195 research outputs found
The Suppression of Star Formation and the Effect of Galaxy Environment in Low-Redshift Galaxy Groups
Understanding the interaction between galaxies and their surroundings is
central to building a coherent picture of galaxy evolution. Here we use GALEX
imaging of a statistically representative sample of 23 galaxy groups at z=0.06
to explore how local and global group environment affect the UV properties and
dust-corrected star formation rates of their member galaxies. The data provide
star formation rates out to beyond 2R_200 in all groups, down to a completeness
limit and limiting galaxy stellar mass of 0.06 M_sun/yr and 10^8 M_sun,
respectively. At fixed galaxy stellar mass, we find that the fraction of
star-forming group members is suppressed relative to the field out to an
average radius of R ~ 1.5 Mpc ~ 2R_200, mirroring results for massive clusters.
For the first time we also report a similar suppression of the specific star
formation rate within such galaxies, on average by 40% relative to the field,
thus directly revealing the impact of the group environment in quenching star
formation within infalling galaxies. At fixed galaxy density and stellar mass,
this suppression is stronger in more massive groups, implying that both local
and global group environment play a role in quenching. The results favor an
average quenching timescale of at least ~2 Gyr and strongly suggest that a
combination of tidal interactions and starvation is responsible. Despite their
past and ongoing quenching, galaxy groups with more than four members still
account for at least ~25% of the total UV output in the nearby universe.Comment: 15 pages, 13 figures. ApJ accepte
Star formation activities in early-type brightest cluster galaxies
We identify a total of 120 early-type Brightest Cluster Galaxies (BCGs) at
0.1<z<0.4 in two recent large cluster catalogues selected from the Sloan
Digital Sky Survey (SDSS). They are selected with strong emission lines in
their optical spectra, with both H{\alpha} and [O II]{\lambda}3727 line
emission, which indicates significant ongoing star formation. They constitute
about ~ 0.5% of the largest, optically-selected, low-redshift BCG sample, and
the fraction is a strong function of cluster richness. Their star formation
history can be well described by a recent minor and short starburst
superimposed on an old stellar component, with the recent episode of star
formation contributing on average only less than 1 percent of the total stellar
mass. We show that the more massive star-forming BCGs in richer clusters tend
to have higher star formation rate (SFR) and specific SFR (SFR per unit galaxy
stellar mass). We also compare their statistical properties with a control
sample selected from X-ray luminous clusters, and show that the fraction of
star-forming BCGs in X-ray luminous clusters is almost one order of magnitude
larger than that in optically-selected clusters. BCGs with star formation in
cooling flow clusters usually have very flat optical spectra and show the most
active star formation, which may be connected with cooling flows.Comment: 15 pages, 10 figures and 2 tables, accepted for publication in MNRA
The properties of Brightest Cluster Galaxies in the SDSS DR6 adaptive matched filter cluster catalogue
We study the properties of Brightest Cluster Galaxies (BCGs) drawn from a
catalogue of more than 69000 clusters in the SDSS DR6 based on the adaptive
matched filter technique (AMF, Szabo et al., 2010). Our sample consists of more
than 14300 galaxies in the redshift range 0.1-0.3. We test the catalog by
showing that it includes well-known BCGs which lie in the SDSS footprint. We
characterize the BCGs in terms of r-band luminosities and optical colours as
well as their trends with redshift. In particular, we define and study the
fraction of blue BCGs, namely those that are likely to be missed by either
colour-based cluster surveys and catalogues. Richer clusters tend to have
brighter BCGs, however less dominant than in poorer systems. 4-9% of our BCGs
are at least 0.3 mag bluer in the g-r colour than the red-sequence at their
given redshift. Such a fraction decreases to 1-6% for clusters above a richness
of 50, where 3% of the BCGs are 0.5 mag below the red-sequence. A preliminary
morphological study suggests that the increase in the blue fraction at lower
richnesses may have a non-negligible contribution from spiral galaxies. We show
that a colour selection based on the g-r red-sequence or on a cut at colour u-r
>2.2 can lead to missing the majority of such blue BCGs. We also extend the
colour analysis to the UV range by cross-matching our catalogue with publicly
available data from Galex GR4 and GR5. We show a clear correlation between
offset from the optical red-sequence and the amount of UV-excess. Finally, we
cross-matched our catalogue with the ACCEPT cluster sample (Cavagnolo et al.,
2009), and find that blue BCGs tend to be in clusters with low entropy and
short cooling times. That is, the blue light is presumably due to recent star
formation associated to gas feeding by cooling flows. (abridged)Comment: 15 pages, 15 figures, submitted to MNRA
The Diverse Nature of Optical Emission Lines in Brightest Cluster Galaxies: IFU Observations of the Central Kiloparsecs
We present integral field spectroscopy of the nebular line emission in a
sample of 9 brightest cluster galaxies (BCGs). The sample was chosen to probe
both cooling flow and non-cooling flow clusters, as well as a range of cluster
X-ray luminosities. The line emission morphology and velocity gradients suggest
a great diversity in the properties of the line emitting gas. While some BGCs
show evidence for filamentary or patchy emission (Abell 1060, Abell 1668 and
MKW3s), others have extended emission (Abell 1204, Abell 2199), while still
others have centrally concentrated emission (Abell 2052). We examine diagnostic
line ratios to determine the dominant ionization mechanisms in each galaxy.
Most of the galaxies show regions with AGN-like spectra, however for two BCGs,
Abell 1060 and Abell 1204, the emission line diagnostics suggest regions which
can be described by the emission from young stellar populations. The diversity
of emission line properties in our sample of BCGs suggests that the emission
mechanism is not universal, with different ionization processes dominating
different systems. Given this diversity, there is no evidence for a clear
distinction of the emission line properties between cooling flow and
non-cooling flow BCGs. It is not always cooling flow BCGs which show emission
(or young stellar populations), and non-cooling flow BCGs which do not.Comment: 23 pages, 23 figures, accepted for publication in MNRAS. Full
resolution images are online http://web.ipac.caltech.edu/staff/louis
The role of environment in low-level active galactic nucleus activity: no evidence for cluster enhancement
We use the AMUSE-Virgo and AMUSE-Field surveys for nuclear X-ray emission in
early-type galaxies to conduct a controlled comparison of low-level
supermassive black hole activity within cluster and field spheroids. While both
the Virgo and the Field samples feature highly sub-Eddington X-ray luminosities
(log L_x/L_Edd between -8 and -4), we find that after accounting for the
influence of host galaxy stellar mass, the field early-type galaxies tend
toward marginally greater (0.38+/-0.14 dex) nuclear X-ray luminosities, at a
given black hole mass, than their cluster counterparts. This trend is
qualitatively consistent with the field black holes having access to a greater
reservoir of fuel, plausibly in the form of cold gas located near the nucleus.
We are able to rule out at high confidence the alternative of enhanced X-ray
activity within clusters. Presuming nuclear X-ray emission correlates with the
total energy and momentum output of these weakly accreting black holes, this
indicates that low-level active galactic nucleus feedback is not generally
stronger within typical cluster galaxies than in the field. These results
confirm that for most cluster early-type galaxies (i.e., excluding brightest
cluster galaxies) direct environmental effects, such as gas stripping, are more
relevant in quenching star formation.Comment: Corrected typos and references; 6 pages emulateapj, 2 tables, 3
figures. Published in ApJ Letter
The Relation Between Galaxy Morphology and Environment in the Local Universe: An RC3-SDSS Picture
We present an analysis of the z ~ 0 morphology-environment relation for 911
bright (M_B < -19) galaxies, matching classical RC3 morphologies to the
SDSS-based group catalog of Yang et al. We study how the relative fractions of
spirals, lenticulars, and ellipticals depend on halo mass over a range of
10^11.7-10^14.8 h^-1 Msol. We pay particular attention to how morphology
relates to central (most massive) vs satellite galaxy status. The fraction of
galaxies which are elliptical is a strong function of stellar mass; it is also
a strong function of halo mass, but only for central galaxies. We interpret
this in a scenario where elliptical galaxies are formed, probably via mergers,
as central galaxies within their halos; satellite ellipticals are previously
central galaxies accreted onto larger halos. The overall fraction of S0
galaxies increases strongly with halo mass, from ~10% to ~70%. We find striking
differences between the central and satellites: 20+/-2% of central M_* >
10^10.5 Msol galaxies are S0 regardless of halo mass, but satellite S0 galaxies
are only found in massive (> 10^13 h^-1 Msol) halos, where they are 69+/-4% of
the M_* > 10^10.5 Msol satellite population. This suggests two channels for S0
formation: one for central galaxies, and another which transforms lower mass
(M_* <~ 10^11 Msol) accreted spirals into satellite S0 galaxies in massive
halos. Analysis of finer morphological structure (bars and rings in disk
galaxies) shows some trends with stellar mass, but none with halo mass; this is
consistent with other recent studies which indicate that bars are not strongly
influenced by galaxy environment. Radio sources in high-mass central galaxies
are common, similarly so for elliptical and S0 galaxies, with a frequency that
increases with halo mass. Emission-line AGN (mostly LINERs) are more common in
S0s, but show no strong environmental trends (abridged).Comment: Accepted for publication in the Astrophysical Journal (ApJ
Optical & Sunyaev-Zel'dovich Observations of a New Sample of Distant Rich Galaxy Clusters in the ROSAT All Sky Survey
Finding a sample of the most massive clusters with redshifts can
provide an interesting consistency check of the cold dark matter
(CDM) model. Here we present results from our search for clusters with
where the initial candidates were selected by
cross-correlating the RASS faint and bright source catalogues with red galaxies
from the Sloan Digital Sky Survey DR8. Our survey thus covers
, much larger than previous studies of this kind.
Deeper follow-up observations in three bands using the William Herschel
Telescope and the Large Binocular Telescope were performed to confirm the
candidates, resulting in a sample of 44 clusters for which we present
richnesses and red sequence redshifts, as well as spectroscopic redshifts for a
subset. At least two of the clusters in our sample are comparable in richness
to RCS2-232727.7020437, one of the richest systems discovered to date. We
also obtained new observations with the Combined Array for Research in
Millimeter Astronomy for a subsample of 21 clusters. For 11 of those we detect
the Sunyaev-Zel'dovich effect signature. The Sunyaev-Zel'dovich signal allows
us to estimate and check for tension with the cosmological standard
model. We find no tension between our cluster masses and the CDM
model.Comment: 29 pages, 13 figures, to be published in MNRAS 450, 4248-4276 (2015
Isolation and characterization of saprophytic and pathogenic strains of Leptospira from water sources in the Midwestern United States
The genus Leptospira is a diverse and unique group of bacteria comprising multiple saprophytic and pathogenic species, which survive and persist in suitable moist environments. Pathogenic species cause human and animal leptospirosis, a global and neglected zoonotic disease. Disease transmission occurs by exposure to contaminated water and moist soil environments or by contact with domestic animals and wildlife acting as reservoir hosts that shed Leptospira via urine. Here, we describe the unexpected diversity of saprophytic and pathogenic species of Leptospira isolated from water in the Midwestern United States. Samples were collected by volunteers in 11 counties in Iowa from water sources, including puddles, sewage, creeks, ponds, lakes, and rivers, during the summer of 2021. One hundred and five water samples were tested by culture for the presence of saprophytic and pathogenic species and by lipL32 qPCR specific for the detection of pathogens; 82 (78.1%) were culture positive and five (4.8%) were positive by lipL32 qPCR. Whole genome sequencing of isolates cultured from water samples identified 10 species of saprophytes, namely L. montravelensis, L. kemamanensis, L. bandrabouensis, L. bourretii, L. bouyouniensis, L. chreensis, L. ellinghausenii, L. terpstrae, L. yanagawae, and L. abararensis, as well as three novel saprophytic species. Whole genome sequencing also identified two novel pathogenic species. The remaining cultures comprised mixed populations of saprophytic species and six comprised a mixture of saprophytic and pathogenic species. One of these mixed cultures was enriched to select for a clonal isolate of pathogenic Leptospira, strain WS101.C1, which was classified as L. interrogans serogroup Djasiman serovar Djasiman. Cumulatively, 9.5% (10/105) of water samples were positive for pathogenic Leptospira. This study emphasizes the diversity of Leptospira present in water sources in the Midwestern United States and provides unique opportunities to explore the geographic diversity and evolution of this genus. The identification of known and novel pathogenic species circulating in local water sources highlights their potential usefulness as diagnostic antigens, as well as the role of water in the transmission of infection to human and animal populations. Integrating knowledge on human, animal, and environmental health is essential to control and predict risk for zoonoses
Resurrecting the Red from the Dead: Optical Properties of BCGs in X-ray Luminous Clusters
We present measurements of surface brightness and colour profiles for the
brightest cluster galaxies (BCGs) in a sample of 48 X-ray luminous galaxy
clusters. These data were obtained as part of the Canadian Cluster Comparison
Project (CCCP). The Kormendy relation of our BCGs is steeper than that of the
local ellipticals, suggesting differences in the assembly history of these
types of systems. We also find that while most BCGs show monotonic colour
gradients consistent with a decrease in metallicity with radius, 25% of the
BCGs show colour profiles that turn bluer towards the centre (blue-cores). We
interpret this bluing trend as evidence for recent star formation. The excess
blue light leads to a typical offset from the red sequence of 0.5 to 1.0 mag in
(g'-r'), thus affecting optical cluster studies that may reject the BCG based
on colour. All of the blue-core BCGs are located within ~10 kpc of the peak in
the cluster X-ray emission. Furthermore, virtually all of the BCGs with recent
star formation are in clusters that lie above the Lx-Tx relation. Based on
photometry alone, these findings suggest that central star formation is a
ubiquitous feature of BCGs in dynamically relaxed cool-core clusters. This
implies that while AGNs and other heating mechanisms are effective at tempering
cooling, they do not full compensate for the energy lost via radiation.Comment: 20 pages, 11 figures, 3 tables. Accepted to MNRAS Updated text in
Introduction and Conclusion Section
Vegetation history and human impact during the last 300 years recorded in a German peat deposit
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