A GBT Survey for HI 21 cm Absorption in the Disks and Halos of Low-Redshift Galaxies

We present an HI 21 cm absorption survey with the Green Bank Telescope (GBT) of galaxy-quasar pairs selected by combining data from the Sloan Digital Sky Survey (SDSS) and the Faint Images of the Radio Sky at Twenty-Centimeters (FIRST) survey. Our sample consists of 23 sightlines through 15 low-redshift foreground galaxy - background quasar pairs with impact parameters ranging from 1.7 kpc up to 86.7 kpc. We detected one absorber in the GBT survey from the foreground dwarf galaxy, GQ1042+0747, at an impact parameter of 1.7 kpc and another possible absorber in our follow-up Very Large Array (VLA) imaging of the nearby foreground galaxy, UGC 7408. Both of the absorbers are narrow (FWHM of 3.6 and 4.8 km/s), have sub Damped Lyman alpha column densities, and most likely originate in the disk gas of the foreground galaxies. We also detected H I emission from three foreground galaxies, including UGC 7408. Although our sample contains both blue and red galaxies, the two H I absorbers as well as the H I emissions are associated with blue galaxies. We discuss the physical conditions in the 21 cm absorbers and some drawbacks of the large GBT beam for this type of survey.Comment: 15 pages, 6 figures, 3 table

Microwave promoted one-pot synthesis of novel A-ring fused steroidal dehydropiperazines

The preparation of ring-A fused steroidal dehydropiperazine at the 3,4-position is herein described. The novel steroidal dehydropiperazines were prepared from the annulation reaction of ethylenediamine with 3-keto-4-en steroids in a one-pot reaction under microwave irradiation. The key step involves base catalysed aerial oxidation of the C-6 methylene group followed by cyclocondensation of ethylenediamine via Michael addition reaction

Microwave-promoted one-pot synthesis of 4H-thiopyrans from a,b-unsaturated ketones via a three-component reaction

—An efficient one-pot synthesis of substituted 4H-thiopyrans has been accomplished from a three-component reaction of a,b-unsaturated ketones, Lawesson’s reagent and alkynes under microwave irradiation

Study on the reactive extraction and stripping kinetics of certain �-lactam antibiotics

The extraction equilibrium and stripping of certain �-lactam antibiotics such as 7-aminocephalosporanic acid (7-ACA), 7-aminodeacetoxy cephalosporanic acid (7-ADCA), 6-aminopenicillanic acid (6-APA), cephalosporin-C (CPC) and cephalexin from aqueous solution of phosphate and carbonate buffers were studied with Aliquat-336 (tricaprylylmethylammonium chloride) dissolved in n-butylacetate as the solvent over an aqueous phase pH range of 5–10. The extraction equilibrium constant Kp was found to increase with aqueous phase pH, which is attributed to the increase in ionisation of the �-lactam. A systematic study on kinetic of stripping or re-extraction of 7-ADCA and cephalexin from the extracted phase was carried out using an aqueous solution of citrate buffer at different pH values and was found to be pH dependent which is also attributable to ionisation behaviour of the �-lactams. Such observation is considered important, as re-extraction at an appropriate pH value is possible. The rate of stripping was found to be weakly dependent on Cl− concentration of the aqueous phase and the same was analysed with a simple mass transfer model based on film theory

A facile three-component solid phase synthesis of steroidal A-ring fused pyrimidines under microwave irradiation

The preparation of ring-A fused pyrimidines at the steroidal 2,3-position is herein described. The novel steroidal pyrimidines were prepared from the solid phase three-component reaction of 2- hydroxymethylene-3-keto steroids, arylaldehydes and ammonium acetate under microwave irradiation

A facile threecomponent solid phase synthesis of steroidal Aring fused pyrimidines under microwave irradiation

The preparation of ringA fused pyrimidines at the steroidal 2,3position is herein described. The novel steroidal pyrimidines were prepared from the solid phase threecomponent reaction of 2hydroxymethylene3keto steroids, arylaldehydes and ammonium acetate under microwave irradiatio

Seyfert's Sextet: where is the gas?

Seyfert's Sextet (a.k.a HCG 79) is one of the most compact and isolated galaxy groups in the local Universe. It shows a prominent diffuse light component that accounts for ~50% of the total observed light. This likely indicates that the group is in an advanced evolutionary phase, which would predict a significant hot gaseous component. Previous X-ray observations had suggested a low luminosity for this system, but with large uncertainties and poor resolution. We present the results from a deep (70 ks), high resolution Chandra observation of Seyfert's Sextet, requested with the aim of separating the X-ray emission associated with the individual galaxies from that of a more extended inter-galactic component. We discuss the spatial and spectral characteristics of this group we derive with those of a few similar systems also studied in the X-ray band. The high resolution X-ray image indicates that the majority of the detected emission does not arise in the compact group but is concentrated towards the NW and corresponds to what appears to be a background galaxy cluster. The emission from the group alone has a total luminosity of ~1x10^40 erg/s in the (0.5-5) keV band. Most of the luminosity can be attributed to the individual sources in the galaxies, and only ~2x10^39 erg/s is due to a gaseous component. However, we find that this component is also mostly associated with the individual galaxies of the Sextet, leaving little or no residual in a truly IGM component. The extremely low luminosity of the diffuse emission in Seyfert's Sextet might be related to its small total mass.Comment: 8 pages, 7 figures. Accepted on A&

Gas Accretion in Star-Forming Galaxies

Cold-mode gas accretion onto galaxies is a direct prediction of LCDM simulations and provides galaxies with fuel that allows them to continue to form stars over the lifetime of the Universe. Given its dramatic influence on a galaxy's gas reservoir, gas accretion has to be largely responsible for how galaxies form and evolve. Therefore, given the importance of gas accretion, it is necessary to observe and quantify how these gas flows affect galaxy evolution. However, observational data have yet to conclusively show that gas accretion ubiquitously occurs at any epoch. Directly detecting gas accretion is a challenging endeavor and we now have obtained a significant amount of observational evidence to support it. This chapter reviews the current observational evidence of gas accretion onto star-forming galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springer. This chapter includes 22 pages with 7 Figure

Metal Enrichment in the Reionization Epoch

The presence of elements heavier than helium ("metals") is of fundamental importance for a large number of astrophysical processes occurring in planet, star and galaxy formation; it also affects cosmic structure formation and evolution in several ways. Even a small amount of heavy elements can dramatically alter the chemistry of the gas, opening the path to complex molecules. Metals might enhance the ability of the gas to radiate away its thermal energy, thus favoring the formation of gravitationally bound objects; they can also condensate in a solid phase (dust grains), partly or totally blocking radiation from luminous sources. Finally, they represent useful tracers of energy deposition by stars and probe the physical properties of the environment by absorption or emission lines. Last, but certainly not least, life -- as we know it on Earth -- is tightly related to the presence of at least some of the heavy elements. In this pedagogical review I will concentrate on the connection between early metal enrichment and cosmic reionization. As we will see these two processes are intimately connected and their joint study might turn out to be fundamental in understanding the overall evolution of the Universe during the first billion years after the Big Bang, an epoch corresponding to redshifts z>6.Comment: Book chapter in Understanding the Epoch of Cosmic Reionization: Challenges and Progress, Springer International Publishing, Ed. Andrei Mesinger, ISBN 978-3-319-21956-1. arXiv admin note: text overlap with arXiv:astro-ph/0007248 by other author