Chemical Composition of the Early Universe

A prediction of standard inflationary cosmology is that the elemental composition of the medium out of which the earliest stars and galaxies condensed consisted primarily of hydrogen and helium 4He with small admixtures of deuterium, lithium 7Li, and 3He. The most red-shifted quasars, galaxies, and Ly-alpha absorbers currently observed, however, all exhibit at least some admixture of heavier elements, as do the most ancient stars in the Galaxy. Here we examine ways in which the abundance of these same elements, if present before the epoch of population III formation, might be observationally established or ruled out.Comment: Accepted by the Astrophysical Journa

TeV Cherenkov Events as Bose-Einstein Gamma Condensations

The recent detection of gamma radiation from Mkn 501 at energies as high as 25 TeV suggests stringent upper bounds on the diffuse, far infrared, extragalactic radiation density. The production of electron-positron pairs through photon-photon collisions would prevent gamma photons of substantially higher energies from reaching us across distances of order 100 Mpc. However, coherently arriving TeV or sub-TeV gammas - Bose-Einstein condensations of photons at these energies - could mimic the Cherenkov shower signatures of extremely energetic gammas. To better understand such events, we describe their observational traits and discuss how they might be generated.Comment: 12 pages, 2 figures, accepted for publication in Ap.J.(Lett.

Photon Orbital Angular Momentum in Astrophysics

Astronomical observations of the orbital angular momentum of photons, a property of electromagnetic radiation that has come to the fore in recent years, have apparently never been attempted. Here, I show that measurements of this property of photons have a number of astrophysical applications.Comment: 17 pages plus two figure

Extremely Luminous Far-infrared Sources (ELFS)

The Infrared Astronomical Satellite (IRAS) survey uncovered a class of Extremely Luminous Far Infrared Sources (ELFS), exhibiting luminosities up to and occasionally exceeding 10 to the 12th power L sub 0. Arguments are presented to show that sources with luminosities L equal to or greater than 3 x 10 to the 10th power L sub 0 may represent gas rich galaxies in collision. The more conventional explanation of these sources as sites of extremely active star formation fails to explain the observed low optical luminosities of ELFS as well as their high infrared excess. In contrast, a collisional model heats gas to a temperature of approx. 10 to the 6th power K where cooling takes place in the extreme ultraviolet. The UV is absorbed by dust and converted into far infrared radiation (FIR) without generation of appreciable optical luminosity. Gas recombination as it cools generates a Lyman alpha photon only once for every two extreme ultraviolet approx. 50eV photons emitted by the 10 to the 6th power gas. That accounts for the high infrared excess. Finally, the model also is able to explain the observed luminosity distribution of ELFS as well as many other traits

SWAS observations of comet 9P/Tempel 1 and Deep Impact

On 4 July 2005 at 1:52 UT the Deep Impact mission successfully completed its goal to hit the nucleus of 9P/Tempel 1 with an impactor, forming a crater on the nucleus and ejecting material into the coma of the comet. The 370 kg impactor collided with the sunlit side of the nucleus with a relative velocity of 10.2 km/s. NASA's Submillimeter Wave Astronomy Satellite (SWAS) observed the 1(10)-1(01) ortho-water ground-state rotational transition in comet 9P/Tempel 1 before, during, and after the impact. No excess emission from the impact was detected by SWAS. However, the water production rate of the comet showed large natural variations of more than a factor of three during the weeks before the impact.Comment: to appear in the proceedings of the IAU Symposium No. 231: "Astrochemistry - Recent Successes and Current Callenges". Typo corrected in author affiliation lis

557 GHz Observations of Water Vapor Outflows from VY CMa and W Hydrae

We report the first detection of thermal water vapor emission in the 557 GHz, $1_{10} - 1_{01}$ ground state transition of ortho-H$_2$O toward VY Canis Majoris. In observations obtained with the Submillimeter Wave Astronomy Satellite (SWAS), we measured a flux of $\sim 450$Jy, in a spectrally resolved line centered on a velocity $v_{LSR} = 25$km s$^{-1}$ with a full width half maximum of $\sim 35$ km s$^{-1}$, somewhat dependent on the assumed line shape. We analyze the line shape in the context of three different radial outflow models for which we provide analytical expressions. We also detected a weaker 557 GHz emission line from W Hydrae. We find that these and other H$_2$O emission line strengths scale as suggested by Zubko and Elitzur (2000).Comment: Astrophysical Journal Letters, accepte

Radiative Torques on Interstellar Grains. III. Dynamics with Thermal Relaxation

In the previous papers in this series, we found that radiative torques can play a major role in the alignment of grains with the interstellar magnetic field. Since the radiative torques can drive the grains to suprathermal rotational speeds, in previous work we made the simplifying assumption that the grain principal axis of greatest moment of inertia is always parallel to the grain angular momentum. This enabled us to describe many of the features of the grain dynamics. However, this assumption fails when the grains enter periods of thermal rotation, which occur naturally in the radiative torque alignment scenario. In the present paper, we relax this assumption and explore the consequences for the grain dynamics. We develop a treatment to follow the grain dynamics including thermal fluctuations and ``thermal flipping'', and show results for one illustrative example. By comparing with a treatment without thermal fluctuations, we see that inclusion of thermal fluctuations can lead to qualitative changes in the grain dynamics. In a future installment in this series, we will use the more complete dynamical treatment developed here to perform a systematic study of grain alignment by radiative torques.Comment: 54 pages, 16 figures, submitted to Ap

Galaxy Mass, Metallicity, Radius and Star Formation Rates

Working with 108,786 Sloan Digital Sky Survey low redshift galaxies we have examined the relation between galaxy mass, metallicity, radius, and star formation rates primarily in the central portions of galaxies. We subdivided the redshift range covered in our sample, 0.07<z<0.3, into three narrower redshift bins, and three sets of radial size. We show that for 72% of the galaxies the observed gas metallicities, Zx, are consistent with (i) a quantitative physical relation for star formation through episodic infall of gas of metallicity Zi = 0.125x10^-3 +/- 1.25x10^-3; (ii) thorough mixing of infalling and native gas before onset of star formation; (iii) a star formation rate (SFR) proportional to the 3/2 power of the infalling mass rate, Mi; and (iv) intermittent quiescent phases devoid of star formation during which the native gas in a galaxy exhibits a characteristic elevated gas metallicity, Z0, dependent on galaxy mass, M*, and a characteristic ratio of stellar mass to native mass of gas, Mg. Most if not all our star-forming galaxies with M* < 2.0x10^10 Msun, and many with M* > 2.0x10^10 Msun and large radii appear fed by infall. Smaller massive galaxies with high Zx and high star formation rates show more complex behavior. A mean-field-theory toy model for the physics of infall accounts for the (SFR) \propto Mi^(3/2) relation and permits us to estimate the mean densities and velocities of clumps of baryonic matter traversing the dark matter halos in which the SDSS galaxies may be embedded.Comment: 34 pages plus bibliography and supplementary figures, 3 main figures, 131 supplementary online figures, ascii data tables availabl