scholarly journals Evidence for Gas Accretion in Galactic Disks

2004 ◽  
Vol 217 ◽  
pp. 122-129 ◽  
Author(s):  
Thijs van der Hulst ◽  
Renzo Sancisi
Keyword(s):  
Galactic Disks ◽  
The Past ◽  
Evolution Of Galaxies ◽  
Stellar Streams ◽  
Nearby Galaxies ◽  
M 31 ◽  
Gas Accretion

Studies of the HI in galaxies have clearly shown that subtle details of the HI distribution and kinematics often harbour key information for understanding the structure and evolution of galaxies. Evidence for the accretion of material has grown over the past many years and clear signatures can be found in HI observations of galaxies. We have obtained new detailed and sensitive HI synthesis observations of three nearby galaxies which are suspected of capturing small amounts of HI and show that indeed accretion of small amounts of gas is taking place in these galaxies. This could be the same kind of phenomenon of material infall as observed in the stellar streams in the halo and outer parts of our galaxy and M 31.

Stellar Evolution

1962 ◽  
Vol 11 (02) ◽  
pp. 137-143
Author(s):  
M. Schwarzschild
Keyword(s):  
Solar System ◽  
Stellar Evolution ◽  
Space Craft ◽  
New Techniques ◽  
Substantial Body ◽  
Individual Stars ◽  
The Past ◽  
Evolution Of Galaxies ◽  
History Of ◽  
Fast Flow

It is perhaps one of the most important characteristics of the past decade in astronomy that the evolution of some major classes of astronomical objects has become accessible to detailed research. The theory of the evolution of individual stars has developed into a substantial body of quantitative investigations. The evolution of galaxies, particularly of our own, has clearly become a subject for serious research. Even the history of the solar system, this close-by intriguing puzzle, may soon make the transition from being a subject of speculation to being a subject of detailed study in view of the fast flow of new data obtained with new techniques, including space-craft.

scholarly journals Shaping Disk Galaxy Stellar Populations via Internal and External Processes

2012 ◽  
Vol 10 (H16) ◽  
pp. 372-372
Author(s):  
Rok Roškar
Keyword(s):  
Galaxy Formation ◽  
Stellar Population ◽  
Milky Way ◽  
Stellar Populations ◽  
Radial Migration ◽  
Disk Formation ◽  
Process Understanding ◽  
History Of ◽  
Nearby Galaxies ◽  
Gas Accretion

AbstractIn recent years, effects such as the radial migration of stars in disks have been recognized as important drivers of the properties of stellar populations. Radial migration arises due to perturbative effects of disk structures such as bars and spiral arms, and can deposit stars formed in disks to regions far from their birthplaces. Migrant stars can significantly affect the demographics of their new locales, especially in low-density regions such as in the outer disks. However, in the cosmological environment, other effects such as mergers and filamentary gas accretion also influence the disk formation process. Understanding the relative importance of these processes on the detailed evolution of stellar population signatures is crucial for reconstructing the history of the Milky Way and other nearby galaxies. In the Milky Way disk in particular, the formation of the thickened component has recently attracted much attention due to its potential to serve as a diagnostic of the galaxy's early history. Some recent work suggests, however, that the vertical structure of Milky Way stellar populations is consistent with models that build up the thickened component through migration. I discuss these developments in the context of cosmological galaxy formation.

scholarly journals COMMISSION 29: STELLAR SPECTRA

2008 ◽  
Vol 4 (T27A) ◽  
pp. 209-210
Author(s):  
Mudumba Parthasarathy ◽  
Nikolai E. Piskunov ◽  
Christopher Sneden ◽  
Kenneth G. Carpenter ◽  
Fiorella Castelli ◽  
...  
Keyword(s):  
Open Clusters ◽  
Time Dependent ◽  
Medium Size ◽  
Composition Analysis ◽  
Stellar Spectra ◽  
X Ray ◽  
The Past ◽  
Nearby Galaxies ◽  
Chemical Composition Analysis ◽  
Accurate Chemical Composition

The members of IAU Commission 29 Stellar Spectra are actively engaged in the quantitative analysis of spectra of various types of stars. With large and medium size telescopes equipped with high resolution spectrographs LTE and Non-LTE analysis of spectra of all types stars are being carried out. Spectra of stars in our Galaxy, in globular and open clusters, stars in LMC and SMC and in nearby galaxies are being studied. Accurate chemical composition analysis of various types of stars has been carried out during the past three years. Now the analysis of stellar spectra covers the wavelength range from X-ray region to IR and sub-millimeter range. Recently stellar spectra are being analysed using time-dependent, 3D, hydrodynamical model atmospheres to derive accurate stellar abundances.

scholarly journals Massive extragalactic eclipsing binaries

2006 ◽  
Vol 2 (14) ◽  
pp. 198-198
Author(s):  
Alceste Z. Bonanos
Keyword(s):  
Gamma Ray ◽  
Local Group ◽  
Galactic Center ◽  
Massive Stars ◽  
Galactic Disk ◽  
Eclipsing Binaries ◽  
Stellar Clusters ◽  
Galactic Clusters ◽  
Nearby Galaxies ◽  
M 31

Masses, radii and luminosities of distant stars can only be measured accurately in eclipsing binaries. The most massive eclipsing binary currently known is WR 20a, which consists of two ~ 80 M⊙ stars in a 3.7 d orbit. Analogs of WR 20a are bound to exist both in massive stellar clusters in our Galaxy and in nearby galaxies. The nearest ones are located in the clusters near the Galactic Center: the Center, Arches, and Quintuplet clusters. The severe amount of reddening in the galactic disk makes the study of galactic clusters challenging. However, with current 8-m class telescopes, the study of massive stars in nearby galaxies is also feasible. The nearest Local Group galaxies (LMC, SMC, M 31, M 33) provide the perfect laboratory for studying massive stars and determining their properties as a function of metallicity. Such studies will constrain models, confirm the dependence of evolution on metallicity and help understand the rate and nature of supernovae and gamma-ray bursts.

scholarly journals H0 from Gravitational Lenses: Recent Results

2005 ◽  
Vol 201 ◽  
pp. 209-218
Author(s):  
Paul L. Schechter
Keyword(s):  
Systematic Uncertainty ◽  
Gravitational Lensing ◽  
Good Deal ◽  
Constrained Systems ◽  
Gravitational Lenses ◽  
Quarter Century ◽  
The Past ◽  
Nearby Galaxies ◽  
Derivatives Of ◽  
Central Concentration

The 0th, 1st and 2nd derivatives of a “Fermat potential” give the three D's of gravitational lensing: delay, deflection and distortion. Observations of these delays, deflections and distortions for doubly and quadruply imaged quasars give estimates of Hubble's constant, H0. The single largest contribution to the uncertainty in H0 arises from the difficulty in constraining the degree of central concentration of the lensing potential. Fortunately, astronomers have spent a good deal of effort over the past quarter century addressing just this question. If galaxies at z = 0.5 are like nearby galaxies, the associated systematic uncertainty in H0 is less than 10%. The expected lens-to-lens scatter is 20%. Results from three particularly well constrained systems are reported.

scholarly journals 5.11. Dense molecular gas in nearby galaxies

1998 ◽  
Vol 184 ◽  
pp. 231-233 ◽  
Author(s):  
Y. Gao ◽  
P.M. Solomon
Keyword(s):  
Dipole Moment ◽  
Surface Brightness ◽  
Galactic Nuclei ◽  
Molecular Gas ◽  
Galactic Disks ◽  
Central Regions ◽  
Nearby Galaxies ◽  
Gas Properties

HCN, one of the most abundant high dipole-moment molecules (traces molecular gas at densities ≳ 3 × 104 cm−3 whereas CO traces at ∼ 500 cm−3), has only been detected in ∼ 25 galaxies, primarily towards the galactic nuclei (Solomon et al. 1992; Nguyen-Q-Rieu et al. 1992; Helfer & Blitz 1993; Aalto et al. 1995). Dense molecular gas properties in “normal” galactic disks, as compared to the centers of “normal” spirals, starbursts, and luminous IR galaxies are not clear. As part of a large HCN survey in 60 galaxies (Gao 1996; Gao & Solomon 1997), we present here HCN observations in central regions of a few nearby galaxies. HCN was mapped at least along the major axes in the inner disks to determine the total HCN luminosity, the distribution with radius of HCN emission, and of the surface brightness ratio of SBR ≡ IHCN/ICO.

scholarly journals Discovery of an edge-on galaxy with X-shaped bi-cone – SDSS J171359.00+333625.5

2019 ◽  
Vol 490 (3) ◽  
pp. 3830-3839 ◽  
Author(s):  
Min Bao ◽  
Yan-mei Chen ◽  
Qi-rong Yuan ◽  
Yong Shi ◽  
Dmitry Bizyaev ◽  
...  
Keyword(s):  
Velocity Dispersion ◽  
Rotation Velocity ◽  
Major Axis ◽  
Joint Effect ◽  
Galactic Winds ◽  
The Galaxy ◽  
Disc Rotation ◽  
Nearby Galaxies ◽  
Field Unit ◽  
Gas Accretion

ABSTRACT Using the integral field unit (IFU) data from Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we study the kinematics of gas and stellar components in an edge-on Seyfert 2 galaxy, SDSS J171359.00+333625.5, with X-shaped bi-conical outflows. The gas and stars therein are found to be counter-rotating, indicating that the collision between the inner and external gas might be an effective way to dissipate the angular momentum, which leads to remarkable gas accretion into the galaxy centre. Large [O iii]λ5007 equivalent width and AGN-like line ratio in the large bi-conical region suggest that the gas is ionized by the central AGN. The gas velocity in the bi-cone region shows that ionized gas is receding relative to the galaxy centre, which could be the joint effect of inflows, outflows, and disc rotation. We are probably witnessing the case where a great amount of gas in the disc is being efficiently accreted into the central black hole, and the AGN-driven galactic winds are blown out along the bi-cone. The kinematics of oxygen, including rotation velocity and velocity dispersion, is different from other elements, like hydrogen, nitrogen, and sulphur. The rotation velocity estimated from oxygen is slower than from other elements. The velocity dispersion of other elements follows galactic gravitational potential, while the velocity dispersion of oxygen stays roughly constant along the galactic major-axis. The further advanced observations, e.g. of cold gas or with an IFU of higher spatial resolution, are required to better understand this object.

scholarly journals Evolution of Galaxies Governed by Disk Dynamics and Spiral Structure

1977 ◽  
Vol 45 ◽  
pp. 31-45
Author(s):  
Raymond J. Talbot
Keyword(s):  
Star Formation ◽  
Spiral Structure ◽  
Disk Galaxies ◽  
Major Topic ◽  
The Past ◽  
Evolution Of Galaxies ◽  
Evolutionary Changes

My major topic will be the evolutionary changes in disk galaxies caused by the continuing process of star formation. The task of interpreting observations to derive the past rate of star formation is treacherous, as I am sure will be evident in the various observational papers presented at this colloquium. Therefore, I will mention only briefly some of the basic aspects of models which have been used to discuss that past evolution.

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