Outflows from evolved stars with OASIS, NAOMI and GLAS

I discuss the potential of integral-field spectroscopy (IFS) with adaptive optics in the study of the outflows from evolved stars of different masses.With IFS, detailed 3-D spatio-kinematical models of the outflows can be built, providing excellent observational datasets to be confronted with the existing dynamical theories. In addition, if multi-epoch observations are able to resolve the apparent expansion of the nebulae in the plane of the sky, then their dynamics can be further constrained, and other basic quantities like the distance via the expansion parallax, can be determined. The kind of results that can be obtained are illustrated by recent HST and VLT observations of the ring nebula around the symbiotic nova He 2-147.Given the present capabilities of the OASIS integral-field spectrograph of the Isaac Newton Group of Telescopes (ING), classical novae ejecta are the most appealing targets for such kind of studies, provided that its AO system NAOMI is complemented with the forthcoming laser guide star system GLAS.IFS+AO is also a powerful technique to detect faint ionized nebulae around bright stars, like for instance the outflows from luminous blue variables.     

On the formation of protostellar disks

An analysis is presented of the hydrodynamic aspects of the growth of protostellar disks from the accretion (or collapse) of a rotating gas cloud. The size, mass, and radiative properties of protostellar disks are determined by the distribution of mass and angular momentum in the clouds from which they are formed, as well as from the dissipative processes within the disks themselves. The angular momentum of the infalling cloud is redistributed by the action of turbulent viscosity on a shear layer near the surface of the disk (downstream of the accretion shock) and on the radial shear across cylindrical surfaces parallel to the rotation axis. The fraction of gas that is fed into a central core (protostar) during accretion depends on the ratio of the rate of viscous diffusion of angular momentum to the accretion rate; rapid viscous diffusion (or a low accretion rate) promotes a large core-to-disk mass ratio. The continuum radiation spectrum of a highly viscous disk is similar to that of a steady-state accretion disk without mass addition. It is possible to construct models of the primitive solar nebula as an accretion disk, formed by the collapse of a slowly rotating protostellar cloud, and containing the minimum mass required to account for the planets. Other models with more massive disks are also possible.     

The small scatter in BH–host correlations and the case for self-regulated BH growth

Supermassive black holes (BHs) obey tight scaling relations between their mass and host galaxy properties such as total stellar mass, velocity dispersion and potential well depth. This has led to the development of self-regulated models for BH growth, in which feedback from the central BH halts its own growth upon reaching a critical threshold. However, models have also been proposed in which feedback plays no role: so long as a fixed fraction of the host gas supply is accreted, relations like those observed can be reproduced. Here, we argue that the scatter in the observed BH–host correlations presents a demanding constraint on any model for these correlations, and that it favours self-regulated models of BH growth. We show that the scatter in the stellar mass fraction within a radius R in observed ellipticals and spheroids increases strongly at small R . At a fixed total stellar mass (or host velocity dispersion), on very small scales near the BH radius of influence, there is an order-of-magnitude scatter in the amount of gas that must have entered and formed stars. In short, the BH appears to 'know more' about the global host galaxy potential on large scales than the stars and gas supply on small scales. This is predicted in self-regulated models; however, models where there is no feedback would generically predict order-of-magnitude scatter in the BH–host correlations. Likewise, models in which the BH feedback in the 'bright' mode does not regulate the growth of the BH itself, but sets the stellar mass of the galaxy by inducing star formation or blowing out a mass in gas much larger than the galaxy stellar mass, are difficult to reconcile with the scatter on small scales.     

Numerical simulations of astrophysical jets from Keplerian discs – III. The effects of mass loading

We present 2.5D time-dependent simulations of the non-linear evolution of non-relativistic outflows from the surface of Keplerian accretion discs. The gas is accelerated from the surface of the disc (which is a fixed platform in these simulations) into a cold corona in stable hydrostatic equilibrium. We explore the dependence of the resulting jet characteristics upon the mass loading of the winds. Two initial configurations of the threading disc magnetic field are studied: a potential field and a uniform vertical field configuration.
We show that the nature of the resulting highly collimated, jet-like outflows (steady or episodic) is determined by the mass load of the disc wind. The mass load controls the interplay between the collimating effects of the toroidal field and the kinetic energy density in the outflow. In this regard, we demonstrate that the onset of episodic behaviour of jets appears to be determined by the quantity     which compares the speed for a toroidal Alfvén wave to cross the diameter of the jet, with the flow speed v _p along the jet. This quantity decreases with increasing load. For sufficiently large N (small mass loads), disturbances appear to grow leading to instabilities and shocks. Knots are then generated and the outflow becomes episodic. These effects are qualitatively independent of the initial magnetic configuration that we employed and are probably generic to a wide variety of magnetized accretion disc models.     

Probing Milky Way’s hot gas halo density distribution using the dispersion measure of pulsars

A number of recent studies indicates a significant amount of ionized gas in a form of the hot gas halo around the Milky Way. The halo extends over the region of 100 kpc and may be acountable for the missing baryon mass. In this paper we calculate the contribution of the proposed halo to the dispersion measure (DM) of the pulsars. The Navarro, Frenk, and White (NFW), Maller and Bullock (MB), and Feldmann, Hooper, and Gnedin (FHG) density distibutions are considered for the gas halo. The data set includes pulsars with the distance known independently from the DM, e.g., pulsars in globular clusters, LMC, SMC and pulsars with known parallax. The results exclude the NFW distribution for the hot gas, while the more realisticMB and FHG models are compatible with the observed dispersion measure.     

The local properties of supernova explosions and their host galaxies

We aim to understand the properties at the locations of supernova(SN) explosions in their host galaxies and compare with the global properties of these host galaxies. We use the integral field spectrograph(IFS) of Mapping Nearby Galaxies at Apache Point Observatory(MaNGA) to generate 2 D maps of the parameter properties for 11 SN host galaxies. The sample galaxies are analyzed one by one in detail in terms of their properties of velocity field, star formation rate, oxygen abundance, stellar mass, etc.This sample of SN host galaxies has redshifts around z~0.03, which is higher than those of previous related works. The higher redshift distribution allows us to obtain the properties of more distant SN host galaxies. Metallicity(gas-phase oxygen abundance) estimated from integrated spectra can represent the local metallicity at SN explosion sites with small bias. All the host galaxies in our sample are metal-rich galaxies(12+log(O/H) 8.5) except for NGC 6387, which means SNe may be more inclined to explode in metallicity-rich galaxies. There is a positive relation between global gas-phase oxygen abundance and the stellar mass of host galaxies. We also try to compare the differences of the host galaxies between SNe Ia and SNe II. In our sample, both SNe Ia and SNe II can explode in normal galaxies, but SNe II can also explode in an interacting or a merging system, in which star formation is occurring in the galaxy.     

The Environment of YSO Jets

It is commonly accepted that stars form in molecular clouds by the gravitational collapse of dense gas. However, it is precisely not the infalling but the outflowing material that is primarily observed. Outflow motions prevail around both low and high mass young stellar objects. We present here results from a family of self-similar models that could possibly help to understand this paradox. The models take into account the heating of the central protostar for the deflection and acceleration of the gas. The models make room for all the ingredients observed around the central objects, i.e. molecular outflows, fast jets, accretion disks and infalling envelopes. We suggest that radiative heating and magnetic field may ultimately be the main energy sources driving outflows for both low and high mass stars. The models show that the ambient medium surrounding the jet is unhomogeneous in density, velocity, magnetic field. Consequently, we suggest that jets and outflows have a prehistory that is inprinted in their environment, and that this should have direct consequences on the setting of jet numerical simulations.     

Active Galactic Nuclei Feedback and Clusters

The Intracluster Medium (ICM) is believed to have been affected by feedback from Active Galactic Nuclei (AGN) and/or supernovae-driven winds. These sources are supposed to have injected entropy into the ICM gas. The recently determined universal pressure profile of the ICM gas has been used and after comparing with the entropy profile of the gas from gravitational effects of the dark matter halo, the additional entropy injected by non-gravitational sources, as a function of the total cluster mass is determined. The current observational data of red-shift evolution of cluster scaling relation is shown that allow models in which the entropy injection decreases at high red-shift.     

The Sunyaev–Zel'dovich effect and Faraday rotation contributions of galaxy groups to the CMB angular power spectrum

The Sunyaev–Zel'dovich (SZ) effect and the Faraday rotation from haloes are examined over a wide mass range, including gas condensation and magnetic field evolution. Contributions to the cosmic microwave background (CMB) angular power spectrum are evaluated for galaxy clusters, galaxy groups and galaxies. Smaller mass haloes are found to play a more important role than massive haloes for the B -mode polarization associated with the SZ CMB anisotropies. The B modes from the Faraday rotation dominate the secondary B modes caused by gravitational lensing at  ℓ > 3000  . Measurement of B -mode polarization in combination with the SZ power spectrum can potentially provide important constraints on intracluster magnetic field and gas evolution at early epochs.     

Impact of magnetic field on the gas mass fraction of galaxy clusters

Magnetic fields have been observed in galaxy clusters with strengths of the order of  ~ μG. The non-thermal pressure exerted by magnetic fields also contributes to the total pressure in galaxy clusters and can in turn affect the estimates of the gas mass fraction, f_gas. In this paper, we have considered a central magnetic field strength of 5μG, motivated by observations and simulations of galaxy clusters. The profile of the magnetic field has also been taken from the results obtained from simulations and observations. The role of magnetic field has been taken into account in inferring the gas density distribution through the hydrostatic equilibrium condition (HSE) by including the magnetic pressure. We have found that the resultant gas mass fraction is smaller with magnetic field as compared to that without magnetic field. However, this decrease is dependent on the strength and the profile of the magnetic field. We have also determined the total mass using the NFW profile to check for the dependency of f_gas estimates on total mass estimators. From our analysis, we conclude that for the magnetic field strength that galaxy clusters seem to possess, the non-thermal pressure from magnetic fields has an impact of  ≈ 1 % on the gas mass fraction of galaxy clusters. However, with upcoming facilities like Square Kilometre Array (SKA), it can be further expected to improve with more precise observations of the magnetic field strength and profile in galaxy clusters, particularly in the interior region.     

A grid of chemical evolution models as a tool to interpret spiral and irregular galaxies data

We present a generalization of the multiphase chemical evolution model (CEM) applied to a wide set of theoretical galaxies with different masses and evolutionary rates. This generalized set of models has been computed using the so-called universal rotation curve from Persic, Salucci & Steel to calculate the radial mass distribution of 44 theoretical protogalaxies. This distribution is a fundamental input which, besides its own effect on the galaxy evolution, defines the characteristic collapse time-scale or gas infall rate on to the disc. We have adopted 10 sets of values, between 0 and 1, for the molecular cloud and star formation efficiencies, as corresponding to their probability nature, for each one of the radial distributions of total mass. Thus, we have constructed a biparametric grid of models, depending on those efficiency sets and on the rotation velocity, whose results are valid in principle for any spiral or irregular galaxy. The model results provide the time-evolution of different regions of the disc and the halo along galactocentric distance, measured by the gas (atomic and molecular) and stellar masses, the star formation rate (SFR) and chemical abundances of 14 elements, for a total of 440 models. This grid may be used to estimate the evolution of a given galaxy for which only present time information, such as radial distributions of elemental abundances, gas densities and/or star formation, which are the usual observational constraints of chemical evolution models (CEMs), is available.     

Halo masses for optically selected and for radio-loud AGN from clustering and galaxy–galaxy lensing

We compute two-point correlation functions and measure the shear signal due to galaxy–galaxy lensing for 80 000 optically identified and 5700 radio-loud active galactic nuclei (AGN) from Data Release 4 of the Sloan Digital Sky Survey. Halo occupation models are used to estimate halo masses and satellite fractions for these two types of AGN. The large sample size allows us to separate AGN according to the stellar mass of their host galaxies. We study how the halo masses of optical and radio AGN differ from those of the parent population at fixed   M _*  . Halo masses deduced from clustering and from lensing agree satisfactorily. Radio AGN are found in more massive haloes than optical AGN: in our samples, their mean halo masses are  1.6 × 10¹³  and  8 × 10¹¹  h ⁻¹ M_⊙  , respectively. Optical AGN follow the same relation between stellar mass and halo mass as galaxies selected without regard to nuclear properties, but radio-loud AGN deviate significantly from this relation. The dark matter haloes of radio-loud AGN are about twice as massive as those of control galaxies of the same stellar mass. This boost is independent of radio luminosity, and persists even when our analysis is restricted to field galaxies. The large-scale gaseous environment of the galaxy clearly plays a crucial role in producing observable radio emission. The dark matter halo masses that we derive for the AGN in our two samples are in good agreement with recent models in which feedback from radio AGN becomes dominant in haloes where gas cools quasi-statically.     

Techniques for reducing fiber‐fed and integral‐field spectroscopy data: An implementation on R3D

This paper describes the general characteristics of raw data from fiber‐fed spectrographs in general and fiber‐fed IFUs in particular. The different steps of the data reduction are presented, and the techniques used to address the unusual characteristics of these data are described in detail. These techniques have been implemented in a specialized software package, R3D, developed to reduce fiber‐based integral field spectroscopy (IFS) data. The package comprises a set of command‐line routines adapted for each of these steps, suitable for creating pipelines. The routines have been tested against simulations, and against real data from various integral field spectrographs (PMAS, PPAK, GMOS, VIMOS and INTEGRAL). Particular attention is paid to the treatment of cross‐talk. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Tip-tilt requirements for coupling starlight into single-mode photonic crystal fibres using a lenslet: A first analysis

Single-mode fibres do not suffer from modal noise and are available in polarisation maintaining form. Single-mode photonic crystal fibres (smPCF) have a wavelength insensitive mode field allowing coupling of the telescope exit pupil into the fibre using a lenslet with a flat spectral response. This may allow single-mode Integral Field Spectroscopy (IFS) and fibre fed integral field spectro-polarimetry. Initial results from a theoretical analysis of telescope/smPCF coupling using a lenslet are presented. Coherent imaging theory is used to determine the coupling efficiency into the fibre and thence the fibre numerical aperture is defined and used to compute the sample size on the sky. A higher degree of tip-tilt correction is shown to be required for coupling into single-mode fibres with a lenslet than the multimode fibre alternative, for sparse sampling integral field and multi-object spectroscopy and interferometry, but the magnitude of which is within the scope of current NIR and planned (extreme) VIS AO systems. Extension of the model to contiguous integral field spectroscopy is also considered.     

The effects of gas on morphological transformation in mergers: implications for bulge and disc demographics

Transformation of discs into spheroids via mergers is a well-accepted element of galaxy formation models. However, recent simulations have shown that the bulge formation is suppressed in increasingly gas-rich mergers. We investigate the global implications of these results in a cosmological framework, using independent approaches: empirical halo-occupation models (where galaxies are populated in haloes according to observations) and semi-analytic models. In both, ignoring the effects of gas in mergers leads to the overproduction of spheroids: low- and intermediate-mass galaxies are predicted to be bulge-dominated (   B / T ∼ 0.5  at  <10¹⁰ M_⊙  , with almost no 'bulgeless' systems), even if they have avoided major mergers. Including the different physical behaviour of gas in mergers immediately leads to a dramatic change: bulge formation is suppressed in low-mass galaxies, observed to be gas-rich (giving   B / T ∼ 0.1  at  <10¹⁰ M_⊙  , with a number of bulgeless galaxies in good agreement with observations). Simulations and analytic models which neglect the similarity-breaking behaviour of gas have difficulty reproducing the strong observed morphology–mass relation. However, the observed dependence of gas fractions on mass, combined with suppression of bulge formation in gas-rich mergers, naturally leads to the observed trends. Discrepancies between observations and models that ignore the role of gas increase with redshift; in models that treat gas properly, galaxies are predicted to be less bulge-dominated at high redshifts, in agreement with the observations. We discuss implications for the global bulge mass density and future observational tests.     

The effect of projection on the observed gas velocity fields in barred galaxies

The problem of determining the pattern of gas motions in the central regions of disk spiral galaxies is considered. Two fundamentally different cases—noncircular motions in the triaxial bar potential and motions in circular orbits but with orientation parameters different from those of the main disk—are shown to have similar observational manifestations in the line-of-sight velocity field of the gas. A reliable criterion is needed for the observational data to be properly interpreted. To find such a criterion, we analyze two-dimensional nonlinear hydrodynamic models of gas motions in barred disk galaxies. The gas line-of-sight velocity and surface brightness distributions in the plane of the sky are constructed for various inclinations of the galactic plane to the line of sight and bar orientation angles. We show that using models of circular motions for inclinations i>60° to analyze the velocity field can lead to the erroneous conclusions of a “tilted (polar) disk” at the galaxy center. However, it is possible to distinguish bars from tilted disks by comparing the mutual orientations of the photometric and dynamical axes. As an example, we consider the velocity field of the ionized gas in the galaxy NGC 972.     

Kinematics and Mass Modelling of NGC 1068

We present the kinematics of the ionized gas over the inner 140″ (10 kpc) from observations with the HIFI Fabry-Perot interferometer. There is clear evidence for density wave streaming and bar-driven streaming across the field, with bi-symmetric arms that penetrate to within 200 pc of the nucleus. CO maps show linear structures along (although slightly offset from) the bar consistent with a strong shock. Along the spiral arms which encircle the bar, the H II regions lie downstream of the CO gas in the rest frame of the bar, as do the dust lanes, only if the gas outruns the stellar bar. As a first step towards understanding the details of the gas kinematics, and attempting to determine the mass inflow rate towards the nucleus, we build a mass model for the central disk constrained by near-infrared images. We plan to use this model as gravitational background potential for hydrodynamical simulations of the gas response to the bar. Comparing these with the data presented should enable us to constrain various quantities such as pattern speed, stellar mass-to-light ratio, central mass concentration, and gas fueling rate. This revised version was published online in July 2006 with corrections to the Cover Date.     

The G-dwarf problem in the Galactic spheroid

This paper has two parts: one about observational constraints, and the other about chemical evolution models. In the first part, the empirical differential metallicity distribution (EDMD) is deduced from two different samples involving (i) 268 K-giant bulge stars [Sadler, E.M., Rich, R.M., Terndrup, D.M., 1996. AJ 112, 171], and (ii) 149 globular clusters [Mackey, A.D., van den Bergh, S., 2005. MNRAS 360, 631], in addition to previous results (Caimmi, R., 2001b, AN 322, 241 (C01)) related to (iii) 372 solar neighbourhood halo subdwarfs [Ryan, S.G., Norris, J.E., 1991. AJ 101, 1865]. Under the assumption that each distribution is typical for the corresponding subsystem, the EDMD of the Galactic spheroid is determined by weighting the mass. The empirical age-metallicity relation (EAMR) involving absolute ages is deduced from recent results related to a homogeneous sample of globular clusters [De Angeli, F., Piotto, G., Cassisi, S., et al., 2005. AJ 130, 116]. In the second part, models of chemical evolution for the Galactic halo and bulge are computed, assuming the instantaneous recycling approximation. The EDMD data are fitted, to an acceptable extent, by simple models of chemical evolution implying both homogeneous and inhomogeneous star formation, provided that star formation is inhibited during halo formation and enhanced during bulge formation, with respect to the disk solar neighbourhood, taken to be representative of the whole disk. The initial mass function (IMF) is assumed to be a universal power law, which implies the same value of the true yield in different subsystems. The theoretical differential metallicity distribution (TDMD) is first determined for the halo and the bulge separately, and then for the Galactic spheroid by weighting the mass. The EAMR cannot be fitted into the Simple model that implies homogeneous star formation, but shows a non-monotonic trend characterized by large dispersion. On the other hand, simple models involving inhomogeneous star formation yield a theoretical age-metallicity relation (TAMR) which reproduces the data to an acceptable extent. For gas ouflow from the proto-halo, acceptable models give rise to different predictions in different alternatives. If the Galactic spheroid and disk underwent decoupled chemical evolution, i.e. no gas exchange between the related reservoirs, less than one third of the bulge mass outflowed from the proto-halo. If the Galactic spheroid and disk underwent coupled chemical evolution, i.e. some gas exchange between the related reservoirs, the existence of an unseen baryonic halo (or equivalent amount of gas lost by the Galaxy) with mass comparable to bulge mass, is necessarily needed. In this view, the outflowing proto-halo gas which remains bound to the Galaxy, produces both the bulge and the disk.     

Late stages of planetary accretion

We derive first-order differential equations for the late stages of planetary accretion (planetesimal mass >10¹³ g). The effect of gravitational encounters, energy exchange, collisions, and gas drag has been included. Two simple models are discussed, namely, (i) when all planetesimals have the same mass and (ii) when there is one large planetesimal and numerous small planetesmals. Gravitational two-body encounters are modeled according to Chandrasekhar's classical theory from stellar dynamics. It is shown that the velocity increase due to mutual encounters can be modeled according to the simple theory of random flights. We find analytical equations for the average velocity decrease due to collisions. Gas drag, if present, is modeled in averaged form up to the first order in the eccentricities and inclinations of the planetesimals. Characteristic time scales for the formation of the terrestrial planets are found for the most favorable models to be of order 10⁸ year. The calculated mass of rock and ice of the giant planets is too low as compared to the observed one. This difficulty of our model could be overcome by assuming a several times larger surface density, an enlarged accretion cross section, and gas accretion during the final stages of accretion of the solid cores of the giant planets. Analytical and numerical results are presebted, the evolutionary tracks showing satisfactory agreement with observations for some models.     

Spiral-Vortex Structure in the Gaseous Disks of Galaxies

General ideas, as well as experimental and theoretical efforts concerning the prediction and discovery of new structures in the disks of spiral galaxies – giant anticyclones - are reviewed. A crucial point is the development of a new method to restore the full vector velocity field of the galactic gas from the line-of-sight velocity field. This method can be used to get self-consistent solutions for the following problems: 1) determination of non-circular velocities associated with spiral-vortex structure; 2) determination of fundamental parameters of this structure: pattern speed, corotation radius, location of giant anticyclones; 3) refinement of galactic rotation curves taking into account regular non-circular motion in the spiral density wave, which makes it possible to build more accurate models of the mass distribution in the galaxy; 4) refinement of parameters of the rotating gaseous disk: inclination angle, center of rotation and position angle of the major dynamical axis, systematic velocity. The method is demonstrated using the restoration of the velocity field of the galaxy NGC 157 as an example. Results for this and some other spiral galaxies suggest that giant anticyclones are a universal property of galaxies with grand design structure.