on the CSO, in the COSMOS field. The first source is significantly detected at the ~11 sigma level, while the second source is tentatively detected at the ~4 sigma level, leading to a positional accuracy of ~0.2-0.3". MM100015+021549 is identified with a faint radio and K-band source. MMJ100047+021021 shows no radio emission and is tentatively identified with a very faint K-band peak which lies at ~1.2" from a clumpy optical source. The submillimeter-to-radio flux ratio for MM100015+021549 yields a redshift of ~4.8, consistent with the redshift implied by the UV-to-submillimeter photometry, z~3.0-5.0. We find evidence for warm dust in this source with an infrared luminosity in the range ~0.9-2.5x10^{13} L_sun, supporting the increasing evidence for a population luminous submillimeter galaxies at z>3. Finally, the lack of photometric data for MMJ100047+021021 does not allow us to investigate its properties in detail, however its submillimeter-to-radio ratio implies z>3.5.Comment: Accepted for publication in ApJ letter

Eddy current damper for the labshare remote laboratory shake table rig

The design and performance of an eddy current damper for the Labshare remotely operated "Shake Table" multi-storey building vibration rig is described. The damper comprises stationary E-cores on either side of a copper plate attached to each storey. An approximate formula for the damper retarding force F is derived, of the form F = -kuI2 for plate velocity u and E-core current I, and a criterion for its validity is established in terms of the magnetic Reynolds number. A close fit to measurements of the force using a load cell is obtained for k = 0.401 N/(ms-1A2). This was about 12% lower than the force determined by three-dimensional (3D) finite element analysis (FEA) using ANSYS 12.1, but the error can be attributed to manufacturing imperfections. Students can use the force formula in their investigation of closed-loop control of the Shake Table vibration. More generally, a formula for the force constant k can be used for the approximate design of any similar E-core damper

Genesis of the dusty Universe: modeling submillimetre source counts

We model the evolution of IR galaxies using a phenomenological approach to match the observed source counts at different IR wavelengths. We introduce a new algorithm for reproducing source counts based on direct integration of probability distributions rather than Monte-Carlo sampling. We construct a simple model for the evolution of the luminosity function and the colour distribution of IR galaxies which utilizes a minimum number of free parameters. Moreover we analyze how each of these parameters is constrained by observational data. The model is based on pure luminosity evolution and adopts the Dale & Helou SED templates. We find that the 850um source counts and their redshift distribution depend strongly on the shape of the luminosity evolution function, but only weakly on the details of the SEDs. We derive the best-fit evolutionary model using the 850um counts and redshift distribution as constraints. Moreover our best-fit shows a flattening of the faint end of the luminosity function towards high redshifts and requires a colour evolution which implies the typical dust temperatures of objects with the same luminosities to decrease with redshift. We compare our best-fit model to observed source counts at shorter and longer wavelengths which indicates our model reproduces the 70um and 1100um source counts remarkably well, but under-produces the counts at intermediate wavelengths. Analysis reveals that the discrepancy arises at low redshifts, indicating that revision of the adopted SED library towards lower dust temperatures (at a fixed infrared luminosity) is required. This modification is equivalent to a population of cold galaxies existing at low redshifts, as also indicated by recent Herschel results, which are underrepresented in IRAS sample. We show that the modified model successfully reproduces the source counts in a wide range of IR and submm wavelengths.Comment: 21 pages, 11 figures, 2 tables. Accepted for publication in MNRAS. Supplementary information could be found at http://www.strw.leidenuniv.nl/genesis

Polarization properties of OH masers in AGB and post-AGB stars

Context: Ground-state OH maser emission from late-type stars is usually polarized and remains a powerful probe of the magnetic field structure in the outer regions of circumstellar envelopes if observed with high angular and spectral resolutions. Observations in all four Stokes parameters are quite sparse and this is the most thorough, systematic study published to date. Aims: We aim to determine polarization properties of OH masers in an extensive sample of stars that show copious mass loss and search for candidate objects that are well-suited for high angular resolution studies. Methods: Full-polarization observations of the OH 1612 and 1667 MHz maser transitions were carried out for a sample of 117 AGB and post-AGB stars. Several targets were also observed in the 1665 MHz line. Results: Polarized features occur in more than 75% of the sources in the complete sample and there is no intrinsic difference in the occurrence of polarized emission between the three classes of objects of different infrared characteristics. The highest fractional polarization occurs for the post-AGB+PN and the Mira+SR classes at 1612 and 1667 MHz, respectively. Differences in the fractional polarization between the sources at different evolutionary stages appear to be related to depolarization caused by blending. The alignment of the polarization angles at the extreme sides of the shell implies a regular structure of the magnetic field of a strength of 0.3-2.3 mG. Conclusions: Polarized OH maser features are widespread in AGB and post-AGB stars. The relationship between the circular and linear fractional polarizations for a representative sample are consistent with the standard models of polarization for the Zeeman splitting higher than the Doppler line width, whereas the polarized features are the sigma components.Comment: Accepted for publication in Astronomy and Astrophysics. A version with appendices (Tab. A.1 and Fig. B.1) can be downloaded from http://paulo.astro.uni.torun.pl/~pw/arXiv_

A backward evolution model for infrared surveys: the role of AGN- and Color-L_TIR distributions

Empirical "backward" galaxy evolution models for infrared bright galaxies are constrained using multi-band infrared surveys. We developed a new Monte-Carlo algorithm for this task, implementing luminosity dependent distribution functions for the galaxies' infrared spectral energy distributions (SEDs) and for the AGN contribution, allowing for evolution of these quantities. The adopted SEDs take into account the contributions of both starbursts and AGN to the infrared emission, for the first time in a coherent treatment rather than invoking separate AGN and star-forming populations. In the first part of the paper we consider the quantification of the AGN contribution for local universe galaxies, as a function of total infrared luminosity. It is made using a large sample of LIRGs and ULIRGs for which mid-infrared spectra are available in the Spitzer archive. In the second part we present the model. Our best-fit model adopts very strong luminosity evolution, $L=L_0(1+z)^{3.4}$, up to $z=2.3$, and density evolution, $\rho=\rho_0(1+z)^2$, up to $z=1$, for the population of infrared galaxies. At higher $z$, the evolution rates drop as $(1+z)^{-1}$ and $(1+z)^{-1.5}$ respectively. To reproduce mid-infrared to submillimeter number counts and redshift distributions, it is necessary to introduce both an evolution in the AGN contribution and an evolution in the luminosity-temperature relation. Our models are in plausible agreement with current photometry-based estimates of the typical AGN contribution as a function of mid-infrared flux, and well placed to be compared to upcoming Spitzer spectroscopic results. As an example of future applications, we use our best-fitting model to make predictions for surveys with Herschel.Comment: Model available at: (http://www.physics.ubc.ca/~valiante/model) ApJ accepte