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

The morphology and kinematics of the gaseous circumgalactic medium of Milky Way mass galaxies - II. Comparison of IllustrisTNG and Illustris simulation results

We have carried out a controlled comparison of the structural and kinematic properties of the circumgalactic medium (CGM) around Milky Way mass galaxies in the Illustris and IllustrisTNG simulations. Very striking differences are found. At z = 0, gas column density and temperature profiles at large radii (~100 kpc) correlate stronglywith disc gasmass fraction in Illustris, but not in TNG. The neutral gas at large radii is preferentially aligned in the plane of the disc in TNG, whereas it is much more isotropic in Illustris. The vertical coherence scale of the rotationally supported gas in the CGM is linked to the gas mass fraction of the galaxy in Illustris, but not in TNG. A tracer particle analysis allows us to show how these differences can be understood as a consequence of the different subgrid models of feedback in the two simulations. A study of spatially matched galaxies in the two simulations shows that in TNG, feedback by supernovae and active galactic nuclei (AGNs) helps to create an extended smooth reservoir of hot gas at high redshifts, which then cools to form a thin, rotationally supported disc at later times. In Illustris, AGNs dump heat in the form of hot gas bubbles that push diffuse material at large radii out of the halo. The disc is formed by accretion of colder, recycled material, and this results in more vertically extended gas distributions above and below the Galactic plane.We conclude that variations in the structure of gas around Milky Way mass galaxies are a sensitive probe of feedback physics in simulations and are worthy of more observational consideration in future

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

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

The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results from the COS-GASS+COS-HALOS Surveys

We use the combined data from the COS-GASS and COS-Halos surveys to characterize the Circum-Galactic Medium (CGM) surrounding typical low-redshift galaxies in the mass range ${M}_{* }\sim \,{10}^{9.5-11.5}\,{M}_{\odot }$, and over a range of impact parameters extending to just beyond the halo virial radius (R vir). We find the radial scale length of the distributions of the equivalent widths of the Lyα and Si iii absorbers to be ~1 and ~0.4 R vir, respectively. The radial distribution of equivalent widths is relatively uniform for the blue galaxies, but highly patchy (i.e., it has a low covering fraction) for the red galaxies. We also find that the Lyα and Si iii equivalent widths show significant positive correlations with the specific star formation rate (sSFR) of the galaxy. We find a surprising lack of correlations between the halo mass (virial velocity) and either the velocity dispersions or velocity offsets of the Lyα lines. The ratio of the velocity offset to the velocity dispersion for the Lyα absorbers has a mean value of ~4, suggesting that a given line of sight is intersecting a dynamically coherent structure in the CGM, rather than a sea of orbiting clouds. The kinematic properties of the CGM are similar in the blue and red galaxies, although we find that a significantly larger fraction of the blue galaxies have large Lyα velocity offsets (>200 km s−1). We show that—if the CGM clouds represent future fuel for star formation—our new results could imply a large drop in the sSFR across the galaxy mass-range we probe

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&

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