It is well known that the interaction between two disk galaxies generates tidal spiral arms and a connection in the form of a bridge. Here we address the question of the formation of tidal arms and bridges from a dynamical point of view. We model the bridges and tails observed in interacting galaxies using the invariant manifolds associated to the Lyapunov orbits of the Lagrangian points of the galactic system, when the two galaxies are considered as two point masses in a circular orbit.

We derive constraints on radio source clustering towards Planck-selected galaxy clusters using the NVSS point source catalog. The constraint can be used for making a more realistic Sunyaev-Zeldovich effect (SZE) mocks, calculating predictions of detectable clusters count and for quantifying source confusion in radio surveys.

Dust is a ubiquities component of the interstellar medium (ISM) of galaxies, and manifests itself in many different ways. Yet, its origin, composition, and size distribution are still a matter of great debate. Most of the thermally condensed dust is produced in the explosively expelled ejecta of core collapse supernovae (CCSNe) and in the quiescent winds of AGB stars. Following its injection into the ISM it is destroyed by supernova (SN) shock waves. Knowing the relative rates of these processes is crucial for understanding the nature and evolution of dust in galaxies. In the following we will review three aspects of the evolution of dust in galaxies: the evolution of dust in the ejecta of SN1987A; the rates of dust production and destruction rates in the Magellanic Clouds (MCs), and the evolution of dust in CLASH 2882, a gravitationally-lensed galaxy at z=1.

Comparing with solar cycles 21-23, the level of solar activity in the current cycle is very low. So far, there have been only five SARs and 45 X class flares. The monthly smoothed total solar irradiance decreased sharply by 0.09% from the maximum of cycle 23 to the minima between cycles 23 and 24. In this contribution, we present new studies on SARs in Cycle 24. The SARs in the current cycle have relatively smaller flare index (Iflare) and composite vector field index (Icom) comparing with the SARs in cycles 22 and 23. There is a clearly linear relationship between Iflare and Icom. The emphasis of this contribution is put on the similarity and different behaviors of vector magnetic fields of the SARs in the current solar cycle and the previous ones. We try to get a satisfactory account for the general characteristics and relatively lower level of solar flare activity in Cycle 24.

The Planck satellite (Planck 2015 results. I) has provided the first FIR/submm all-sky survey with a sensitivity allowing us to identify the rarest, most luminous hig-z dusty star-forming sources on the sky. The Planck list of high-z source candidates (PHZ, PIP XXXIX subm) has been built and charcaterized over 25% of the sky by selecting the 2151 brightest red submm sources at a 5' resolution (Montier et al. 2010). Follow-up observations with Herschel/SPIRE over 228 Planck candidates have already shown that 93% of these candidates are actually overdensities of red sources (PIP XXVII 2015), while 12 Planck high-z candidates are identified as strongly lensed star-forming galaxies at redshift between 2.2 and 3.6 (Canameras et al. 2015). The first confirmed Planck proto-cluster candidate has been revealed to be a double structure at z = 1.7 and zz = 2.03 (Flores-Cacho et al. 2015). The PHZ opens a new window on these extreme star-forming systems at high-z, providing a powerful laboratory to study the mechanisms of galaxy evolution and enrichment in the frame of the large scale structure growth.

An unresolved X-ray emission extends along the Galactic plane, so-called the Galactic diffuse X-ray emission (GDXE). The characteristic feature is three K-shell lines of Fe at 6.4, 6.7, and 6.9 keV. Recently, superposition of faint point sources, such as Cataclysmic variables (CVs) and Active binaries (ABs) is thought to be a major origin, although it is under debate which sub-class mostly contribute. We re-analyzed the Suzaku archive data and constructed spectral models of ABs, magnetic CVs (mCVs), and non-magnetic CVs (non-mCVs). The GBXE is explained by combination of those models; non-mCVs and ABs mainly contribute while mCVs account for ~10% or less of the 5–10 keV flux. On the other hand, the GCXE and GRXE spectra cannot be represented by any combination of the point sources, indicating another origin would be required.

A compendium of over 8000 galaxy distances has been accumulated. Distance measurements permit the separation of observed velocities into cosmic expansion and peculiar velocity components. Only the radial component of peculiar velocities can be measured and individual errors are large, but a Wiener Filter procedure permits the reconstruction of three-dimensional motions and the density field that is responsible for these motions. A coherent flow pervades the entire domain of ± 15,000 km/s. Techniques are discussed for the separation of local and tidal components of the flow. Laniakea supercluster is identified as a region of contiguous infalling flows.

Over the past 15 years, the molecular complex Sgr C has been repeatedly observed with both XMM-Newton and Chandra. These observations reveal new features indicating that the region might be more complex than previously thought. We find that its strong iron line emission at 6.4 keV varies significantly over time, which supports the X-ray reflection scenario.

In this study, we aim to trace formation of the primordial globular cluster, ultra faint dwarf galaxy, and ultra compact dwarf in a cosmological context of a high-resolution hydrodynamic zoom-in simulation. We show that the baryon-dominated systems have experienced more interactions with the mini halos before infalling to the main halo.

The European Large-Area ISO Survey (ELAIS) N1 field is one of the extragalactic windows where the lack of the Galactic ISM allows us to analyze the unbiased FIR properties of extragalactic objects. The field was investigated recently based on Herschel observations by the HerMES key project. We present a survey of the field covering a larger area than HerMES (12.54 deg2 vs 3.47 deg2). We provide accurate 250, 350, and 500 micrometer flux densities for about 8000 point sources using the latest Herschel analysis and calibration procedures. Based on SDSS spectroscopic and SWIRE photometric data our sample has approximately 4000 and 4500 galaxies with 0.2 < z < 0.5 and z > 0.5 redshifts, respectively. The new flux densities are crucial limiting the star-forming activity of galaxies outside the Local Universe, as it is demonstrated in the star-forming galaxy 2MASS J16072472+5412119.

Based on the New Vacuum Solar Telescope observations, some new results about the solar activities are obtained. (1) In the Hα line, a flux rope tracked by filament activation is detected for the first time. There may exist some mild heating during the filament activation. (2) The direct observations illustrate the mechanism of confined flares, i.e., the flares are triggered by magnetic reconnection between the emerging loops and the pre-existing loops and prevented from being eruptive by the overlying loops. (3) The solid observational evidence of magnetic reconnection between two sets of small-scale loops is reported. The successive slow reconnection changes the conditions around the reconnection area and leads to the rapid reconnection. (4) An ensemble of oscillating bright features rooted in a light bridge is observed and given a new name, light wall. The light wall oscillations may be due to the leakage of p-modes from below the photosphere.

The star formation rate (SFR) is a fundamental property of galaxies and it is crucial to understand the build-up of their stellar content, their chemical evolution, and energetic feedback. The SFR of galaxies is typically obtained by observing the emission by young stellar populations directly in the ultraviolet, the optical nebular line emission from gas ionized by newly-formed massive stars, the reprocessed emission by dust in the infrared range, or by combining observations at different wavelengths and fitting the full spectral energy distributions of galaxies. In this brief review we describe the assumptions, advantages and limitations of different SFR indicators, and we discuss the most promising SFR indicators for high-redshift studies.

Diverse variable phenomena in the Universe are periodic. Astonishingly many of the periodic signals present in stars have timescales coinciding with human ones (from minutes to years). The periods of signals often have to be deduced from time series which are irregularly sampled and sparse, furthermore correlations between the brightness measurements and their estimated uncertainties are common. The uncertainty on the frequency estimation is reviewed. We explore the astronomical and statistical literature, in both cases of regular and irregular samplings. The frequency uncertainty is depending on signal to noise ratio, the frequency, the observational timespan. The shape of the light curve should also intervene, since sharp features such as exoplanet transits, stellar eclipses, raising branches of pulsation stars give stringent constraints. We propose several procedures (parametric and nonparametric) to estimate the uncertainty on the frequency which are subsequently tested against simulated data to assess their performances.

We report on our ongoing project “Statistical studies of HII regions in the nearby extra-galaxies”. We present an overview of our detailed study of warm dust in the nearby Galaxy NGC 4321 (M100), measuring the flux values in the 4 Spitzer-IRAC bands of some 275 HII regions in M100. In addition, we present new measurements of the flux values in the 4 Spitzer-IRAC bands of a complete sample of 70 isolated luminous HII regions in NGC 4736 and 157 regions in NGC 4254. We study the relations between the Hα luminosity and the near-IR luminosity and temperature of HII regions in the three galaxies. We estimate the near-IR luminosities and compare them with the Hα luminosities from archive and literature sources. We find a linear relation between the Hα luminosity and the IRAC luminosity for the HII regions, but no apparent relation between the luminosity and the colour temperature of the regions in any of the three galaxies. The colour temperatures of regions especially in M100 and NGC4254 are confined to a surprisingly narrow range, with a small fraction forming a higher temperature tail to the distribution. These results give new insight into the size function and the 3D distribution of the dust in these regions, and we propose scenarios to explain them.

The origin of spiral structure in disks of galaxies remains an open question. One of the theories predicts that two-armed, grand design spiral arms originate from tidal interactions with another body. Using N-body simulations we find that a Milky Way-like galaxy can develop spiral arms due to tidal force from a cluster-size dark matter halo.

Late-type stars with thick convective zones and rapid rotations exhibit magnetic activity phenomena, such as starspots, plages, and flares. However, in many such kinds of eclipsing binaries, the details of the active phenomena are not well understood. In order to improve our understanding of stellar magnetic activities, we are carrying out an extensive study of the magnetic activities of eclipsing binaries by multi-color CCD photometry using several telescopes (SARA 90cm at KPNO, and NAOC 85cm and 60 cm telescopes at Xinglong). In this paper, we will present our preliminary results with revised orbital parameters, starspot parameters, and stellar flare events on DV Psc and BX Tri.

We investigated the stellar density substructures around four metal-poor globular clusters (NGC 6266, NGC 6626, NGC 6642, and NGC 6723) in the Galactic bulge. Wide-field near-infrared (JHKs) imaging data were obtained from WFCAM of UKIRT telescope. Field stars contamination around the globular clusters was reduced by using a statistical weighted filtering algorithm. Tidal stripping stellar substructures in the form of tidal tail (NGC 6266 and NGC 6626) or small density lobes/chunk (NGC 6642 and NGC 6723) were found around the four globular clusters in the two-dimensional density contour maps. We also find the overdensity features, which deviate from the theoretical models, in the outer region of radial density profiles. The observed results imply that the four globular clusters have experienced a strong tidal force or the bulge/disk shock effect of the Galaxy.

We present a study exploring the reliability of recovering the mass and velocity anisotropy profiles of dark matter haloes using the Schwarzschild method of modeling galaxies.

We present a set of time dependent chemical evolution models (based on the UMIST† astrochemistry 2012 code, Woodall et al. (2007); McElroy et al. (2013) for a range of initial physical cloud parameters: 10 K < T < 20 K; 103 cm−3 < n(H2) < 5 · 104 cm−3; 1 < AV < 10 and with estimated values of scaled interstellar ultraviolet radiation field. Our computation model included the full UMIST gas-phase reaction network for 467 species Garrod et al. (2008), Graedel et al. (1982). We compare our chemical model results with the relative abundances of: CO, CH, OH, HCO+, HCN, HNC, NH3, N2H+ and H2CO molecules. We find significant time dependent variations of the chemical ratios of: X(NH3/H2); X(HCO+/H2) and X(HCO+/NH3). We derive an ammonia age spread for the parts of TMC-1 (Taurus Molecular Cloud-1) that looks more complex than previous estimated showed. Age estimates based on X(NH3/H2); X(HCO+/H2) and X(HCO+/NH3) were compared in 3 selected positions, and were found to be very similar (with ±9% differences).

We undertake a comprehensive comparative test of seven widely-used spectral synthesis models using multi-band HST photometry of a sample of eight YMCs in two galaxies. We provide a first quantitative estimate of the accuracies and uncertainties of new models, show the good progress of models in fitting high-quality observations, and highlight the need of further comprehensive comparative tests.