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Massive Galaxies (massive + galaxy)
Selected AbstractsRed star-forming and blue passive galaxies in clustersMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009Smriti Mahajan ABSTRACT We explore the relation between colour (measured from photometry) and specific star formation rate (derived from optical spectra obtained by the Sloan Digital Sky Survey Data Release 4) of over 6000 galaxies (Mr,,20.5) in and around (<3 r200) low-redshift (z < 0.12) Abell clusters. Even though, as expected, most red sequence galaxies have little or no ongoing star formation, and most blue galaxies are currently forming stars, there are significant populations of red star-forming and blue passive galaxies. This paper examines various properties of galaxies belonging to the latter two categories, to understand why they deviate from the norm. These properties include morphological parameters, internal extinction, spectral features such as EW(H,) and the 4000 Ĺ break, and metallicity. Our analysis shows that the blue passive galaxies have properties very similar to their star-forming counterparts, except that their large range in H, equivalent width indicates recent truncation of star formation. The red star-forming galaxies fall into two broad categories, one of them being massive galaxies in cluster cores dominated by an old stellar population, but with evidence of current star formation in the core (possibly linked with active galactic nuclei). For the remaining red star-forming galaxies, it is evident from spectral indices, stellar and gas-phase metallicities and mean stellar ages that their colours result from the predominance of a metal-rich stellar population. Only half of the red star-forming galaxies have extinction values consistent with a significant presence of dust. The implication of the properties of these star-forming galaxies on environmental studies, like that of the Butcher,Oemler effect, is discussed. [source] A census of metals and baryons in stars in the local UniverseMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008Anna Gallazzi ABSTRACT We combine stellar metallicity and stellar mass estimates for a large sample of galaxies drawn from the Sloan Digital Sky Survey Data Release 2 (SDSS DR2) spanning wide ranges in physical properties, in order to derive an inventory of the total mass of metals and baryons locked up in stars in the local Universe. Physical parameter estimates are derived from galaxy spectra with high signal-to-noise ratio (S/N) (of at least 20). Co-added spectra of galaxies with similar velocity dispersions, absolute r -band magnitudes and 4000-Ĺ break values are used for those regions of parameter space where individual spectra have lower S/N. We estimate the total density of metals ,Z and of baryons ,* in stars and, from these two quantities, we obtain a mass- and volume-averaged stellar metallicity of ,Z*,= 1.04 ± 0.14 Z,, i.e. consistent with solar. We also study how metals are distributed in galaxies according to different properties, such as mass, morphology, mass- and light-weighted age, and we then compare these distributions with the corresponding distributions of stellar mass. We find that the bulk of metals locked up in stars in the local Universe reside in massive, bulge-dominated galaxies, with red colours and high 4000-Ĺ break values corresponding to old stellar populations. Bulge-dominated and disc-dominated galaxies contribute similar amounts to the total stellar mass density, but have different fractional contributions to the mass density of metals in stars, in agreement with the mass,metallicity relation. Bulge-dominated galaxies contain roughly 40 per cent of the total amount of metals in stars, while disc-dominated galaxies less than 25 per cent. Finally, at a given galaxy stellar mass, we define two characteristic ages as the median of the distributions of mass and metals as a function of age. These characteristic ages decrease progressively from high-mass to low-mass galaxies, consistent with the high formation epochs of stars in massive galaxies. [source] Probing galactic dark matter in dense environments: on the strong lensing efficiency of galaxies in rich clustersMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007Lindsay J. King ABSTRACT The recent detection by Limousin et al. of five new strong lensing events dominated by galaxy cluster members in Abell 1689, and outside the critical regime of the cluster itself, offers a way to obtain constraints on the cluster mass distribution in a region inaccessible to standard lensing analysis. In addition, modelling such systems will provide another window on the dark matter haloes of galaxies in very dense environments. Here, it is shown that the boost in image separation due to the external shear and convergence from a smooth cluster component means that more numerous, less massive galaxies have the potential to create multiple images with detectable separations, relative to isolated field galaxies. This comes in addition to a potential increase in their lensing (source plane) cross-section. To gain insight into the factors involved and as a precursor to a numerical study using N -body simulations, a simple analytic model of a cluster at z= 0.3 lensing background galaxies at z= 2 is considered here. The fiducial model has cluster members with isothermal density profiles and luminosities L, distributed in a Schechter function (faint-end slope ,=,1.25), related to their velocity dispersions , via the Faber,Jackson scaling L,,4. Just outside the critical regime of the cluster, the scale of galaxy-dominated image separations is significantly increased. Folding in the fact that less massive galaxies present a lower lensing cross-section, and that the cross-section can itself be enhanced in an external field leads to a factor of a few times more detected events relative to field galaxies. These values will be higher closer to the critical curve. Given that the events in Abell 1689 were detected over a very small region of the cluster where ACS data were available, this motivates the search for such events in other clusters. [source] Constraints on the merging time-scale of luminous red galaxies, or, where do all the haloes go?MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007Charlie Conroy ABSTRACT In the , cold dark matter cosmology, dark matter haloes grow primarily through the accretion of smaller haloes. Much of the mass in a halo of 1014 M, comes in through accretion of ,1013 M, haloes. If each such halo hosted one luminous red galaxy (LRG) then the accretion of so many haloes is at odds with the observed number of LRGs in clusters unless these accreted LRGs merge or disrupt on relatively short time-scales (,2 Gyr). These time-scales are consistent with classical dynamical friction arguments, and imply that two to three LRGs have merged or disrupted within each halo more massive than 1014 M, by z= 0. The total amount of stellar mass brought into these massive haloes by z= 0 is consistent with observations once the intracluster light (ICL) is included. If disrupted LRGs build up the ICL, then the hierarchical growth of massive haloes implies that a substantial amount of ICL should also surround satellite LRGs, as suggested by recent observations of the Virgo cluster. Finally, we point out that these results are entirely consistent with a non-evolving clustering strength and halo occupation distribution, and note that observations of the latter in fact support the hypothesis that merging/disruption of massive galaxies does indeed take place at late times. [source] The first appearance of the red sequence of galaxies in proto-clusters at 2 ,z, 3MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007Tadayuki Kodama ABSTRACT We explore the evolved galaxy population in the proto-clusters around four high- z radio galaxies at 2 ,z, 3 based on wide-field near-infrared (NIR) imaging. Three of the four fields are known proto-clusters as demonstrated by overdensities of line-emitting galaxies at the same redshifts as the radio galaxies found by narrow-band surveys and spectroscopic follow-up observations. We imaged the fields of three targets (PKS 1138,262, USS 0943,242 and MRC 0316,257) to a depth of Ks, 22 (Vega magnitude, 5,) over a 4 × 7 arcmin2 area centred on the radio galaxies with a new wide-field NIR camera, Multi-Object Infra-Red Camera and Spectrograph (MOIRCS), on the Subaru Telescope. Another target (USS 1558,003) was observed with Son of ISAAC on the New technology Telescope (NTT) to a depth of Ks= 20.5 (5,) over a 5 × 5 arcmin2 area. We apply colour cuts in J,Ks and/or JHKs in order to exclusively search for galaxies located at high redshifts: z > 2. To the 5, limiting magnitudes, we see a significant excess of NIR-selected galaxies by a factor of 2 to 3 compared to those found in the field of GOODS-South. The spatial distribution of these NIR-selected galaxies is not uniform and traces structures similar to those of emission-line galaxies, although the samples of NIR-selected galaxies and emitters show little overlap, from which we conclude that the former tend to be an evolved population with much higher stellar mass than the latter, young and active emitters. We focus on the NIR colour,magnitude sequence of the evolved population and find that the bright-end (Mstars > 1011 M,) of the red sequence is well populated by z, 2 but much less so in the z, 3 proto-clusters. This may imply that the bright-end of the colour,magnitude sequence first appeared between z= 3 and 2, an era coinciding with the appearance of sub-mm galaxies and the peak of the cosmic star formation rate. Our observations show that during the same epoch, massive galaxies are forming in high-density environments by vigorous star formation and assembly. [source] The halo mass function from the dark ages through the present dayMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2007Darren S. Reed ABSTRACT We use an array of high-resolution N -body simulations to determine the mass function of dark matter haloes at redshifts 10,30. We develop a new method for compensating for the effects of finite simulation volume that allows us to find an approximation to the true ,global' mass function. By simulating a wide range of volumes at different mass resolution, we calculate the abundance of haloes of mass 105,12 h,1 M,. This enables us to predict accurately the abundance of the haloes that host the sources that reionize the Universe. In particular, we focus on the small mass haloes (,105.5,6 h,1 M,) likely to harbour Population III stars where gas cools by molecular hydrogen emission, early galaxies in which baryons cool by atomic hydrogen emission at a virial temperature of ,104K (,107.5,8 h,1 M,), and massive galaxies that may be observable at redshift ,10. When we combine our data with simulations that include high-mass haloes at low redshift, we find that the best fit to the halo mass function depends not only on the linear overdensity, as is commonly assumed in analytic models, but also on the slope of the linear power spectrum at the scale of the halo mass. The Press,Schechter model gives a poor fit to the halo mass function in the simulations at all epochs; the Sheth-Tormen model gives a better match, but still overpredicts the abundance of rare objects at all times by up to 50 per cent. Finally, we consider the consequences of the recently released WMAP 3-yr cosmological parameters. These lead to much less structure at high redshift, reducing the number of z= 10,mini-haloes' by more than a factor of two and the number of z= 30 galaxy hosts by nearly four orders of magnitude. Code to generate our best-fitting halo mass function may be downloaded from http://icc.dur.ac.uk/Research/PublicDownloads/genmf_readme.html. [source] Extracting star formation histories from medium-resolution galaxy spectraMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006H. Mathis ABSTRACT We adapt an existing data compression algorithm, moped, to the extraction of median-likelihood star formation histories from medium-resolution galaxy spectra. By focusing on the high-pass components of galaxy spectra, we minimize potential uncertainties arising from the spectrophotometric calibration and intrinsic attenuation by dust. We validate our approach using model high-pass spectra of galaxies with different star formation histories covering the wavelength range 3650,8500 Ĺ at a resolving power of ,2000. We show that the method can recover the full star formation histories of these models, without prior knowledge of the metallicity, to within an accuracy that depends sensitively on the signal-to-noise ratio. The investigation of the sensitivity of the flux at each wavelength to the mass fraction of stars of different ages allows us to identify new age-sensitive features in galaxy spectra. We also highlight a fundamental limitation in the recovery of the star formation histories of galaxies for which the optical signatures of intermediate-age stars are masked by those of younger and older stars. As an example of application, we use this method to derive average star formation histories from the highest-quality spectra of typical (in terms of their stellar mass), morphologically identified early- and late-type galaxies in the Early Data Release (EDR) of the Sloan Digital Sky Survey (SDSS). We find that, in agreement with the common expectation, early-type galaxies must have formed most of their stars over 8 Gyr ago, although a small fraction of the total stellar mass of these galaxies may be accounted for by stars with ages down to 4 Gyr. In contrast, late-type galaxies appear to have formed stars at a roughly constant rate. We also investigate the constraints set by the high-pass signal in the stacked spectra of a magnitude-limited sample of 20 623 SDSS-EDR galaxies on the global star formation history of the Universe and its distribution among galaxies in different mass ranges. We confirm that the stellar populations in the most massive galaxies today appear to have formed on average earlier than those in the least massive galaxies. Our results do not support the recent suggestion of a statistically significant peak in the star formation activity of the Universe at redshifts below unity, although such a peak is not ruled out. [source] Drag-gravity torques on galaxies in clusters: radial small-scale alignment effectsMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010Alejandro González-Sánchez ABSTRACT We calculate the torque on galaxies in clusters due to gravity and to dynamical friction forces in order to study the possible origin of small-scale alignment effects as the result of interactions with their environment. The equation of motion for the position angle of a galaxy is derived by using a simple model. We find that weak radial alignment effects can be produced by this mechanism involving only the most massive galaxies. We also introduce a dependence on the cluster eccentricity to our equations in order to explore the alignment of galaxies with the cluster's major axis. We find that in the inner regions of high eccentricity clusters, alignments of massive galaxies with the cluster's major axis dominate over the radial ones. This mechanism could account for the observed alignment effects of the most massive galaxies with the major axis of their host cluster. Our results suggest that dynamical friction is a viable generator of alignment only for the most massive cluster galaxies. For the observed alignments of normal galaxies a primordial origin has to be explored. [source] Revisiting the origin of the high metallicities of sub-damped Lyman-alpha systems,MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2009Miroslava Dessauges-Zavadsky ABSTRACT Sub-damped Lyman-alpha systems (sub-DLAs) have previously been found to exhibit a steeper metallicity evolution than the classical damped Lyman-alpha systems (DLAs), evolving to close to solar metallicity by z, 1. From new high-resolution spectra of 17 sub-DLAs, we have increased the number of measurements of [Fe/H] at z < 1.7 by 25 per cent and compiled the most complete literature sample of sub-DLA and DLA abundances to date. We find that sub-DLAs are indeed significantly more metal-rich than DLAs, but only at z < 1.7; the metallicity distributions of sub-DLAs and DLAs at z > 1.7 are statistically consistent. We also present the first evidence that sub-DLAs follow a velocity width,metallicity correlation over the same velocity range as DLAs, but the relation is offset to higher metallicities than the DLA relation. On the basis of these results, we revisit the previous explanation that the systematically higher metallicities observed in sub-DLAs are indicative of higher host galaxy masses. We discuss the various problems that this interpretation encounters and conclude that in general sub-DLAs are not uniquely synonymous with massive galaxies. We rule out physically related sources of bias (dust, environment, ionization effects) and examine systematics associated with the selection and analysis of low-redshift sub-DLAs. We propose that the high metallicities of sub-DLAs at z < 1.7 that drives an apparently steep evolution may be due to the selection of most low-redshift sub-DLAs based on their high Mg ii equivalent widths. [source] A weak lensing estimate from GEMS of the virial to stellar mass ratio in massive galaxies to z, 0.8MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2006Catherine 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] The evolution of cluster early-type galaxies over the past 8 GyrASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009A. 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 Jřrgensen 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 Granada workshop on High Redshift Radio Galaxies: An overviewASTRONOMISCHE NACHRICHTEN, Issue 2-3 2006H. J. A. Röttgering Abstract The Granada workshop on High Redshift Radio Galaxies (HzRGs) gave an excellent overview of the progress that has been made in this field during the last 3 years. Here we briefly review some of the results, with an emphasis on what studies of HzRGs can teach us about the formation and evolution of massive galaxies, clusters and active galactic nuclei (AGN). Of great relevance for this workshop are scenarios that describe certain aspects of the evolution of radio galaxies, including (i) the sequence of events after merging of galaxies that ultimately lead to extended powerful radio sources and (ii) the mass assembly and virialization of the hosting massive galaxies and their associated (proto-)clusters. Furthermore, I briefly discuss two projects that are important for a further understanding of AGN and high redshift radio galaxies. First, using the MIDI instrument mounted on the VLT Interferometer, the dusty tori of nearby AGN can be studied in the range of 8,13 micron at high angular resolution. The first result on the nearby AGN NGC 1068 as presented by Jaffe et al. (2004) indicated the presence of a hot (T > 800 K), compact (,1 pc) component, possible identified with the base of the jet and a warm (270 K), well-resolved (3 × 4 pc) component associated with the alleged torus. Second, LOFAR is a new low frequency radio telescope that is currently being build in the Netherlands and is expected to be operational in 2008. With 50 stations spread over an area of 100 km in diameter, its resolution and sensitivity will be unprecedented in the frequency range 10,240 MHz. LOFAR will be a unique instrument that will impact a broad range of astrophysical topics varying from the epoch of reionisation, to gamma ray bursts and cosmic rays. Surveys with LOFAR will be of paramount importance for studies of HzRGs: It will enable (i) defining samples of radio galaxies with redshifts higher than 6, (ii) observations of starbursting galaxies in proto-clusters, and (iii) mapping out the low-frequency radio emission of virtually all northern radio-loud AGN in revolutionary detail. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Models of the Cosmic Horseshoe gravitational lens J1004+4112MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2008S. Dye ABSTRACT We model the extremely massive and luminous lens galaxy in the Cosmic Horseshoe Einstein ring system J1004+4112, recently discovered in the Sloan Digital Sky Survey. We use the semilinear method of Warren & Dye, which pixelizes the source surface brightness distribution, to invert the Einstein ring for sets of parametrized lens models. Here, the method is refined by exploiting Bayesian inference to optimise adaptive pixelization of the source plane and to choose between three differently parametrized models: a singular isothermal ellipsoid, a power-law model and a Navarro, Frenk & White (NFW) profile. The most probable lens model is the power law with a volume mass density ,,r,1.96±0.02 and an axis ratio of ,0.8. The mass within the Einstein ring (i.e. within a cylinder with projected distance of ,30 kpc from the centre of the lens galaxy) is (5.02 ± 0.09) × 1012 M ,, and the mass-to-light ratio is ,30. Even though the lens lies in a group of galaxies, the preferred value of the external shear is almost zero. This makes the Cosmic Horseshoe unique amongst large separation lenses, as almost all the deflection comes from a single, very massive galaxy with little boost from the environment. [source] | ||||||||||