scholarly journals Gas Mixing, Gas Cycles and the Chemical Evolution of Dwarf Irregular Galaxies

2004 ◽  
Vol 217 ◽  
pp. 178-187 ◽  
Author(s):  
Gerhard Hensler ◽  
Joachim Köppen ◽  
Jan Pflamm ◽  
Andreas Rieschick
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Chemical Evolution ◽  
Dwarf Galaxies ◽  
Type Ii ◽  
Gas Mixing ◽  
Active Star ◽  
Active Star Formation ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies

Dwarf galaxies are ideal laboratories to study influential effects on galaxy evolution. In particular, their gas-rich variant with very active star formation, starbursting dwarf irregulars, shows chemical and structural signatures that lead unambiguously to the conclusion that they are standing in a vital contact with their surroundings. Gas infall cannot only trigger star formation but also allows for a reduction of the metal content. on the other hand, active star formation ignites numerous supernovae type II which accumulate and can produce a galactic wind. This again depletes the metals pushing them into a gas mixing cycle with different timescales, locally of about 10 Myrs, but an galactic scales of at least 1 Gyr. This paper illuminates the different processes like gas infall and outflow and their effects on the chemical evolution, the star formation, and the gas mixing in dwarf irregular galaxies.

scholarly journals Star Formation Thresholds in Low Surface Brightness Dwarf Galaxies

1999 ◽  
Vol 171 ◽  
pp. 274-281
Author(s):  
Liese van Zee
Keyword(s):  
Star Formation ◽  
Comparative Study ◽  
Column Density ◽  
Surface Brightness ◽  
Dwarf Galaxies ◽  
Critical Threshold ◽  
Active Star ◽  
Comparison Sample ◽  
Active Star Formation ◽  
Low Surface Brightness

AbstractThe results of a comparative study of star formation thresholds in gas-rich, low surface brightness, dwarf galaxies are presented. Approximately half the galaxies in the study were “high MH/LB” galaxies, which appear to have inefficient star formation properties. The comparison sample comprised of otherwise “normal” dwarf galaxies, with moderate current star formation rates. In all systems, sites of active star formation were associated with local peaks in the HI column density. For both types of galaxies, the azimuthally averaged gas column density is low. Similar to other LSB systems, the global gas densities are well below the critical threshold for star formation throughout the system. Thus, star formation is inhibited globally, but occurs locally in these gas-rich dwarf galaxies.

scholarly journals Testing Evolutionary Models of Dwarf Irregular Galaxies through Gas and Stellar Metallicity Determinations in HII Galaxies

2012 ◽  
Vol 8 (S292) ◽  
pp. 254-254
Author(s):  
Pieter Westera ◽  
François Cuisinier ◽  
Didier Curty ◽  
Roland Buser
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Line Strength ◽  
Star Formation History ◽  
High Mass ◽  
Evolutionary Models ◽  
Homogeneous Sample ◽  
Irregular Galaxies ◽  
Low Metallicity ◽  
Dwarf Irregular Galaxies

AbstractDwarf irregular galaxies are usually low-metallicity objects, and show ongoing or very recent star formation, giving rise to their irregular appearance. Especially HII galaxies, a sub-category of dwarf irregulars showing unusually high star formation activity, are believed to be among the least evolved galaxies in existence today. Therefore, they are very interesting objects for studies of early galaxy evolution and of metallicity enrichment mechanisms.Several groups have developed theoretical evolutionary models of galaxies of this type, describing different possible formation and evolutionary scenarii, and varying factors such as gas infall and outflow, as well as the star formation history, and making predictions about their chemical evolution. One way to evaluate these models is by determining the metallicities of the different components of these galaxies, their gas and stars.We examine a sample of HII galaxies from the Sloan Digital Sky Survey, which possibly contains the largest homogeneous sample of HII galaxy spectra to date. Using very restrictive selection criteria, which guarantee a sample of high quality spectra and avoid “contamination” by spectra of objects of other nature, we defined a sample of ∼ 700 HII galaxies spectra.Through emission line strength calibrations and a detailed stellar population synthesis, we determined the metallicities of both the gas and the stellar content of these galaxies.For HII galaxies up to stellar masses of 5 × 109M⊙, we find enrichment mechanisms not to vary with galactic mass, being the same for low- and high-mass galaxies on average. They do seem to present a greater variety at the high-mass end, though, indicating a more complex assembly history. Our results favour galaxy evolutionary models featuring constantly infalling low-metallicity clouds that retain part of the galactic winds. Above 5 × 109M⊙ stellar mass, the retention of high metallicity gas by the galaxies' gravitational potential dominates.I would like to thank the Fundação de Amparo à Pesquisa do Estado do São Paulo (FAPESP) for financial support.

scholarly journals Investigating environmental trends in the outer visible edges of dwarf irregular galaxies

2016 ◽  
Vol 11 (S321) ◽  
pp. 282-282
Author(s):  
Jacqueline M. Dunn
Keyword(s):  
Star Formation ◽  
Galaxy Evolution ◽  
Environmental Effects ◽  
Environmental Influence ◽  
High Density ◽  
Exact Nature ◽  
Effective Surface ◽  
Irregular Galaxies ◽  
Absolute Magnitudes ◽  
Dwarf Irregular Galaxies

AbstractThe star formation histories and evolution of 28 dwarf irregular galaxies (dIs) that reside in differing local and global environments are investigated. The shallow gravitational potentials of dwarf galaxies make these objects highly susceptible to changes in morphology or dynamics by external perturbations. Additionally, the lack of more complicated structures such as spiral arms makes environmental effects more easily discernible. Therefore, dIs are ideal candidates for a study of the role of environment in galaxy evolution. The local environment is defined by the local galaxy number density, where high indicates at least one neighbor within 200 kpc and low indicates no neighbors within 1 Mpc. The global environment is classified as either the field or a galaxy group / cluster.Absolute magnitudes, colors, central surface brightnesses, star formation rates and color profiles were compared using photometry from UBVR and Hα imaging. While some environmental trends are noted (galaxies in local high density environments have brighter central and effective surface brightnesses, while those in global high density environments have brighter absolute magnitudes, central and effective surface brightnesses, and higher star formation rates), no systematic environmental trends are seen in the shape of the color profiles or spatial distribution of recent star formation. A lack of environmental trend in star formation and galaxy color indicates that either internal processes dominate the formation and subsequent evolution of the outskirts of dIs, or there is no systematic environmental effect on such. The appearance of environmental effects should be more noticeable at the outermost edges of these systems. The lack of a trend in such implies that the exact nature of the environmental influence varies greatly depending on the exact nature of the interaction occurring.

scholarly journals Booms and Busts: the Burstiness of Star Formation in Nearby Dwarf Galaxies

2010 ◽  
Vol 27 (3) ◽  
pp. 234-241 ◽  
Author(s):  
A. A. Cole
Keyword(s):  
Galaxy Evolution ◽  
Local Group ◽  
Dwarf Galaxies ◽  
Starburst Galaxy ◽  
Ic 10 ◽  
Irregular Galaxies ◽  
Magnitude Diagram ◽  
Nearby Galaxies ◽  
Dwarf Irregular Galaxies ◽  
The Universe

AbstractIn this review I summarise recent advances in our understanding of the importance of starburst events to the evolutionary histories of nearby galaxies. Ongoing bursts are easily diagnosed in emission-line surveys, but assessing the timing and intensity of fossil bursts requires more effort, usually demanding color–magnitude diagrams or spectroscopy of individual stars. For ages older than ∼1 Gyr, this type of observation is currently limited to the Local Group and its immediate surroundings. However, if the Local Volume is representative of the Universe as a whole, then studies of the age and metallicity distributions of star clusters and resolved stellar populations should give statistical clues as to the frequency and importance of bursts to the histories of galaxies in general. Based on starburst statistics in the literature and synthetic colour-magnitude diagram studies of Local Group galaxies, I attempt to distinguish between systemic starbursts that strongly impact galaxy evolution and stochastic bursts that can appear impressive but are ultimately of little significance on gigayear timescales. As a specific case, it appears as though IC 10, the only starburst galaxy in the Local Group, falls into the latter category and is not fundamentally different from other nearby dwarf irregular galaxies.

Exploring 3D data of Dwarf Galaxies

2018 ◽  
Vol 14 (S344) ◽  
pp. 359-362
Author(s):  
Katarzyna Bensch ◽  
Christina Thöne ◽  
Antonio de Ugarte Postigo ◽  
Luca Izzo ◽  
David Alexander Kann
Keyword(s):  
Star Formation ◽  
Dwarf Galaxies ◽  
Hii Regions ◽  
Local Universe ◽  
3D Data ◽  
Irregular Galaxies ◽  
Low Metallicity ◽  
Field Unit ◽  
Dwarf Irregular Galaxies ◽  
Integral Field

AbstractDwarf irregular galaxies are places of ongoing star-formation in the low-redshift Universe. Low metallicity dwarfs were originally thought to be the youngest galaxies in the local Universe, however, there is now evidence that they consist of matter which has previously undergone evolution and is enriched by star-formation. Here we present a sample of seven nearby metal-poor dwarf galaxies with a young stellar populations selected from the SDSS which we study using integral field unit (IFU) data from the VIMOS instrument, covering the spectral range between the He II 4686 line and the [SII] 6718/6733 Å doublet. We present property maps across the galaxies and compare different galaxies and different HII regions within the same galaxy. We find that the properties within one galaxy are not uniform and they also differ between different galaxies concerning star-formation, kinematics and metallicity and morphology. The observed differences across individual galaxies together with disturbed kinematics and morphologies can be interpreted as possible signs of recent interactions and/or mergers. Additionally, we present a comparison of different metallicity calibrations and search for systematic differences obtained using different methods.

scholarly journals HI Distribution in Extreme Dwarf Irregulars and Dwarf Spheroidals

1998 ◽  
Vol 11 (1) ◽  
pp. 121-122
Author(s):  
Claude Carignan
Keyword(s):  
Star Formation ◽  
Stellar Population ◽  
Large Fraction ◽  
Dwarf Spheroidal Galaxies ◽  
Irregular Galaxies ◽  
Single Burst ◽  
Dwarf Spheroidals ◽  
Dwarf Irregular Galaxies ◽  
Spheroidal Galaxies

Recent studies (Puche & Westpfahl 1994, Young & Lo 1996) have shown that the distribution of HI in some extreme low luminosity dwarf irregular galaxies (e.g. M81dwA, Holmberg I, Leo A) tends to have a ring-like (or shell-like) distribution which suggests that a single burst of star formation could expell most of the remaining ISM (or at least a large fraction of it) from the system. In view of this, Puche & Westpfahl (1994) suggested that in dwarf spheroidal galaxies, the HI should be found at large radii since no young stellar population is observed in most of them.

Stellar feedback in dwarf irregular galaxies with radio continuum observations

2018 ◽  
Vol 14 (S344) ◽  
pp. 255-258
Author(s):  
Volker Heesen ◽  
Aritra Basu ◽  
Elias Brinks ◽  
George Heald ◽  
Andrew Fletcher ◽  
...  
Keyword(s):  
Star Formation ◽  
Low Frequency ◽  
Cosmic Ray ◽  
Radio Continuum ◽  
Very Large Array ◽  
Radio Halo ◽  
Spatially Resolved ◽  
Ic 10 ◽  
Irregular Galaxies ◽  
Dwarf Irregular Galaxies

AbstractLow-mass dwarf irregular galaxies are subject to outflows, in which cosmic rays may play a very important role; they can be traced via their electron component, the cosmic ray electrons (CRe), in the radio continuum as non-thermal synchrotron emission. With the advent of sensitive low-frequency observations, such as with the Low-Frequency Array (LOFAR), we can trace CRe far away from star formation sites. Together with GHz-observations, such as with the Very Large Array (VLA), we can study spatially resolved radio continuum spectra at matched angular resolution and sensitivity. Here, we present results from our 6-GHz VLA survey of 40 nearby dwarf galaxies and our LOFAR study of the nearby starburst dwarf irregular galaxy IC 10. We explore the relation of RC emission with star formation tracers and study in IC 10 the nature of a low-frequency radio halo, which we find to be the result of a galactic wind.

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