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Formation History (formation + history)

Distribution by Scientific Domains

Physics and Astronomy	93%
Earth and Environmental Science	6%

Kinds of Formation History

star formation history

Selected Abstracts

Petrology, Mineralogy and Geochemisty of Antarctic Mesosiderite GRV 020175: Implications for Its Complex Formation History

ACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2010
Linyan WANG
Abstract: GRV 020175 is an Antarctic mesosiderite, containing about 43 vol% silicates and 57 vol% metal. Metal occurs in a variety of textures from irregular large masses, to veins penetrating silicates, and to matrix fine grains. The metallic portion contains kamacite, troilite and minor taenite. Terrestrial weathering is evident as partial replacement of the metal and troilite veins by Fe oxides. Silicate phases exhibit a porphyritic texture with pyroxene, plagioclase, minor silica and rare olivine phenocrysts embedded in a fine-grained groundmass. The matrix is ophitic and consists mainly of pyroxene and plagioclase grains. Some orthopyroxene phenocrysts occur as euhedral crystals with chemical zoning from a magnesian core to a ferroan overgrowth; others are characterized by many fine inclusions of plagioclase composition. Pigeonite has almost inverted to its orthopyroxene host with augite lamellae, enclosed by more magnesian rims. Olivine occurs as subhedral crystals, surrounded by a necklace of tiny chromite grains (about 2,3 ,m). Plagioclase has a heterogeneous composition without zoning. Pyroxene geothermometry of GRV 020175 gives a peak metamorphic temperature (,1000°C) and a closure temperature (,875°C). Molar Fe/Mn ratios (19,32) of pyroxenes are consistent with mesosiderite pyroxenes (16,35) and most plagioclase compositions (An87.5,96.6) are within the range of mesosiderite plagioclase grains (An88,95). Olivine composition (Fo53.8) is only slightly lower than the range of olivine compositions in mesosiderites (Fo55,90). All petrographic characteristics and chemical compositions of GRV 020175 are consistent with those of mesosiderite and based on its matrix texture and relatively abundant plagioclase, it can be further classified as a type 3A mesosiderite. Mineralogical, petrological, and geochemical studies of GRV 020175 imply a complex formation history starting as rapid crystallization from a magma in a lava flow on the surface or as a shallow intrusion. Following primary igneous crystallization, the silicate underwent varying degrees of reheating. It was reheated to 1000°C, followed by rapid cooling to 875°C. Subsequently, metal mixed with silicate, during or after which, reduction of silicates occurred; the reducing agent is likely to have been sulfur. After redox reaction, the sample underwent thermal metamorphism, which produced the corona on the olivine, rims on the inverted pigeonite phenocrysts and overgrowths on the orthopyroxene phenocrysts, and homogenized matrix pyroxenes. Nevertheless, metamorphism was not extensive enough to completely reequilibrate the GRV 020175 materials. [source]

The properties of the stellar populations in ULIRGs , I. Sample, data and spectral synthesis modelling

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2009
J. Rodríguez Zaurín
ABSTRACT We present deep long-slit optical spectra for a sample of 36 ultraluminous infrared galaxies (ULIRGs), taken with the William Herschel Telescope on La Palma with the aim of investigating the star formation histories and testing evolutionary scenarios for such objects. Here we present the sample, the analysis techniques and a general overview of the properties of the stellar populations; a more detailed discussion will be presented in a forthcoming paper. Spectral synthesis modelling has been used in order to estimate the ages of the stellar populations found in the diffuse light sampled by the spectra in both the nuclear and extended regions of the target galaxies. We find that adequate fits can be obtained using combinations of young stellar populations (YSPs; tYSP, 2 Gyr), with ages divided into two groups: very young stellar populations (VYSPs; tVYSP, 100 Myr) and intermediate-young stellar populations (IYSPs; 0.1 < tIYSP, 2 Gyr). Our results show that YSPs are present at all locations of the galaxies covered by our slit positions, with the exception of the northern nuclear region of the ULIRG IRAS 23327+2913. Furthermore, VYSPs are present in at least 85 per cent of the 133 extraction apertures used for this study, being more significant in the nuclear regions of the galaxies. Old stellar populations (OSPs; tOSP > 2 Gyr) do not make a major contribution to the optical light in the majority of the apertures extracted. In fact they are essential for fitting the spectra in only 5 per cent (seven) of the extracted apertures. The estimated total masses for the YSPs (VYSPs + IYSPs) are in the range 0.18 × 1010,MYSP, 50 × 1010 M,. We have also estimated the bolometric luminosities associated with the stellar populations detected at optical wavelengths, finding that they fall in the range 0.07 × 1012 < Lbol < 2.2 × 1012 L,. In addition, we find that reddening is significant at all locations in the galaxies. This result emphasizes the importance of accounting for reddening effects when modelling the stellar populations of star-forming galaxies. [source]

Formation and evolution of dwarf elliptical galaxies , II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2009
Spatially resolved star formation histories
ABSTRACT We present optical Very Large Telescope spectroscopy of 16 dwarf elliptical galaxies (dEs) comparable in mass to NGC 205, and belonging to the Fornax cluster and to nearby groups of galaxies. Using full-spectrum fitting, we derive radial profiles of the SSP-equivalent ages and metallicities. We make a detailed analysis with ulyss and steckmap of the star formation history in the core of the galaxies and in an aperture of one effective radius. We resolved the history into one to four epochs. The statistical significance of these reconstructions was carefully tested; the two programs give remarkably consistent results. The old stellar population of the dEs, which dominates their mass, is likely coeval with that of massive ellipticals or bulges, but the star formation efficiency is lower. Important intermediate age (1,5 Gyr) populations and frequently tails of star formation until recent times are detected. These histories are reminiscent of their lower mass dwarf spheroidal counterparts of the Local Group. Most galaxies (10/16) show significant metallicity gradients, with metallicity declining by 0.5 dex over one half-light radius on average. These gradients are already present in the old population. The flattened (or discy), rotating objects (6/16) have flat metallicity profiles. This may be consistent with a distinct origin for these galaxies or it may be due to their geometry. The central single stellar population equivalent age varies between 1 and 6 Gyr, with the age slowly increasing with radius in the vast majority of objects. The group and cluster galaxies have similar radial gradients and star formation histories. The strong and old metallicity gradients place important constraints on the possible formation scenarios of dEs. Numerical simulations of the formation of spherical low-mass galaxies reproduce these gradients, but they require a longer time for them to build up. A gentle depletion of the gas, by ram pressure stripping or starvation, could drive the gas-rich, star-forming progenitors to the present dEs. [source]

A census of young stellar populations in the warm ULIRG PKS 1345+12

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
J. Rodríguez Zaurín
ABSTRACT We present a detailed investigation of the young stellar populations (YSP) in the radio-loud ultraluminous infrared galaxy (ULIRG), PKS 1345+12 (z= 0.12), based on high-resolution Hubble Space Telescope (HST) imaging and long-slit spectra taken with the William Herschel Telescope (WHT) at La Palma. While the images clearly show bright knots suggestive of super star clusters (SSCs), the spectra reveal the presence of YSP in the diffuse light across the full extent of the halo of the merging double nucleus system. Spectral synthesis modelling has been used to estimate the ages of the YSP for both the SSC and the diffuse light sampled by the spectra. For the SSC, we find ages tSSC < 6 Myr with reddenings 0.2 < E(B,V) < 0.5 and masses 106 < MYSPSSC < 107 M,. In the region to the south of the western nucleus that contains the SSC our modelling of the spectrum of the diffuse light is also consistent with a relatively young age for the YSP (,5 Myr), although older YSP ages cannot be ruled out. However, in other regions of the galaxy we find that the spectra of the diffuse light component can only be modelled with a relatively old post-starburst YSP (0.04,1.0 Gyr) or with a disc galaxy template spectrum. The results demonstrate the importance of accounting for reddening in photometric studies of SSC and highlight the dangers of focusing on the highest surface brightness regions when trying to obtain a general impression of the star formation activity in the host galaxies of ULIRGs. The case of PKS 1345+12 provides clear evidence that the star formation histories of the YSP in ULIRGs are complex. While the SSC represent the vigorous phase of star formation associated with the final stages of the merger, the YSP in the diffuse light are likely to represent star formation in one or more of the merging galaxies at an earlier stage or prior to the start of the merger. Intriguingly, our long-slit spectra show line splitting at the locations of the SSC, indicating that they are moving at up to 450 km s,1 with respect to the local ambient gas. Given their kinematics, it is plausible that the SSCs have been formed either in fast moving gas streams/tidal tails that are falling back into the nuclear regions as part of the merger process or as a consequence of jet-induced star formation linked to the extended, diffuse radio emission detected in the halo of the galaxy. [source]

The stellar mass density at z, 6 from Spitzer imaging of i,-drop galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2007
Laurence P. Eyles
ABSTRACT We measure the ages, stellar masses, and star formation histories of z, 6 galaxies, observed within 1 Gyr of the big bang. We use imaging from the Hubble Space Telescope (HST) and the Spitzer Space Telescope from the public ,Great Observatories Origins Deep Survey' (GOODS), coupled with ground-based near-infrared imaging, to measure their spectral energy distributions (SEDs) from 0.8,5 ,m, spanning the rest-frame ultraviolet (UV) and optical. From our sample of ,50 ,i,-drop' Lyman-break star-forming galaxies in GOODS-South with z,AB < 27, we focus on ,30 with reliable photometric or spectroscopic redshifts. Half of these are confused with foreground sources at Spitzer resolution, but from the 16 with clean photometry we find that a surprisingly large fraction (40 per cent) have evidence for substantial Balmer/4000-Å spectral breaks. This indicates the presence of old underlying stellar populations that dominate the stellar masses. For these objects, we find ages of ,200,700 Myr, implying formation redshifts of 7 ,zf, 18, and large stellar masses in the range ,1,3 × 1010 M,. Analysis of seven i,-drops that are undetected at 3.6 ,m indicates that these are younger, considerably less massive systems. We calculate that emission line contamination should not severely affect our photometry or derived results. Using SED fits out to 8 ,m, we find little evidence for substantial intrinsic dust reddening in our sources. We use our individual galaxy results to obtain an estimate of the global stellar mass density at z, 6. Correcting for incompleteness in our sample, we find the z, 6 comoving stellar mass density to be 2.5 × 106 M, Mpc,3. This is a lower limit, as post-starburst and dust-obscured objects, and also galaxies below our selection thresholds, are not accounted for. From our results, we are able to explore the star formation histories of our selected galaxies, and we suggest that the past global star formation rate may have been much higher than that observed at the z, 6 epoch. The associated UV flux we infer at z > 7 could have played a major role in reionizing the Universe. [source]

The stellar content of the isolated transition dwarf galaxy DDO210,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
Alan W. McConnachie
ABSTRACT We use Subaru Suprime-Cam and VLT FORS1 photometry of the dwarf galaxy DDO210 to study the global stellar content and structural properties of a transition-type galaxy (with properties intermediate between dwarf irregular and dwarf spheroidal systems). This galaxy is sufficiently isolated that tidal interactions are not likely to have affected its evolution in any way. The colour,magnitude diagrams of DDO210 show a red giant branch (RGB) population (with an RGB bump), a bright asymptotic giant branch population, a red clump, young main-sequence stars and blue-loop stars. The youngest stars formed within the last 60 Myr and have a distinct radial distribution compared to the main population. Whereas the overall stellar spatial distribution and H i spatial distribution are concentric, the young stars are offset from the centre of DDO210 and are coincident with a ,dent' in the H i distribution. The implied recent star formation rate required to form the young population is significantly higher than the derived current star formation rate, by a factor of >10. Most of the stars in DDO210 are found in a red clump, and its mean I -band magnitude suggests that the majority of stars in DDO210 have an average age of 4+2,1 Gyr. Given this age, the colour of the RGB implies a mean metallicity of [Fe/H],,1.3. By comparing the shape of the red clump with models for a variety of star formation histories, we estimate that an old (>10 Gyr) stellar population can contribute ,20,30 per cent of the stars in DDO210 at most. The unusual star formation history of DDO210, its low-mass estimate and its isolated nature, provide insight into how star formation proceeds in the lowest mass, unperturbed, dwarf galaxy haloes. [source]

Extracting star formation histories from medium-resolution galaxy spectra

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2006
H. 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 Å 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]

Dwarf elliptical galaxies: structure, star formation and colour,magnitude diagrams

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2001
Giovanni Carraro
The aim of this paper is to cast light on the formation and evolution of elliptical galaxies by means of N -body hydrodynamical simulations that include star formation, feedback and chemical evolution. Particular attention is paid to the case of dwarf spheroidals of the Local Group which, thanks to their proximity and modern ground-based and space instrumentation, can be resolved into single stars so that independent determinations of their age and star formation history can be derived. Indeed, the analysis of the colour,magnitude diagram of their stellar content allows us to infer the past history of star formation and chemical enrichment, thus setting important constraints on galactic models. Dwarf galaxies are known to exhibit complicated histories of star formation ranging from a single very old episode to a series of bursts over most of the Hubble time. By understanding the physical process driving star formation in these objects, we might be able to infer the mechanism governing star formation in more massive elliptical galaxies. Given these premises, we start from virialized haloes of dark matter, and follow the infall of gas into the potential wells and the formation of stars. We find that in objects of the same total mass, different star formation histories are possible, if the collapse phase started at different initial densities. We predict the final structure of dwarf spheroidal galaxies, their kinematics, their large-scale distribution of gas and stars, and their detailed histories of the star formation and metal enrichment. Using a population synthesis technique, star formation and metal enrichment rates are then adopted to generate the present colour,magnitude diagrams of the stellar populations hosted by dwarf spheroidal galaxies. The simulations are made assuming the redshift of galaxy formation and varying the cosmological parameters H0 and q0. The resulting colour,magnitude diagrams are then compared with the observational ones for some dwarf spheroidals of the Local Group. [source]

Constraining the star formation histories of spiral bulges

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000
R. N. Proctor
Stellar populations in spiral bulges are investigated using the Lick system of spectral indices. Long-slit spectroscopic observations of line strengths and kinematics made along the minor axes of four spiral bulges are reported. Comparisons are made between central line strengths in spiral bulges and those in other morphological types [elliptical, spheroidal (Sph) and S0]. The bulges investigated are found to have central line strengths comparable to those of single stellar populations of approximately solar abundance or above. Negative radial gradients are observed in line strengths, similar to those exhibited by elliptical galaxies. The bulge data are also consistent with correlations between Mg2, Mg2 gradient and central velocity dispersion observed in elliptical galaxies. In contrast to elliptical galaxies, central line strengths lie within the loci defining the range of ,Fe, and Mg2 achieved by Worthey's solar abundance ratio, single stellar populations (SSPs). The implication of solar abundance ratios indicates significant differences in the star formation histories of spiral bulges and elliptical galaxies. A ,single zone with infall' model of galactic chemical evolution, using Worthey's SSPs, is used to constrain the possible star formation histories of our sample. We show that the ,Fe,, Mg2 and H, line strengths observed in these bulges cannot be reproduced using primordial collapse models of formation but can be reproduced by models with extended infall of gas and star formation (2,17 Gyr) in the region modelled. One galaxy (NGC 5689) shows a central population with a luminosity-weighted average age of ,5 Gyr, supporting the idea of extended star formation. Kinematic substructure, possibly associated with a central spike in metallicity, is observed at the centre of the Sa galaxy NGC 3623. [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]

Dwarf spheroidal galaxies in the M81 group of galaxies

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
S. Lianou
Abstract We study the properties of the dwarf galaxy population in the nearby interacting M81 group of galaxies. In particular, we are deriving the metallicity distribution functions, the ages and the star formation histories of these dwarf galaxies based on data from the Hubble Space Telescope's Advanced Camera for Surveys and the Sloan Digital Sky Survey. We are correlating this information with the dwarf galaxies' position in the group in order to derive the impact of interactions and environment on their evolution. Here we present preliminary results on the metallicity distribution functions of dwarf spheroidals in the M81 group (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Ultraviolet color-magnitude relation of early-type dwarf galaxies in the Virgo cluster

ASTRONOMISCHE NACHRICHTEN, Issue 9-10 2009
S. Kim
Abstract We present ultraviolet (UV) color-magnitude relations (CMRs) for dwarf ellipticals (dEs) and dwarf lenticulars (dS0s) in the Virgo cluster. We used the Galaxy Evolution Explorer (GALEX) GR3 photometric data in far-ultraviolet (FUV) and near-ultraviolet (NUV) passbands combined with SDSS DR5 data. We found that dS0s as well as peculiar dEs (dEs with blue center and disk) found by Lisker et al. (2006a, b) show distinct locus from that of ordinary dEs in UV CMRs. The dS0s and peculiar dEs have bluer UV colors than ordinary dEs at a fixed optical luminosity. Furthermore, UV colors of dEs in outer region of the cluster are systematically bluer than those in inner region. Since UV flux is sensitive to the presence of young stellar population from recent star formation activity, our results suggest that there are different star formation histories among different subsample of early-type dwarf galaxies in Virgo cluster concerning their morphology and environmental effect (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Formation processes at the Ohalo II submerged prehistoric campsite, Israel, inferred from soil micromorphology and magnetic susceptibility studies

GEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 4 2003
Alexander Tsatskin
Soil-geomorphic analysis coupled with micromorphology, SEM/EDS, magnetic susceptibility, and conventional sedimentological studies allowed us to reconstruct the site formation history and validate the archaeologically observed variability of human activities in the prehistoric camp of Ohalo II (19.5 ka B.P.), Sea of Galilee, Israel. The cultural layers rest upon the Late Pleistocene Lake Lisan deposits that accumulated under conditions of changing water supply and increasing rate of sedimentation from deep-water varvelike deposits to basalt-derived, near-shore sandy lacustrine deposits. Intermittent occupation is recorded in some localities, indicating short-term inundation episodes, which led to partial truncation and deformation of the sediments, primarily in the eastern lakeward part of the site. On the elevated, landward positions, incipient soils with strongly bioturbated profiles formed. Micromorphology demonstrates that intentional flooring was applied within the remains of brush huts, where millimeter-sized, horizontally organized burnt and unheated vegetal tissues were likely to have been placed upon the compacted ground. In fireplaces, the cultural deposits in thin sections are composed of strongly mixed, abundant wood charcoal, ashes, and fishbone remains. Post-depositional alterations were controlled by intermittent inundation of the site and salinization, which induced gypsum and pyrite deposition, primarily along decayed roots, and eventual pyrite oxidation. Accumulation of sodium and chlorine in the post-occupation deposits is likely to have occurred because of discharge of saline groundwater. Although only suggestive at this stage of research, the conclusions drawn from magnetic susceptibility parameters of archaeologically related deposits at Ohalo II fit well with the micromorphological reconstructions and provide new information on the Late Pleistocene evolution of the Lake Lisan/Sea of Galilee fluctuating system. © 2003 Wiley Periodicals, Inc. [source]

Formation and evolution of dwarf elliptical galaxies , II.

The poorly constrained cluster disruption time-scale in the Large Magellanic Cloud

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 3 2008
Geneviève Parmentier
ABSTRACT We use Monte Carlo simulations, combined with homogeneously determined age and mass distributions, based on multiwavelength photometry, to constrain the cluster formation history and the rate of bound cluster disruption in the Large Magellanic Cloud (LMC) star cluster system. We evolve synthetic star cluster systems formed with a power-law initial cluster mass function (ICMF) of spectral index ,=,2 assuming different cluster disruption time-scales. For each of these cluster disruption time-scales, we derive the corresponding cluster formation rate (CFR) required to reproduce the observed cluster age distribution. We then compare, in a ,Poissonian',2 sense, model mass distributions and model two-dimensional distributions in log(mass) versus log(age) space of the detected surviving clusters to the observations. Because of the bright detection limit (MlimV,,4.7 mag) above which the observed cluster sample is complete, one cannot constrain the characteristic cluster disruption time-scale for a 104 M, cluster, tdis4[where the disruption time-scale depends on cluster mass as tdis=tdis4(Mcl/104 M,),, with ,, 0.62], to better than a lower limit, tdis4, 1 Gyr. We conclude that the CFR has been increasing steadily from 0.3 clusters Myr,1 5 Gyr ago to a present rate of (20,30) clusters Myr,1 for clusters spanning a mass range of ,100,107 M,. For older ages, the derived CFR depends sensitively on our assumption of the underlying CMF shape. If we assume a universal Gaussian ICMF, then the CFR has increased steadily over a Hubble time from ,1 cluster Gyr,1 15 Gyr ago to its present value. On the other hand, if the ICMF has always been a power law with a slope close to ,=,2, the CFR exhibits a minimum some 5 Gyr ago, which we tentatively identify with the well-known age gap in the LMC's cluster age distribution. [source]

Generating dark matter halo merger trees

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2008
Hannah Parkinson
ABSTRACT We present a new Monte Carlo algorithm to generate merger trees describing the formation history of dark matter haloes. The algorithm is a modification of the algorithm of Cole et al. used in the galform semi-analytic galaxy formation model. As such, it is based on the Extended Press,Schechter theory and so should be applicable to hierarchical models with a wide range of power spectra and cosmological models. It is tuned to be in accurate agreement with the conditional mass functions found in the analysis of merger trees extracted from the , cold dark matter Millennium N -body simulation. We present a comparison of its predictions not only with these conditional mass functions, but also with additional statistics of the Millennium Simulation halo merger histories. In all cases, we find it to be in good agreement with the Millennium Simulation and thus it should prove to be a very useful tool for semi-analytic models of galaxy formation and for modelling hierarchical structure formation in general. We have made our merger tree generation code and code to navigate the trees available at http://star-www.dur.ac.uk/~cole/merger_trees. [source]

Multiwavelength study of the nuclei of a volume-limited sample of galaxies , II.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2007
Optical, infrared, radio observations
ABSTRACT We present optical and infrared broad-band images, radio maps, and optical spectroscopy for the nuclear region of a sample of nearby galaxies. The galaxies have been drawn from a complete volume-limited sample for which we have already presented X-ray imaging. We modelled the stellar component of the spectroscopic observations to determine the star formation history of our targets. Diagnostic diagrams were used to classify the emission-line spectra and determine the ionizing mechanism driving the nuclear regions. All those sources classified as active galactic nuclei present small Eddington ratios (,10,3,10,6), implying a very slow growth rate of their black holes. We finally investigate the relative numbers of active and normal nuclei as a function of host galaxy luminosity and find that the fraction of active galaxies slowly rises as a function of host absolute magnitude in the MB,,12 to ,22 range. [source]

Constraints on Type Ia supernova progenitor time delays from high- z supernovae and the star formation history

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2006
F. Förster
ABSTRACT We re-assess the question of a systematic time delay between the formation of the progenitor and its explosion in a Type Ia supernova (SN Ia) using the Hubble Higher- z Supernova Search sample. While a previous analysis indicated a significant time delay, with a most likely value of 3.4 Gyr, effectively ruling out all previously proposed progenitor models, our analysis shows that the time-delay estimate is dominated by systematic errors, in particular due to uncertainties in the star formation history (SFH). We find that none of the popular progenitor models under consideration can be ruled out with any significant degree of confidence. The inferred time delay is mainly determined by the peak in the assumed SFH. We show that, even with a much larger supernova sample, the time-delay distribution cannot be reliably reconstructed without better constraints on the SFH. [source]

Extracting star formation histories from medium-resolution galaxy spectra

Lyman break galaxies and the star formation rate of the Universe at z, 6

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2003
Elizabeth R. Stanway
ABSTRACT We determine the space density of UV-luminous starburst galaxies at z, 6 using deep HST ACS SDSS- i, (F775W) and SDSS- z, (F850LP) and VLT ISAAC J and Ks band imaging of the Chandra Deep Field South. We find eight galaxies and one star with (i,,z,) > 1.5 to a depth of z,AB= 25.6 (an 8, detection in each of the 3 available ACS epochs). This corresponds to an unobscured star formation rate of ,15 h,270 M, yr,1 at z= 5.9, equivalent to L* for the Lyman-break population at z= 3,4 (,,= 0.7, ,M= 0.3). We are sensitive to star-forming galaxies at 5.6 ,z, 7.0 with an effective comoving volume of ,1.8 × 105h,370 Mpc3 after accounting for incompleteness at the higher redshifts due to luminosity bias. This volume should encompass the primeval subgalactic-scale fragments of the progenitors of about a thousand L* galaxies at the current epoch. We determine a volume-averaged global star formation rate of (6.7 ± 2.7) × 10,4h70 M, yr,1 Mpc,3 at z, 6 from rest-frame UV selected starbursts at the bright end of the luminosity function: this is a lower limit because of dust obscuration and galaxies below our sensitivity limit. This measurement shows that at z, 6 the star formation density at the bright end is a factor of ,6 times less than that determined by Steidel et al. for a comparable sample of UV-selected galaxies at z= 3,4, and so extends our knowledge of the star formation history of the Universe to earlier times than previous work and into the epoch where reionization may have occurred. [source]

Probing the dark ages with redshift distribution of gamma-ray bursts

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002
T. Roy Choudhury
Abstract In this article, we explore the possibility of using the properties of gamma-ray bursts (GRBs) to probe the physical conditions in the epochs prior to reionization. The redshift distribution of GRBs is modelled using the Press,Schechter formalism with an assumption that they follow the cosmic star formation history. We reproduce the observed star formation rate obtained from galaxies in the redshift range 0 < z < 5, as well as the redshift distribution of the GRBs inferred from the luminosity,variability correlation of the burst light curve. We show that the fraction of GRBs at high redshifts, the afterglows of which cannot be observed in the R and I bands owing to H i Gunn,Peterson optical depth can, at the most, account for one third of the dark GRBs. The observed redshift distribution of GRBs, with much less scatter than the one available today, can put stringent constraints on the epoch of reionization and the nature of gas cooling in the epochs prior to reionization. [source]

Merger histories in warm dark matter structure formation scenarios

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2002
Alexander Knebe
Observations on galactic scales seem to be in contradiction with recent high-resolution N -body simulations. This so-called cold dark matter (CDM) crisis has been addressed in several ways, ranging from a change in fundamental physics by introducing self-interacting cold dark matter particles to a tuning of complex astrophysical processes such as global and/or local feedback. All these efforts attempt to soften density profiles and reduce the abundance of satellites in simulated galaxy haloes. In this paper, we explore a different approach that consists of filtering the dark matter power spectrum on small scales, thereby altering the formation history of low-mass objects. The physical motivation for damping these fluctuations lies in the possibility that the dark matter particles have a different nature, i.e. are warm (WDM) rather than cold. We show that this leads to some interesting new results in terms of the merger history and large-scale distribution of low-mass haloes, compared with the standard CDM scenario. However, WDM does not appear to be the ultimate solution, in the sense that it is not able to fully solve the CDM crisis, even though one of the main drawbacks, namely the abundance of satellites, can be remedied. Indeed, the cuspiness of the halo profiles still persists, at all redshifts, and for all haloes and sub-haloes that we investigated. Despite the persistence of the cuspiness problem of DM haloes, WDM seems to be still worth taking seriously, as it alleviates the problems of over-abundant sub-structures in galactic haloes and possibly the lack of angular momentum of simulated disc galaxies. WDM also lessens the need to invoke strong feedback to solve these problems, and may provide a natural explanation of the clustering properties and ages of dwarfs. [source]

Gigamasers: the key to the dust-obscured star formation history of the Universe?

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001
R.H.D. Townsend
We discuss the possibility of using OH and H2O gigamasers to trace the redshift distribution of luminous, dust-obscured, star-forming galaxies. It has long been thought that ultraluminous, interacting galaxies should host gigamasers, owing to their vast pumping infrared (IR) luminosity, the large column density of molecules available to populate the maser states and the turbulent motion of the gas in these dynamically complex systems, which allows unsaturated maser emission. OH masers may thus be well suited to the redshift-blind detection of ultraluminous and hyperluminous infrared galaxies such as those uncovered by the SCUBA submillimetre camera. The bandwidth requirement is low, <1 GHz for (lower still if additional redshift constraints are available) and the dual-line 1665-/1667-MHz OH spectral signature can act as a check on the reality of detections. [source]

Dwarf elliptical galaxies: structure, star formation and colour,magnitude diagrams

SDSS J150634.27+013331.6: the second compact elliptical galaxy in the NGC 5846 group,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2010
Igor V. Chilingarian
ABSTRACT We report the discovery of the second compact elliptical (cE) galaxy SDSS J150634.27+013331.6 in the nearby NGC 5846 group by the Virtual Observatory (VO) workflow. This object (MB=,15.98 mag, Re= 0.24 kpc) becomes the fifth cE where the spatially resolved kinematics and stellar populations can be obtained. We used archival HST WFPC2 images to demonstrate that its light profile has a two-component structure, and integrated photometry from GALEX, SDSS, UKIDSS and Spitzer to build the multiwavelength spectral energy distribution to constrain the star formation history (SFH). We observed this galaxy with the PMAS IFU spectrograph at the Calar-Alto 3.5-m telescope and obtained two-dimensional maps of its kinematics and stellar population properties using the full-spectral fitting technique. Its structural, dynamical and stellar population properties suggest that it had a massive progenitor heavily tidally stripped by NGC 5846. [source]

On the evolution of the Fe abundance and of the Type Ia supernova rate in clusters of galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY: LETTERS (ELECTRONIC), Issue 1 2007
F. Calura
ABSTRACT The study of the Fe abundance in the intracluster medium (ICM) provides strong constraints on the integrated star formation history and supernova rate of the cluster galaxies, as well as on the ICM enrichment mechanisms. In this Letter, using chemical evolution models for galaxies of different morphological types, we study the evolution of the Fe content of clusters of galaxies. We assume that the ICM Fe enrichment occurs by means of galactic winds arising from elliptical galaxies and from gas stripped from the progenitors of S0 galaxies via external mechanisms, due to the interaction of the interstellar medium with the ICM. The Fe-rich gas ejected by ellipticals accounts for the XFe,ICM values observed at z > 0.5, whereas the gas stripped from the progenitors of the S0 galaxies accounts for the increase of XFe,ICM observed at z < 0.5. We test two different scenarios for Type Ia supernova (SN) progenitors and we model the Type Ia SN rate observed in clusters, finding a good agreement between our predictions and the available observations. [source]

Dust attenuation in starburst galaxies determined by measuring the dependence of the optical color indices on galaxy inclination

ASTRONOMISCHE NACHRICHTEN, Issue 7 2010
O. Vince
Abstract We use optical color indices (colors) from the SDSS database to study the effect of dust in starburst galaxies by mea-suring the dependence of colors on galaxy inclination. Starburst galaxies with ongoing star formation, are rich with metals/dust and are, therefore, an excellent objects for studying the effect of dust in galaxies. They are selected using the [O III], 5007/H, vs. [N II], 6584/H, diagram, that is, the BPT-diagram. We use Kauffmann's empirical demarcation line in the BPT-diagram to exclude galaxies with active galactic nuclei (AGN) from the sample because they have different physical and dust properties from normal galaxies. The sample is divided into bins according to galaxy stellar mass and 4000 Å break (which is a coarse measure of a galaxy star formation history; SFH) and the reddening with inclination is studied as a function of these two physical parameters. Assuming that the dust effect is negligible in the SDSS z -band, we derive the attenuation curves for these galaxies. We fit the attenuation curves with a simple power law and use power law index to interpret the relative distribution of dust and stars in the starburst galaxies (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]