Formation Rate Function Research Articles

Mass-dependent evolution of the relation between the supermassive black hole mass and host spheroid mass sincez∼ 1

We investigate the evolution of supermassive black hole mass (M_BH) and the host spheroid mass (M_sph) in order to track the history of the M_BH-M_sph relationship. The typical mass increase of M_BH is calculated by a continuity equation and accretion history, which is estimated from the active galactic nucleus (AGN) luminosity function. The increase in M_sph is also calculated by using a continuity equation and a star formation model, which uses observational data for the formation rate and stellar mass function. We find that the black hole to spheroid mass ratio is expected to be substantially unchanged since z~1.2 for high mass objects (M_BH>10^8.5M_SUN and M_sph>10^11.3M_SUN). In the same redshift range, the spheroid mass is found to increase more rapidly than the black hole mass if M_sph>10^11M_SUN. The proposed mass-dependent model is consistent with the current available observational data in the M_BH-M_sph diagram.

OBSERVATIONAL CONSTRAINTS ON THE CO-EVOLUTION OF SUPERMASSIVE BLACK HOLES AND GALAXIES

The star formation rate (SFR) and black hole accretion rate (BHAR) functions are measured to be proportional to each other at z < ~3. This close correspondence between SF and BHA would naturally yield a BH mass-galaxy mass correlation, whereas a BH mass-bulge mass correlation is observed. To explore this apparent contradiction we study the SF in spheroid-dominated galaxies between z=1 and the present day. We use 903 galaxies from the COMBO-17 survey with M* >2x10^10M_sun, ultraviolet and infrared-derived SFRs from Spitzer and GALEX, and morphologies from GEMS HST/ACS imaging. Using stacking techniques, we find that <25% of all SF occurs in spheroid-dominated galaxies (Sersic index n>2.5), while the BHAR that we would expect if the global scalings held is three times higher. This rules out the simplest picture of co-evolution, in which SF and BHA trace each other at all times. These results could be explained if SF and BHA occur in the same events, but offset in time, for example at different stages of a merger event. However, one would then expect to see the corresponding star formation activity in early-stage mergers, in conflict with observations. We conclude that the major episodes of SF and BHA occur in different events, with the bulk of SF happening in isolated disks and most BHA occurring in major mergers. The apparent global co-evolution results from the regulation of the BH growth by the potential well of the galactic spheroid, which includes a major contribution from disrupted disk stars.

Effects of AGN feedback on ΛCDM galaxies

We study the effects of Active Galactic Nuclei (AGN) feedback on the formation and evolution of galaxies in a semi-analytic model of galaxy formation. This model is an improved version of the one described by Cora (2006), which now considers the growth of black holes (BHs) as driven by (i) gas accretion during merger-driven starbursts and mergers with other BHs, (ii) accretion during starbursts triggered by disc instabilities, and (iii) accretion of gas cooled from quasi-hydrostatic hot gas haloes. It is assumed that feedback from AGN operates in the later case. The model has been calibrated in order to reproduce observational correlations between BH mass and mass, velocity dispersion, and absolute magnitudes of the galaxy bulge. AGN feedback has a strong impact on reducing or even suppressing gas cooling, an effect that becomes important at lower redshifts. This phenomenon helps to reproduce the observed galaxy luminosity function (LF) in the optical and near IR bands at z=0, and the cosmic star formation rate and stellar mass functions over a wide redshift range (0 1, which are mostly early-type and have older and redder stellar populations than lower mass galaxies, reproducing the observed bimodality in the galaxy colour distribution, and the morphological fractions. The evolution of the optical QSO LF is also reproduced, provided that the presence of a significant fraction of obscured QSOs is assumed. We explore the effects of AGN feedback during starbursts and new recent prescriptions for dynamical friction time-scales. (ABRIDGED)

Short Gamma-ray bursts: a bimodal origin?

Abstract Short-hard Gamma-Ray Bursts (SGRBs) are currently thought to arise from gravitational wave driven coalescences of double neutron star systems forming either in the field or dynamically in globular clusters. For both channels, we fit the peak flux distribution of BATSE SGRBs to derive the local burst formation rate and luminosity function. We then compare the resulting redshift distribution with Swift 2-yr data, showing that both formation channels are needed in order to reproduce the observations. Double neutron stars forming in globular clusters are found to dominate the distribution at z≲ 0.3, whereas the field population from primordial binaries can account for the high-z SGRBs. This result is not in contradiction with the observed host galaxy type of SGRBs.

Comparison of the Hα Equivalent Width of HiiRegions in a Flocculent and a Grand‐Design Galaxy: Possible Evidence for Initial Mass Function Variations

We present here a study of the Hα equivalent widths of the flocculent galaxy NGC 4395 and the grand-design galaxy NGC 5457. A difference between the mean values of the Hα equivalent widths for the two galaxies has been found. Several hypotheses are presented in order to explain this difference: differences in age, metallicity, star formation rate, photon leakage, and initial mass function. Various tests and Monte Carlo models are used to find out the most probable cause of this difference. The results show that the possible cause for the difference could be a variation in the initial mass function. This difference is such that it seems to favor a fraction of more massive stars in the grand-design galaxy when compared with the flocculent galaxy. This could be due to a change of the environmental conditions due to a density wave.

The Star Formation Rate Function of the Local Universe

We have derived the bivariate luminosity function for the far-ultraviolet (1530 A) and far-infrared (60 μm). We use matched GALEX and IRAS data, and redshifts from NED and the PSCz survey. We have derived a total formation luminosity function (Ltot), with Ltot = LFUV + LFIR. Using these, we determined the cosmic star formation rate (SFR) function and density for the local universe. The total SFR function (Ltot) is fitted very well by a lognormal distribution over 5 decades of luminosity. We find that the bivariate luminosity function (LFUV, LFIR) shows a bimodal behavior, with LFIR tracking LFUV for Ltot < 1010 L☉ and LFUV saturating at ~1010 L☉, while Ltot ~ LFIR for higher luminosities. We also calculate the SFR density and compare it with other measurements.

Co-evolution of Galaxies and AGNs in Hierarchical Galaxy Formation Models

I present the results of a semi-analytic model of galaxy formation which includes a physical description of starbursts. These originate from the destabilization of cold galactic gas occuring in galaxy encounters, which in part feeds the accretion onto black holes powering quasars, and in part drives circumnuclear starsbursts at redshifts z≈ 2–4, preferentially in massive objects. This speeds up the formation of stars in massive galaxies at high redshifts without altering it in low mass galactic haloes. Meanwhile, part of the destabilized gas fuels the accretion onto the central supermassive black holes that the quasar emit at their full Eddington rates. At lower z the galactic dynamical events are mostly encountered in hierarchically growing groups; now the refueling peters out, as the residual gas is exhausted while the destabilizing encounters dwindle. So, our model uniquely produces at z > 3 a rise, and at z ≲ 2.5 a decline of the bright quasar population as steep as observed. In addition, our results closely fit the observed luminosity functions of quasars, their space density at different magnitudes from z≈ 5 to z≈ 0, and the local m BH –σ relation. The star formation in massive haloes declines sharply due to the lack of available cold gas already converted into stars during the starbursts at high z. The resulting high-z star formation rate and B-band luminosity functions, and the luminosity and redshift distribution of galaxies in K-band at z ≲ 2 are all in good agreement with the existing observations concerning the bright galaxy population.

IAC-STAR: A Code for Synthetic Color-Magnitude Diagram Computation

The code IAC-star is presented. It generates synthetic HR and color-magnitude diagrams (CMDs) and is mainly aimed to star formation history studies in nearby galaxies. Composite stellar populations are calculated on a star by star basis, by computing the luminosity, effective temperature and gravity of each star by direct bi-logarithmic interpolation in the metallicity and age grid of a library of stellar evolution tracks. Visual (broad band and HST) and infrared magnitudes are also provided for each star after applying bolometric corrections. The Padua (Bertelli et al. 1994, Girardi et al. 2000) and Teramo (Pietrinferni et al. 2004) stellar evolution libraries and various bolometric corrections libraries are used in the current version. A variety of star formation rate functions, initial mass functions and chemical enrichment laws are allowed and binary stars can be computed. Although the main motivation of the code is the computation of synthetic CMDs, it also provides integrated masses, luminosities and magnitudes as well as surface brightness fluctuation luminosities and magnitudes for the total synthetic stellar population, and therefore it can also be used for population synthesis research. The code is offered for free use and can be executed at the site {\tt http://iac-star.iac.es}, with the only requirement of referencing this paper and crediting as indicated in the site.

Early Hierarchical Formation of Massive Galaxies Triggered by Interactions

To address the problem concerning the early formation of stars in massive galaxies, we present the results of a semianalytic model of galaxy formation that includes a physical description of starbursts triggered by galaxy interactions. These originate from the destabilization of cold galactic gas that occurs in galaxy encounters, which in part feeds the accretion onto black holes that powers quasars and in part drives circumnuclear starbursts at redshifts z ≈ 2-4, preferentially in massive objects. This speeds up the formation of stars in massive galaxies at high redshifts without altering it in low-mass galactic halos. Thus, at intermediate z, ≈1.5-2, we find that a considerable fraction of the stellar content of massive galaxies is already in place, at variance with the predictions of previous hierarchical models. The resulting high-z star formation rate and B-band luminosity functions and the luminosity and redshift distribution of galaxies in the K band at z 2 are all in good agreement with the existing observations concerning the bright galaxy population.

Stochastic approach to the pit growth kinetics of Inconel alloy 600 in Cl − ion-containing thiosulphate solution at temperatures 25–150 °C by analysis of the potentiostatic current transients

The pit growth kinetics of Inconel alloy 600 in aqueous 0.1 M Na 2S 2O 3 + 0.1 M NaCl solutions was investigated as a function of solution temperature by analysis of the potentiostatic current transient, based upon a stochastic theory. Potentiostatic current transients revealed that time necessary for pit embryo formation, t pit,form decreased with increasing solution temperature. Analysis of the statistical distribution of t pit,form demonstrated that the pit embryo formation rate function at higher solution temperature exhibits a weaker dependence on exposure time compared with that at lower solution temperature. This is attributable to the increase in the active sites necessary for pit embryo formation due to the increase of the defects in oxide film grown at higher solution temperature. Moreover, it was found that the rate of pit growth decreased with increasing solution temperature over the whole applied potential range. Based upon the experimental findings, the kinetics of pit growth with respect to solution temperature is discussed in terms of the changes of the shape parameter derived from the stochastic theory, the pit growth rate parameter determined from the logarithmic potentiostatic current transient and fractal dimension of the pits formed on the electrode surface.

The Hα SFR of the Universe at z = 0.24 and z = 0.4

The evolution of the Star Formation Rate (SFR) density of the Universe has been a major topic of study during the last years. The most recent picture considers a drop of an order of magnitude from z = 1 to z = 0, but this conclusion is the result of combining several samples with different statistics, selection effects and SFR tracers (Ferguson et al., 2000). Our group has recently determined the local Ha luminosity function (i.e. the Star Formation Rate function) and the SFR density of the local Universe (Gallego et al.,1995). This measurement is based on the Ha luminosity of a complete sample of 178 galaxies detected by their Ha in emission. We have extended now this study to z = 0.24 and z = 0.4 by studying a complete sample of star-forming galaxies. The objects were selected by their Ha emission in narrow-band filters centered at Hα redshifted to z = 0.24 (8200A) and z = 0.4 (9200A), where the sky emission has a minimum. The extinction and contamination by [NII]λ6584 were corrected using average values for the local sample (Gallego et al., 1997).

A new calculation technique of muonium formation rate

In condensed matter the formation of a muonium atom from a positive muon and an election is described usually with a first order kinetic equation which assumes that the process is random and that the charge distribution is uniform. According to this model the muon polarization function as a function of time should reduce to an exponential law. Experiments in superfluid helium demonstrates that this is incorrect. Our proposed technique allows to reconstruct the muonium formation rate function from the μSR histogram in low transverse magnetic field without presupposing a particular theoretical form, i.e. with no parametrization. The technique is based on solving the integral equation of the first kind for the muon polarization function using the maximum likelihood method. The obtained results are of fundamental importance for the analysis of the charge kinetics in superfluid helium.

Surface formation rates and impact crater densities on Venus

Impact crater density has been used to estimate relative ages of major Venus geologic units, typically based on the assumption of short, globally synchronous formation periods. The total number density of craters is the only parameter which may be quantified for most Venus subregions, in contrast to the size‐frequency analysis often used for other planetary studies. This paper examines the statistical limits on such crater counts and the predicted crater density for various possible time‐varying surface formation rate functions. These results show that (1) the true mean crater density is poorly constrained due to the limited sample size provided by aggregate geologic units, and (2) any given crater density can be accommodated by a very short pulse of unit formation at some age T, Gaussian‐distributed formation functions of mean age &lt;T, exponential functions with initiation ages between T and 2T, or a host of other more complicated rate functions. These results, when coupled with the unknown rate of crater removal by tectonic or volcanic activity, indicate that the crater counts for specific landforms on Venus offer little constraint on the relative timing or duration of their development. The hypothesis of globally synchronous formation of landforms such as volcanoes or coronae cannot be validated with the available crater data.

Physical Conditions of Molecular Gas in the Galaxy

Physical conditions of molecular gas are key parameters to the formation rate and initial mass function of stars formed in molecular clouds. The ongoing Tokyo-NRO survey has been observing the Galactic CO (J=2–1) emission with a beamsize matched to the Columbia CO (J=1–0) survey. Intensities of the two lines should reflect physical conditions of the CO-emitting gas. An out-of-plane survey of the inner Galaxy which covers from 20° to 60° in galactic longitude and from −1° to +1° in galactic latitude with grid spacings of 0.25° has already been made (Sakamoto et al. 1994). Its coverage is large enough to draw conclusions on global properties of molecular gas in the inner Galaxy.