Found 22 talks width keyword high-redshift galaxies

Fernando_Buitrago_181128s
Wednesday November 28, 2018
Fernando Buitrago
Institute of Astrophysics and Space Sciences (IA)

Abstract

There are galaxies that remain untouched since the ancient
Universe. These unique objects, the so-called relic galaxies, are several times
more massive than our Milky Way but with much smaller sizes, and
containing very old (>10 Gyr) stellar populations. For the very few of
them already found and analysed (most of them by our IAC colleagues),
they seem to host "too heavy" central
super massive black holes, also displaying an overabundance of low mass
versus high mass stars and retaining their primeval morphologies and
kinematics. How did they survive until the present day? Simulations
predict that they reside in galaxy overdensities whose large internal
random motions prevent galaxies from merging. However, we have not yet
determined observationally neither the environments these galaxies
inhabit nor how many there are (their number densities). We make use
of the GAMA survey, that allows us to conduct a complete
census of this elusive galaxy population, because of its large area and
spectroscopic completeness. After inspecting 180 square degrees of the sky
using the deepest photometric images available, we identified 29
massive ultracompact galaxies in the nearby Universe (0.02 < z < 0.3),
that are true windows to the ancient Universe. I will present the first paper
about this exceptional sample, describing their properties and
highlighting the fact that while some galaxies seem to be satellites
of bigger objects, others are not located in clusters, at odds with the
theoretical expectations.


jorge_sanchez_almeida_151015s
Thursday October 15, 2015
Dr. Jorge Sanchez Almeida
IAC

Abstract

Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter haloes. Although these predictions are unambiguous, the observational support has been indirect so far. I will report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of localized starbursts associated with gas having low metallicity. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr),  the observed metallicity inhomogeneities are only possible if the metal-poor gas producing stars fell onto the disk recently. I will analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. In addition, I will show model galaxies in cosmological numerical simulations with starbursts of low metallicity like to the star-forming regions in XMPs.


martin_lopez_corredoira_150630s
Tuesday June 30, 2015
Dr. Martin Lopez Corredoira
IAC

Abstract

Almost all cosmologists accept nowadays that the redshift of the galaxies is due to the expansion of the Universe (cosmological redshift), plus some Doppler effect of peculiar motions, but can we be sure of this fact by means of some other independent cosmological test? Here I will review some recent tests: CMBR temperature versus redshift, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczynski test. Some tests favour expansion and others favour a static Universe. Almost all the cosmological tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, an evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.


javier_piqueras_150602s
Tuesday June 2, 2015
Dr. Dr. Javier Piqueras
Centro de Astrobiología CSIC-INTA

Abstract

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.


stefan_geier_150326s
Thursday March 26, 2015
Dr. Stefan Geier
GTC

Abstract

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.


julie_wardlow_150226s
Thursday February 26, 2015
Dr. Julie Wardlow
Dark Cosmology Centre (Copenhagen)

Abstract

 

Over the past ~20 years the high-redshift Universe has been increasingly opened to scrutiny at far-infrared wavelengths, where cool dust emission from star-formation dominates. The dusty star-forming galaxies (DSFGs) and submillimeter galaxies (SMGs), selected at these wavelengths likely represent an important, but short-lived phase in the growth of massive galaxies. These DSFGs often have star-formation rates in excess of ~1000 solar masses per year and are confirmed out to at least z~6, although their redshifts and high dust contents make them faint and difficult to study at other wavelengths. Now, using data from the Herschel Space Observatory we have identified a population of DSFGs that are strongly gravitationally lensed and therefore magnified and available for unprecedented multi-wavelength scrutiny. I will describe how this important gravitationally lensed population is identified, and present and interpret the data from our extensive multi-wavelength, multi-facility follow-up studies. I will also present follow-up observations of an intriguing sample of the highest redshift DSFGs (z>4) that are also selected via Herschel data, and that are proving troublesome to explain in galaxy formation simulations.

 


pablo_g_perez_gonzalez_140515s
Thursday May 15, 2014
Dr. Pablo G. Pérez González
Universidad Complutense de Madrid

Abstract

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.


andreas_pawlik_140410s
Thursday April 10, 2014
Dr. Andreas Pawlik
MPA (Garching)

Abstract

The first galaxies are thought to have started the reionization of the Universe, that is the transformation of the cosmic hydrogen from its initial neutral to its present ionized state that occurred during the first few hundred million years after the Big Bang. I will review the key physics of reionization by the first galaxies and highlight the computational challenges of simulating the relevant processes, primarily the transport of ionizing photons. I will introduce the radiative transfer method TRAPHIC that we have developed to address these challenges. I will discuss the application of TRAPHIC in zoomed cosmological simulations of the first galaxies and evaluate the prospects for observing these galaxies with the upcoming James Webb Space Telescope. I will conclude by presenting first results from Aurora, a new suite of simulations to investigate reionization and galaxy formation across a large range of scales.


francisco_prada_140121s
Tuesday January 21, 2014
Prof. Francisco Prada
Instituto de Física Teórica UAM/CSIC, Madrid

Abstract

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.


anna_ferre_mateu_140114s
Tuesday January 14, 2014
Dr. Anna Ferré-Mateu
National Astronomical Observatory of Japan

Abstract

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.


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