Regions Of Early-type Galaxies Research Articles

Elliptical galaxies/stellar halos connection

AbstractCosmological simulations predict that early-type galaxies (ETGs) are the results of extended mass accretion histories. The latter are characterized by different numbers of mergers, mergers’ mass ratios and gas fractions, and timing. Depending on the sequence and nature of these mergers that follow the first phase of the in-situ star formation, these accretion histories may lead to ETGs that have low or high mass halos, and that rotate fast or slow. Since the stellar halos maintain the fossil records of the events that led to their formation, a discontinuity may be in place between the inner regions of ETGs and their outer halos, because the time required for the halos’ stars to exchange their energies and momenta is very long compared with the age of these systems. Exquisite deep photometry and extended spectroscopy for significant samples of ETGs are then used to quantify the occurrence and significance of such a transition in the galaxies’ structural and kinematical parameters. Once this transition radius is measured, its dependency with the effective radius of the galaxies’ light distribution and total stellar masses can be investigated. Such correlations can then be compared with the predictions of accreted, i.e. ex-situ vs. in-situ components from cosmological simulations to validate such models.

Constraining the Rastall parameters in static space–times with galaxy-scale strong gravitational lensing

Recently, Rastall gravity is undergoing a significant surge in popularity. We obtain a power-law total mass-density profile for the inner region (within several effective radius) of early-type galaxies (ETGs) from the space-time structures which are described by the static spherically-symmetric solutions of Rastall gravity under the assumption of perfect fluid matter. We find that in the inner region of ETGs, the Rastall dimensionless parameter $\beta=\kappa\lambda$ determines the mass distribution. We then use 118 galaxy-galaxy strong gravitational lensing systems to constrain the Rastall dimensionless parameter $\beta$. We find that the mean value of $\beta$ for total 118 ETGs is $\beta=0.163\pm0.001$(68\% CL) with a minor intrinsic scatter of $\delta=0.020\pm 0.001$. Our work observationally illustrates the physical meaning of the Rastall dimensionless parameter in galaxy scale. From the Newtonian approximation of Rastall gravity, we also find that an absolute isothermal mass distribution for ETGs is not allowed in the framework of Rastall gravity.

Dark matter in massive early-type galaxies: 100 years of the jeans equations

In 1919 James Jeans published the book Problems of Cosmogony and Stellar Dynamics in which he summarized his work on dynamics of stellar systems based on his papers published from 1915 onwards. To mark the centenary of this publication we present here one application of his work relevant for contemporary research of galaxies: we analyze the problem of dark matter in massive early-type galaxies (ellipticals and lenticulars) using various available observational data. After discussing the basics of the Jeans equations we study their application on the integrated stellar spectra of galaxies, planetary nebula data and, especially, globular cluster data. We rely on both Newtonian and MOND frameworks and show their advantages and drawbacks. To infer the contribution of the dark component in early-type galaxies we rely on several stellar population synthesis models. It is shown that dark matter does not dominate in the inner regions of early-type galaxies, but becomes more important beyond three effective radii.

Two-dimensional kinematics of SLACS lenses - III. Mass structure and dynamics of early-type lens galaxies beyond z ≃ 0.1

We combine in a self-consistent way the constraints from both gravitational lensing and stellar kinematics to perform a detailed investigation of the internal mass distribution, amount of dark matter, and dynamical structure of the 16 early-type lens galaxies from the SLACS Survey, at z = 0.08 - 0.33, for which both HST/ACS and NICMOS high-resolution imaging and VLT VIMOS IFU spectroscopy are available. Based on this data set, we analyze the inner regions of the galaxies, i.e. typically within one (3D) effective radius r_e, under the assumption of axial symmetry and by constructing dynamical models supported by two-integral stellar DFs. For all systems, the total mass density distribution is found to be well approximated by a simple power-law: this profile is on average slightly super-isothermal, with a logarithmic slope <gamma'> = 2.074^{+0.043}_{-0.041} (68% CL) and an intrinsic scatter 0.144^{+0.055}_{-0.014}, and is fairly round, with an average axial ratio <q> = 0.77+/-0.04. The lower limit for the dark matter fraction (fDM) inside r_e ranges, in individual systems, from nearly zero to almost a half, with a median value of 12%. By including stellar masses derived from SPS models with a Salpeter IMF, we obtain an average fDM = 31%. The fDM rises to 61% if, instead, a Chabrier IMF is assumed. For both IMFs, the dark matter fraction increases with the total mass of the galaxy (3-sigma correlation). Based on the intrinsic angular momentum parameter calculated from our models, we find that the galaxies can be divided into two dynamically distinct groups, which are shown to correspond to the usual classes of the slow and fast rotators. Overall, the SLACS systems are structurally and dynamically very similar to their nearby counterparts, indicating that the inner regions of early-type galaxies have undergone little, if any, evolution since redshift z ~ 0.35. (Abridged)

Self‐similar Models for the Mass Profiles of Early‐Type Lens Galaxies

We introduce a self-similar mass model for early-type galaxies and constrain it using the aperture mass-radius relations determined from the geometries of 22 gravitational lenses. The model consists of two components: a concentrated component, which traces the light distribution, and a more extended power-law component (ρ ∝ r-n), which represents the dark matter. We find that lens galaxies have total mass profiles that are nearly isothermal, or slightly steeper, on the several-kiloparsec radial scale spanned by the lensed images. In the limit of a single-component, power-law radial profile, the model implies n = 2.07 ± 0.13, consistent with isothermal (n = 2). Models in which mass traces light are excluded at higher than 99% confidence. An n = 1 cusp (such as the Navarro-Frenk-White profile) requires a projected dark matter mass fraction of fcdm = 0.22 ± 0.10 inside two effective radii. These are the best statistical constraints yet obtained on the mass profiles of lenses and provide clear evidence for a small but nonzero dark matter mass fraction in the inner regions of early-type galaxies. In addition, we derive the first strong-lensing constraint on the relation between the stellar mass-to-light ratio ϒ and galaxy luminosity L, ϒ ∝ L, which is consistent with the relation suggested by the fundamental plane. Finally, we apply our self-similar mass models to current problems regarding the interpretation of time delays and flux ratio anomalies in gravitational lens systems.

Cool Dense Gas in Early-Type Galaxies

CO observations have shown that many lenticular and elliptical galaxies contain significant amounts of cool dense gas. This review summarizes the observational results related to the neutral gas phase and presents a systematic comparison with other interstellar and stellar data. The discovery of very dense molecular gas in the nuclear regions of early-type galaxies, the possible existence of a dust component neither seen optically nor in CO, internal inconsistencies of cooling flow scenarios, the origin of the cool gas, the presence of massive stars, aspects of galaxy evolution, and possibilities for future research are discussed in the light of the new data.

Ring formation in triaxial potentials

The formation of rings of gas in the outer regions of early-type galaxies is considered. It has previously been shown that the stable orbital planes lie perpendicular to the major and minor axes. Discs initially inclined in other directions will precess about one of the symmetry axes. The precession rate varies with radius and will thus cause the disc to warp. This induces a local viscosity which acts so as to oppose relative motion and causes the disc to settle into one of the preferred planes. The simulations show a qualitatively different behavior : viscosity is insufficient to prevent break-up of the disc and so gas clouds move to fill the available tube orbit. After a few precession times particles have differentially precessed through 180° at a given radius and collisions occur in the symmetry plane of the tube orbit forming a ring in situ.

Neutral hydrogen streams in groups of galaxies. I - Observations

view Abstract Citations (98) References (35) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Neutral hydrogen streams in groups of galaxies. I. Observations. Haynes, M. P. Abstract Groups of nearby, loose galaxies are the object of a search for H I streams, the neutral hydrogen appendages extending outward from the disks of member galaxies. Galaxy parameter tables are presented which summarize observational data gathered with the Arecibo telescope on 15 nearby groups, containing at least one pair of galaxies separated by less than 250 kpc. Of the 15 groups, nine show no evidence of neutral hydrogen appendages, while in the remaining six H I streams associated with at least one member of the aggregate are identified. While previously recognized H I streams have been almost exclusively associated with late-type spiral galaxies, several of those newly identified extend in the regions of early-type galaxies. The 15 nearby groups considered are comprised of 47 galaxies observed in the course of the H I stream search. Publication: The Astronomical Journal Pub Date: August 1981 DOI: 10.1086/112993 Bibcode: 1981AJ.....86.1126H Keywords: Galactic Clusters; Hydrogen Clouds; Intergalactic Media; Neutral Gases; Astronomical Catalogs; Astronomical Maps; Galactic Structure; Gas Density; Spiral Galaxies; Astronomy full text sources ADS | data products SIMBAD (15) NED (9)