93 research outputs found
The Tully-Fisher Zero Point Problem
A long standing problem for hierarchical disk galaxy formation models has
been the simultaneous matching of the zero point of the Tully-Fisher relation
and the galaxy luminosity function (LF). We illustrate this problem for a
typical disk galaxy and discuss three solutions: low stellar mass-to-light
ratios, low initial dark halo concentrations, and no halo contraction. We
speculate that halo contraction may be reversed through a combination of mass
ejection through feedback and angular momentum exchange brought about by
dynamical friction between baryons and dark matter during the disk formation
process.Comment: 4 pages, 1 figure, to appear in proceedings of "Formation and
Evolution of Galaxy Disks", Rome, October 2007, Eds. J.G. Funes, S.J. and
E.M. Corsin
The Bulge-Halo Connection in Galaxies: A Physical Interpretation of the Vcirc-sigma_0 Relation
We explore the dependence of the ratio of a galaxy's circular velocity,
Vcirc, to its central velocity dispersion, sigma_0, on morphology, or
equivalently total light concentration. Such a dependence is expected if light
traces the mass. Over the full range of galaxy types, masses and brightnesses,
and assuming that the gas velocity traces the circular velocity, we find that
galaxies obey the relation log(Vcirc/sigma_0)= 0.63-0.11*C28 where
C28=5log(r80/r20) and the radii are measured at 80 percent and 20 percent of
the total light. Massive galaxies scatter about the Vcirc = sqrt(2)*sigma_0
line for isothermal stellar systems. Disk galaxies follow the simple relation
Vcirc/sigma_0=2(1-B/T), where B/T is the bulge-to-total light ratio. For pure
disks, C28~2.8, B/T -> 0, and Vcirc~=2*sigma_0. Self-consistent equilibrium
galaxy models from Widrow & Dubinski (2005) constrained to match the
size-luminosity and velocity-luminosity relations of disk galaxies fail to
match the observed Vcirc/sigma_0 distribution. Furthermore, the matching of
dynamical models for Vcirc(r)/sigma(r) with observations of dwarf and
elliptical galaxies suffers from limited radial coverage and relatively large
error bars; for dwarf systems, however, kinematical measurements at the galaxy
center and optical edge suggest Vcirc(Rmax) > 2*sigma_0 (in contrast with past
assumptions that Vcirc = sqrt(2)*sigma_0 for dwarfs.) The Vcirc-sigma_0-C28
relation has direct implications for galaxy formation and dynamical models,
galaxy scaling relations, the mass function of galaxies, and the links between
respective formation and evolution processes for a galaxy's central massive
object, bulge, and dark matter halo.Comment: Accepted for publication in ApJL. Current version matches ApJL page
requiremen
MaNGA galaxy properties -- II. A detailed comparison of observed and simulated spiral galaxy scaling relations
We present a catalogue of dynamical properties for 2368 late-type galaxies
from the MaNGA survey. The latter complements the catalogue of photometric
properties for the same sample based on deep optical DESI photometry processed
with AutoProf. Rotation curves (RCs), extracted by model fitting H
velocity maps from the MaNGA Data Analysis Pipeline, extend out to 1.4 (1.9)
R for the primary (secondary) MaNGA samples. The RCs and ancillary MaNGA
Pipe3D data products were used to construct various fundamental galaxy scaling
relations that are also compared uniformly with similar relations from NIHAO
zoom-in simulations. Simulated NIHAO galaxies were found to broadly reproduce
the observed MaNGA galaxy population for .
Some discrepancies remain, such as those pertaining to central stellar
densities and the diversity of RCs due to strong feedback schemes. Also
presented are spatially-resolved scatters for the velocity-size-stellar mass
(VRM) structural relations using MaNGA and NIHAO samples. The scatter for
these relations in the galaxian interiors is a consequence of the diversity of
inner RC shapes, while scatter in the outskirts is dictated by the large range
of stellar surface densities which itself is driven by sporadic star formation.
The detailed spatially-resolved scatter analysis highlights the complex
interplay between local and global astrophysical processes and provides a
strong constraint to numerical simulations.Comment: 21 pages, 13 Figures, Accepted for publication in MNRA
Bulge-Disk Decompositions and Structural Bimodality of Ursa Major Cluster Spiral Galaxies
We present bulge and disk (B/D) decompositions of existing K'-band surface
brightness profiles for 65 Ursa Major cluster spiral galaxies. This improves
upon the disk-only fits of Tully et al. (1996). The 1996 disk fits were used by
Tully & Verheijen (1997) for their discovery of the bimodality of structural
parameters in the UMa cluster galaxies. It is shown that our new 1D B/D
decompositions yield disk structural parameters that differ only slightly from
the basic fits of Tully et al. and evidence for structural bimodality of UMa
galaxies is maintained. Our B/D software for the decomposition of 1D surface
brightness profiles of galaxies uses a non-linear minimization scheme to
recover the best fitting Sersic bulge and exponential disk while accounting for
the possible presence of a compact nucleus and spiral arms and for the effects
of seeing and disk truncations. In agreement with Tully & Verheijen, we find
that the distribution of near-infrared disk central surface brightnesses is
bimodal with an F-test confidence of 80%. There is also strong evidence for a
local minimum in the luminosity function at M_K' ~ -22. A connection between
the brightness bimodality and a dynamical bimodality, based on new HI line
widths, is identified. The B/D parameters are presented in an Appendix.Comment: Accepted for publication in MNRA
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