arXiv subjects

Manolis Plionis

Publications and source records attributed to Manolis Plionis.

At least 37 records · Page 2Linked to original sources

arXiv2016

Constraining the Dark Energy Equation of State with HII Galaxies

We use the HII galaxies $L - σ$ relation and the resulting Hubble expansion cosmological probe of a sample of just 25 high-$z$ (up to $z \sim 2.33$) HII galaxies, in a joint likelihood analysis with other well tested cosmological probes (CMB, BAOs) in an attempt to constrain the dark energy equation of state (EoS). The constraints, although still weak, are in excellent agreement with those of a similar joint analysis using the well established SNIa Hubble expansion probe. Interestingly, even with the current small number of available high redshift HII galaxies, the HII/BAO/CMB joint analysis gives a 13% improvement of the quintessence dark energy cosmological constraints compared to the BAO/CMB joint analysis. We have further performed extensive Monte Carlo simulations, with a realistic redshift sampling, to explore the extent to which the use of the $L - σ$ relation, observed in HII galaxies, can constrain effectively the parameter space of the dark energy EoS. The simulations predict substantial improvement in the constraints when increasing the sample of high-$z$ HII galaxies to 500, a goal that can be achieved in reasonable observing times with existing large telescopes and state-of-the-art instrumentation.

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arXiv2016

Direct measurement of lensing amplification in Abell S1063 using a strongly lensed high redshift HII Galaxy

ID11 is an actively star forming extremely compact galaxy and Ly alpha emitter at z=3.117 that is gravitationally magnified by a factor of ~17 by the cluster of galaxies Hubble Frontier Fields AS1063. Its observed properties resemble those of low luminosity HII galaxies or Giant HII regions like 30-Doradus in the LMC. Using the tight correlation correlation between the Balmer-line luminosities and the width of the emission lines (typically L(Hbeta)-sigma(Hbeta)) valid for HII galaxies and Giant HII regions to estimate its total luminosity, we are able to measure the lensing amplification of ID11. We obtain an amplification of 23 +- 11 similar within errors to the value of ~17 estimated or predicted by the best lensing models of the massive cluster Abell S1063. We also compiled from the literature luminosities and velocity dispersions for a set of lensed compact starforming regions. There is more scatter in the L-sigma correlation for these lensed systems but on the whole the results tend to support the lensing models estimates of the magnification. Our result indicates that the amplification can be independently measured using the L-sigma relation in lensed Giant HII regions or HII galaxies. It also supports the suggestion, even if lensing model dependent, that the L-sigma relation is valid for low luminosity high-z objects. Ad-hoc observations of lensed starforming systems are required to accurately determine the lensing amplification.

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arXiv2015

On the road to precision cosmology with high redshift HII galaxies

We report the first results of a programme aimed at studying the properties of high redshift galaxies with on-going massive and dominant episodes of star formation (HII galaxies). We use the $L(\mathrm{H}β) - σ$ distance estimator based on the correlation between the ionized gas velocity dispersions and Balmer emission line luminosities of HII galaxies and Giant HII regions to trace the expansion of the Universe up to $z \sim 2.33$. This approach provides an independent constraint on the equation of state of dark energy and its possible evolution with look-back time. Here we present high-dispersion (8,000 to 10,000 resolution) spectroscopy of HII galaxies at redshifts between 0.6 and 2.33, obtained at the VLT using XShooter. Using six of these HII galaxies we obtain broad constraints on the plane $Ω_m - w_0$. The addition of 19 high-z HII galaxies from the literature improves the constraints and highlights the need for high quality emission line profiles, fluxes and reddening corrections. The 25 high-z HII galaxies plus our local compilation of 107 HII galaxies up to $z=0.16$ were used to impose further constraints. Our results are consistent with recent studies, although weaker due to the as yet small sample and low quality of the literature data of high-z HII galaxies. We show that much better and competitive constraints can be obtained using a larger sample of high redshift HII galaxies with high quality data that can be easily obtained with present facilities like KMOS at the VLT.

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arXiv2014

Precision growth index using the clustering of cosmic structures and growth data

We use the clustering properties of Luminous Red Galaxies (LRGs) and the growth rate data provided by the various galaxy surveys in order to constrain the growth index ($γ$) of the linear matter fluctuations. We perform a standard $χ^2$-minimization procedure between theoretical expectations and data, followed by a joint likelihood analysis and we find a value of $γ=0.56\pm 0.05$, perfectly consistent with the expectations of the $Λ$CDM model, and $Ω_{m0} =0.29\pm 0.01$, in very good agreement with the latest Planck results. Our analysis provides significantly more stringent growth index constraints with respect to previous studies, as indicated by the fact that the corresponding uncertainty is only $\sim 0.09 γ$. Finally, allowing $γ$ to vary with redshift in two manners (Taylor expansion around $z=0$, and Taylor expansion around the scale factor), we find that the combined statistical analysis between our clustering and literature growth data alleviates the degeneracy and obtain more stringent constraints with respect to other recent studies.

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arXiv2014

The $L - σ$ relation for massive bursts of star formation

The validity of the emission line luminosity vs. ionised gas velocity dispersion ($L - σ$) correlation for HII galaxies (HIIGx), and its potential as an accurate distance estimator are assessed. For a sample of 128 local ($0.02\lesssim z\lesssim 0.2$) compact HIIGx with high equivalent widths of their Balmer emission lines we obtained ionised gas velocity dispersion from high S/N high-dispersion spectroscopy (Subaru-HDS and ESO VLT-UVES) and integrated H$β$ fluxes from low dispersion wide aperture spectrophotometry. We find that the $L - σ$ relation is strong and stable against restrictions in the sample (mostly based on the emission line profiles). The `gaussianity' of the profile is important for reducing the rms uncertainty of the distance indicator, but at the expense of substantially reducing the sample. By fitting other physical parameters into the correlation we are able to significantly decrease the scatter without reducing the sample. The size of the starforming region is an important second parameter, while adding the emission line equivalent width or the continuum colour and metallicity, produces the solution with the smallest rms scatter=$δ\log L(\mathrm{H}β) = 0.233$. The derived coefficients in the best $L - σ$ relation are very close to what is expected from virialized ionising clusters, while the derived sum of the stellar and ionised gas masses are similar to the dynamical mass estimated using the HST corrected Petrosian radius. These results are compatible with gravity being the main mechanism causing the broadening of the emission lines in these very young and massive clusters. The derived masses range from about 2 $\times10^6$ $\mathrm{M}_{\odot}$ to $10^9$ $\mathrm{M}_{\odot}$ and their `corrected' Petrosian radius, from a few tens to a few hundred parsecs.

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arXiv2012

Determining the Hubble constant using Giant extragalactic HII regions and HII galaxies

We report the first results of a long term program aiming to provide accurate independent estimates of the Hubble constant (H0) using the L-sigma distance estimator for Giant extragalactic HII regions (GEHR) and HII galaxies. We have used VLT and Subaru high dispersion spectroscopic observations of a local sample of HII galaxies, identified in the SDSS DR7 catalogue in order to re-define and improve the L(Hbeta)-sigma 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 HII galaxies and 23 GEHR in 9 galaxies we obtain H0=74.3 +- 3.1 (statistical) +- 2.9 (systematic) km /s Mpc, in excellent agreement with, and independently confirming, the most recent SNe Ia based results.

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arXiv2012

Dynamics and constraints of the dissipative Liouville cosmology

In this article we investigate the properties of the FLRW flat cosmological models in which the cosmic expansion of the Universe is affected by a dilaton dark energy (Liouville scenario). In particular, we perform a detailed study of these models in the light of the latest cosmological data, which serves to illustrate the phenomenological viability of the new dark energy paradigm as a serious alternative to the traditional scalar field approaches. By performing a joint likelihood analysis of the recent supernovae type Ia data (SNIa), the differential ages of passively evolving galaxies, and the Baryonic Acoustic Oscillations (BAOs) traced by the Sloan Digital Sky Survey (SDSS), we put tight constraints on the main cosmological parameters. Furthermore, we study the linear matter fluctuation field of the above Liouville cosmological models. In this framework, we compare the observed growth rate of clustering measured with those predicted by the current Liouville models. Performing a chi^2 statistical test we show that the Liouville cosmological model provides growth rates that match sufficiently well with the observed growth rate. To further test the viability of the models under study, we use the Press-Schechter formalism to derive their expected redshift distribution of cluster-size halos that will be provided by future X-ray and Sunyaev-Zeldovich cluster surveys. We find that the Hubble flow differences between the Liouville and the LambdaCDM models provide a significantly different halo redshift distribution, suggesting that the models can be observationally distinguished.

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arXiv2011

Hubble expansion and structure formation in the "running FLRW model" of the cosmic evolution

A new class of FLRW cosmological models with time-evolving fundamental parameters should emerge naturally from a description of the expansion of the universe based on the first principles of quantum field theory and string theory. Within this general paradigm, one expects that both the gravitational Newton's coupling, G, and the cosmological term, Lambda, should not be strictly constant but appear rather as smooth functions of the Hubble rate. This scenario ("running FLRW model") predicts, in a natural way, the existence of dynamical dark energy without invoking the participation of extraneous scalar fields. In this paper, we perform a detailed study of these models in the light of the latest cosmological data, which serves to illustrate the phenomenological viability of the new dark energy paradigm as a serious alternative to the traditional scalar field approaches. By performing a joint likelihood analysis of the recent SNIa data, the CMB shift parameter, and the BAOs traced by the Sloan Digital Sky Survey, we put tight constraints on the main cosmological parameters. Furthermore, we derive the theoretically predicted dark-matter halo mass function and the corresponding redshift distribution of cluster-size halos for the "running" models studied. Despite the fact that these models closely reproduce the standard LCDM Hubble expansion, their normalization of the perturbation's power-spectrum varies, imposing, in many cases, a significantly different cluster-size halo redshift distribution. This fact indicates that it should be relatively easy to distinguish between the "running" models and the LCDM cosmology using realistic future X-ray and Sunyaev-Zeldovich cluster surveys.

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arXiv2009

Interacting Dark Matter as an Alternative to Dark Energy

We investigate the global dynamics of the universe within the framework of the Interacting Dark Matter (IDM) scenario. Considering that the dark matter obeys the collisional Boltzmann equation, we can obtain analytical solutions of the global density evolution, which can accommodate an accelerated expansion, equivalent to either the {\em quintessence} or the standard $Λ$ models. This is possible if there is a disequilibrium between the DM particle creation and annihilation processes with the former process dominating, which creates an effective source term with negative pressure. Comparing the predicted Hubble expansion of one of the IDM models (the simplest) with observational data, we find that the effective annihilation term is quite small, as suggested by various experiments.

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arXiv2009

Precision Cosmology from X-ray AGN clustering

We place tight constraints on the main cosmological parameters of spatially flat cosmological models by using the recent angular clustering results of XMM-{\it Newton} soft (0.5-2 keV) X-ray sources (Ebrero et al. 2009a), which have a redshift distribution with a median of $z\sim 1$. Performing a standard likelihood procedure, assuming a constant in comoving coordinates AGN clustering evolution, the AGN bias evolution model of Basilakos et al. (2008) and the WMAP5 value of $σ_8$, we find stringent simultaneous constraints in the ($Ω_{m}, $w) plane, with $Ω_{m}= 0.26\pm 0.05$, w$=-0.93^{+0.11}_{-0.19}$.

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arXiv2008

The Aspen--Amsterdam Void Finder Comparison Project

Despite a history that dates back at least a quarter of a century studies of voids in the large--scale structure of the Universe are bedevilled by a major problem: there exist a large number of quite different void--finding algorithms, a fact that has so far got in the way of groups comparing their results without worrying about whether such a comparison in fact makes sense. Because of the recent increased interest in voids, both in very large galaxy surveys and in detailed simulations of cosmic structure formation, this situation is very unfortunate. We here present the first systematic comparison study of thirteen different void finders constructed using particles, haloes, and semi--analytical model galaxies extracted from a subvolume of the Millennium simulation. The study includes many groups that have studied voids over the past decade. We show their results and discuss their differences and agreements. As it turns out, the basic results of the various methods agree very well with each other in that they all locate a major void near the centre of our volume. Voids have very underdense centres, reaching below 10 percent of the mean cosmic density. In addition, those void finders that allow for void galaxies show that those galaxies follow similar trends. For example, the overdensity of void galaxies brighter than $m_B = -20 $ is found to be smaller than about -0.8 by all our void finding algorithms.

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arXiv2007

Environmental Influences on the Morphology and Dynamics of Group Size Haloes

We use group size haloes identified with a ``friends of friends'' (FOF) algorithm in a concordance $Λ\rm{CDM}$ GADGET2 (dark matter only) simulation to investigate the dependence of halo properties on the environment at $z=0$. The study is carried out using samples of haloes at different distances from their nearest massive {\em cluster} halo. We find that the fraction of haloes with substructure typically increases in high density regions. The halo mean axial ratio $ $ also increases in overdense regions, a fact which is true for the whole range of halo mass studied. This can be explained as a reflection of an earlier halo formation time in high-density regions, which gives haloes more time to evolve and become more spherical. Moreover, this interpretation is supported by the fact that, at a given halo-cluster distance, haloes with substructure are more elongated than their equal mass counterparts with no substructure, reflecting that the virialization (and thus sphericalization) process is interrupted by merger events. The velocity dispersion of low mass haloes with strong substructure shows a significant increase near massive clusters with respect to equal mass haloes with low-levels of substructure or with haloes found in low-density environments. The alignment signal between the shape and the velocity ellipsoid principal axes decreases going from lower to higher density regions, while such an alignment is stronger for haloes without substructure. We also find, in agreement with other studies, a tendency of halo major axes to be aligned and of minor axes to lie roughly perpendicular with the orientation of the filament within which the halo is embedded, an effect which is stronger in the proximity of the massive clusters.

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arXiv2007

Cosmology from XMM High-Z AGN Clustering

We review the high-redshift X-ray selected AGN clustering, based on the XMM/2dF survey, and compare it with other recent XMM-based results. Using the recent Hasinger et al. (2005) and La Franca et al. (2005) luminosity functions we find that the spatial clustering lengths, derived using Limber's inversion equation, are $\sim 17$ and 20 $h^{-1}$ Mpc for the soft and hard band sources while their median redshifts are ${\bar z}\sim 1.2$ and 0.8, respectively. The corresponding bias factors at $z=\bar{z}$ are $\sim 5.3\pm 0.9$ and $\sim 5.1\pm1.1$, respectively. Within the framework of a flat cosmological model we find that our results support a model with $Ω_m \simeq 0.26$, $σ_8\simeq 0.75$, $h\simeq 0.72$, w$\simeq -0.9$ (in excellent agreement with the 3 year WMAP results). We also find the present day bias of X-ray AGNs to be $b_{\circ}\sim 2$.

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arXiv2006

The PSCz Dipole Revisited

We re-examine the gravitational acceleration (dipole) induced on the Local Group of galaxies by the Infrared Astronomical Satellite (IRAS) galaxy distribution of the Point Source Catalogue redshift survey (PSCz). We treat the cirrus-affected low galactic latitudes by utilizing a spherical harmonic expansion of the galaxy surface density field up to the octapole order. We find strong indications for significant contributions to the Local Group motion from depths up to $\sim 185$ $h^{-1}$ Mpc and possible contribution even from $\sim 210$ $h^{-1}$ Mpc, in agreement with the recent analysis of Kocevski & Ebeling of a whole sky X-ray cluster survey.What changes with respect to the previous PSCz dipole analyses is: (a) the large-scale dipole contributions and (b) an increase of the overall dipole amplitude due to the important contribution of the local volume ($\mincir 4 h^{-1}$Mpc), which we now take into account. This results in a lower value of the $β(\equiv Ω_{\rm m}^{0.6}/b)$ parameter, which we find to be $β_{\rm IRAS} \simeq 0.49$ in real space. Therefore, for the concordance cosmological model ($Ω_{\rm m}=1-Ω_Λ=0.3$) the IRAS galaxies bias factor is $b_{\rm IRAS}\simeq 1$ which means that IRAS galaxies are good traces of the underlying matter distribution.

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arXiv2006

Constraining the CDM spectrum normalization in flat dark energy cosmologies

We study the relation between the rms mass fluctuations on 8$h^{-1}$Mpc scales and $Ω_{\rm m}$ using the recent clustering results of XMM-{\it Newton} soft (0.5-2 keV) X-ray sources, which have a median redshift of $z\sim 1.2$. The relation can be represented in the form $σ_{8}=0.34 (\pm 0.01) Ω_{\rm m}^{-γ}$ where $γ\equiv γ(Ω_{\rm m},w)$ and it is valid for all $w<-1/3$ models. By combining the X-ray clustering and SNIa data we find that the model which best reproduces the observational data is that with: $Ω_{\rm m}\simeq 0.26$, $w\simeq -0.90$ and $σ_{8}\simeq 0.73$, which is in excellent agreement with the recent 3-year Wilkinson Microwave Anisotropy Probe results.

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arXiv2006

High-z X-ray AGN Clustering and Cosmological Implications

I review recent results of the high-redshift X-ray selected AGN clustering, based on the XMM/2dF survey. Using the luminosity-dependent density evolution luminosity function we find that the spatial clustering lengths, derived using Limber's inversion equation, are ~16 and ~19 h-1 Mpc respectively (for the comoving clustering evolution model) while the median redshifts of the soft and hard X-ray sources are z~ 1.2 and 0.75, respectively. Within the framework of flat cosmological models we find that these results support a model with Omega_m=0.26, σ_8=0.75, w=-0.9 (in excellent agreement with the 3 year WMAP results). We also find the present day bias of X-ray AGNs to be b_o=2.

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arXiv2006

A 3-Dimensional study of the Local Environment of Bright IRAS Galaxies: The AGN/Starburst connection

We present a 3-dimensional study of the local ($\leq 100 h^{-1}$ kpc) and the large scale ($\leq$ 1 $h^{-1}$ Mpc) environment of Bright IRAS Galaxies (BIRGs). For this purpose we use 87 BIRGs located at high galactic latitudes (with 0.008$\leq z \leq$0.018) as well as a control sample of non-active galaxies having the same morphological, redshift and diameter size distributions as the corresponding BIRG sample. Using the Center for Astrophysics (CfA2) and Southern Sky Redshift Survey (SSRS) galaxy catalogues ($m_b\lesssim 15.5$)as well as our own spectroscopic observations ($m_b\lesssim19.0$) for a subsample of the original BIRG sample, we find that the fraction of BIRGs with a close neighbor is significantly higher than that of their control sample. Comparing with a related analysis of Sy1 and Sy2 galaxies of Koulouridis et al. (2006) we find that BIRGs have a similar environment as Sy2s, although the fraction of BIRGs with a bright close neighbor is even higher than that of Sy2 galaxies. An additional analysis of the relation between FIR colors and the type of activity of each BIRG shows a significant difference between the colors of strongly-interacting and non-interacting starbursts and a resemblance between the colors of non-interacting starbursts and Sy2s. Our results support the view where close interactions can drive molecular clouds towards the galactic center, triggering starburst activity and obscuring the nuclear activity. When the close neighbor moves away, starburst activity is reduced with the simultaneous appearance of an obscured (type 2) AGN. Finally, the complete disentanglement of the pair gives birth to an unobscured (type 1) AGN.

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arXiv2006

Halo Shapes, Dynamics and Environment

In the hierarchical structure formation model cosmic halos are supposed to form by accretion of smaller units along anisotropic direction, defined by large-scale filamentary structures. After the epoch of primary mass aggregation (which depend on the cosmological model), violent relaxation processes will tend to alter the halo phase-space configuration producing quasi-spherical halos with a relatively smooth density profiles. Here we attempt to investigate the relation between halos shapes, their environment and their dynamical state. To this end we have run a large ($L=500 h^{-1}$ Mpc, $N_{p}=512^3$ particles) N-body simulation of a flat low-density cold dark matter model with a matter density $Ω_{\rm m}=1-Ω_Λ=0.3$, Hubble constant $H_{\circ}=70$ km s$^{-1}$ Mpc$^{-1}$ and a normalization parameter of $σ_{8}=0.9$. The particle mass is $m_{\rm p}\ge 7.7\times 10^{10} h^{-1} M_{\odot}$ comparable to the mass of one single galaxy. The halos are defined using a friends-of-friend algorithm with a linking length given by $l=0.17\barν$ where $\barν$ is the mean density. This linking length corresponds to an overdensity $ρ/ρ_{\rm mean}\simeq 200$ at the present epoch ($z=0$) and the total number of halos with more than 130 particles ($M>3 \times 10^{13} h^{-1} M_{\odot}$) is 57524.

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