The presence of a massive black hole has been invoked to match the observed rotation velocities and velocity dispersions at the centres of M31, M32, NGC 3115 and NGC 4594, Here we determine stellar line-of-sight velocity profiles of these galaxies, from high spatial resolution, high S/N spectra centred on the G-band, the Mg b triplet and the Ca II IR triplet. For all spectra we determine rotation velocities, V, velocity dispersions, |$\sigma$|, and deviations of the velocity profiles from a Gaussian shape, as quantified by the Gauss-Hermite moments |$h_3, \ldots, h_6$|. Significant deviations of the velocity profiles from a Gaussian are present in all objects. The strongest deviations are asymmetries quantified by |$h_3$| and are found primarily along the major axis. The amplitude of |$h_3$| is typically |$|h_3| \lesssim 0.15$| and is correlated with |$V/\sigma$|. Its sign always indicates an excess of stars at low rotation velocities, and results in the mean stellar streaming velocity being lower than the mean of the best-fitting Gaussian, the quantity conventionally used to characterize rotation. The difference is |$\sim 10$| per cent for M31, M32 and NGC 3115, and |$\sim 20$| per cent for NGC 4594. It is thus important that models take the observed velocity profile shapes into account. We demonstrate that the observed deviations from Gaussian velocity profiles are for the most part not the result of projection and seeing convolution. We calculate the velocity profiles predicted by Tonry's model for M32, taking seeing and projection into account, but assuming the local (unprojected) velocity distributions to be Gaussian. The predicted velocity profiles are nearly Gaussian, in conflict with our data. Self-consistent dynamical models must thus be constructed to fit the observed velocity profiles. Such models should constrain the central structure quite strongly, and will hence provide improved constraints on the mass and presence of a supermassive central object.
We use a semi-analytic galaxy catalogue constructed from the Millennium Simulation (MS) to study the satellites of isolated galaxies in the Λ cold dark matter (ΛCDM) cosmogony. The large volume surveyed by the MS (5003 h−3 Mpc3), together with its unprecedented numerical resolution, enable the compilation of a large sample of ∼80 000 bright (Mr < −20.5) primaries, surrounded by ∼178 000 satellites down to the faint magnitude limit (Mr=−17) of our catalogue. This sample allows the characterization, with minimal statistical uncertainty, of the dynamical properties of satellite/primary galaxy systems in a ΛCDM universe. The details of this characterization are sensitive to the details of the modelling, such as its assumptions on galaxy merging and dynamical friction time-scales, but many of its general predictions should be applicable to hierarchical formation models such as ΛCDM. We find that, overall, the satellite population traces the dark matter rather well: its spatial distribution and kinematics may be approximated by a Navarro, Frenk & White profile with a mildly anisotropic velocity distribution. Their spatial distribution is also mildly anisotropic, with a well-defined 'anti-Holmberg' effect that reflects the misalignment between the major axis and angular momentum of the host halo. Our analysis also highlights a number of difficulties afflicting studies that rely on satellite velocities to constrain the primary halo mass. These arise from variations in the star formation efficiency and assembly history of isolated galaxies, which result in a scatter of up to approximately two decades in halo mass at a fixed primary luminosity. Our isolation criterion (primaries may only have companions at least 2 mag fainter within 1 h−1 Mpc) contributes somewhat to the scatter, since it picks not only galaxies in sparse environments, but also a number of primaries at the centre of 'fossil' groups. We find that the abundance and luminosity function of these unusual systems are in reasonable agreement with the few available observational constraints. Much tighter halo mass–luminosity relations are found when splitting the sample by colour: red primaries inhabit haloes more than twice as massive as those surrounding blue primaries, a difference that vanishes, however, when considering stellar mass instead of luminosity. The large scatter in the halo mass–luminosity relation hinders the interpretation of the velocity dispersion of satellites stacked according to the luminosity of the primary. We find L∝σ3 (the natural scaling expected for ΛCDM) for truly isolated primaries, that is, systems where the central galaxy contributes more than 85 per cent of the total luminosity within its virial radius. Less-strict primary selection, however, leads to substantial modification of the scaling relation: blindly stacking satellites of all primaries results in a much shallower L–σ relation that is only poorly approximated by a power law.
We have developed methods for extracting line-of-sight velocity distributions (LOSVDs) from the broadening of absorption lines in early-type galaxies. These methods operate exclusively in pixel space, they use the full information content of the data, they permit a rigorous treatment of the errors, and they relax the standard a priori assumption that the LOSVD is a Gaussian. We have considered two problems: optimal noise filtering for model-independent extraction of the LOSVD, subject only to the constraint that it be bandwidth-limited; and optimal parameter estimation when the LOSVD can be assumed to belong to a parametrized family of models, for example, single or double Gaussians. The latter broadening model is of particular interest when a disc-like, rotating component is suspected to coexist with a dynamically hot spheroid. We find that for typical instrumental set-ups a signal-to-noise ratio (S/N) of 30 per pixel is required to discriminate between such a two-component LOSVD and a single Gaussian. Monte-Carlo simulations demonstrate that mismatch of spectral features between galaxy and template can produce significant systematic errors in the reconstructed LOSVD. These errors are substantially reduced if an optimally matched composite template is used. Applying our methods to two elliptical galaxies with kinematically distinct cores (NGC 5322 and NGC 3610), we find LOSVDs which deviate significantly from a Gaussian. Interpreting these LOSVDs in terms of a disc spheroid model, we find order-of-magnitude variations in the degree of rotational support in the discs; |$v/\sigma \approx 1.4$| in NGC 5322, whereas |$v/\sigma \approx 4.5$| in NGC 3610. By modelling NGC 5322 in some detail, we show explicitly that a small disc embedded in the spheroid is a viable explanation for all the available photometric and kinematic information on this galaxy.
The paper 'The size distribution of galaxies in the Sloan Digital Sky Survey' was published in Mon.Not.R. Astron.Soc.343, 978-994 (2003).The value of fitting parameter b in equation ( 17) of fig.11 given in table 1 is wrong.The correct value is 2.88 × 10 -6 .However, the corresponding parameter a in equation ( 17) is unchanged, and the changed quantity makes no difference to any of our results and conclusions.
We study the population of galactic discs expected in current hierarchical clustering models for structure formation. A rotationally supported disc with exponential surface density profile is assumed to form with a mass and angular momentum which are fixed fractions of those of its surrounding dark halo. We assume that haloes respond adiabatically to disc formation, and that only stable discs can correspond to real systems. With these assumptions the predicted population can match both present-day discs and the damped Lyα absorbers in QSO spectra. Good agreement is found provided that: (i) the masses of discs are a few per cent of those of their haloes; (ii) the specific angular momenta of discs are similar to those of their haloes; (iii) present-day discs were assembled recently (at z ≤ 1). In particular, the observed scatter in the size—rotation velocity plane is reproduced, as are the slope and scatter of the Tully—Fisher (TF) relation. The zero-point of the TF relation is matched for a stellar mass-to-light ratio of 1 to 2 h in the I-band, consistent with observational values derived from disc dynamics. High-redshift discs are predicted to be small and dense, and could plausibly merge together to form the observed population of elliptical galaxies. In many (but not all) currently popular cosmogonies, discs with rotation velocities exceeding 200 km s−1 can account for a third or more of the observed damped Lyα systems at z ∼ 2.5. Half of the lines of sight to such systems are predicted to intersect the absorber at r ≳ 3 h−1 kpc and about 10 per cent at r > 10 h−1 kpc. The cross-section for absorption is strongly weighted towards discs with large angular momentum and therefore large size for their mass. The galaxy population associated with damped absorbers should thus be biased towards low surface brightness systems.
We present the catalogue, mask, redshift data and selection function for the PSCz survey of 15 411 IRAS galaxies across 84 per cent of the sky. Most of the IRAS data are taken from the Point Source Catalog, but this has been supplemented and corrected in various ways to improve the completeness and uniformity. We quantify the known imperfections in the catalogue, and we assess the overall uniformity, completeness and data quality. We find that overall the catalogue is complete and uniform to within a few per cent at high latitudes and 10 per cent at low latitudes. Ancillary information, access details, guidelines and caveats for using the catalogue are given.
We develop and test a new statistical method to measure the kinematic Sunyaev-Zel'dovich (kSZ) effect. A sample of independently detected clusters is combined with the cosmic flow field predicted from a galaxy redshift survey in order to derive a matched filter that optimally weights the kSZ signal for the sample as a whole given the noise involved in the problem. We apply this formalism to realistic mock microwave skies based on cosmological N-body simulations, and demonstrate its robustness and performance. In particular, we carefully assess the various sources of uncertainty, cosmic microwave background primary fluctuations, instrumental noise, uncertainties in the determination of the velocity field, and effects introduced by miscentring of clusters and by uncertainties of the mass-observable relation (normalization and scatter). We show that available data (Planck maps and the MaxBCG catalogue) should deliver a 7.7σ detection of the kSZ. A similar cluster catalogue with broader sky coverage should increase the detection significance to ∼13σ. We point out that such measurements could be binned in order to study the properties of the cosmic gas and velocity fields, or combined into a single measurement to constrain cosmological parameters or deviations of the law of gravity from General Relativity.
We use a novel technique to simulate the growth of the most massive progenitor of a protocluster region from redshift z~80, when its mass was about 10 Msun until the present day. Our nested sequence of N-body resimulations allows us to study in detail the structure both of the dark matter object itself and of its environment. Our effective resolution is optimal at redshifts of 49, 29, 12, 5 and 0 when the dominant object has mass 1.2e5, 5e7, 2e10, 3e12 and 8e14 Msun/hrespectively, and contains ~1e6 simulation particles within its virial radius. Extended Press-Schechter theory correctly predicts both this rapid growth and the substantial overabundance of massive haloes we find at early times in regions surrounding the dominant object. Although the large-scale structure in these regions differs dramatically from a scaled version of its present-day counterpart, the internal structure of the dominant object is remarkably similar. Molecular hydrogen cooling could start as early as z~49 in this object, while cooling by atomic hydrogen becomes effective at z~39. If the first stars formed in haloes with virial temperature ~2000, their comoving abundance by z=49 would be similar to that of dwarf galaxies today, while their comoving correlation length would be ~2.5Mpc/h.
We argue that a universal density profile for dark matter haloes arises as a natural consequence of hierarchical structure formation: it is a fixed point in the process of repeated mergers. We present analytic and numerical arguments for the emergence of a particular form of the central cusp profile. At small radii, the density should vary as r−α, with α determined by the way in which the characteristic density of haloes scales with their mass. If small haloes are dense, then α is large. The mass-density relation can be related to the power spectrum of initial fluctuations, P(k), through 'formation time' arguments. Early structure formation leads to steep cusps. For P(k) ∼ kn we find α ≃ 3(3 + n)/(5 + n). The universal profile is generated by tidal stripping of small haloes as they merge with larger objects.
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