Found 217 talks archived in Galaxies

The importance of Luminous and Ultraluminous infrared galaxies (U/LIRGs) in the context of the cosmological evolution of the star-formation has been well established in the last decades. They have been detected in large numbers at high-z (z>1) in deep surveys with Spitzer and Herschel, and they seem to be the dominant component to the star formation rate (SFR) density of the Universe beyond z~2. Although rare locally, nearby U/LIRGs are valuable candidates to study extreme cases of compact star-formation and coeval AGN. In particular, the study of local U/LIRGs using near-IR integral field spectroscopic techniques allows us to disentangle the 2D distribution of the gas and the star-formation using high spatial resolution, and characterise dust-enshrouded, spatially-resolved star-forming regions with great amount of detail. In that context, we are carrying on a comprehensive 2D IFS near-IR survey of local 10 LIRGs and 12 ULIRGs, based on VLT-SINFONI observations. I will review different topics on the spatially resolved study of the ISM and the star-formation at different spatial scales. I will focus on the analysis of the multi-phase gas morphology and kinematics, and on the study of the spatially-resolved distribution of the extinction-corrected star-formation rate (SFR) and star-formation rate surface density (ΣSFR). In particular, I will present some recent results on the characterization of individual star-forming regions, in terms of their sizes and Paα luminosities.

The immediate surroundings of our Milky Way galaxy are home to a number of dwarf galaxies, whose variety in shape, size, spatial location and velocity tells us that these Galactic satellites all have different tales to tell. While some look round, pristine and undisturbed, others have disturbed morphologies or show gradients in their metallicity, while yet others have unusual kinematic features or clearly show their dissolution into a stellar stream. Very few of them contain significant levels of gas, also prompting the question of what mechanism is responsible for stripping out their gas content. This talk will explore the eclectic mix of Milky Way dwarf galaxies and what their properties can reveal to us about their different stories, and also what they can collectively tell us of our own Galaxy. I will also discuss how looking at the Galactic vicinity is aiding us, via this population of Galactic satellites, in the increasingly popular area of near-field cosmology.

Little is known about the mid-infrared (MIR) polarization at high-angular resolution of Active Galactic Nuclei (AGN), however, the polarimetric mode of CanariCam on the 10.4-m Gran Telescopio CANARIAS has opened a new window to reveal its core. We have found a variety of results: 1) A Highly polarized synchrotron emission in the core of Cygnus A; 2) a very complex MIR polarization structures in and around the core of NGC 1068; and 3) a very low polarized core of Mrk 231. In this talk, I will present new CanariCam polarimetric results on several AGN which provide key information on our understanding of the AGN structure and jet formation.

 I will present a multiwavelength study of a large MIPS selected galaxies and satisfy a certain IRAC color criterion. Stellar population modeling and IRS spectra together demonstrate that the double criteria used to select this sample have efficiently isolated massive star-forming galaxies at /z/ ~ 1.9. This is the first starburst (SB)-dominated ultraluminous infrared galaxies (ULIRG) sample at high redshift with total infrared luminosity measured directly from Spitzer, Herschel FIR and millimeter photometry, and as such gives us the first accurate view of broadband spectral energy distributions for SB galaxies at extremely high luminosity and at all wavelengths. The HST images in optical and NIR bands show that most objects have very extended morphologies in the rest-frame ultraviolet and optical band, thus extended distribution of PAH molecules. We conclude that objects in this sample are ULIRGs powered mainly by SB; and the total infrared luminosity density contributed by this type of objects at /z/ ~ 1.9.

Our Universe is filled with a mind-blowing diversity and different types and appearances of galaxies. Finding out about how they formed and evolved is one of the most challenging tasks in astronomy. When looking about 10 billion years back, to an epoch about 3 billion years after the big bang, we can see galaxies at earlier stages of their lives. In this talk, studies of different kinds of galaxies in the early universe will be presented. Two examples of the very intriguing population of massive quiescent z~2 galaxies were analyzed in terms of their stellar populations and morphologies. As the spectroscopic sample is still small, especially for galaxies at the faint end of the luminosity function, we make use of the biggest available "telescopes" in the universe: We search for red z~2 galaxies whose apparent brightnesses have been boosted by the Gravitational Lensing effect of intermediate redshift galaxy clusters with available mass models. Our findings indicate older ages for these galaxies than expected. Also, their remarkable compactness was corroborated. Furthermore, I'm going to present a study of a special case of so-called Damped Lyman-alpha Absorbers (DLAs), with two intervening galaxies in the line of sight of a higher-redshift QSO, which is also one example of only about a dozen known galaxy counterparts of a DLA. It fits into the emerging paradigm that galaxies which are responsible for higher metallicity DLAs are more massive and luminous than typical DLA galaxies. Motivated by that particular discovery, during the past few years we have undertaken a survey targeting candidate dust-reddened quasars missing in the sample from Sloan Digital Sky Survey. Spectroscopic follow-up with the NOT and the NTT has demonstrated a very high success rate of our selection (>90%). The main motivation is to search for quasars reddened by foreground dusty galaxies and we have found several such examples. We have also serendipitously found quasars with abnormal, very UV-steep extinction curves as well as a large number of broad absorption line quasars (BALs). The latter allow us to study the dependence of the BAL QSO population on redshift, reddening and luminosity. The results show a strong evolution of the BAL QSO fraction with cosmic time, with a peak at z~2.5 where several quantities in the Universe are also found to peak or vary. In addition,the dependence of this fraction with reddening and luminosity provides new constraints on the models for broad absorption origin in quasars. We are currently carrying out a pilot study of a search for even redder quasars selected from a combination of SDSS, UKIDSS and WISE photometry with the aim of selecting very dust-obscurred quasars or high-redshift BALs at z>2. Preliminary results from the first run et the NOT in March 2015 of the brightest candidates show very promising results which will also be briefly shown in the talk.

Recent works show that the restframe colours of X-ray selected AGN host galaxies at z~1 are no different from those of inactive galaxies once stellar mass selection effects are taken into account. However, there is a clear deficit of AGN among quiescent galaxies, and the average star formation rates of AGN hosts are comparable or higher than those of inactive star-forming galaxies. These apparently contradictory findings could be a consequence of higher extinction in star-forming AGN hosts compensating for their younger stellar populations in observed colours. In this talk I will present a new method of extinction correction that breaks the degeneracy with stellar age and metallicity by comparing the restframe U-V colour with measurements of the Dn(4000) index on intermediate band photospectra from SHARDS. I'll show that the distribution of extinction corrected U-V colours and Dn(4000) for AGN hosts at z<1 is significantly different from that of comparison samples of inactive galaxies, with a clear deficit of AGN in intrinsic red galaxies and a higher prevalence among those with intermediate age stellar populations.

Evidence is mounting for the presence of complex low surface brightness structures in the outer regions of galaxies. While the most spectacular examples are provided by systems hosting coherent debris streams, the most common examples may be extremely diffuse stellar envelopes. Wide-field imagers on large telescopes are allowing us to quantitatively explore the resolved stellar populations in these components within and well beyond the Local Group. I will highlight some recent  results from our work and discuss the insight these outer structures provide on understanding massive  galaxy assembly.  I will also discuss how we are using deep HST studies of M31's outer regions to probe its evolutionary history in unprecedented detail.

Dwarf spheroidal (dSph) galaxies are the smallest, closest and most abundant galaxies in the Universe and therefore excellent laboratories to study star formation (SF) history and chemical evolution on the smallest
scales. However, the complexity within---and variations between---these objects are poorly understood, not least because the vast majority of present-day data is restricted to the most central regions of these systems.
Thus, the scope of this talk is to present the results from our chemodynamical analysis (i.e., combining chemical abundances, stellar
ages, and precise dynamical measurements from high-resolution spectra) of the outer regions of Fornax and to put them in a general context of the chemical evolution in dSphs and their key-regulating factors. On this basis, possible (and impossible) evolutionary scenarios for Fornax are discussed and compared with model predictions.  Furthermore, Fornax is one amongst very few dSphs with an own globular cluster population. In the last part of my talk I use the results from our analysis and discuss
ongoing projects designed to address the impact of globular clusters on the evolution of this galaxy, and vice versa.

One of the important questions in extragalactic astronomy concerns the debate between nature and nurture scenarios. Are the observed galaxy local properties the end product of the different conditions at birth or the product of the interactions, or other local processes, since a galaxy is not an isolated object? In this talk I will present the results of the analysis of some galaxy properties, morphologies and mass functions, obtained comparing, for the first time in a consistent manner, galaxies in the widest range of environments at low redshift (groups, clusters, binary systems, isolated galaxies). The aim was to understand the most important factors that drive galaxy evolution, trying to disentangle the importance of galaxy mass and global environment.

In addition I will present the first results concerning the two projects in which I am involved at IAC: the ALBA project, aimed to explore the signs of a proto-cluster at z~6.5, and the analysis of dust emission of a sample of local tadpole galaxies.