853 research outputs found
Digging for Formational Clues in the Halos of Early-type Galaxies
Many of the fundamental properties of early-type galaxies (ellipticals and
lenticulars) can only be accessed by venturing beyond their oft-studied centers
into their large-radius halo regions. Advances in observations of kinematical
tracers allow early-type halos to be increasingly well probed. This review
focuses on recent findings on angular momentum and dark matter content, and
discusses some possible implications for galaxy structure and formation.Comment: 4 pages, 2 figures, to appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista &
C.C. Popescu, AIP Conf. Ser., in pres
Structural and dynamical uncertainties in modeling axisymmetric elliptical galaxies
Quantitative dynamical models of galaxies require deprojecting the observed
surface brightness to determine the luminosity density of the galaxy. Existing
deprojection methods for axisymmetric galaxies assume that a unique
deprojection exists for any given inclination, even though the projected
density is known to be degenerate to the addition of "konus densities" that are
invisible in projection. We develop a deprojection method based on linear
regularization that can explore the range of luminosity densities statistically
consistent with an observed surface brightness distribution. The luminosity
density is poorly constrained at modest inclinations (i > ~30 deg), even in the
limit of vanishing observational errors. In constant mass-to-light ratio,
axisymmetric, two-integral dynamical models, the uncertainties in the
luminosity density result in large uncertainties in the meridional plane
velocities. However, the projected line-of-sight velocities show variations
comparable to current typical observational uncertainties.Comment: 20 pages, 8 Postscript figures, LaTeX, aaspp4.sty, submitted to
MNRAS; paper w/figs (600 kb) also available at
http://cfa-www.harvard.edu/~romanow/ell.mn.ps.gz GIF-format figures replaced
by PostScrip
Dynamics of Stars and Globular Clusters in M87
We examine the dynamics of the stars and globular clusters in the nearby
giant galaxy M87 and constrain the mass distribution, using all the available
data over a large range of radii, including higher-order moments of the stellar
line-of-sight velocity distributions and the discrete velocities of over two
hundred globular clusters. We introduce an extension of spherical orbit
modeling methods that makes full use of all the information in the data, and
provides very robust constraints on the mass models. We conclusively rule out a
constant mass-to-light ratio model, and infer that the radial density profile
of the galaxy's dark halo falls off more slowly than 1/r^2, suggesting that the
potential of the Virgo Cluster is already dominant at r ~ 300" ~ 20 kpc.Comment: Revised version accepted by ApJ: expanded Results with new mass
models; 26 pages, with 12 inline Postscript figures, LaTeX, aaspp4.st
Optical and near-infrared velocity dispersions of early-type galaxies
We have carried out a systematic, homogeneous comparison of optical and
near-infrared dispersions. Our magnitude-limited sample of early-type galaxies
in the Fornax cluster comprises 11 elliptical and 11 lenticular galaxies more
luminous than MB = -17. We were able to determine the central dispersions based
on the near-infrared CO absorption band head for 19 of those galaxies. The
velocity dispersions range from less than 70 km/s to over 400 km/s. We compare
our near-infrared velocity dispersions to the optical dispersions measured by
Kuntschner (2000). Contrary to previous studies, we find a one-to-one
correspondence with a median fractional difference of 6.4%. We examine the
correlation between the relative dust mass and the fractional difference of the
velocity dispersions, but find no significant trend. Our results suggest that
early-type galaxies are largely optically thin, which is consistent with recent
Herschel observations.Comment: 10 pages, 9 figures, accepted for publication in MNRA
Central dark matter content of early-type galaxies: scaling relations and connections with star formation histories
We examine correlations between masses, sizes and star formation histories for a large sample of low-redshift early-type galaxies, using a simple suite of dynamical and stellar population models. We confirm an anticorrelation between the size and stellar age and go on to survey for trends with the central content of dark matter (DM). An average relation between the central DM density and galaxy size of ăÏDMăâRâ2eff provides the first clear indication of cuspy DM haloes in these galaxies â akin to standard Î cold dark matter haloes that have undergone adiabatic contraction. The DM density scales with galaxy mass as expected, deviating from suggestions of a universal halo profile for dwarf and late-type galaxies. We introduce a new fundamental constraint on galaxy formation by finding that the central DM fraction decreases with stellar age. This result is only partially explained by the sizeâage dependencies, and the residual trend is in the opposite direction to basic DM halo expectations. Therefore, we suggest that there may be a connection between age and halo contraction and that galaxies forming earlier had stronger baryonic feedback, which expanded their haloes, or lumpier baryonic accretion, which avoided halo contraction. An alternative explanation is a lighter initial mass function for older stellar populations
Galaxies in LCDM with Halo Abundance Matching: luminosity-velocity relation, baryonic mass-velocity relation, velocity function and clustering
It has long been regarded as difficult for a cosmological model to account
simultaneously for the galaxy luminosity, mass, and velocity distributions. We
revisit this issue using a modern compilation of observational data along with
the best available large-scale cosmological simulation of dark matter. We find
that the standard cosmological model, used in conjunction with halo abundance
matching (HAM) and simple dynamical corrections, fits all basic statistics of
galaxies with circular velocities Vcirc > 80 km/s. Our observational constraint
is the luminosity-velocity relation which allows all types of galaxies to be
included. We have compiled data for a variety of galaxies ranging from dwarf
irregulars to giant ellipticals. The data present a clear monotonic
luminosity-velocity relation from 50 km/s to 500 km/s, with a bend below 80
km/s and a systematic offset between late- and early-type galaxies. For
comparison to theory, we employ our LCDM "Bolshoi" simulation of dark matter,
which has unprecedented mass and force resolution. We use halo abundance
matching to assign rank-ordered galaxy luminosities to the dark matter halos.
The resulting predictions for the luminosity-velocity relation are in excellent
agreement with the available data on both early-type and late-type galaxies for
the luminosity range from Mr = -14-22. We also compare our predictions for the
"cold" baryon mass (i.e., stars and cold gas) of galaxies as a function of
circular velocity with the available observations, again finding a very good
agreement. The predicted circular velocity function is in agreement with the
galaxy velocity function for 80-400 km/s. However, we find that the dark matter
halos with Vcirc < 80 km/s are much more abundant than observed galaxies with
the same Vcirc . We find that the two-point correlation function of galaxies in
our model matches very well the results from the SDSS.Comment: 40 pages, 18 figures, published in Ap
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