48 research outputs found
NRO/OVRO CO(1-0) survey: central regions of nearby spiral galaxies
We have done a CO(1-0) imaging survey of the central regions of nearby spiral galaxies using the Nobeyama and Owens Valley Millimeter Arrays. The survey aims to reveal the nuclear gas properties in normal galaxies that have been paid relatively little attention compared to Seyferts, mergers, and ultraluminous IRAS galaxies. The sample consists of 20 galaxies that meet the following criteria: (1) i +5° (3) I_(CO) dV â„ 10 K(Tâ_A)km s^(â1) in the FCRAO Extragalactic CO Survey (4) no evidence of significant perturbation (e.g. merging). No selection was made on the basis of nuclear activity or IRAS data. The average distance of the galaxies is 15 Mpc and the average linear resolution is 300 pc
NRO/OVRO CO(1-0) survey: central regions of nearby spiral galaxies
We have done a CO(1-0) imaging survey of the central regions of nearby spiral galaxies using the Nobeyama and Owens Valley Millimeter Arrays. The survey aims to reveal the nuclear gas properties in normal galaxies that have been paid relatively little attention compared to Seyferts, mergers, and ultraluminous IRAS galaxies. The sample consists of 20 galaxies that meet the following criteria: (1) i +5° (3) I_(CO) dV â„ 10 K(Tâ_A)km s^(â1) in the FCRAO Extragalactic CO Survey (4) no evidence of significant perturbation (e.g. merging). No selection was made on the basis of nuclear activity or IRAS data. The average distance of the galaxies is 15 Mpc and the average linear resolution is 300 pc
Bar-driven Transport of Molecular Gas to Galactic Centers and Its Consequences
We study the characteristics of molecular gas in the central regions of
spiral galaxies on the basis of our CO(J=1-0) imaging survey of 20 nearby
spiral galaxies using the NRO and OVRO millimeter arrays. Condensations of
molecular gas at galactic centers with sizescales < 1 kpc and CO-derived masses
M_gas(R<500pc) = 10^8 - 10^9 M_sun are found to be prevalent in the gas-rich
L^* galaxies. Moreover, the degree of gas concentration to the central kpc is
found to be higher in barred systems than in unbarred galaxies. This is the
first statistical evidence for the higher central concentration of molecular
gas in barred galaxies, and it strongly supports the theory of bar-driven gas
transport. It is most likely that more than half of molecular gas within the
central kpc of a barred galaxy was transported there from outside by the bar.
The supply of gas has exceeded the consumption of gas by star formation in the
central kpc, resulting in the excess gas in the centers of barred systems. The
mean rate of gas inflow is statistically estimated to be larger than 0.1 - 1
M_sun/yr.
The correlation between gas properties in the central kpc and the type of
nuclear spectrum (HII, LINER, or Seyfert) is investigated. A correlation is
found in which galaxies with larger gas-to-dynamical mass ratios tend to have
HII nuclear spectra, while galaxies with smaller ratios show spectra indicating
AGN.
Also, the theoretical prediction of bar-dissolution by condensation of gas to
galactic centers is observationally tested. It is suggested that the timescale
for bar dissolution is larger than 10^8 - 10^10 yr, or a bar in a L^* galaxy is
not destroyed by a condensation of 10^8 - 10^9 M_sun gas in the central kpc.Comment: AASTeX, 20 pages, 8 eps figs, ApJ in press (10 Nov. 1999 issue
Starbursting Nuclear CO Disks of Early-type Spiral Galaxies
We have initiated the first CO interferometer survey of early-type spiral
galaxies (S0-Sab). We observed five early-type spiral galaxies with HII nuclei
(indicating circumnuclear starburst activities). These observations indicate
gas masses for the central kiloparsec of \sim 1-5% of the dynamical masses.
Such low gas mass fractions suggest that large-scale gravitational instability
in the gas is unlikely to be the driving cause for the starburst activities.
The Toomre Q values were >1 (mostly >3) within the central kiloparsec,
indicating that the gas disks are globally gravitationally stable. The area
filling factor of the gas disks is estimated to be about 0.05. This small value
indicates the existence of lumpy structure, i.e. molecular clouds, in the
globally-gravitationally stable disks. The typical surface density of the
molecular clouds is as high as \sim 3000 Msun pc^{-2}. We reconsider the nature
of the Toomre Q criterion, and conclude that the Q derived from CO observations
indicates neither star formation nor molecular cloud formation. This argument
should be valid not only for the circumnuclear disks but also for any region in
galactic disks. We tentatively explore an alternative model, i.e. cloud-cloud
collisions, as an initiating mechanism of star formation.Comment: 7pages, including 2 figures ; A&A accepted (19 Oct. 2004
Dynamics of Barred Galaxies
Some 30% of disc galaxies have a pronounced central bar feature in the disc
plane and many more have weaker features of a similar kind. Kinematic data
indicate that the bar constitutes a major non-axisymmetric component of the
mass distribution and that the bar pattern tumbles rapidly about the axis
normal to the disc plane. The observed motions are consistent with material
within the bar streaming along highly elongated orbits aligned with the
rotating major axis. A barred galaxy may also contain a spheroidal bulge at its
centre, spirals in the outer disc and, less commonly, other features such as a
ring or lens. Mild asymmetries in both the light and kinematics are quite
common. We review the main problems presented by these complicated dynamical
systems and summarize the effort so far made towards their solution,
emphasizing results which appear secure. (Truncated)Comment: This old review appeared in 1993. Plain tex with macro file. 82 pages
18 figures. A pdf version with figures at full resolution (3.24MB) is
available at http://www.physics.rutgers.edu/~sellwood/bar_review.pd
Use of Gold Nanoparticles To Enhance Capillary Electrophoresis
We describe here the use of gold nanoparticles to manipulate the selectivity between solutes in capillary electrophoresis. Two different gold-based nanoparticles were added to the run buffer. In one case, the nanoparticles were stabilized with citrate ions, but in another study, the gold nanoparticles were capped with mercaptopropionate ions (thiol-stablized). Citrate-stabilized gold nanoparticles were used in conjunction with capillaries treated with poly(diallyldimethylammonium chloride) (PDADMAC). The positively charged PDADMAC layer on the capillary walls adsorbs the negatively charged gold nanoparticles. The model solutes that were used to study the effect of the presence of the citrate-stabilized gold nanoparticles are structural isomers of aromatic acids and bases. The presence of the PDADMAC layer and the PDADMAC plus the gold nanoparticles changes both the electroosmotic mobility and the observed mobility of the solutes. These changes in the mobilities influence the observed selectivities and the separations of the system. Thiol-stabilized gold nanoparticles were used without PDADMAC in the capillary. The model solutes studied in this part are various aromatic amines. In this case as well, the presence of the gold nanoparticles modifies the electroosmotic mobility and the observed mobility of the solutes. These changes in the mobilities are manifested in selectivity alterations. The largest change in the selectivities occurs at low concentrations of the gold nanoparticles in the run buffer. The presence of nanoparticles improves the precision of the analysis and increases the separation efficiency. Nanodispersions have attracted extensive attention in various fields of physics, biology, and chemistry. [1][2][3][4][5] Physicists and chemists are intrigued by the gradual transition of the nanomaterial properties from molecule-like to those of solid-state properties by a change of a single variable, the particle size. This property has practical and future applications for nonlinear optics and electronics. The large surface area of nanomaterials intrigues chemical engineers and catalysis scientists. Surprisingly, very little research has been devoted to the application of nanoparticles for chemical separation. In this work, we demonstrate the utility and versatility of organically modified gold nanoparticles in capillary electrophoresis (CE) separations. The nanoparticles serve as large surface area platforms for organofunctional groups that interact with the capillary surface, the analytes, or both. Thus, the apparent mobilities of target analytes, as well as the electroosmotic flow, can be altered leading to enhanced selectivities. Separation of various benzene derivatives demonstrates these capabilities. Metallic nanodispersions can be prepared in aqueous and organic solvents using diverse procedures. 1,2,6-9 Nanodispersions can be stabilized in organic solvents by the solvent itself, 10 by the addition of long chain surfactants, 11,12 or by specific ligands. 13 Stabilization of metal nanodispersions in aqueous solutions is somewhat more complicated. Several successful stabilization methods are available that are based on capping of the metal nanoparticles (e.g., citrate, 6 3-mercaptopropionate, 1