Found 219 talks archived in Galaxies

Different components of galaxies are the result of internal and environmental processes during their lifetimes. Disentangling these processes is an important issue for understanding how galaxies form and evolve. In this context isolated galaxies provide a fruitful sample for exploring galaxies which have evolved mainly by internal processes (minimal merger/accretion/tidal effects). I will present the structural analysis performed as part of the AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies; http://www.amiga.iaa.es) project. The analysis of the stellar mass-size relation of our spiral galaxies reveals a larger size for disks in low-density environments, as well as a dependence of disk size on the number of satellites. A 2D bulge/disk/bar decomposition of SDSS i-band images was performed in order to identify the pseudobulges in our sample. We derived (g-i) bulge colors and find a large fraction of pseudobulges in the red sequence of early-type galaxies. The bluer pseudobulges in our sample tend to be located in those galaxies more affected by tidal interactions. The properties of the majority of bulges in isolated galaxies suggest that pseudobulges formed most of their mass at an early epoch, and that specific environmental events may rejuvenate pseudobulges.

One of the most widely researched topics in Extragalactic Astrophysics
in the last decades is how early-type galaxies have formed their stars
and assembled. In this context, we now have unequivocal observational
evidences about the existence of a numerous population of massive
galaxies which not only had assembled a considerable amount of stars
(~10^{^11} M_sun) by z~2, but were already evolving passively by that
time. These galaxies, the likely progenitors of nearby ellipticals,
are also quite compact in comparison with local galaxies of the same
mass. These result are mainly based on measurements designed to obtain
stellar masses and sizes, and our estimations of these parameters are
now quite robust. Now we need a more secure determination of how
exactly they formed and assembled their stellar mass in just 2-3 Gyr
(z>2). In other words, how was their Star Formation History and which
are the properties (age, metallicity, dust content) of their stellar
populations? And how could they end up with such high masses and small
sizes? In this talk, we will present our results about the SFH (mainly
ages and duty cycles) of massive galaxies at z=1-3 based on the
deepest spectro-photometric data ever taken. These data were gathered
by the Survey for High-z Absorption Red and Dead Sources (SHARDS), a
ESO/GTC Large Program aimed at obtaining R~50 optical spectra of
distant galaxies. This resolution is especially suited to measure
absorption indices such as D(4000), Mg_UV, the Balmer break,etc.. for
galaxies up to z~3 (merging our SHARDS data with HST/WFC3 grism
observations) or emission-line fluxes for faint targets up to
z~6. These measurements represent a big step forward for the robust
determination of the stellar population properties, providing a much
more certain characterization of the stellar content of distant
galaxies than the typical broad-band studies. Our results uniquely
allow to study the stellar content of red and dead galaxies at z~2 and
identify progenitors at higher redshifts, as well as helping to
constrain the models of galaxy formation.

Most massive galaxies have supermassive black holes at their centres, and the masses of the black holes correlate with properties of the host-galaxy bulge component. These empirical scaling relations are important for distinguishing between various theoretical models of galaxy evolution, and they furthermore form the basis for all black-hole mass measurements at large distances. Observations have shown that the mass of the black hole is typically 0.1 per cent of the mass of the stellar bulge of the galaxy. Our spectroscopic survey with the Hobby-Eberly Telescope of 1000 nearby galaxies revealed several compact lenticular galaxies with extremely high velocity dispersions. The first example is NGC1277, which is a small, Re=1kpc, compact, lenticular galaxy with a mass of 1.2×10^11 solar masses. From the stellar kinematics we determined that the mass of the central black hole is 10^10 solar masses, more than 10 per cent of its bulge mass. I will present HST images and IFU spectroscopy of a dozen more compact galaxies that all appear to host extremely big black holes and have Salpeter-like IMFs. These local systems, with distances less than 100 Mpc, could be the passively evolved descendents of the quiescent compact nugget galaxies found at z~2 and the >10e9 Msun quasars that are found at z>6.

Dwarf galaxies are a complex population. They comprise objects with young and old stellar populations, slow and fast rotation, as well as single- and multi-component structure. These characteristics show correlations with environmental density - we thus believe that dwarf galaxies hold a fossil record of how environment affected galaxy evolution. In this talk I will review and discuss recent progress on our understanding of dwarf galaxies in clusters, both from the observational and the modelling side. In particular, I will attempt to reconcile the proposed formation mechanisms of early-type dwarf galaxies - the most abundant population in clusters - with the continuous environmental influence predicted by cosmological simulations.

Majority of galaxies reside in groups and clusters where they are understood to evolve also through galaxy-galaxy interactions. Multiple mergers at the core of galaxy groups can develop a luminosity deficiency or gap, which is quantified as the difference between the luminosity of the two brightest galaxies in groups and clusters. This observable carries important information about the evolution of galaxy groups, for instance, there are indications that collapsed groups with a large luminosity gap, known as fossil groups, are associated with the halos that are relatively old. In a series of recent studies, employing X-ray, optical and radio observations complemented by cosmological simulations, we have utilised the luminosity gap to probe the formation scenarios for galaxies and specially the most luminous galaxies in groups and clusters, introduce a powerful age-date routine for galaxy groups, and also obtain clues about the AGN activities and the IGM heating.

1) López-Corredoira & Gutiérrez (2012, RAA, 12, 249): Extremely luminous QSOs exist at high redshift but they are absent at low redshift. Our analyses show that it is not due to any significant evolution of black hole masses or Eddington ratios for equal luminosity QSOs, so the problem can be translated into a "Why are not there QSOs with very high black hole masses at low redshift?". 2) López-Corredoira & Perucho (2012, A&A, 544, 56): The MOJAVE survey contains 101 quasars with a total of 354 observed radio components that are different from the radio cores, among which 95% move with apparent projected superluminal velocities with respect to the core, and 45% have projected velocities larger than 10c (with a maximum velocity 60c). Relativistic Doppler boosting explains these apparent anomalies, but it requires a huge average kinetic power to produce such powerful ejections: ~7×10^{47} erg/s, a significant portion of the Eddington luminosity and on the order of the bolometric luminosity. This amount is much higher than previous estimates of kinetic power on kpc-scales. 3) There are many other pending problems in QSOs in the literature (review at López-Corredoira 2011, IJAA, 1, 73): the different structure of the clouds along the QSO's line of sight and their tangential directions; the spatial correlation between QSOs and galaxies; inconsistencies in the AGN unification model; etc.

The nearby spiral galaxy M81 contains a population of 3 kinds of stellar clusters - super star clusters, globular clusters and fuzzy clusters. Over the past few years, we have taken GTC longslit spectra of around 20 of these clusters, with the intention of obtaining their spectroscopic ages. These spectra have allowed us to understand the nature of the brightest globular cluster in this galaxy. In addition, we were able to address the problem of the origin of the fuzzy clusters. In the talk, I will summarize the results we have obtained so far.

DESI is a massively multiplexed fiber-fed spectrograph that will make the next
major advance in dark energy in the timeframe 2018-2022. On the Mayall
telescope, DESI will obtain spectra and redshifts for tens of millions of
galaxies and cuasars with 5,000 fiber postioner robots, constructing a
3-dimensional map spanning the nearby universe to 10 billion light years. DESI
is supported by the US Department of Energy Office of Science to perform this
Stage IV dark energy measurement using baryon acoustic oscillations and other
techniques that rely on spectroscopic measurements. Spain has a major role in
DESI with the construction of the Focal Plate and the development of the fiber
positioners. I will give an overview of the DESI science, instrument, and Spain
participation in the project.

Galaxy clusters are the perfect places to study both the always controversial nature vs nurture problem and the still not well understood evolution that galaxies follow. By studying the properties of the galaxies at different locations of the cluster we can assess the first problem, while studying the same properties over cosmic time, helps constraining the different proposed evolutionary theories. In this work we have focused in an intermediately-redshift rich cluster, RX J0152.7-1357 (z=0.83), by fully characterizing its stellar population properties with new state-of-the-art tools . By this means, we have derived for the first time in such a high-z cluster the ages, metallicities, abundance patterns and Star Formation Histories of the cluster ETGs on an individual galaxy-basis . The relations that these properties follow with galaxy velocity dispersion allow us to discuss a passive evolution scenario with respect to a cluster at z~0. Our results favor a downsizing picture where the relation between the position within the cluster, the velocity dispersion and the type of star formation history of the galaxies allow us to better understand the cluster evolution. We find that the most massive galaxies evolve passively while the lower-mass ones, generally located at the outskirts of the cluster, experience a more extended star formation history related to their later incorporation in the cluster.