23 research outputs found
Exploring the AGN-ram pressure stripping connection in local clusters
No full textRam-pressure stripping by the intracluster medium (ICM) is one of the most
advocated mechanisms that affect the properties of cluster galaxies. A recent
study based on a small sample has found that many galaxies showing strong
signatures of ram-pressure stripping also possess an active galactic nucleus
(AGN), suggesting a possible correlation between the two phenomena. This result
has not been confirmed by a subsequent study. Building upon previous findings,
here we combine MUSE observations conducted within the GASP program and a
general survey of the literature to robustly measure the AGN fraction in
cluster's ram pressure stripped galaxies using BPT emission line diagrams.
Considering a sample of 115 ram pressure stripped galaxies with stellar masses
, we find an AGN fraction of . This fraction
strongly depends on stellar mass: it raises to 51% when only ram-pressure
stripped galaxies of masses are considered. We
then investigate whether the AGN incidence is in excess in ram pressure
stripped galaxies compared to non-stripped galaxies, using as comparison a
sample of non-cluster galaxies observed by the survey MaNGA. Considering
mass-matched samples, we find that the incidence of AGN activity is
significantly higher (at a confidence level ) when ram-pressure
stripping is on act, supporting the hypothesis of an AGN-ram pressure
connection
Investigating the evolution of galaxies in groups using X-ray observations
No full textWe present results from the XXL and GAMA surveys that show at fixed optical group luminosity, galaxy groups with high X-ray luminosity are systematically different from groups with lower X-ray luminosity. We use optical group catalogues matched with X-ray aperture photometry to create samples of groups separated by X-ray luminosity, for a given group optical luminosity. We compare the galaxy properties of group members in these samples to test whether differences in the X-ray emitting gas are linked to differences in the group age or feedback history. We find that galaxy groups with high X-ray luminosity contain fewer blue, star forming galaxies, when compared to low X-ray luminosity groups. The X-ray bright groups also have a more dominant, passive central galaxy, than seen in groups with low X-ray luminosity. We find that these X-ray bright groups are therefore likely to be further in their evolution than those without significant X-ray luminosity, and have virialised at earlier epochs
Investigating the evolution of galaxies in groups using X-ray observations
No full textWe present results from the XXL and GAMA surveys that show at fixed optical group luminosity, galaxy groups with high X-ray luminosity are systematically different from groups with lower X-ray luminosity. We use optical group catalogues matched with X-ray aperture photometry to create samples of groups separated by X-ray luminosity, for a given group optical luminosity. We compare the galaxy properties of group members in these samples to test whether differences in the X-ray emitting gas are linked to differences in the group age or feedback history. We find that galaxy groups with high X-ray luminosity contain fewer blue, star forming galaxies, when compared to low X-ray luminosity groups. The X-ray bright groups also have a more dominant, passive central galaxy, than seen in groups with low X-ray luminosity. We find that these X-ray bright groups are therefore likely to be further in their evolution than those without significant X-ray luminosity, and have virialised at earlier epochs
Quantifying the role of ram pressure stripping of galaxies within galaxy groups
No full textIt is often stated that the removal of gas by ram-pressure stripping of a galaxy disc is not a common process in galaxy groups. In this study, with the aid of an observational classification of galaxies and a simple physical model, we show that this may not be true. We examined and identified 45 ram-pressure-stripped galaxy candidates from a sample of 1311 galaxy group members within 125 spectroscopically selected galaxy groups. Of these, 13 galaxies are the most secure candidates with multiple distinct features. These candidate ram-pressure-stripped galaxies have similar properties to those found in clusters – they occur at a range of stellar masses, are largely blue and star-forming, and have phase-space distributions consistent with being first infallers into their groups. The only stand-out feature of these candidates is they exist not in clusters, but in groups, with a median halo mass of 1013.5 M⊙. Although this may seem surprising, we employ an analytic model of the expected ram-pressure stripping force in groups and find that reasonable estimates of the relevant infall speeds and intragroup medium content would result in ram-pressure-stripped galaxies at these halo masses. Finally, given the considerable uncertainty on the lifetime of the ram-pressure phase, this physical mechanism could be the dominant quenching mechanism in galaxy groups, if our ram-pressure-stripped candidates can be confirmed
Patterson Irrigation District
No full textPresented at the 2002 USCID/EWRI conference, Energy, climate, environment and water - issues and opportunities for irrigation and drainage on July 9-12 in San Luis Obispo, California.Making accurate, informed operational decisions in water and energy management can have significant resource and fiscal impacts on irrigation districts. The need for accurate and reliable real-time and historical data is key in making these vital decisions. The use of every acre-foot of water and every kilowatt-hour of energy, resource management, has become the topic of scrutiny in today's world. The protection of these valuable water and energy resources, held in trust and managed by the irrigation district, on behalf of its' landowner constituents, is one of the vital functions of the Patterson Irrigation District (PIO). Plant Control and Supervisory Control and Data Acquisition (SCADA) systems can provide the link between data and effective District operations and management. This case study will outline the initial development, expansion and subsequent upgrade of the Patterson Irrigation District's Plant Control and SCADA systems, the role in data acquisition and daily district operations, the benefits the district and its water users have accrued from accurate real-time and historical data and finally, the lessons learned in the development, implementation and evolution of a state-of-the-art Plant Control and SCADA system for irrigation district use. In its first full year of operation, 1999, historical data verified an increase of 23% in total Station #1 pumping plant efficiency on a kW-hr per acre-foot basis
Assessment of Northern Bobwhite Survival and Fitness at Felsenthal National Wildlife Refuge, Arkansas
No full textIn the West Gulf Coastal Plains (WGCP) northern bobwhite (Colinus virginianus) numbers are declining faster than range-wide averages and such declines have been linked to the consequences of land management within the region. Management for the endangered red-cockaded woodpecker (Picoides borealis) has benefitted northern bobwhite by restoring mature pine-grassland ecosystems in some areas of the region; however, at Felsenthal National Wildlife Refuge, Crossett, Arkansas, USA, the bobwhite population was not increasing despite the availability of seemingly suitable habitat from management for the endangered species. To understand factors that may be affecting bobwhite survival on Felsenthal National Wildlife Refuge I conducted a telemetry study and assessed summer survival, brood survival, and nest success during 1 April − 11 August in 2013 and 1 April − 15 August in 2014. I also calculated homerange sizes and measured microhabitat characteristics around nests. Summer survival rates were 71% (SE=0.17) and 47% (SE=0.14); while nest success was 47% (SE=0.02) and 100% for 2013 and 2014, respectively. Between years, both 95% and 50% kernel homeranges were not significantly different (pooled, 63.92±6.07 ha and 14.94±1.75 ha); however minimum convex polygon home-range sizes were (113.8 ± 20.1 ha in 2013; and 393.1 ± 49.0 ha in 2014, P \u3c 0.001). Only numerical differences in microhabitat vegetation characteristics of nest sites and non- nest sites were observed. I suggest management for red-cockaded woodpeckers supports bobwhite populations but only as a buffer against more severe declines. Since bobwhites are declining range-wide, I believe areas federally managed for red-cockaded woodpeckers will become increasingly more important for sustaining regional bobwhite population levels
Environments and morphologies of red sequence galaxies with residual star formation in massive clusters
No full textWe present a photometric investigation into recent star formation in galaxy clusters at z ~ 0.1. We use spectral energy distribution templates to quantify recent star formation in large Xray- selected clusters from the LARCS survey using matched GALEX near-ultraviolet (NUV) photometry. These clusters all have signs of red sequence galaxy recent star formation (as indicated by the blue NUV - R colour), regardless of the cluster morphology and size. A trend in environment is found for these galaxies, such that they prefer to occupy low-density, highcluster- radius environments. The morphology of these UV-bright galaxies suggests that they are in fact red spirals, which we confirm with light profiles and Galaxy Zoo voting percentages as morphological proxies. These UV-bright galaxies are therefore seen to be either truncated spiral galaxies, caught by ram pressure infalling into the cluster, or high-mass spirals, with the photometry dominated by the older stellar population
Heterogeneity of inverted calcium ii H:K ratio cluster galaxies
No full text© 2019 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society The ratio of calcium II H plus H∊ to calcium II K inverts as a galaxy stellar population moves from being dominated by older stars to possessing more A and B class stars. This ratio – the H:K ratio – can serve as an indicator of stellar populations younger than 200 Myr. In this work, we provide a new method to determine H:K, and apply it to spectra taken of cluster galaxies in Abell 3888. Although H:K is on average systematically lower for the cluster than for a wider field sample, we show that H:K does not have a simple relationship with other indices such as the equivalent widths of Hδ and [O II] beyond having a high value for strong [O II] emission. Moreover, strongly inverted galaxies with H:K > 1.1 have no preferred location within the cluster and are only slightly lower in their velocity dispersions around the cluster compared to strongly emitting [O II] galaxies. Our results indicate that selecting galaxies on H:K inversion results in a heterogeneous sample formed via a mixture of pathways that likely includes, but may not be limited to, merging spiral galaxies, and quiescent galaxies accreting lower mass, gas-rich companions. In concert with other selection criteria, H:K can provide a means to select a more ‘pure’ passive sample or to aid in the selection of highly star-forming galaxies, especially where other spectral line indicators such as H α may not have been observed
Near-ultraviolet signatures of environment-driven galaxy quenching in Sloan Digital Sky Survey groups
No full textWe have investigated the effect of group environment on residual star formation in galaxies, using Galaxy Evolution Explorer near-ultraviolet (NUV) galaxy photometry with the Sloan Digital Sky Survey group catalogue of Yang et al. We compared the (NUV - r) colours of grouped and non-grouped galaxies, and find a significant increase in the fraction of red sequence galaxies with blue (NUV - r) colours outside of groups. When comparing galaxies in mass-matched samples of satellite (non-central), and non-grouped galaxies, we found a >4 sigma difference in the distribution of (NUV - r) colours, and an (NUV - r) blue fraction >3 sigma higher outside groups. A comparison of satellite and non-grouped samples has found the NUV fraction is a factor of similar to 2 lower for satellite galaxies between 10(10.5) and 10(10.7)M(circle dot), showing that higher mass galaxies are more likely to have residual star formation when not influenced by a group potential. There was a higher (NUV - r) blue fraction of galaxies with lower Sersic indices (n <3) outside of groups, not seen in the satellite sample. We have used stellar population models of Bruzual & Charlot with multiple burst, or exponentially declining star formation histories to find that many of the (NUV - r) blue non-grouped galaxies can be explained by a slow (similar to 2 Gyr) decay of star formation, compared to the satellite galaxies. We suggest that taken together, the difference in (NUV - r) colours between samples can be explained by a population of secularly evolving, non-grouped galaxies, where star formation declines slowly. This slow channel is less prevalent in group environments where more rapid quenching can occur
A photometrically and spectroscopically confirmed population of passive spiral galaxies
No full textWe have identified a population of passive spiral galaxies from photometry and integral field spectroscopy. We selected z < 0.035 spiral galaxies that have WISE colours consistent with little mid-infrared emission from warm dust. Matched aperture photometry of 51 spiral galaxies in ultraviolet, optical and mid-infrared show these galaxies have colours consistent with passive galaxies. Six galaxies form a spectroscopic pilot study and were observed using the Wide-Field Spectrograph to check for signs of nebular emission from star formation. We see no evidence of substantial nebular emission found in previous red spiral samples. These six galaxies possess absorption-line spectra with 4000 Å breaks consistent with an average luminosity-weighted age of 2.3 Gyr. Our photometric and integral field spectroscopic observations confirm the existence of a population of local passive spiral galaxies, implying that transformation into early-type morphologies is not required for the quenching of star formation
