Physical Properties of Complex C Halo Clouds

Observations from the Galactic Arecibo L-Band Feed Array HI (GALFA-HI) Survey of the tail of Complex C are presented and the halo clouds associated with this complex cataloged. The properties of the Complex C clouds are compared to clouds cataloged at the tail of the Magellanic Stream to provide insight into the origin and destruction mechanism of Complex C. Magellanic Stream and Complex C clouds show similarities in their mass distributions (slope = -0.7 and -0.6, respectively) and have a common linewidth of 20 - 30 km/s (indicative of a warm component), which may indicate a common origin and/or physical process breaking down the clouds. The clouds cataloged at the tail of Complex C extend over a mass range of 10^1.1 to 10^4.8 solar masses, sizes of 10^1.2 to 10^2.6 pc, and have a median volume density of 0.065 cm^(-3) and median pressure of (P/k) = 580 K cm^{-3}. We do not see a prominent two-phase structure in Complex C, possibly due to its low metallicity and inefficient cooling compared to other halo clouds. From assuming the Complex C clouds are in pressure equilibrium with a hot halo medium, we find a median halo density of 5.8 x 10^(-4) cm^(-3), which given a constant distance of 10 kpc, is at a z-height of ~3 kpc. Using the same argument for the Stream results in a median halo density of 8.4 x 10^(-5) x (60kpc/d) cm^(-3). These densities are consistent with previous observational constraints and cosmological simulations. We also assess the derived cloud and halo properties with three dimensional grid simulations of halo HI clouds and find the temperature is generally consistent within a factor of 1.5 and the volume densities, pressures and halo densities are consistent within a factor of 3.Comment: Accepted for publication in AJ. 54 pages, including 6 tables and 16 figure

The Relationship Between Baryons and Dark Matter in Extended Galaxy Halos

The relationship between gas-rich galaxies and Ly-alpha absorbers is addressed in this paper in the context of the baryonic content of galaxy halos. Deep Arecibo HI observations are presented of two gas-rich spiral galaxies within 125 kpc projected distance of a Ly-alpha absorber at a similar velocity. The galaxies investigated are close to edge-on and the absorbers lie almost along their major axes, allowing for a comparison of the Ly-alpha absorber velocities with galactic rotation. This comparison is used to examine whether the absorbers are diffuse gas rotating with the galaxies' halos, outflow material from the galaxies, or intergalactic gas in the low redshift cosmic web. The results indicate that if the gas resides in the galaxies' halos it is not rotating with the system and possibly counter-rotating. In addition, simple geometry indicates the gas was not ejected from the galaxies and there are no gas-rich satellites detected down to 3.6 - 7.5 x 10^6 Msun, or remnants of satellites to 5-6 x 10^{18} cm^{-2}. The gas could potentially be infalling from large radii, but the velocities and distances are rather high compared to the high velocity clouds around the Milky Way. The most likely explanation is the galaxies and absorbers are not directly associated, despite the vicinity of the spiral galaxies to the absorbers (58-77 kpc from the HI edge). The spiral galaxies reside in a filament of intergalactic gas, and the gas detected by the absorber has not yet come into equilibrium with the galaxy. These results also indicate that the massive, extended dark matter halos of spiral galaxies do not commonly have an associated diffuse baryonic component at large radii.Comment: Accepted by AJ, 33 pages preprint format, see http://www.astro.lsa.umich.edu/~mputman/putman1.pdf for a higher resolution versio

Metallicity and Physical Conditions in the Magellanic Bridge

We present a new analysis of the diffuse gas in the Magellanic Bridge (RA>3h) based on HST/STIS E140M and FUSE spectra of 2 early-type stars lying within the Bridge and a QSO behind it. We derive the column densities of HI (from Ly\alpha), NI, OI, ArI, SiII, SII, and FeII of the gas in the Bridge. Using the atomic species, we determine the first gas-phase metallicity of the Magellanic Bridge, [Z/H]=-1.02+/-0.07 toward one sightline, and -1.7<[Z/H]<-0.9 toward the other one, a factor 2 or more smaller than the present-day SMC metallicity. Using the metallicity and N(HI), we show that the Bridge gas along our three lines of sight is ~70-90% ionized, despite high HI columns, logN(HI)=19.6-20.1. Possible sources for the ongoing ionization are certainly the hot stars within the Bridge, hot gas (revealed by OVI absorption), and leaking photons from the SMC and LMC. From the analysis of CII*, we deduce that the overall density of the Bridge must be low (<0.03-0.1 cm^-3). We argue that our findings combined with other recent observational results should motivate new models of the evolution of the SMC-LMC-Galaxy system.Comment: Accepted for publication in the Ap

GEOS-5 Chemistry Transport Model User's Guide

The Goddard Earth Observing System version 5 (GEOS-5) General Circulation Model (GCM) makes use of the Earth System Modeling Framework (ESMF) to enable model configurations with many functions. One of the options of the GEOS-5 GCM is the GEOS-5 Chemistry Transport Model (GEOS-5 CTM), which is an offline simulation of chemistry and constituent transport driven by a specified meteorology and other model output fields. This document describes the basic components of the GEOS-5 CTM, and is a user's guide on to how to obtain and run simulations on the NCCS Discover platform. In addition, we provide information on how to change the model configuration input files to meet users' needs

FUSE Observations of the Magellanic Bridge Gas toward Two Early-Type Stars: Molecules, Physical Conditions, and Relative Abundance

We discuss FUSE observations of two early-type stars, DI1388 and DGIK975, in the low density and low metallicity gas of Magellanic Bridge (MB). Toward DI1388, the FUSE observations show molecular hydrogen, O VI, and numerous other atomic or ionic transitions in absorption, implying the presence of multiple gas phases in a complex arrangement. The relative abundance pattern in the MB is attributed to varying degrees of depletion onto dust similar to that of halo clouds. The N/O ratio is near solar, much higher than N/O in damped Ly-alpha systems, implying subsequent stellar processing to explain the origin of nitrogen in the MB. The diffuse molecular cloud in this direction has a low column density and low molecular fraction. H2 is observed in both the Magellanic Stream and the MB, yet massive stars form only in the MB, implying significantly different physical processes between them. In the MB some of the H2 could have been pulled out from the SMC via tidal interaction, but some also could have formed in situ in dense clouds where star formation might have taken place. Toward DGIK975, the presence of neutral, weakly and highly ionized species suggest that this sight line has also several complex gas phases. The highly ionized species of O VI, C IV, and Si IV toward both stars have very broad features, indicating that multiple components of hot gas at different velocities are present. Several sources (a combination of turbulent mixing layer, conductive heating, and cooling flows) may be contributing to the production of the highly ionized gas in the MB. Finally, this study has confirmed previous results that the high-velocity cloud HVC 291.5-41.2+80 is mainly ionized composed of weakly and highly ions. The high ion ratios are consistent with a radiatively cooling gas in a fountain flow model.Comment: Accepted for publication in the ApJ (October 10, 2002). Added reference (Gibson et al. 2000

A Very Sensitive 21cm Survey for Galactic High-Velocity HI

Very sensitive HI 21cm observations have been made in 860 directions at dec >= -43deg in search of weak, Galactic, high-velocity HI emission lines at moderate and high Galactic latitudes. One-third of the observations were made toward extragalactic objects. The median 4-sigma detection level is NHI = 8x10^{17} cm^-2 over the 21' telescope beam. High-velocity HI emission is detected in 37% of the directions; about half of the lines could not have been seen in previous surveys. The median FWHM of detected lines is 30.3 km/s. High- velocity HI lines are seen down to the sensitivity limit of the survey implying that there are likely lines at still lower values of NHI. The weakest lines have a kinematics and distribution on the sky similar to that of the strong lines, and thus do not appear to be a new population. Most of the emission originates from objects which are extended over several degrees; few appear to be compact sources. At least 75%, and possibly as many as 90%, of the lines are associated with one of the major high-velocity complexes. The Magellanic Stream extends at least 10 deg to higher Galactic latitude than previously thought and is more extended in longitude as well. Although there are many lines with low column density, their numbers do not increase as rapidly as NHI^-1, so most of the HI mass in the high-velocity cloud phenomenon likely resides in the more prominent clouds. The bright HI features may be mere clumps within larger structures, and not independent objects.Comment: 88 pages includes 22 figures Accepted for Publication in ApJ Suppl. June 200

The Parkes HI Survey of the Magellanic System

We present the first fully and uniformly sampled, spatially complete HI survey of the entire Magellanic System with high velocity resolution, performed with the Parkes Telescope. The final data-cubes have an rms noise of sigma ~ 0.05 K and an effective angular resolution of 16 arcmin. The Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are associated with huge gaseous features with a total HI mass of M(HI) = 4.87 10^8 M_sun [d/55 kpc]^2, if all HI gas is at the same distance of 55 kpc. Approximately two thirds of this HI gas is located close to the Magellanic Clouds (Magellanic Bridge and Interface Region), and 25% of the HI gas is associated with the Magellanic Stream. The Leading Arm has a four times lower HI mass than the Magellanic Stream, corresponding to 6% of the total HI mass of the gaseous features. We have analyzed the velocity field of the Magellanic Clouds and their neighborhood introducing a LMC-standard-of-rest frame. The HI in the Magellanic Bridge shows low velocities relative to the Magellanic Clouds suggesting an almost parallel motion, while the gas in the Interface Region has significantly higher relative velocities indicating that this gas is leaving the Magellanic Bridge building up a new section of the Magellanic Stream. The clouds in the Magellanic Stream and the Leading Arm show significant differences, both in the column density distribution and in the shapes of the line profiles. The HI gas in the Magellanic Stream is more smoothly distributed than the gas in the Leading Arm. These morphological differences can be explained if the Leading Arm is at considerably lower z-heights and embedded in a higher pressure ambient medium.Comment: 23 pages, 18 figures, accepted for publication in A&

FUSE Observations of Atomic Abundances and Molecular Hydrogen in the Leading Arm of the Magellanic Stream

We present Far Ultraviolet Spectroscopic Explorer observations of the atomic and molecular absorption in high velocity cloud HVC 287.5+22.5+240, which lies in front of the ultraviolet-bright nucleus of the Seyfert 1 galaxy NGC 3783. We detect H2, N I, N II, Si II, and Fe II absorption and set limits on the amount of absorption due to P III, Ar I, and Fe III. We extend the earlier metallicity and dust-depletion measurements made by Lu and collaborators by examining the relative gas-phase abundances of Si, P, S, and Fe. Corrections to the derived gas-phase abundances due to ionized gas in the HVC are less than 15%. The HVC has a metallicity of 0.2-0.4 solar, similar to that of the Small Magellanic Cloud. The relative abundance pattern for the elements studied resembles that of warm gas in the SMC, which supports the idea that this HVC is part of the tidally stripped Leading Arm of the Magellanic Stream. The abundance pattern implies that the HVC contains dust grains that have been processed significantly. It is likely that the grain mantles have been modified or stripped back to expose the grain cores. We have identified more than 30 lines of H2 arising in the HVC from rotational levels J = 0 to J = 3. Synthetic spectra and a curve-of-growth fit to these lines with b = 12 km/sec indicate that log N(H2) = 16.80+/-0.10 and f(H2) = 2N(H2)/[N(H I)+2N(H2)] = 0.0016. From an analysis of the H2 rotational populations, we find an absorption rate (at 1000 A) that is less than one-tenth the average value in the solar neighborhood. The presence of molecular gas in the HVC requires that either the H2 formed in situ or that molecules formed within the SMC survived tidal stripping. We favor the latter possibility because of the long formation time derived for molecules in this HVC.Comment: 28 pages (includes 6 figures). AASTeX preprint format. Accepted for publication in the February 2001 issue of the Astronomical Journa

Proton Motive Force-Dependent Hoechst 33342 Transport by the ABC Transporter LmrA of Lactococcus lactis

The fluorescent compound Hoechst 33342 is a substrate for many multidrug resistance (MDR) transporters and is widely used to characterize their transport activity. We have constructed mutants of the adenosine triphosphate (ATP) binding cassette (ABC)-type MDR transporter LmrA of Lactococcus lactis that are defective in ATP hydrolysis. These mutants and wild-type LmrA exhibited an atypical behavior in the Hoechst 33342 transport assay. In membrane vesicles, Hoechst 33342 transport was shown to be independent of the ATPase activity of LmrA, and it was not inhibited by orthovanadate but sensitive to uncouplers that collapse the proton gradient and to N,N'-dicyclohexylcarbodiimide, an inhibitor of the F0F1-ATPase. In contrast, transport of Hoechst 33342 by the homologous, heterodimeric MDR transporter LmrCD showed a normal ATP dependence and was insensitive to uncouplers of the proton gradient. With intact cells, expression of LmrA resulted in an increased rate of Hoechst 33342 influx while LmrCD caused a decrease in the rate of Hoechst 33342 influx. Cellular toxicity assays using a triple knockout strain, i.e., L. lactis ΔlmrA ΔlmrCD, demonstrate that expression of LmrCD protects cells against the growth inhibitory effects of Hoechst 33342, while in the presence of LmrA, cells are more susceptible to Hoechst 33342. Our data demonstrate that the LmrA-mediated Hoechst 33342 transport in membrane vesicles is influenced by the transmembrane pH gradient due to a pH-dependent partitioning of Hoechst 33342 into the membrane.