bluuebunny/crossref_metadata_2025_split huggingface dataset:
Kinematical evidence for secular evolution in Spitzer Survey of Stellar Structure in Galaxies (S4G) spirals
Authors: Erroz-Ferrer Santiago , Knapen Johan H. , Font Joan , Beckman John E. ,   the S4G team
Published: March 2015

AbstractWe present a study of the kinematics of a sample of isolated spiral galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S4G). We use Hα Fabry-Perot data from the GHαFaS instrument at the William Herschel Telescope (WHT) in La Palma, complemented with images at 3.6 microns, in the R band and in the Hα filter. The resulting data cubes and velocity field maps allow a complete study of the kinematics of a galaxy, including in-depth investigations of the rotation curve, velocity moment maps, velocity residual maps, gradient maps and position-velocity (PV) diagrams. We find clear evidence of the secular evolution processes going on in these galaxies, such as asymmetries in the velocity field in the bar zone, and non-circular motions, probably in response to the potential of the structural components of the galaxies, or to past or present interactions.
Characterization of peculiar early-type galaxies in the local universe
Authors: Ramos Beatriz H. F. , Menéndez-Delmestre Karín , Kim Taehyun , Sheth Kartik ,   S4G team
Published: March 2015

AbstractEarly-type galaxies (ETGs) have been characterized as objects dominated by old stellar populations, containing little or no cold gas and dust, and thus, non-existent star formation. However, there are indications in the literature that some ETGs deviate from this: some have significant amounts of gas and dust, are forming stars, and/or display stellar substructures (tidal features, disks or shells, e.g., Kormendy et al. 1997, Rix, Carollo & Freeman 1999). A better understanding of the evolution of ETGs and the details of their “peculiarities” is critical to properly constrain models of galaxy formation. We present preliminary results on a photometric analysis of substructures in local ETGs, based on 3.6μm IRAC images from the Spitzer Survey of Stellar Structure in Galaxies (S4G; Sheth et al. 2010), which comprises one of the largest mid-IR photometric surveys of the local Universe. Relatively unhindered by extinction and dominated by the low-mass stellar populations that dominate a galaxy's stellar mass budget, the IR is the ideal waveband to trace the details of stellar structures in galaxies. Based on 2D GALFIT (Peng et al. 2002) decomposition, we find tidal features in 17% of 146 ETGs from S4G. For both the GALFIT model and the galaxy residual images, we calculate the total counts inside an annular region centered on the galaxy, where the inner radius is the effective radius of the galaxy. Assuming that a tidal feature and its host galaxy have the same mass-to-luminosity ratio (M/L), the ratio of the residual counts over model counts translates into the ratio of their stellar masses. We find that the tidal features in the majority of peculiar ETGs in our sample account for no more than 11% of the galaxy's total stellar mass. Considering that simulations (Canalizo et al. 2007) suggest an upper limit in relative stellar mass of 25% for shells resulting from a past major merger, the values we find support a merger origin. We are in the process of applying the decomposition method to GALEX UV images and optical SDSS images of these peculiar ETGs in order to characterize the underlying substructure and provide constraints on astrophysical properties such as star formation rates and stellar masses associated to these tidal features, based on broad-band SED template fitting techniques.
The origin of thick discs
Authors: Comerón Sébastien 
Published: March 2015

AbstractThick discs are defined to be disc-like components with a scale height larger than that of the classical discs. They are ubiquitous (Yoachim & Dalcanton 2006; Comerón et al. 2011a), they are made of mostly old and metal-poor stars and are most easily detected in close to edge-on galaxies. Their origin has been considered mysterious and several formation theories have been proposed:• The thick disc being formed secularly by thin disc stars heated by disc overdensities such as giant molecular clouds or spiral arms (Villumsen 1985, ApJ, 290, 75) and by stars moved outwards from their original orbits by radial migration mechanisms (Schönrich & Binney 2009).• The thick disc being formed by the heating of the thin disc by satellites (Quinn et al. 1993) and the tidal stripping of them (Abadi et al. 2003).• The thick disc being formed fast and already thick at high redshift in an highly unstable disc. Inside that thick disc, a thin disc would form afterwards as suggested by Elemgreen & Elmegreen (2006).• The thick disc being formed originally thick at high redshift by the merger of gas-rich protogalactic fragments and a thin disc forming afterwards within it (Brook et al. 2007).The first mechanism is a secular evolution mechanism. The time-scale of the second one is dependent on the merger history of the main galaxy. In the two last mechanisms, the thick disc forms already thick in a short time-scale at high redshift.Recent Milky Way studies, (see, e.g., Bovy et al. 2012), have shown indications that there is no discontinuity between the thin and the thick disc chemical and kinematic properties. Instead, those studies indicate the presence of a monotonic distribution of disc thicknesses. This would suggest a secular origin for the Milky Way thick disc.Studies in external galaxies (Yoachim & Dalcanton 2006; Comerón et al. 2011b), have shown that low-mass disc galaxies have thick disc relative masses much larger than those found in large-mass galaxies. Because low-mass galaxies are dynamically younger than their larger counterparts, it seems difficult for their thick discs to have a secular evolution origin, but simulations show that their thick disc masses are compatible with those of a thick disc formed at high redshift.Thus, recent studies seem to indicate that large-mass galaxies have their thick discs formed mainly due to secular evolution and that low-mass galaxies have them formed at high redshift.
Radial migration in barred galaxies
Authors: Di Matteo P. , Haywood M. , Combes F. , Semelin B. , Babusiaux C. , Gomez A. 
Published: March 2015

AbstractIn this talk, I will present the result of high resolution numerical simulations of disk galaxies with various bulge/disk ratios evolving isolated, showing that:
•Most of migration takes place when the bar strength is high and decreases in the phases of low activity (in agreement with the results by Brunetti et el. 2011, Minchev et al. 2011).•Most of the stars inside the corotation radius (CR) do not migrate in the outer regions, but stay confined in the inner disk, while stars outside CR can migrate either inwards or outwards, diffusing over the whole disk.•Migration is accompanied by significative azimuthal variations in the metallicity distribution, of the order of 0.1 dex for an initial gradient of ~-0.07 dex/kpc.•Boxy bulges are an example of stellar structures whose properties (stellar content, vertical metallicity, [α/Fe] and age gradients, ..) are affected by radial migration (see also Fig. 1).
Disk structures in the CGS Survey
Authors: Li Zhao-Yu , Ho Luis , Barth Aaron , Peng Chien 
Published: March 2015

AbstractThe Carnegie-Irvine Galaxy Survey (CGS) is a long term program to investigate the photometric and spectroscopic properties of a statistically complete sample of 605 bright (BT < 12.9 mag), southern (delta < 0 deg) galaxies using the facilities at Las Campanas Observatory. For each galaxy, we have broadband images (BVRI) with good seeing (≈1″) and deep surface brightness (≈27.5 B-band). Using the IRAF task ELLIPSE and the fourier decomposition method, we measured the bar and the lopsidedness properties of disk galaxies in the CGS sample. Our results show that the bar fraction is lower in the early-type galaxies than that in the late-type ones. The (relative) bar length is longer in early-type ones, and strong bars are rare (the one with large ellipticity). We find that the lopsidedness is independent on the galaxy environment, and correlation studies suggest that the lopsided disk may have helped drive gas inward to form stars.
Dynamical evolution of star clusters in transient spiral arms
Authors: Fujii Michiko , Baba Junichi 
Published: March 2015

AbstractStar clusters are one of fundamental building blocks of galactic disks. They form in a potential well of spiral arms and travel in the disk. We performed N-body simulation of star clusters in stellar disk with “live” spiral arms. In this simulation, both star clusters and stellar disks are modeled as N-body systems. We found that star clusters migrated in the galactic disk in a timescale of their galactic rotation. The tidal tails spread over a few kpc, but they might be detectable if we are able to measure their velocity.
The influence of halo evolution on galaxy structure
Authors: White Simon 
Published: March 2015

AbstractIf Einstein-Newton gravity holds on galactic and larger scales, then current observations demonstrate that the stars and interstellar gas of a typical bright galaxy account for only a few percent of its total nonlinear mass. Dark matter makes up the rest and cannot be faint stars or any other baryonic form because it was already present and decoupled from the radiation plasma at z = 1000, long before any nonlinear object formed. The weak gravito-sonic waves so precisely measured by CMB observations are detected again at z = 4 as order unity fluctuations in intergalactic matter. These subsequently collapse to form today's galaxy/halo systems, whose mean mass profiles can be accurately determined through gravitational lensing. High-resolution simulations link the observed dark matter structures seen at all these epochs, demonstrating that they are consistent and providing detailed predictions for all aspects of halo structure and growth. Requiring consistency with the abundance and clustering of real galaxies strongly constrains the galaxy-halo relation, both today and at high redshift. This results in detailed predictions for galaxy assembly histories and for the gravitational arena in which galaxies live. Dark halos are not expected to be passive or symmetric but to have a rich and continually evolving structure which will drive evolution in the central galaxy over its full life, exciting warps, spiral patterns and tidal arms, thickening disks, producing rings, bars and bulges. Their growth is closely related to the provision of new gas for galaxy building.
Galaxies in most dense environments at z ~ 1.4
Authors: Strazzullo V. 
Published: March 2015

AbstractThe X-ray luminous system XMMU J2235-2557 at z~1.4 is among the most massive of the very distant galaxy clusters, and remains a unique laboratory to observe environment-biased galaxy evolution already 9 Gyr ago (Lidman et al.2008, Rosati et al.2009, Strazzullo et al.2010). At a cosmic time when cluster cores start showing evidence of a still active galaxy population, star-forming (M>1010M⊙) galaxies in XMMU J2235-2557 are typically located beyond ~250kpc from the cluster center, with the cluster core already effectively quenched and dominated by massive galaxies on a tight red sequence, showing early-type spectral features and bulge-dominated morphologies. While masses and stellar populations of these red-sequence galaxies suggest that they have largely completed their formation, their size is found to be typically smaller that similarly massive early-type galaxies in the local Universe, in agreement with many high-redshift studies. This would leave room for later evolution, likely through non-secular processes, changing their structure to match their local counterparts. On the other hand, uncertainties and biases in the determination of masses and sizes, as well as in the local mass-size relation, and the possible effect of progenitor bias, still hamper a final conclusion on the actual relevance of size evolution for early-type galaxies in this dense high-redshift environment.
Testing galaxy formation models with the GHOSTS survey: The stellar halo of M81
Authors: Monachesi A. , Bell E. , Radburn-Smith D. , Vlajić M. , de Jong R. , Bailin J. , Dalcanton J. , Holwerda B. , Streich D. 
Published: March 2015

AbstractThe GHOSTS survey is the largest study to date of the resolved stellar populations in the outskirts of disk galaxies (Radburn-Smith et al.2011). The sample currently consists of 16 nearby disk galaxies, whose outer disks and halos are imaged with the Hubble Space Telescope (HST). I will present new results obtained from the study of 19 GHOSTS fields in M81's outermost part. The observed fields probe the stellar halo of M81 out to projected distances of ~50 kpc, an unprecedented distance for halo studies outside the Local Group. The 50% completeness levels of the color magnitude diagrams are typically at 2.5 mag below the tip of the red giant branch. When considering only fields located at galactocentric radius R > 15 kpc, we detect no color gradient in the stellar halo of M81. We compare these results with model predictions for the colors of stellar halos formed purely via accretion of satellite galaxies (Bullock & Johnston 2005). When we analyze the cosmologically motivated models in the same way as the HST data, we find that they predict no color gradient for the stellar halos, in good agreement with the observations (see Fig. 1).
Near-infrared Polarimetry and Interstellar Magnetic Fields in the Galactic Center
Authors: Nishiyama S. , Hatano H. , Nagata T. , Tamura M. 
Published: March 2015

AbstractWe present a large-scale view of the magnetic field (MF) in the central 3° × 2° region of our Galaxy. There is a smooth transition of the large-scale MF configuration in this region.
MAGMO: Mapping the Galactic Magnetic field through OH masers
Authors: Green James A. , McClure-Griffiths Naomi M. , Caswell James L. , Robishaw Tim , Harvey-Smith Lisa , Mao Sui Ann 
Published: March 2015

AbstractWe are undertaking a project (MAGMO) to examine large-scale magnetic fields pervading regions of high-mass star formation. The project will test if the orientations of weak large-scale magnetic fields can be maintained in the contraction (and field amplification) to the high densities encountered in high-mass star forming regions. This will be achieved through correlating targeted observations of ground-state hydroxyl (OH) maser emission towards hundreds of sites of high-mass star formation spread throughout the spiral arms of the Milky Way. Through the Zeeman splitting of the OH maser emission these observations will determine the strength and orientation of the in-situ magnetic field. The completion of the southern hemisphere Methanol Multibeam survey has provided an abundance of targets for ground-state OH maser observations, approximately 1000 sites of high-mass star formation. With this sample, much larger and more homogeneous than previously available, we will have the statistics necessary to outweigh random fluctuations and observe an underlying Galactic magnetic field if it exists. We presented details of the overall progress of the project illustrated by the results of a pilot sample of sources towards the Carina-Sagittarius spiral arm tangent, where a coherent field is implied.
MHD turbulence in the intracluster medium
Authors: Falceta-Gonçalves Diego , Kowal G. , de Gouveia Dal Pino E. , Santos-Lima R. , Nakwacki S. , Lazarian A. 
Published: March 2015

AbstractIn this work we discuss the turbulent evolution of structures in the intracluster medium based on the two fluid approximations: MHD and collisionless plasma under Chew Goldberger Low (CGL) closure. Turbulence excited by galactic motions and gas inflow in intracluster medium will develop in very different ways considering the two fluid approaches. Statistics of density distributions, and velocity and magnetic fields are provided. Compared to the standard MHD case, the instabilities that arise from CGL-MHD models strongly modify the probability distribution functions of the plasma velocity and density, basically increasing their dispersion. Moreover, the spectra of both density and velocity show increased power at small scales, due to the instabilities growth rate that are larger as smaller scales. Finally, in high beta plasmas, i.e. B2 << P, a fast increase of the magnetic energy density is observed in the CGL-MHD models, faster than the standard MHD turbulent dynamo that operates at timescales τ ~ L/vL. The signatures of the increased power at small scales and the increase of magnetic field intensity from CGL-MHD models could be observed at radio wavelengths. A comparison of the structure function of the synchrotron emission, as well as the statistics of Faraday rotation effects on the synchrotron polarization, for both the MHD and CGL-MHD models is provided.
SpS5 - I. Obscured and distant clusters
Authors: Hanson M. M. , Froebrich D. , Martins F. , Chené A.-N. , Rosslowe C. , Herrero A. , Kim H.-J. 
Published: March 2015

AbstractThis first part of Special Session 5 explored the current status of infrared-based observations of obscured and distant stellar clusters in the Milky Way galaxy. Recent infrared surveys, either serendipitously or using targeted searches, have uncovered a rich population of young and massive clusters. However, cluster characterization is more challenging as it must be obtained often entirely in the infrared due to high line-of-sight extinction. Despite this, much is to be gained through the identification and careful analysis of these clusters, as they allow for the early evolution of massive stars to be better constrained. Further, they act as beacons delineating the Milky Way's structure and as nearby, resolved analogues to the distant unresolved massive clusters studied in distant galaxies.
Astronomy for a Better World: IAU OAD Task Force-1 Programs for Advancing Astronomy Education and Research in Universities in Developing Countries
Authors: Guinan Edward , Kolenberg Katrien 
Published: March 2015

AbstractWe discuss the IAU Commission 46 and Office for Astronomy Development (OAD) programs that support advancing Astronomy education and research primarily in universities in developing countries. The bulk of these operational activities will be coordinated through the OAD's newly installed Task Force 1. We outline current (and future) IAU/OAD Task Force-1 programs that promote the development of University-level Astronomy at both undergraduate and graduate levels. Among current programs discussed are the past and future expanded activities of the International School for Young Astronomers (ISYA) and the Teaching Astronomy for Development (TAD) programs. The primary role of the ISYA program is the organization of a three week School for students for typically M.Sc. and Ph.D students. The ISYA is a very successful program that will now be offered more frequently through the generous support of the Kavli Foundation. The IAU/TAD program provides aid and resources for the development of teaching, education and research in Astronomy. The TAD program is dedicated to assist countries that have little or no astronomical activity, but that wish to develop or enhance Astronomy education. Over the last ten years, the ISYA and TAD programs have supported programs in Africa, Asia, Central America and the Caribbean, the Middle East, South East and West Asia, and South America. Several examples are given.Several new programs being considered by OAD Task Force-1 are also discussed. Other possible programs being considered are the introduction of modular Astronomy courses into the university curricula (or improve present courses) as well as providing access to “remote learning“ courses and Virtual Astronomy labs in developing countries. Another possible new program would support visits of astronomers from technically advanced countries to spend their sabbatical leaves teaching and advising University Astronomy programs in developing countries. Suggestions for new Task Force -1 programs are also welcomed. Useful information about the participation of IAU members and volunteers in these programs will be discussed and practical information will be provided.
NAOJ's activities on Astronomy for Development: Aiding Astronomy Education in Developing Nations
Authors: Sekiguchi K. , Yoshida F. 
Published: March 2015

AbstractWe summarize NAOJ's efforts to promote astronomy in developing nations. The Office of International Relations, collaborations with the Office of Public Outreach at NAOJ and with the East Asia Core Observatories Association (EACOA), has engaged children, students and educators about astronomy development in the Asia-Pacific region. In particular, we introduce “You are Galileo!“ project, which is a very well received astronomy education program for children. We also report on a continuing effort by the Japanese Government in support of astronomy programs in the developing nations.
Modern view of the warm ionized medium
Authors: Hill A. , Reynolds R. , Haffner L. , Wood K. , Madsen G. 
Published: March 2015

AbstractWe review the observational evidence that the warm ionized medium (WIM) is a major and physically distinct component of the Galactic interstellar medium. Although up to ~ 20% of the faint, high-latitude Hα emission in the Milky Way may be scattered light emitted in midplane Hii regions, recent scattered light models do not effectively challenge the well-established properties of the WIM.
Formation of structures around HII regions: ionization feedback from massive stars
Authors: Tremblin P. , Audit E. , Minier V. , Schmidt W. , Schneider N. 
Published: March 2015

AbstractWe present a new model for the formation of dense clumps and pillars around HII regions based on shocks curvature at the interface between a HII region and a molecular cloud. UV radiation leads to the formation of an ionization front and of a shock ahead. The gas is compressed between them forming a dense shell at the interface. This shell may be curved due to initial interface or density modulation caused by the turbulence of the molecular cloud. Low curvature leads to instabilities in the shell that form dense clumps while sufficiently curved shells collapse on itself to form pillars. When turbulence is high compared to the ionized-gas pressure, bubbles of cold gas have sufficient kinetic energy to penetrate into the HII region and detach themselves from the parent cloud, forming cometary globules.Using computational simulations, we show that these new models are extremely efficient to form dense clumps and stable and growing elongated structures, pillars, in which star formation might occur (see Tremblin et al.2012a). The inclusion of turbulence in the model shows its importance in the formation of cometary globules (see Tremblin et al.2012b). Globally, the density enhancement in the simulations is of one or two orders of magnitude higher than the density enhancement of the classical “collect and collapse“ scenario. The code used for the simulation is the HERACLES code, that comprises hydrodynamics with various equation of state, radiative transfer, gravity, cooling and heating.Our recent observations with Herschel (see Schneider et al.2012a) and SOFIA (see Schneider et al.2012b) and additional Spitzer data archives revealed many more of these structures in regions where OB stars have already formed such as the Rosette Nebula, Cygnus X, M16 and Vela, suggesting that the UV radiation from massive stars plays an important role in their formation. We present a first comparison between the simulations described above and recent observations of these regions.
ISM simulations: an overview of models
Authors: de Avillez M. A. , Breitschwerdt D. , Asgekar A. , Spitoni E. 
Published: March 2015

AbstractUntil recently the dynamical evolution of the interstellar medium (ISM) was simulated using collisional ionization equilibrium (CIE) conditions. However, the ISM is a dynamical system, in which the plasma is naturally driven out of equilibrium due to atomic and dynamic processes operating on different timescales. A step forward in the field comprises a multi-fluid approach taking into account the joint thermal and dynamical evolutions of the ISM gas.