Found 219 talks archived in Galaxies

Two competing effects appear to govern galaxy multiplicity (pairs orgroups) at low masses: while associations of low-mass haloes are naturally expected in a LCDM cosmology, galaxy formation within these haloes is thought to be rendered inefficient due to the action of several ionizing agents. Yet associations of dwarf galaxies are known to exist in the Local Volume, and their frequency appears to be unexpectedly high for LCDM expectations even in our own Local Group. Unfortunately, it is not yet well understood what role do interactions between low-mass galaxies play in determining their star formation histories, structural properties, and neutral gas content. Here I will present an investigation of the impact of dwarf-dwarf galaxy tidal interactions on their morphological and star formation properties. The UGC5205 close pair consists of two low-mass (M* ~ 5E7 Msun), late-type galaxies with a relative projected distance of only 10 kpc, and no nearby massive companions. I will show that these equal-mass interactions can be an important 'pre-processing' mechanism that acts before dwarfs are affected by a more massive central galaxy, profoundly impacting their star formation histories and morphologies.

In this talk I will show how we can study cosmolgy in a photometric redshift galaxy survey, by means of the angular clustering of galaxies. Previously to fit your data to a cosmological model, the need for a representative, clean and reliable galaxy catalog imposes many constrains in the selection of your data, from the day the data was taken, up to the final galaxy catalog used in the cosmological Analysis. I will try to introduce those issues that are most important for the analysis of galaxy clustering: data reduction and detection limit, catalog pruning, sample selection, photometric redshifts, star/galaxy separation and the need for a detailed angular and depth mask. Once a neat catalog is build upon the raw data of the survey, the cosmological analysis can start confidently. In this context, I will show as an example, the last cosmological results obtained from the DR8 SDSS-III photometric sample, conveniently corrected from systematic errors.

I will present the first Large Millimiter Telescope spectra of 4 nearby galaxies with known high star formation rates. The individual spectra were acquired with the Redshift Search Receiver, a 3 mm spectrograph that covers simultaneously the 3 mm band from 75 to 110 GHz. The spectra show rms temperatures of around 4 mK that allow us to detect not only common molecular species such as CO, HCN, HCO+, HCN, 13CO reported widely in the literature but also other more rare molecular transitions (HC3N, CN, CH3OH, CH3C2H) and even Hydrogen recombination lines (from H39alpha to H42alpha). We are making use of theoretical radiative transfer models to analize these spectra in order to understand the variations of the observed line ratios of different lines in galaxies classified as ultraluminous infrared galaxies where the star formation rate may be as high as 100 solar masses per year. These data will help to understand the physical conditions of the gas in regions that are forming stars very efficiently. The observed line ratios in star forming galaxies are also compared to those galaxies that is known to contain an AGN.

Based on the double exponential behaviour of the gas mass profile and on the O/H gradient, Robles-Valdez, Carigi & Peimbert (2013) built a sucessful chemical evolution model for M33. The model predicts that in the inner parts of M33 the star formation history follows an inside-out scenario, like M31 or the MW, but in the outer parts of M33 the star formation history follows an outside-in scenario, as dwarf galaxies of the Local Group.

 How does the group environment hamper star-formation in star-forming galaxies?

Abstract: We present the first results from the H-alpha Galaxy Groups Imaging Survey (HAGGIS), a narrow-band imaging survey of SDSS groups at z < 0.05 conducted using the Wide Field Imager (WFI) on the ESO/MPG 2.2 meter telescope and the Wide Field Camera (WFC) on the Issac Newton Telescope (INT). In total, we observed 100 galaxy groups with wide range of halo mass 10^12 - 10^14 M_sun in pairs of narrow-band filters selected to get continuum subtracted rest-frame H-alpha images for each galaxy in these groups. The excellent data allows us to detect H-alpha down to the 10^(-18) ergs/s/cm^2/arcsec^2 level. Here, we examine the role played by halo mass and galaxy stellar mass in deciding the overall star formation activity in star forming disks by comparing stacked H-alpha profiles of galaxies in different halo mass and stellar mass bins. With this preliminary study, we have found that the star-formation activity in star-forming galaxies decreases in larger halos compared to the field galaxies. Using median equivalent width profiles, we can infer how environmental processes affect star-forming galaxies differently at different radii.

As early as 10 Gyr ago, galaxies with more than 10^11 M* in stars already existed. While most of these massive galaxies must have subsequently transformed through on-going star formation and mergers with other galaxies, a small fraction (<0.1%) may have survived untouched till today. Searches for such relic galaxies, useful windows to explore the early Universe, have been inconclusive to date. In this talk, we will present the first case of a nearby galaxy, NGC1277 (at a distance of 73 Mpc in the Perseus galaxy cluster), which fulfils many criteria to be considered a relic galaxy. Using deep optical spectroscopy, we derive the star formation history along the structure of the galaxy: the stellar populations are uniformly old (>10 Gyr) with no evidence for more recent star formation episodes. The metallicity of their stars is super-solar ([Fe/H]=0.20+-0.04 with a smooth decline towards the outer regions) and alpha enriched ([alpha/Fe]=0.4+-0.1). This suggests a very short formation time scale for the bulk of stars of this galaxy. This object also rotates very fast (V_{rot}~300 km/s) and has a large central velocity dispersion (sigma>300 km/s). NGC1277 allows the explorations in full detail of properties such as the structure, internal dynamics, metallicity and initial mass function at ~10-12 Gyr back in time when the first massive galaxies were built.

Clusters grow by mergers, events which release huge quantities of energy and can produce massive outward-travelling shock waves that can have an important effect on cluster gas and galaxies. Giant radio relics form at these shock fronts, where accelerated electrons emit synchrotron radiation. Despite the great interest in relics, candidates with simple geometry, undisturbed morphology and high surface brightness are scarce. The complex interaction between the merger, the shock wave and gas is likely a fundamental driver of galaxy evolution. The effects of dense environments have been previously investigated for relaxed clusters, but never before in highly disturbed, merging clusters hosting a relic. The Sausage and the Toothbrush clusters are providing us with the chance to study this phenomenon and its effects on the relativistic particles and the cluster galaxies. In order to address many of the unanswered questions, we use a unique combination of facilities (GMRT, WSRT, INT) to obtain the first cluster-wide, multi-wavelength, multi-method analysis aimed at giving a complete picture of merging clusters hosting relics. We derive physical parameters such as the Mach number and injection spectral index for the diffuse sources in the field. We present index and curvature maps pinpointing spectral trends conclusive for shock acceleration of relativistic particles and test injection models such as the Jaffe-Perola and Kardashev-Pacholczyk. This analysis is fully complemented by an Halpha mapping of the cluster volume and outskirts. We provide the first direct test whether the shock drives or prohibits star formation to decipher the role of the merger in shaping the Halpha luminosity function.

The ALHAMBRA (Advance Large Homogeneous Area Medium Band Redshift Astronomical; Moles et al. 2008) survey has observed 8 different regions of the sky, including sections of the COSMOS, DEEP2, ELAIS, GOODS-N, SDSS and Groth fields using a new photometric system with 20 contiguous, ~300A width, filters covering the optical range, plus deep JHKs imaging. The observations, carried out with the Calar Alto 3.5m telescope using the wide field (0.25 deg2 FOV) optical camera LAICA and the NIR instrument Omega-2000, correspond to ~700hrs of on-target science images. The photometric system was specifically designed to maximize the effective depth of the survey in terms of accurate spectral-type and photometric redshift estimation along with the capability of identification of relatively faint emission lines.

The ALHAMBRA Gold catalogue corresponds to a subsample of ~100k bright galaxies (+20.000 stars in the galactic halo and ~1000 AGN candidates), photometrically complete down to magnitude I=23AB, with very accurate and reliable photometric redshift estimations.

Considering that the Spanish community will have privileged access to the data until Nov15th 2013, this seminar is intended to be a brief introduction to the potential (doable) science with the ALHAMBRA-survey.

Galaxies in different environments have different properties. In dense environments galaxies are more likely to be red, passive ellipticals than in less dense environments. This difference can be detected both on small and large-scale environments. In this talk, I will present results on galaxy populations in different environments on two scales: the group scale and the supercluster scale. The goal of our project is to find out if there are differences between massive galaxies in similar groups, but different large-scale environments. The results will tell if the evolution of galaxies is fully determined by the mass of their dark matter halo, or if the large-scale environment also play a role. 

Today we largely understand the large scale evolution of the Universe but we have only little knowledge of the small scale physics involved in forming and evolving the baryonic structure (gas, stars and dust) of galaxies. Dwarf galaxies are considerd to be the ideal ”galactic laboratories” to gain insight into the astrophysical processes governing galaxy evolution in general. The obvious main feature of a dwarf galaxy is, that it is small - about 1/10 of the Milky Way’s size. Their relatively shallow gravitational potential makes them very sensitive to the different (astro)physical processes that affect galaxy evolution and counteract gravity. Hence we can use these galaxies to try to understand and answer the questions we still have about how, when and why galaxies form stars, stop forming stars, and recycle stellar-synthesised elements in the interstellar medium. Experimenting in these “galactic laboratories” is of course confined to the virtual universe, which we do by running state- of-the-art Nbody-SPH simulations of dwarf galaxy formation and evolution. Due to their small dimensions, these can achieve much higher resolution and physical detail than any other type of galactic simulations. In this talk, I will discuss the main prop- erties/parameters determining the behaviour and appearance of the dwarf galaxy models, and use the results to compare with and explain observations.