38 research outputs found
The evolution of the star formation rate function and cosmic star formation rate density of galaxies at z Ë 1-4
We investigate the evolution of the galaxy star formation rate function (SFRF) and cosmic star formation rate density (CSFRD) of z Ë 1-4 galaxies, using cosmological smoothed particle hydrodynamic (SPH) simulations and a compilation of ultraviolet (UV), infrared (IR) and Hα observations. These tracers represent different populations of galaxies with the IR light being a probe of objects with high star formation rates and dust contents, while UV and Hα observations provide a census of low star formation galaxies where mild obscuration occurs. We compare the above SFRFs with the results of SPH simulations run with the code P-GADGET3(XXL). We focus on the role of feedback from active galactic nuclei (AGN) and supernovae in form of galactic winds. The AGN feedback prescription that we use decreases the simulated CSFRD at z < 3 but is not sufficient to reproduce the observed evolution at higher redshifts. We explore different wind models and find that the key factor for reproducing the evolution of the observed SFRF and CSFRD at z Ë 1-4 is the presence of a feedback prescription that is prominent at high redshifts (z â„ 4) and becomes less efficient with time. We show that variable galactic winds which are efficient at decreasing the SFRs of low-mass objects are quite successful in reproducing the observables
The relation between star formation rate and stellar mass of galaxies at z 1-4
The relation between the Star Formation Rate (SFR) and stellar mass () of galaxies represents a fundamental constraint on galaxy
formation and has been studied extensively both in observations and
cosmological simulations. However, the observed amplitude has not been
successfully reproduced in simulations, indicating either that the halo
accretion history and baryonic physics are poorly modeled or that observations
contain biases. We examine the evolution of the SFR relation
of galaxies and display the inconsistency between observed
relations that are obtained using different techniques. We employ cosmological
hydrodynamic simulations and compare these with a range of observed SFR relations. We find that numerical results are consistent with
observations that use Spectral Energy Distribution (SED) techniques to estimate
star formation rates and dust corrections. On the contrary, simulations are not
able to reproduce results that were obtained by combining only UV and IR
luminosities. These imply SFRs at a fixed stellar mass that are larger almost
by a factor of 5 than those of SED measurements for . Furthermore,
we find remarkable agreement between the numerical results from various authors
who have employed different cosmological codes and run simulations with
different resolutions. This is interesting for two reasons. A) simulations can
produce realistic populations of galaxies within representative cosmological
volumes even at relatively modest resolutions. B) It is likely that current
numerical codes that rely on similar subgrid multiphase Inter-Stellar Medium
(ISM) models and are tuned to reproduce statistical properties of galaxies,
produce similar results for the SFR relation by construction,
regardless of resolution, box size and, to some extent, the adopted feedback
prescriptions.Comment: 16 pages, 6 figures, 3 tables, accepted for publication in PAS
A Characteristic Mass Scale in the Mass-Metallicity Relation of Galaxies
We study the shape of the gas-phase mass-metallicity relation (MZR) of a
combined sample of present-day dwarf and high-mass star-forming galaxies using
IZI, a Bayesian formalism for measuring chemical abundances presented in Blanc
et al. 2015. We observe a characteristic stellar mass scale at M, above which the ISM undergoes a sharp increase in its
level of chemical enrichment. In the M range the MZR
follows a shallow power-law () with slope
. At approaching M the MZR
steepens significantly, showing a slope of in the
M range, and a flattening towards a constant
metallicity at higher stellar masses. This behavior is qualitatively different
from results in the literature that show a single power-law MZR towards the low
mass end. We thoroughly explore systematic uncertainties in our measurement,
and show that the shape of the MZR is not induced by sample selection, aperture
effects, a changing N/O abundance, the adopted methodology used to construct
the MZR, secondary dependencies on star formation activity, nor diffuse ionized
gas (DIG) contamination, but rather on differences in the method used to
measure abundances. High resolution hydrodynamical simulations can
qualitatively reproduce our result, and suggest a transition in the ability of
galaxies to retain their metals for stellar masses above this threshold. The
MZR characteristic mass scale also coincides with a transition in the scale
height and clumpiness of cold gas disks, and a typical gas fraction below which
the efficiency of star formation feedback for driving outflows is expected to
decrease sharply.Comment: 24 pages, 11 figures, 4 tables, accepted for publication in Ap
An Aegean History and Archaeology Written through Radiocarbon Dates
This dataset is the outcome of an INSTAP-funded project âAn Aegean Prehistory Written in Radiocarbon Datesâ. It includes 3159 14C dates from 353 sites in Greece and reflects an attempt to exhaustively collect and cross-check all published radiocarbon dates from existing databases, original publications and preliminary reports using both international and Greek sources (376 sources in total). Although originally targeting prehistoric dates, all dates coming from archaeological or environmental sampling were integrated in the final dataset regardless of chronological period. Sites have been identified and positioned as accurately as possible, while additional information on sampling procedures, sample material and stratigraphic context have been recorded
Long-term trends of land use and demography in Greece: a comparative study
This paper offers a comparative study of land use and demographic development in northern and southern Greece from the Neolithic to the Byzantine period. Results from summed probability densities (SPD) of archaeological radiocarbon dates and settlement numbers derived from archaeological site surveys are combined with results from cluster-based analysis of published pollen core assemblages to offer an integrated view of human pressure on the Greek landscape through time. We demonstrate that SPDs offer a useful approach to outline differences between regions and a useful complement to archaeological site surveys, evaluated here especially for the onset of the Neolithic and for the Final Neolithic (FN)/Early Bronze Age (EBA) transition. Pollen analysis highlight differences in vegetation between the two sub-regions, but also several parallel changes. The comparison of land cover dynamics between two sub-regions of Greece further demonstrates the significance of the bioclimatic conditions of core locations and that apparent oppositions between regions may in fact be two sides of the same coin in terms of socio-ecological trajectories. We also assess the balance between anthropogenic and climate-related impacts on vegetation and suggest that climatic variability was as an important factor for vegetation regrowth. Finally, our evidence suggests that the impact of humans on land cover is amplified from the Late Bronze Age (LBA) onwards as more extensive herding and agricultural practices are introduced.Domesticated Landscapes of the Peloponnese (DoLP
The evolution of the star formation rate function in the EAGLE simulations: a comparison with UV, IR and Hα observations from z ⌠8 to z ⌠0
Galaxy And Mass Assembly (GAMA) : the sSFR-M* relation part I - ÏsSFR-M* as a function of sample, SFR indicator, and environment
Recently, a number of studies have proposed that the dispersion along the star formation rate (SFR) â stellar mass relation (ÏsSFRâM*) â is indicative of variations in star formation history driven by feedback processes. They found a âUâ-shaped dispersion and attribute the increased scatter at low and high stellar masses to stellar and active galactic nuclei feedback, respectively. However, measuring ÏsSFR and the shape of the ÏsSFRâM* relation is problematic and can vary dramatically depending on the sample selected, chosen separation of passive/star-forming systems, and method of deriving SFRs (i.e. Hâα emission versus spectral energy distribution fitting). As such, any astrophysical conclusions drawn from measurements of ÏsSFR must consider these dependencies. Here, we use the Galaxy And Mass Assembly survey to explore how ÏsSFR varies with SFR indicator for a variety of selections for disc-like âmain-sequenceâ star-forming galaxies including colour, SFR, visual morphology, bulge-to-total mass ratio, SĂ©rsic index, and mixture modelling. We find that irrespective of sample selection and/or SFR indicator, the dispersion along the sSFRâM* relation does follow a âUâ-shaped distribution. This suggests that the shape is physical and not an artefact of sample selection or method. We then compare the ÏsSFRâM* relation to state-of-the-art hydrodynamical and semi-analytic models and find good agreement with our observed results. Finally, we find that for group satellites this âUâ-shaped distribution is not observed due to additional high scatter population at intermediate stellar masses.Publisher PDFPeer reviewe
Geographic Visualization in Archaeology
Archaeologists are often considered frontrunners in employing spatial approaches within the social sciences and humanities, including geospatial technologies such as geographic information systems (GIS) that are now routinely used in archaeology. Since the late 1980s, GIS has mainly been used to support data collection and management as well as spatial analysis and modeling. While fruitful, these efforts have arguably neglected the potential contribution of advanced visualization methods to the generation of broader archaeological knowledge. This paper reviews the use of GIS in archaeology from a geographic visualization (geovisual) perspective and examines how these methods can broaden the scope of archaeological research in an era of more user-friendly cyber-infrastructures. Like most computational databases, GIS do not easily support temporal data. This limitation is particularly problematic in archaeology because processes and events are best understood in space and time. To deal with such shortcomings in existing tools, archaeologists often end up having to reduce the diversity and complexity of archaeological phenomena. Recent developments in geographic visualization begin to address some of these issues, and are pertinent in the globalized world as archaeologists amass vast new bodies of geo-referenced information and work towards integrating them with traditional archaeological data. Greater effort in developing geovisualization and geovisual analytics appropriate for archaeological data can create opportunities to visualize, navigate and assess different sources of information within the larger archaeological community, thus enhancing possibilities for collaborative research and new forms of critical inquiry