			Home About us Contact

Galaxy Sample (galaxy + sample)

Distribution by Scientific Domains

Physics and Astronomy	100%

Selected Abstracts

The SCUBA Local Universe Galaxy Survey , II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2001
m data: evidence for cold dust in bright IRAS galaxies
This is the second in a series of papers presenting results from the SCUBA Local Universe Galaxy Survey. In our first paper we provided 850-,m flux densities for 104 galaxies selected from the IRAS Bright Galaxy Sample and we found that the 60-, 100-,m (IRAS) and 850-,m (SCUBA) fluxes could be adequately fitted by emission from dust at a single temperature. In this paper we present 450-,m data for the galaxies. With the new data, the spectral energy distributions of the galaxies can no longer be fitted with an isothermal dust model , two temperature components are now required. Using our 450-,m data and fluxes from the literature, we find that the 450/850-,m flux ratio for the galaxies is remarkably constant, and this holds from objects in which the star formation rate is similar to our own Galaxy, to ultraluminous infrared galaxies (ULIRGs) such as Arp 220. The only possible explanation for this is if the dust emissivity index for all of the galaxies is ,2 and the cold dust component has a similar temperature in all galaxies . The 60-,m luminosities of the galaxies were found to depend on both the dust mass and the relative amount of energy in the warm component, with a tendency for the temperature effects to dominate at the highest L60. The dust masses estimated using the new temperatures are higher by a factor of ,2 than those determined previously using a single temperature. This brings the gas-to-dust ratios of the IRAS galaxies into agreement with those of the Milky Way and other spiral galaxies which have been intensively studied in the submm. [source]

Morphological properties of isolated galaxies vs. isolation criteria

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
I.B. Vavilova
Abstract We studied the morphological properties of isolated galaxies samples in dependence on the isolation parameter and properties of primary catalogs. With this aim we identified the samples of single and isolated galaxies from SDSS DR5 (Single and QIsol) with the 3D Voronoi tessellation method (Elyiv et al. 2009). We found that in comparison with other samples of isolated galaxies, the QIsol sample contains an excess of late-type galaxies, especially with a low luminosity and BCG/Im/Irr morphology. We also showed that the fractions of early type galaxies in QIsol SDSS DR5 sample and samples 2MIG (Karachentseva et al. 2010) and CIG (Karachentseva et al. 1973; Hernandez-Toledo et al. 2008) are in a good agreement (16,19 %), but Allam's (Allam et al. 2005) and Prada's (Prada et al. 2003) SDSS DR1 samples show a higher excess of the early type galaxies that can be explained by the selection criteria and morphology definition method. We found a weak relation between isolation parameter and color index for the Single sample that may indicate that even in the low dense environment the morphology density relation is observed. We conclude that morphological properties of the resulting sample of isolated galaxies are highly dependent on the primary catalogue from which the galaxies were selected. Moreover, the selection criterion is also important but plays a secondary role in the resulting morphological content, color indices distribution and other parameters of the isolated galaxy samples. Only four galaxies are common in the 2MIG, QIsol, and CIG samples, namely UGC5184, UGC6121, UGC8495, and UGC9598, that allows to consider them as really most isolated galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Estimating the redshift distribution of photometric galaxy samples , II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009
Applications, tests of a new method
ABSTRACT In Lima et al. we presented a new method for estimating the redshift distribution, N(z), of a photometric galaxy sample, using photometric observables and weighted sampling from a spectroscopic subsample of the data. In this paper, we extend this method and explore various applications of it, using both simulations and real data from the Sloan Digital Sky Survey (SDSS). In addition to estimating the redshift distribution for an entire sample, the weighting method enables accurate estimates of the redshift probability distribution, p(z), for each galaxy in a photometric sample. Use of p(z) in cosmological analyses can substantially reduce biases associated with traditional photometric redshifts, in which a single redshift estimate is associated with each galaxy. The weighting procedure also naturally indicates which galaxies in the photometric sample are expected to have accurate redshift estimates, namely those that lie in regions of photometric-observable space that are well sampled by the spectroscopic subsample. In addition to providing a method that has some advantages over standard photo- z estimates, the weights method can also be used in conjunction with photo- z estimates e.g. by providing improved estimation of N(z) via deconvolution of N(zphot) and improved estimates of photo- z scatter and bias. We present a publicly available p(z) catalogue for ,78 million SDSS DR7 galaxies. [source]

Delaunay Tessellation Field Estimator analysis of the PSCz local Universe: density field and cosmic flow

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007
Emilio Romano-Díaz
ABSTRACT We apply the Delaunay Tessellation Field Estimator (DTFE) to reconstruct and analyse the matter distribution and cosmic velocity flows in the local Universe on the basis of the PSCz galaxy survey. The prime objective of this study is the production of optimal resolution 3D maps of the volume-weighted velocity and density fields throughout the nearby universe, the basis for a detailed study of the structure and dynamics of the cosmic web at each level probed by underlying galaxy sample. Fully volume-covering 3D maps of the density and (volume-weighted) velocity fields in the cosmic vicinity, out to a distance of 150 h,1 Mpc, are presented. Based on the Voronoi and Delaunay tessellation defined by the spatial galaxy sample, DTFE involves the estimate of density values on the basis of the volume of the related Delaunay tetrahedra and the subsequent use of the Delaunay tessellation as natural multidimensional (linear) interpolation grid for the corresponding density and velocity fields throughout the sample volume. The linearized model of the spatial galaxy distribution and the corresponding peculiar velocities of the PSCz galaxy sample, produced by Branchini et al., forms the input sample for the DTFE study. The DTFE maps reproduce the high-density supercluster regions in optimal detail, both their internal structure as well as their elongated or flattened shape. The corresponding velocity flows trace the bulk and shear flows marking the region extending from the Pisces,Perseus supercluster, via the Local Superclusters, towards the Hydra,Centaurus and the Shapley concentration. The most outstanding and unique feature of the DTFE maps is the sharply defined radial outflow regions in and around underdense voids, marking the dynamical importance of voids in the local Universe. The maximum expansion rate of voids defines a sharp cut-off in the DTFE velocity divergence probability distribution function. We found that on the basis of this cut-off DTFE manages to consistently reproduce the value of ,m, 0.35 underlying the linearized velocity data set. [source]

The DEEP2 galaxy redshift survey: the evolution of the blue fraction in groups and the field

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
Brian F. Gerke
ABSTRACT We explore the behaviour of the blue galaxy fraction over the redshift range 0.75 ,z, 1.3 in the DEEP2 Survey, both for field galaxies and for galaxies in groups. The primary aim is to determine the role that groups play in driving the evolution of galaxy colour at high z. In pursuing this aim, it is essential to define a galaxy sample that does not suffer from redshift-dependent selection effects in colour,magnitude space. We develop four such samples for this study: at all redshifts considered, each one is complete in colour,magnitude space, and the selection also accounts for evolution in the galaxy luminosity function. These samples will also be useful for future evolutionary studies in DEEP2. The colour segregation observed between local group and field samples is already in place at z, 1: DEEP2 groups have a significantly lower blue fraction than the field. At fixed z, there is also a correlation between blue fraction and galaxy magnitude, such that brighter galaxies are more likely to be red, both in groups and in the field. In addition, there is a negative correlation between blue fraction and group richness. In terms of evolution, the blue fraction in groups and the field remains roughly constant from z= 0.75 to 1, but beyond this redshift the blue fraction in groups rises rapidly with z, and the group and field blue fractions become indistinguishable at z, 1.3. Careful tests indicate that this effect does not arise from known systematic or selection effects. To further ensure the robustness of this result, we build on previous mock DEEP2 catalogues to develop mock catalogues that reproduce the colour,overdensity relation observed in DEEP2 and use these to test our methods. The convergence between the group and field blue fractions at z, 1.3 implies that DEEP2 galaxy groups only became efficient at quenching star formation at z, 2; this result is broadly consistent with other recent observations and with current models of galaxy evolution and hierarchical structure growth. [source]

Halo model at its best: constraints on conditional luminosity functions from measured galaxy statistics

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2006
Asantha Cooray
ABSTRACT Using the conditional luminosity function (CLF; the luminosity distribution of galaxies in a dark matter halo) as the fundamental building block, we present an empirical model for the galaxy distribution. The model predictions are compared with the published luminosity function (LF) and clustering statistics from the Sloan Digital Sky Survey (SDSS) at low redshifts, galaxy correlation functions from the Classifying Objects by Medium-Band Observations 17 (COMBO-17) survey at a redshift of 0.6, the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey at a redshift of unity, the Great Observatories Deep Origins Survey (GOODS) at a redshift around 3 and the Subaru/XMM,Newton Deep Field data at a redshift of 4. The comparison with statistical measurements allows us to constrain certain parameters related to analytical descriptions on the relation between a dark matter halo and its central galaxy luminosity, its satellite galaxy luminosity, and the fraction of early- and late-type galaxies of that halo. With the SDSS r -band LF at Mr < ,17, the lognormal scatter in the central galaxy luminosity at a given halo mass in the central galaxy,halo mass, Lc(M), relation is constrained to be 0.17+0.02,0.01, with 1, errors here and below. For the same galaxy sample, we find no evidence for a low-mass cut-off in the appearance of a single central galaxy in dark matter haloes, with the 68 per cent confidence level upper limit on the minimum mass of dark matter haloes to host a central galaxy, with luminosity Mr < ,17, is 2 × 1010 h,1 M,. If the total luminosity of a dark matter halo varies with halo mass as Lc(M) (M/Msat),s when M > Msat, using SDSS data, we find that Msat= (1.2+2.9,1.1) × 1013 h,1 M, and power-law slope ,s= 0.56+0.19,0.17 for galaxies with Mr < ,17 at z < 0.1. At z, 0.6, the COMBO-17 data allows these parameters for MB < ,18 galaxies to be constrained as (3.3+4.9,3.0) × 1013 h,1 M, and (0.62+0.33,0.27), respectively. At z, 4, Subaru measurements constrain these parameters for MB < ,18.5 galaxies as (4.12+5.90,4.08) × 1012 h,1 M, and (0.55+0.32,0.35), respectively. The redshift evolution associated with these parameters can be described as a combination of the evolution associated with the halo mass function and the luminosity,halo mass relation. The single parameter well constrained by clustering measurements is the average of the total satellite galaxy luminosity corresponding to the dark matter halo distribution probed by the galaxy sample. For SDSS, ,Lsat,= (2.1+0.8,0.4) × 1010 h,2 L,, while for GOODS at z, 3, ,Lsat, < 2 × 1011 h,2 L,. For SDSS, the fraction of galaxies that appear as satellites is 0.13+0.03,0.03, 0.11+0.05,0.02, 0.11+0.12,0.03 and 0.12+0.33,0.05 for galaxies with luminosities in the r, band from ,22 to ,21, ,21 to ,20, ,20 to ,19 and ,19 to ,18, respectively. In addition to constraints on central and satellite CLFs, we also determine model parameters of the analytical relations that describe the fraction of early- and late-type galaxies in dark matter haloes. We use our CLFs to establish the probability distribution of halo mass in which galaxies of a given luminosity could be found either at halo centres or as satellites. Finally, to help establish further properties of the galaxy distribution, we propose the measurement of cross-clustering between galaxies divided into two distinctly different luminosity bins. Our analysis shows how CLFs provide a stronger foundation to built-up analytical models of the galaxy distribution when compared with models based on the halo occupation number alone. [source]

Star formation in close pairs selected from the Sloan Digital Sky Survey

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2004
B. Nikolic
ABSTRACT The effect of galaxy interactions on star formation has been investigated using Data Release One of the Sloan Digital Sky Survey (SDSS). Both the imaging and spectroscopy data products have been used to construct a catalogue of nearest companions to a volume-limited (0.03 < z < 0.1) sample of galaxies drawn from the main galaxy sample of SDSS. Of the 13 973 galaxies in the volume-limited sample, we have identified 12 492 systems with companions at projected separations less than 300 kpc. Star formation rates for the volume-limited sample have been calculated from extinction and aperture corrected H, luminosities and, where available, IRAS data. Specific star formation rates were calculated by estimating galaxy masses from z -band luminosities, and r -band concentration indices were used as an indicator of morphological class. The mean specific star formation rate is significantly enhanced for projected separations less than 30 kpc. For late-type galaxies, the correlation extends out to projected separations of 300 kpc and is most pronounced in actively star-forming systems. The specific star formation rate is observed to decrease with increasing recessional velocity difference, but the magnitude of this effect is small compared to that associated with the projected separation. We also observe a tight relationship between the concentration index and pair separation; the mean concentration index is largest for pairs with separations of approximately 75 kpc and declines rapidly for separations smaller than this. This is interpreted as being due to the presence of tidally triggered nuclear starbursts in close pairs. Further, we find no dependence of star formation enhancement on the morphological type or mass of the companion galaxy. [source]

A weak lensing estimate from GEMS of the virial to stellar mass ratio in massive galaxies to z, 0.8

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006
Catherine Heymans
ABSTRACT We present constraints on the evolution of the virial to stellar mass ratio of galaxies with high stellar masses in the redshift range 0.2 < z < 0.8, by comparing weak lensing measurements of virial mass Mvir with estimates of stellar mass Mstar. For a complete sample of galaxies with log (Mstar/M,) > 10.5, where the majority show an early-type morphology, we find that the virial mass to stellar mass ratio is given by Mvir/Mstar= 53+13,16. Assuming a baryon fraction from the concordance cosmology, this corresponds to a stellar fraction of baryons in massive galaxies of ,*b/,b= 0.10 ± 0.03. Analysing the galaxy sample in different redshift slices, we find little or no evolution in the virial to stellar mass ratio, and place an upper limit of ,2.5 on the growth of massive galaxies through the conversion of gas into stars from z= 0.8 to the present day. [source]

Comparisons of the environmental dependence of galaxy properties between blue late-types and red late-types

ASTRONOMISCHE NACHRICHTEN, Issue 7 2010
X.F. Deng
Abstract Using the volume-limited Main galaxy sample of the Sloan Digital Sky Survey Data Release 6 (SDSS DR6), we investigate the difference of the environmental dependence of galaxy properties between blue late-types and red late-types, and find that the galaxy luminosity and concentration index are almost independent of the local density in the two samples. We also note a strong correlation between g , r color and the environment in the red late-type sample, while this correlation is very weak in the blue late-type sample (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The evolution of cluster early-type galaxies over the past 8 Gyr

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
A. Fritz
Abstract We present the Fundamental Plane (FP) of early-type galaxies in the clusters of galaxies RXJ1415.1+3612 at z = 1.013. This is the first detailed FP investigation of cluster early-type galaxies at redshift z = 1. The distant cluster galaxies follow a steeper FP relation compared to the local FP. The change in the slope of the FP can be interpreted as a massdependent evolution. To analyse in more detail the galaxy population in high redshift galaxy clusters at 0.8 < z < 1, we combine our sample with a previous detailed spectroscopic study of 38 early-type galaxies in two distant galaxy clusters, RXJ0152.7,1357 at z = 0.83 and RXJ1226.9+3332 at z = 0.89. For all clusters Gemini/GMOS spectroscopy with high signal-to-noise and intermediate-resolution has been acquired to measure the internal kinematics and stellar populations of the galaxies. From HST/ACS imaging, surface brightness profiles, morphologies and structural parameters were derived for the galaxy sample. The least massive galaxies (M = 2 x 1010 M,) in our sample have experienced their most recent major star formation burst at zform , 1.1. For massive galaxies (M > 2 x 1011 M,) the bulk of their stellar populations have been formed earlier zform , 1.6. Our results confirm previous findings by Jørgensen et al. This suggests that the less massive galaxies in the distant clusters have much younger stellar populations than their more massive counterparts. One explanation is that low-mass cluster galaxies have experienced more extended star formation histories with more frequent bursts of star formation with shorter duration compared to the formation history of high-mass cluster galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

The evolution of spheroidal galaxies in different environments

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
A. Fritz
Abstract We analyse the kinematic and chemical evolution of 203 distant spheroidal (elliptical and S0) galaxies at 0.2 < z < 0.8 which are located in different environments (rich clusters, low-mass clusters and in the field). VLT/FORS and CAHA/MOSCA spectra with intermediate-resolution have been acquired to measure the internal kinematics and stellar populations of the galaxies. From HST/ACS and WFPC2 imaging, surface brightness profiles and structural parameters were derived for half of the galaxy sample. The scaling relations of the Faber-Jackson relation and Kormendy relation as well as the Fundamental Plane indicate a moderate evolution for the whole galaxy population in each density regime. In all environments, S0 galaxies show a faster evolution than elliptical galaxies. For the cluster galaxies a slight radial dependence of the evolution out to one virial radius is found. Dividing the samples with respect to their mass, a mass dependent evolution with a stronger evolution of lower-mass galaxies (M < 2 × 1011 M,) is detected. Evidence for recent star formation is provided by blue colours and weak [OII] emission or strong H, absorption features in the spectra. The results are consistent with a down-sizing formation scenario which is independent from the environment of the galaxies (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Estimating the redshift distribution of photometric galaxy samples , II.

Morphological properties of isolated galaxies vs. isolation criteria

Toward an unbiased sample of X-ray selected normal galaxies outside the local Universe

ASTRONOMISCHE NACHRICHTEN, Issue 2 2008
A. GeorgakakisArticle first published online: 14 FEB 200
Abstract This paper shows that our understanding of the statistical properties of X-ray selected normal galaxies (e.g. X-ray luminosity function) can be significantly improved by combining a wide-area XMM-Newton survey with the moderare resolution and high S/N optical spectroscopy of the SDSS. Such a combined dataset has the potential to minimise uncertainties that affect existing normal galaxy samples at X-rays, such as small number statistics, cosmic variance, AGN contamination and incompleteness at bright X-ray luminosities. It is demonstrated that a 100 deg2 XMM-Newton survey in the SDSS area to the limit fX(0.5,2 keV) , 5 × 10,15 erg cm,2 s,1 will detect over 400 X-ray selected normal galaxies with excellent control over systematic biases, thereby providing tight contraints on the X-ray luminosity function at z , 0.1. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]