Abstract
We derive the spatial and wavelength behavior of dust attenuation in the multiple-armed spiral galaxy VV 191b using backlighting by the superimposed elliptical system VV 191a in a pair with ...an exceptionally favorable geometry for this measurement. Imaging using the James Webb Space Telescope and Hubble Space Telescope spans the wavelength range 0.3–4.5
μ
m with high angular resolution, tracing the dust in detail from 0.6–1.5
μ
m. Distinct dust lanes continue well beyond the bright spiral arms, and trace a complex web, with a very sharp radial cutoff near 1.7 Petrosian radii. We present attenuation profiles and coverage statistics in each band at radii 14–21 kpc. We derive the attenuation law with wavelength; the data both within and between the dust lanes clearly favor a stronger reddening behavior (
R
=
A
V
/
E
B
−
V
≈ 2.0 between 0.6 and 0.9
μ
m, approaching unity by 1.5
μ
m) than found for starbursts and star-forming regions of galaxies. Power-law extinction behavior ∝
λ
−
β
gives
β
= 2.1 from 0.6–0.9
μ
m.
R
decreases at increasing wavelengths (
R
≈ 1.1 between 0.9 and 1.5
μ
m), while
β
steepens to 2.5. Mixing regions of different column density flattens the wavelength behavior, so these results suggest a different grain population than in our vicinity. The NIRCam images reveal a lens arc and counterimage from a background galaxy at
z
≈ 1, spanning 90° azimuthally at 2.″8 from the foreground elliptical-galaxy nucleus, and an additional weakly lensed galaxy. The lens model and imaging data give a mass/light ratio
M
/
L
B
= 7.6 in solar units within the Einstein radius 2.0 kpc.
ABSTRACT
Galaxies fall broadly into two categories: star-forming (blue) galaxies and quiescent (red) galaxies. In between, one finds the less populated ‘green valley’. Some of these galaxies are ...suspected to be in the process of ceasing their star formation through a gradual exhaustion of gas supply, or already dead and experiencing a rejuvenation of star formation through fuel injection. We use the Galaxy And Mass Assembly (GAMA) database and the Galaxy Zoo citizen science morphological estimates to compare the morphology of galaxies in the green valley with those in the red sequence and blue cloud. Our goal is to examine the structural differences within galaxies that fall in the green valley, and what brings them there. Previous results found that disc features such as rings and lenses are more prominently represented in the green-valley population. We revisit this with a similar sized data set of galaxies with morphology labels provided by the Galaxy Zoo for the GAMA fields based on new Kilo-Degree Survey (KiDS) images. Our aim is to compare the results from expert classification qualitatively with those of citizen science. We observe that ring structures are indeed found more commonly in green-valley galaxies compared with their red and blue counterparts. We suggest that ring structures are a consequence of disc galaxies in the green valley actively exhibiting the characteristics of fading discs and evolving disc morphology of galaxies. We note that the progression from blue to red correlates with loosening spiral-arm structure.
Abstract The Balmer decrement (H α /H β ) provides a constraint on attenuation, the cumulative effects of dust grains in the ISM. The ratio is a reliable spectroscopic tool for deriving the dust ...properties of galaxies that determine many different quantities such as star formation rate, metallicity, and SED models. Here, we measure independently both the attenuation and H α /H β of an occulting galaxy pair: VV 191. Attenuation measurements in the visible spectrum ( A V ,stars ) from dust maps derived from the F606W filter of HST and the F090W filter of JWST are matched with spaxel-by-spaxel H α /H β observations from the George and Cynthia Mitchell Spectrograph of the McDonald Observatory. The 0.5–0.7 μ m bandpass covers the Balmer lines for VV 191. The dust maps of JWST and HST provide the high sensitivity necessary for comparisons and tracking trends of the geometrically favorable galaxy. We present maps and plots of the Balmer lines for the VV 191 galaxy pair and for a specific region highlighting dust lanes for VV 191b in the overlap region. We compute A V ,H II from H α /H β and plot both quantities against A V ,stars . Our results show that regions with higher dust content, residing closer to the spiral center, dominate ionized gas attenuation, leading to an overestimation of A V ,H II by a factor of 2. Further out in the spiral arms, the lower dust content leads to more agreement between the attenuations, indicating a lower star formation rate and larger contribution from older stars to the stellar continuum outside the Petrosian radius.
ABSTRACT
Low-mass (sub)stellar objects represent the low end of the initial mass function, the transition to free-floating planets and a prominent interloper population in the search for ...high-redshift galaxies. To what accuracy can photometry only classify these? JWST/NIRCam has several advantages over Hubble Space Telescope (HST)/WFC3 near-infrared (NIR): more filters, a greater wavelength range, and greater spatial resolution. Here, we present a catalogue of (sub)stellar dwarfs identified in the cosmic evolution early release science survey (CEERS). We identify 518 stellar objects down to mF200W 28 using half-light radius, a full three magnitudes deeper than typical HST/WFC3 images. A k-means nearest neighbour (kNN) algorithm identifies and types these sources, using four HST/WFC3 and four NIRCam filters, trained on IRTF/spex spectra of nearby brown dwarfs. The kNN with four neighbours classifies well within two subtypes: e.g. M2±2, achieving ∼95 per cent precision and recall. In CEERS, we find 9 M8±2, 2 L6±2, 1 T4±2, and 15 T8±2. We compare the observed long wavelength NIRCam colours – not used in the kNN – to those expected for brown dwarf atmospheric models. The NIRCam F356W−F444W and F410M−F444W colours are redder by a magnitude for the type assigned by the kNN, hinting at a wider variety of atmospheres for these objects. We find a 300–350 pc scale height for M6±2 dwarfs plus a second structural component and a 150–200 pc scale height for T6±2 type dwarfs, consistent with literature values. A single M8±2 dwarf is spectroscopically confirmed at 4 kpc distance.
Abstract James Webb Space Telescope NIRCam images have revealed 154 reliable globular cluster (GC) candidates around the z = 0.0513 elliptical galaxy VV 191a after subtracting 34 likely interlopers ...from background galaxies inside our search area. NIRCam broadband observations are made at 0.9–4.5 μ m using the F090W, F150W, F356W, and F444W filters. Using point-spread-function-matched photometry, the data are analyzed to present color–magnitude diagrams and color distributions that suggest a relatively uniform population of GCs, except for small fractions of reddest (5%–8%) and bluest (2%–4%) outliers. GC models in the F090W versus (F090W–F150W) diagram fit the NIRCam data well and show that the majority of GCs detected have a mass of ∼10 6.5 M ⊙ , with metallicities Fe/H spanning the typical range expected for GCs (−2.5 ≲ Fe/H≲ 0.5). However, the models predict ∼0.3–0.4 mag bluer (F356W–F444W) colors than the NIRCam data for a reasonable range of GC ages, metallicities, and reddening. Although our data do not quite reach the luminosity function turnover, the measured luminosity function is consistent with previous measurements, suggesting an estimated peak at m AB ∼ −9.4 ± 0.2 mag in the F090W filter.
This thesis examines social cohesion, reproduction, and change through three complementary perspectives. The first part of the paper discusses the topics of resistance and social change, as addressed ...by several prominent social theorists, as well as how the "agent" or "subject" of resistance is constituted and how "the social" is constructed and reproduced. The second part of the paper discusses some historical foundations of social cohesion and change by examining theories regarding the movement from "traditional" forms of social solidarity to a so-called "modern" emphasis on individualization and "rationalization," which has been accompanied, according to some social theorists, by the progression from social harmony and effervescence to anomie, alienation, and disenchantment. Lastly, the role of language and how subjects are constructed and emerge through discursive practices (and the interdependent relationship between language and social structure and social relations) is considered in the third part of the paper.
In this paper we describe our search for galaxy protocluster candidates at
$4.5< z < 10$ and explore the environmental and physical properties of their
member galaxies identified through JWST ...wide-field surveys within the CEERS,
JADES, and PEARLS NEP-TDF fields. Combining with HST data, we identify 2948
robust $z>4.5$ candidates within an area of 185.4 arcmin$^2$. We determine
nearest neighbour statistics and galaxy environments. We find that high-$z$
galaxies in overdense environments exhibit higher star formation activity
compared to those in underdense regions. Galaxies in dense environments have a
slightly increased SFR at a given mass compared with galaxies in the lower
density environments. At the high mass end we also find a gradual flattening of
the $M_{\star}$-SFR slope. We find that galaxies in high-density regions often
have redder UV slopes than those in low-density regions, suggesting more dust
extinction, weaker Lyman-alpha emission and / or a higher damped Lyman-alpha
absorption. We also find that the mass-size relation remains consistent and
statistically similar across all environments. Furthermore, we quantitatively
assess the probability of a galaxy belonging to a protocluster candidate. In
total, we identified 26 overdensities at $z=5-7$ and estimate their dark matter
halo masses. We find that all protocluster candidates could evolve into
clusters with $M_{\rm halo} > 10^{14}M_{\odot}$ at $z = 0$, thereby supporting
the theoretical and simulation predictions of cluster formation. Notably, this
marks an early search for protocluster candidates in JWST wide field based on
photometric data, providing valuable candidates to study cosmic structure
formation at the early stages.
Low mass (sub)stellar objects represent the low end of the initial mass function, the transition to free-floating planets and a prominent interloper population in the search for high-redshift ...galaxies. Without proper motions or spectroscopy, can one identify these objects photometrically? JWST/NIRCam has several advantages over HST/WFC3 NIR: more filters, a greater wavelength range, and greater spatial resolution. Here, we present a catalogue of (sub)stellar dwarfs identified in the Cosmic Evolution Early Release Science Survey (CEERS). We identify 518 stellar objects down to \(m_F200W \sim 28\) using half-light radius, a full three magnitudes deeper than typical HST/WFC3 images. A kNN nearest neighbour algorithm identifies and types these sources, using four HST/WFC3 and four NIRCam filters, trained on SpeX spectra of nearby brown dwarfs. The kNN with four neighbors classifies well within two subtypes: e.g M2\(\pm\)2 or T4\(\pm\)2, achieving \(\sim\)95% precision and recall. More granular typing results in worse metrics. In CEERS, we find 9 M8\(\pm\)2, 2 L6\(\pm\)2, 1 T4\(\pm\)2, and 15 T8\(\pm\)2. We compare the observed long wavelength NIRCam colours -- not used in the kNN -- to those expected for brown dwarf atmospheric models. The NIRCam F356W-F444W and F410M-F444W colours are redder by a magnitude for the type assigned by the kNN, hinting at a wider variety of atmospheres for these objects. We find a 300-350pc scale-height for M6\(\pm\)2 dwarfs plus a second structural component and a 150-200pc scale-height for T6\(\pm\)2 type dwarfs, consistent with literature values.
James Webb Space Telescope NIRCam images have revealed 154 reliable globular cluster (GC) candidates around the \(z = 0.0513\) elliptical galaxy VV~191a after subtracting 34 likely interlopers from ...background galaxies inside our search area. NIRCam broadband observations are made at 0.9-4.5 \(\mu\)m using the F090W, F150W, F356W, and F444W filters. Using PSF-matched photometry, the data are analyzed to present color-magnitude diagrams (CMDs) and color distributions that suggest a relatively uniform population of GCs, except for small fractions of reddest (5-8%) and bluest (2-4%) outliers. GC models in the F090W vs. (F090-F150W) diagram fit the NIRCam data well and show that the majority of GCs detected have a mass of approximately $\sim$$10^{6.5}$$M_{\odot}\(, with metallicities Fe/H spanning the typical range expected for GCs (-2.5\)\le\( Fe/H\)\le\( 0.5). However, the models predict \)\sim\(0.3-0.4 mag bluer (F356W-F444W) colors than the NIRCam data for a reasonable range of GC ages, metallicities, and reddening. Although our data does not quite reach the luminosity function turnover, the measured luminosity function is consistent with previous measurements, suggesting an estimated peak at \)m_{\rm AB}$$\sim\(-9.4 mag, \)\pm$0.2 mag in the F090W filter.
Galaxies broadly fall into two categories: star-forming (blue) galaxies and quiescent (red) galaxies. In between, one finds the less populated ``green valley". Some of these galaxies are suspected to ...be in the process of ceasing their star-formation through a gradual exhaustion of gas supply or already dead and are experiencing a rejuvenation of star-formation through fuel injection. We use the Galaxy And Mass Assembly database and the Galaxy Zoo citizen science morphological estimates to compare the morphology of galaxies in the green valley against those in the red sequence and blue cloud. Our goal is to examine the structural differences within galaxies that fall in the green valley, and what brings them there. Previous results found disc features such as rings and lenses are more prominently represented in the green valley population. We revisit this with a similar sized data set of galaxies with morphology labels provided by the Galaxy Zoo for the GAMA fields based on new KiDS images. Our aim is to compare qualitatively the results from expert classification to that of citizen science. We observe that ring structures are indeed found more commonly in green valley galaxies compared to their red and blue counterparts. We suggest that ring structures are a consequence of disc galaxies in the green valley actively exhibiting characteristics of fading discs and evolving disc morphology of galaxies. We note that the progression from blue to red correlates with loosening spiral arm structure.
