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 $z=2-4$ 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 $33\pm15$% of the flux of a Planck cold source on average. After this correction, we obtain a total star formation rate of $7.3\pm3.2 \times 10^3\ M_{\odot} {\rm yr}^{-1}$and a total stellar mass of$4.9\pm 2.2\times 10^{12}\ M_{\odot}$. Our results indicate that protoclusters have, on average, 2x more star formation and 4x more stellar mass than the total contribution from individually-detected galaxies in spectroscopically-confirmed protoclusters. This suggests that much of the total flux within$z=2-4$protoclusters comes from galaxies with luminosities lower than the detection limit of SPIRE ($L_{IR} < 3 \times 10^{12} L_{\odot}$). 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 $\sim$ 9.5 sq. degree area in early data from the ongoing One-hundred-deg$^2$ 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 $\sim$ 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$_{\text{max}} / [\text{erg}/\text{s}]$) = 45.7 from slowly fading ztf-$\it{g}$ and ztf-$r$ light curves spanning over 1000 observer-frame days. The host galaxy is not detected in archival Pan-STARRS observations ($g > 23.3$ 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] $\lambda$1892, C III] $\lambda$1909, and C II] $\lambda$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 $\approx 14 M_{\odot}$ star and a supermassive black hole of mass $M_{\text{BH}} \sim$ $10^{8} M_{\odot}$. 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