Holmberg IX: The Nearest Young Galaxy

Sabbi, E.; Gallagher, John S.; Smith, L. J.; Mello, D. F. de; Mountain, Matt

doi:10.1086/587548

Cited by 40 publications

(61 citation statements)

References 26 publications

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“…Recent (∼30-70 Myr) star formation has been found not only in the outskirts of M81 itself (Barker et al 2009) but also in nearby tidal dwarf galaxies such as Holmberg IX (Weisz et al 2008;Sabbi et al 2008), BK3N (Makarova et al 2002), and in other nearby tidal debris DeCesar et al 2004;Davidge 2008;de Mello et al 2008;Chiboucas et al 2009;). However, in all of these cases, the recent star formation has occurred in areas with higher H i column densities (N H i > 4 − 8 × 10 20 cm −2 ) than that observed in our field, and is thus consistent with the lack of recent (i.e., τ 10 8 yr) star formation in our field.…”

Section: Blue Starsmentioning

confidence: 99%

DEEPHST/ACS PHOTOMETRY OF THE M81 HALO

Durrell

Sarajedini

Chandar

2010

ApJ

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We present a deep color-magnitude diagram (CMD) for individual stars in the halo of the nearby spiral galaxy M81, at a projected distance of 19 kpc, based on data taken with the Advanced Camera for Surveys on the Hubble Space Telescope (HST). The CMD reveals a red giant branch (RGB) that is narrow and fairly blue, and a horizontal branch that has stars that lie mostly redward of the RR Lyrae instability strip. We derive a mean metallicity of [M/H] = −1.15 ± 0.11 and age of 9 ± 2 Gyr for the dominant population in our field, from the shape of the RGB, the magnitude of the red clump, and the location of the RGB bump. We compare our metallicity and age results with those found previously for stars in different locations within M81 and in the spheroids of other nearby galaxies.

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Section: Blue Starsmentioning

confidence: 99%

DEEPHST/ACS PHOTOMETRY OF THE M81 HALO

Durrell

Sarajedini

Chandar

2010

ApJ

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“…The ANGST sample includes three putative tidal dwarf galaxies (Holmberg IX, A0952 + 69, and BK3N; Makarova et al 2002;Sabbi et al 2008;Weisz et al 2008), which have no counterparts in the LG. Their status as true galaxies is ambiguous (e.g., Weisz et al 2008), and we thus exclude them from this comparison.…”

Section: The Angst Dwarf Galaxy Samplementioning

confidence: 99%

How Typical Are the Local Group Dwarf Galaxies?

Weisz¹,

Dolphin²,

Dalcanton³

et al. 2011

ApJ

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We compare the cumulative star formation histories (SFHs) of Local Group (LG) dwarf galaxies with those in the volume-limited ACS Nearby Galaxy Survey Treasury (ANGST) sample (D 4 Mpc), in order to understand how typical the LG dwarf galaxies are relative to those in the nearby universe. The SFHs were derived in a uniform manner from high-quality optical color-magnitude diagrams constructed from Hubble Space Telescope imaging. We find that the mean cumulative SFHs of the LG dwarfs are comparable to the mean cumulative SFHs of the ANGST sample for the three different morphological types (dwarf spheroidals/ellipticals: dSph/dE; dwarf irregulars: dI; transition dwarfs: dTrans). We also discuss effects such as population gradients and systematic uncertainties in the stellar models that may influence the derived SFHs. Both the ANGST and LG dwarf galaxies show a consistent and strong morphology-density relationship, emphasizing the importance of environment in the evolution of dwarf galaxies. Specifically, we confirm that dIs are found at lower densities and higher luminosities than dSphs, within this large sample. We also find that dTrans are located in similar environments to those occupied by dwarf irregular galaxies, but have systematically lower luminosities that are more comparable to those of dwarf spheroidals. The similarity of the SFHs and morphology-density relationships of the LG and ANGST dwarf galaxies suggests that the LG dwarfs are a good representation of dwarf galaxies in the local universe.

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“…They are believed to form out of the dark matter free material that was expelled during the tidal interaction of the parent galaxies (Bournaud et al 2007; and references therein). One possible tidal dwarf galaxy candidate has been identified in the M 81 group, namely Holmberg IX (Makarova et al 2002;Sabbi et al 2008) and these are favoured to be detected in such recently interacting groups. These systems contain a young stellar component, while their older stellar populations are believed to consist of stars from their parent galaxies, which is M 81 in the case of Holmberg IX.…”

Section: Photometric Metallicity Distribution Functionsmentioning

confidence: 99%

Dwarf spheroidals in the M 81 group – Metallicity distribution functions and population gradients

Lianou

Grebel

Koch³

2010

A&A

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Aims. We study the dwarf spheroidal galaxies in the nearby M 81 group in order to construct their photometric metallicity distributions and to investigate the potential presence of population gradients. We select all the dwarf spheroidals with available Hubble Space Telescope / Advanced Camera for Surveys archival observations, nine in total. Methods. We interpolate isochrones so as to assign a photometric metallicity to each star within a selection box in the color-magnitude diagram of each dwarf galaxy. We assume that the dwarf spheroidals contain mainly an old stellar population. In order to search for metallicity gradients, we examine the spatial distribution of two stellar populations that we separate according to their metallicities. Results. As a result, we present the photometric metallicity distribution functions, the cumulative histograms and smoothed density maps of the metal-poor and metal-rich stars as well as of the intermediate-age stars. Conclusions. From our photometric data we find that all the dwarf spheroidals show a wide range in metallicities, with mean values that are typical for old and metal-poor systems, with the exception of one dwarf spheroidal, namely IKN. Some of our dwarf spheroidals exhibit characteristics of transition-type dwarfs. Compared to the Local Group transition type dwarfs, the M 81 group ones appear to have mean metallicity values slightly more metal-rich at a given luminosity. All the dwarf spheroidals considered here appear to exhibit either population gradients or spatial variations in the centroids of their metal-poor and metal-rich population. In addition, there are luminous AGB stars detected in all of them with spatial distributions suggesting that they are well mixed with the old stars.

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Holmberg IX: The Nearest Young Galaxy

Cited by 40 publications

References 26 publications

DEEPHST/ACS PHOTOMETRY OF THE M81 HALO

DEEPHST/ACS PHOTOMETRY OF THE M81 HALO

How Typical Are the Local Group Dwarf Galaxies?

Dwarf spheroidals in the M 81 group – Metallicity distribution functions and population gradients

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