448 research outputs found
The Stellar Mass Evolution of Galaxies in the NICMOS Ultra Deep Field
We measure the build-up of the stellar mass of galaxies from z=6 to z=1.
Using 15 band multicolor imaging data in the NICMOS Ultra Deep Field we derive
photometric redshifts and masses for 796 galaxies down to H(AB)=26.5. The
derived evolution of the global stellar mass density of galaxies is consistent
with previous star formation rate density measurements over the observed range
of redshifts. Beyond the observed range, maintaining consistency between the
global stellar mass and the observed star formation rate suggests the epoch of
galaxy formation was z=16.Comment: 18 pages, 3 figures, submitted to AJ. Data at:
http://orca.phys.uvic.ca/~gwyn/MMM/nicmos.htm
Galaxy-Galaxy Lensing in the Hubble Deep Field: The Halo Tully-Fisher Relation at Intermediate Redshift
A tangential distortion of background source galaxies around foreground lens
galaxies in the Hubble Deep Field is detected at the 99.3% confidence level. An
important element of our analysis is the use of photometric redshifts to
determine distances of lens and source galaxies and rest-frame B-band
luminosities of the lens galaxies. The lens galaxy halos obey a Tully-Fisher
relation between halo circular velocity and luminosity; the typical lens
galaxy, at a redshift z = 0.6, has a circular velocity of 210 +/-40 km/s at M_B
= -18.5, if q_0 = 0.5. Control tests, in which lens and source positions and
source ellipticities are randomized, confirm the significance level of the
detection quoted above. Furthermore, a marginal signal is also detected from an
independent, fainter sample of source galaxies without photometric redshifts.
Potential systematic effects, such as contamination by aligned satellite
galaxies, the distortion of source shapes by the light of the foreground
galaxies, PSF anisotropies, and contributions from mass distributed on the
scale of galaxy groups are shown to be negligible. A comparison of our result
with the local Tully-Fisher relation indicates that intermediate-redshift
galaxies are fainter than local spirals by 1.0 +/- 0.6 B mag at a fixed
circular velocity. This is consistent with some spectroscopic studies of the
rotation curves of intermediate-redshift galaxies. This result suggests that
the strong increase in the global luminosity density with redshift is dominated
by evolution in the galaxy number density.Comment: Revised version with minor changes. 13 pages, 7 figures, LaTeX2e,
uses emulateapj and multicol styles (included). Accepted by Ap
The Statistical Approach to Quantifying Galaxy Evolution
Studies of the distribution and evolution of galaxies are of fundamental
importance to modern cosmology; these studies, however, are hampered by the
complexity of the competing effects of spectral and density evolution.
Constructing a spectroscopic sample that is able to unambiguously disentangle
these processes is currently excessively prohibitive due to the observational
requirements. This paper extends and applies an alternative approach that
relies on statistical estimates for both distance (z) and spectral type to a
deep multi-band dataset that was obtained for this exact purpose.
These statistical estimates are extracted directly from the photometric data
by capitalizing on the inherent relationships between flux, redshift, and
spectral type. These relationships are encapsulated in the empirical
photometric redshift relation which we extend to z ~ 1.2, with an intrinsic
dispersion of dz = 0.06. We also develop realistic estimates for the
photometric redshift error for individual objects, and introduce the
utilization of the galaxy ensemble as a tool for quantifying both a
cosmological parameter and its measured error. We present deep, multi-band,
optical number counts as a demonstration of the integrity of our sample. Using
the photometric redshift and the corresponding redshift error, we can divide
our data into different redshift intervals and spectral types. As an example
application, we present the number redshift distribution as a function of
spectral type.Comment: 40 pages (LaTex), 21 Figures, requires aasms4.sty; Accepted by the
Astrophysical Journa
Simulated Extragalactic Observations with a Cryogenic Imaging Spectrophotometer
In this paper we explore the application of cryogenic imaging
spectrophotometers. Prototypes of this new class of detector, such as
superconducting tunnel junctions (STJs) and transition edge sensors (TESs),
currently deliver low resolution imaging spectrophotometry with high quantum
efficiency (70-100%) and no read noise over a wide bandpass in the visible to
near-infrared. In order to demonstrate their utility and the differences in
observing strategy needed to maximize their scientific return, we present
simulated observations of a deep extragalactic field. Using a simple analytic
technique, we can estimate both the galaxy redshift and spectral type more
accurately than is possible with current broadband techniques. From our
simulated observations and a subsequent discussion of the expected migration
path for this new technology, we illustrate the power and promise of these
devices.Comment: 30 pages, 10 figures, accepted for publication in the Astronomical
Journa
The properties of the Malin 1 galaxy giant disk: A panchromatic view from the NGVS and GUViCS surveys
Low surface brightness galaxies (LSBGs) represent a significant percentage of
local galaxies but their formation and evolution remain elusive. They may hold
crucial information for our understanding of many key issues (i.e., census of
baryonic and dark matter, star formation in the low density regime, mass
function). The most massive examples - the so called giant LSBGs - can be as
massive as the Milky Way, but with this mass being distributed in a much larger
disk. Malin 1 is an iconic giant LSBG, perhaps the largest disk galaxy known.
We attempt to bring new insights on its structure and evolution on the basis of
new images covering a wide range in wavelength. We have computed surface
brightness profiles (and average surface brightnesses in 16 regions of
interest), in six photometric bands (FUV, NUV, u, g, i, z). We compared these
data to various models, testing a variety of assumptions concerning the
formation and evolution of Malin 1. We find that the surface brightness and
color profiles can be reproduced by a long and quiet star-formation history due
to the low surface density; no significant event, such as a collision, is
necessary. Such quiet star formation across the giant disk is obtained in a
disk model calibrated for the Milky Way, but with an angular momentum
approximately 20 times larger. Signs of small variations of the star-formation
history are indicated by the diversity of ages found when different regions
within the galaxy are intercompared.For the first time, panchromatic images of
Malin 1 are used to constrain the stellar populations and the history of this
iconic example among giant LSBGs. Based on our model, the extreme disk of Malin
1 is found to have a long history of relatively low star formation (about 2
Msun/yr). Our model allows us to make predictions on its stellar mass and
metallicity.Comment: Accepted in Astronomy and Astrophysic
An Ultrasoft X-ray Flare from 3XMM J152130.7+074916: a Tidal Disruption Event Candidate
We report on the discovery of an ultrasoft X-ray transient source, 3XMM
J152130.7+074916. It was serendipitously detected in an XMM-Newton observation
on 2000 August 23, and its location is consistent with the center of the galaxy
SDSS J152130.72+074916.5 (z=0.17901 and d_L=866 Mpc). The high-quality X-ray
spectrum can be fitted with a thermal disk with an apparent inner disk
temperature of 0.17 keV and a rest-frame 0.24-11.8 keV unabsorbed luminosity of
~5e43 erg/s, subject to a fast-moving warm absorber. Short-term variability was
also clearly observed, with the spectrum being softer at lower flux. The source
was covered but not detected in a Chandra observation on 2000 April 3, a Swift
observation on 2005 September 10, and a second XMM-Newton observation on 2014
January 19, implying a large variability (>260) of the X-ray flux. The optical
spectrum of the candidate host galaxy, taken ~11 yrs after the XMM-Newton
detection, shows no sign of nuclear activity. This, combined with its transient
and ultrasoft properties, leads us to explain the source as tidal disruption of
a star by the supermassive black hole in the galactic center. We attribute the
fast-moving warm absorber detected in the first XMM-Newton observation to the
super-Eddington outflow associated with the event and the short-term
variability to a disk instability that caused fast change of the inner disk
radius at a constant mass accretion rate.Comment: 9 pages, 5 figures. ApJ, in pres
Type Ia Supernovae Rates and Galaxy Clustering from the CFHT Supernova Legacy Survey
The Canada-France-Hawaii Telescope Supernova Legacy Survey (SNLS) has created
a large homogeneous database of intermediate redshift (0.2 < z < 1.0) type Ia
supernovae (SNe Ia). The SNLS team has shown that correlations exist between SN
Ia rates, properties, and host galaxy star formation rates. The SNLS SN Ia
database has now been combined with a photometric redshift galaxy catalog and
an optical galaxy cluster catalog to investigate the possible influence of
galaxy clustering on the SN Ia rate, over and above the expected effect due to
the dependence of SFR on clustering through the morphology-density relation. We
identify three cluster SNe Ia, plus three additional possible cluster SNe Ia,
and find the SN Ia rate per unit mass in clusters at intermediate redshifts is
consistent with the rate per unit mass in field early-type galaxies and the SN
Ia cluster rate from low redshift cluster targeted surveys. We also find the
number of SNe Ia in cluster environments to be within a factor of two of
expectations from the two component SNIa rate model.Comment: 21 pages, 2 figures, 6 tables, accepted for publication in A
Pleiotropic effects of Syntaxin16 identified by gene editing in cultured adipocytes
Adipocytes play multiple roles in the regulation of glucose metabolism which rely on the regulation of membrane traffic. These include secretion of adipokines and serving as an energy store. Central to their energy storing function is the ability to increase glucose uptake in response to insulin, mediated through translocation of the facilitative glucose transporter GLUT4 to the cell surface. The trans-Golgi reticulum localized SNARE protein syntaxin 16 (Sx16) has been identified as a key component of the secretory pathway required for insulin-regulated trafficking of GLUT4. We used CRISPR/Cas9 technology to generate 3T3-L1 adipocytes lacking Sx16 to understand the role of the secretory pathway on adipocyte function. GLUT4 mRNA and protein levels were reduced in Sx16 knockout adipocytes and insulin stimulated GLUT4 translocation to the cell surface was reduced. Strikingly, neither basal nor insulin-stimulated glucose transport were affected. By contrast, GLUT1 levels were upregulated in Sx16 knockout cells. Levels of sortilin and insulin regulated aminopeptidase were also increased in Sx16 knockout adipocytes which may indicate an upregulation of an alternative GLUT4 sorting pathway as a compensatory mechanism for the loss of Sx16. In response to chronic insulin stimulation, Sx16 knockout adipocytes exhibit elevated insulin-independent glucose transport and significant alterations in lactate metabolism. We further show that the adipokine secretory pathways are impaired in Sx16 knockout cells. Together this demonstrates a role for Sx16 in the control of glucose transport, the response to elevated insulin, cellular metabolic profiles and adipocytokine secretion. [Abstract copyright: Copyright © 2022 Bremner, Al Shammari, Milligan, Hudson, Sutherland, Bryant and Gould.
The Size Function of Galaxy Disks out to z ~ 1 from the Canada-France-Hawaii-Telescope Legacy Survey
The formation and growth of galaxy disks over cosmic time is crucial to our
understanding of galaxy formation. Despite steady improvements in the size and
quality of disk samples over the last decade, many aspects of galaxy disk
evolution remain unclear. Using two square degrees of deep, wide-field i'-band
imaging from the Canada-France-Hawaii Telescope Legacy Survey, we compute size
functions for 6000 disks from z=0.2 to z=1 and explore luminosity and number
density evolution scenarios with an emphasis on the importance of selection
effects on the interpretation of the data. We also compute the size function of
a very large sample of disks from the Sloan Digital Sky Survey to use as a
local (z ~ 0.1) comparison. CFHTLS size functions computed with the same fixed
luminosity-size selection window at all redshifts exhibit evolution that
appears to be best modelled by a pure number density evolution. The z = 0.3
size function is an excellent match to the z = 0.9 one if disks at the highest
redshift are a factor of 2.5 more abundant than in the local universe. The SDSS
size function would also match the z = 0.9 CFHTLS size function very well with
a similar change in number density. On the other hand, the CFHTLS size
functions computed with a varying luminosity-size selection window with
redshift remain constant if the selection window is shifted by 1.01.5 mag
towards fainter magnitudes with decreasing redshift. There is a weak dependence
on disk scale length with smaller ( 4 kpc) disks requiring more
luminosity evolution than larger ones. Given that changes in number density are
primarily due to mergers and that current estimates of merger rates below z = 1
are low, luminosity evolution appears to be a more plausible scenario to
explain the observations.Comment: 11 pages, 9 figures, Accepted for publication in Ap
X-Ray Groups of Galaxies in the Aegis Deep and Wide Fields
We present the results of a search for extended X-ray sources and their
corresponding galaxy groups from 800-ks Chandra coverage of the All-wavelength
Extended Groth Strip International Survey (AEGIS). This yields one of the
largest X-ray selected galaxy group catalogs from a blind survey to date. The
red-sequence technique and spectroscopic redshifts allow us to identify 100
of reliable sources, leading to a catalog of 52 galaxy groups. The groups span
the redshift range and virial mass range
. For the 49 extended
sources which lie within DEEP2 and DEEP3 Galaxy Redshift Survey coverage, we
identify spectroscopic counterparts and determine velocity dispersions. We
select member galaxies by applying different cuts along the line of sight or in
projected spatial coordinates. A constant cut along the line of sight can cause
a large scatter in scaling relations in low-mass or high-mass systems depending
on the size of cut. A velocity dispersion based virial radius can more
overestimate velocity dispersion in comparison to X-ray based virial radius for
low mass systems. There is no significant difference between these two radial
cuts for more massive systems. Independent of radial cut, overestimation of
velocity dispersion can be created in case of existence of significant
substructure and also compactness in X-ray emission which mostly occur in low
mass systems. We also present a comparison between X-ray galaxy groups and
optical galaxy groups detected using the Voronoi-Delaunay method (VDM) for
DEEP2 data in this field.Comment: Accepted for publication in AP
- …