4,915 research outputs found
The Mass Growth and Stellar Ages of Galaxies: Observations versus Simulations
Using observed stellar mass functions out to , we measure the main
progenitor stellar mass growth of descendant galaxies with masses of
at using an evolving
cumulative number density selection. From these mass growth histories, we are
able to measure the time at which half the total stellar mass of the descendant
galaxy was assembled, , which, in order of decreasing mass corresponds
to redshifts of and . We compare this to the
median light-weighted stellar age ( and
) of a sample of low redshift SDSS galaxies (from the literature) and
find the timescales are consistent with more massive galaxies forming a higher
fraction of their stars ex-situ compared to lower mass descendants. We find
that both and strongly correlate with mass which is in contrast
to what is found in the EAGLE hydrodynamical simulation which shows a flat
relationship between and . However, the semi-analytic model of
\citet{henriques2015} is consistent with the observations in both and
with , showing the most recent semi-analytic models are better
able to decouple the evolution of the baryons from the dark matter in
lower-mass galaxies.Comment: 6 pages, 3 figures, accepted for publication in ApJ
High Redshift Massive Quiescent Galaxies are as Flat as Star Forming Galaxies: The Flattening of Galaxies and the Correlation with Structural Properties in CANDELS/3D-HST
We investigate the median flattening of galaxies at in all five
CANDELS/3D-HST fields via the apparent axis ratio . We separate the sample
into bins of redshift, stellar-mass, s\'ersic index, size, and UVJ determined
star-forming state to discover the most important drivers of the median
(). Quiescent galaxies at are
rounder than those at lower masses, consistent with the hypothesis that they
have grown significantly through dry merging. The massive quiescent galaxies at
higher redshift become flatter, and are as flat as star forming massive
galaxies at , consistent with formation through direct
transformations or wet mergers. We find that in quiescent galaxies,
correlations with and , and are driven by the
evolution in the s\'ersic index (), consistent with the growing accumulation
of minor mergers at lower redshift. Interestingly, does not drive these
trends fully in star-forming galaxies. Instead, the strongest predictor of
in star-forming galaxies is the effective radius, where larger galaxies are
flatter. Our findings suggest that is tracing bulge-to-total ()
galaxy ratio which would explain why smaller/more massive star-forming galaxies
are rounder than their extended/less massive analogues, although it is unclear
why s\'ersic index correlates more weakly with flattening for star forming
galaxies than for quiescent galaxies.Comment: 13 pages, 11 figures, accepted to Ap
The mass, colour, and structural evolution of today's massive galaxies since z~5
In this paper, we use stacking analysis to trace the mass-growth, colour
evolution, and structural evolution of present-day massive galaxies
() out to . We utilize the exceptional depth
and area of the latest UltraVISTA data release, combined with the depth and
unparalleled seeing of CANDELS to gather a large, mass-selected sample of
galaxies in the NIR (rest-frame optical to UV). Progenitors of present-day
massive galaxies are identified via an evolving cumulative number density
selection, which accounts for the effects of merging to correct for the
systematic biases introduced using a fixed cumulative number density selection,
and find progenitors grow in stellar mass by since
. Using stacking, we analyze the structural parameters of the progenitors
and find that most of the stellar mass content in the central regions was in
place by , and while galaxies continue to assemble mass at all radii,
the outskirts experience the largest fractional increase in stellar mass.
However, we find evidence of significant stellar mass build up at
probing an era of significant mass assembly in
the interiors of present day massive galaxies. We also compare mass assembly
from progenitors in this study to the EAGLE simulation and find qualitatively
similar assembly with at . We identify as a
distinct epoch in the evolution of massive galaxies where progenitors
transitioned from growing in mass and size primarily through in-situ star
formation in disks to a period of efficient growth in consistent with
the minor merger scenario.Comment: 19 pages, 14 figures, accepted for publicatio
The evolution in the stellar mass of Brightest Cluster Galaxies over the past 10 billion years
Using a sample of 98 galaxy clusters recently imaged in the near infra-red
with the ESO NTT, WIYN and WHT telescopes, supplemented with 33 clusters from
the ESO archive, we measure how the stellar mass of the most massive galaxies
in the universe, namely Brightest Cluster Galaxies (BCG), increases with time.
Most of the BCGs in this new sample lie in the redshift range ,
which has been noted in recent works to mark an epoch over which the growth in
the stellar mass of BCGs stalls. From this sample of 132 clusters, we create a
subsample of 102 systems that includes only those clusters that have estimates
of the cluster mass. We combine the BCGs in this subsample with BCGs from the
literature, and find that the growth in stellar mass of BCGs from 10 billion
years ago to the present epoch is broadly consistent with recent semi-analytic
and semi-empirical models. As in other recent studies, tentative evidence
indicates that the stellar mass growth rate of BCGs may be slowing in the past
3.5 billion years. Further work in collecting larger samples, and in better
comparing observations with theory using mock images is required if a more
detailed comparison between the models and the data is to be made.Comment: 15 pages, 8 tables, 7 figures - Accepted for publication in MNRA
Anomalous Microwave Emission from the HII region RCW175
We present evidence for anomalous microwave emission in the RCW175 \hii
region. Motivated by 33 GHz 13\arcmin resolution data from the Very Small
Array (VSA), we observed RCW175 at 31 GHz with the Cosmic Background Imager
(CBI) at a resolution of 4\arcmin. The region consists of two distinct
components, G29.0-0.6 and G29.1-0.7, which are detected at high signal-to-noise
ratio. The integrated flux density is Jy at 31 GHz, in good
agreement with the VSA. The 31 GHz flux density is Jy
() above the expected value from optically thin free-free emission
based on lower frequency radio data and thermal dust constrained by IRAS and
WMAP data. Conventional emission mechanisms such as optically thick emission
from ultracompact \hii regions cannot easily account for this excess. We
interpret the excess as evidence for electric dipole emission from small
spinning dust grains, which does provide an adequate fit to the data.Comment: 5 pages, 2 figures, submmited to ApJ Letter
Neutrino mass matrix with U(2) flavor symmetry and neutrino oscillations
The three neutrino mass matrices in the model are studied
focusing on the neutrino oscillation experiments. The atmospheric neutrino
anomaly could be explained by the large oscillation.
The long baseline experiments are expected to detect signatures of the neutrino
oscillation even if the atmospheric neutrino anomaly is not due to the neutrino
oscillation. However, the model cannot solve the solar neutrino deficit while
it could be reconciled with the LSND data.Comment: 12 pages, LaTex file, to be published in PR
Oxidative costs of reproduction in mouse strains selected for different levels of food intake and which differ in reproductive performance
We are grateful to the animal house staff for their care of the animals. This work was supported in part by the US National Institute of Health grants R01AG043972 to J.R.S. and D.B.A. and P30AG050886 and P30DK056336 to D.B.A. The opinions expressed are those of the authors and do not necessarily represent those of the N.I.H. or any other organization. A.H.A.J. was supported by an Iraqi government student scholarship.Peer reviewedPublisher PD
IR-correlated 31 GHz radio emission from Orion East
Lynds dark cloud LDN1622 represents one of the best examples of anomalous
dust emission, possibly originating from small spinning dust grains. We present
Cosmic Background Imager (CBI) 31 GHz data of LDN1621, a diffuse dark cloud to
the north of LDN1622 in a region known as Orion East. A broken ring with
diameter g\approx 20 arcmin of diffuse emission is detected at 31 GHz, at
\approx 20-30 mJy beam with an angular resolution of \approx 5 arcmin.
The ring-like structure is highly correlated with Far Infra-Red emission at
m with correlation coefficients of r \approx 0.7-0.8, significant
at . Multi-frequency data are used to place constraints on other
components of emission that could be contributing to the 31 GHz flux. An
analysis of the GB6 survey maps at 4.85 GHz yields a upper limit on
free-free emission of 7.2 mJy beam (\la 30 per cent of the observed
flux) at the CBI resolution. The bulk of the 31 GHz flux therefore appears to
be mostly due to dust radiation. Aperture photometry, at an angular resolution
of 13 arcmin and with an aperture of diameter 30 arcmin, allowed the use of
IRAS maps and the {\it WMAP} 5-year W-band map at 93.5 GHz. A single modified
blackbody model was fitted to the data to estimate the contribution from
thermal dust, which amounts to \sim\sim100 \mu18.1\pm4.4 \mu^{-1}$, consistent with the values found for
LDN1622.Comment: 8 pages, 3 figures, 3 tables, submitted to MNRA
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