bluuebunny/crossref_metadata_2025_split huggingface dataset:
Star Formation and Molecular Gas in Extremely Metal-poor Galaxies: Insights from the Thermal Balance in the Neutral Gas
Authors: Lebouteiller Vianney 
Published: October 2019

AbstractThe apparent lack of cold molecular gas in blue compact dwarf (BCD) galaxies is at variance with their intense star-formation episode. The CO molecule, often used a tracer of H2 through a conversion function, is selectively photodissociated in dust-poor environments and, as a result, a potentially large fraction of H2 is expected to reside in the so-called CO-dark gas, where it could be traced instead by infrared cooling lines [CI], [CII], and [OI]. Although the fraction of CO-dark gas to total molecular gas is in theory expected to be relatively large in metal-poor galaxies, many uncertainties remain due to the difficulty in identifying the main heating mechanism associated to the cooling lines observed in such galaxies.Investigations of the Herschel Dwarf Galaxy Survey (DGS; Madden et al.2013) show that the heating mechanism in the neutral gas of BCDs cannot be dominated by the photoelectric effect on dust grains below some threshold metallicity due to the low abundance of dust and polycyclic aromatic hydrocarbons, implying that other heating mechanisms need to be invoked, along with a new interpretation of the corresponding infrared line diagnostics. In the study presented here and in Lebouteiller et al. (2017), we use optical and infrared lines to constrain the physical conditions in the HII region + HI region of the BCD I Zw 18 (18 Mpc; ≍2% solar metallicity) within a consistent photoionization and photodissociation model. We show that the HI region is entirely heated by a single ultraluminous X-ray source with important consequences on the applicability of [CII] to trace the star-formation rate and to trace the CO-dark gas. We derive stringent upper limits on the size of H2 clumps that may be detected in the future with JWST and IRAM/NOEMA. We also show that the nature of the X-ray source can be inferred from the corresponding signatures in the ISM. Finally we speculate that star formation may be quenched in extremely metal-poor dwarf galaxies due to X-ray photoionization.
The major merger origin of the Andromeda II kinematics
Authors: Ebrová Ivana , Łokas Ewa L. , Fouquet Sylvain , del Pino Andrés 
Published: October 2019

AbstractProlate rotation (i.e. rotation around the long axis) has been reported for two Local Group dwarf galaxies: Andromeda II, a dwarf spheroidal satellite of M31, and Phoenix, a transition type dwarf galaxy. The prolate rotation may be an exceptional indicator of a past major merger between dwarf galaxies. We showed that this type of rotation cannot be obtained in the tidal stirring scenario, in which the satellite is transformed from disky to spheroidal by tidal forces of the host galaxy. However, we successfully reproduced the observed Andromeda II kinematics in controlled, self-consistent simulations of mergers between equal-mass disky dwarf galaxies on a radial or close-to-radial orbit. In simulations including gas dynamics, star formation and ram pressure stripping, we are able to reproduce more of the observed properties of Andromeda II: the unusual rotation, the bimodal star formation history and the spatial distribution of the two stellar populations, as well as the lack of gas. We support this scenario by demonstrating the merger origin of prolate rotation in the cosmological context for sufficiently resolved galaxies in the Illustris large-scale cosmological hydrodynamical simulation.
A numerical study on the distribution of the debris of the Milky Way satellites
Authors: Mazzarini Matteo , Just Andreas 
Published: October 2019

AbstractWe perform six N-body simulations reproducing the interaction between the Milky Way and its satellite galaxies, in order to address the deposit of satellite debris in the Galactic environment. We find that most of the baryons survive inside their host satellites and that most of the baryonic debris ends up in the inner regions of the Milky Way, in contrast to the more uniform distribution of dark matter debris. We also look at the debris Inertia tensor in the inner regions of the Milky Way and find a lower minor-to-major axis ratio for baryons than dark matter. We plan to explore the phase-space distribution of the debris ending in the Galactic disk and bulge. We also plan further simulations including gas dynamics to study the impact of gas on the process.
Early chemical enrichment of the Milky Way dwarf satellites from high-resolution and NLTE analysis of VMP stars
Authors: Mashonkina Lyudmila , Jablonka Pascale , Sitnova Tatyana , Pakhomov Yuri , North Pierre , Tatarnikov Andrey , Burlak Marina , Vozyakova Olga 
Published: October 2019

AbstractWe present the NLTE abundances of 10 chemical species in 65 very metal-poor stars in eight dSphs and the Milky Way halo. The classical dSphs Sculptor, Ursa Minor, Sextans, and Fornax reveal a similar plateau at [α/Fe] = 0.3 for each of Mg, Ca, and Ti, similarly to the MW halo. We provide the evidence for a decline in α/Fe in the Boötes I UFD, that is probably due to the ejecta of SNeIa. The dichotomy in the [Sr/Ba] versus [Ba/H] diagram is observed in the classical dSphs, similarly to the MW halo, calling for two different nucleosynthesis channels for Sr. The Boötes I and UMa II UFDs reveal very similar ratios of [Sr/Mg] = −1.3 and [Ba/Mg] = –1. The stars in the Coma Berenices and Leo IV UFDs are even poorer in Sr and Ba. The subsolar Sr/Ba ratios of Boötes I and UMa II indicate a common r-process origin of their n-capture elements.
Dark Memories of the Past: Discovery of Ultra-Diffuse Objects around NGC 1068
Authors: Tanaka Ichi , Yagi Masafumi , Taniguchi Yoshiaki 
Published: October 2019

AbstractWe have searched for a sign of the past dynamical disturbance events on NGC 1068, an archetypical Type-2 Seyfert galaxy, using deep and wide optical imaging data by the Subaru telescope. The data taken by Hyper Suprime-Cam (HSC) as well as the archived data by Suprime-Cam reveal several faint outer structures of the galaxy, most of which were never reported before. We discover three large (re= 3 -5.5 kpc), extremely diffuse objects (UDOs) within 45 kpc from the center of NGC 1068. We suggest that two of these UDOs are actually a part of a large loop-like structure surrounding NGC 1068. Such an extremely faint loop or stream is the direct evidence for a past minor merger event. The third UDO has a distorted morphology, suggesting that it is under the influence of strong tidal field. Furthermore, we have identified another ultra-diffuse but compact (μ0,r> 25 mag arcsec-2, re~ 0.8kpc) dwarf galaxy within ~140 kpc from NGC 1068. We speculate that this ultra-diffuse dwarf could be the object related to the ancient tidal disruption event (tidal dwarf) during the early mass assembly period of NGC 1068. We also detect an asymmetric outer one-arm structure emanated from the western edge of the outermost disk of NGC 1068 together with a ripple-like structure at the opposite side. These structures are also expected to arise in a late phase (up to several billion years ago) of a minor merger, according to numerical simulations. Our findings are consistent with the idea that the AGN activity in NGC 1068 is caused by a past minor merger.
Evolution of dwarf galaxies in a semi-analytic galaxy formation model
Authors: Nagashima Masahiro , Enoki Motohiro , Ishiyama Tomoaki , Kobayashi Masakazu A. R. , Makiya Ryu , Ogura Kazuyuki , Okamoto Takashi , Okoshi Katsuya , Oogi Taira , Shirakata Hikari 
Published: October 2019

AbstractDwarf galaxies provide us many important clues to understanding of galaxy formation. By using the current version of our own semi-analytic model of galaxy formation, in which cosmic structure forms and evolves based on the cold dark matter model of cosmology, we analyze dwarf galaxies. We find that the model well reproduces many properties such as magnitudes, sizes, and velocity dispersions of, especially, dwarf elliptical galaxies. We also find that the dynamical response of the gravitational potential well of dwarf galaxies to the supernova-induced gas removal plays a very important role to obtain large sizes and small velocity dispersions as observed.
Multiple Feedback in Low-Metallicity Massive Star Formation
Authors: Tanaka Kei E. I. , Tan Jonathan C. , Zhang Yichen , Hosokawa Takashi 
Published: October 2019

AbstractWe theoretically investigate the impact of feedback and its metallicity dependence in massive star formation from prestellar cores at all metallicity range. We include the feedback by MHD disk winds, radiation pressure, and photoevaporation solving the evolution of protostars and accretion flows self-consistently. Interestingly, we find that the feedback does not set the upper mass limit of stellar birth mass at any metallicity. At the solar metallicity, the MHD disk wind is the dominant feedback to set the star formation efficiencies (SFEs) from the prestellar cores similar to low-mass star formation. The SFE is found to be lower at lower surface density environment. The photoevaporation becomes significant at the low metallicity of Z < 10−2 Z⊙. Considering this efficient photoevaporation, we conclude that the IMF slope is steeper, i.e., massive stars are rarer at the extremely metal-poor environment of 10−5 − 10−3Z⊙. Our study raises a question on the common assumption of the universal IMF with a truncated at 100M⊙. Since the total feedback strength in the cluster/galaxy scale is sensitive to the number fraction of massive stars, the re-evaluations of IMF at various environments are necessary.
Population gradients in dwarf spheroidal galaxies KKs 3 and ESO 269-66
Authors: Sharina M. E. , Makarova L. N. , Makarov D. I. 
Published: October 2019

AbstractWe compare the properties of stellar populations for globular clusters (GCs) and field stars in two dwarf spheroidal galaxies (dSphs): ESO269-66, a close neighbour of NGC5128, and KKs3, one of the few isolated dSphs within 10 Mpc. We analyse the surface density profiles of low and high metallicity (blue and red) stars in two galaxies using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favour of the metallicity and age gradients in dSphs; 2) globular clusters in KKs3 and ESO 269-66 contain 4 and 40 percent of all stars with [Fe / H] ~ 1.6 dex and the age of 12 Gyr, correspondingly. Therefore, GCs are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO269-66, probably, thanks to its isolation.
The Lifecycle of Dust and Metals in Low-Abundance Galaxies
Authors: Hirschauer Alec S. , Gray Laurin , Paranzino William , Meixner Margaret , Boyer Martha L. , Jones Olivia C. 
Published: October 2019

AbstractThe earliest generations of stars were produced in galaxies at high redshift. The physical conditions in which these stars formed, produced heavy elements and dust, and subsequently ended their life cycles, however, are vastly different from those in the Milky Way. Nearby low metal-abundance galaxies provide critical laboratories within which it is possible to observe conditions similar to those at high redshift, shedding light on the lifecycle of dust and metals in the early Universe. Does the process of star formation change at low metallicity? How did galaxies in the early Universe produce significant amounts of dust without the elapsed time necessary for stars to evolve to the asymptotic giant branch (AGB) phase and contribute via mass loss? Here we present work cataloging dust-producing sources in the nearby metal-poor galaxy NGC 6822 and outline forthcoming GTO observations of this system and the blue compact dwarf I Zw 18 with JWST.
A whirling plane of satellite galaxies around Centaurus A challenges CDM cosmology
Authors: Müller Oliver 
Published: October 2019

AbstractThe phase-space correlation of dwarf galaxies around the Milky Way and the Andromeda galaxy pose a serious challenge to our understanding of structure formation. Recently, another planar structure was discovered around Cen A, the major galaxy of the Centaurus group. We have surveyed this galaxy group for new dwarf galaxies and presented the discovery of 57 new dwarf member candidates. Furthermore, we have studied the kinematics of previously known dwarfs and again found a kinematic coherence in their movement, similar to the Local Group satellites. In CDM simulations, such an alignment appears in less than 0.5 percent.
Cosmic Web Research: Where are the Missing Dwarf Galaxies and the Inter-Galactic Hi Clouds
Authors: Carignan Claude 
Published: October 2019

AbstractWe know that the observed H i (and H2) content cannot explain the SFR observed in galaxies. The only way galaxies can sustain that SFR is by accreting HI-rich dwarf galaxies or Inter-Galactic HI clouds. However, no observation to detect those accretion events has been conclusive so far. Instruments having the necessary sensitivity (e.g. GBT) lack the necessary spatial resolution and those with the proper resolution (e.g. VLA) lack the sensitivity. I will show that both are necessary to detect those illusive Hi clouds. The SKA precursor MeerKAT is starting its operation as we speak and will start the Large Survey Programs at the end of 2018. FAST has started its observations in drift scan mode with CRAFTS (Commensal Radio Astronomy Fast Survey). In the near future (2019-20), the best combination to study low column density H i will be to combine the sensitivity of FAST with the spatial resolution of MeerKAT.
Understanding planes of satellites
Authors: Santos-Santos I. , Artal H. , Domínguez-Tenreiro R. , Tissera P. B. , Pedrosa S. E. , Gómez-Flechoso M. A. , Brook C. B. , Bignone L. , Serna A. 
Published: October 2019

AbstractReproducing the planes of co-orbiting satellites observed in the MW and M31 so far has represented a challenge for cosmological simulations. We have developed a new method to search for kinematically-coherent groups of satellites and applied it to 2 different cosmological hydro-simulations of disc galaxies. In each simulation we have found such a group, that represents roughly half of the total satellite population and is distributed on a fairly thin plane that persists in time. These results are compatible with the MW and M31 observed planes.
Modeling low mass stellar populations
Authors: Bruzual Gustavo , Magris Gladis C. , Hernández-Pérez Fabiola 
Published: October 2019

AbstractModeling low mass stellar populations, like clusters and dwarf galaxies, with population synthesis models requires that we evaluate the role played by stochastic fluctuations in the sampling of the IMF on the spectro-photometric properties of these sparse populations. Interacting binaries may also modify the integrated spectra of these systems depending on the final product of the binary interaction and on the frequency of binary stars. In this work we compare the relative importance of stochastic fluctuations and binary evolution on low mass galaxy properties as a function of the population age and total mass. In most cases the effects of stochastic fluctuations dominate those produced by binary interactions. We explore and quantify the relative importance of these effects through cosmic times.
Chemical evolution model to derive metallicity distributions for each stellar population
Authors: Homma Hidetomo 
Published: October 2019

AbstractWe have constructed a chemical evolution model in order to reproduce the both metallicity distribution functions (MDFs) of red giant branch stars (RGBs) and RR Lyrae stars (RRLs) of a dwarf galaxy, simultaneously. The detailed chemical abundances of RGBs of the Local Group dwarf galaxies have been measured by spectroscopic observations. Moreover, the metallicity of RRLs of a dwarf galaxy are estimated by using the theoretical period-luminosity relations in the previous study and it is found that the mean metallicity of RRLs are lower than that of RGBs. In order to investigate the MDFs of RGBs and RRLs, we combine our chemical evolution model with the stellar evolutionally isochrones and calculate the metallicity of RGBs and RRLs, respectively. As a result, our chemical evolution model reproduces the peak metallicity of both MDFs of RGBs and RRLs of Sculptor and Fornax dwarf spheroidal galaxies (dSphs), simultaneously. Therefore, it is found that the difference of the mean metallicity between RGBs and RRLs are caused by the effects of stellar evolution. Moreover, by using the theoretical period-luminosity-metallicity relation of the RRLs, our chemical evolution model determines that the distance modulus of Sculptor and Fornax dSphs are 19.68 ± 0.09 and ${20.81^{+0.13}_{-0.11}}$, respectively. However, our model underestimates the number of metal-rich RRLs ([Fe/H] > −1.5) of Fornax dSph. This result suggests that the mass-loss rate of metal-rich RGBs would be larger than that of metal-poor RGBs.
DDO68-V1: an extremely metal-poor LBV in a void galaxy
Authors: Perepelitsyna Yulia , Pustilnik Simon 
Published: October 2019

AbstractThe lowest metallicity massive stars in the Local Universe with $Z\sim \left( {{Z}_{\odot }}/50-{{Z}_{\odot }}/30 \right)$ are the crucial objects to test the validity of assumptions in the modern models of very low-metallicity massive star evolution. These models, in turn, have major implications for our understanding of galaxy and massive star formation in the early epochs. DDO68-V1 in a void galaxy DDO68 is a unique extremely metal-poor massive star. Discovered by us in 2008 in the HII region Knot3 with $Z={{Z}_{\odot }}/35\,\left[ 12+\log \left( \text{O/H} \right)\sim 7.14 \right]$, DDO68-V1 was identified as an LBV star. We present here the LBV lightcurve in V band, combining own new data and the last archive and/or literature data on the light of Knot3 over the 30 years. We find that during the years 2008-2011 the LBV have experienced a very rare event of ‘giant eruption’ with V-band amplitude of 4.5 mag ($V\sim {{24.5}^{m}}-{{20}^{m}}$).
Neutral Gas Phase Metallicities Associated with Dwarf Galaxies
Authors: Rao Sandhya M. , Turnshek David A. , Monier Eric M. 
Published: October 2019

AbstractAbsorption line spectroscopy of foreground gas in the spectra of background quasars has revealed some clear cases where neutral gas is present and associated with dwarf galaxies. Spectroscopy of Lyα and low-ionization metal lines can be combined to derive neutral gas phase metallicities. The damped Lyα absorbers (DLAs) in quasar spectra are the clearest cases of absorption by predominantly neutral gas regions. Here we present some results on neutral gas phase metallicities for cases where the DLA is clearly associated with a dwarf galaxy. We find that the neutral gas phase metallicities in these systems are similar to those in other DLAs. We argue that there may be many unrecognized cases where a DLA is actually associated with a dwarf galaxy even though there is a luminous galaxy within 100 kpc of the quasar sightline.
Neutral Hydrogen in Nearby Dwarf Galaxies
Authors: Koribalski Bärbel S. 
Published: October 2019

AbstractHere I briefly highlight our studies of the gas content, kinematics and star formation in nearby dwarf galaxies (D < 10 Mpc) based on the ‘Local Volume Hi Survey’ (LVHIS, Koribalski et al. 2018), which was conducted with the Australia Telescope Compact Array (ATCA). The LVHIS sample consists of nearly 100 galaxies, including new discoveries, spanning a large diversity in size, shape, mass and degree of peculiarity. The hydrogen properties of dwarf galaxies in two nearby groups, Sculptor and CenA / M83, are analysed and compared with many rather isolated dwarf galaxies. Around 10% of LVHIS galaxies are transitional or mixed-type dwarf galaxies (dIrr/dSph), the formation of which is explored. — I also provide a brief update on WALLABY Early Science, where we focus on studying the Hi properties of galaxies as a function of environment. WALLABY (Dec < +30 degr, z < 0.26) is conducted with the Australian SKA Pathfinder (ASKAP), a ∽6-km diameter array of 36 × 12-m dishes, each equipped with wide-field (30 sq degr) Chequerboard Phased Array Feeds.
Stellar feedback in dwarf irregular galaxies with radio continuum observations
Authors: Heesen Volker , Basu Aritra , Brinks Elias , Heald George , Fletcher Andrew , Horellou Cathy , Hoeft Matthias , Chyży Krzysztof 
Published: October 2019

AbstractLow-mass dwarf irregular galaxies are subject to outflows, in which cosmic rays may play a very important role; they can be traced via their electron component, the cosmic ray electrons (CRe), in the radio continuum as non-thermal synchrotron emission. With the advent of sensitive low-frequency observations, such as with the Low-Frequency Array (LOFAR), we can trace CRe far away from star formation sites. Together with GHz-observations, such as with the Very Large Array (VLA), we can study spatially resolved radio continuum spectra at matched angular resolution and sensitivity. Here, we present results from our 6-GHz VLA survey of 40 nearby dwarf galaxies and our LOFAR study of the nearby starburst dwarf irregular galaxy IC 10. We explore the relation of RC emission with star formation tracers and study in IC 10 the nature of a low-frequency radio halo, which we find to be the result of a galactic wind.
Exploring 3D data of Dwarf Galaxies
Authors: Bensch Katarzyna , Thöne Christina , de Ugarte Postigo Antonio , Izzo Luca , Kann David Alexander 
Published: October 2019

AbstractDwarf irregular galaxies are places of ongoing star-formation in the low-redshift Universe. Low metallicity dwarfs were originally thought to be the youngest galaxies in the local Universe, however, there is now evidence that they consist of matter which has previously undergone evolution and is enriched by star-formation. Here we present a sample of seven nearby metal-poor dwarf galaxies with a young stellar populations selected from the SDSS which we study using integral field unit (IFU) data from the VIMOS instrument, covering the spectral range between the He II 4686 line and the [SII] 6718/6733 Å doublet. We present property maps across the galaxies and compare different galaxies and different HII regions within the same galaxy. We find that the properties within one galaxy are not uniform and they also differ between different galaxies concerning star-formation, kinematics and metallicity and morphology. The observed differences across individual galaxies together with disturbed kinematics and morphologies can be interpreted as possible signs of recent interactions and/or mergers. Additionally, we present a comparison of different metallicity calibrations and search for systematic differences obtained using different methods.
Dwarf Galaxies: From the Epoch of Peak Star Formation to the Epoch of Reionization
Authors: Atek Hakim 
Published: October 2019

AbstractDwarf galaxies represent the dominant population at high redshift and they most likely contributed in great part to star formation history of the Universe and cosmic reionization. The importance of dwarf galaxies at high redshift has been mostly recognized in the last decade due to large progress in observing facilities allowing deep galaxy surveys to identify low-mass galaxies. This population appear to have extreme emission lines and ionizing properties that challenge stellar population models. Star formation follows a stochastic process in these galaxies, which has important implication on the ionizing photon production and its escape fraction whose measurements are challenging for both simulations and observations. Outstanding questions include: what are the physical properties at the origin of such extreme properties? What are the smallest dark matter halos that host star formation? Are dwarf galaxies responsible for cosmic reionization?