Star Formation Histories Of Dwarf Galaxies Research Articles

Star-formation-driven outflows in local dwarf galaxies as revealed from [CII] observations by Herschel

We characterize the physical properties of star-formation-driven outflows in a sample of 29 local dwarf galaxies drawn from the Dwarf Galaxy Survey. We made use of Herschel/PACS archival data to search for atomic outflow signatures in the wings of individual [CII] 158 μm spectra and in their stacked line profile. We find a clear excess of emission in the high-velocity tails of 11 sources, which can be explained with an additional broad component (tracing the outflowing gas) in the modeling of their spectra. The remaining objects are likely hosts of weaker outflows that can still be detected in the average stacked spectrum. In both cases, we estimate the atomic mass outflow rates which result to be comparable with the star-formation rates of the galaxies, implying mass-loading factors (i.e., outflow efficiencies) of the order of unity. Outflow velocities in all the 11 galaxies with individual detections are larger than (or compatible with) the escape velocities of their dark matter halos, with an average fraction of 40% of gas escaping into the intergalactic medium (IGM). Depletion timescales due to outflows are lower than those due to gas consumption by star formation in most of our sources, ranging from one hundred million to a few billion years. From the energetic point of view, our outflows are mostly consistent with momentum-driven winds generated by the radiation pressure of young stellar populations on dust grains, although the energy-driven scenario is not excluded if considering a coupling efficiency up to 20% between the energy injected by supernovae and the interstellar medium. Overall, our results suggest that, despite their low efficiencies, galactic outflows can regulate the star-formation history of dwarf galaxies. Specifically, they are able to enrich with metals the circumgalactic medium of these sources, bringing on average a non-negligible amount of gas into the IGM, where it will no longer be available for new star formation. Our findings are suitable for tuning chemical evolution models attempting to describe the physical processes shaping the evolution of dwarf galaxies.

Predictions for complex distributions of stellar elemental abundances in low-mass galaxies

ABSTRACTWe investigate stellar elemental abundance patterns at $z$ = 0 in eight low-mass ($M_{*}=10^{6}{-}10^{9}\ \text{M}_{\odot }$) galaxies in the Feedback in Realistic Environments cosmological simulations. Using magnesium (Mg) as a representative α-element, we explore stellar abundance patterns in magnesium-to-iron ([Mg/Fe]) versus iron-to-hydrogen ([Fe/H]), which follow an overall monotonic trend that evolved slowly over time. Additionally, we explore three notable secondary features in enrichment (in three different case-study galaxies) that arise from a galaxy merger or bursty star formation. First, we observe a secondary track with a lower [Mg/Fe] than the main trend. At $z$ = 0, stars from this track are predominantly found within 2–6 kpc of the centre; they were accreted in a 1:3 total-mass-ratio merger ∼0.4 Gyr ago. Second, we find a distinct elemental bimodality that forms following a strong burst in star formation in a galaxy at $t_{\text{lookback}}\, \sim 10$ Gyr. This burst quenched star formation for ∼0.66 Gyr, allowing Type Ia supernovae to enrich the system with iron (Fe) before star formation resumed. Third, we examine stripes in enrichment that run roughly orthogonal to the dominant [Mg/Fe] versus [Fe/H] trend; these stripes correspond to short bursts of star formation during which core-collapse supernovae enrich the surrounding medium with Mg (and Fe) on short time-scales. If observed, these features would substantiate the utility of elemental abundances in revealing the assembly and star-formation histories of dwarf galaxies. We explore the observability of these features for upcoming spectroscopic studies. Our results show that precise measurements of elemental abundance patterns can reveal critical events in the formation histories of low-mass galaxies.

Star Formation History of Dwarf Galaxies in Cosmological Hydrodynamic Simulations

We examine the past and current work on the star formation (SF) histories of dwarf galaxies in cosmological hydrodynamic simulations. The results obtained from different numerical methods are still somewhat mixed, but the differences are understandable if we consider the numerical and resolution effects. It remains a challenge to simulate the episodic nature of SF history in dwarf galaxies at late times within the cosmological context of a cold dark matter model. More work is needed to solve the mysteries of SF history of dwarf galaxies employing large‐scale hydrodynamic simulations on the next generation of supercomputers.