2,461 research outputs found
Breaking the Curve with CANDELS: A Bayesian Approach to Reveal the Non-Universality of the Dust-Attenuation Law at High Redshift
Dust attenuation affects nearly all observational aspects of galaxy
evolution, yet very little is known about the form of the dust-attenuation law
in the distant Universe. Here, we model the spectral energy distributions
(SEDs) of galaxies at z = 1.5--3 from CANDELS with rest-frame UV to near-IR
imaging under different assumptions about the dust law, and compare the amount
of inferred attenuated light with the observed infrared (IR) luminosities. Some
individual galaxies show strong Bayesian evidence in preference of one dust law
over another, and this preference agrees with their observed location on the
plane of infrared excess (IRX, ) and UV slope
(). We generalize the shape of the dust law with an empirical model,
where
is the dust law of Calzetti et al. (2000), and show that there
exists a correlation between the color excess and tilt with
+ . Galaxies with high
color excess have a shallower, starburst-like law, and those with low color
excess have a steeper, SMC-like law. Surprisingly, the galaxies in our sample
show no correlation between the shape of the dust law and stellar mass,
star-formation rate, or . The change in the dust law with color excess
is consistent with a model where attenuation is caused by by scattering, a
mixed star-dust geometry, and/or trends with stellar population age,
metallicity, and dust grain size. This rest-frame UV-to-near-IR method shows
potential to constrain the dust law at even higher () redshifts.Comment: 20 pages, 18 figures, resubmitted to Ap
The formation of bulges, discs and two-component galaxies in the CANDELS Survey at z < 3
We examine a sample of 1495 galaxies in the CANDELS fields to determine the evolution of two-component galaxies, including bulges and discs, within massive galaxies at the epoch 1 < z < 3 when the Hubble sequence forms. We fit all of our galaxies’ light profiles with a single Sersic fit, as well as with a combination of exponential and Sersic profiles. The latter is done in order to describe a galaxy with an inner and an outer component, or bulge and disc component. We develop and use three classification methods (visual, F-test and the residual flux fraction) to separate our sample into one-component galaxies (disc/spheroids-like galaxies) and two-component galaxies (galaxies formed by an ‘inner part’ or bulge and an ‘outer part’ or disc). We then compare the results from using these three different ways to classify our galaxies. We find that the fraction of galaxies selected as two-component galaxies increases on average 50 per cent from the lowest mass bin to the most massive galaxies, and decreases with redshift by a factor of 4 from z = 1 to 3. We find that single Sersic ‘disc-like’ galaxies have the highest relative number densities at all redshifts, and that two-component galaxies have the greatest increase and become at par with Sersic discs by z = 1. We also find that the systems we classify as two-component galaxies have an increase in the sizes of their outer components, or ‘discs’, by about a factor of 3 from z = 3 to 1.5, while the inner components or ‘bulges’ stay roughly the same size. This suggests that these systems are growing from the inside out, whilst the bulges or protobulges are in place early in the history of these galaxies. This is also seen to a lesser degree in the growth of single ‘disc-like’ galaxies versus ‘spheroid-like’ galaxies over the same epoch
The Evolution of the Galaxy Stellar Mass Function at z= 4-8: A Steepening Low-mass-end Slope with Increasing Redshift
We present galaxy stellar mass functions (GSMFs) at 4-8 from a
rest-frame ultraviolet (UV) selected sample of 4500 galaxies, found via
photometric redshifts over an area of 280 arcmin in the CANDELS/GOODS
fields and the Hubble Ultra Deep Field. The deepest Spitzer/IRAC data
yet-to-date and the relatively large volume allow us to place a better
constraint at both the low- and high-mass ends of the GSMFs compared to
previous space-based studies from pre-CANDELS observations. Supplemented by a
stacking analysis, we find a linear correlation between the rest-frame UV
absolute magnitude at 1500 \AA\ () and logarithmic stellar mass
() that holds for galaxies with . We
use simulations to validate our method of measuring the slope of the - relation, finding that the bias is minimized with a hybrid
technique combining photometry of individual bright galaxies with stacked
photometry for faint galaxies. The resultant measured slopes do not
significantly evolve over 4-8, while the normalization of the trend
exhibits a weak evolution toward lower masses at higher redshift. We combine
the - distribution with observed rest-frame UV luminosity
functions at each redshift to derive the GSMFs, finding that the low-mass-end
slope becomes steeper with increasing redshift from
at to at
. The inferred stellar mass density, when integrated over
-, increases by a factor of
between and and is in good agreement with the time integral of the
cosmic star formation rate density.Comment: 27 pages, 17 figures, ApJ, in pres
The mass evolution of the first galaxies: stellar mass functions and star formation rates at in the CANDELS GOODS-South field
We measure new estimates for the galaxy stellar mass function and star
formation rates for samples of galaxies at using data in
the CANDELS GOODS South field. The deep near-infrared observations allow us to
construct the stellar mass function at directly for the first time.
We estimate stellar masses for our sample by fitting the observed spectral
energy distributions with synthetic stellar populations, including nebular line
and continuum emission. The observed UV luminosity functions for the samples
are consistent with previous observations, however we find that the observed
- M relation has a shallow slope more consistent with a constant
mass to light ratio and a normalisation which evolves with redshift. Our
stellar mass functions have steep low-mass slopes (),
steeper than previously observed at these redshifts and closer to that of the
UV luminosity function. Integrating our new mass functions, we find the
observed stellar mass density evolves from at to at . Finally, combining the measured UV continuum
slopes () with their rest-frame UV luminosities, we calculate dust
corrected star-formation rates (SFR) for our sample. We find the specific
star-formation rate for a fixed stellar mass increases with redshift whilst the
global SFR density falls rapidly over this period. Our new SFR density
estimates are higher than previously observed at this redshift.Comment: 28 pages, 23 figures, 2 appendices. Accepted for publication in
MNRAS, August 7 201
Interplay of cis and trans mechanisms driving transcription factor binding and gene expression evolution
Noncoding regulatory variants play a central role in the genetics of human diseases and in evolution. Here we measure allele-specific transcription factor binding occupancy of three liver-specific transcription factors between crosses of two inbred mouse strains to elucidate the regulatory mechanisms underlying transcription factor binding variations in mammals. Our results highlight the pre-eminence of cis-acting variants on transcription factor occupancy divergence. Transcription factor binding differences linked to cis-acting variants generally exhibit additive inheritance, while those linked to trans-acting variants are most often dominantly inherited. Cis-acting variants lead to local coordination of transcription factor occupancies that decay with distance; distal coordination is also observed and may be modulated by long-range chromatin contacts. Our results reveal the regulatory mechanisms that interplay to drive transcription factor occupancy, chromatin state, and gene expression in complex mammalian cell states.We thank the CRUK—CI Genomics, BRU, and Bioinformatics Cores for technical assistance and the EMBL-EBI systems team for management of computational resources. This research was supported by the European Molecular Biology Laboratory (E.S.W., D.T., J.C.M., P.F.), Cancer Research UK (B.M.S., T.F.R., F.C., C.F., A.R., D.T.O.), the BOLD ITN (B.M.S.), Darwin Fellowship (A.K.), the Wellcome Trust (WT202878/B/16/Z, WT108749/Z/15/Z) (P.F.), (WT202878/A/16/Z) (D.T.O), (WT095606) (A.C.F.-S) and (WT098051) (P.F., D.T.O.), EMBO Long-term (ALTF1518-2012) and Advanced Fellowships (aALTF1672-2014) (E.S.W.), and by the European Research Council (award 615584) and EMBO Young Investigator Programme (D.T.O.)
Stellar Nucleosynthesis in the Hyades Open Cluster
We report a comprehensive light element (Li, C, N, O, Na, Mg, and Al)
abundance analysis of three solar-type main sequence (MS) dwarfs and three red
giant branch (RGB) clump stars in the Hyades open cluster using high-resolution
and high signal-to-noise spectroscopy. For each group (MS or RGB), the CNO
abundances are found to be in excellent star-to-star agreement. Our results
confirm that the giants have undergone the first dredge-up and that material
processed by the CN cycle has been mixed to the surface layers. The observed
abundances are compared to predictions of a standard stellar model based on the
Clemson-American University of Beirut (CAUB) stellar evolution code. The model
reproduces the observed evolution of the N and O abundances, as well as the
previously derived 12C/13C ratio, but it fails to predict by a factor of 1.5
the observed level of 12C depletion. Li abundances are derived to determine if
non-canonical extra mixing has occurred in the Hyades giants. The Li abundance
of the giant gamma Tau is in good accord with the predicted level of surface Li
dilution, but a ~0.35 dex spread in the giant Li abundances is found and cannot
be explained by the stellar model. Possible sources of the spread are
discussed; however, it is apparent that the differential mechanism responsible
for the Li dispersion must be unrelated to the uniformly low 12C abundances of
the giants. Na, Mg, and Al abundances are derived as an additional test of our
stellar model. All three elements are found to be overabundant by 0.2-0.5 dex
in the giants relative to the dwarfs. Such large enhancements of these elements
are not predicted by the stellar model, and non-LTE effects significantly
larger (and, in some cases, of opposite sign) than those implied by extant
literature calculations are the most likely cause.Comment: 40 pages, 6 figures, 6 tables; accepted by Ap
The Grizzly, February 11, 1983
Bookstore Explains Pricing Policy • Scottish Scholarships Offered to Sophomores • Weekend Alcohol Policy: Campus is Dry • Ursinus Gets Bucks From Sears Roebuck • President\u27s Corner • Visser Fills Exhibits in Corson • Letters to the Editor: Professor Laments Social Conditions at UC; I.F.C. President Irate; President\u27s Response; Bitter About Policy • Varying Viewpoints • Stravinsky to End Winterfest • U.C. Flu Flattens Students • Reaganomics Forum • Key Shooting Aids Lady Hoopsters\u27 Record • Basketball Laments Second Half Loss • Swimmers Glide to Third Straight Victory • Grapplers Deemed Tough • Basketball: End of an Era?? • Swimmers Stroke for Two Wins • Gymnasts Win by 0.75https://digitalcommons.ursinus.edu/grizzlynews/1093/thumbnail.jp
The Discovery of New Galaxy Members in the NGC 5044 and NGC 1052 Groups
We present the results of neutral hydrogen (HI) observations of the NGC 5044
and NGC 1052 groups, as part of a GEMS (Group Evolution Multiwavelength Study)
investigation into the formation and evolution of galaxies in nearby groups.
Two new group members have been discovered during a wide-field HI imaging
survey conducted using the ATNF Parkes telescope. These results, as well as
those from followup HI synthesis and optical imaging, are presented here.
J1320-1427, a new member of the NGC 5044 Group, has an HI mass of
M_HI=1.05e9Msun and M_HI/L_B=1.65 Msun/Lsun, with a radial velocity of
v=2750km/s. The optical galaxy is characterised by two regions of star
formation, surrounded by an extended, diffuse halo. J0249-0806, the new member
of the NGC 1052 Group, has M_HI=5.4e8Msun, M_HI/L_R=1.13 Msun/Lsun and
v=1450km/s. The optical image reveals a low surface brightness galaxy. We
interpret both of these galaxies as irregular type, with J0249-0806 possibly
undergoing first infall into the NGC 1052 group.Comment: Accepted for publication in MNRAS. 21 pages, 13 figures. Also
available with high-resolution figures at
http://www.astro.livjm.ac.uk/~npfm/Papers/mmb04.ps.g
The Mass Evolution of the First Galaxies: Stellar Mass Functions and Star Formation Rates at 4 \u3c \u3cem\u3ez\u3c/em\u3e \u3c 7 in the CANDELS GOODS-South Field
We measure new estimates for the galaxy stellar mass function and star formation rates for samples of galaxies at z ∼ 4, 5, 6 and 7 using data in the CANDELS GOODS South field. The deep near-infrared observations allow us to construct the stellar mass function at z ≥ 6 directly for the first time. We estimate stellar masses for our sample by fitting the observed spectral energy distributions with synthetic stellar populations, including nebular line and continuum emission. The observed UV luminosity functions for the samples are consistent with previous observations; however, we find that the observed MUV - M* relation has a shallow slope more consistent with a constant mass-to-light ratio and a normalization which evolves with redshift. Our stellar mass functions have steep low-mass slopes (α ≈ −1.9), steeper than previously observed at these redshifts and closer to that of the UV luminosity function. Integrating our new mass functions, we find the observed stellar mass density evolves from log10ρ* = 6.64+0.58-0.89 at z ∼ 7 to 7.36 ± 0.06 M⊙ Mpc− 3 at z ∼ 4. Finally, combining the measured UV continuum slopes (β) with their rest-frame UV luminosities, we calculate dust-corrected star formation rates (SFR) for our sample. We find the specific SFR for a fixed stellar mass increases with redshift whilst the global SFR density falls rapidly over this period. Our new SFR density estimates are higher than previously observed at this redshift
The Exhibition as an Experiment: An Analogy and its Implications
The analogy of the exhibition as an experiment suggests innovative curatorial approaches that challenge institutional practices. This analogy has however a historical precedence in modernism when itbecame paradigmatic of the exhibitions at the Museum of ModernArt in New York in the 1940s, defining the curatorial approach of its founding director Alfred J Barr. This article considers this early useof the analogy of the exhibition as an experiment and further reflects on its redefinition at the turn of the 20th century by examining how both the notions of the exhibition and of the experiment havechanged over time. In particular, the article examines the different meanings and practices inferred by the concepts of the exhibition and the experiment in the first decades of the 20th century and in the present. It outlines how correspondences between cultural and scientific paradigms can be deployed to tease unacknowledged synergies between two modes of knowledge production (i.e. the art exhibition and the experiment) and address questions of presentness, authority and legitimacy that they imply
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