Ultra-Compact High Velocity Clouds as Minihalos and Dwarf Galaxies

Faerman, Yakov; Sternberg, A.; McKee, Christopher F.

doi:10.1088/0004-637x/777/2/119

Cited by 54 publications

(58 citation statements)

References 72 publications

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“…These systems might re-start forming stars at later times (e.g. Ricotti 2009;Faerman et al 2013) and explain observations of HI-rich dwarf galaxies that show recent episodes of star formation (e.g. LeoT: Irwin et al 2007;de Jong et al 2008;Weisz et al 2012).…”

Section: Star Formation Historiesmentioning

confidence: 81%

Carbon-enhanced metal-poor stars in dwarf galaxies

Salvadori

Skúladóttir

Tolstoy

2015

Mon. Not. R. Astron. Soc.

104

139

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We investigate the frequency and origin of carbon-enhanced metal-poor (CEMP) stars in Local Group dwarf galaxies by means of a statistical, data-calibrated cosmological model for the hierarchical build-up of the Milky Way and its dwarf satellites. The model self-consistently explains the variation with dwarf galaxy luminosity of the observed: i) frequency and [Fe/H] range of CEMP stars; ii) metallicity distribution functions; iii) star formation histories. We show that if primordial faint supernovae dominated the early metal enrichment, then CEMP-no stars enriched by the first stellar generations should be present in all dwarf galaxies, with similar number of stars and CEMP fractions at [Fe/H]< −4. We demonstrate that the probability to observe a star that is carbon-enhanced within a given [Fe/H] range strongly depends on the luminosity of the dwarf galaxy and, on average, it is an order of magnitude lower in "classical" Sculptor-like dSph galaxies (P 0.02) than in the least luminous ultrafaint dwarfs (P ≈ 0.1). In addition, we explain why it may be easier to find CEMP-no stars at [Fe/H]≈ −2 in classical dSph galaxies than in ultra-faint dwarfs. These are consequences of the dramatic variation in the fraction of stars at [Fe/H]< −3 with galaxy luminosity: 40% for galaxies with L < 10 5 L ⊙ , and 0.2% for L > 10 7 L ⊙ . We present model predictions for the low Fe-tail and CEMP fraction of stars in dwarf galaxies, with particular emphasis on the Sculptor dSph, that can be used to shed light on the properties of the first stars.

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Section: Star Formation Historiesmentioning

confidence: 81%

Carbon-enhanced metal-poor stars in dwarf galaxies

Salvadori

Skúladóttir

Tolstoy

2015

Mon. Not. R. Astron. Soc.

104

139

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“…Similar analyses on independent observables that also probe the hot gas, such as the pulsar dispersion measure toward the Large Magellanic Cloud and the ram-pressure stripping of Milky Way satellites favor an extended halo (Fang et al 2013;Salem et al 2015). Finally, a recent analysis of both Galactic and extragalactic sightlines for L * galaxies finds that the O VII traces hot gas (Faerman et al 2016). Thus, we adopted the spherical density profile of Miller & Bregman (2015).…”

Section: Halo and Disk Modelsmentioning

confidence: 99%

The Rotation of the Hot Gas Around the Milky Way

Hodges-Kluck

Miller

Bregman

2016

ApJ

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The hot gaseous halos of galaxies likely contain a large amount of mass and are an integral part of galaxy formation and evolution. The Milky Way has a2 10 6 K halo that is detected in emission and by absorption in the O VII resonance line against bright background active galactic nuclei (AGNs), and for which the best current model is an extended spherical distribution. Using XMM-Newton Reflection Grating Spectrometer data, we measure the Doppler shifts of the O VII absorption-line centroids toward an ensemble of AGNs. These Doppler shifts constrain the dynamics of the hot halo, ruling out a stationary halo at about s 3 and a co-rotating halo at s 2 , and leading to a best-fit rotational velocity of =  f v 183 41 km s −1 for an extended halo model. These results suggest that the hot gas rotates and that it contains an amount of angular momentum comparable to that in the stellar disk. We examined the possibility of a model with a kinematically distinct disk and spherical halo. To be consistent with the emission-line X-ray data, the disk must contribute less than 10% of the column density, implying that the Doppler shifts probe motion in the extended hot halo.

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“…In the picture of Mo & Miralda-Escude (1996) and Maller & Bullock (2004), the hot gas is at the virial temperature (T hot ∼ 10 6 K) and has an over-density that follows the dark matter over-density (≈ 80ρ b at R vir for the profile shown in Figure 9). Such a scenario has recently been analyzed analytically by Faerman et al (2016). For the O vi phase to be in pressure equilibrium with this hot phase, the O vi density needs to have a density of ∼ 10 6 K/(3 × 10 4 K) · 80ρ b = 2700ρ b .…”

Section: 7mentioning

confidence: 99%

A Universal Density Structure for Circumgalactic Gas

Stern

Hennawi

Prochaska

et al. 2016

ApJ

126

157

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We develop a new method to constrain the physical conditions in the cool (∼ 10 4 K) circumgalactic medium (CGM) from measurements of ionic column densities, by assuming that the cool CGM spans a large range of gas densities and that small high-density clouds are hierarchically embedded in large low-density clouds. The new method combines the information available from different sightlines during the photoionization modeling, thus yielding tighter constraints on CGM properties compared to traditional methods which model each sightline individually. Applying this new technique to the COS-Halos survey of low-redshift ∼ L * galaxies, we find that we can reproduce all observed ion columns in all 44 galaxies in the sample, from the low-ions to O vi, with a single universal density structure for the cool CGM. The gas densities span the range 50 ρ/ρ b 5 × 10 5 (ρ b is the cosmic mean), while the physical size of individual clouds scales as ∼ ρ −1 , from ≈ 35 kpc of the low density O vi clouds to ≈ 6 pc of the highest density low-ion clouds. The deduced cloud sizes are too small for this density structure to be driven by self-gravity, thus its physical origin is unclear. The implied cool CGM mass within the virial radius is (1.3 ± 0.4) × 10 10 M (∼1% of the halo mass), distributed rather uniformly over the four decades in density. The mean cool gas density profile scales as R −1.0±0.3 , where R is the distance from the galaxy center. We construct a 3D model of the cool CGM based on our results, which we argue provides a benchmark for the CGM structure in hydrodynamic simulations. Our results can be tested by measuring the coherence scales of different ions.

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Ultra-Compact High Velocity Clouds as Minihalos and Dwarf Galaxies

Cited by 54 publications

References 72 publications

Carbon-enhanced metal-poor stars in dwarf galaxies

Carbon-enhanced metal-poor stars in dwarf galaxies

The Rotation of the Hot Gas Around the Milky Way

A Universal Density Structure for Circumgalactic Gas

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