High Surface Mass Research Articles

RADIATION TRANSFER OF MODELS OF MASSIVE STAR FORMATION. I. DEPENDENCE ON BASIC CORE PROPERTIES

Radiative transfer calculations of massive star formation are presented. These are based on the Turbulent Core Model of McKee & Tan and self-consistently included a hydrostatic core, an inside-out expansion wave, a zone of free-falling rotating collapse, wide-angle dust-free outflow cavities, an active accretion disk, and a massive protostar. For the first time for such models, an optically thick inner gas disk extends inside the dust destruction front. This is important to conserve the accretion energy naturally and for its shielding effect on the outer region of the disk and envelope. The simulation of radiation transfer is performed with the Monte Carlo code of Whitney, yielding spectral energy distributions (SEDs) for the model series, from the simplest spherical model to the fiducial one, with the above components each added step-by-step. Images are also presented in different wavebands of various telescope cameras, including Spitzer IRAC and MIPS, SOFIA FORCAST and Herschel PACS and SPIRE. The existence of the optically thick inner disk produces higher optical wavelength fluxes but reduces near- and mid-IR emission. The presence of outflow cavities, the inclination angle to the line of sight, and the thickness of the disk all affect the SEDs and images significantly. For the high mass surface density cores considered here, the mid-IR emission can be dominated by the outflow cavity walls, as has been suggested by De Buizer. The effect of varying the pressure of the environment bounding the surface of the massive core is also studied. With lower surface pressures, the core is larger, has lower extinction and accretion rates, and the observed mid-IR flux from the disk can then be relatively high even though the accretion luminosity is lower. In this case the silicate absorption feature becomes prominent, in contrast to higher density cores forming under higher pressures.

CONSTRAINTS ON THE ASSEMBLY AND DYNAMICS OF GALAXIES. I. DETAILED REST-FRAME OPTICAL MORPHOLOGIES ON KILOPARSEC SCALE OFz∼ 2 STAR-FORMING GALAXIES

We present deep and high-resolution HST/NIC2 F160W imaging at 1.6micron of six z~2 star-forming galaxies with existing near-IR integral field spectroscopy from SINFONI at the VLT. The unique combination of rest-frame optical imaging and nebular emission-line maps provides simultaneous insight into morphologies and dynamical properties. The overall rest-frame optical emission of the galaxies is characterized by shallow profiles in general (Sersic index n<1), with median effective radii of ~5kpc. The morphologies are significantly clumpy and irregular, which we quantify through a non-parametric morphological approach, estimating the Gini (G), Multiplicity (Psi), and M_20 coefficients. The strength of the rest-frame optical emission lines in the F160W bandpass indicates that the observed structure is not dominated by the morphology of line-emitting gas, and must reflect the underlying stellar mass distribution of the galaxies. The sizes and structural parameters in the rest-frame optical continuum and Halpha emission reveal no significant differences, suggesting similar global distributions of the on-going star formation and more evolved stellar population. While no strong correlations are observed between stellar population parameters and morphology within the NIC2/SINFONI sample itself, a consideration of the sample in the context of a broader range of z~2 galaxy types indicates that these galaxies probe the high specific star formation rate and low stellar mass surface density part of the massive z~2 galaxy population, with correspondingly large effective radii, low Sersic indices, low G, and high Psi and M_20. The combined NIC2 and SINFONI dataset yields insights of unprecedented detail into the nature of mass accretion at high redshift. [Abridged]

Estimation of the Greenland ice sheet surface mass balance for the 20th and 21st centuries

Abstract. Results from a regional climate simulation (1970–2006) over the Greenland ice sheet (GrIS) reveals that more than 97% of the interannual variability of the modelled Surface Mass Balance (SMB) can be explained by the GrIS summer temperature anomaly and the GrIS annual precipitation anomaly. This multiple regression is then used to empirically estimate the GrIS SMB since 1900 from climatological time series. The projected SMB changes in the 21st century are investigated with the set of simulations performed with atmosphere-ocean general circulation models (AOGCMs) of the Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR4). These estimates show that the high surface mass loss rates of recent years are not unprecedented in the GrIS history of the last hundred years. The minimum SMB rate seems to have occurred earlier in the 1930s and corresponds to a zero SMB rate. The AOGCMs project that the SMB rate of the 1930s would be common at the end of 2100. The temperature would be higher than in the 1930s but the increase of accumulation in the 21st century would partly offset the acceleration of surface melt due to the temperature increase. However, these assumptions are based on an empirical multiple regression only validated for recent/current climatic conditions, and the accuracy and time homogeneity of the data sets and AOGCM results used in these estimations constitute a large uncertainty.

Submillimeter Galaxies atz∼ 2: Evidence for Major Mergers and Constraints on Lifetimes, IMF, and CO‐H2Conversion Factor

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

Intense starbursts at z~5: first significant stellar mass assembly in the progenitors of present-day spheroids

AbstractHigh redshift galaxies play a key role in our developing understanding of galaxy formation and evolution. Since such galaxies are being studied within a Gyr of the big bang, they provide a unique probe of the physics of one of the first generations of large-scale star-formation. We have performed a complete statistical study of the physical properties of a robust sample of z~5 UV luminous galaxies selected using the Lyman-break technique. The characteristic properties of this sample differ from LBGs at z~3 of comparable luminosity in that they are a factor of ten less massive (~few×109 M⊙) and the majority (~70%) are considerably younger (&lt;100Myr). Our results support no more than a modest decline in the global star formation rate density at high redshifts and suggest that ~1% of the stellar mass density of the universe had already assembled at z~5. The constraint derived for the latter is affected by their young ages and short duty cycles which imply existing z~5 LBG samples may be highly incomplete. These intense starbursts have high unobscured star formation rate surface densities (~100s M⊙ yr−1 kpc−2), suggesting they drive outflows and winds that enrich the intra- and inter-galactic media with metals. These properties imply that the majority of z~5 LBGs are in formation meaning that most of their star-formation has likely occurred during the last few crossing times. They are experiencing their first (few) generations of large-scale star formation and are accumulating their first significant stellar mass. As such, z~5 LBGs are the likely progenitors of the spheroidal components of present-day massive galaxies (supported by their high stellar mass surface densities and their core phase-space densities).

Lyman-break galaxies at z 5 - I. First significant stellar mass assembly in galaxies that are not simply z 3 LBGs at higher redshift

We determine the ensemble properties of z~5 Lyman break galaxies (LBGs) selected as V-band dropouts to i(AB) 70%), whereas they comprise <30% of LBG samples at z~3. This result is robust under all reasonable modelling assumptions. These intense starbursts appear to be experiencing their first (few) generations of large-scale star formation and are accumulating their first significant stellar mass. Their dominance in luminous LBG samples suggests that z~5 witnesses a period of wide-spread, recent galaxy formation. As such, z~5 LBGs are the likely progenitors of the spheroidal components of present-day massive galaxies. This is supported by their high stellar mass surface densities, their core phase-space densities, as well as the ages of stars in the bulge of our Galaxy and other massive systems. Their high star formation rates per unit area suggest that these systems host outflows or winds that enrich the intra- and inter-galactic media with metals. Their estimated young ages are consistent with inefficient metal-mixing on galaxy-wide scales. Therefore these galaxies may contain a significant fraction of metal-free stars as has been proposed for z~3 LBGs (Jimenez & Haiman 2006). [Abridged]

The dependence of the pairwise velocity dispersion on galaxy properties

We present measurements of the pairwise velocity dispersion (PVD) for different classes of galaxies in the Sloan Digital Sky Survey (SDSS). For a sample of about 200 000 galaxies with redshifts in the interval 0.01 < z < 0.3, and r-band magnitudes M-0.1r between - 16 and - 23, we study the dependence of the PVD on galaxy properties such as luminosity, stellar mass (M-*), colour (g - r), 4000-angstrom break strength (D-4000), concentration index (C), and stellar surface mass density (mu(*)). The luminosity dependence of the PVD is in good agreement with the results of Jing & Borner for the two-degree Field Galaxy Redshift Survey catalogue, once the photometric bandpass difference between the two surveys is taken into account. The value of sigma(12) measured at k = 1 h Mpc(-1) decreases as a function of increasing galaxy luminosity for galaxies fainter than L*, before increasing again for the most luminous galaxies in our sample. Each of the galaxy subsamples selected according to luminosity or stellar mass is divided into two further subsamples according to colour, D4000, C and mu(*). We find that galaxies with redder colours and higher D4000, C, and mu(*) values have larger PVDs on all scales and at all luminosities/stellar masses. The dependence of the PVD on the parameters related to recent star formation ( colour, D4000) is stronger than on the parameters related to galaxy structure (C, mu(*)), especially on small scales and for faint galaxies. The reddest galaxies and galaxies with high surface mass densities and intermediate concentrations have the highest pairwise peculiar velocities, that is, these move in the strongest gravitational fields. We conclude that the faint red population located in rich clusters is responsible for the high PVD values that are measured for low-luminosity galaxies on small scales.

Orbits in disc galaxies with rapidly rotating massive nuclei: comparison with data from observations

An axially symmetric galactic dynamic model is used, with a disc, a massive nucleus and halo components, in order to reproduce recently obtained observation data in disc galaxies. The model reproduces very well two basic physical quantities, i.e. the high-velocity rotation and the high surface mass density in the central regions of some galaxies such as the galaxy NGC 3079. Going a step further, we investigate the properties of orbits in the model, the behaviour of the velocities of the system and their connections with the value of the conserved L z component of the angular momentum. The regular or chaotic nature of motion is also studied. All the above studies are made in two different cases: firstly, when the model is time independent and, secondly, when the model evolves with time.

The dependence of star formation history and internal structure on stellar mass for 105low-redshift galaxies

We study the relations between stellar mass, star formation history, size and internal structure for a complete sample of 122 808 galaxies drawn from the Sloan Digital Sky Survey. We show that low-redshift galaxies divide into two distinct families at a stellar mass of 3 × 1010 M⊙. Lower-mass galaxies have young stellar populations, low surface mass densities and the low concentrations typical of discs. Their star formation histories are more strongly correlated with surface mass density than with stellar mass. A significant fraction of the lowest-mass galaxies in our sample have experienced recent starbursts. At given stellar mass, the sizes of low-mass galaxies are lognormally distributed with dispersion δ (ln R50) ∼ 0.5, in excellent agreement with the idea that they form with little angular momentum loss through cooling and condensation in a gravitationally dominant dark matter halo. Their median stellar surface mass density scales with stellar mass as µ* ∝ M0.54*, suggesting that the stellar mass of a disc galaxy is proportional to the three halves power of its halo mass. All of this suggests that the efficiency of the conversion of baryons into stars in low-mass galaxies increases in proportion to halo mass, perhaps as a result of supernova feedback processes. At stellar masses above 3 × 1010 M⊙, there is a rapidly increasing fraction of galaxies with old stellar populations, high surface mass densities and the high concentrations typical of bulges. In this regime, the size distribution remains lognormal, but its dispersion decreases rapidly with increasing mass and the median stellar mass surface density is approximately constant. This suggests that the star formation efficiency decreases in the highest-mass haloes, and that little star formation occurs in massive galaxies after they have assembled.

High-Resolution CO Observations of Luminous Infrared Galaxies

We have performed a high-resolution imaging survey of the CO J = 1 → 0 emission in seven galaxies with infrared (IR) luminosities exceeding 3 × 1011 L☉—five of which are mergers. The resultant maps show that the molecular gas is very highly concentrated towards the cores of the mergers, with gas surface densities approaching or exceeding 104 M☉ pc-2 within 300–400 pc of the nuclei in three cases. This result supports earlier findings based on data from a smaller sample of luminous mergers. In the two mergers that show closely spaced double IR (stellar) nuclei, CO emission peaks between the nuclei and shows an extent roughly equal to the nuclear separation. The gas cores of the individual merging galaxies appear to be coalescing, while the stellar cores remain distinct. In the three single nucleus mergers, the CO peaks are coincident with the stellar nuclei, consistent with the hypothesis that these are relatively evolved merger remnants. In two of the three mergers with the most compact CO emission (Mrk 231 and NGC 6240), the empirical Galactic conversion factor from CO luminosity to molecular gas mass appears to overestimate the nuclear gas mass by a factor of more than 2 (3.6 in the case of Mrk 231). For Mrk 231, the high brightness temperature of the CO emission (Tb > 34 K) is the likeliest explanation for this overestimate. In the third such merger (NGC 2623), however, the geometry and kinematics suggest that the molecular gas mass is within a factor of 2 of the value given by using the Galactic conversion factor. Nonetheless, in all three of these objects, the molecular gas probably dominates the nuclear gravitational potential. We suggest that the molecular gas in objects with such high gas mass surface densities (~104 M☉ pc-2) is distributed in nuclear disks. These disks must be thin because of their self-gravity, with a full width of 30–40 pc (compared to radii of 300–400 pc) for a vertical velocity dispersion of 90 km s-1. The mean volume density of molecular hydrogen in such disks must be over 104 cm-3. The trend of increasing LFIR/LCO with increasing CO surface brightness is confirmed. The high concentrations of molecular gas thus appear intimately related to the high luminosities of these systems and probably serve as the fuel.

Interallelic recombination in the merozoite surface protein 1( MSP-1) gene of Plasmodium vivax from Thai isolates

The merozoite of Plasmodium vivax possesses a high molecular mass surface protein called Pv-merozoite surface protein 1, PvMSP-1, which exhibits antigenic diversity among isolates. In this study, the extent of sequence variation in the polymorphic region and the flanking interspecies conserved blocks (ICBs) 5 and 6 of the PvMSP-1 gene was analyzed using the polymerase chain reaction to amplify the DNA fragment encompassing these regions, followed by sequencing. Twenty different alleles were obtained from 15 Thai isolates. Results revealed five distinct sequence types of the polymorphic region, two of which were newly identified in this study: one probably generated by intragenic recombination at a site different from that previously reported and the other by duplication of a 30 nucleotide (nt) sequence at the 3′ end of the region. On the other hand, almost all nucleotide substitutions in the flanking regions, ICB5 and ICB6, were dimorphic, creating microheterogeneity in the region. Furthermore, stretches of nucleotide substitutions were found to be linked in ICB6, suggesting the potential recombination sites between these stretches. It is also noted that extensive sequence variation in the PvMSP-1 gene and eoinfection with different PvMSP-1 alleles occurred among the P. vivax population in the endemic areas of Thailand.

Laser-based dynamic surface tension detection for liquid chromatography by probing a repeating drop radius

Modifications to the design of the time-based dynamic surface tension detection (DSTD) system are reported. Both a theoretical and experimental evaluation of the modifications are presented to demonstrate a reduction in flow-rate fluctuation derived systematic noise. The instrument-based limit of detection in relative surface tension change for the improved volume-based DSTD is determined to be 0.15% (3 × root-mean-square noise) as compared to the 0.45% level achieved and previously reported for the time-based method. The radius-based limit of detection for the drop is determined to be 0.5 μm, and may be limited by the vibrational stability of the drop. Detector selectivity is shown to remain unchanged after the modifications as only the observed noise levels are affected. Limits of detection for a variety of commercially available surfactant solutions are presented, along with those for a number of common organic and ionic chromatographic mobile phase modifiers, in order to demonstrate the enhanced selectivity of the DSTD for surface active species. The utility of the volume-based DSTD is demonstrated for the detection of trace intermediate to high molecular mass impurities in a high concentration low molecular mass surface active polymer matrix by comparing the response of refractive index and volume-based dynamic surface tension detection of a Carbowax sample analyzed using size-exclusion chromatography.

Implications for gravitational lensing and the dark matter content in clusters of galaxies from spatially resolved x-ray spectra

A simple method for deriving well-behaved temperature solutions to the equation of hydrostatic equilibrium for intracluster media with X-ray imaging observations is presented and applied to a series of generalized models as well as to observations of the Perseus cluster and Abell 2256. In these applications the allowed range in the ratio of nonbaryons to baryons as a function of radius is derived, taking into account the uncertainties and crude spatial resolution of the X-ray spectra and considering a range of physically reasonable mass models with various scale heights. Particular attention is paid to the central regions of the cluster, and it is found that the dark matter can be sufficiently concentrated to be consistent with the high central mass surface densities for moderate-redshift clusters from their gravitational lensing properties.

Capillary wave study of linear and branched polysiloxanes at the air/water interface

AbstractThe surface properties of two commercially available polysiloxanes, AK 1000 and AV 1000, have been examined at the air/water (A/W) interface in terms of the surface quasi‐elastic light scattering technique (SLS) in conjunction with surface pressure‐area (II–A) isotherm studies. Both are found to form stable, insoluble and promptly equilibrating monolayers at A/W. Being a mixture of linear poly(dimethylsiloxanes) (PDMS), AK 1000 is shown to follow the well established surface properties of PDMS. On the other hand, AV 1000, a mixture of linear and phenylsiloxane‐branched PDMS, referred to as PPMS, shows a different isotherm. The profiles of the surface dynamic viscoelastic parameters deduced from SLS, i.e., the surface dilational elasticity, ϵd, and the corresponding viscosity, K, relative to the surface mass density, γ, are rather different. The magnitudes of ϵd and K for both monolayers are comparable, while small but distinct differences are observed. In particular, in the high surface mass density region, the dynamic surface viscosity of PPMS films is about twice that of PDMS, but all values are still in the regime of very small viscosities (K&lt; 5×10−8 kg/s). These findings are discussed in the context of the differences found in thermocapillary experiments between the two polymers.

Cell Surface-associated Proteins of Gastrointestinal Strains of Lactobacilli

Twenty-eight strains of gastrointestinal lactobacilli, comprising isolates classified as Lactobacillus reuteri , L. acidophilus , L. delbrueckii , L. fermentum , L. gasseri and L. salivarius , were examined for the presence of cell-surface polypeptides. Whole cells were radioactively labelled with 125 I using lactoperoxidase or chloramine T as catalyst, proteins were extracted with sodium dodecyl sulphate (SDS) and separated by SDS-polyacrylamide gel electrophoresis. All lactobacilli tested had between 5 and 20 proteins that were accessible to the labelling agents on the surface of whole cells. Strains of L. reuteri had similar surface polypeptide profiles and were characterised by the presence of a high molecular mass band of approximately 185 kDa. Strains of L. acidophilus could be grouped on the basis of their surface protein patterns. In one group (five strains) the surface protein profile was dominated by a surface array protein of molecular mass 45 kDa. In the other groups approximately 15 polypeptides were identified as being surface exposed and these ranged in molecular mass from c . 15 to 100 kDa. Strains of L. fermentum had either a characteristic surface protein profile (with bands at 135 kDa) or were poorly surface labelled. Fowl or rodent strains of different species possessed high molecular mass surface proteins (> 130 kDa). There was no correlation however between the presence of a specific polypeptide and the ability of a strain to adhere to stratified, squamous epithelial surfaces either in vitro or in vivo . Surface protein profiles may provide an aid to classification of lactobacillus strains of some species. Keywords: Gastrointestinal lactobacilli; Surface proteins; Lactobacillus proteins; Cell-surface labelling.

Surface array protein of Campylobacter fetus. Cloning and gene structure.

The high molecular mass (97-149 kDa) surface array proteins (SAP) of Campylobacter fetus are critical to virulence. We created a bank of 160,000 random 1.0-6.5-kilobase (kb) chromosomal DNA fragments of C. fetus strain 84-32 (23D) using lambda gt11. Screening this bank in Escherichia coli Y1090 with antibody raised against purified SAP permitted isolation and purification of a clone with a 4.0-kb insert. Subcloning this insert in the E. coli vector, pUC9, permitted expression of a protein of approximately 100 kDa, not fused with beta-galactoside or inducible by isopropyl-beta-D-thiogalactopyranoside. Digestion with restriction endonucleases, and construction of deletion mutations indicated that the gene extended over 2.8 kb, proceeding toward the start of the beta-galactosidase gene. Taking advantage of a unique PstI site at 1.7 kb, we subcloned PstI-EcoRI fragments in both orientations into M13 vectors, then generated and sequenced 48 deletion mutants. In the 3974-base insert, an open reading frame, beginning at nucleotide 24 and terminating at 2825, was found to encode a 933-amino acid polypeptide having a calculated molecular mass of 96,758 daltons. The first 20 amino acids exactly match those determined from amino-terminal sequencing, indicating that this protein is secreted without a leader sequence. The deduced amino acid composition matches that of the purified SAP. We identified a ribosomal binding site 9 bases upstream, and a putative transcription terminator (delta G = -12.4) 21 bases downstream. There is partial homology of primary and secondary structure with five other bacterial S-layer proteins.

Surface array protein of Campylobacter fetus. Cloning and gene structure.

The high molecular mass (97-149 kDa) surface array proteins (SAP) of Campylobacter fetus are critical to virulence. We created a bank of 160,000 random 1.0-6.5-kilobase (kb) chromosomal DNA fragments of C. fetus strain 84-32 (23D) using lambda gt11. Screening this bank in Escherichia coli Y1090 with antibody raised against purified SAP permitted isolation and purification of a clone with a 4.0-kb insert. Subcloning this insert in the E. coli vector, pUC9, permitted expression of a protein of approximately 100 kDa, not fused with beta-galactoside or inducible by isopropyl-beta-D-thiogalactopyranoside. Digestion with restriction endonucleases, and construction of deletion mutations indicated that the gene extended over 2.8 kb, proceeding toward the start of the beta-galactosidase gene. Taking advantage of a unique PstI site at 1.7 kb, we subcloned PstI-EcoRI fragments in both orientations into M13 vectors, then generated and sequenced 48 deletion mutants. In the 3974-base insert, an open reading frame, beginning at nucleotide 24 and terminating at 2825, was found to encode a 933-amino acid polypeptide having a calculated molecular mass of 96,758 daltons. The first 20 amino acids exactly match those determined from amino-terminal sequencing, indicating that this protein is secreted without a leader sequence. The deduced amino acid composition matches that of the purified SAP. We identified a ribosomal binding site 9 bases upstream, and a putative transcription terminator (delta G = -12.4) 21 bases downstream. There is partial homology of primary and secondary structure with five other bacterial S-layer proteins.

Gravitational microlensing at large optical depth

view Abstract Citations (283) References (10) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Gravitational Microlensing at Large Optical Depth Paczynski, B. Abstract A large number of numerical models of gravitational microlensing by stars in the lensing galaxy have been calculated, and properties of the models are described. The expected light intensity variations are more rapid when optical depth to microlensing is large, but the time scale is a few years in the best cases, and much longer in a typical case. However, microlensing introduces considerable scatter, up to two or three orders of magnitude, to the intensity of macroimages expected at any given time, and this may considerably complicate the analysis of the observed lenses. It is shown that macroimage is surrounded with a faint 'halo' made of a large number of microimages from individual stars with average surface brightness falling off as R to the -4th. It is also shown that a high surface mass density of continuously distributed matter may affect very strongly properties of microlensing, making possible very large declines in observed intensity, up to two or three orders of magnitude. Publication: The Astrophysical Journal Pub Date: February 1986 DOI: 10.1086/163919 Bibcode: 1986ApJ...301..503P Keywords: Gravitational Lenses; Optical Thickness; Quasars; Stellar Gravitation; Computational Astrophysics; Light Curve; Mass Distribution; Monte Carlo Method; Point Sources; Star Distribution; Astrophysics; GRAVITATION; QUASARS; RELATIVITY full text sources ADS |

Body weight exponents of metabolic rate and minimal thermal conductance in burrowing desert rodents

Most small burrowing desert rodents have basal metabolic rates (BMR or M) and minimal thermal conductance (C) which are lower than expected. These values are also lower than the values for non-desert species of similar mass. Metabolism–mass and conductance–mass relationships for burrowing desert rodents have been proposed as follows: M = 3·334W−0·95; C = 0·897W−0·499; where M, C, and W are expressed in units of cm3 O2/g/h, cm3 O2/g/h/°C and g, respectively. Combination of high BMR and low C values in very small mammals may compensate in thermoregulation for a high surface–mass ratio. Differences in metabolism–mass and conductance–mass functions for heteromyid, cricetid and murid rodents are discussed.