scholarly journals The Extreme Outer Regions of Disk Galaxies: Star Formation and Metal Abundances

1999 ◽  
Vol 171 ◽  
pp. 196-203
Author(s):  
Annette Ferguson ◽  
Rosemary Wyse ◽  
Jay Gallagher
Keyword(s):  
Star Formation ◽  
Gas Phase ◽  
Massive Star ◽  
Spiral Galaxies ◽  
Disk Galaxies ◽  
Physical Conditions ◽  
First Results ◽  
Disk Evolution ◽  
Metal Abundances ◽  
Optical Radius

AbstractThe extreme outer regions of disk galaxies, lying at or beyond the classical optical radius defined by R25, present an opportunity to study star formation and chemical evolution under unique physical conditions, possibly reminscent of those which existed during the early stages of disk evolution. We present here some of the first results from a large study to measure star formation rates and metallicities in the extreme outer limits of a sample of nearby spiral galaxies. Despite their low gas column densities, massive star formation is often observed in these outer parts, but at an azimuthally–averaged rate much lower than that seen in the inner disk. Gas-phase O/H abundances of roughly 10% solar characterize the gas at 1.5–2 R25. The implications of our results for star formation ‘laws’ and models of disk evolution are discussed.

scholarly journals A deep dive into NGC 604 with Gemini/NIRI imaging

2009 ◽  
Vol 5 (S266) ◽  
pp. 391-394
Author(s):  
Cecilia Fariña ◽  
Guillermo L. Bosch ◽  
Rodolfo R. Barbá
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Near Infrared ◽  
Mass Function ◽  
Initial Mass Function ◽  
Infrared Study ◽  
Infrared Excess ◽  
Deep Dive ◽  
Physical Conditions ◽  
First Results

AbstractThe giant Hii region NGC 604 constitutes a complex and rich population to study in detail many aspects of massive star formation, such as their environments and physical conditions, the evolutionary processes involved, the initial mass function for massive stars and star-formation rates, among many others. Here, we present our first results of a near-infrared study of NGC 604 performed with NIRI images obtained with Gemini North. Based on deep JHK photometry, 164 sources showing infrared excess were detected, pointing to the places where we should look for star-formation processes currently taking place. In addition, the color–color diagram reveals a great number of objects that could be giant/supergiant stars or unresolved, small, tight clusters. An extinction map obtained based on narrow-band images is also shown.

scholarly journals Ram Pressure Stripping of Spiral Galaxies in Clusters

2004 ◽  
Vol 217 ◽  
pp. 376-381
Author(s):  
Elke Schumacher ◽  
Gerhard Hensler
Keyword(s):  
Mass Loss ◽  
Spiral Galaxies ◽  
Disk Galaxies ◽  
Helmholtz Instability ◽  
Restoring Force ◽  
Ram Pressure ◽  
First Results ◽  
Two Phases ◽  
Gas Loss ◽  
Long Timescales

We investigate the process of ram pressure stripping by means of numerical simulations with a 2D hydrodynamical code. We present some first results of a set of simulations with varying galaxy velocities and ICM densities. We find that in typical cluster core environments disk galaxies lose a substantial amount of their gas, whereas in the outskirts of galaxy clusters the mass loss is quite small. Furthermore, the gas loss happens in two phases: In the initial phase gas is pushed out of regions where the ram pressure overcomes the gravitational restoring force; most of the overall gas loss happens in this phase. Afterwards the Kelvin-Helmholtz instability leads to a further mass loss at a small rate, that could be important on long timescales.

scholarly journals Molecular Gas and Star Formation in Local Early–type Galaxies

2010 ◽  
Vol 6 (S277) ◽  
pp. 55-58
Author(s):  
M. Bureau ◽  
T. A. Davis ◽  
K. Alatalo ◽  
A. F. Crocker ◽  
L. Blitz ◽  
...  
Keyword(s):  
Star Formation ◽  
Far Infrared ◽  
Gas Content ◽  
Molecular Gas ◽  
Disk Galaxies ◽  
Formation Processes ◽  
Early Type ◽  
High Detection Rate ◽  
Physical Conditions ◽  
Multi Wavelength

AbstractThe molecular gas content of local early-type galaxies is constrained and discussed in relation to their evolution. First, as part of the ATLAS3D survey, we present the first complete, large (260 objects), volume-limited single-dish survey of CO in normal local early-type galaxies. We find a surprisingly high detection rate of 22%, independent of luminosity and at best weakly dependent on environment. Second, the extent of the molecular gas is constrained with CO synthesis imaging, and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of the systems, although this behaviour is drastically diffferent between field and cluster environments. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Last, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation, following the standard Schmidt-Kennicutt law but not the far infrared-radio correlation. This may suggest a greater diversity in star formation processes than observed in disk galaxies. Using multiple molecular tracers, we are thus starting to probe the physical conditions of the cold gas in early-types.

scholarly journals The Physical Conditions for Massive Star Formation: Dust Continuum Maps and Modeling

2002 ◽  
Vol 143 (2) ◽  
pp. 469-497 ◽  
Author(s):  
Kaisa E. Mueller ◽  
Yancy L. Shirley ◽  
Neal J. Evans II ◽  
Heather R. Jacobson
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Massive Star Formation ◽  
Physical Conditions

scholarly journals Cold Molecular Gas as a Possible Component of Dark Matter in the Outer Parts of Disk Galaxies

2004 ◽  
Vol 220 ◽  
pp. 249-250
Author(s):  
Ronald J. Allen ◽  
Rosa Diaz-Miller
Keyword(s):  
Dark Matter ◽  
Star Formation ◽  
Small Area ◽  
Physical State ◽  
Filling Factor ◽  
Massive Star ◽  
Molecular Gas ◽  
Disk Galaxies ◽  
Dust Grain ◽  
New Evidence

In the last few years new evidence has been presented for the presence of ongoing massive star formation in the outer HI disks of galaxies. These discoveries strongly suggest that precursor molecular gas must also be present in some physical state which is escaping detection by the usual means (CO(1-0), IR, etc.). We present a model for such a gas in a framework which views the HI as the result of an ongoing “photodissociation ↔ dust grain reformation” equilibrium in a cold, clumpy molecular medium with a small area filling factor.

scholarly journals Metal Abundances of Damped Lyα Systems and the Chemical Evolution of Spiral Galaxies

1995 ◽  
Vol 164 ◽  
pp. 457-457
Author(s):  
Uta Fritze-V. Alvensleben ◽  
Klaus J. Fricke
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Spiral Galaxies ◽  
Metal Abundances ◽  
Enrichment Process

Our chemical evolution models describe in detail the enrichment process of a number of individual elements from 12C to 56Fe, including delayed SNI contributions. Variation of the characteristic timescale of star formation (SF) t∗ not only results in differences in the abundance evolution but also changes abundance ratios of elements originating from different nucleosvnthetic sites, as e.g. [C/O], [O/Fe], or [Mg/Fe].

scholarly journals Properties of H ɪɪ Regions Along Galactic Bars

1996 ◽  
Vol 157 ◽  
pp. 70-75
Author(s):  
P. Martin
Keyword(s):  
Star Formation ◽  
Spiral Galaxies ◽  
H Ii Regions ◽  
Electron Densities ◽  
Physical Conditions ◽  
General Properties

AbstractA study of general properties of H ɪɪ regions along the bars of 11 spiral galaxies is presented. From Hα imaging, distributions, morphology and star formation rates are established. Physical conditions derived from spectrophotometry reveal that strong shocks are absent in H ɪɪ regions along bars and electron densities appear to be normal. Abundance distributions indicate that mixing of the ISM is taking place along bars.

scholarly journals Massive Star Formation

2004 ◽  
Vol 221 ◽  
pp. 169-180
Author(s):  
Guido Garay
Keyword(s):  
Star Formation ◽  
Formation Process ◽  
Massive Star ◽  
Massive Stars ◽  
Critical Role ◽  
Detailed Knowledge ◽  
Theoretical Studies ◽  
Cloud Environment ◽  
Physical Processes ◽  
Physical Conditions

The understanding of the formation process of massive stars requires a detailed knowledge of the physical conditions of the cloud environment which is thought to play a critical role in determining the formation mechanism. In recent years there has been a rapid growth of observational and theoretical studies concerning the formation of massive stars. Here I review observational data gathered during the last few years which are providing key evidence concerning the physical processes that take place during the formation of massive stars.

scholarly journals Gas inflow and nuclear star formation in galaxies with non-axisymmetric bulges

2013 ◽  
Vol 9 (S303) ◽  
pp. 171-173
Author(s):  
E. Kim ◽  
S. S. Kim ◽  
G.-H. Lee ◽  
M. G. Lee ◽  
R. de Grijs
Keyword(s):  
Star Formation ◽  
Spiral Galaxies ◽  
Starburst Galaxies ◽  
Disk Galaxies ◽  
Early Type ◽  
Limited Sample ◽  
Density Region ◽  
Axis Ratio ◽  
Final Sample ◽  
Star Formation In Galaxies

AbstractWe present the dependence of the amount of nuclear star formation on the non-axisymmetry of a bulge of disk galaxies. For this, we use a volume-limited sample of spiral galaxies at 0.02 < = z < 0.055 from the SDSS DR7. Among 3173 final sample galaxies with an axis ratio b/a > 0.6 and a bulge fraction ranged in B/T <= 0.41, nuclear starburst galaxies are 10%. We find that a fraction of the nuclear starburst galaxies become higher when ellipticity of a bulge increases in early type galaxies. Also, the fraction increases clearly when early type galaxies are isolated and in low density region. Our results indicate that the non-axisymmetry of bulges assists gas to fall inside and affects the nuclear starburst process in disk galaxies.

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