Search

The Galaxy Zoo project has provided quantitative visual morphologies for over a million galaxies, and has been part of a reinvigoration of interest in the morphologies of galaxies and what they reveal about galaxy evolution. Morphological information collected by GZ has shown itself to be a powerful tool for studying galaxy evolution, and GZ continues to collect classifications - currently serving imaging from DECaLS in its main site, and running a variety of related projects hosted by the Zooniverse; the citizen science platform which came out of the early success of GZ. I highlight some of the results from the last twelve years, with a particular emphasis on linking morphology and dynamics, look forward to future projects in the GZ family, and provide a quick start guide for how you can easily make use of citizen science techniques to analysis your own large and complex data sets. [ABSTRACT FROM AUTHOR]

In this paper we study the relations between the main characteristics of groups and clusters of galaxies using the archival data of the SDSS and 2MASX catalogs. We have developed and implemented a new method of determining the size of galaxy systems and their effective radius which contains half of the galaxies and not half the luminosity, since the luminosity of the brightest galaxy in a group can account for over 50% of the total luminosity of the group. The derived parameters (log L , log R , and log σ ) for 94 systems of galaxies (0.0038 < z < 0.09) determine the Fundamental Plane (FP), which, with a scatter of 0.15, is similar in form to the FP of galaxy clusters obtained by Schaeffer et al. (1993) and D'Onofrio et al. (2013) with other methods and for different bands. We show that the FP in the near-infrared region (NIR) for 94 galaxy systems has the form of L ∝ $$R_e^{0.70 \pm {{0.13}_\sigma }1.34 \pm 0.13}$$ , whereas in x-rays it has the form of- L ∝ $$R_e^{1.15 \pm {{0.39}_\sigma }2.56 \pm 0.40}$$ . The form of the FP for groups and clusters is consistent with the FP for early-type galaxies determined in the same way. The form of the FP for galaxy systems deviates from the shape that one would expect from virial predictions. Adding the mass-to-light ratio as a fourth independent parameter has little effect on this deviation, but decreases the scatter of the FP for a sample of rich galaxy clusters by 12%. [ABSTRACT FROM AUTHOR]

Intermediate surface brightness (ISB) galaxies are less numerous than their counterparts at high and low surface brightness (HSB and LSB). Investigating ISB characteristics from a sample from the Spitzer Survey of Stellar Structure in Galaxies survey, complete down to MB = -16, we find that they have intermediate stellar, gas and baryonic masses and on average as much gas as stars. They lie on the (baryonic) Tully-Fisher relation between HSBs and LSBs, although they present a higher scatter than the latter. Their stellar to baryonic mass ratios have intermediate values unlike their condensed baryonic fractions. By comparing their environments, as classified by the eigenvalues of the velocity shear tensor of local constrained simulations, ISBs have a 5-10 per cent probability higher (smaller) to be in sheets (filaments) with respect to HSBs and LSBs. Additionally, for galaxies in filaments (with close neighbours), the mass and μ0 are correlated at 2.5 (2)σ more than for those in sheets. ISBs live in regions where the divergence of the velocity field is smaller than where HSBs and LSBs live, a result at more than 50 per cent significance. ISBs may exist as an unstable transition state between LSBs and HSBs, the low flow activity environment maximally encouraging their formation. Interaction events altering the central baryon fraction could happen at a lower rate in these less dense environment, whilst in the higher density environments the LSBs are primarily satellite galaxies, whose accretion is sufficiently constrained that it fails to promote them to HSBs. [ABSTRACT FROM AUTHOR]

Context. Some observations indicate that the MilkyWay has two inner components, a bulge and a long bar, which present a misalignment of Δα≃ 20° that is against the predictions of some theoretical models that are based on numerical simulations. Aims. We wish to determine whether this misalignment between the bar and the bulge can be observed in barred galaxies other than the Milky Way. Methods. Each galaxy of our sample was decomposed based on its Ks-band 2MASS image by fitting and modelling in a threedimensional (3D) space the following components: a disc, a bar, and a bulge. The χ2 goodness-of-fit estimation allowed retrieving the best-fit angle values for the bar and the bulge to detect any misalignment. Results. From the 3D decomposition of six barred galaxies, we have detected at least three galaxies (NGC 2217, NGC 3992, and NGC 4593) that present a significant misalignment between the bar and the bulge of Δα > 20°. [ABSTRACT FROM AUTHOR]

Using three volume-limited samples of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6), we have investigated how other properties of galaxies depend on the environment at fixed luminosity. At fixed luminosity, we still observe strong environmental dependence of g - r color, concentration index, and morphology of galaxies: red, highly concentrated, and early type galaxies exist preferentially in the densest regions of the universe, while blue, poorly concentrated, and late type galaxies are located preferentially in low density regions. This shows that luminosity is not fundamental in correlations between galaxy properties and the environment. [ABSTRACT FROM AUTHOR]

The star formation history (SFH) of galaxies is a principle uncertainty in SED modeling, and simple parameterizations of the SFH in typical SED fitting techniques may introduce biases in the resulting derived parameters. It is possible to constrain the SFH of galaxies more tightly through the observations of resolved stellar colour-magnitude diagrams with HST. This work is a first attempt to combine constraints on galaxy SFH from resolved stars with broadband SED modeling from the UV to the IR. This combination allows for the effects of different realistic SFHs on the SED to be quantified. [ABSTRACT FROM PUBLISHER]

We have used the Parkes Multibeam system and the Sloan Digital Sky Survey to assemble a sample of 195 galaxies selected originally from their H i signature to avoid biases against unevolved or low surface brightness objects. For each source nine intrinsic properties are measured homogeneously, as well as inclination and an optical spectrum. The sample, which should be almost entirely free of either misidentification or confusion, includes a wide diversity of galaxies ranging from inchoate, low surface brightness dwarfs to giant spirals. Despite this diversity there are five clear correlations among their properties. They include a common dynamical mass-to-light ratio within their optical radii, a correlation between surface brightness and luminosity and a common H i surface density. Such correlation should provide strong constrains on models of galaxy formation and evolution. [ABSTRACT FROM AUTHOR]

Blind HI surveys provide a census of galaxies in the local universe that is unbiased by their optical properties. Even the Arecibo Dual-Beam Survey with a sample of only 265 galaxies discovered many low surface brightness galaxies and one galaxy with no obvious stellar component. Overall the galaxies in this survey display a diverse range of gas-to-stellar properties. The environment in which a galaxy resides is shown to be one of the factors responsible for this diversity, but it is not the only one. Clearly there are other factors affecting the complex processes responsible for the conversion of gas into stars rapidly in some galaxies, slowly in others, and rapidly in the center while slowly in the outskirts in still other galaxies. Nevertheless, even the inefficient star formation observed in a large fraction of the gas-rich galaxies appears to be a significant contributor to the overall star-formation rate density locally and therefore an important driver of galaxy evolution that must be understood. We focus on a discussion of the stellar and star formation properties in a 21 cm selected sample of galaxies because it is these measurements that contain the most information about the nature of star formation in galaxies. [ABSTRACT FROM PUBLISHER]

I will discuss the connection between the luminosity function of a population of high-mass X-ray binaries in a galaxy and the star formation rate in the this galaxy. The understanding of this connection provides on the one hand an independent measure of an important galaxy property, and on the other hand new insights into populations of high-mass X-ray binaries. In particular, observations with the Chandra X-ray telescope are uniquely suited to investigate the X-ray part of this connection and I will present examples of this. [ABSTRACT FROM PUBLISHER]

Galaxy bimodality is caused by the bulge-disc nature of galaxies as opposed to two distinct galaxy classes. This is evident in the colour-structure plane which clearly shows that elliptical galaxies (bulge-only) lie in the red compact peak and late-type spiral galaxies (disc-dominated) lie in the blue diffuse peak. Early-type spirals (bulge plus disc systems) sprawl across both peaks. However after bulge-disc decomposition the bulges of early-type spirals lie exclusively in the red compact peak and their discs in the blue diffuse peak (exceptions exist but are rare, e.g., dust reddened edge-on discs and blue pseudo-bulges). Movement between these two peaks is not trivial because whilst switching off star-formation can transform colours from blue to red, modifying the orbits of ~1 billion stars from a planar diffuse structure to a triaxial compact structure is problematic (essentially requiring an equal mass merger). We propose that the most plausible explanation for the dual structure of galaxies is that galaxy formation proceeds in two stages. First an initial collapse phase (forming a centrally concentrated core and black hole), followed by splashback, infall and accretion (forming a planar rotating disc). Dwarf systems coule perhaps follow the same scenario but the lack of low luminosity bulge-disc systems would imply that the two components must rapidly blend to form a single flattened spheroidal system. [ABSTRACT FROM PUBLISHER]