Star Formation Triggering Mechanisms in Dwarf Galaxies: The Far‐Ultraviolet, Hα, and H<scp>i</scp>Morphology of Holmberg II

Stewart, S. G.; Fanelli, M. N.; Byrd, G. G.; Hill, J. K.; Westpfahl, David J.; Cheng, K. S.; O’Connell, R. W.; Roberts, M. S.; Neff, Susan G.; Smith, Andrew M.; Stecher, T. P.

doi:10.1086/308241

Cited by 65 publications

(81 citation statements)

References 60 publications

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“…The orientation is the same as in Fig. 1. irregular Holmberg II by Stewart et al (2000), where it is described in full detail. Circular apertures are used to identify areas of associated FUV and Ha Ñux with the aid of a FUV, Ha di †erence image, shown in Figure 3.…”

Section: Fuv Optical and H I Morphologymentioning

confidence: 99%

“…The 12 regions are deÐned by selecting the circular aperture enclosing as much of the FUV and Ha emission from a single region as possible. This rather loose criterion obviously neglects to include all the associated Ñux from a single region and has the potential to mix regions of di †erent populations, but it is sufficient to discern the relative ages of star formation regions (see Stewart et al 2000 and the references therein).…”

Section: Fuv Optical and H I Morphologymentioning

confidence: 99%

“…For example, Rhode et al (1999) could not detect the expected number of remnant A and F stars (as derived from the H I observations) of the clusters that supposedly created the expanding H I holes in Holmberg II. However, Stewart et al (2000) detected OB stellar populations interior to several H I holes in Holmberg II using ultraviolet data, a direct tracer of the massive stellar component.…”

Section: Introductionmentioning

confidence: 99%

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Ultraviolet Observations of the Powering Source of the Supergiant Shell in IC 2574

Stewart

Walter

2000

The Astronomical Journal

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A multiband analysis of the region containing the supergiant H I shell in the nearby dwarf irregular galaxy IC 2574 presents evidence of a causal relationship between a central star cluster, the surrounding expanding H I shell, and secondary star formation sites on the rim of the H I shell. Comparisons of the far-UV (FUV, 1521 optical broad band, Ha, X-ray, and H I morphologies suggest that the region is A ), in an auspicious moment of star formation triggered by the central stellar cluster. The derived properties of the H I shell, the central stellar cluster, and the star-forming regions on the rim support this scenario : The kinematic age of the H I shell is \14 Myr and in agreement with the age of the central stellar cluster derived from the FUV observations (D11 Myr). An estimate for the mechanical energy input from supernovae and stellar winds of the central stellar cluster, made from FUV photometry and the derived cluster age, is 4.1 ] 1052 ergs, roughly a few times higher than the kinetic energy of the H I shell. The requisite energy input needed to create the H I shell, derived in the "" standard ÏÏ fashion from the H I observations (using the numerical models of Chevalier), is 2.6 ] 1053 ergs, which is almost 1 order of magnitude higher than the estimated energy input as derived from the FUV data. Given the overwhelming observational evidence that the central cluster is responsible for the expanding H I shell, this discrepancy suggests that the required energy input is overestimated using the "" standard ÏÏ method. This may explain why some other searches for remnant stellar clusters in giant H I holes have been unsuccessful so far. Our observations also show that stellar clusters are indeed able to create supergiant H I shells, even at large galactocentric radii ; a scenario that has recently been questioned by a number of authors.

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Section: Fuv Optical and H I Morphologymentioning

confidence: 99%

Section: Fuv Optical and H I Morphologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Ultraviolet Observations of the Powering Source of the Supergiant Shell in IC 2574

Stewart

Walter

2000

The Astronomical Journal

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“…For many large shells, the energy needed to create them must have come from the whole cluster of stars, from OB associations. Proving this connection is not completely straightforward since many shells are older than the expected lifetime of massive stars and the results are often confusing (Rhode et al 1999;Stewart et al 2000). However, the statistical correspondence between HI shells and stars (Ehlerová & Palouš 2013;Suad et al 2014) indicates the relation.…”

Section: Introductionmentioning

confidence: 99%

Correlation of HI shells and CO clumps in the outer Milky Way

Ehlerová

Palouš

2016

A&A

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Context. HI shells, which may be formed by the activity of young and massive stars, or connected to energy released by interactions of high-velocity clouds with the galactic disk, may be partly responsible both for the destruction of CO clouds and for the creation of others. It is not known which effect prevails. Aims. We study the relation between HI shells and CO in the outer parts of the Milky Way, using HI and CO surveys and a catalogue of previously identified HI shells. Methods. For each individual location, the distance to the nearest HI shell is calculated and it is specified whether it lies in the interior of an HI shell, in its walls, or outside an HI shell. The method takes into account irregular shapes of HI shells. Results. We find a lack of CO clouds in the interiors of HI shells and their increased occurrence in walls. Properties of clouds differ for different environments: interiors of HI shells, their walls, and unperturbed medium. Conclusions. CO clouds found in the interiors of HI shells are those that survived and were robbed of their more diffuse gas. Walls of HI shells have a high molecular content, indicative of an increased rate of CO formation. Comparing the CO fractions within HI shells and outside in the unperturbed medium, we conclude that HI shells are responsible for a ∼20% increase in the total amount of CO in the outer Milky Way.

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“…Cavities in the ISM of gas-rich dwarfs are believed to originate from the combined effects of photo-ionization, stellar winds and supernovae explosions from the sequential formation of massive stars. There are factors that contribute to making cavities a long-lived feature in the ISM, namely (1) the slow solid-body rotation of the gas; (2) the low gas densities; (3) the reduced shear; and (4) the absence of spiral density waves (Stewart et al 2000). Young & Lo (1997) presented high resolution VLA observations showing that the SagDIG H  content extended significantly farther out than the stellar component.…”

Section: Introductionmentioning

confidence: 99%

The H i hole and AGB stellar population of the Sagittarius dwarf irregular galaxy

Momany

Clemens

Bedin

et al. 2014

A&A

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Using two HST/ACS data sets that are separated by about two years has allowed us to derive the relative proper motion for the Sagittarius dwarf irregular (SagDIG) and reduce the heavy foreground Galactic contamination. The proper-motion decontaminated SagDIG catalog provides a much clearer view of the young red-supergiant and intermediate-age asymptotic giant branch populations. Previously identified carbon-and oxygen-rich star samples, which are based on narrow-band filter photometry, were complemented by membership criteria. We report identifying three Milky Way carbon-rich dwarf stars, which probably belong to the thin disk, and pointing to the high incidence of this class at low Galactic latitudes. A subgroup of four oxygen-rich candidate stars depicts a faint, red extension of the well-defined SagDIG carbon-rich sequence. The origin of these oxygen-rich candidate stars remains unclear, reflecting the uncertainty in the ratio of carbon-and oxygen-rich stars. Finally, SagDIG is a gas-rich galaxy characterized by a single large cavity in the gas disk (H  hole), which is offset by ∼360 pc from the optical center of the galaxy. We nonetheless investigate the stellar feedback hypothesis by comparing the proper-motion cleaned stellar populations within the H  hole with appropriately selected comparison regions that have higher H  densities external to the hole. The comparison shows no significant differences. In particular, the center of the H  hole (and the comparison regions) lack stellar populations younger than ∼400 Myr, which are otherwise abundant in the inner body of the galaxy. We conclude that there is no convincing evidence that the SagDIG H  hole is the result of stellar feedback and that gravitational and thermal instabilities in the gas are the most likely mechanism for its formation.

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Star Formation Triggering Mechanisms in Dwarf Galaxies: The Far‐Ultraviolet, Hα, and HiMorphology of Holmberg II

Abstract: Far-ultraviolet (FUV), Hα, and HI observations of dwarf galaxy Holmberg II are used to investigate the means by which star formation propagates in galaxies lacking

Cited by 65 publications

References 60 publications

Ultraviolet Observations of the Powering Source of the Supergiant Shell in IC 2574

Ultraviolet Observations of the Powering Source of the Supergiant Shell in IC 2574

Correlation of HI shells and CO clumps in the outer Milky Way

The H i hole and AGB stellar population of the Sagittarius dwarf irregular galaxy

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