112 research outputs found
Bars in early- and late-type disks in COSMOS
We investigate the (large-scale) bar fraction in a mass-complete sample of M
> 10^10.5 Msun disk galaxies at 0.2 < z < 0.6 in the COSMOS field. The fraction
of barred disks strongly depends on mass, disk morphology, and specific star
formation rate (SSFR). At intermediate stellar mass (10^10.5 < M < 10^11 Msun)
the bar fraction in early-type disks is much higher, at all redshifts, by a
factor ~2, than that in late-type disks. This trend is reversed at higher
stellar mass (M > 10^11 Msun), where the fraction of bars in early-type disks
becomes significantly lower, at all redshifts, than that in late-type disks.
The bar fractions for galaxies with low and high SSFRs closely follow those of
the morphologically-selected early-type and late-type populations,
respectively. This indicates a close correspondence between morphology and SSFR
in disk galaxies at these earlier epochs. Interestingly, the total bar fraction
in 10^10.5 < M < 10^11 Msun disks is built up by a factor of ~2 over the
redshift interval explored, while for M > 10^11 Msun disks it remains roughly
constant. This indicates that, already by z ~ 0.6, spectral and morphological
transformations in the most massive disk galaxies have largely converged to the
familiar Hubble sequence that we observe in the local Universe, while for
intermediate mass disks this convergence is ongoing until at least z ~ 0.2.
Moreover, these results highlight the importance of employing mass-limited
samples for quantifying the evolution of barred galaxies. Finally, the
evolution of the barred galaxy populations investigated does not depend on the
large-scale environmental density (at least, on the scales which can be probed
with the available photometric redshifts).Comment: 10 pages, 4 figures, updated to reflect version accepted by MNRA
Accretion in the Early Kuiper Belt I. Coagulation and Velocity Evolution
We describe planetesimal accretion calculations in the Kuiper Belt.
Our evolution code simulates planetesimal growth in a single annulus and
includes velocity evolution but not fragmentation. Test results match analytic
solutions and duplicate previous simulations at 1 AU.
In the Kuiper Belt, simulations without velocity evolution produce a single
runaway body with a radius of 1000 km on a time scale inversely proportional to
the initial mass in the annulus. Runaway growth occurs in 100 Myr for 10 earth
masses and an initial eccentricity of 0.001 in a 6 AU annulus centered at 35
AU. This mass is close to the amount of dusty material expected in a minimum
mass solar nebula extrapolated into the Kuiper Belt.
Simulations with velocity evolution produce runaway growth on a wide range of
time scales. Dynamical friction and viscous stirring increase particle
velocities in models with large (8 km radius) initial bodies. This velocity
increase delays runaway growth by a factor of two compared to models without
velocity evolution. In contrast, collisional damping dominates over dynamical
friction and viscous stirring in models with small (80--800 m radius) initial
bodies. Collisional damping decreases the time scale to runaway growth by
factors of 4--10 relative to constant velocity calculations. Simulations with
minimum mass solar nebulae, 10 earth masses, reach runaway growth on time
scales of 20-40 Myr with 80 m initial bodies, 50-100 Myr with 800 m bodies, and
75-250 Myr for 8 km initial bodies. These growth times vary linearly with the
mass of the annulus but are less sensitive to the initial eccentricity than
constant velocity models.Comment: 45 pages of text (including 5 tables), 31 pages of figur
Bulge growth through disk instabilities in high-redshift galaxies
The role of disk instabilities, such as bars and spiral arms, and the
associated resonances, in growing bulges in the inner regions of disk galaxies
have long been studied in the low-redshift nearby Universe. There it has long
been probed observationally, in particular through peanut-shaped bulges. This
secular growth of bulges in modern disk galaxies is driven by weak,
non-axisymmetric instabilities: it mostly produces pseudo-bulges at slow rates
and with long star-formation timescales. Disk instabilities at high redshift
(z>1) in moderate-mass to massive galaxies (10^10 to a few 10^11 Msun of stars)
are very different from those found in modern spiral galaxies. High-redshift
disks are globally unstable and fragment into giant clumps containing 10^8-10^9
Msun of gas and stars each, which results in highly irregular galaxy
morphologies. The clumps and other features associated to the violent
instability drive disk evolution and bulge growth through various mechanisms,
on short timescales. The giant clumps can migrate inward and coalesce into the
bulge in a few 10^8 yr. The instability in the very turbulent media drives
intense gas inflows toward the bulge and nuclear region. Thick disks and
supermassive black holes can grow concurrently as a result of the violent
instability. This chapter reviews the properties of high-redshift disk
instabilities, the evolution of giant clumps and other features associated to
the instability, and the resulting growth of bulges and associated sub-galactic
components.Comment: 37 pages, 9 figures. Invited refereed review to appear in "Galactic
Bulges", E. Laurikainen, D. Gadotti, R. Peletier (eds.), Springe
The Morphology of Galaxies in the Baryon Oscillation Spectroscopic Survey
We study the morphology of luminous and massive galaxies at 0.3<z<0.7
targeted in the Baryon Oscillation Spectroscopic Survey (BOSS) using publicly
available Hubble Space Telescope imaging from COSMOS. Our sample (240 objects)
provides a unique opportunity to check the visual morphology of these galaxies
which were targeted based solely on stellar population modelling. We find that
the majority (74+/-6%) possess an early-type morphology (elliptical or S0),
while the remainder have a late-type morphology. This is as expected from the
goals of the BOSS target selection which aimed to predominantly select slowly
evolving galaxies, for use as cosmological probes, while still obtaining a fair
fraction of actively star forming galaxies for galaxy evolution studies. We
show that a colour cut of (g-i)>2.35 selects a sub-sample of BOSS galaxies with
90% early-type morphology - more comparable to the earlier Luminous Red Galaxy
(LRG) samples of SDSS-I/II. The remaining 10% of galaxies above this cut have a
late-type morphology and may be analogous to the "passive spirals" found at
lower redshift. We find that 23+/-4% of the early-type galaxies are unresolved
multiple systems in the SDSS imaging. We estimate that at least 50% of these
are real associations (not projection effects) and may represent a significant
"dry merger" fraction. We study the SDSS pipeline sizes of BOSS galaxies which
we find to be systematically larger (by 40%) than those measured from HST
images, and provide a statistical correction for the difference. These details
of the BOSS galaxies will help users of the data fine-tune their selection
criteria, dependent on their science applications. For example, the main goal
of BOSS is to measure the cosmic distance scale and expansion rate of the
Universe to percent-level precision - a point where systematic effects due to
the details of target selection may become important.Comment: 18 pages, 11 figures; v2 as accepted by MNRA
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb Space Telescope (JWST), as determined from the six month commissioning period. We summarize the performance of the spacecraft, telescope, science instruments, and ground system, with an emphasis on differences from pre-launch expectations. Commissioning has made clear that JWST is fully capable of achieving the discoveries for which it was built. Moreover, almost across the board, the science performance of JWST is better than expected; in most cases, JWST will go deeper faster than expected. The telescope and instrument suite have demonstrated the sensitivity, stability, image quality, and spectral range that are necessary to transform our understanding of the cosmos through observations spanning from near-earth asteroids to the most distant galaxies
Galaxy bulges and their massive black holes: a review
With references to both key and oft-forgotten pioneering works, this article
starts by presenting a review into how we came to believe in the existence of
massive black holes at the centres of galaxies. It then presents the historical
development of the near-linear (black hole)-(host spheroid) mass relation,
before explaining why this has recently been dramatically revised. Past
disagreement over the slope of the (black hole)-(velocity dispersion) relation
is also explained, and the discovery of sub-structure within the (black
hole)-(velocity dispersion) diagram is discussed. As the search for the
fundamental connection between massive black holes and their host galaxies
continues, the competing array of additional black hole mass scaling relations
for samples of predominantly inactive galaxies are presented.Comment: Invited (15 Feb. 2014) review article (submitted 16 Nov. 2014). 590
references, 9 figures, 25 pages in emulateApJ format. To appear in "Galactic
Bulges", E. Laurikainen, R.F. Peletier, and D.A. Gadotti (eds.), Springer
Publishin
The Science Performance of JWST as Characterized in Commissioning
This paper characterizes the actual science performance of the James Webb
Space Telescope (JWST), as determined from the six month commissioning period.
We summarize the performance of the spacecraft, telescope, science instruments,
and ground system, with an emphasis on differences from pre-launch
expectations. Commissioning has made clear that JWST is fully capable of
achieving the discoveries for which it was built. Moreover, almost across the
board, the science performance of JWST is better than expected; in most cases,
JWST will go deeper faster than expected. The telescope and instrument suite
have demonstrated the sensitivity, stability, image quality, and spectral range
that are necessary to transform our understanding of the cosmos through
observations spanning from near-earth asteroids to the most distant galaxies.Comment: 5th version as accepted to PASP; 31 pages, 18 figures;
https://iopscience.iop.org/article/10.1088/1538-3873/acb29
The Intrinsic Characteristics of Galaxies on the SFR– M
We use the deep CANDELS observations in the GOODS North and South fields to revisit the correlations between stellar mass (M-*), star formation rate (SFR) and morphology, and to introduce a fourth dimension, the mass-weighted stellar age, in galaxies at 1.2 < z < 4. We do this by making new measures of M-*, SFR, and stellar age thanks to an improved SED fitting procedure that allows various star formation history for each galaxy. Like others, we find that the slope of the main sequence (MS) of star formation in the (M-*; SFR) plane bends at high mass. We observe clear morphological differences among galaxies across the MS, which also correlate with stellar age. At all redshifts, galaxies that are quenching or quenched, and thus old, have high Sigma(1) (the projected density within the central 1 kpc), while younger, star-forming galaxies span a much broader range of Sigma(1), which includes the high values observed for quenched galaxies, but also extends to much lower values. As galaxies age and quench, the stellar age and the dispersion of Sigma(1) for fixed values of M* shows two different regimes: one at the low-mass end, where quenching might be driven by causes external to the galaxies; the other at the high-mass end, where quenching is driven by internal causes, very likely the mass given the low scatter of Sigma(1) (mass quenching). We suggest that the monotonic increase of central density as galaxies grow is one manifestation of a more general phenomenon of structural transformation that galaxies undergo as they evolve.NASA [NAS5-26555]; NASA through Hubble Fellowship grant - Space Telescope Science Institute [HF2-51368]; Downsbrough familyThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]
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