IRAC Excess in Distant Star-Forming Galaxies: Tentative Evidence for the 3.3μ\mum Polycyclic Aromatic Hydrocarbon Feature ?

We present evidence for the existence of an IRAC excess in the spectral energy distribution (SED) of 5 galaxies at 0.6<z<0.9 and 1 galaxy at z=1.7. These 6 galaxies, located in the Great Observatories Origins Deep Survey field (GOODS-N), are star forming since they present strong 6.2, 7.7, and 11.3 um polycyclic aromatic hydrocarbon (PAH) lines in their Spitzer IRS mid-infrared spectra. We use a library of templates computed with PEGASE.2 to fit their multiwavelength photometry and derive their stellar continuum. Subtraction of the stellar continuum enables us to detect in 5 galaxies a significant excess in the IRAC band pass where the 3.3 um PAH is expected. We then assess if the physical origin of the IRAC excess is due to an obscured active galactic nucleus (AGN) or warm dust emission. For one galaxy evidence of an obscured AGN is found, while the remaining four do not exhibit any significant AGN activity. Possible contamination by warm dust continuum of unknown origin as found in the Galactic diffuse emission is discussed. The properties of such a continuum would have to be different from the local Universe to explain the measured IRAC excess, but we cannot definitively rule out this possibility until its origin is understood. Assuming that the IRAC excess is dominated by the 3.3 um PAH feature, we find good agreement with the observed 11.3 um PAH line flux arising from the same C-H bending and stretching modes, consistent with model expectations. Finally, the IRAC excess appears to be correlated with the star-formation rate in the galaxies. Hence it could provide a powerful diagnostic for measuring dusty star formation in z>3 galaxies once the mid-infrared spectroscopic capabilities of the James Webb Space Telescope become available.Comment: 25 pages, 4 figures, accepted by Ap

High Resolution Infrared Imaging of the Compact Nuclear Source in NGC4258

We present high resolution imaging of the nucleus of NGC4258 from 1 micron to 18 microns. Our observations reveal that the previously discovered compact source of emission is unresolved even at the near-infrared resolution of about 0.2 arcsec FWHM which corresponds to about 7 pc at the distance of the galaxy. This is consistent with the source of emission being the region in the neighborhood of the purported 3.5*10^7 M_sun black hole. After correcting for about 18 mags of visual extinction, the infrared data are consistent with a F_nu \propto nu^(-1.4+/-0.1) spectrum from 1.1 micron to 18 micron, implying a non-thermal origin. Based on this spectrum, the total extinction corrected infrared luminosity (1-20 micron) of the central source is 2*10^8 L_sun. We argue that the infrared spectrum and luminosity of the central source obviates the need for a substantial contribution from a standard, thin accretion disk at these wavelengths and calculate the accretion rate through an advection dominated accretion flow to be Mdot \sim 10^(-3) M_sun/yr. The agreement between these observations and the theoretical spectral energy distribution for advection dominated flows provides evidence for the existence of an advection dominated flow in this low luminosity AGN.Comment: 21 pages, 5 figures, Appearing in Mar 2000 ApJ vol. 53

Differential Calculi on Some Quantum Prehomogeneous Vector Spaces

This paper is devoted to study of differential calculi over quadratic algebras, which arise in the theory of quantum bounded symmetric domains. We prove that in the quantum case dimensions of the homogeneous components of the graded vector spaces of k-forms are the same as in the classical case. This result is well-known for quantum matrices. The quadratic algebras, which we consider in the present paper, are q-analogues of the polynomial algebras on prehomogeneous vector spaces of commutative parabolic type. This enables us to prove that the de Rham complex is isomorphic to the dual of a quantum analogue of the generalized Bernstein-Gelfand-Gelfand resolution.Comment: LaTeX2e, 51 pages; changed conten

Interconnections of Reactive Oxygen Species Homeostasis and Circadian Rhythm in Neurospora crassa.

Abstract Significance: Both circadian rhythm and the production of reactive oxygen species (ROS) are fundamental features of aerobic eukaryotic cells. The circadian clock enhances the fitness of organisms by enabling them to anticipate cycling changes in the surroundings. ROS generation in the cell is often altered in response to environmental changes, but oscillations in ROS levels may also reflect endogenous metabolic fluctuations governed by the circadian clock. On the other hand, an effective regulation and timing of antioxidant mechanisms may be crucial in the defense of cellular integrity. Thus, an interaction between the circadian timekeeping machinery and ROS homeostasis or signaling in both directions may be of advantage at all phylogenetic levels. Recent Advances: The Frequency-White Collar-1 and White Collar-2 oscillator (FWO) of the filamentous fungus Neurospora crassa is well characterized at the molecular level. Several members of the ROS homeostasis were found to be controlled by the circadian clock, and ROS levels display circadian rhythm in Neurospora. On the other hand, multiple data indicate that ROS affect the molecular oscillator. Critical Issues: Increasing evidence suggests the interplay between ROS homeostasis and oscillators that may be partially or fully independent of the FWO. In addition, ROS may be part of a complex cellular network synchronizing non-transcriptional oscillators with timekeeping machineries based on the classical transcription-translation feedback mechanism. Future Directions: Further investigations are needed to clarify how the different layers of the bidirectional interactions between ROS homeostasis and circadian regulation are interconnected. Antioxid. Redox Signal. 00, 000-000

Galaxy Evolution in Overdense Environments at High Redshift: Passive Early-type Galaxies in a Cluster at z ~ 2

We present a study of galaxy populations in the central region of the IRAC-selected, X-ray-detected galaxy cluster Cl J1449+0856 at z = 2. Based on a sample of spectroscopic and photometric cluster members, we investigate stellar populations and the morphological structure of cluster galaxies over an area of ~0.7 Mpc^2 around the cluster core. The cluster stands out as a clear overdensity both in redshift space and in the spatial distribution of galaxies close to the center of the extended X-ray emission. The cluster core region (r < 200 kpc) shows a clearly enhanced passive fraction with respect to field levels. However, together with a population of massive, passive galaxies mostly with early-type morphologies, the cluster core also hosts massive, actively star-forming, often highly dust reddened sources. Close to the cluster center, a multi-component system of passive and star-forming galaxies could represent the future brightest cluster galaxy still forming. We observe a clear correlation between passive stellar populations and an early-type morphology, in agreement with field studies at similar redshift. Passive early-type galaxies in this cluster are typically a factor of 2-3 smaller than similarly massive early types at z ~ 0. On the other hand, these same objects are on average larger by a factor of ~2 than field early-types at similar redshift, lending support to recent claims of an accelerated structural evolution in high-redshift dense environments. These results point toward the early formation of a population of massive galaxies, already evolved both in their structure and stellar populations, coexisting with still actively forming massive galaxies in the central regions of young clusters 10 billion years ago

INSAT-2A and 2B development mechanisms

The Indian National Satellite (INSAT) 2A and 2B have deployment mechanisms for deploying the solar array, two C/S band antenna reflectors and a coilable lattice boom with sail. The mechanisms have worked flawlessly on both satellites. The configuration details, precautions taken during the design phase, the test philosophy, and some of the critical analysis activities are discussed

Infrared Imaging of GRB 970508

We have observed the field of the gamma-ray burst GRB 970508 at infrared wavelengths (2.2 μm) and have found a variable source coincident with the visible transient thought to be associated with the burst. The source was decaying in brightness with Ks magnitudes of 18.2±0.1, 18.8±0.1, and 19.0±0.3 mag on May 13.25, 16.25, and 20.21 UT, respectively. A 1 σ upper limit of K=21.3 mag was obtained for the brightness of the source on June 14.27 UT. The infrared light curve during this period is consistent with a ~t^(-1.2) power law, similar to the visible light curve. We do not find evidence for extended structure around the burst, as has been claimed for GRB 970228, and we obtain an upper limit of 0.04L_* for the luminosity of an underlying galaxy at the position of the infrared transient