scholarly journals Virgo and other Late-Type Dwarfs

1998 ◽  
Vol 11 (1) ◽  
pp. 105-106
Author(s):  
N. Brosch ◽  
A. Heller ◽  
E. Almoznino
Keyword(s):  
Star Formation ◽  
Virgo Cluster ◽  
Disk Galaxies ◽  
Late Type ◽  
Morphological Classification ◽  
External Effects ◽  
Low Mass ◽  
Galaxy Collisions ◽  
Intracluster Matter

We attempt to solve the question of star formation triggers and star formation laws by studying samples of simple objects and defining carefully the possible external effects. Among the star formation (SF) triggers there are some that can operate only in large disk galaxies. These are shear instabilities and density waves, and we can eliminate them if we restrict the sample to diskless objects of low mass. Such galaxies, which do show star formation, are late-type dwarf galaxies (DGs). Other SF triggers are related to the neighborhood a galaxy finds itself in. Such triggers are galaxy-galaxy collisions and galaxy-intracluster matter interactions (stripping, shocks, etc.). These also can be eliminated by properly choosing the sample to study; one selects galaxies from neigh-borhoods of widely different densities (of galaxies) and compares their SF parameters. We selected our first samples in a region of relatively high galaxy density, where a complete morphological classification of objects was available, and suitable depth in brightness sampling could readily be achieved. This is the Virgo cluster, where Binggeli, Sandage and Tammann (1985, BST) provide a sample of more than 2000 DGs. Among those, some 25% are of late type and are classified by BST as blue compact dwarfs (BCDs), as Magellanic irregulars (Im) of five possible sub-classes, or as combinations of those two classifications.

scholarly journals X-ray Flare Rate of T Tauri Stars in Taurus

1995 ◽  
Vol 151 ◽  
pp. 216-217
Author(s):  
R. Neuhäuser ◽  
Th. Preibisch
Keyword(s):  
Star Formation ◽  
Main Sequence ◽  
T Tauri Stars ◽  
Medium Size ◽  
Late Type ◽  
Large Sample ◽  
X Ray ◽  
T Tauri ◽  
Sky Survey ◽  
Low Mass

AbstractWe study the X-ray emission of several hundred (young, low-mass, late-type, pre-main sequence) T Tauri stars (TTS) in the Taurus T association, a nearby well-studied region of ongoing star formation. We report on X-ray emission variability of TTS as observed with the flux-limited ROSAT All-Sky Survey (RASS). Since RASS observations are spatially unbiased, we can investigate the X-ray flare rate of TTS on a large sample. We find that large flares are very rare (once per year), while medium-size flares can occur once in ∼ 40 days.

scholarly journals Disk Galaxy Models Driven by Stochastic Self-Propagating Star Formation

2010 ◽  
Vol 19 (1-2) ◽  
Author(s):  
T. Mineikis ◽  
V. Vansevičius
Keyword(s):  
Star Formation ◽  
Observational Data ◽  
Galaxy Formation ◽  
Spiral Galaxy ◽  
Gas Dynamics ◽  
Disk Galaxy ◽  
Disk Galaxies ◽  
Test Results ◽  
Late Type ◽  
Adequate Accuracy

AbstractWe present a model of chemical and spectrophotometric evolution of disk galaxies based on a stochastic self-propagating star formation scenario. The model incorporates galaxy formation through the process of accretion, chemical and photometric evolution treatment, based on simple stellar populations (SSP), and parameterized gas dynamics inside the model. The model reproduces observational data of the late-type spiral galaxy M33 reasonably well. Promising test results prove the applicability of the model and the adequate accuracy for the interpretation of disk galaxy properties.

scholarly journals Nature of bulges in the Hubble sequence

2007 ◽  
Vol 3 (S245) ◽  
pp. 309-310
Author(s):  
Eija Laurikainen ◽  
H. Salo ◽  
R. Buta ◽  
J. H. Knapen
Keyword(s):  
Star Formation ◽  
Strong Evidence ◽  
Disk Galaxies ◽  
Early Type ◽  
Late Type ◽  
Hubble Sequence

AbstractWe evaluate the nature of bulges in the Hubble sequence, based on an analysis of 216 disk galaxies of all morphological types (S0-Sd). For this purpose we collect our various analysis made separately for early and late-type galaxies, published in a series of papers. Using the criteria by Kormendy & Kennicutt we find strong evidence of pseudobulges in all Hubble types, including S0s. However, due to the relatively massive bulges in S0-S0/a galaxies it is not probable that the (pseudo)bulges in these galaxies were formed in a similar manner as in spirals. More likely, pseudobulges particularly in strongly barred early-type disk galaxies are suggested to be a combination of star formation and the nearly exponential central components of bars.

scholarly journals The star formation history of low-mass disk galaxies: A case study of NGC 300

2015 ◽  
Vol 585 ◽  
pp. A20 ◽  
Author(s):  
Xiaoyu Kang ◽  
Fenghui Zhang ◽  
Ruixiang Chang ◽  
Lang Wang ◽  
Liantao Cheng
Keyword(s):  
Star Formation ◽  
Star Formation History ◽  
Disk Galaxies ◽  
Formation History ◽  
History Of ◽  
Low Mass

Star Formation, Supernovae and the Structure of Disk Galaxies

1988 ◽  
Vol 101 ◽  
pp. 493-508
Author(s):  
Michael A. Dopita ◽  
Mt. Stromlo
Keyword(s):  
Star Formation ◽  
Molecular Clouds ◽  
Collective Effects ◽  
Disk Galaxies ◽  
Solar Mass ◽  
Low Mass Stars ◽  
T Tauri ◽  
Steady Rate ◽  
Supernova Explosions ◽  
Low Mass

AbstractA physical model for bi-modal star formation and the structure of the interstellar medium and the self-regulating evolution of disk galaxies is presented. Stars heavier than about one solar mass are produced as a result of collisions of molecular clouds or in cloud crushing events whereas low-mass stars are produced at a steady rate in dense molecular clouds and the T-Tauri winds resulting maintain the support of these clouds against rapid collapse and fragmentation. Supernova explosions and stellar winds associated with the massive stars maintain the phase structure, and the scale height of the gas. The collective effects of these energetic processes may create a hole in the disk gas, and allow a galactic wind of metalenriched gas to develop.

scholarly journals Simulating High-Redshift Disk Galaxies: Applications to Long Duration Gamma-Ray Burst Hosts

2008 ◽  
Vol 4 (S254) ◽  
pp. 35-40
Author(s):  
Brant E. Robertson
Keyword(s):  
Star Formation ◽  
Molecular Hydrogen ◽  
Gamma Ray ◽  
High Redshift ◽  
Disk Galaxies ◽  
Host Galaxies ◽  
Long Duration ◽  
Low Mass ◽  
Hydrodynamical Simulations ◽  
The Impact

AbstractThe efficiency of star formation governs many observable properties of the cosmological galaxy population, yet many current models of galaxy formation largely ignore the important physics of star formation and the interstellar medium (ISM). Using hydrodynamical simulations of disk galaxies that include a treatment of the molecular ISM and star formation in molecular clouds (Robertson & Kravtsov 2008), we study the influence of star formation efficiency and molecular hydrogen abundance on the properties of high-redshift galaxy populations. In this work, we focus on a model of low-mass, star forming galaxies at 1 ≲ z ≲ 2 that may host long duration gamma-ray bursts (GRBs). Observations of GRB hosts have revealed a population of faint systems with star formation properties that often differ from Lyman-break galaxies (LBGs) and more luminous high-redshift field galaxies. Observed GRB sightlines are deficient in molecular hydrogen, but it is unclear to what degree this deficiency owes to intrinsic properties of the galaxy or the impact the GRB has on its environment. We find that hydrodynamical simulations of low-stellar mass systems at high-redshifts can reproduce the observed star formation rates and efficiencies of GRB host galaxies at redshifts 1 ≲ z ≲ 2. We show that the compact structure of low-mass high-redshift GRB hosts may lead to a molecular ISM fraction of a few tenths, well above that observed in individual GRB sightlines. However, the star formation rates of observed GRB host galaxies imply molecular gas masses of 108 – 109M⊙ similar to those produced in the simulations, and may therefore imply fairly large average H2 fractions in their ISM.

scholarly journals Dissecting early-type dwarf galaxies into their multiple components

2012 ◽  
Vol 10 (H16) ◽  
pp. 364-364
Author(s):  
Joachim Janz ◽  
Eija Laurikainen ◽  
Thorsten Lisker ◽  
Heikki Salo
Keyword(s):  
Near Infrared ◽  
Dwarf Galaxies ◽  
Signal To Noise Ratio ◽  
Transformation Process ◽  
Virgo Cluster ◽  
Early Type ◽  
Late Type ◽  
Component Structure ◽  
Lenticular Galaxies ◽  
Low Mass

AbstractEarly-type dwarf galaxies are often thought to be either more diffuse versions of giant ellipticals or to be low-mass disk galaxies that were quenched and heated by the environment. In both cases, the picture that most astronomers have in mind probably is that of a dynamically hot, regular shaped galaxy, in which any previous substructure has either been smeared out, or has never been there. However, the early-type dwarfs are not that simple.We analyzed ~100 such objects in the Virgo cluster using deep near-infrared images and found that the majority has a multi-component structure, sometimes even with bars or lenses. The study was done by applying GALFIT to images from the SMAKCED collaboration (Stellar content, MAss and K inematics of Cluster Early-type Dwarfs, http://www.smakced.net). The sample comprises early-type galaxies in the Virgo cluster in a brightness range of −19 ≤ Mr ≤ −16 mag, and the data is complete down to Mr=−16.73 mag. The images typically reach a signal-to-noise ratio of 1 per pixel of ~0.25” at a surface brightness of ~22.5 mag/arcsec2 in the H-band. The galaxies were fitted with two-dimensional models, either with a simple Sérsic model or inner and outer components, as well as bars and lenses. Only a fraction of 31% of the galaxies can be fitted with a single Sérsic function. This fraction of “simple“ galaxies turns out to be a strong function of luminosity, with a smaller fraction for brighter objects. The bar fraction is 14% and also in 14% of the galaxies lenses were fitted.When comparing the flattening distribution, the early-type dwarfs are more similar to spiral galaxies than to elliptical or lenticular galaxies. It is disputable whether or not the dwarfs follow a common relation with the bright elliptical galaxies, e.g. in the brightness versus size diagram. At the same time, they appear as smooth continuation of bright late-type galaxies in this diagram. The inner and outer components, as well as the simple galaxies have similar flattening distributions. The inner components are mostly fitted with Sérsic-n values close to~1, i.e. with nearly exponential profiles. We argue that the inner components in the early-type dwarfs are not be bulges but may form parts of the disks, in which the matter was re-distributed during the transformation process from a late-type progenitor.

scholarly journals The Last Stages of Star Formation in dEs?

2006 ◽  
Vol 2 (S235) ◽  
pp. 317-317
Author(s):  
T. Lisker ◽  
K. Glatt ◽  
P. Westera ◽  
E. K. Grebel
Keyword(s):  
Spectral Analysis ◽  
Star Formation ◽  
Dwarf Galaxies ◽  
Stellar Mass ◽  
Virgo Cluster ◽  
Significant Fraction ◽  
Early Type ◽  
Late Type ◽  
Morphological Transformation

AbstractA significant fraction of Virgo cluster early-type dwarf galaxies have blue central colours caused by recent or ongoing star formation. A spectral analysis shows that even in their centers, stellar mass is dominated by an old population. These galaxies are an unrelaxed cluster population that possibly formed from morphological transformation of late-type galaxies.

scholarly journals The dust distribution in late-type low surface brightness disks

2011 ◽  
Vol 7 (S284) ◽  
pp. 101-103
Author(s):  
John MacLachlan ◽  
Lynn Matthews ◽  
Kenny Wood ◽  
Jay Gallagher
Keyword(s):  
Surface Brightness ◽  
High Surface ◽  
Stellar Disk ◽  
Disk Galaxies ◽  
Late Type ◽  
Vertical Scale ◽  
Low Surface Brightness ◽  
Multi Wavelength ◽  
Low Mass ◽  
Dust Distribution

AbstractLate-type low surface brightness (LSB) disk galaxies are common in the local universe and appear dynamically and chemically under evolved compared to their high surface brightness (HSB) counterparts. We have utilized multi-wavelength imaging and photometry of three edge-on, low-mass LSB disk galaxies to investigate the dust distribution in such systems. Through the use of Monte Carlo radiation transfer models to interpret the data, we find that the dust disk appears to have a vertical scale height similar to the stellar disk. This is in contrast to previous findings from HSB galaxies, where the dust is believed to be more concentrated in the galactic mid-plane. We believe the change in the relative scale heights of the dust and stellar disks is likely associated with the increased stability of the ISM against vertical collapse and the thin nature of the stellar disks.

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