Extended star formation in 
dwarf spheroidal galaxies: The cases of Draco, Sextans, 
and Ursa Minor

Ikuta, Chisato; Arimoto, N.

doi:10.1051/0004-6361:20020609

Cited by 74 publications

(110 citation statements)

References 59 publications

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“…In an old stellar population the mass-loss rate from stars is _ M M % 10 À2 ð5 GyrÞ=t ½ (e.g., Schulz, Fritze-von Alvensleben, & Fricke 2002). Over an e8 Gyr span appropriate to the time since star formation stopped in these two dwarfs (Carrera et al 2002;Ikuta & Arimoto 2002), we expect about 5% of the stellar mass to return to the interstellar medium. A significant fraction of the gas returned by stars therefore cannot be in the form of H i, but even with our new limits, this material could remain hidden in a diffuse ionized interstellar medium.…”

Section: Discussionmentioning

confidence: 99%

A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies

Gallagher

Madsen

Reynolds

et al. 2003

ApJ

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The Wisconsin H Mapper has been used to set the first deep upper limits on the intensity of diffuse H emission from warm ionized gas in the Draco and Ursa Minor dwarf spheroidal galaxies (dSphs). Assuming a velocity dispersion of 15 km s À1 for the ionized gas, we set limits of I H 0:024 R and I H 0:021 R for the Draco and Ursa Minor dSphs, respectively, averaged over our 1 circular beam. Adopting a simple model for the ionized interstellar medium, these limits translate to upper bounds on the mass of ionized gas of d10% of the stellar mass, or $10 times the upper limits for the mass of neutral hydrogen. Note that the Draco and Ursa Minor dSphs could contain substantial amounts of interstellar gas, equivalent to all of the gas injected by dying stars since the end of their main star-forming episodes e8 Gyr in the past, without violating these limits on the mass of ionized gas.

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Section: Discussionmentioning

confidence: 99%

A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies

Gallagher

Madsen

Reynolds

et al. 2003

ApJ

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“…Although there are examples of Local Group dwarf spheroidals with predominantly old and metal-poor populations (e.g., Ursa Minor, Draco), the case of a single, ancient starburst is quite unlikely for most of them; on the contrary, large metallicity spreads have been detected, and the early star formation appears to have been low and continuous (e.g., Ikuta & Arimoto 2002;Grebel et al 2003;Koch et al 2006;Coleman & de Jong 2008;Koleva et al 2009). Different models arrive at different durations to explain the observed metallicity spread (e.g., Ikuta & Arimoto 2002;Lanfranchi & Matteucci 2004;Marcolini et al 2008). Assuming that the spread in metallicity is predominantly due to a spread in age, we repeated the metallicity interpolation process by choosing the three most metal-poor isochrones to have an age of 12 Gyr, and the most metal-rich ones an age of 8 Gyr.…”

Section: Age Assumptionmentioning

confidence: 99%

A close look at the Centaurus A group of galaxies

Crnojević¹,

Grebel²,

Koch³

2010

A&A

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Aims. We study dwarf galaxies in the Centaurus A group to investigate their metallicity and possible environmental effects. The Centaurus A group (at ∼4 Mpc from the Milky Way) contains about 50 known dwarf companions of different morphologies and stellar contents, thus making it a very interesting target to study how these galaxies evolve. Methods. Here we present results for the early-type dwarf galaxy population in this group. We used archival HST/ACS data to study the resolved stellar content of 6 galaxies, together with isochrones from the Dartmouth stellar evolutionary models. Results. We derive photometric metallicity distribution functions of stars on the upper red giant branch via isochrone interpolation. The 6 galaxies are moderately metal-poor ( [Fe/H] = −1.56 to −1.08), and metallicity spreads are observed (internal dispersions of σ[Fe/H] = 0.10−0.41 dex). We also investigate whether intermediate-age stars are present, and discuss how these affect our results. The dwarfs exhibit flat to weak radial metallicity gradients. For the two most luminous, most metal-rich galaxies, we find statistically significant evidence of at least two stellar subpopulations: the more metal-rich stars are found in the center of the galaxies, while the metal-poor ones are more broadly distributed within the galaxies. Conclusions. We find no clear trend in the derived physical properties as a function of (present-day) galaxy position in the group, which may come from the small sample we investigate. We compare our results to the early-type dwarf population of the Local Group, and find no outstanding differences, even though the Centaurus A group is a denser environment that is possibly in a more advanced dynamical stage.

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“…At a first glance, knowledge derived for the solar neighborhood provides a reasonable explanation for the origin of the observed low-α signature as being due to the additional supply of Fe from type Ia Supernovae (SNe Ia). Based on this supposition, theoretical models of evolutionary change in [α/Fe] against [Fe/H] in dSph galaxies have been proposed (Ikuta & Arimoto 2002;Lanfranchi & Matteucci 2004;Robertson et al 2005). However, there is no compelling evidence for the contribution of SNe Ia to other elemental ratios such as [Mn/Fe] or [n-capture/Fe] (see Tsujimoto & Shigeyama 2002).…”

Section: Introductionmentioning

confidence: 99%

Implications of elemental abundances in dwarf spheroidal galaxies

Tsujimoto¹

2006

A&A

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Unusual elemental abundance patterns observed for stars belonging to nearby dwarf spheroidal (dSph) galaxies are discussed. Analysis of the [α/H] vs. [Fe/H] diagrams where α represents Mg or an average of α-elements reveals that Fe from type Ia supernovae (SNe Ia) does not contribute to the stellar abundances in the dSph galaxies where the member stars exhibit low α/Fe ratios except for the most massive dSph galaxy, Sagitarrius. The more massive dwarf (irregular) galaxy, the Large Magellanic Cloud, also has an SNe Ia signature in the stellar abundances. These findings suggest that whether SNe Ia contribute to chemical evolution in dwarf galaxies is likely to depend on the mass scale of galaxies. Unusual Mg abundances in some dSph stars are also found to be the origin of the large scatter in the [Mg/Fe] ratios and are responsible for a seemingly decreasing [Mg/Fe] feature with increasing [Fe/H]. In addition, the lack of massive stars in the dSph galaxies does not satisfactorily account for the low-α signature. Considering the assembly of deficient elements (O, Mg, Si, Ca, Ti and Zn), all of which are synthesized in pre-SN massive stars and in SN explosions, the low-α signature appears to reflect the heavy-element yields of massive stars with less rotation compared to solar neighborhood stars.

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Extended star formation in dwarf spheroidal galaxies: The cases of Draco, Sextans, and Ursa Minor

Cited by 74 publications

References 59 publications

A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies

A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies

A close look at the Centaurus A group of galaxies

Implications of elemental abundances in dwarf spheroidal galaxies

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