Dark influences: imprints of dark satellites on dwarf galaxies

In the context of the current $\Lambda$CDM cosmological model small dark matter haloes are abundant and satellites of dwarf galaxies are expected to be predominantly dark. Since low mass galaxies have smaller baryon fractions interactions with these satellites may leave particularly dramatic imprints. We uncover the influence of the most massive of these dark satellites on disky dwarf galaxies and the possible dynamical and morphological transformations that result from these interactions. We use a suite of carefully set-up, controlled simulations of isolated dwarf galaxies. The primary dwarf galaxies have solely a stellar disk in the dark matter halo and the secundaries are completely devoid of baryons. We vary the disk mass, halo concentration, initial disk thickness and inclination of the satellite orbit. The disky dwarf galaxies are heated and disrupted due to the minor merger event, more extremely for higher satellite over disk mass ratios, and the morphology and kinematics are significantly altered. Moreover, for less concentrated haloes the minor merger can completely destroy the disk leaving a low-luminosity spheroidal-like galaxy instead. We conclude that dwarf galaxies are very much susceptible to being disturbed by dark galaxies and that even a minor merger event can significantly disrupt and alter the structure and kinematics of a dwarf galaxy. This process may be seen as a new channel for the formation of dwarf spheroidal galaxies.Comment: 16 pages, 13 figures, A&A accepted. For movies or a higher resolution version see http://www.astro.rug.nl/~starkenb/dwarfsanddarks.htm

Polygamy in the Marsh Harrier, Circus aeruginosus: Individual Variation in Hunting Performance and Number of Mates

1. Theories postulating that sexual task differentiation may lead to polygamy such that the sex investing the least effort in raising the offspring, engages in simultaneous matings, contrast with polygyny in raptors where the male provides most of the food for its females and nestlings. A field study was undertaken to describe parental effort and success in marsh harriers of different mating status to elucidate this controversy. 2. Data on clutch size and laying date were collected on 421 nests in two Dutch land reclamations, Flevoland and Lauwersmeer. 156 nests were known to have monogamous parents, 30 males had two females and nests. Bigamous males raised on average twice as many fledglings (5.7) than monogamous males (3.0). However, their primary females had more success (3.5) than secondary females (2.3), related to increased nestling mortality in secondary nests. Male fledglings were significantly heavier in primary than in secondary nests. 3. Nest observations made on 22 nests (5 of monogamous, 17 of polygamous males) revealed that daily prey deliveries by males were fewer in mono- than in bigamous males. The latter delivered prey by preference to their primary nests. The prey delivered by a trigamous male were consistently larger than those of a bigamous and monogamous male in the same area. 4. Time budget observations revealed that hunting effort was maximal in the nestling phase (ca 8 hrs foraging per day for all three males observed; at other times of year foraging was reduced in early morning and late afternoon. Net hunting yield (prey brought to nests per hour of hunting) increased in three males with their number (1, 2, or 3) of mates. With progress of the breeding season, male hunting ranges extended further outside the breeding territories and had a great measure of overlap, suggesting that territory quality was not a major factor in male hunting yield. 5. Secondary females participated in provisioning for the nestlings more than primary or monogamy-females, thus compensating for reduced male prey deliveries. 6. Classical polygyny theory addresses the question of female choice: which benefits compensate a secondary female for reduced breeding success by mating with an already paired male? Several hypotheses (enhanced offspring survival, offspring genetic quality, parent chances of future reproduction) are discussed, but evidence is nearly completely lacking. 7. An alternative approach stresses the male's role in the decision process. Males may have more interindividual variation in their capacity to bring food than females in their capacity to lay and incubate eggs. Optimal strategies for males would then range with increasing quality from non-breeding via polyandry and monogamy to polygyny. In species like harriers, non-breeding may be optimal for yearling males with submaximal hunting skills, thus creating a skewed sex ratio forcing some females to accept secondary status as mate of older, high quality males. Polygyny is then associated with slower male than female maturation. The evolution of polyandrous traits in species living isolated in poor environments is likewise explained by this model.

Chemical enrichment in very low-metallicity environments: Bootes I

We present different chemical evolution models for the ultrafaint dwarf galaxy Bootes I. We either assume that the galaxy accretes its mass through smooth infall of gas of primordial chemical composition (classical models) or adopt mass accretion histories derived from the combination of merger trees with semi-analytical modelling (cosmologically-motivated models). Furthermore, we consider models with and without taking into account inhomogeneous mixing in the ISM within the galaxy. The theoretical predictions are then compared to each other and to the body of the available data. From this analysis, we confirm previous findings that Bootes I has formed stars with very low efficiency but, at variance with previous studies, we do not find a clear-cut indication that supernova explosions have sustained long-lasting galactic-scale outflows in this galaxy. Therefore, we suggest that external mechanisms such as ram pressure stripping and tidal stripping are needed to explain the absence of neutral gas in Bootes I today.Comment: 13 pages, 11 figures, accepted for publication in MNRA

Grow Up

We need to be about the work of building and strengthening God’s kingdom. Posting about ­­­­­­­­focusing on God\u27s task for us from In All Things - an online journal for critical reflection on faith, culture, art, and every ordinary-yet-graced square inch of God’s creation. http://inallthings.org/grow-up

Misunderstandings

As sinful and selfish people, it’s easy for us to misunderstand God’s warnings and patience. Posting about ­­­­­­­­God\u27s judgment and His mercy from In All Things - an online journal for critical reflection on faith, culture, art, and every ordinary-yet-graced square inch of God’s creation. https://inallthings.org/misunderstandings

Dark influences III. Structural characterization of minor mergers of dwarf galaxies with dark satellites

In the current concordance cosmology small halos are expected to be completely dark and can significantly perturb low-mass galaxies during minor merger interactions. These interactions may well contribute to the diversity of the dwarf galaxy population. Dwarf galaxies in the field are often observed to have peculiarities in their structure, morphology, and kinematics, as well as strong bursts of star formation without apparent cause. We aim to characterize the signatures of minor mergers of dwarf galaxies with dark satellites to aid their observational identification. We explore and quantify a variety of structural, morphological, and kinematic indicators of merging dwarf galaxies and their remnants using a suite of hydrodynamical simulations. The most sensitive indicators of mergers with dark satellites are large asymmetries in the gaseous and stellar distributions, enhanced central surface brightness and starbursts, and velocity offsets and misalignments between the cold gas and stellar components. In general, merging systems span a wide range of values of the most commonly used indicators, while isolated objects tend to have more confined values. Interestingly, we find in our simulations that a significantly off-centered burst of star formation can pinpoint the location of the dark satellite. Observational systems with such characteristics are perhaps the most promising for unveiling the presence of the hitherto, missing satellites.Comment: 9 pages, 7 figures. Accepted in A&

The "Building Blocks" of Stellar Halos

The stellar halos of galaxies encode their accretion histories. In particular, the median metallicity of a halo is determined primarily by the mass of the most massive accreted object. We use hydrodynamical cosmological simulations from the APOSTLE project to study the connection between the stellar mass, the metallicity distribution, and the stellar age distribution of a halo and the identity of its most massive progenitor. We find that the stellar populations in an accreted halo typically resemble the old stellar populations in a present-day dwarf galaxy with a stellar mass $\sim 0.2-0.5$ dex greater than that of the stellar halo. This suggest that had they not been accreted, the primary progenitors of stellar halos would have evolved to resemble typical nearby dwarf irregulars.Comment: 7 pages, 3 figures, published in the proceedings of "On the Origin (and Evolution) of Baryonic Galaxy Halos", Puerto Ayora, Ecuador, March 13-17 2017, Eds. Duncan A. Forbes and Ericson D. Lope

Lasting Promise

You have a delightful inheritance and a faith that results in salvation and everlasting life. Posting about celebrating new life in Christ from In All Things - an online journal for critical reflection on faith, culture, art, and every ordinary-yet-graced square inch of God’s creation. http://inallthings.org/a-lasting-promise