27 research outputs found
Measuring the Total Ultraviolet Light from Galaxy Clusters at z=0.5-1.6: The Balance of Obscured and Unobscured Star-Formation
Combined observations from UV to IR wavelengths are necessary to fully
account for the star-formation in galaxy clusters. Low mass (log M/Msun<10)
galaxies are typically not individualy detected, particularly at higher
redshifts (z~1-2) where galaxy clusters are undergoing rapid transitions from
hosting mostly active, dust-obscured star-forming galaxies to quiescent,
passive galaxies. To account for these undetected galaxies, we measure the
total light emerging from GALEX/NUV stacks of galaxy clusters between
z=0.5-1.6. Combined with existing measurements from Spitzer, WISE, and
Herschel, we study the average UV through far-infrared (IR) spectral energy
distribution (SED) of clusters. From the SEDs, we measure the total stellar
mass and amount of dust-obscured and unobscured star-formation arising from all
cluster-member galaxies, including the low mass population. The relative
fraction of unobscured star-formation we observe in the UV is consistent with
what is observed in field galaxies. There is tentative evidence for lower than
expected unobscured star-formation at z~0.5, which may arise from rapid
redshift evolution in the low mass quenching efficiency in clusters reported by
other studies. Finally, the GALEX data places strong constraints on derived
stellar-to-halo mass ratios at z<1 which anti-correlate with the total halo
mass, consistent with trends found from local X-ray observations of clusters.
The data exhibit steeper slopes than implementations of the cluster
star-formation efficiency in semi-analytical models.Comment: 13 pages, 5 figures, accepted to Ap
Tracing the Total Stellar Mass and Star Formation of High-Redshift Protoclusters
As the progenitors of present-day galaxy clusters, protoclusters are
excellent laboratories to study galaxy evolution. Since existing observations
of protoclusters are limited to the detected constituent galaxies at UV and/or
infrared wavelengths, the details of how typical galaxies grow in these young,
pre-virialized structures remain uncertain. We measure the total stellar mass
and star formation within protoclusters, including the contribution from faint
undetected members by performing a stacking analysis of 211
protoclusters selected as Planck cold sources. We stack WISE and Herschel/SPIRE
images to measure the angular size and the spectral energy distribution of the
integrated light from the protoclusters. The fluxes of protoclusters selected
as Planck cold sources can be contaminated by line of sight interlopers. Using
the WebSky simulation, we estimate that a single protocluster contributes
% of the flux of a Planck cold source on average. After this
correction, we obtain a total star formation rate of $7.3\pm3.2 \times 10^3\
M_{\odot} {\rm yr}^{-1}4.9\pm 2.2\times 10^{12}\
M_{\odot}z=2-4L_{IR} < 3 \times 10^{12} L_{\odot}$). Lastly, we find that protoclusters
subtend a half-light radius of 2.8' (4.2-5.8 cMpc) which is consistent with
simulations.Comment: Accepted for publication in Ap
Measuring the total infrared light from galaxy clusters at z=0.5-1.6: connecting stellar populations to dusty star formation
Massive galaxy clusters undergo strong evolution from z~1.6 to z~0.5, with
overdense environments at high-z characterized by abundant dust-obscured star
formation and stellar mass growth which rapidly give way to widespread
quenching. Data spanning the near- to far-infrared (IR) spectrum can directly
trace this transformation; however, such studies have largely been limited to
the massive galaxy end of cluster populations. In this work, we present ``total
light" stacking techniques spanning 3.4-500{\mu}m aimed at revealing the total
cluster IR emission, including low mass members and potential intracluster
dust. We detail our procedures for WISE, Spitzer, and Herschel imaging,
including corrections to recover the total stacked emission in the case of high
fractions of detected galaxies. We apply our stacking techniques to 232
well-studied massive (log M200/Msun~13.8) clusters across multiple z bins,
recovering extended cluster emission at all wavelengths, typically at >5sigma.
We measure the averaged near- to far-IR radial profiles and SEDs, quantifying
the total stellar and dust content. The near-IR radial profiles are well
described by an NFW model with a high (c~7) concentration parameter. Dust
emission is similarly concentrated, albeit suppressed at small radii
(r<0.2Mpc). The measured SEDs lack warm dust, consistent with the colder SEDs
expected for low mass galaxies. We derive total stellar masses consistent with
the theoretical Mhalo-M_star relation and specific-star formation rates that
evolve strongly with redshift, echoing that of massive (log Mstar/Msun>10)
cluster galaxies. Separating out the massive galaxy population reveals that the
majority of cluster far-IR emission (~70-80%) is provided by the low mass
constituents, which differs from field galaxies. This effect may be a
combination of mass-dependent quenching and excess dust in low mass cluster
galaxies.Comment: 32 pages, 16 figures, 7 tables. Submitted to MNRAS, comments welcome
ODIN: Where Do Lyman-alpha Blobs Live? Contextualizing Blob Environments within the Large-Scale Structure
While many Lyman-alpha Blobs (LABs) are found in and around several
well-known protoclusters at high redshift, how they trace the underlying
large-scale structure is still poorly understood. In this work, we utilize
5,352 Lyman-alpha emitters (LAEs) and 129 LABs at z=3.1 identified over a
9.5 sq. degree area in early data from the ongoing One-hundred-deg
DECam Imaging in Narrowbands (ODIN) survey to investigate this question. Using
LAEs as tracers of the underlying matter distribution, we identify overdense
structures as galaxy groups, protoclusters, and filaments of the cosmic web. We
find that LABs preferentially reside in regions of higher-than-average density
and are located in closer proximity to overdense structures, which represent
the sites of protoclusters and their substructures. Moreover, protoclusters
hosting one or more LABs tend to have a higher descendant mass than those which
do not. Blobs are also strongly associated with filaments of the cosmic web,
with 70% of the population being within a projected distance of 2.4 pMpc
from a filament. We show that the proximity of LABs to protoclusters is
naturally explained by their association with filaments as large cosmic
structures are where many filaments converge. The contiguous wide-field
coverage of the ODIN survey allows us for the first time to firmly establish a
connection between LABs as a population and their environment.Comment: 24 pages, 17 figures; submitted to Ap
Scary Barbie: An Extremely Energetic, Long-Duration Tidal Disruption Event Candidate Without a Detected Host Galaxy at z = 0.995
We report multi-wavelength observations and characterization of the
ultraluminous transient AT 2021lwx (ZTF20abrbeie; aka ``Barbie'') identified in
the alert stream of the Zwicky Transient Facility (ZTF) using a Recommender
Engine For Intelligent Transient Tracking (REFITT) filter on the ANTARES alert
broker. From a spectroscopically measured redshift of 0.995, we estimate a peak
observed pseudo-bolometric luminosity of log (L) = 45.7 from slowly fading ztf- and ztf-
light curves spanning over 1000 observer-frame days. The host galaxy is not
detected in archival Pan-STARRS observations ( mag), implying a lower
limit to the outburst amplitude of more than 5 mag relative to the quiescent
host galaxy. Optical spectra from Lick and Keck Observatories exhibit strong
emission lines with narrow cores from the H Balmer series and ultraviolet
semi-forbidden lines of Si III] 1892, C III] 1909, and C II]
2325. Typical nebular lines in AGN spectra from ions such as [O II]
and [O III] are not detected. These spectral features, along with the smooth
light curve that is unlike most AGN flaring activity, and the luminosity that
exceeds any observed or theorized supernova, lead us to conclude that AT
2021lwx is most likely an extreme tidal disruption event (TDE). Modeling of ZTF
photometry with MOSFiT suggests that the TDE was between a star and a supermassive black hole of mass
. Continued monitoring of the still-evolving light curve
along with deep imaging of the field once AT 2021lwx has faded can test this
hypothesis and potentially detect the host galaxy.Comment: 15 pages, 4 figures, 1 Table; Version as published in The
Astrophysical Journal Letters. Observations of AT 2021lwx published in the
paper can be found at https://bsubraya.github.io/research
Violence against female sex workers in Karnataka state, south India: impact on health, and reductions in violence following an intervention program
<p>Abstract</p> <p>Background</p> <p>Violence against female sex workers (FSWs) can impede HIV prevention efforts and contravenes their human rights. We developed a multi-layered violence intervention targeting policy makers, secondary stakeholders (police, lawyers, media), and primary stakeholders (FSWs), as part of wider HIV prevention programming involving >60,000 FSWs in Karnataka state. This study examined if violence against FSWs is associated with reduced condom use and increased STI/HIV risk, and if addressing violence against FSWs within a large-scale HIV prevention program can reduce levels of violence against them.</p> <p>Methods</p> <p>FSWs were randomly selected to participate in polling booth surveys (PBS 2006-2008; short behavioural questionnaires administered anonymously) and integrated behavioural-biological assessments (IBBAs 2005-2009; administered face-to-face).</p> <p>Results</p> <p>3,852 FSWs participated in the IBBAs and 7,638 FSWs participated in the PBS. Overall, 11.0% of FSWs in the IBBAs and 26.4% of FSWs in the PBS reported being beaten or raped in the past year. FSWs who reported violence in the past year were significantly less likely to report condom use with clients (zero unprotected sex acts in previous month, 55.4% vs. 75.5%, adjusted odds ratio (AOR) 0.4, 95% confidence interval (CI) 0.3 to 0.5, p < 0.001); to have accessed the HIV intervention program (ever contacted by peer educator, 84.9% vs. 89.6%, AOR 0.7, 95% CI 0.4 to 1.0, p = 0.04); or to have ever visited the project sexual health clinic (59.0% vs. 68.1%, AOR 0.7, 95% CI 0.6 to 1.0, p = 0.02); and were significantly more likely to be infected with gonorrhea (5.0% vs. 2.6%, AOR 1.9, 95% CI 1.1 to 3.3, p = 0.02). By the follow-up surveys, significant reductions were seen in the proportions of FSWs reporting violence compared with baseline (IBBA 13.0% vs. 9.0%, AOR 0.7, 95% CI 0.5 to 0.9 p = 0.01; PBS 27.3% vs. 18.9%, crude OR 0.5, 95% CI 0.4 to 0.5, p < 0.001).</p> <p>Conclusions</p> <p>This program demonstrates that a structural approach to addressing violence can be effectively delivered at scale. Addressing violence against FSWs is important for the success of HIV prevention programs, and for protecting their basic human rights.</p
Using sensitivity analyses to understand bistable system behavior
Abstract Background Bistable systems, i.e., systems that exhibit two stable steady states, are of particular interest in biology. They can implement binary cellular decision making, e.g., in pathways for cellular differentiation and cell cycle regulation. The onset of cancer, prion diseases, and neurodegenerative diseases are known to be associated with malfunctioning bistable systems. Exploring and characterizing parameter spaces in bistable systems, so that they retain or lose bistability, is part of a lot of therapeutic research such as cancer pharmacology. Results We use eigenvalue sensitivity analysis and stable state separation sensitivity analysis to understand bistable system behaviors, and to characterize the most sensitive parameters of a bistable system. While eigenvalue sensitivity analysis is an established technique in engineering disciplines, it has not been frequently used to study biological systems. We demonstrate the utility of these approaches on a published bistable system. We also illustrate scalability and generalizability of these methods to larger bistable systems. Conclusions Eigenvalue sensitivity analysis and separation sensitivity analysis prove to be promising tools to define parameter design rules to make switching decisions between either stable steady state of a bistable system and a corresponding monostable state after bifurcation. These rules were applied to the smallest two-component bistable system and results were validated analytically. We showed that with multiple parameter settings of the same bistable system, we can design switching to a desirable state to retain or lose bistability when the most sensitive parameter is varied according to our parameter perturbation recommendations. We propose eigenvalue and stable state separation sensitivity analyses as a framework to evaluate large and complex bistable systems