We examine the long-term stability (on decade-like timescales) of optical ‘high polarisation’ (HP) state with ${p_{opt}}$ ${> 3\%}$ , which commonly occurs in flat-spectrum (i.e., beamed) radio quasars (FSRQs) and is a prominent marker of blazar state. Using this clue, roughly a quarter of the FSRQ population has been reported to undergo HP $\leftrightarrow$ non-HP state transition on year-like timescales. This work examines the extent to which HP (i.e., blazar) state can endure in a FSRQ, despite these ‘frequent’ state transitions. This is the first attempt to verify, using purely opto-polarimetric data for a much enlarged sample of blazars, the recent curious finding that blazar state in individual quasars persists for at least a few decades, despite its changing/swinging observed fairly commonly on year-like timescales. The present analysis is based on a well-defined sample of 83 radio quasars, extracted from the opto-polarimetric survey RoboPol (2013–2017), for which old opto-polarimetric data taken prior to 1990 could be found in the literature. By a source-wise comparison of these two datasets of the same observable ( $p_{opt}$ ), we find that $\sim$ 90% of the 63 quasars found in blazar state in our RoboPol sample, were also observed to be in that state about three decades before. On the other hand, within the RoboPol survey itself, we find that roughly a quarter of the blazars in our sample migrated to the other polarisation state on year-like timescales, by crossing the customary $p_{opt}$ = 3% threshold. Evidently, these relatively frequent transitions (in either direction) do not curtail the propensity of a radio quasar to retain its blazar (i.e., HP) state for at least a few decades. The observed transitions/swings of polarisation state are probably manifestation of transient processes, like ejections of synchrotron plasma blobs (VLBI radio knots) from the active nucleus.

We investigate how the properties of spiral arms relate to other fundamental galaxy properties. To this end, we use previously published measurements of those properties, and our own measurements of arm-interarm luminosity contrasts for a large sample of galaxies, using 3.6μm images from the Spitzer Survey of Stellar Structure in Galaxies. Flocculent galaxies are clearly distinguished from other spiral arm classes, especially by their lower stellar mass and surface density. Multi-armed and grand-design galaxies are similar in most of their fundamental parameters, excluding some bar properties and the bulge-to-total luminosity ratio. Based on these results, we discuss dense, classical bulges as a necessary condition for standing spiral wave modes in grand-design galaxies. We further find a strong correlation between bulge-to-total ratio and bar contrast, and a weaker correlation between arm and bar contrasts.

The VISCACHA (VIsible Soar photometry of star Clusters in tApii and Coxi HuguA†) Survey is an ongoing project based on deep and spatially resolved photometric observations of Magellanic Cloud star clusters, collected using the SOuthern Astrophysical Research (SOAR) telescope together with the SOAR Adaptive Module Imager. So far we have used >300h of telescope time to observe ∼150 star clusters, mostly with low mass (M < 104M⊙) on the outskirts of the LMC and SMC. With this high-quality data set, we homogeneously determine physical properties using deep colour-magnitude diagrams (ages, metallicities, reddening, distances, mass, luminosity and mass functions) and structural parameters (radial density profiles, sizes) for these clusters which are used as a proxy to investigate the interplay between the Magellanic Clouds and their evolution. We present the VISCACHA survey and its initial results, based on our first two papers. The project’s long term goals and expected legacy to the community are also addressed.

The Fornax Deep Survey (FDS) is a multi-band imaging survey of the Fornax cluster of galaxies, executed with the ESO VLT Survey Telescope (VST). The survey is designed to reach unprecedented surface brightness and point-source magnitude depth over one virial radius of the cluster. The scientific objectives of the survey are numerous: the study of the galaxy luminosity function, derivation of galaxy scaling relations, determination of the properties of compact stellar systems, an accurate determination of distances and 3-D geometry of the Fornax cluster, analysis of diffuse stellar light and galaxy interactions, etc.

In this contribute we give an overview on the interest of the survey on globular clusters (GC) populations, and present a report the status of the study of GCs also providing some preliminary results of our analysis, with particular regard to the two-dimensional distribution of GC candidates over ∼20 sq. degree area of Fornax centered on NGC 1399.

We present our new, spatially-resolved, photometry in FUV and NUV from images obtained by GALEX, and IRAC1 (3.6 μm) photometry obtained by the Spitzer Space Telescope. We analyzed the surface brightness profiles μFUV, μNUV, μ[3.6], as well as the radial evolution of the (FUV-NUV), (FUV - [3.6]), and (NUV - [3.6]) colors in the Spitzer Survey of Stellar Structures in Galaxies (S4G) galaxies (d < 40 Mpc) sample. We defined the GALEX Blue Sequence (GBS) and GALEX Red Sequence (GBR) from the (FUV - NUV) versus (NUV - [3.6]) color-color diagram, populated by late-type star forming galaxies and quiescent early-type galaxies respectively. While most disk becomes radially bluer for GBS galaxies, and stay constant for GRS galaxies, a large fraction ( > 50%) of intermediary GALEX Green Valley (GGV) galaxies’ outer disks are becoming redder. An outside-in quenching mechanism such as environmentally-related mechanisms such as starvation or ram-pressure-stripping could explain our results.

We show how present-day 10 meter class telescopes can provide broadband imaging 1.5-2 mag deeper than most previous results within a reasonable amount of time ( ~ 8h on source integration). We illustrate the ability of the 10.4 m Gran Telescopio de Canarias (GTC) telescope to produce imaging with a limiting surface brightness of 31.5 mag/arcsec2 (3σ in 10 × 10 arcsec boxes). We explore the stellar halos of nearby galaxies obtaining surface brightness radial profiles down to μr ~ 33 mag/arcsec2. This depth is similar to that obtained using star counts techniques of Local Group galaxies, but is achieved at a distance where this technique is unfeasible.

Models of galaxy formation in a hierarchical universe predict substantial scatter in the halo-to-halo stellar properties, owing to stochasticity in galaxies’ merger histories. Currently, only few detailed observations of galaxy’s halos are available, mainly for the Milky Way and M31. The Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters (GHOSTS) HST survey is the largest study to date of the resolved stellar populations in the outskirts of disk galaxies and its observations offer a direct test of model predictions. Here we present the results we obtain for six highly inclined nearby Milky Way-mass spiral galaxies. We find a great diversity in the properties of their stellar halos.

I review briefly some dynamical models of structures in the outer parts of disc galaxies, including models of polar rings, tidal tails and bridges. I then discuss the density distribution in the outer parts of discs. For this, I compare observations to results of a model in which the disc galaxy is in fact the remnant of a major merger, and find good agreement. This comparison includes radial profiles of the projected surface density and of stellar age, as well as time evolution of the break radius and of the inner and outer disc scale lengths. I also compare the radial projected surface density profiles of dynamically motivated mono-age populations and find that, compared to older populations, younger ones have flatter density profiles in the inner region and steeper in the outer one. The break radius, however, does not vary with stellar age, again in good agreement with observations.

The outskirts of early-type galaxies (ETGs) play a key role to shed light on the mass assembly of galaxies. Deep imaging has become one of the main tools to study these regions, however artificial halos caused by bright sources hampers the photometric analysis. To get around the problem, extended PSFs are built and deconvolution is performed on images.

Faint dwarf galaxies such as those found around the Milky Way (MW) display the largest known dynamical mass-to-light ratios (up to several 100s M⊙/L⊙). However, tidal interaction with the MW may impact the dynamical equilibrium in the outer parts of some of these objects, and partly affect the derived dynamical M/L. Assessing this is crucial for the study of the dark matter content of these galaxies. A clear sign of ongoing tidal disturbance would be the presence of tidal tails. These are expected to be low surface brightness features, hence difficult to detect from star counts in systems where contamination is also present, e.g. from foreground MW stars. At present we have searched for these sorts of tidal features in the Sextans dwarf spheroidal galaxy (dSph), by adopting the Matched Filter Method (e.g. Rockosi et al. 2002), a very efficient technique to decontaminate stellar density maps with a high ratio of contamination versus source density (dwarf galaxies outer regions or ultra faint dwarf galaxies). We also calculate structural parameters from the position of stars without requiring spatial binning (Richardson et al. 2011), through a Bayesian MCMC (Foreman-Mackey et al. 2013).

We present the results from the state-of-the-art wide-field survey of the M81 galaxy group that we are conducting with Hyper Suprime-Cam on Subaru Telescope. Our photometry reaches about 2 mag below the tip of the red giant branch (RGB) and reveals the spatial distribution of both old and young stars over an area of 5°2 around the M81. The young main-sequence (MS) stars closely follow the HI distribution and can be found in a stellar stream between M81 and NGC 3077 and in numerous outlying stellar associations. Our survey also reveals for the first time the very extended (>2 × R25) halos of RGB stars around M81, M82, and NGC 3077, as well as faint tidal streams that link these systems. The gravitational interactions between M81, M82 and NGC 3077 galaxies induced star formation in tidally stripped gas, and also significantly perturbed the older stellar components leading to disturbed halo morphologies.

We report about an ongoing study of the evolution of 24 S0s with UV-bright ring/arm-like structures observed with SWIFT-UVOT and interpreted via SPH simulations with chemo-photometric implementation.

Models of galaxy formation in a hierarchical universe predict substantial scatter in the halo-to-halo stellar properties, owing to stochasticity in galaxies' merger histories. Currently, only few detailed observations of stellar halos are available, mainly for the Milky Way and M31. We present the stellar halo color/metallicity and density profiles of red giant branch stars out to ~60 kpc along the minor axis of six massive nearby Milky Way-like galaxies beyond the Local Group from the Galaxy Halos, Outer disks, Substructure, Thick disks and Star clusters (GHOSTS) HST survey. This enlargement of the sample of galaxies with observations of stellar halo properties is needed to understand the range of possible halo properties, i.e. not only the mean properties but also the halo-to-halo scatter, what a ‘typical’ halo looks like, and how similar the Milky Way halo is to other halos beyond the Local Group.

We studied the unbiased optical brightness distribution which was calculated from the survival analysis of host galaxies (HGs) data and its relationship with the Swift GRB data of the host galaxies observed by the Keck telescope. Based on the sample obtained from merging the Swift GRB table and the Keck optical data we also studied the dependence of this distribution on the GRB's data. Finally, we compared the HGs distribution with standard galaxies distribution of the DEEP2 redshift survey and checked the result with the VIPERS catalogue too.

We present the results of a multi-wavelength photometric study of the high redshift supercluster RCS2319+00. RCS2319+00 is a high-redshift (z ~ 0.9) supercluster comprising three spectroscopically confrmed cluster cores discovered in the Red Sequence Cluster Survey (RCS) (Gladders & Yee 2005). Core proximities and merger rates estimate coalescence into a 1015M⊙ cluster by z ~ 0.5 (Gilbank et al. 2008). Spectroscopic studies of the system have revealed over 300 supercluster members located in the cores and several infalling groups (Faloon et al. 2013). RCS2319 presents a diverse range of dynamical systems and densities making it an ideal laboratory in which to study the effects of environment on galaxy properties.

Imaging in optical and near infrared (griz' from MegaCam, JKs from WIRCam, both at CFHT), as well as 3.6 μm and 4.5μm from IRAC have enabled the assembly of a large photometric catalogue. Coupled with an extensive spectroscopic survey (Faloon et al. 2013) providing nearly 2400 redshifts across the field, photometric redshifts were determined using the template fitting code EAZY (Brammer et al. 2008). Nearly 80 000 photometric redshifts were measured providing a sample of nearly 3000 cluster members.

To investigate effects of global environment, analysis was done utilizing a friend-of-friends group finding algorithm identifying several large and small infalling groups along with the three cluster cores. The cores are found to be dominated by massive, red galaxies and the field galaxies are populated by low mass, blue galaxies, as is the case in the local universe. Interestingly, the large groups exhibit intermediate properties between field and core populations, suggesting possible pre-processing as they are being accreted into the core halos.

Relative fifth-nearest neighbour overdensity, log(1+δ5), is used as a proxy for local environment to investigate environmental dependence on galaxy colour. While there is an overall dependence of colour on local density, when controlled for stellar mass the dependence largely disappears. Indeed, galaxy mass is the dominant factor in determining colour, with local density a secondary effect only noticeable in lower mass galaxies at the 3 σ level for both colour and red fraction.

RCS2319+00 presents a rare opportunity to probe many different densities and environments all located within the same object. We're able to investigate how galaxy evolution is affected by the environment, from field galaxies to infalling to groups to dense cluster cores, as well as the different density regions within each environment.

Quiescent galaxy candidates are typically identified by their low unobscured star formation rates from deep field photometric surveys. However, their selection technique relies on the assumption of a universal dust attenuation curve. It is important to verify the selection through independent SFR indicators at longer wavelengths. Current mid-, far-infrared and radio surveys are limited to detecting only galaxies with very strong star formation or AGN activity. Here, I present the first comprehensive stacking results across mid-, far-infrared and radio wavelengths using Spitzer, Herschel and VLA data in the COSMOS field (Man et al. 2014). We find that the rest-frame NUV-r and r-J color criteria, combined with low 24 μm emission, provides a robust selection of truly quiescent galaxies out to z = 3. Additionally, we find evidence of radio emission in excess of the expected total star formation in quiescent galaxies at z ~ 0-1.5, indicative of a ubiquitous presence of low-luminosity radio AGN among them.

We present a systematic photometric search for spectroscopically confirmed anomalously red galaxies members of 748 low redshift clusters between 0.03 z 0.17 from the SDSS-C4 cluster catalogue (Miller et al. 2005). For each cluster we spectroscopically determine cluster membership, construct a colour-magnitude diagram and fit the red sequence using a robust bi-weight fit. We define an “anomalously red galaxy” as having a (g - r) colour of greater than 3σ redward of the fitted cluster colour-magnitude relation. We find that of 7485 galaxies at r ≤ 17.77 in (g - r), 7 galaxies are anomalously red – 0.0935 per cent of all galaxies in our sample. We show that two of the red outliers are caused by red contamination from nearby sources and are therefore not intrinsically anomalous red. However, 5 have no underlying cause to be so red and we speculate that they may have a high internal dust content. These intrinsically red galaxies are rare – comprising no more than 0.0668 per cent of all cluster galaxies. Most are morphologically early type galaxies, with a few probable late type galaxies that are viewed edge-on and one low surface brightness late type. One of our anomalously red galaxies appears to be a dust-shrouded starburst and we speculate that this may be a unique galaxy amoungst this galaxy set.

The majority of Fermi-LAT detected (2FGL) sources are AGN, mostly blazars. However, the second largest category in the 2FGL are unassociated sources (~30% or 575 sources), whose multi-wavelength counterpart is either inconclusive or absent. Follow-up observations and archival data at X-ray, optical, and radio frequencies suggest that many unassociated 2FGL sources are strong candidates to be AGN. Typical observed characteristics of 2FGL detected AGN include variability at all frequencies and a spectral energy distribution (SED) with two “bumps”; a low-frequency synchrotron peak in the radio to optical/X-ray region and a high-frequency peak, possibly due to synchrotron self-Compton or Inverse Compton processes, that extends up to TeV energies. We present optical follow-up observations of a sample of Fermi unassociated sources with one or more potential X-ray counterparts detected within the LAT error circle.

Several clues for understanding the nature and evolution of galaxies can be gained by studying galactic structures and their evolution with time and environment. However, even for nearby galaxies, detailed structural decomposition is not a straightforward task. Choosing the number of structural components and the limits placed on their parameters can have a large effect on the derived characteristics of galaxies. For distant galaxies, structural analysis is further hampered by the spatial resolution limits of the imaging. However, by using a relatively robust two-component bulge+disk modelling, galaxies in the nearby Universe can be compared to distant galaxies for tracing signs of evolution in the extracted structures. We start such a study by analysing first a well observed nearby sample of galaxies, using ∼600 targets from the CALIFA survey. We show that even in this small sample of nearby galaxies, the effects of environmental density are already well apparent.

The intermediate results of the ongoing study of deep samples of ∼200 galaxies residing in nearby voids, are presented. Their properties are probed via optical spectroscopy, ugri surface photometry, and HI 21-cm line measurements, with emphasis on their evolutionary status. We derive directly the hydrogen mass M(HI), the ratio M(HI)/LB and the evolutionary parameter gas-phase O/H. Their luminosities and integrated colours are used to derive stellar mass M* and the second evolutionary parameter – gas mass-fraction fg). The colours of the outer parts, typically representative of the galaxy oldest stellar population, are used to estimate the upper limits on time since the beginning of the main SF episode. We compare properties of void galaxies with those of the similar late-type galaxies in denser environments. Most of void galaxies show smaller O/H for their luminosity, in average by ∼30\%, indicating slower evolution. Besides, the fraction of ∼10\% of the whole void sample or ∼30\% of the least luminous void LSB dwarfs show the oxygen deficiency by a factor of 2–5. The majority of this group appear very gas-rich, with fg ∼(95–99)%, while their outer parts appear rather blue, indicating the time of onset of the main star-formation episode of less than 1–4 Gyr. Such unevolved LSBD galaxies appear not rare among the smallest void objects, but turned out practically missed to date due to the strong observational selection effects. Our results evidense for unusual evolutionary properties of the sizable fraction of void galaxies, and thus, pose the task of better modelling of dwarf galaxy formation and evolution in voids.