scholarly journals TheSpitzerView of Low‐Metallicity Star Formation. II. Mrk 996, a Blue Compact Dwarf Galaxy with an Extremely Dense Nucleus

2008 ◽  
Vol 689 (2) ◽  
pp. 897-912 ◽  
Author(s):  
Trinh X. Thuan ◽  
Leslie K. Hunt ◽  
Yuri I. Izotov
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Low Metallicity ◽  
Dense Nucleus ◽  
Blue Compact Dwarf Galaxy

scholarly journals The Herschel Dwarf Galaxy Survey

2019 ◽  
Vol 626 ◽  
pp. A23 ◽  
Author(s):  
D. Cormier ◽  
N. P. Abel ◽  
S. Hony ◽  
V. Lebouteiller ◽  
S. C. Madden ◽  
...  
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Spectral Synthesis ◽  
Line Emission ◽  
Ionized Gas ◽  
Star Forming ◽  
Gas Phases ◽  
Physical Conditions ◽  
Radiation Fields ◽  
Low Metallicity

The sensitive infrared telescopes, Spitzer and Herschel, have been used to target low-metallicity star-forming galaxies, allowing us to investigate the properties of their interstellar medium (ISM) in unprecedented detail. Interpretation of the observations in physical terms relies on careful modeling of those properties. We have employed a multiphase approach to model the ISM phases (H II region and photodissociation region) with the spectral synthesis code Cloudy. Our goal is to characterize the physical conditions (gas densities, radiation fields, etc.) in the ISM of the galaxies from the Herschel Dwarf Galaxy Survey. We are particularly interested in correlations between those physical conditions and metallicity or star-formation activity. Other key issues we have addressed are the contribution of different ISM phases to the total line emission, especially of the [C II]157 μm line, and the characterization of the porosity of the ISM. We find that the lower-metallicity galaxies of our sample tend to have higher ionization parameters and galaxies with higher specific star-formation rates have higher gas densities. The [C II] emission arises mainly from PDRs and the contribution from the ionized gas phases is small, typically less than 30% of the observed emission. We also find a correlation – though with scatter – between metallicity and both the PDR covering factor and the fraction of [C II] from the ionized gas. Overall, the low metal abundances appear to be driving most of the changes in the ISM structure and conditions of these galaxies, and not the high specific star-formation rates. These results demonstrate in a quantitative way the increase of ISM porosity at low metallicity. Such porosity may be typical of galaxies in the young Universe.

scholarly journals Environmental Mechanisms Shaping the Nature of Dwarf Spheroidal Galaxies: The View of Computer Simulations

2010 ◽  
Vol 2010 ◽  
pp. 1-21 ◽  
Author(s):  
Lucio Mayer
Keyword(s):  
Star Formation ◽  
Galaxy Formation ◽  
Dwarf Galaxy ◽  
Feedback Mechanism ◽  
Gas Stripping ◽  
Morphological Transformation ◽  
Dwarf Spheroidal Galaxies ◽  
Tidal Forces ◽  
Ram Pressure ◽  
Low Metallicity

We review numerical works carried out over the last decade on the role of environmental mechanisms in shaping nature of the faintest galaxies known, dwarf spheroidals (dSphs). The combination of tidally induced morphological transformation, termed tidal stirring, with mass loss due to tidal and ram-pressure stripping aided by heating due to the cosmic ionizing background can turn late-type dwarfs resembling present-day dIrrs into classic dSphs. The time of infall into the primary halo is shown to be a key parameter. Dwarfs accreting at when the cosmic ultraviolet ionizing flux was much higher than today, and was thus able to keep the gas in the dwarfs warm and diffuse, were rapidly stripped of their baryons via ram pressure and tidal forces, producing very dark-matter-dominated objects with truncated star-formation histories, such as the Draco dSph. The low star-formation efficiency expected in such low-metallicity objects prior to their infall was crucial for keeping their disks gas dominated until stripping took over.Therefore gas stripping along with inefficient star-formation provides a new feedback mechanism, alternative to photoevaporation or supernovae feedback, playing a crucial role in dwarf galaxy formation and evolution. We also discuss how the ultra-faint dSphs belong to a different population of lower-mass dwarf satellites that were mostly shaped by reionization rather than by environmental mechanisms (“reionization fossils”). Finally, we scrutinize the various caveats in the current understanding of environmental effects as well as other recent ideas on the origin of Local Group dSphs.

scholarly journals New ALMA constraints on the star-forming interstellar medium at low metallicity: a 50 pc view of the blue compact dwarf galaxy SBS 0335−052

2017 ◽  
Vol 468 (1) ◽  
pp. L87-L91 ◽  
Author(s):  
D. Cormier ◽  
G. J. Bendo ◽  
S. Hony ◽  
V. Lebouteiller ◽  
S. C. Madden ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Dwarf Galaxy ◽  
Star Forming ◽  
Low Metallicity ◽  
Blue Compact Dwarf Galaxy

scholarly journals Haro15: Is it actually a low metallicity galaxy?

2009 ◽  
Vol 5 (S265) ◽  
pp. 243-244
Author(s):  
Verónica Firpo ◽  
Guillermo Bosch ◽  
Guillermo Hägele ◽  
Ángeles I. Díaz ◽  
Nidia Morrell
Keyword(s):  
Dwarf Galaxy ◽  
Empirical Methods ◽  
Chemical Abundances ◽  
Physical Conditions ◽  
Ionization Structure ◽  
The Galaxy ◽  
Low Metallicity ◽  
Echelle Spectroscopy ◽  
Abundance Determination ◽  
Blue Compact Dwarf Galaxy

AbstractWe present a detailed study of the physical properties of the nebular material in multiple knots of the blue compact dwarf galaxy Haro 15. Using long slit and echelle spectroscopy, obtained at Las Campanas Observatory, we study the physical conditions (electron density and temperature), ionic and total chemical abundances of several atoms, reddening and ionization structure. The latter was derived by comparing the oxygen and sulphur ionic ratios to their corresponding observed emission line ratios (the η and η' plots) in different regions of the galaxy. Applying direct and empirical methods for abundance determination, we perform a comparative analysis between these regions.

scholarly journals Multiwavelength Observations of the Low-Metallicity Blue Compact Dwarf Galaxy SBS 0335−052

2001 ◽  
Vol 122 (4) ◽  
pp. 1736-1746 ◽  
Author(s):  
Daniel A. Dale ◽  
George Helou ◽  
Gerry Neugebauer ◽  
B. T. Soifer ◽  
David T. Frayer ◽  
...  
Keyword(s):  
Dwarf Galaxy ◽  
Low Metallicity ◽  
Blue Compact Dwarf Galaxy ◽  
Multiwavelength Observations

scholarly journals Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas

2020 ◽  
Vol 643 ◽  
pp. A141 ◽  
Author(s):  
S. C. Madden ◽  
D. Cormier ◽  
S. Hony ◽  
V. Lebouteiller ◽  
N. Abel ◽  
...  
Keyword(s):  
Star Formation ◽  
Mass Fraction ◽  
Conversion Factor ◽  
Dwarf Galaxies ◽  
Dwarf Galaxy ◽  
Molecular Gas ◽  
Star Forming ◽  
Forming Efficiency ◽  
Low Metallicity ◽  
Co Observations

Context. Molecular gas is a necessary fuel for star formation. The CO (1−0) transition is often used to deduce the total molecular hydrogen but is challenging to detect in low-metallicity galaxies in spite of the star formation taking place. In contrast, the [C II]λ158 μm is relatively bright, highlighting a potentially important reservoir of H2 that is not traced by CO (1−0) but is residing in the C+-emitting regions. Aims. Here we aim to explore a method to quantify the total H2 mass (MH2) in galaxies and to decipher what parameters control the CO-dark reservoir. Methods. We present Cloudy grids of density, radiation field, and metallicity in terms of observed quantities, such as [O I], [C I], CO (1−0), [C II], LTIR, and the total MH2. We provide recipes based on these models to derive total MH2 mass estimates from observations. We apply the models to the Herschel Dwarf Galaxy Survey, extracting the total MH2 for each galaxy, and compare this to the H2 determined from the observed CO (1−0) line. This allows us to quantify the reservoir of H2 that is CO-dark and traced by the [C II]λ158 μm. Results. We demonstrate that while the H2 traced by CO (1−0) can be negligible, the [C II]λ158 μm can trace the total H2. We find 70 to 100% of the total H2 mass is not traced by CO (1−0) in the dwarf galaxies, but is well-traced by [C II]λ158 μm. The CO-dark gas mass fraction correlates with the observed L[C II]/LCO(1−0) ratio. A conversion factor for [C II]λ158 μm to total H2 and a new CO-to-total-MH2 conversion factor as a function of metallicity are presented. Conclusions. While low-metallicity galaxies may have a feeble molecular reservoir as surmised from CO observations, the presence of an important reservoir of molecular gas that is not detected by CO can exist. We suggest a general recipe to quantify the total mass of H2 in galaxies, taking into account the CO and [C II] observations. Accounting for this CO-dark H2 gas, we find that the star-forming dwarf galaxies now fall on the Schmidt–Kennicutt relation. Their star-forming efficiency is rather normal because the reservoir from which they form stars is now more massive when introducing the [C II] measures of the total H2 compared to the small amount of H2 in the CO-emitting region.

scholarly journals VLT/X-shooter observations of the low-metallicity blue compact dwarf galaxy PHL 293B including a luminous blue variable star

2011 ◽  
Vol 533 ◽  
pp. A25 ◽  
Author(s):  
Y. I. Izotov ◽  
N. G. Guseva ◽  
K. J. Fricke ◽  
C. Henkel
Keyword(s):  
Variable Star ◽  
Dwarf Galaxy ◽  
Low Metallicity ◽  
Luminous Blue Variable ◽  
Blue Compact Dwarf Galaxy

scholarly journals Weak CS emission in an extremely metal-poor galaxy DDO 70

2020 ◽  
Vol 496 (1) ◽  
pp. L38-L42
Author(s):  
Kaiyi Du ◽  
Yong Shi ◽  
Zhi-Yu Zhang ◽  
Junzhi Wang ◽  
Yu Gao
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Dwarf Galaxy ◽  
Signal To Noise Ratio ◽  
Formation Rate ◽  
Far Infrared ◽  
Molecular Gas ◽  
Solar Metallicity ◽  
Low Metallicity ◽  
Co Emission

ABSTRACT In most galaxies like the Milky Way, stars form in clouds of molecular gas. Unlike the CO emission that traces the bulk of molecular gas, the rotational transitions of HCN and CS molecules mainly probe the dense phase of molecular gas, which has a tight and almost linear relation with the far-infrared luminosity and star formation rate (SFR). However, it is unclear whether dense molecular gas exists at very low metallicity, and if exists, how it is related to star formation. In this work, we report ALMA observations of the CS J = 5 → 4 emission line of DDO 70, a nearby gas-rich dwarf galaxy with $\sim \!7{{\ \rm per\ cent}}$ solar metallicity. We did not detect CS emission from all regions with strong CO emission. After stacking all CS spectra from CO-bright clumps, we find no more than a marginal detection of CS J = 5 → 4 transition, at a signal-to-noise ratio of ∼3.3. This 3σ upper limit deviates from the $L^\prime _{\rm CS}$–LIR and $L^\prime _{\rm CS}$–SFR relationships found in local star-forming galaxies and dense clumps in the Milky Way, implying weaker CS emission at given infrared luminosity and SFR. We discuss the possible mechanisms that suppress CS emission at low metallicity.

A multifrequency study of star formation in the blue compact dwarf galaxy IZw 36

1983 ◽  
Vol 269 ◽  
pp. 444 ◽  
Author(s):  
F. Viallefond ◽  
T. X. Thuan
Keyword(s):  
Star Formation ◽  
Dwarf Galaxy ◽  
Blue Compact Dwarf Galaxy

scholarly journals Comparative Morphology of the HST Color-Magnitude Diagram of the Nearby Blue Compact Dwarf Galaxy VII Zw 403 with that of Local Group Dwarfs

1999 ◽  
Vol 192 ◽  
pp. 464-468
Author(s):  
R.E. Schulte-Ladbeck ◽  
U. Hopp ◽  
M. M. Crone
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Dwarf Galaxy ◽  
Comparative Morphology ◽  
Star Formation History ◽  
Stellar Content ◽  
Halo Structure ◽  
Formation History ◽  
Magnitude Diagram ◽  
Blue Compact Dwarf Galaxy

There are no examples of Blue Compact Dwarf (BCD) galaxies known within the Local Group (LG). Multicolor HST/WFPC2 observations of the nearby BCD VII Zw 403 (= UGC 6456) now resolve single stars with the quality (in terms of limiting magnitude and completeness) previously achieved for LG dwarfs from the ground. We use the MI, V - I color-magnitude diagrams (CMDs) of several LG dwarfs as templates to assess the stellar content and star-formation history (SFH) of the BCD VII Zw 403. This is the first BCD for which a clear spatial segregation of the resolved stellar content into a “core-halo” structure is detected: active star formation is observed in the central region of VII Zw 403, while in “Baade's red sheet”, this young population is strikingly absent. If BCD halos are home to dominant ancient stellar populations, then the fossil record conflicts with delayed-format ion scenarios for dwarfs. We present a sketch of the SFH in the core and halo of VII Zw 403.

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