M. Capaccioli

On the shape of the light profiles of early-type galaxies

We have obtained the best fit to the light profiles of a luminosity-limited sample of elliptical and S0 galaxies with a power law r 1/n , letting the exponent remain free rather than keeping it fixed at 1/n=1/4 as in the well-known de Vaucouleurs formula. The introduction of a free parameter in the fitting formula (ranging from n=0.5 for =0.3 kpc to n=16 for =25 kpc) is justified by the existence of a good correlation between n and the global galaxian parameters, such as total luminosity and scale-radius. This result seems to be in line with the segregation of properties between the ordinary and bright families of early-type galaxies, and has consequences for the claimed independence of the shape of galaxy profiles with respect to the Fundamental Plane parameters

Kinematic properties of early-type galaxy haloes using planetary nebulae★

We present new planetary nebulae (PNe) positions, radial velocities and magnitudes for six early-type galaxies obtained with the Planetary Nebulae Spectrograph (PNS), along with derived two-dimensional velocity and velocity dispersion fields, and the α parameters (i.e. the number of PNe per unit luminosity). We also present new deep absorption-line long-slit kinematics for three galaxies in the sample, obtained with the FOcal Reducer and low dispersion Spectrograph (FORS2) at the Very Large Telescope (VLT). We extend this study to include additional 10 early-type galaxies with PNe radial velocity measurements available from the literature, including previous PNS studies, in order to obtain a broader description of the outer-halo kinematics in early-type galaxies. These data extend the information derived from stellar absorption-line kinematics to typically several and up to 8 effective radii. The combination of photometry, absorption-line and PNe kinematics shows (i) a good agreement between the PNe number density distribution and the stellar surface brightness in the region where the two data sets overlap; (ii) a good agreement between PNe and absorption-line kinematics; (iii) that the mean rms velocity profiles fall into two groups, with part of the galaxies characterized by slowly decreasing profiles and the remainder having steeply falling profiles; (iv) a larger variety of velocity dispersion radial profiles; (v) that twists and misalignments in the velocity fields are more frequent at large radii, including some fast rotator galaxies; (vi) that outer haloes are characterized by more complex radial profiles of the specific angular momentum-related λ_R parameter than observed within 1 R_e; (vii) that many objects are more rotationally dominated at large radii than in their central parts and (viii) that the halo kinematics are correlated with other galaxy properties, such as total B band and X-ray luminosity, isophotal shape, total stellar mass, V/σ and α parameter, with a clear separation between fast and slow rotators. Based in part on observations made with the William Herschel Telescope operated by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos on the island of La Palma, of the Instituto de Astrofisica de Canarias, and on observations collected at the European Southern Observatory, Chile, Program: 76.B-0788(A). E-mail: lcoccato@mpe.mpg.de

Discovery of Nine Lya Emitters at Redshift z ~ 3.1 Using Narrowband Imaging and VLT Spectroscopy

Narrowband imaging surveys aimed at detecting the faint emission from the 5007 A [O III] line of intracluster planetary nebulae in Virgo also probe high-redshift z ~ 3.1 Lyα emitters. Here we report on the spectroscopic identification of nine Lyα emitters at z = 3.13 with fluxes between 2 × 10-17 and 2 × 10-16 ergs cm-2 s-1 obtained with the FORS spectrograph at Unit 1 of the ESO Very Large Telescope (VLT UT1). The spectra of these high-redshift objects show a narrow, isolated Lyα emission with very faint (frequently undetected) continuum, indicating a large equivalent width. No other features are visible in our spectra. Our Lyα emitters are quite similar to those found by Hu, Cowie, and colleagues in 1998. For a flat universe with H0 = 70 km s-1 Mpc-1 and q0 = 0.5 (ΩΛ = 0), the Lyα luminosity of the brightest source is 1.7 × 109 L☉, and the comoving space density of the Lyα emitters in the searched volume is 5 × 10-3 Mpc-3. Using simple population synthesis models, on the assumption that these sources are regions of star formation, we conclude that the nebulae are nearly optically thick and must have a very low dust content in order to explain the high observed Lyα equivalent widths. For the cosmological and star formation parameters we adopted, the total stellar mass produced would seem to correspond to the formation of rather small galaxies, some of which are perhaps destined to merge. However, one of our sources might become a serious candidate for a protogiant spheroidal galaxy if we assumed continuous star formation, a low mass cutoff of 0.1 M☉ in the initial mass function (IMF), and a flat accelerating universe with Ω0 = 0.2 and ΩΛ = 0.8. The implied star formation density in our sampled comoving volume is probably somewhat smaller than, but of the same order of magnitude as, the star formation density at z ~ 3 derived by other authors from Lyman break galaxy surveys. This result agrees with the expectation that the Lyα emitters are a low-metallicity (or low-dust) tail in a distribution of star-forming regions at high redshifts. Finally, the Lyα emitters may contribute as many H-ionizing photons as QSOs at z ~ 3. They are therefore potentially significant for the ionization budget of the early universe.

Central mass-to-light ratios and dark matter fractions in early-type galaxies

Dynamical studies of local elliptical galaxies and the Fundamental Plane point to a strong dependence of the total mass-to-light ratio (M/L) on luminosity with a relation of the form M/L ∝ L γ . The ‘tilt’ γ may be caused by various factors, including stellar population properties (metallicity, age and star formation history), initial mass function, rotational support, luminosity profile non-homology and dark matter (DM) fraction. We evaluate the impact of all these factors using a large uniform data set of local early-type galaxies from Prugniel & Simien. We take particular care in estimating the stellar masses, using a general star formation history, and comparing different population synthesis models. We find that the stellar M/L contributes little to the tilt. We estimate the total M/L using simple Jeans dynamical models, and find that adopting accurate luminosity profiles is important but does not remove the need for an additional tilt component, which we ascribe to DM. We survey trends of the DM fraction within one effective radius, finding it to be roughly constant for galaxies fainter than M B ∼− 20.5, and increasing with luminosity for the brighter galaxies; we detect no significant differences between S0s and fast- and slow-rotating ellipticals. We construct simplified cosmological mass models and find general consistency, where the DM transition point is caused by a change in the relation between luminosity and effective radius. A more refined model with varying galaxy star formation efficiency suggests a transition from total mass profiles (including DM) of faint galaxies distributed similarly to the light to near-isothermal profiles for the bright galaxies. These conclusions are sensitive to various systematic uncertainties which we investigate in detail, but are consistent with the results of dynamical studies at larger radii.

The Planetary Nebula Spectrograph elliptical galaxy survey: the dark matter in NGC 4494

We present new Planetary Nebula Spectrograph observations of the ordinary elliptical galaxy NGC 4494, resulting in positions and velocities of 255 planetary nebulae out to seven effective radii (25 kpc). We also present new wide-field surface photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2. The spatial and kinematical distributions of the planetary nebulae agree with the field stars in the region of overlap. The mean rotation is relatively low, with a possible kinematic axis twist outside 1Re. The velocity dispersion profile declines with radius, though not very steeply, down to ∼70 km s − 1 at the last data point. We have constructed spherical dynamical models of the system, including Jeans analyses with multi-component A cold dark matter (CDM) motivated galaxies as well as logarithmic potentials. These models include special attention to orbital anisotropy, which we constrain using fourth-order velocity moments. Given several different sets of modelling methods and assumptions, we find consistent results for the mass profile within the radial range constrained by the data. Some dark matter (DM) is required by the data; our best-fitting solution has a radially anisotropic stellar halo, a plausible stellar mass-to-light ratio and a DM halo with an unexpectedly low central density. We find that this result does not substantially change with a flattened axisymmetric model. Taken together with other results for galaxy halo masses, we find suggestions for a puzzling pattern wherein most intermediate-luminosity galaxies have very low concentration haloes, while some high-mass ellipticals have very high concentrations. We discuss some possible implications of these results for DM and galaxy formation.

A deep kinematic survey of planetary nebulae in the Andromeda galaxy using the Planetary Nebula Spectrograph

This thesis presents a survey of compact emission-line objects in the Andromeda Galaxy (M31), performed using a novel new instrument, the Planetary Nebula Spectrograph. The final catalogue contains the positions, magnitudes and velocities for 3300 objects displaying [O III] emission at 5007 Angstroms, of which 2615 are found likely to be planetary nebulae (PNe) associated with M31. The survey area covers some 6 square degrees, taking in the whole of M31s disk out to a projected radius of 1.5 degrees, with extensions along the major and minor axes, and the Northern Spur and Southern Stream regions. The calibrated data have been checked for internal consistency and compared with other catalogues. With the exception of the very central, high surface brightness region of M31, this survey is complete to a magnitude limit of m(5007) ~ 23.75, 3.5 magnitudes into the planetary nebula luminosity function. A number of satellite and background galaxies are located within the M31 survey area and emission line objects associated with these have been identified. Analyses of the basic kinematic properties associated with each of these galaxies are presented. The PN catalogue has been analysed for non-kinematic, kinematic and dynamical properties. We have examined the planetary nebula luminosity function across M31, the spatial distribution of PNe, and the luminosity specific PN density. These analyses indicate that apart from a small change in the luminosity specific PN density there are no other non-kinematic differences between the bulge and disk PN populations suggesting that the sample of PNe is not strongly populated by objects whose progenitors are more massive stars. There is no indication of a significant halo PN population. Rotation curves for both the surveyed PNe and H II regions have been produced as well as the PN velocity dispersion profile. The H II rotation curve is seen to be in good agreement with those in the literature, while the PN rotation curve and velocity dispersion profile exhibit some peculiarities. However, under the approximation of an axisymmetric disk these are shown to be mutually consistent, but require the disk to flare with radius if the shape of its velocity ellipsoid remains invariant. The kinematic properties of photometric substructures are examined and kinematic substructures are searched for. A possible kinematic extension of the Southern Stream has been discovered. A new approach is taken in order to search for dynamical streams in the disk of the galaxy, involving an examination of the energy angular momentum plane. This also provides a new way of looking at the distribution function of a tracer population in a disk galaxy.

Detection, photometry and slitless radial velocities of 535 planetary nebulae in the flattened elliptical galaxy ngc 4697

We have detected 535 planetary nebulae (PNs) in the flattened elliptical galaxy NGC 4697 using the classic on-band, off-band filter technique with the Focal Reducer and Spectrograph at the Cassegrain focus of the first 8 m telescope unit of the ESO Very Large Telescope. From our photometry, we have built the [O III] ?5007 planetary nebula luminosity function (PNLF) of NGC 4697. It indicates a distance of 10.5 ? 1 Mpc to this galaxy, in good agreement with the distance obtained from surface brightness fluctuations and substantially smaller than a previous estimate of 24 Mpc used in earlier dynamical studies. The PNLF also provides an estimate of the specific PN formation rate: (6 ? 2) ? 10-12 PNs yr-1 L?-1. Combining the information from on-band images with PN positions on dispersed, slitless grism images, we have obtained radial velocities for 531 of the 535 PNs. We describe the slitless velocity method and the calibration procedures that we have followed. The radial velocities have errors of about 40 km s-1 and provide kinematic information up to a distance of almost three effective radii from the nucleus. Some rotation is detected in the outer regions, but the rotation curve of this galaxy appears to drop beyond one effective radius. Assuming an isotropic velocity distribution, the velocity dispersion profile is consistent with no dark matter within three effective radii of the nucleus (however, some dark matter can be present if the velocity distribution is anisotropic). We obtain a blue mass-to-light ratio of 11. Earlier M/L ratios for NGC 4697 were too small because of the too large distance used for their derivation.

Dearth of dark matter or massive dark halo? Mass-shape-anisotropy degeneracies revealed by nmagic dynamical models of the elliptical galaxy NGC 3379

Recent results from the Planetary Nebula Spectrograph (PNS) survey have revealed a rapidly falling velocity dispersion profile in the nearby elliptical galaxy NGC 3379, casting doubts on whether this intermediate-luminosity galaxy has the kind of dark matter (DM) halo expected in � cold dark matter (� CDM) cosmology. We present a detailed dynamical study of this galaxy, combining ground based long-slit spectroscopy, integral-field data from the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON) instrument and PNS data reaching to more than seven effective radii. We construct dynamical models with the flexible χ 2 -made-to-measure (χ 2 M2M) particle method implemented in the NMAGIC code. We fit spherical, axisymmetric and some triaxial models to the photometric and combined kinematic data in a sequence of gravitational potentials whose circular velocity curves at large radii vary between a near-Keplerian decline and the nearly flat shapes generated by massive haloes. We find that models with a range of halo masses, anisotropies, shapes and inclinations are good representations of the data. In particular, the data are consistent both with nearisotropic systems dominated by the stellar mass and with models in moderately massive haloes with strongly radially anisotropic outer parts (β 0.8 at 7Re). Formal likelihood limits would exclude (at 1σ ) the model with stars only, as well as halo models with vcirc(7Re) 250 km s −1 . All valid models fitting all the data are dynamically stable over gigayears, including the most anisotropic ones. Overall the kinematic data for NGC 3379 out to 7Re are consistent with a range of mass distributions in this galaxy. NGC 3379 may well have a DM halo as predicted by recent merger ¯

Properties of the Nova Population in M31

Observations of M31 novae are reviewed, and the implications of the results for the understanding of how novae distribute in galaxies and galactic subsystems are discussed. After correction for systematic errors, an annual rate of outbursts of 29 + or - 4 novae/yr is found. The data confirm that at least about 85 percent of the novae considered belong to the bulge (and the halo) of M31, and provide a distance modulus of (m - M)0 = 24.27 + or - 0.20 mag. 61 refs.

Morphological and Physical Classification of Galaxies

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