115 research outputs found
The Properties of Brightest Cluster Galaxies in X-Ray Selected Clusters
We present the K-band Hubble diagram for 162 brightest cluster galaxies
(BCGs) in X-ray selected clusters, 0.01<z<0.83. The sample incorporates that of
Burke, Collins, & Mann (2000) and includes additional infrared data from the
2MASS extended source catalogue. We show that below z=0.1 the BCGs show no
correlation with their environment, however, above z=0.1 BCGs in more X-ray
luminous clusters are more uniform in their photometric properties. This
suggests that there may be two populations of BCGs which have different
evolutionary histories.Comment: 2 pages, to appear in the proceedings of the Sesto 2001 conference on
tracing cosmic evolution with galaxy cluster
Comparative nanostructure analysis of gasoline turbocharged direct injection and diesel soot-in-oil with carbon black
Two gasoline turbocharged direct injection (GTDI) and two diesel soot-in-oil samples were compared with one flame-generated soot sample. High resolution transmission electron microscopy imaging was employed for the initial qualitative assessment of the soot morphology. Carbon black and diesel soot both exhibit core-shell structures, comprising an amorphous core surrounded by graphene layers; only diesel soot has particles with multiple cores. In addition to such particles, GTDI soot also exhibits entirely amorphous structures, of which some contain crystalline particles only a few nanometers in diameter. Subsequent quantification of the nanostructure by fringe analysis indicates differences between the samples in terms of length, tortuosity, and separation of the graphitic fringes. The shortest fringes are exhibited by the GTDI samples, whilst the diesel soot and carbon black fringes are 9.7% and 15.1% longer, respectively. Fringe tortuosity is similar across the internal combustion engine samples, but lower for the carbon black sample. In contrast, fringe separation varies continuously among the samples. Raman spectroscopy further confirms the observed differences. The GTDI soot samples contain the highest fraction of amorphous carbon and defective graphitic structures, followed by diesel soot and carbon black respectively. The AD1:AG ratios correlate linearly with both the fringe length and fringe separation
Galaxy and mass assembly (GAMA): The connection between metals, specific SFR and Hi gas in galaxies: The Z-SSFR relation
We study the interplay between gas phase metallicity (Z), specific star formation rate (SSFR) and neutral hydrogen gas (HI) for galaxies of different stellar masses. Our study uses spectroscopic data from Galaxy and Mass Assembly and Sloan Digital Sky Su
The SAMI galaxy survey: Can we trust aperture corrections to predict star formation?
In the low-redshift Universe (z < 0.3), our view of galaxy evolution is primarily based on fibre optic spectroscopy surveys. Elaborate methods have been developed to address aperture effects when fixed aperture sizes only probe the inner regions for galaxies of ever decreasing redshift or increasing physical size. These aperture corrections rely on assumptions about the physical properties of galaxies. The adequacy of these aperture corrections can be tested with integral-field spectroscopic data. We use integral-field spectra drawn from 1212 galaxies observed as part of the SAMI Galaxy Survey to investigate the validity of two aperture correction methods that attempt to estimate a galaxy's total instantaneous star formation rate. We show that biases arise when assuming that instantaneous star formation is traced by broad-band imaging, and when the aperture correction is built only from spectra of the nuclear region of galaxies. These biases may be significant depending on the selection criteria of a survey sample. Understanding the sensitivities of these aperture corrections is essential for correct handling of systematic errors in galaxy evolution studies
The SAMI Pilot Survey: stellar kinematics of galaxies in Abell 85, 168 and 2399
We present the SAMI Pilot Survey, consisting of integral field spectroscopy of 106 galaxies across three galaxy clusters, Abell 85, Abell 168 and Abell 2399. The galaxies were selected by absolute magnitude to have Mr < -20.25 mag. The survey, using the Sydney-AAO Multi-object Integral field spectrograph (SAMI), comprises observations of galaxies of all morphological types with 75 per cent of the sample being early-type galaxies (ETGs) and 25 per cent being late-type galaxies (LTGs). Stellar velocity and velocity dispersion maps are derived for all 106 galaxies in the sample. The lambdaR parameter, a proxy for the specific stellar angular momentum, is calculated for each galaxy in the sample. We find a trend between lambdaR and galaxy concentration such that LTGs are less concentrated higher angular momentum systems, with the fast-rotating ETGs (FRs) more concentrated and lower in angular momentum. This suggests that some dynamical processes are involved in transforming LTGs to FRs, though a significant overlap between the lambdaR distributions of these classes of galaxies implies that this is just one piece of a more complicated picture. We measure the kinematic misalignment angle, Psi, for the ETGs in the sample, to probe the intrinsic shapes of the galaxies. We find the majority of FRs (83 per cent) to be aligned, consistent with them being oblate spheroids (i.e. discs). The slow rotating ETGs (SRs), on the other hand, are significantly more likely to show kinematic misalignment (only 38 per cent are aligned). This confirms previous results that SRs are likely to be mildly triaxial systems
The SAMI Galaxy Survey: a new method to estimate molecular gas surface densities from star formation rates
Stars form in cold molecular clouds. However, molecular gas is difficult to observe because the most abundant molecule (H_2) lacks a permanent dipole moment. Rotational transitions of CO are often used as a tracer of H_2, but CO is much less abundant and the conversion from CO intensity to H2 mass is often highly uncertain. Here we present a new method for estimating the column density of cold molecular gas (Σ_(gas)) using optical spectroscopy. We utilize the spatially resolved Hα maps of flux and velocity dispersion from the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey. We derive maps of Σ_(gas) by inverting the multi-freefall star formation relation, which connects the star formation rate surface density (Σ_(SFR)) with Σ_(gas) and the turbulent Mach number (M). Based on the measured range of Σ_(SFR) = 0.005-1.5M⊙ yr^(−1) kpc^(−2) and M=18–130, we predict Σ_(gas) = 7–200 M⊙ pc^(−2)
in the star-forming regions of our sample of 260 SAMI galaxies. These values are close to previously measured Σ_(gas) obtained directly with unresolved CO observations of similar galaxies at low redshift. We classify each galaxy in our sample as ‘star-forming’ (219) or ‘composite/AGN/shock’ (41), and find that in ‘composite/AGN/shock’ galaxies the average Σ_(SFR),
M and Σ_(gas) are enhanced by factors of 2.0, 1.6 and 1.3, respectively, compared to star-forming galaxies. We compare our predictions of Σ_(gas) with those obtained by inverting the Kennicutt–Schmidt relation and find that our new method is a factor of 2 more accurate in predicting Σ_(gas), with an average deviation of 32 per cent from the actual Σ_(gas)
Defective ALC1 nucleosome remodeling confers PARPi sensitization and synthetic lethality with HRD.
Chromatin is a barrier to efficient DNA repair, as it hinders access and processing of certain DNA lesions. ALC1/CHD1L is a nucleosome-remodeling enzyme that responds to DNA damage, but its precise function in DNA repair remains unknown. Here we report that loss of ALC1 confers sensitivity to PARP inhibitors, methyl-methanesulfonate, and uracil misincorporation, which reflects the need to remodel nucleosomes following base excision by DNA glycosylases but prior to handover to APEX1. Using CRISPR screens, we establish that ALC1 loss is synthetic lethal with homologous recombination deficiency (HRD), which we attribute to chromosome instability caused by unrepaired DNA gaps at replication forks. In the absence of ALC1 or APEX1, incomplete processing of BER intermediates results in post-replicative DNA gaps and a critical dependence on HR for repair. Hence, targeting ALC1 alone or as a PARP inhibitor sensitizer could be employed to augment existing therapeutic strategies for HRD cancers.Work in I.A.’s group is funded by the WellcomeTrust (grant number 210634), BBSRC (BB/R007195/1), and Cancer ResearchUK (C35050/A22284). Work in D.A.’s group is funded by the Cancer ResearchUK Career Development Fellowship (grant number 16304). Work in the S.J.B.lab is supported by the Coun, which receives its core fundingfrom Cancer Research UK (FC0010048), the UK Medical Research Council(FC0010048), and the Wellcome Trust (FC0010048); a European Research Council (ERC) Advanced Investigator Grant (TelMetab); and Wellcome TrustSenior Investigator and Collaborative Grants. S.S.-B. was the recipient of an EMBO Long Term Fellowship (ALTF 707-2019) and a MSCA individual fellow-ship (grant 886577). Work in the J.R.C. group is funded by CRUK Career Devel-opment Fellowship (C52690/A19270) with infrastructural support from Well-come core award 090532/Z/09/ZS
Galaxy and mass assembly (GAMA): A deeper view of the mass, metallicity and SFR relationships
A full appreciation of the role played by gasmetallicity (Z), star formation rate (SFR) and stellar mass (M*) is fundamental to understanding how galaxies form and evolve. The connections between these three parameters at different redshifts significantl
The anatomy of the NGC 5044 group - I. Group membership and dynamics
We use a combination of new AAOmega multi-object wide-field spectroscopic
observations and literature data to define 111 spectroscopically confirmed
members of the massive NGC 5044 group with M_B <= -13.5 mag, providing a
three-fold increase in group members over previous analyses of this group. We
find the group to have a dynamical mass of 9.2 x 10^13 solar masses, placing it
on the border between rich groups and poor clusters. However, comparison to the
L_x-sigma and L_x-mass relations shows it more closely follows cluster scaling
relations. Using a combination of crossing time, X-ray contours and
line-of-sight velocity profile we are able to preclude growth of the NGC 5044
group via major sub-group mergers within the last ~1 Gyr. While the majority of
dynamical indicators for the group suggest it is virialised, we find evidence
for a small, dynamically distinct sub-group at 1.4 Mpc from the group centre,
suggesting that the NGC 5044 group is the dominant structure in its local
environment, and is currently accreting smaller groups.Comment: 18 pages, 17 figures, accepted by MNRAS. Updated to match proof
versio
The early-type galaxies NGC 1407 and NGC 1400 - I: spatially resolved radial kinematics and surface photometry
This is the first paper of a series focused on investigating the star
formation and evolutionary history of the two early-type galaxies NGC 1407 and
NGC 1400. They are the two brightest galaxies of the NGC 1407 (or Eridanus-A)
group, one of the 60 groups studied as part of the Group Evolution
Multi-wavelength Study (GEMS). Here we present new high signal-to-noise
long-slit spectroscopic data obtained at the ESO 3.6m telescope and
high-resolution multi-band imaging data from the HST/ACS and wide-field imaging
from Subaru Suprime-Cam. We spatially resolved integrated spectra out to 0.6
(NGC 1407) and 1.3 (NGC 1400) effective radii. The radial profiles of the
kinematic parameters v(rot), sigma, h3 and h4 are measured. The surface
brightness profiles are fitted to different galaxy light models and the colour
distributions analysed. The multi-band images are modelled to derive isophotal
shape parameters and residual galaxy images. The parameters from the surface
brightness profile fitting are used to estimate the mass of the possible
central supermassive black hole in NGC 1407. The galaxies are found to be
rotationally supported and to have a flat core in the surface brightness
profiles. Elliptical isophotes are observed at all radii and no fine structures
are detected in the residual galaxy images. From our results we can also
discard a possible interaction between NGC 1400, NGC 1407 and the group
intergalactic medium. We estimate a mass of 1.03x10^9 M(sun) for the
supermassive black hole in NGC 1407 galaxy.Comment: 11 pages, 6 tables, 6 figures, Accepted for publication in MNRA
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