I Zw 18 Revisited with<i>HST</i>ACS and Cepheids: New Distance and Age

Aloisi, Alessandra; Clementini, G.; Tosi, M.; Annibali, F.; Contreras, Rodrigo A.; Fiorentino, G.; Mack, J.; Marconi, M.; Musella, I.; Saha, Abhijit; Sirianni, M.; Marel, Roeland P. van der

doi:10.1086/522368

Cited by 142 publications

(173 citation statements)

References 24 publications

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“…At velocities from ∼750 to ∼720 km s −1 , extended emission also appears to the south. Figure 2 (top-left) shows the integrated H i map, superimposed on a V-band HST image (from Aloisi et al 2007). I Zw 18 A is associated with a strong concentration of gas, while diffuse emission extends beyond the optical galaxy, covering an angular size of ∼3.…”

Section: The Low-resolution Viewmentioning

confidence: 99%

“…Optical luminosities were calculated using the apparent magnitudes from Papaderos et al (2002), the distance from Aloisi et al (2007) and the solar absolute magnitudes from Binney & Merrifield (1998). The H i mass of I Zw 18 C refers to the extended emission described in Sect.…”

Section: Figmentioning

confidence: 99%

“…Papaderos et al 2002;Izotov & Thuan 2004). However, Aloisi et al (2007), using HST observations, detected stars older than 1-2 Gyr and ruled out the possibility that I Zw 18 is a truly primordial galaxy (as suggested by e.g. Aloisi et al 1999, Östlin & Mouhcine 2005.…”

Section: Introductionmentioning

confidence: 96%

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Dynamics of starbursting dwarf galaxies: I Zw 18

Lelli

Verheijen

Fraternali

et al. 2012

A&A

124

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I Zw 18 is a prototype blue compact dwarf (BCD) galaxy, characterized by a strong starburst and extremely low metallicity (Z ∼ 0.02 Z ). It has long been considered a candidate young galaxy in the Local Universe, but recent studies have found that it contains old stars. We analysed archival VLA observations of the 21 cm line and found that the H i associated to the starburst region forms a compact rapidly rotating disk. The H i column densities are very high, up to ∼50-100 M pc −2 (∼0.6−1.2 × 10 22 atoms cm −2 ). The rotation curve is flat with a steep rise in the inner parts, indicating that there is a strong central concentration of mass. Mass models with a dark matter halo show that baryons may dominate the gravitational potential in the inner regions. A radial inflow/outflow motion of ∼15 km s −1 is also present. I Zw 18 appears to be structurally different from typical dwarf irregulars in terms of its gas distribution, stellar distribution, and dynamics. It may be considered as a "miniature" high-surface-brightness disk galaxy. These dynamical properties must be tightly related to the starburst. They also shed new light on the question of the descendants of BCDs. There is also extended H i emission towards the outlying stellar complex I Zw 18 C and a ∼13.5 kpc H i tail. An interaction/merger between gas-rich dwarfs is the most likely explanation of the starburst.

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Section: The Low-resolution Viewmentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

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Dynamics of starbursting dwarf galaxies: I Zw 18

Lelli

Verheijen

Fraternali

et al. 2012

A&A

124

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“…The observations were obtained in 12 different epochs in F606W and F814W to: (1) build a deeper CMD to search for RGB stars; (2) detect and characterize Cepheids at the lowest metallicity available in the local universe; and (3) use both the Cepheids and a possible TRGB detection to determine an accurate distance to I Zw 18 (see Aloisi et al 2007).…”

Section: New Hst/acs Observationsmentioning

confidence: 99%

A New Age and Distance for I Zw 18, the Most Metal-Poor Galaxy in the Nearby Universe

et al. 2008

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Abstract. The blue compact dwarf galaxy I Zw 18 holds the record of the lowest metallicity ever observed in the local universe. As such, it represents the closest analog to primordial galaxies in the early universe. More interestingly, it has recurrently been regarded as a genuinely young galaxy caught in the process of forming in the nearby universe. However, stars of increasingly older ages are found within I Zw 18 every time deeper high-resolution photometric observations are performed with the Hubble Space Telescope (HST): from the original few tens of Myrs to, possibly, several Gyrs. Here we summarize the history of I Zw 18 age and present an ongoing HST/ACS project which allowed us to precisely derive the galaxy distance by studying its Cepheid variables, and to firmly establish the age of its faintest resolved populations.

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“…Tosi 2009, and references therein). For instance, NGC 6822 is close enough to allow detection of RR Lyrae variables (Clementini et al 2003); i.e., stars 10 Gyr old, IC 10, NGC 4449, and IZw18 are too far away to let their horizontal branch stars be visible with current instruments, but HST has shown that they contain red giants (Holtzman et al 2006;Aloisi et al 2007;Annibali et al 2008), i.e. stars at least 2 Gyr old.…”

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confidence: 99%

Chemical composition and evolution of irregular and blue compact galaxies. The dawn of a thirty year journey

Tosi

2009

A&A

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Vigroux et al. 1976, online), but none of them dealt explicitly with late-type dwarf galaxies. Lequeux et al. (1979) set the stage for all subsequent studies of the evolution of irregular and blue compact dwarfs (BCDs). The term pioneer is often used (and sometimes misused) in the astronomical literature. In their case, pioneers is really what they were.The aims of their study were manifold and quite challenging for the time: a) derive the primeval abundance of helium by extrapolating the (He/H) vs (O/H) relation to zero oxygen abundance; b) estimate the primary fraction of 14 N by studying the (N/O) vs (O/H) relation; c) derive the heavy element content vs the total galactic mass relation; d) derive the heavy element yield p(Z) by means of the (O/H) vs. M gas /M tot relation; e) put limits on the evolutionary properties of irregulars and BCDs by comparing the results of the previous items with the predictions of chemical evolution models. Quite an ambitious plan, considering the number of papers devoted to each of these topics in the last decades. "Everything you always wanted to know about dwarf galaxies, but were afraid to ask", Woody Allen would have said...It is impressive to see how valid the results they achieved were, in spite of the poor tools available at the time, but isn't this exactly what pioneers do?! Consider, for instance, their analysis of the nitrogen evolution, aimed at checking the revolutionary suggestion of a partial primary origin of nitrogen done by Edmunds & Pagel (1978) and Alloin et al. (1979) on the basis of observations of Galactic and extragalactic HII regions. To this aim, LPRST observed the HII regions in six late-type dwarfs and computed chemical evolution models to compare the resulting abundances. Their chemical evolution models were run assuming the instantaneous recycling approximation, an oversimplifying assumption (as they were aware of), especially for an element mostly produced by intermediate-mass, relatively longlived stars. No appropriate tables with nucleosynthesis yields

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I Zw 18 Revisited withHSTACS and Cepheids: New Distance and Age

Cited by 142 publications

References 24 publications

Dynamics of starbursting dwarf galaxies: I Zw 18

Dynamics of starbursting dwarf galaxies: I Zw 18

A New Age and Distance for I Zw 18, the Most Metal-Poor Galaxy in the Nearby Universe

Chemical composition and evolution of irregular and blue compact galaxies. The dawn of a thirty year journey

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