scholarly journals Abundance patterns and the chemical enrichment of nearby dwarf galaxies

2009 ◽  
Vol 5 (S265) ◽  
pp. 219-226 ◽  
Author(s):  
Vanessa Hill
Keyword(s):  
Star Formation ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
First Stars ◽  
Potential Wells ◽  
Dwarf Spheroidal Galaxies ◽  
Massive Galaxies ◽  
Chemical Enrichment ◽  
Abundance Patterns ◽  
Spheroidal Galaxies

AbstractAs the least massive galaxies we know, dwarf spheroidal galaxies (dSph) allow to probe chemical enrichement on the smallest scales, and perhaps in its simplest expression. Particularly interesting are the issues concerning the efficency with which metals are retained or lost in these shallow potential wells (supernovae feedback), and the effect of this on star formation itself. Another fundamental issue concerns the earliest epochs of star formation: are first stars formed in similar ways and proportions in all halos ? Finally, as the smallest galaxies know, dSph have been suggested to be the surviving cousins of galaxy building blocs that (in λ-CDM) assemble to make larger galaxies. This parenthood would not necessarily hold at all late times, when survivors have lived their own differentiated life, but is expected at least at the earliest epochs.I review here the chemical abundances of individual stars in the nearest dwarf spheroidal galaxies, that have become available in increasing numbers (sample size and galaxies probed) in the last decade. Special emphasis is given to: a) recent results obtain with FLAMES on VLT, highlighting the power of detailed chemical abundance patterns of large samples of stars to unravel the various evolutionnary paths followed by dSph; b) the oldest and most metal-poor populations in dSph.

scholarly journals Complexity in small-scale dwarf spheroidal galaxies

2009 ◽  
Vol 5 (S265) ◽  
pp. 227-232
Author(s):  
Andreas Koch ◽  
Daniel Adén ◽  
Eva K. Grebel ◽  
Sofia Feltzing
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Galactic Halo ◽  
Photometric Data ◽  
Small Scale ◽  
Chemical Abundance ◽  
First Stars ◽  
Dwarf Spheroidal Galaxies ◽  
Chemical Enrichment ◽  
Large Numbers

AbstractOur knowledge about the chemical evolution of the more luminous dwarf spheroidal (dSph) galaxies is constantly growing. However, little is known about the enrichment of the ultrafaint systems recently discovered in large numbers in large Sky Surveys. Low-resolution spectroscopy and photometric data indicate that these galaxies are predominantly metal-poor. On the other hand, the most recent high-resolution abundance analyses indicate that some of these galaxies experienced highly inhomogenous chemical enrichment, where star formation proceeds locally on the smallest scales. Furthermore, these galaxy-contenders appear to contain very metal-poor stars with [Fe/H]< −3 dex and could be the sites of the first stars. Here, we consider the presently available chemical abundance information of the (ultra-) faint Milky Way satellite dSphs. In this context, some of the most peculiar element and inhomogeneous enrichment patterns will be discussed and related to the question of to what extent the faintest dSph candidates and outer halo globular clusters could have contributed to the metal-poor Galactic halo.

scholarly journals Stellar population astrophysics (SPA) with the TNG

2019 ◽  
Vol 629 ◽  
pp. A117 ◽  
Author(s):  
L. Origlia ◽  
E. Dalessandro ◽  
N. Sanna ◽  
A. Mucciarelli ◽  
E. Oliva ◽  
...  
Keyword(s):  
Spectral Synthesis ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Dust Extinction ◽  
Chemical Enrichment ◽  
Abundance Patterns ◽  
The Galaxy ◽  
Red Supergiants ◽  
Molecular Lines ◽  
Width Measurements

Aims. The Scutum complex in the inner disk of the Galaxy hosts a number of young clusters and associations of red supergiant stars that are heavily obscured by dust extinction. These stars are important tracers of the recent star formation and chemical enrichment history in the inner Galaxy. Methods. Within the SPA Large Programme at the TNG, we secured GIANO-B high-resolution (R ≃ 50 000) YJHK spectra of 11 red supergiants toward the Alicante 7 and Alicante 10 associations near the RSGC3 cluster. Taking advantage of the full YJHK spectral coverage of GIANO in a single exposure, we were able to measure several hundreds of atomic and molecular lines that are suitable for chemical abundance determinations. We also measured a prominent diffuse interstellar band at λ1317.8 nm (vacuum). This provides an independent reddening estimate. Results. The radial velocities, Gaia proper motions, and extinction of seven red supergiants in Alicante 7 and three in Alicante 10 are consistent with them being members of the associations. One star toward Alicante 10 has kinematics and low extinction that are inconsistent with a membership. By means of spectral synthesis and line equivalent width measurements, we obtained chemical abundances for iron-peak, CNO, alpha, other light, and a few neutron-capture elements. We found average slightly subsolar iron abundances and solar-scaled [X/Fe] abundance patterns for most of the elements, consistent with a thin-disk chemistry. We found depletion of [C/Fe], enhancement of [N/Fe], and relatively low 12C/13C <  15, which is consistent with CN cycled material and possibly some additional mixing in their atmospheres.

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.

scholarly journals THE SPLASH SURVEY: INTERNAL KINEMATICS, CHEMICAL ABUNDANCES, AND MASSES OF THE ANDROMEDA I, II, III, VII, X, AND XIV DWARF SPHEROIDAL GALAXIES,

2010 ◽  
Vol 711 (2) ◽  
pp. 671-692 ◽  
Author(s):  
Jason S. Kalirai ◽  
Rachael L. Beaton ◽  
Marla C. Geha ◽  
Karoline M. Gilbert ◽  
Puragra Guhathakurta ◽  
...  
Keyword(s):  
Chemical Abundances ◽  
Dwarf Spheroidal Galaxies ◽  
Spheroidal Galaxies

scholarly journals Impact of NLTE on research of early chemical enrichment of the dwarf galaxies

2015 ◽  
Vol 11 (S317) ◽  
pp. 334-335
Author(s):  
Lyudmila Mashonkina ◽  
Pascale Jablonka ◽  
Pierre North ◽  
Tatyana Sitnova
Keyword(s):  
Dwarf Galaxies ◽  
Local Thermodynamic Equilibrium ◽  
Stellar Atmosphere ◽  
Complete Sample ◽  
Major Step ◽  
Chemical Abundances ◽  
Elemental Ratios ◽  
Dwarf Spheroidal Galaxies ◽  
Chemical Enrichment ◽  
Non Local

AbstractBased on high-resolution observed spectra, the non-local thermodynamic equilibrium (NLTE) line formation, and precise stellar atmosphere parameters, we present the first complete sample of dwarf spheroidal galaxies (dSphs) with accurate chemical abundances in the very metal-poor (VMP) regime. The obtained stellar elemental ratios are compared with chemical enrichment models, and we show that NLTE is a major step forward for studies of the dSph and the Milky Way (MW) chemical evolution.

scholarly journals Star-Formation and Nuclear Activity in Three Galaxies with Nuclear Rings

1994 ◽  
Vol 159 ◽  
pp. 460-460
Author(s):  
Thaisa Storchi–Bergmann ◽  
Andrew S. Wilson ◽  
Jack A. Baldwin
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Galactic Nuclei ◽  
High Spectral Resolution ◽  
Nuclear Region ◽  
Chemical Abundance ◽  
Chemical Abundances ◽  
Nuclear Activity ◽  
Line Region ◽  
Low Dispersion

We investigate two current problems in active galactic nuclei – the mode of fueling the putative black hole, and the question whether the circumnuclear regions have experienced unusual chemical processing – by studying the kinematics and chemical abundance of the gas in the nuclear region of galaxies with sites of ongoing star formation near the active nucleus. We discuss the results for three galaxies with nuclear rings: NGC1097 – for which we recently discovered broad double peaked Hα and Hβ emission from its LINER nucleus (Storchi-Bergmann, Baldwin & Wilson 1993, ApJ 410, L11); NGC1672, which also presents a LINER nucleus; and NGC5248, a galaxy with a ring but no nuclear activity, used as a comparison. Narrow–band images obtained with the CTIO 1.5m telescope were used to map the emitting gas. Longslit spectroscopy obtained with the 4m telescope at high spectral resolution (at several positions over the nuclear region) was used to obtain the gas velocity field. In the two galaxies with LINER nucleus, the starforming rings are located in the turnover of the rotation curves, which show that the gas is rotating faster at the rings than farther out. We conclude that the rings are associated with inner Lindblad ressonances, which may be particularly effective in forcing gas inwards and fuelling the black hole (Wilson et al. 1986, ApJ 310, 121). From the emission line ratios the gas excitation is maped, and it is found that even in NGC5248, the nucleus presents a different excitation, suggesting a very mild LINER activity. Low-dispersion spectroscopy was also obtained in order to calculate the chemical abundances and compare the values obtained for the nuclear gas with those obtained for the HII regions in the ring and beyond the ring (when present). The goal is to check the results of recent studies (Storchi-Bergmann & Pastoriza 1989, ApJ 347, 195; 1990, PASP 102, 1359), based on spectroscopy of the nucleus, which indicate an enhanced abundance of nitrogen, up to 5 times solar for the gas of the narrow line region of LINER and Seyfert 2 nuclei.

The Local Group Dwarf Spheroidal Galaxies: A Key to Building Blocks in the Universe

2005 ◽  
Vol 201 ◽  
pp. 469-470
Author(s):  
Hiroyuki. Hirashita ◽  
Naoyuki. Tamura ◽  
Tsutomu T. Takeuchi
Keyword(s):  
Star Formation ◽  
Local Group ◽  
Building Blocks ◽  
Star Formation History ◽  
High Mass ◽  
Dwarf Spheroidal Galaxies ◽  
The Hierarchical Structure ◽  
History Of ◽  
Low Mass ◽  
Spheroidal Galaxies

Recent studies have been revealing the properties of dwarf spheroidal galaxies (dSphs). Their low mass indicates that the dSphs may provide a clue to physical properties of the building blocks in the hierarchical structure formation. We select the Local Group dSphs as a sample. To obtain the information on the star formation history of dSphs, we investigate the relation between their metallicity and virial mass. According to our scenario, the star formation efficiency of the dSphs is low because of strong regulation. This is consistent with their high mass-to-light ratios. We also comment on the environmental effects on the dSphs.

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