58 research outputs found
Chemical Potential of a Flexible Polymer Liquid in a Coarse-Grained Representation
While the excess chemical potential is the key quantity in determining phase
diagrams, its direct computation for high-density liquids of long polymer
chains has posed a significant challenge. Computationally, the excess chemical
potential is calculated using the Widom insertion method, which involves
monitoring the change in internal energy as one incrementally introduces
individual molecules in the liquid. However, when dealing with dense polymer
liquids, inserting long chains requires generating trial configurations with a
bias that favors those at low energy on a unit-by-unit basis: a procedure that
becomes more challenging as the number of units increases. Thus, calculating
the excess chemical potential of dense polymer liquids using this method
becomes computationally intractable as the chain length exceeds . Here,
we adopt a coarse-grained model derived from integral equation theory, for
which inserting long polymer chains becomes feasible. The Integral Equation
theory of Coarse-Graining (IECG) represents a polymer as a sphere or a
collection of blobs interacting through a soft potential. We employ the IECG
approach to compute the excess chemical potential using Widom's method for
polymer chains of increasing lengths, extending up to monomers, and at
densities reaching up to g/cm. From a fundamental
perspective, we demonstrate that the excess chemical potentials remain nearly
constant across various levels of coarse-graining, offering valuable insights
into the consistency of this type of procedure. Ultimately, we argue that
current Monte Carlo (MC) algorithms, originally designed for atomistic
simulations, such as Configurational Bias Monte Carlo (CBMC) methods, can
significantly benefit from the integration of the IECG approach, thereby
enhancing their performance in the study of phase diagrams of polymer liquids
Inter-comparison of Radio-Loudness Criteria for Type 1 AGNs in the XMM-COSMOS Survey
Limited studies have been performed on the radio-loud fraction in X-ray
selected type 1 AGN samples. The consistency between various radio-loudness
definitions also needs to be checked. We measure the radio-loudness of the 407
type 1 AGNs in the XMM-COSMOS quasar sample using nine criteria from the
literature (six defined in the rest-frame and three defined in the observed
frame): , ,
, ,
, ,
(observed frame),
(observed frame), and (observed frame). Using any single criterion
defined in the rest-frame, we find a low radio-loud fraction of
in the XMM-COSMOS type 1 AGN sample, except for . Requiring that any
two criteria agree reduces the radio-loud fraction to for about
3/4 of the cases. The low radio-loud fraction cannot be simply explained by the
contribution of the host galaxy luminosity and reddening. The
gives the smallest radio-loud fraction. Two
of the three radio-loud fractions from the criteria defined in the observed
frame without k-correction ( and ) are much larger than
the radio-loud fractions from other criteria.Comment: 12 pages, 7 figures, MNRAS submitte
CANDELS/GOODS-S, CDFS, ECDFS: Photometric Redshifts For Normal and for X-Ray-Detected Galaxies
We present photometric redshifts and associated probability distributions for
all detected sources in the Extended Chandra Deep Field South (ECDFS). The work
makes use of the most up-to-date data from the Cosmic Assembly Near-IR Deep
Legacy Survey (CANDELS) and the Taiwan ECDFS Near-Infrared Survey (TENIS) in
addition to other data. We also revisit multi-wavelength counterparts for
published X-ray sources from the 4Ms-CDFS and 250ks-ECDFS surveys, finding
reliable counterparts for 1207 out of 1259 sources (). Data used for
photometric redshifts include intermediate-band photometry deblended using the
TFIT method, which is used for the first time in this work. Photometric
redshifts for X-ray source counterparts are based on a new library of
AGN/galaxy hybrid templates appropriate for the faint X-ray population in the
CDFS. Photometric redshift accuracy for normal galaxies is 0.010 and for X-ray
sources is 0.014, and outlier fractions are and respectively. The
results within the CANDELS coverage area are even better as demonstrated both
by spectroscopic comparison and by galaxy-pair statistics. Intermediate-band
photometry, even if shallow, is valuable when combined with deep broad-band
photometry. For best accuracy, templates must include emission lines.Comment: The paper has been accepted by ApJ. The materials we provide are
available under [Surveys] > [CDFS] through the portal
http://www.mpe.mpg.de/XraySurvey
CANDELS Multi-wavelength Catalogs: Source Detection and Photometry in the GOODS-South Field
We present a UV-to-mid infrared multi-wavelength catalog in the
CANDELS/GOODS-S field, combining the newly obtained CANDELS HST/WFC3 F105W,
F125W, and F160W data with existing public data. The catalog is based on source
detection in the WFC3 F160W band. The F160W mosaic includes the data from
CANDELS deep and wide observations as well as previous ERS and HUDF09 programs.
The mosaic reaches a 5 limiting depth (within an aperture of radius
0.17 arcsec) of 27.4, 28.2, and 29.7 AB for CANDELS wide, deep, and HUDF
regions, respectively. The catalog contains 34930 sources with the
representative 50% completeness reaching 25.9, 26.6, and 28.1 AB in the F160W
band for the three regions. In addition to WFC3 bands, the catalog also
includes data from UV (U-band from both CTIO/MOSAIC and VLT/VIMOS), optical
(HST/ACS F435W, F606W, F775W, F814W, and F850LP), and infrared (HST/WFC3 F098M,
VLT/ISAAC Ks, VLT/HAWK-I Ks, and Spitzer/IRAC 3.6, 4.5, 5.8, 8.0 m)
observations. The catalog is validated via stellar colors, comparison with
other published catalogs, zeropoint offsets determined from the best-fit
templates of the spectral energy distribution of spectroscopically observed
objects, and the accuracy of photometric redshifts. The catalog is able to
detect unreddened star-forming (passive) galaxies with stellar mass of
10^{10}M_\odot at a 50% completeness level to z3.4 (2.8), 4.6 (3.2), and
7.0 (4.2) in the three regions. As an example of application, the catalog is
used to select both star-forming and passive galaxies at z2--4 via the
Balmer break. It is also used to study the color--magnitude diagram of galaxies
at 0<z<4.Comment: The full resolution article is now published in ApJS (2013, 207, 24).
22 pages, 21 figures, and 5 tables. The catalogue is available on the CANDELS
website: http://candels.ucolick.org/data_access/GOODS-S.html MAST:
http://archive.stsci.edu/prepds/candels and Rainbow Database:
https://arcoiris.ucolick.org/Rainbow_navigator_public and
https://rainbowx.fis.ucm.es/Rainbow_navigator_publi
The Nature of Optically Dull Active Galactic Nuclei in COSMOS
We present infrared, optical, and X-ray data of 48 X-ray bright, optically
dull AGNs in the COSMOS field. These objects exhibit the X-ray luminosity of an
active galactic nucleus (AGN) but lack broad and narrow emission lines in their
optical spectrum. We show that despite the lack of optical emission lines, most
of these optically dull AGNs are not well-described by a typical passive red
galaxy spectrum: instead they exhibit weak but significant blue emission like
an unobscured AGN. Photometric observations over several years additionally
show significant variability in the blue emission of four optically dull AGNs.
The nature of the blue and infrared emission suggest that the optically
inactive appearance of these AGNs cannot be caused by obscuration intrinsic to
the AGNs. Instead, up to ~70% of optically dull AGNs are diluted by their
hosts, with bright or simply edge-on hosts lying preferentially within the
spectroscopic aperture. The remaining ~30% of optically dull AGNs have
anomalously high f_x/f_o ratios and are intrinsically weak, not obscured, in
the optical. These optically dull AGNs are best described as a weakly accreting
AGN with a truncated accretion disk from a radiatively inefficient accretion
flow.Comment: 12 pages, 10 figures. Accepted for publication in the Ap
A CANDELS WFC3 Grism Study of Emission-Line Galaxies at z~2: A Mix of Nuclear Activity and Low-Metallicity Star Formation
We present Hubble Space Telescope Wide Field Camera 3 slitless grism
spectroscopy of 28 emission-line galaxies at z~2, in the GOODS-S region of the
Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The
high sensitivity of these grism observations, with 1-sigma detections of
emission lines to f > 2.5x10^{-18} erg/s/cm^2, means that the galaxies in the
sample are typically ~7 times less massive (median M_* = 10^{9.5} M_sun) than
previously studied z~2 emission-line galaxies. Despite their lower mass, the
galaxies have OIII/Hb ratios which are very similar to previously studied z~2
galaxies and much higher than the typical emission-line ratios of local
galaxies. The WFC3 grism allows for unique studies of spatial gradients in
emission lines, and we stack the two-dimensional spectra of the galaxies for
this purpose. In the stacked data the OIII emission line is more spatially
concentrated than the Hb emission line with 98.1 confidence. We additionally
stack the X-ray data (all sources are individually undetected), and find that
the average L(OIII)/L(0.5-10 keV) ratio is intermediate between typical z~0
obscured active galaxies and star-forming galaxies. Together the compactness of
the stacked OIII spatial profile and the stacked X-ray data suggest that at
least some of these low-mass, low-metallicity galaxies harbor weak active
galactic nuclei.Comment: ApJ accepted. 8 pages, 6 figure
Accretion Rate and the Physical Nature of Unobscured Active Galaxies
We show how accretion rate governs the physical properties of a sample of
unobscured broad-line, narrow-line, and lineless active galactic nuclei (AGNs).
We avoid the systematic errors plaguing previous studies of AGN accretion rate
by using accurate accretion luminosities (L_int) from well-sampled
multiwavelength SEDs from the Cosmic Evolution Survey (COSMOS), and accurate
black hole masses derived from virial scaling relations (for broad-line AGNs)
or host-AGN relations (for narrow-line and lineless AGNs). In general, broad
emission lines are present only at the highest accretion rates (L_int/L_Edd >
0.01), and these rapidly accreting AGNs are observed as broad-line AGNs or
possibly as obscured narrow-line AGNs. Narrow-line and lineless AGNs at lower
specific accretion rates (L_int/L_Edd < 0.01) are unobscured and yet lack a
broad line region. The disappearance of the broad emission lines is caused by
an expanding radiatively inefficient accretion flow (RIAF) at the inner radius
of the accretion disk. The presence of the RIAF also drives L_int/L_Edd < 10^-2
narrow-line and lineless AGNs to 10 times higher ratios of radio to optical/UV
emission than L_int/L_Edd > 0.01 broad-line AGNs, since the unbound nature of
the RIAF means it is easier to form a radio outflow. The IR torus signature
also tends to become weaker or disappear from L_int/L_Edd < 0.01 AGNs, although
there may be additional mid-IR synchrotron emission associated with the RIAF.
Together these results suggest that specific accretion rate is an important
physical "axis" of AGN unification, described by a simple model.Comment: Accepted for publication in the Astrophysical Journal. 15 pages, 9
figure
CANDELS: The progenitors of compact quiescent galaxies at z~2
We combine high-resolution HST/WFC3 images with multi-wavelength photometry
to track the evolution of structure and activity of massive (log(M*) > 10)
galaxies at redshifts z = 1.4 - 3 in two fields of the Cosmic Assembly
Near-infrared Deep Extragalactic Legacy Survey (CANDELS). We detect compact,
star-forming galaxies (cSFGs) whose number densities, masses, sizes, and star
formation rates qualify them as likely progenitors of compact, quiescent,
massive galaxies (cQGs) at z = 1.5 - 3. At z > 2 most cSFGs have specific
star-formation rates (sSFR = 10^-9 yr^-1) half that of typical, massive SFGs at
the same epoch, and host X-ray luminous AGN 30 times (~30%) more frequently.
These properties suggest that cSFGs are formed by gas-rich processes (mergers
or disk-instabilities) that induce a compact starburst and feed an AGN, which,
in turn, quench the star formation on dynamical timescales (few 10^8 yr). The
cSFGs are continuously being formed at z = 2 - 3 and fade to cQGs by z = 1.5.
After this epoch, cSFGs are rare, thereby truncating the formation of new cQGs.
Meanwhile, down to z = 1, existing cQGs continue to enlarge to match local QGs
in size, while less-gas-rich mergers and other secular mechanisms shepherd
(larger) SFGs as later arrivals to the red sequence. In summary, we propose two
evolutionary scenarios of QG formation: an early (z > 2), fast-formation path
of rapidly-quenched cSFGs that evolve into cQGs that later enlarge within the
quiescent phase, and a slow, late-arrival (z < 2) path for SFGs to form QGs
without passing through a compact state.Comment: Submitted to the Astrophysical Journal Letters, 6 pages, 4 figure
A CANDELS WFC3 Grism Study of Emission-Line Galaxies at Z approximates 2: A mix of Nuclear Activity and Low-Metallicity Star Formation
We present Hubble Space Telescope Wide Field Camera 3 slitless grism spectroscopy of 28 emission-line galaxies at z approximates 2, in the GOODS-S region of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS). The high sensitivity of these grism observations, with > 5-sigma detections of emission lines to f > 2.5 X 10(exp -18( erg/s/ square cm, means that the galaxies in the sample are typically approximately 7 times less massive (median M(star). = 10(exp 9.5)M(solar)) than previously studied z approximates 2 emission-line galaxies. Despite their lower mass, the galaxies have [O-III]/H-Beta ratios which are very similar to previously studied z approximates 2 galaxies and much higher than the typical emission-line ratios of local galaxies. The WFC3 grism allows for unique studies of spatial gradients in emission lines, and we stack the two-dimensional spectra of the galaxies for this purpose. In the stacked data the [O-III] emission line is more spatially concentrated than the H-Beta emission line with 98.1% confidence. We additionally stack the X-ray data (all sources are individually undetected), and find that the average L(sub [O-III])/L(sub 0.5.10keV) ratio is intermediate between typical z approximates 0 obscured active galaxies and star-forming galaxies. Together the compactness of the stacked [O-III] spatial profile and the stacked X-ray data suggest that at least some of these low-mass, low-metallicity galaxies harbor weak active galactic nuclei
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