An Origin of the Huge Far-Infrared Luminosity of Starburst Mergers

Recently Taniguchi and Ohyama found that the higher $^{12}$CO to $^{13}$CO integrated intensity ratios at a transition $J$=1--0, $R = I(^{12}$CO)$/I(^{13}$CO) $\gtrsim 20$, in a sample of starburst merging galaxies such as Arp 220 are mainly attributed to the depression of $^{13}$CO emission with respect to $^{12}$CO. Investigating the same sample of galaxies analyzed by Taniguchi & Ohyama, we find that there is a tight, almost linear correlation between the dust mass and $^{13}$CO luminosity. This implies that dust grains are also depressed in the high-$R$ starburst mergers, leading to the higher dust temperature ($T_{\rm d}$) in them because of the relative increase in the radiation density. Nevertheless, the average dust mass ($M_{\rm d}$) of the high-$R$ starburst mergers is higher significantly than that of non-high $R$ galaxies. This is naturally understood because the galaxy mergers could accumulate a lot of dust grains from their progenitor galaxies together with supply of dust grains formed newly in the star forming regions. Since $L$(FIR) $\propto M_{\rm d} T_{\rm d}^5$ given the dust emissivity law, $S_\nu \propto \lambda^{-1}$, the increases in both $M_{\rm d}$ and $T_{\rm d}$ explain well why the starburst mergers are so bright in the FIR. We discuss that the superwind activity plays an important role in destroying dust grains as well as dense gas clouds in the central region of mergers.Comment: 10 pages (aaspp4.sty), 3 postscript figures (embedded). Accepted for publication in Astrophysical Journal Letter

Far infrared and submillimeter brightness temperatures of the giant planets

The brightness temperatures of Jupiter, Saturn, Uranus, and Neptune in the range 35 to 1000 micron. The effective temperatures derived from the measurements, supplemented by shorter wavelength Voyager data for Jupiter and Saturn, are 126.8 + or - 4.5 K, 93.4 + or - 3.3 K, 58.3 + or - 2.0 K, and 60.3 + or - 2.0 K, respectively. The implications of the measurements for bolometric output and for atmospheric structure and composition are discussed. The temperature spectrum of Jupiter shows a strong peak at approx. 350 microns followed by a deep valley at approx. 450 to 500 microns. Spectra derived from model atmospheres qualitatively reproduced these features but do not fit the data closely

Extrapolation of Galactic Dust Emission at 100 Microns to CMBR Frequencies Using FIRAS

We present predicted full-sky maps of submillimeter and microwave emission from the diffuse interstellar dust in the Galaxy. These maps are extrapolated from the 100 micron emission and 100/240 micron flux ratio maps that Schlegel, Finkbeiner, & Davis (1998; SFD98) generated from IRAS and COBE/DIRBE data. Results are presented for a number of physically plausible emissivity models. We find that no power law emissivity function fits the FIRAS data from 200 - 2100 GHz. In this paper we provide a formalism for a multi-component model for the dust emission. A two-component model with a mixture of silicate and carbon-dominated grains (motivated by Pollack et al., 1994}) provides a fit to an accuracy of about 15% to all the FIRAS data over the entire high-latitude sky. Small systematic differences are found between the atomic and molecular phases of the ISM. Our predictions for the thermal (vibrational) emission from Galactic dust at \nu < 3000 GHz are available for general use. These full-sky predictions can be made at the DIRBE resolution of 40' or at the higher resolution of 6.1 arcmin from the SFD98 DIRBE-corrected IRAS maps.Comment: 48 pages, AAS LaTeX, 6 figures, ApJ (accepted). Data described in the text, as well as 4 additional figures, are available at http://astro.berkeley.edu/dus

Star Formation in the Northern Cloud Complex of NGC 2264

We have made continuum and spectral line observations of several outflow sources in the Mon OB1 dark cloud (NGC 2264) using the Heinrich Hertz Telescope (HHT) and ARO 12m millimeter-wave telescope. This study explores the kinematics and outflow energetics of the young stellar systems observed and assesses the impact star formation is having on the surrounding cloud environment. Our data set incorporates 12CO(3-2), 13CO(3-2), and 12CO(1-0) observations of outflows associated with the sources IRAS 06382+1017 and IRAS 06381+1039, known as IRAS 25 and 27, respectively, in the northern cloud complex. Complementary 870 micron continuum maps were made with the HHT 19 channel bolometer array. Our results indicate that there is a weak (approximately less than 0.5%) coupling between outflow kinetic energy and turbulent energy of the cloud. An analysis of the energy balance in the IRAS 25 and 27 cores suggests they are maintaining their dynamical integrity except where outflowing material directly interacts with the core, such as along the outflow axes.Comment: 28 pages including 6 figures, to be published in ApJ 01 July 2006, v645, 1 issu

Large Area Mapping at 850 Microns. IV. Analysis of the Clump Distribution in the Orion B South Molecular Cloud

We present results from a survey of a 1300 arcmin^2 region of the Orion B South molecular cloud, including NGC 2024, NGC 2023, and the Horsehead Nebula (B33), obtained using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope. Submillimeter continuum observations at 450 microns and 850 microns are discussed. Using an automated algorithm, 57 discrete emission features (``clumps'') are identified in the 850 micron map. The physical conditions within these clumps are investigated under the assumption that the objects are in quasi-hydrostatic equilibrium. The best fit dust temperature for the clumps is found to be T_d = 18 +/- 4 K, with the exception of those associated with the few known far infrared sources residing in NGC 2024. The latter internally heated sources are found to be much warmer. In the region surrounding NGC 2023, the clump dust temperatures agree with clump gas temperatures determined from molecular line excitation measurements of the CO molecule. The bounding pressure on the clumps lies in the range log(k^-1 P cm^3 K^-1) = 6.1 +/- 0.3. The cumulative mass distribution is steep at the high mass end, as is the stellar Initial Mass Function. The distribution flattens significantly at lower masses, with a turn-over around 3 -- 10 M_sun.Comment: 41 pages, 16 figures, accepted by Ap

Dust and the Infrared Kinematic Properties of Early-Type Galaxies

We have obtained spectra and measured the stellar kinematics in a sample of 25 nearby early-type galaxies (with velocity dispersions from less than 100 km/s to over 300 km/s) using the near-infrared CO absorption bandhead at 2.29 microns. Our median uncertainty for the dispersions is ~10%. We examine the effects of dust on existing optical kinematic measurements. We find that the near-infrared velocity dispersions are in general smaller than optical velocity dispersions, with differences as large as 30%. The median difference is 11% smaller, and the effect is of greater magnitude for higher dispersion galaxies. The lenticular galaxies (18 out of 25) appear to be causing the shift to lower dispersions while the classical ellipticals (7 out of 25) are consistent between the two wavelength regimes. If uniformly distributed dust causes these differences, we would expect to find a correlation between the relative amount of dust in a galaxy and the fractional change in dispersion, but we do not find such a correlation. We do see correlations both between velocity dispersion and CO bandhead equivalent width, and velocity dispersion and Mg2 index. The differences in dispersion are not well explained by current models of dust absorption. The lack of correlation between the relative amount of dust and shift in dispersion possibly suggets that dust does not have a similar distribution from galaxy to galaxy. The CO equivalent widths of these galaxies are quite high (>10 angstroms for almost all), requiring the light at these wavelengths to be dominated by very cool stars.Comment: 17 pages, 14 figures, accepted to The Astronomical Journa

A Submillimeter Study of the Star-Forming Region NGC7129

New molecular (13CO J=3-2) and dust continuum (450 and 850 micron) SCUBA maps of the NGC7129 star forming region are presented, complemented by C18O J=3-2 spectra at several positions within the mapped region. The maps include the Herbig Ae/Be star LkHalpha 234, the far-infrared source NGC 7129 FIRS2 and several other pre-stellar sources embedded within the molecular ridge. The SCUBA maps help us understand the nature of the pre-main sequence stars in this actively star forming region. A deeply embedded submillimeter source, SMM2, not clearly seen in any earlier data set, is shown to be a pre-stellar core or possibly a protostar. The highest continuum peak emission is identified with the deeply embedded source IRS6, a few arcseconds away from LkHalpha 234, and also responsible for both the optical jet and the molecular outflow. The gas and dust masses are found to be consistent, suggesting little or no CO depletion onto grains. The dust emissivity index is lower towards the dense compact sources, beta ~1 - 1.6, and higher, beta ~ 2.0, in the surrounding cloud, implying small size grains in the PDR ridge, whose mantles have been evaporated by the intense UV radiation.Comment: Accepted by Ap

High Mass Star Formation. II. The Mass Function of Submillimeter Clumps in M17

We have mapped an approximately 5.5 by 5.5 pc portion of the M17 massive star-forming region in both 850 and 450 micron dust continuum emission using the Submillimeter Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). The maps reveal more than 100 dusty clumps with deconvolved linear sizes of 0.05--0.2 pc and masses of 0.8--120 solar masses, most of which are not associated with known mid-infrared point sources. Fitting the clump mass function with a double power law gives a mean power law exponent of alpha_high = -2.4 +/- 0.3 for the high-mass power law, consistent with the exponent of the Salpeter stellar mass function. We show that a lognormal clump mass distribution with a peak at about 4 solar masses produces as good a fit to the clump mass function as does a double power law. This 4 solar mass peak mass is well above the peak masses of both the stellar initial mass function and the mass function of clumps in low-mass star-forming regions. Despite the difference in intrinsic mass scale, the shape of the M17 clump mass function appears to be consistent with the shape of the core mass function in low-mass star-forming regions. Thus, we suggest that the clump mass function in high-mass star-forming regions may be a scaled-up version of that in low-mass regions, instead of its extension to higher masses.Comment: 33 pages, 6 figures, 3 tables. Accepted for publication in the Astrophysical Journa

The structure of protostellar envelopes derived from submillimeter continuum images

High dynamic range imaging of submillimeter dust emission from the envelopes of eight young protostars in the Taurus and Perseus star-forming regions has been carried out using the SCUBA submillimeter camera on the James Clerk Maxwell Telescope. Good correspondence between the spectral classifications of the protostars and the spatial distributions of their dust emission is observed, in the sense that those with cooler spectral energy distributions also have a larger fraction of the submillimeter flux originating in an extended envelope compared with a disk. This results from the cool sources having more massive envelopes rather than warm sources having larger disks. Azimuthally-averaged radial profiles of the dust emission are used to derive the power-law index of the envelope density distributions, p (defined by rho proportional to r^-p), and most of the sources are found to have values of p consistent with those predicted by models of cloud collapse. However, the youngest protostars in our sample, L1527 and HH211-mm, deviate significantly from the theoretical predictions, exhibiting values of p somewhat lower than can be accounted for by existing models. For L1527 heating of the envelope by shocks where the outflow impinges on the surrounding medium may explain our result. For HH211-mm another explanation is needed, and one possibility is that a shallow density profile is being maintained in the outer envelope by magnetic fields and/or turbulence. If this is the case star formation must be determined by the rate at which the support is lost from the cloud, rather than the hydrodynamical properties of the envelope, such as the sound speed.Comment: Accepted for publication in the Astrophysical Journa

TurbEFA: an interdisciplinary effort to investigate the turbulent flow across a forest clearing

the atmosphere within turbulence closure models is mainly limited by a realistic three-dimensional (3D) representation of the vegetation architecture. Within this contribution we present a method to record the 3D vegetation structure and to use this information to derive model parameters that are suitable for numerical flow models. A mixed conifer forest stand around a clearing was scanned and represented by a dense 3D point cloud applying a terrestrial laser scanner. Thus, the plant area density (PAD) with a resolution of one cubic meter was provided for analysis and for numerical simulations. Multi-level high-frequency wind velocity measurements were recorded simultaneously by 27 ultrasonic anemometers on 4 towers for a period of one year. The relationship between wind speed, Reynolds stress and PAD was investigated and a parametrization of the drag coefficient CD by the PAD is suggested. The derived 3D vegetation model and a simpler model (based on classical forest assessments of the site) were applied in a boundary layer model (BLM) and in large-eddy simulations (LES). The spatial development of the turbulent flow over the clearing is further demonstrated by the results of a wind tunnel experiment. The project showed, that the simulation results were improved significantly by the usage of realistic vegetation models. 3D simulations are necessary to depict the influence of heterogeneous canopies on the turbulent flow. Whereas we found limits for the mapping of the vegetation structure within the wind tunnel, there is a considerable potential for numerical simulations. The field measurements and the LES gave new insight into the turbulent flow in the vicinity and across the clearing. The results show that the zones of intensive turbulence development can not be restricted to the locations found in previous studies with more idealized canopies