132 research outputs found
The extraordinary structural evolution of massive galaxies
Galaxies have changed drastically over the past 10 billion years. This thesis deals with these changes, focusing on evolution in the structure of very massive galaxies with a range of stellar population properties. The main subjects addressed are the rapid changes in the sizes of old galaxies, the gradients in stellar population content within galaxies, and the predictions from theoretical models regarding these properties.UBL - phd migration 201
An HI survey of the Bootes Void. II. The Analysis
We discuss the results of a VLA HI survey of the Bootes void and compare the
distribution and HI properties of the void galaxies to those of galaxies found
in a survey of regions of mean cosmic density. The Bootes survey covers 1100
Mpc, or 1\% of the volume of the void and consists of 24 cubes of
typically 2 Mpc * 2 Mpc * 1280 km/s, centered on optically known galaxies.
Sixteen targets were detected in HI; 18 previously uncataloged objects were
discovered directly in HI. The control sample consists of 12 cubes centered on
IRAS selected galaxies with FIR luminosities similar to those of the Bootes
targets and located in regions of 1 to 2 times the cosmic mean density. In
addition to the 12 targets 29 companions were detected in HI. We find that the
number of galaxies within 1 Mpc of the targets is the same to within a factor
of two for void and control samples, and thus that the small scale clustering
of galaxies is the same in regions that differ by a factor of 6 in
density on larger scales. A dynamical analysis of the galaxies in the void
suggests that on scales of a few Mpc the galaxies are gravitationally bound,
forming interacting galaxy pairs, loose pairs and loose groups. One group is
compact enough to qualify as a Hickson compact group. The galaxies found in the
void are mostly late-type, gas rich systems. A careful scrutiny of their HI and
optical properties shows them to be very similar to field galaxies of the same
morphological type. This, combined with our finding that the small scale
clustering of the galaxies in the void is the same as in the field, suggests
that it is the near environment that mostly affects the evolution of galaxies.Comment: Latex file of abstract. The postscript version of the complete paper
(0.2 Mb in gzipped format) including all the figures can be retrieved from
http://www.astro.rug.nl:80/~secr/ To appear in the February 1996 issue of the
Astronomical Journa
The stellar mass structure of massive galaxies from z=0 to z=2.5; surface density profiles and half-mass radii
We present stellar mass surface density profiles of a mass-selected sample of
177 galaxies at 0.5 < z < 2.5, obtained using very deep HST optical and
near-infrared data over the GOODS-South field, including recent CANDELS data.
Accurate stellar mass surface density profiles have been measured for the first
time for a complete sample of high-redshift galaxies more massive than 10^10.7
M_sun. The key advantage of this study compared to previous work is that the
surface brightness profiles are deconvolved for PSF smoothing, allowing
accurate measurements of the structure of the galaxies. The surface brightness
profiles account for contributions from complex galaxy structures such as rings
and faint outer disks. Mass profiles are derived using radial rest-frame u-g
color profiles and a well-established empirical relation between these colors
and the stellar mass-to-light ratio. We derive stellar half-mass radii from the
mass profiles, and find that these are on average ~25% smaller than rest-frame
g band half-light radii. This average size difference of 25% is the same at all
redshifts, and does not correlate with stellar mass, specific star formation
rate, effective surface density, Sersic index, or galaxy size. Although on
average the difference between half-mass size and half-light size is modest,
for approximately 10% of massive galaxies this difference is more than a factor
two. These extreme galaxies are mostly extended, disk-like systems with large
central bulges. These results are robust, but could be impacted if the central
dust extinction becomes high. ALMA observations can be used to explore this
possibility. These results provide added support for galaxy growth scenarios
wherein massive galaxies at these epochs grow by accretion onto their outer
regions.Comment: 11 pages, 8 figures, 3 tables, accepted for publication in Ap
An HI survey of the bootes void; 1, the data
We present the results of a neutral hydrogen survey of the Bootes void carried out with the VLA in D-array. The survey covers \sim 1100 Mpc^{3}, about 1\% of the volume of the void as defined by Kirshner \etal 1987. We observed 24 fields, centered on known void galaxies; 16 of these were detected in HI. Eighteen uncataloged companion galaxies were discovered directly in the HI line at distances of 45\sec to 14.5\min from the target galaxies. We also present the results of follow-up optical imaging observations and discovery of one additional Bootes void galaxy, found through spectroscopy of a number of apparent companions to known void members. Our angular resolution is \sim 1\min (45 kpc) \footnote{Throughout this paper, we have assumed {H_{0}} = {\rm 100\,km\,s^{-1}Mpc^{-1}}.}, each field has a size of \sim 1\deg (2.7 Mpc). The detected HI masses range from 8\times 10^{8} to 1\times 10^{10} \msol. Typically our 2\sigma HI column density sensitivity is 2\times 10^{19} {\rm cm^{-2}}. The radio and optical data are analyzed and discussed in the following companion article (Paper~2, Szomoru, van Gorkom, Gregg and Strauss 1996)
WSRT Ultra-Deep Neutral Hydrogen Imaging of Galaxy Clusters at z=0.2, a Pilot Survey of Abell 963 and Abell 2192
A pilot study with the powerful new backend of the Westerbork Synthesis Radio
Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen
emission from 42 galaxies. The WSRT probes a total combined volume of 3.4x10^4
Mpc^3 at resolutions of 54x86 kpc^2 and 19.7 km/s, surveying both clusters and
the large scale structure in which they are embedded. In Abell 963, a
dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction,
most of the gas-rich galaxies are located between 1 and 3 Mpc in projection,
northeast from the cluster core. Their velocities are slightly redshifted with
respect to the cluster, and this is likely a background group. None of the blue
galaxies in the core of Abell 963 are detected in HI, although they have
similar colors and luminosities as the HI detected galaxies in the cluster
outskirts and field. Abell 2192 is less massive and more diffuse. Here, the
gas-rich galaxies are more uniformly distributed. The detected HI masses range
from 5x10^9 to 4x10^10 Msun. Some galaxies are spatially resolved, providing
rudimentary rotation curves useful for detailed kinematic studies of galaxies
in various environments. This is a pilot for ultra-deep integrations down to HI
masses of 8x10^8 Msun, providing a complete survey of the gas content of
galaxies at z=0.2, probing environments ranging from cluster cores to voids.Comment: 5 pages, 6 figures + 1 Plate, accepted for publication in the
Astrophysical Journal Letter
The Stellar Mass Structure of Massive Galaxies from z = 0 to z = 2.5: Surface Density Profiles and Half-mass Radii
We present stellar mass surface density profiles of a mass-selected sample of 177 galaxies at 0.5 {lt} z {lt} 2.5, obtained using very deep Hubble Space Telescope optical and near-infrared data over the GOODS-South field, including recent CANDELS data. Accurate stellar mass surface density profiles have been measured for the first time for a complete sample of high-redshift galaxies more massive than 10 M . The key advantage of this study compared to previous work is that the surface brightness profiles are deconvolved for point-spread function smoothing, allowing accurate measurements of the structure of the galaxies. The surface brightness profiles account for contributions from complex galaxy structures such as rings and faint outer disks. Mass profiles are derived using radial rest-frame ug color profiles and a well-established empirical relation between these colors and the stellar mass-to-light ratio. We derive stellar half-mass radii from the mass profiles, and find that these are on average ~{}25% smaller than rest-frame g-band half-light radii. This average size difference of 25% is the same at all redshifts, and does not correlate with stellar mass, specific star formation rate, effective surface density, Sérsic index, or galaxy size. Although on average the difference between half-mass size and half-light size is modest, for approximately 10% of massive galaxies this difference is more than a factor of two. These extreme galaxies are mostly extended, disk-like systems with large central bulges. These results are robust, but could be impacted if the central dust extinction becomes high. ALMA observations can be used to explore this possibility. These results provide added support for galaxy growth scenarios wherein massive galaxies at these epochs grow by accretion onto their outer regions
Extinction Curves, Distances, and Clumpiness of Diffuse Interstellar Dust Clouds
We present CCD photometry in UBVRI of several thousand Galactic field stars
in four large (>1 degree^2) regions centered on diffuse interstellar dust
clouds, commonly referred to as ``cirrus'' clouds (with optical depth A_V less
than unity). Our goal in studying these stars is to investigate the properties
of the cirrus clouds. A comparison of the observed stellar surface density
between on-cloud and off-cloud regions as a function of apparent magnitude in
each of the five bands effectively yields a measure of the extinction through
each cloud. For two of the cirrus clouds, this method is used to derive UBVRI
star counts-based extinction curves, and U-band counts are used to place
constraints on the cloud distance. The color distribution of stars and their
location in (U-B, B-V) and (B-V, V-I) color-color space are analyzed in order
to determine the amount of selective extinction (reddening) caused by the
cirrus. The color excesses, A_lambda-A_V, derived from stellar color histogram
offsets for the four clouds, are better fit by a reddening law that rises
steeply towards short wavelengths [R_V==A_V/E(B-V)<=2] than by the standard law
(R_V=3.1). This may be indicative of a higher-than-average abundance of small
dust grains relative to larger grains in diffuse cirrus clouds. The shape of
the counts-based effective extinction curve and a comparison of different
estimates of the dust optical depth (extinction optical depth derived from
background star counts/colors; emission optical depth derived from far infrared
measurements), are used to measure the degree of clumpiness in clouds. The set
of techniques explored in this paper can be readily adapted to the Sloan
Digital Sky Survey data set in order to carry out a systematic, large-scale
study of cirrus clouds.Comment: 22 pages, 13 figures (postscript, gif, jpg). Accepted for publication
in the Astronomical Journal, scheduled for the May 1999 issue. Full
resolution postscript versions of all figures are available at
http://www.ucolick.org/~arpad
The SFXC software correlator for Very Long Baseline Interferometry: Algorithms and Implementation
In this paper a description is given of the SFXC software correlator,
developed and maintained at the Joint Institute for VLBI in Europe (JIVE). The
software is designed to run on generic Linux-based computing clusters. The
correlation algorithm is explained in detail, as are some of the novel modes
that software correlation has enabled, such as wide-field VLBI imaging through
the use of multiple phase centres and pulsar gating and binning. This is
followed by an overview of the software architecture. Finally, the performance
of the correlator as a function of number of CPU cores, telescopes and spectral
channels is shown.Comment: Accepted by Experimental Astronom
The formation of voids in a universe with cold dark matter and a cosmological constant
A spherical Lagrangian hydrodynamical code has been written to study the
formation of cosmological structures in the early Universe. In this code we
take into account the presence of collisionless non-baryonic cold dark matter
(CDM), the cosmological constant and a series of physical processes present
during and after the recombination era, such as photon drag resulting from the
cosmic background radiation and hydrogen molecular production. We follow the
evolution of the structure since the recombination era until the present epoch.
As an application of this code we study the formation of voids starting from
negative density perturbations which evolved during and after the recombination
era. We analyse a set of COBE-normalized models, using different spectra to see
their influence on the formation of voids. Our results show that large voids
with diameters ranging from 10h^{-1} Mpc up to 50h^{-1} Mpc can be formed in a
universe model dominated by the cosmological constant (\Omega_\Lambda ~ 0.8).
This particular scenario is capable of forming large and deep empty regions
(with density contrasts \delta < -0.6). Our results also show that the physical
processes acting on the baryonic matter produce a transition region where the
radius of the dark matter component is greater than the baryonic void radius.
The thickness of this transition region ranges from about tens of kiloparsecs
up to a few megaparsecs, depending on the spectrum considered. Putative objects
formed near voids and within the transition region would have a different
amount of baryonic/dark matter when compared with \Omega_b/\Omega_d. If one
were to use these galaxies to determine, by dynamical effects or other
techniques, the quantity of dark matter present in the Universe, the result
obtained would be only local and not representative of the Universe as a whole.Comment: MNRAS (in press); 9 pages, no figure
An analysis of spectra in the Red Rectangle nebula
This paper presents an analysis of a series of spectra in the Red Rectangle
nebula. Only the reddest part of the spectra can safely be attributed to light
from the nebula, and indicates Rayleigh scattering by the gas, in conformity
with the large angles of scattering involved and the proximity of the star. In
the blue, light from HD44179, refracted or scattered in the atmosphere,
dominates the spectra. This paper questions the reliability of ground-based
observations of extended objects in the blue.Comment: 25 figure
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