1,414 research outputs found
Urban structure and commuting in Australian cities
Studies looking at the relationship between urban form and travel behaviour have generally considered spatial information at coarse metropolitan or local government area scales. We analyse ABS census data at the Collection District level for the metropolitan areas of the mainland Australian state capital cities, and at various spatial scales for an in-depth analysis of commuting in Sydney. The analyses suggest that the relationship between travel behaviour and urban form is complex, and that simple analyses of density alone are likely to overstate the effect of both metropolitan and neighbourhood scale population density on mode choice, but that these variables serve as useful proxies for more complex measures of urban structure
Urban Structure and Energy -- A Review
The nature and form of the urban environment is a critical determinant of the sustainability of our society, as it is responsible directly for a large proportion of consumed energy, and influences indirectly the patterns and modes of energy consumed in everyday activities. We examine the current state of research into the energy and greenhouse gas emissions attributable directly or indirectly to urban form. Specifically, we look at the embodied (construction) and operational energy attributable to the construction, maintenance and use of residential dwellings, and we review the literature on the relationship between urban structure and private travel behaviour. While there is clear evidence from both intra- and inter-city comparisons that higher density, transit-oriented cities have lower per-capita transport energy use, the effect of housing density on residential (in-house) energy use is less clear. More detailed research is needed to examine the relationships between urban form and overall energy use
The Redshift One LDSS-3 Emission line Survey (ROLES) II: Survey method and z~1 mass-dependent star-formation rate density
Motivated by suggestions of 'cosmic downsizing', in which the dominant
contribution to the cosmic star formation rate density (SFRD) proceeds from
higher to lower mass galaxies with increasing cosmic time, we describe the
design and implementation of the Redshift One LDSS3 Emission line Survey
(ROLES). ROLES is a K-selected (22.5 < K_AB < 24.0) survey for dwarf galaxies
[8.5<log(M*/Msun)< 9.5] at 0.89 < z < 1.15 drawn from two extremely deep fields
(GOODS-S and MS1054-FIRES). Using the [OII]3727 emission line, we obtain
redshifts and star-formation rates (SFRs) for star-forming galaxies down to a
limit of ~0.3 Msun/yr. We present the [OII] luminosity function measured in
ROLES and find a faint end slope of alpha_faint ~ -1.5, similar to that
measured at z~0.1 in the SDSS. By combining ROLES with higher mass surveys, we
measure the SFRD as a function of stellar mass using [OII] (with and without
various empirical corrections), and using SED-fitting to obtain the SFR from
the rest-frame UV luminosity for galaxies with spectroscopic redshifts. Our
best estimate of the corrected [OII]-SFRD and UV SFRD both independently show
that the SFRD evolves equally for galaxies of all masses between z~1 and z~0.1.
The exact evolution in normalisation depends on the indicator used, with the
[OII]-based estimate showing a change of a factor of ~2.6 and the UV-based a
factor of ~6. We discuss possible reasons for the discrepancy in normalisation
between the indicators, but note that the magnitude of this uncertainty is
comparable to the discrepancy between indicators seen in other z~1 works. Our
result that the shape of the SFRD as a function of stellar mass (and hence the
mass range of galaxies dominating the SFRD) does not evolve between z~1 and
z~0.1 is robust to the choice of indicator. [abridged]Comment: Resubmitted to MNRAS following first referee report. 20 pages, 16
figures. High resolution version available at
http://astro.uwaterloo.ca/~dgilbank/papers/roles2.pd
The Mass Assembly Histories of Galaxies of Various Morphologies in the GOODS Fields
We present an analysis of the growth of stellar mass with cosmic time
partitioned according to galaxy morphology. Using a well-defined catalog of
2150 galaxies based, in part, on archival data in the GOODS fields, we assign
morphological types in three broad classes (Ellipticals, Spirals,
Peculiar/Irregulars) to a limit of z_AB=22.5 and make the resulting catalog
publicly available. We combine redshift information, optical photometry from
the GOODS catalog and deep K-band imaging to assign stellar masses. We find
little evolution in the form of the galaxy stellar mass function from z~1 to
z=0, especially at the high mass end where our results are most robust.
Although the population of massive galaxies is relatively well established at
z~1, its morphological mix continues to change, with an increasing proportion
of early-type galaxies at later times. By constructing type-dependent stellar
mass functions, we show that in each of three redshift intervals, E/S0's
dominate the higher mass population, while spirals are favored at lower masses.
This transition occurs at a stellar mass of 2--3 times 10^{10} Msun at z~0.3
(similar to local studies) but there is evidence that the relevant mass scale
moves to higher mass at earlier epochs. Such evolution may represent the
morphological extension of the ``downsizing'' phenomenon, in which the most
massive galaxies stop forming stars first, with lower mass galaxies becoming
quiescent later. We infer that more massive galaxies evolve into spheroidal
systems at earlier times, and that this morphological transformation may only
be completed 1--2 Gyr after the galaxies emerge from their active star forming
phase. We discuss several lines of evidence suggesting that merging may play a
key role in generating this pattern of evolution.Comment: 24 pages, 1 table, 8 figures, accepted for publication in Ap
Galaxy Morphology from NICMOS Parallel Imaging
We present high resolution NICMOS images of random fields obtained in
parallel to other HST observations. We present galaxy number counts reaching
H=24. The H-band galaxy counts show good agreement with the deepest I- and
K-band counts obtained from ground-based data. We present the distribution of
galaxies with morphological type to H<23. We find relatively fewer irregular
galaxies compared to an I-band sample from the Hubble Deep Field, which we
attribute to their blue color, rather than to morphological K-corrections. We
conclude that the irregulars are intrinsically faint blue galaxies at z<1.Comment: 13 pages, including 4 figures. Accepted for publication in ApJ
Letter
The Near-Infrared Number Counts and Luminosity Functions of Local Galaxies
This study presents a wide-field near-infrared (K-band) survey in two fields;
SA 68 and Lynx 2. The survey covers an area of 0.6 deg., complete to
K=16.5. A total of 867 galaxies are detected in this survey of which 175 have
available redshifts. The near-infrared number counts to K=16.5 mag. are
estimated from the complete photometric survey and are found to be in close
agreement with other available studies. The sample is corrected for
incompleteness in redshift space, using selection function in the form of a
Fermi-Dirac distribution. This is then used to estimate the local near-infrared
luminosity function of galaxies. A Schechter fit to the infrared data gives:
M, and Mpc (for H Km/sec/Mpc and q). When
reduced to , this agrees with other available estimates of the local
IRLF. We find a steeper slope for the faint-end of the infrared luminosity
function when compared to previous studies. This is interpreted as due to the
presence of a population of faint but evolved (metal rich) galaxies in the
local Universe. However, it is not from the same population as the faint blue
galaxies found in the optical surveys. The characteristic magnitude
() of the local IRLF indicates that the bright red galaxies ( mag.) have a space density of Mpc and hence,
are not likely to be local objects.Comment: 24 pages, 8 figures, AASTEX 4.0, published in ApJ 492, 45
The connection between the peaks in velocity dispersion and star-forming clumps of turbulent galaxies
We present Keck/OSIRIS adaptive optics observations with 150-400 pc spatial
sampling of 7 turbulent, clumpy disc galaxies from the DYNAMO sample
(). DYNAMO galaxies have previously been shown to be well matched
in properties to main sequence galaxies at . Integral field
spectroscopy observations using adaptive optics are subject to a number of
systematics including a variable PSF and spatial sampling, which we account for
in our analysis. We present gas velocity dispersion maps corrected for these
effects, and confirm that DYNAMO galaxies do have high gas velocity dispersion
(\kms), even at high spatial sampling. We find statistically
significant structure in 6 out of 7 galaxies. The most common distance between
the peaks in velocity dispersion and emission line peaks is ~kpc, we
note this is very similar to the average size of a clump measured with HST
H maps. This could suggest that the peaks in velocity dispersion in
clumpy galaxies likely arise due to some interaction between the clump and the
surrounding ISM of the galaxy, though our observations cannot distinguish
between outflows, inflows or velocity shear. Observations covering a wider area
of the galaxies will be needed to confirm this result.Comment: Accepted for publication in MNRA
Galaxy bimodality versus stellar mass and environment
We analyse a z<0.1 galaxy sample from the Sloan Digital Sky Survey focusing
on the variation of the galaxy colour bimodality with stellar mass and
projected neighbour density Sigma, and on measurements of the galaxy stellar
mass functions. The characteristic mass increases with environmental density
from about 10^10.6 Msun to 10^10.9 Msun (Kroupa IMF, H_0=70) for Sigma in the
range 0.1--10 per Mpc^2. The galaxy population naturally divides into a red and
blue sequence with the locus of the sequences in colour-mass and
colour-concentration index not varying strongly with environment. The fraction
of galaxies on the red sequence is determined in bins of 0.2 in log Sigma and
log mass (12 x 13 bins). The red fraction f_r generally increases continuously
in both Sigma and mass such that there is a unified relation: f_r =
F(Sigma,mass). Two simple functions are proposed which provide good fits to the
data. These data are compared with analogous quantities in semi-analytical
models based on the Millennium N-body simulation: the Bower et al. (2006) and
Croton et al. (2006) models that incorporate AGN feedback. Both models predict
a strong dependence of the red fraction on stellar mass and environment that is
qualitatively similar to the observations. However, a quantitative comparison
shows that the Bower et al. model is a significantly better match; this appears
to be due to the different treatment of feedback in central galaxies.Comment: 19 pages, 17 figures; accepted by MNRAS, minor change
Lens or Binary? Chandra Observations of the Wide Separation Broad Absorption Line Quasar Pair UM425
We have obtained a 110 ksec Chandra ACIS-S exposure of UM425, a pair of QSOs
at z=1.47 separated by 6.5 arcsec, which show remarkably similar emission and
broad absorption line (BAL) profiles in the optical/UV. Our 5000 count X-ray
spectrum of UM425A (the brighter component) is well-fit with a power law
(photon spectral index Gamma=2.0) partially covered by a hydrogen column of
3.8x10^22 cm^-2. The underlying power-law slope for this object and for other
recent samples of BALQSOs is typical of radio-quiet quasars, lending credence
to the hypothesis that BALs exist in every quasar. Assuming the same Gamma for
the much fainter image of UM425B, we detect an obscuring column 5 times larger.
We search for evidence of an appropriately large lensing mass in our Chandra
image and find weak diffuse emission near the quasar pair, with an X-ray flux
typical of a group of galaxies at redshift z ~ 0.6. From our analysis of
archival HST WFPC2 and NICMOS images, we find no evidence for a luminous
lensing galaxy, but note a 3-sigma excess of galaxies in the UM425 field with
plausible magnitudes for a z=0.6 galaxy group. However, the associated X-ray
emission does not imply sufficient mass to produce the observed image
splitting. The lens scenario thus requires a dark (high M/L ratio) lens, or a
fortuitous configuration of masses along the line of sight. UM425 may instead
be a close binary pair of BALQSOs, which would boost arguments that
interactions and mergers increase nuclear activity and outflows.Comment: 13 pages, 9 figures, Accepted for publication in the Astrophysical
Journa
Pair Analysis of Field Galaxies from the Red-Sequence Cluster Survey
We study the evolution of the number of close companions of similar
luminosities per galaxy (Nc) by choosing a volume-limited subset of the
photometric redshift catalog from the Red-Sequence Cluster Survey (RCS-1). The
sample contains over 157,000 objects with a moderate redshift range of 0.25 < z
< 0.8 and absolute magnitude in Rc (M_Rc) < -20. This is the largest sample
used for pair evolution analysis, providing data over 9 redshift bins with
about 17,500 galaxies in each. After applying incompleteness and projection
corrections, Nc shows a clear evolution with redshift. The Nc value for the
whole sample grows with redshift as (1+z)^m, where m = 2.83 +/- 0.33 in good
agreement with N-body simulations in a LCDM cosmology. We also separate the
sample into two different absolute magnitude bins: -25 < M_Rc < -21 and -21 <
M_Rc < -20, and find that the brighter the absolute magnitude, the smaller the
m value. Furthermore, we study the evolution of the pair fraction for different
projected separation bins and different luminosities. We find that the m value
becomes smaller for larger separation, and the pair fraction for the fainter
luminosity bin has stronger evolution. We derive the major merger remnant
fraction f_rem = 0.06, which implies that about 6% of galaxies with -25 < M_Rc
< -20 have undergone major mergers since z = 0.8.Comment: ApJ, in pres
- …