ABSTRACT
We report the first results of a long‐term programme aiming to provide accurate independent estimates of the Hubble constant (H0) using the L(Hβ)–σ distance estimator for giant extragalactic ...H ii regions (GEHR) and H ii galaxies.
We have used Very Large Telescope and Subaru high‐dispersion spectroscopic observations of a local sample of H ii galaxies, identified in the Sloan Digital Sky Survey Data Release 7 (SDSS DR7) catalogue in order to redefine and improve the L(Hβ)–σ distance indicator and to determine the Hubble constant. To this end, we utilized as local calibration or ‘anchor’ of this correlation GEHR in nearby galaxies which have accurate distance measurements determined via primary indicators. Using our best sample of 69 nearby H ii galaxies and 23 GEHR in nine galaxies, we obtain H0= 74.3 ± 3.1 (statistical) ± 2.9 (systematic) km s−1 Mpc−1, in excellent agreement with, and independently confirming, the most recent Type Ia supernovae based results.
The impact of climate change on the biosphere and atmosphere is well documented but its impact on the anthroposphere needs to be better understood. Indeed, divergent views remain both at the regional ...level -as shown by (i) the EU case-by-case approach (ii) the African
Kampala Convention
(2009) and (iii) the Latin-American
Lineamientos regionales
(2018)- and finally the international one. As the Paris Agreement (2015) urges States to use best available scientific knowledge to counter the negative effects of climate change, we argue that Earth Observation (EO) could be potentially exploited by policy-makers as an efficient platform for modeling, forecasting, characterizing and understanding the severity of migration flows, contributing to evidence-based Anticipatory Action (A-A) for the effective management of climate migration, and setting the direction for future policies in this field that would be equitable on both regional and international scales. Hence, in implementing the Paris Agreement, States should increase the funding and use of EO and Causality as policy-supporting tools, to reduce the need for reactive and costly responses to displacement, and promote the safety, dignity, and well-being of people affected by climate change. However, based on said input, a well-adapted framework for the legal protection of climate migrants should be adopted.
The XXL Survey Butler, Andrew; Huynh, Minh; Delvecchio, Ivan ...
Astronomy and astrophysics (Berlin),
12/2018, Volume:
620
Journal Article
Peer reviewed
Open access
The classification of the host galaxies of the radio sources in the 25 deg2 ultimate XMM extragalactic survey south field (XXL-S) is presented. XXL-S was surveyed at 2.1 GHz with the Australia ...Telescope Compact Array (ATCA) and is thus far the largest area radio survey conducted down to rms flux densities of σ ~ 41 μJy beam−1. Of the 6287 radio sources in XXL-S, 4758 (75.7%) were cross-matched to an optical counterpart using the likelihood ratio technique. There are 1110 spectroscopic redshifts and 3648 photometric redshifts available for the counterparts, of which 99.4% exist out to z ~ 4. A number of multiwavelength diagnostics, including X-ray luminosities, mid-infrared colours, spectral energy distribution fits, radio luminosities, and optical emission lines and colours, were used to classify the sources into three types: low-excitation radio galaxies (LERGs), high-excitation radio galaxies (HERGs), and star-forming galaxies (SFGs). The final sample contains 1729 LERGs (36.3%), 1159 radio-loud HERGs (24.4%), 296 radio-quiet HERGs (6.2%), 558 SFGs (11.7%), and 1016 unclassified sources (21.4%). The XXL-S sub-mJy radio source population is composed of ~75% active galactic nuclei and ~20% SFGs down to 0.2 mJy. The host galaxy properties of the HERGs in XXL-S are independent of the HERG selection, but the XXL-S LERG and SFG selection is, due to the low spectral coverage, largely determined by the known properties of those populations. Considering this caveat, the LERGs tend to exist in the most massive galaxies with low star formation rates and redder colours, whereas the HERGs and SFGs exist in galaxies of lower mass, higher star formation rates, and bluer colours. The fraction of blue host galaxies is higher for radio-quiet HERGs than for radio-loud HERGs. LERGs and radio-loud HERGs are found at all radio luminosities, but radio-loud HERGs tend to be more radio luminous than LERGs at a given redshift. These results are consistent with the emerging picture in which LERGs exist in the most massive quiescent galaxies typically found in clusters with hot X-ray halos and HERGs are associated with ongoing star formation in their host galaxies via the accretion of cold gas.
ABSTRACT
We develop an optimization algorithm, using simulated annealing for the quantification of patterns in astronomical data based on techniques developed for robotic vision applications. The ...methodology falls in the category of cost minimization algorithms and it is based on user-determined interaction – among the pattern elements – criteria that define the properties of the sought structures. We applied the algorithm on a large variety of mock images and we constrained the free parameters; α and k, which express the amount of noise in the image and how strictly the algorithm seeks for cocircular structures, respectively. We find that the two parameters are interrelated and also that, independently of the pattern properties, an appropriate selection for most of the images would be log k = −2 and 0 < α ≲ 0.04. The width of the effective α-range, for different values of k, is reduced when more interaction coefficients are taken into account for the definition of the patterns of interest. Finally, we applied the algorithm on N-body simulation dark-matter halo data and on the HST image of the lensing Abell 2218 cluster to conclude that this versatile technique could be applied for the quantification of structure and for identifying coherence in astronomical patterns.
Precision cosmology from X-ray AGN clustering Basilakos, Spyros; Plionis, Manolis
Monthly notices of the Royal Astronomical Society. Letters,
November 2009, Volume:
400, Issue:
1
Journal Article
Peer reviewed
Open access
We place tight constraints on the main cosmological parameters of spatially flat cosmological models by using the recent angular clustering results of XMM–Newton soft (0.5–2 keV) X-ray sources, which ...have a redshift distribution with a median of z∼ 1. Performing a standard likelihood procedure, assuming a constant in comoving coordinates active galactic nuclei (AGN) clustering evolution, the AGN bias evolution model of Basilakos, Plionis & Ragone-Figueroa and the Wilkinson Microwave Anisotropy Probe5 value of σ8, we find stringent simultaneous constraints in the (Ωm, w) plane, with Ωm= 0.26 ± 0.05, w=−0.93+0.11−0.19.
Aims.
We study the dependence of the dynamical properties of massive (
M
≥ 1.5 × 10
13
M
⊙
h
−1
) dark matter halos on their environment in a whole-sky ΛCDM light-cone simulation extending to
z
...∼ 0.65. The properties of interest for this study are the halo shape (parametrized via its principal axes), spin and virialization status, the alignment of halo spin and shape, as well as the shape-shape and spin-spin alignments among halo neighbors.
Methods.
We define the halo environment using the notion of halo isolation status determined by the distance to its nearest neighbor. This defines a maximum spherical region around each halo devoid of other halos, above the catalog threshold mass. We consider “close halo pairs” to be pairs separated by a distance that is lower than a specific threshold. In order to decontaminate our results from the known dependence of halo dynamical properties on mass, we used a random sampling procedure to compare properties of similar halo abundance distributions.
Results.
We find that: (a) there is a strong dependence on the part of the halo properties with regard to their environment, confirming that isolated halos are more aspherical and more prolate with lower spin values; (b) correlations between halo properties exist and are mostly independent of the halo environment; (c) halo spins are aligned with the minor axis, regardless of halo shape; and (d) close halo neighbors have their major axes statistically aligned, while they show a slight but statistically significant preference for anti-parallel spin directions. The latter result is enhanced for the case of close halo pairs in low-density environments. Furthermore, we find a tendency for the spin vectors to be oriented perpendicular to the line that connects such close halo pairs.
Aims.
The main purpose of this study is to investigate aspects regarding the validity of the active galactic nucleus (AGN) unification paradigm (UP). In particular, we focus on the AGN host galaxies, ...which according to the UP should show no systematic differences depending on the AGN classification.
Methods.
For the purpose of this study, we used (a) the spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 14 catalogue, in order to select and classify AGNs using emission line diagnostics, up to a redshift of
z
= 0.2, and (b) the Galaxy Zoo Project catalogue, which classifies SDSS galaxies in two broad Hubble types: spirals and ellipticals.
Results.
We find that the fraction of type 1 Seyfert nuclei (Sy1) hosted in elliptical galaxies is significantly larger than the corresponding fraction of any other AGN type, while there is a gradient of increasing spiral-hosts from Sy1 to LINER, type 2 Seyferts (Sy2) and composite nuclei. These findings cannot be interpreted within the simple unified model, but possibly by a co-evolution scheme for supermassive black holes and galactic bulges. Furthermore, for the case of spiral host galaxies we find the Sy1 population to be strongly skewed towards face-on configurations, while the corresponding Sy2 population range in all host galaxy orientation configurations has a similar, but not identical, orientation distribution to star-forming galaxies. These results also cannot be interpreted by the standard unification paradigm, but point towards a significant contribution of the galactic disc to the obscuration of the nuclear region. This is also consistent with the observed preference of Sy1 nuclei to be hosted by ellipticals, that is, the dusty disc of spiral hosts contributes to the obscuration of the broad-line region, and thus relatively more ellipticals are expected to appear hosting Sy1 nuclei.
Abstract
The relationship between the integrated H β line luminosity and the velocity dispersion of the ionized gas of H ii galaxies and giant H ii regions represents an exciting standard candle that ...presently can be used up to redshifts z ∼ 4. Locally it is used to obtain precise measurements of the Hubble constant by combining the slope of the relation obtained from nearby (z ≤ 0.2) H ii galaxies with the zero-point determined from giant H ii regions belonging to an ‘anchor sample’ of galaxies for which accurate redshift-independent distance moduli are available. We present new data for 36 giant H ii regions in 13 galaxies of the anchor sample that includes the megamaser galaxy NGC 4258. Our data are the result of the first 4 yr of observation of our primary sample of 130 giant H ii regions in 73 galaxies with Cepheid determined distances. Our best estimate of the Hubble parameter is 71.0 ± 2.8(random) ± 2.1(systematic) km s− 1Mpc− 1. This result is the product of an independent approach and, although at present less precise than the latest SNIa results, it is amenable to substantial improvement.
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