Low-redshift Observations Research Articles

THE LUMINOSITY AND STELLAR MASS FUNCTIONS OF GRB HOST GALAXIES: INSIGHT INTO THE METALLICITY BIAS

Long-Duration Gamma-Ray Bursts (GRBs) are powerful probes of the Universe star formation history, but correlation between the two depends on the highly debated presence/strength of a metallicity bias. To investigate this correlation, we use a phenomenological model that successfully describes star formation rates, luminosities and stellar masses of star forming galaxies, applying it to GRB production. We predict luminosities, stellar masses, and metallicities of host galaxies depending on the metallicity bias. Our best-fitting model includes a moderate metallicity bias, broadly consistent with the large majority of long-duration GRBs in metal-poor environments originating from collapsars (probability ~83%), but with a secondary contribution (~17%) from metal-independent production channels, such as binary evolution. Because of the mass-metallicity relation of galaxies, the maximum likelihood model predicts that the metal-independent channel becomes dominant at z<2, where hosts have higher metallicities and collapsars are suppressed. This possibly explains why some studies find no clear evidence of a metal-bias based on low-z samples. However, while metallicity predictions match observations well at high redshift, there is tension with low redshift observations, since a significant fraction of GRB hosts are predicted to have (near-)solar metallicity. This is in contrast to observations, unless obscured, metal-rich hosts are preferentially missed in current datasets, and suggests that lower efficiencies of the metal-independent GRB channel might be preferred following a comprehensive fit from complete samples. Overall, we are able to establish the presence of a metallicity bias for GRB production, but continued characterization of GRB host galaxies is needed to quantify its strength.

The EAGLE project: simulating the evolution and assembly of galaxies and their environments

We introduce the Virgo Consortium's EAGLE project, a suite of hydrodynamical simulations that follow the formation of galaxies and black holes in representative volumes. We discuss the limitations of such simulations in light of their finite resolution and poorly constrained subgrid physics, and how these affect their predictive power. One major improvement is our treatment of feedback from massive stars and AGN in which thermal energy is injected into the gas without the need to turn off cooling or hydrodynamical forces, allowing winds to develop without predetermined speed or mass loading factors. Because the feedback efficiencies cannot be predicted from first principles, we calibrate them to the z~0 galaxy stellar mass function and the amplitude of the galaxy-central black hole mass relation, also taking galaxy sizes into account. The observed galaxy mass function is reproduced to $\lesssim 0.2$ dex over the full mass range, $10^8 < M_*/M_\odot \lesssim 10^{11}$, a level of agreement close to that attained by semi-analytic models, and unprecedented for hydrodynamical simulations. We compare our results to a representative set of low-redshift observables not considered in the calibration, and find good agreement with the observed galaxy specific star formation rates, passive fractions, Tully-Fisher relation, total stellar luminosities of galaxy clusters, and column density distributions of intergalactic CIV and OVI. While the mass-metallicity relations for gas and stars are consistent with observations for $M_* \gtrsim 10^9 M_\odot$, they are insufficiently steep at lower masses. The gas fractions and temperatures are too high for clusters of galaxies, but for groups these discrepancies can be resolved by adopting a higher heating temperature in the subgrid prescription for AGN feedback. EAGLE constitutes a valuable new resource for studies of galaxy formation.

Supersonic relative velocity between dark matter and baryons: A review

Our understanding of astrophysical and cosmological phenomena in recent years has improved enormously, thanks to precision measurements of various cosmic signals such as Cosmic Microwave Background radiation, emission of galaxies and dust, spectral lines attributed to various elements, etc. Despite this, our knowledge at intermediate redshifts (10 &lt; z &lt; 1100) remains fragmentary and incomplete, and as a consequence, various physical processes happening between the epochs of hydrogen recombination and reionization remain still highly unconstrained. Moreover, some important fragments of the theoretical description that are less decisive for the universe today, but that had an important impact at intermediate redshifts, have been omitted in some of the studies concerning the universe at high redshifts. One such neglected phenomenon, which is the central topic of this review, is the fact that after hydrogen recombination the large-scale baryons and dark matter fluctuations had supersonic relative velocities. The relative velocities between dark matter and baryons formally introduce a second-order effect on the standard results and thus have been neglected in the framework of linear theory. However, when properly considered, the velocities yield a nonperturbative contribution to the growth of structures which is then inherited by the majority of cosmic signals coming from redshifts above z ~ 10, and in certain cases may even propagate to various low-redshift observables such as the Baryon Acoustic Oscillations measured from the distribution of galaxies. At higher redshifts, the supersonic velocities have thus strong impact affecting the abundance of M ~ 106M⊙halos in an inhomogeneous way, hindering the formation of first stars, leaving traces in the redshifted 21-cm signal of neutral hydrogen, as well as having other important contributions at high redshifts all of which we review in this manuscript.

Future prospects in observational galaxy evolution: towards increased resolution

AbstractFuture prospects in observational galaxy evolution are reviewed from a personal perspective. New insights will especially come from high-redshift integral field kinematic data and similar low-redshift observations in very large and definitive surveys. We will start to systematically probe the mass structures of galaxies and their haloes via lensing from new imaging surveys and upcoming near-IR spectroscopic surveys will finally obtain large numbers of rest frame optical spectra at high-redshift routinely. ALMA will be an important new ingredient, spatially resolving the molecular gas fuelling the high star-formation rates seen in the early Universe.

A Tachyonic Scalar Field with Mutually Interacting Components

We investigate the tachyonic cosmological potential $V(\phi)$ in two different cases of the quasi-exponential expansion of universe and discuss various forms of interaction between the two components---matter and the cosmological constant--- of the tachyonic scalar field, which leads to the viable solutions of their respective energy densities. The distinction among the interaction forms is shown to appear in the $O_{m}(x)$ diagnostic. Further, the role of the high- and low-redshift observations of the Hubble parameter is discussed to determine the proportionality constants and hence the correct form of matter--cosmological constant interaction.

Coupled dark matter-dark energy in light of near universe observations

Cosmological analysis based on currently available observations are unable to rule out a sizeable coupling among the dark energy and dark matter fluids. We explore a variety of coupled dark matter-dark energy models, which satisfy cosmic microwave background constraints, in light of low redshift and near universe observations. We illustrate the phenomenology of different classes of dark coupling models, paying particular attention in distinguishing between effects that appear only on the expansion history and those that appear in the growth of structure. We find that while a broad class of dark coupling models are effectively models where general relativity (GR) is modified — and thus can be probed by a combination of tests for the expansion history and the growth of structure —, there is a class of dark coupling models where gravity is still GR, but the growth of perturbations is, in principle modified. While this effect is small in the specific models we have considered, one should bear in mind that an inconsistency between reconstructed expansion history and growth may not uniquely indicate deviations from GR. Our low redshift constraints arise from cosmic velocities, redshift space distortions and dark matter abundance in galaxy voids. We find that current data constrain the dimensionless coupling to be |ξ| < 0.2, but prospects from forthcoming data are for a significant improvement. Future, precise measurements of the Hubble constant, combined with high-precision constraints on the growth of structure, could provide the key to rule out dark coupling models which survive other tests. We shall exploit as well weak equivalence principle violation arguments, which have the potential to highly disfavour a broad family of coupled models.

Robust neutrino constraints by combining low redshift observations with the CMB

We illustrate how recently improved low-redshift cosmological measurements can tighten constraints on neutrino properties. In particular we examine the impact of the assumed cosmological model on the constraints. We first consider the new HST H0 = 74.2±3.6 measurement by Riess et al. (2009) and the σ8(Ωm/0.25)0.41 = 0.832±0.033 constraint from Rozo et al. (2009) derived from the SDSS maxBCG Cluster Catalog. In a ΛCDM model and when combined with WMAP5 constraints, these low-redshift measurements constrain ∑mν < 0.4 eV at the 95% confidence level. This bound does not relax when allowing for the running of the spectral index or for primordial tensor perturbations. When adding also Supernovae and BAO constraints, we obtain a 95% upper limit of ∑mν < 0.3eV. We test the sensitivity of the neutrino mass constraint to the assumed expansion history by both allowing a dark energy equation of state parameter w≠−1 and by studying a model with coupling between dark energy and dark matter, which allows for variation in w, Ωk, and dark coupling strength ξ. When combining CMB, H0 and the SDSS LRG halo power spectrum from Reid et al. 2009, we find that in this very general model, ∑mν < 0.51 eV with 95% confidence. If we allow the number of relativistic species Nrel to vary in a ΛCDM model with ∑mν = 0, we find Nrel = 3.76+0.63−0.68(+1.38−1.21) for the 68% and 95% confidence intervals. We also report prior-independent constraints, which are in excellent agreement with the Bayesian constraints.

Cluster Structure in Cosmological Simulations. I. Correlation to Observables, Mass Estimates, and Evolution

We use Enzo, a hybrid Eulerian AMR/N-body code including non-gravitational heating and cooling, to explore the morphology of the X-ray gas in clusters of galaxies and its evolution in current generation cosmological simulations. We employ and compare two observationally motivated structure measures: power ratios and centroid shift. Overall, the structure of our simulated clusters compares remarkably well to low-redshift observations, although some differences remain that may point to incomplete gas physics. We find no dependence on cluster structure in the mass-observable scaling relations, T_X-M and Y_X-M, when using the true cluster masses. However, estimates of the total mass based on the assumption of hydrostatic equilibrium, as assumed in observational studies, are systematically low. We show that the hydrostatic mass bias strongly correlates with cluster structure and, more weakly, with cluster mass. When the hydrostatic masses are used, the mass-observable scaling relations and gas mass fractions depend significantly on cluster morphology, and the true relations are not recovered even if the most relaxed clusters are used. We show that cluster structure, via the power ratios, can be used to effectively correct the hydrostatic mass estimates and mass-scaling relations, suggesting that we can calibrate for this systematic effect in cosmological studies. Similar to observational studies, we find that cluster structure, particularly centroid shift, evolves with redshift. This evolution is mild but will lead to additional errors at high redshift. Projection along the line of sight leads to significant uncertainty in the structure of individual clusters: less than 50% of clusters which appear relaxed in projection based on our structure measures are truly relaxed.

Gemini Near-Infrared Spectroscopy of Luminousz~ 6 Quasars: Chemical Abundances, Black Hole Masses, and MgiiAbsorption

We present Gemini near-infrared spectroscopic observations of six luminous quasars at z = 5.8 to ∼6.3. Five of them were observed using Gemini South GNIRS, which provides a simultaneous wavelength coverage of 0.9-2.5 μm in cross-dispersion mode. The other source was observed in the K band with Gemini North NIRI. We calculate line strengths for all detected emission lines and use their ratios to estimate gas metallicity in the broad-line regions of the quasars. The metallicity is found to be supersolar, with a typical value of ∼4 Z⊙, and a comparison with low-redshift observations shows no strong evolution in metallicity up to z ∼ 6. The Fe II/Mg II ratio of the quasars is 4.9 ± 1.4, consistent with low-redshift measurements. We estimate central black hole masses of 109-1010 M⊙ and Eddington luminosity ratios of order unity. We identify two Mg II λλ2796, 2803 absorbers with rest equivalent width W > 1 Å at 2.2 < z < 3 and three Mg II absorbers with W > 1.5 Å at z > 3 in the spectra, with the two most distant absorbers at z = 4.8668 and 4.8823, respectively. The redshift number densities (dN/dz) of Mg II absorbers with W > 1.5 Å are consistent with no cosmic evolution up to z > 4.

Observational constraints on a variable dark energy model

We study the effect of a phenomenological parameterized quintessence model on low, intermediate and high redshift observations. At low and intermediate redshifts, we use the Gold sample of supernova Type Ia (SNIa) data and recently observed size of baryonic acoustic peak from Sloan Digital Sky Survey (SDSS), to put constraint on the parameters of the quintessence model. At the high redshift, the same fitting procedure is done using WAMP data, comparing the location of acoustic peak with that obtain from the dark energy model. As a complementary analysis in a flat universe, we combine the results from the SNIa, CMB and SDSS. The best fit values for the model parameters are ${\ensuremath{\Omega}}_{m}={0.27}_{\ensuremath{-}0.02}^{+0.02}$ (the present matter content) and ${w}_{0}=\ensuremath{-}{1.45}_{\ensuremath{-}0.60}^{+0.35}$ (dark energy equation of state). Finally we calculate the age of universe in this model and compare it with the age of old stars and high redshift objects.

The connections between QSO absorption systems and galaxies: low-redshift observations

Quasar absorption lines have long been recognised to be a sensitive probe of the abundances, physical conditions, and kinematics of gas in a wide variety of environments including low-density intergalactic regions that probably cannot be studied by any other means. While some pre-Hubble Space Telescope (HST) observations indicated that Mg II absorption lines arise in gaseous galactic halos with a large covering factor, many early QSO absorber studies were hampered by a lack of information about the context of the absorbers and their connections with galaxies. By providing access to crucial ultraviolet resonance lines at low redshifts, deployment of HST and the Far Ultraviolet Spectroscopic Explorer enabled detailed studies of the relationships between QSO absorbers and galaxies. The advent of large surveys such as the Sloan Digital Sky Survey (SDSS) has also advanced the topic by greatly improving the size of absorber and galaxy samples. This paper briefly reviews some observational results on absorber-galaxy connections that have been obtained in the HST/SDSS era, including Mg II absorbers, the low absorbers, and O VI systems.

Cosmic Concordance and Quintessence

We present a comprehensive study of the observational constraints on spatially flat cosmological models containing a mixture of matter and quintessence --- a time varying, spatially inhomogeneous component of the energy density of the universe with negative pressure. Our study also includes the limiting case of a cosmological constant. Low red shift constraints include the Hubble parameter, baryon fraction, cluster abundance, age of the universe, bulk velocity and shape of the mass power spectrum; intermediate red shift constraints are due to type 1a supernovae, gravitational lensing, the Ly-a forest, and the evolution of large scale structure; high red shift constraints are based on cosmic microwave background temperature anisotropy. Mindful of systematic errors, we adopt a conservative approach in applying these constraints. We determine that quintessence models in which the matter density parameter is $0.2 \ls \Omega_m \ls 0.5$ and the effective, density-averaged equation of state is $-1 \le w \ls -0.2$, are consistent with the most reliable, current low red shift and CMB observations at the $2\sigma$ level. Factoring in the constraint due to type 1a SNe, the range for the equation of state is reduced to $-1 \le w \ls -0.4$, where this range represents models consistent with each observational constraint at the 2$\sigma$ level or better (concordance analysis). A combined maximum likelihood analysis suggests a smaller range, $-1 \le w \ls -0.6$. We find that the best-fit and best-motivated quintessence models lie near $\Omega_m \approx 0.33$, $h \approx 0.65$, and spectral index $n_s=1$, with an effective equation of state $w \approx -0.65$ for ``tracker'' quintessence and $w=-1$ for ``creeper'' quintessence. (abstract shortened)

Cosmology with powerful extended radio sources

view Abstract Citations (69) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Cosmology with Powerful Extended Radio Sources Daly, Ruth A. Abstract Distant powerful radio sources would provide a useful cosmological tool if an intrinsic length or luminosity could be estimated from the observations in a way that is independent of the coordinate distance to the source. A model for the propagation of the radio lobes of powerful extended radio sources is presented here; the model is written in terms of fundamental physical variables such as the luminosity in directed kinetic energy and the ambient gas density, rather than observables such as the radio power. It is shown that the fundamental physical variables may be estimated from observed quantities. The model parameter β that relates the characteristic time the central engine is producing a collimated outflow to the luminosity in directed kinetic energy is constrained by low-redshift observations and extrapolated to high redshift. The application of the model to powerful extended radio sources allows an estimate of the characteristic source sizes that is nearly independent of the coordinate distance to the source, and thus is basically independent of the de/acceleration parameter q_0_. The characteristic source sizes estimated in the context of the model may be compared with the observed median source sizes, where each source size is determined directly from the angular extent of the source, the source redshift, and the coordinate distance to the source. The comparison of the intrinsic source sizes estimated using the model, which are nearly independent of q_0_ with the median source sizes estimated using the angular sizes of the sources, which depend on q_0_ constrains the allowed range of q_0_. The basic model and method is presented and discussed and is applied to one published data set consisting of 10 radio galaxies. Taken at face value, the data favor a low value of q_0_; a low value of q_0_ implies that either space curvature or a cosmological constant is important at the present epoch. Note that Doppler boosting and beaming of radio emission are unlikely to be important in these systems since the relevant flow velocities are small compared with the speed of light. This analysis has broad implications for the environments of powerful extended radio sources and for models for extracting the luminosity in directed kinetic energy from the central compact object. Publication: The Astrophysical Journal Pub Date: May 1994 DOI: 10.1086/174037 Bibcode: 1994ApJ...426...38D Keywords: Astronomical Models; Cosmology; Luminosity; Quasars; Radio Astronomy; Radio Galaxies; Radio Transmission; Red Shift; Size Determination; Distance; Doppler Effect; Gas Density; Kinetic Energy; Astrophysics; COSMOLOGY: THEORY; COSMOLOGY: OBSERVATIONS; RADIO CONTINUUM: GALAXIES; RADIO CONTINUUM: GENERAL full text sources ADS |