442 research outputs found
Dark and Baryonic Matter in Bright Spiral Galaxies: I.Near-infrared and Optical Broadband Surface Photometry of 30 Galaxies
We present photometrically calibrated images and surface photometry in the B,
V, R, J, H, and K-bands of 25, and in the g, r, and K-bands of 5 nearby bright
(Bo_T<12.5 mag) spiral galaxies with inclinations between 30-65 degrees
spanning the Hubble Sequence from Sa to Scd. Data are from The Ohio State
University Bright Spiral Galaxy Survey, the Two Micron All Sky Survey, and the
Sloan Digital Sky Survey Second Data Release. Radial surface brightness
profiles are extracted, and integrated magnitudes are measured from the
profiles. Axis ratios, position angles, and scale lengths are measured from the
near-infrared images. A 1-dimensional bulge/disk decomposition is performed on
the near-infrared images of galaxies with a non-negligible bulge component, and
an exponential disk is fit to the radial surface brightness profiles of the
remaining galaxies.Comment: 28 page
On the Evolution of the Velocity-Mass-Size Relations of Disk-Dominated Galaxies over the Past 10 Billion Years
We study the evolution of the scaling relations between maximum circular
velocity, stellar mass and optical half-light radius of star-forming
disk-dominated galaxies in the context of LCDM-based galaxy formation models.
Using data from the literature combined with new data from the DEEP2 and AEGIS
surveys we show that there is a consistent observational and theoretical
picture for the evolution of these scaling relations from z\sim 2 to z=0. The
evolution of the observed stellar scaling relations is weaker than that of the
virial scaling relations of dark matter haloes, which can be reproduced, both
qualitatively and quantitatively, with a simple, cosmologically-motivated model
for disk evolution inside growing NFW dark matter haloes. In this model optical
half-light radii are smaller, both at fixed stellar mass and maximum circular
velocity, at higher redshifts. This model also predicts that the scaling
relations between baryonic quantities evolve even more weakly than the
corresponding stellar relations. We emphasize, though, that this weak evolution
does not imply that individual galaxies evolve weakly. On the contrary,
individual galaxies grow strongly in mass, size and velocity, but in such a way
that they move largely along the scaling relations. Finally, recent
observations have claimed surprisingly large sizes for a number of star-forming
disk galaxies at z \sim 2, which has caused some authors to suggest that high
redshift disk galaxies have abnormally high spin parameters. However, we argue
that the disk scale lengths in question have been systematically overestimated
by a factor \sim 2, and that there is an offset of a factor \sim 1.4 between
H\alpha sizes and optical sizes. Taking these effects into account, there is no
indication that star forming galaxies at high redshifts (z\sim 2) have
abnormally high spin parameters.Comment: 19 pages, 10 figures, accepted to MNRAS, minor changes to previous
versio
Disruption of Star Clusters in the Interacting Antennae Galaxies
We reexamine the age distribution of star clusters in the Antennae in the
context of N-body+hydrodynamical simulations of these interacting galaxies. All
of the simulations that account for the observed morphology and other
properties of the Antennae have star formation rates that vary relatively
slowly with time, by factors of only 1.3 - 2.5 in the past 10^8 yr. In
contrast, the observed age distribution of the clusters declines approximately
as a power law, dN/dt \propto t^{gamma} with gamma = -1.0, for ages 10^6 yr \la
t \la 10^9 yr. These two facts can only be reconciled if the clusters are
disrupted progressively for at least 10^8 yr and possibly 10^9 yr. When we
combine the simulated formation rates with a power-law model, f_surv \propto
t^{delta}, for the fraction of clusters that survive to each age t, we match
the observed age distribution with exponents in the range -0.9 \la delta \la
-0.6 (with a slightly different delta for each simulation). The similarity
between delta and gamma indicates that dN/dt is shaped mainly by the disruption
of clusters rather than variations in their formation rate. Thus, the situation
in the interacting Antennae resembles that in relatively quiescent galaxies
such as the Milky Way and the Magellanic Clouds.Comment: 9 pages, 5 figures, 1 table, accepted for publication in the
Astrophysical Journal, including revisions after referee repor
Do low surface brightness galaxies have dense disks?
The disk masses of four low surface brightness galaxies (LSB) were estimated
using marginal gravitational stability criterion and the stellar velocity
dispersion data which were taken from Pizzella et al., 2008 [1]. The
constructed mass models appear to be close to the models of maximal disk. The
results show that the disks of LSB galaxies may be significantly more massive
than it is usually accepted from their brightnesses. In this case their surface
densities and masses appear to be rather typical for normal spirals. Otherwise,
unlike the disks of many spiral galaxies, the LSB disks are dynamically
overheated.Comment: 14 pages, 10 figures, submitted to Astronomy Report
Geometry of Star-Forming Galaxies from SDSS, 3D-HST and CANDELS
We determine the intrinsic, 3-dimensional shape distribution of star-forming
galaxies at 0<z<2.5, as inferred from their observed projected axis ratios. In
the present-day universe star-forming galaxies of all masses 1e9 - 1e11 Msol
are predominantly thin, nearly oblate disks, in line with previous studies. We
now extend this to higher redshifts, and find that among massive galaxies (M* >
1e10 Msol) disks are the most common geometric shape at all z < 2. Lower-mass
galaxies at z>1 possess a broad range of geometric shapes: the fraction of
elongated (prolate) galaxies increases toward higher redshifts and lower
masses. Galaxies with stellar mass 1e9 Msol (1e10 Msol) are a mix of roughly
equal numbers of elongated and disk galaxies at z~1 (z~2). This suggests that
galaxies in this mass range do not yet have disks that are sustained over many
orbital periods, implying that galaxies with present-day stellar mass
comparable to that of the Milky Way typically first formed such sustained
stellar disks at redshift z~1.5-2. Combined with constraints on the evolution
of the star formation rate density and the distribution of star formation over
galaxies with different masses, our findings imply that, averaged over cosmic
time, the majority of stars formed in disks.Comment: Published in ApJ Letter
Keck-I MOSFIRE spectroscopy of compact star-forming galaxies at z2: High velocity dispersions in progenitors of compact quiescent galaxies
We present Keck-I MOSFIRE near-infrared spectroscopy for a sample of 13
compact star-forming galaxies (SFGs) at redshift with star
formation rates of SFR100M y and masses of
log(M/M). Their high integrated gas velocity dispersions of
=230 km s, as measured from emission
lines of H and [OIII], and the resultant
M relation and MM all
match well to those of compact quiescent galaxies at , as measured from
stellar absorption lines. Since log(M/M)
dex, these compact SFGs appear to be dynamically relaxed and more evolved,
i.e., more depleted in gas and dark matter (13\%) than their
non-compact SFG counterparts at the same epoch. Without infusion of external
gas, depletion timescales are short, less than 300 Myr. This discovery
adds another link to our new dynamical chain of evidence that compact SFGs at
are already losing gas to become the immediate progenitors of
compact quiescent galaxies by .Comment: 12 pages, 7 figures, submitted to Ap
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