Found 183 talks archived in Galaxies
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.
The flow of gas from the cosmic web into galaxies provides the necessary fuel for star formation and galaxy assembly. I will review our current knowledge about gas accretion into galaxies and its consequences for galaxy formation at high and low redshifts. Special attention will be given to the detectability of cold streams as Lyman-alpha blobs or Lyman-Limit systems, as well as the current challenges to the cold-flow picture.
It is now clear that supermassive black holes (M>1e6 Msun) live in the center of most (all) galaxies, including our own Milky Way. Furthermore, the energy released during the growth of this black hole is a critical ingredient in understanding galaxy formation and evolution. In this talk, I will show what we know about how, when and where these supermassive black holes are acquiring their masses. In particular, I will focus on the effects of obscuration, as it is now clear that the majority of this black hole growth is hidden from our view by large amounts of gas and dust. I will present statistical evidence suggesting that while most nuclear activity is triggered by internal secular processes, the most violent episodes are linked to major galaxy mergers. Finally, I will show how future data obtained combining observations with the ALMA radio telescope and the NuSTAR X-ray observatory will allow us to understand the physical details of the connection between black hole growth and galaxy evolution.
Crucial issues in cosmology and astrophysics are to understand the
process of galaxy formation and evolution and the nature of what
appears to be the dominant form of matter in the Universe, i.e. dark
matter. Dwarf galaxies provide important information on both of these
issues. In this talk, I will focus on the dwarf galaxies found in the
Local Group, as it is the galaxy population that can be studied in
the greatest detail than any other from the properties of their
resolved stellar populations. I will show how wide-area surveys have
led to a leap forward in our observational understanding of these
galaxies and discuss future prospects.
AzTEC is a sensitive bolometer camera that, coupled with 10-15m-class sub-mm telescopes, has mapped more than 3 sq. deg of the extragalactic sky to depths between 0.7 and 1.1 mJy at 1.1mm, prior to its current installation and operation on the 32m Large Millimeter Telescope (LMT). These extragalactic surveys targeted towards blank-fields and biased high-z environments alike have allowed us to identify regions of the sky where submillimeter galaxies (SMGs), powerful obscured starbursts at high-redshifts (z>1), cluster, and possibly mark the potential wells of accelerated galaxy-formation that will eventually form massive clusters. In this talk I will describe the evidence we have found for these overdense regions of massive galaxies, their structure and possible interpretation, as well as the follow-up observations we are carrying out with the LMT nowadays.
The direct accretion of pristine gas streams is predicted to be the main mode of galaxy disk growth in the early universe (cold-flows). We (think we) have discovered this physical process at work in the local Universe. The finding is one of the outcomes of our in-depth study of local extremely metal poor (XMP) galaxies. I will explain the main observational properties of XMPs, in particular, their tendency to have cometary or tadpole morphology, with a bright peripheral clump (the head) on a faint tail. Tadpole galaxies are rare in the nearby universe but turn out to be very common at high redshift, where they are usually interpreted as disk galaxies in early stages of assembling. We have found the heads to be giant HII regions displaced with respect to the rotation center, with the galaxy metallicity being smallest at the head and larger elsewhere. The resulting chemical abundance gradient is opposite to the one observed in local spirals, and suggests a recent gas accretion episode onto the head. Thus, local XMP galaxies seem to be primitive disks, with their star formation sustained by accretion of external metal poor gas. I will argue how the same mechanism may be driving the star formation in many other local galaxies. Ongoing observational projects to confirm these findings and conjectures will be briefly mentioned.
Chemical abundances derived using emission-line spectra in ionized gaseous nebulae are between the most useful properties that can be derived to understand the evolution of galaxies from the local Universe up to very high redshifts. Since nitrogen is one of the most abundant metals in the gas-phase of galaxies and its emission-lines can be measured many times instead of those emitted by oxygen, it is important to be aware of the implications of the variations in the nitrogen-to-oxygen ratio for the derivation of total metallicity and what are the advantages of using this abundance ratio to derive other evolutionary properties in different emission-line objects. We will also see the utility of some observational techniques, such integral field spectroscopy, to disentangle between different processes implied in the excess of observed nitrogen as derived from integrated observations.
- Understanding the post-merger requiem of binary black holesDr. Juan Calderón BustilloMonday September 24, 2018 - 12:30 (Aula)
- Pyroclastic Blowout: Dust Survival in Isolated versus Clustered SupernovaeDr. Sergio Martínez-GonzálezThursday September 27, 2018 - 10:30 (Aula)