79 research outputs found
Implications for the origin of dwarf early-type galaxies: a detailed look at the isolated rotating dwarf early-type galaxy CG 611, with ramifications for the Fundamental Plane's (S_K)^2 kinematic scaling and the spin-ellipticity diagram
Selected from a sample of nine, isolated, dwarf early-type galaxies (ETGs)
having the same range of kinematic properties as dwarf ETGs in clusters, we use
CG 611 (LEDA 2108986) to address the Nature versus Nurture debate regarding the
formation of dwarf ETGs. The presence of faint disk structures and rotation
within some cluster dwarf ETGs has often been heralded as evidence that they
were once late-type spiral or dwarf irregular galaxies prior to experiencing a
cluster-induced transformation into an ETG. However, CG 611 also contains
significant stellar rotation (~20 km/s) over its inner half light radius,
R_(e,maj)=0.71 kpc, and its stellar structure and kinematics resemble those of
cluster ETGs. In addition to hosting a faint young nuclear spiral within a
possible intermediate-scale stellar disk, CG 611 has accreted an
intermediate-scale, counter-rotating gas disk. It is therefore apparent that
dwarf ETGs can be built by accretion events, as opposed to disk-stripping
scenarios. We go on to discuss how both dwarf and ordinary ETGs with
intermediate-scale disks, whether under (de)construction or not, are not fully
represented by the kinematic scaling S_0.5=sqrt{ 0.5(V_rot)^2 + sigma^2 }, and
we also introduce a modified spin-ellipticity diagram, lambda(R)-epsilon(R),
with the potential to track galaxies with such disks.Comment: 15 pages (includes 9 figures and an extensive 2+ page reference list
Dwarf galaxies in the Perseus Cluster: further evidence for a disc origin for dwarf ellipticals
We present the results of a Keck-ESI (Echellette Spectrograph and Imager) spectroscopic study of six dwarf elliptical (dE) galaxies in the Perseus Cluster core, and confirm two dwarfs as cluster members for the first time. All six dEs follow the sizeâmagnitude relation for dE/dSph galaxies. Central velocity dispersions are measured for three Perseus dwarfs in our sample, and all lie on the Ïâluminosity relation for early-type, pressure-supported systems. We furthermore examine SA 0426-002, a unique dE in our sample with a bar-like morphology surrounded by low surface brightness wings/lobes (ÎŒB = 27 mag arcsecÂŻÂČ). Given its morphology, velocity dispersion (Ïâ = 33.9 ± 6.1 km sâ»Âč), velocity relative to the brightest cluster galaxy NGC 1275 (2711 km sâ»Âč), size (Râ = 2.1 ± 0.10 kpc), and Sersic index ( ÂŽ n = 1.2 ± 0.02), we hypothesize the dwarf has morphologically transformed from a low-mass disc to dE via harassment. The low surface brightness lobes can be explained as a ring feature, with the bar formation triggered by tidal interactions via speed encounters with Perseus Cluster members. Alongside spiral structure found in dEs in Fornax and Virgo, SA 0426-002 provides crucial evidence that a fraction of bright dEs have a disc infall origin, and are not part of the primordial cluster population
Ultracompact dwarfs in the Perseus Cluster:UCD formation via tidal stripping
We present the results of a Keck/DEIMOS survey of Ultra Compact Dwarfs (UCDs)
in the Perseus Cluster core. We confirm cluster membership for 14 UCDs, with
radial velocities ~5300 km s. Two of these confirmed Perseus UCDs have
extremely blue colours ( mag), reside in star forming filaments
surrounding NGC 1275, and have likely formed as massive star clusters in the
last ~100 Myr. We also measure a central velocity dispersion of a third, UCD13
( km s), the most extended UCD in our sample. We
determine it to have radius pc, a dynamical mass of ( M, and a metallicity [Z/H] dex. UCD13 and the cluster's central galaxy, NGC 1275,
have a projected separation of 30 kpc and a radial velocity difference of ~20
km s. Based on its size, red colour, internal velocity dispersion,
dynamical mass, metallicity and proximity to NGC 1275, we argue that UCD13 is
likely the remnant nucleus of a tidally stripped dE, with this progenitor dE
having mag and mass M.Comment: 9 pages, 5 figures, accepted for publication in MNRA
Hubble Space Telescope survey of the Perseus Cluster -IV: Compact stellar systems in the Perseus Cluster core and Ultra Compact Dwarf formation in star forming filaments
We present the results of the first search for Ultra Compact Dwarfs (UCDs) in
the Perseus Cluster core, including the region of the cluster around the
unusual Brightest Cluster Galaxy (BCG) NGC 1275. Utilising Hubble Space
Telescope Advanced Camera for Surveys imaging, we identify a sample of 84 UCD
candidates with half-light radii 10 pc < r_e < 57 pc out to a distance of 250
kpc from the cluster centre, covering a total survey area of ~70 armin^2. All
UCDs in Perseus lie in the same size-luminosity locus seen for confirmed UCDs
in other regions of the local Universe. The majority of UCDs are brighter than
M_R = -10.5, and lie on an extrapolation of the red sequence followed by the
Perseus Cluster dwarf elliptical population to fainter magnitudes. However,
three UCD candidates in the vicinity of NGC 1275 are very blue, with colours
(B-R)_0 < 0.6 implying a cessation of star formation within the past 100 Myr.
Furthermore, large blue star clusters embedded in the star forming filaments
are highly indicative that both proto-globular clusters (GCs) and proto-UCDs
are actively forming at the present day in Perseus. We therefore suggest star
forming filaments as a formation site for some UCDs, with searches necessary in
other low redshift analogues of NGC 1275 necessary to test this hypothesis. We
also suggest that tidal disruption of dwarf galaxies is another formation
channel for UCD formation in the core of Perseus as tidal disruption is ongoing
in this region as evidenced by shells around NGC 1275. Finally, UCDs may simply
be massive GCs based on strong similarities in the colour trends of the two
populations.Comment: 18 pages, 20 figures, 3 tables. Accepted for publication in MNRA
The Resolved Stellar Halo of NGC 253
We have obtained Magellan/IMACS and HST/ACS imaging data that resolve red
giant branch stars in the stellar halo of the starburst galaxy NGC 253. The HST
data cover a small area, and allow us to accurately interpret the ground-based
data, which cover 30% of the halo to a distance of 30 kpc, allowing us to make
detailed quantitative measurements of the global properties and structure of a
stellar halo outside of the Local Group. The geometry of the halo is
significantly flattened in the same sense as the disk, with a projected axis
ratio of b/a ~ 0.35 +/- 0.1. The total stellar mass of the halo is estimated to
be M_halo ~ 2.5 +/- 1.5 x 10^9 M_sun, or 6% of the total stellar mass of the
galaxy, and has a projected radial dependence that follows a power law of index
-2.8 +/- 0.6, corresponding to a three-dimensional power law index of ~ -4. The
total luminosity and profile shape that we measure for NGC 253 are somewhat
larger and steeper than the equivalent values for the Milky Way and M31, but
are well within the scatter of model predictions for the properties of stellar
halos built up in a cosmological context. Structure within the halo is seen at
a variety of scales: there is small kpc-scale density variation and a large
shelf-like feature near the middle of the field. The techniques that have been
developed will be essential for quantitatively comparing our upcoming larger
sample of observed stellar halos to models of halo formation.Comment: ApJ, in press. Version with full resolution figures available at
http://www.astro.lsa.umich.edu/~jbailin/papers/bailin_n253halo.pd
The AIMSS Project : I. Bridging the star cluster-galaxy divide
We describe the structural and kinematic properties of the first compact stellar systems discovered by the Archive of Intermediate Mass Stellar Systems project. These spectroscopically confirmed objects have sizes (~6 e [pc] 6 */Mâ9) spanning the range of massive globular clusters, ultracompact dwarfs (UCDs) and compact elliptical galaxies (cEs), completely filling the gap between star clusters and galaxies. Several objects are close analogues to the prototypical cE, M32. These objects, which are more massive than previously discovered UCDs of the same size, further call into question the existence of a tight mass-size trend for compact stellar systems, while simultaneously strengthening the case for a universal 'zone of avoidance' for dynamically hot stellar systems in the mass-size plane. Overall, we argue that there are two classes of compact stellar systems (1) massive star clusters and (2) a population closely related to galaxies. Our data provide indications for a further division of the galaxy-type UCD/cE population into two groups, one population that we associate with objects formed by the stripping of nucleated dwarf galaxies, and a second population that formed through the stripping of bulged galaxies or are lower mass analogues of classical ellipticals. We find compact stellar systems around galaxies in low- to high-density environments, demonstrating that the physical processes responsible for forming them do not only operate in the densest clusters.Facultad de Ciencias AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
The AIMSS Project : I. Bridging the star cluster-galaxy divide
We describe the structural and kinematic properties of the first compact stellar systems discovered by the Archive of Intermediate Mass Stellar Systems project. These spectroscopically confirmed objects have sizes (~6 e [pc] 6 */Mâ9) spanning the range of massive globular clusters, ultracompact dwarfs (UCDs) and compact elliptical galaxies (cEs), completely filling the gap between star clusters and galaxies. Several objects are close analogues to the prototypical cE, M32. These objects, which are more massive than previously discovered UCDs of the same size, further call into question the existence of a tight mass-size trend for compact stellar systems, while simultaneously strengthening the case for a universal 'zone of avoidance' for dynamically hot stellar systems in the mass-size plane. Overall, we argue that there are two classes of compact stellar systems (1) massive star clusters and (2) a population closely related to galaxies. Our data provide indications for a further division of the galaxy-type UCD/cE population into two groups, one population that we associate with objects formed by the stripping of nucleated dwarf galaxies, and a second population that formed through the stripping of bulged galaxies or are lower mass analogues of classical ellipticals. We find compact stellar systems around galaxies in low- to high-density environments, demonstrating that the physical processes responsible for forming them do not only operate in the densest clusters.Facultad de Ciencias AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
Socioeconomic inequalities in attitudes to cancer: an international cancer benchmarking study
Socioeconomic status (SES) differences in attitudes towards cancer have been implicated in the differential screening uptake and the timeliness of symptomatic presentation. However, the predominant emphasis of this work has been on cancer fatalism, and many studies focus on specific community subgroups. This study aimed to assess SES differences in positive and negative attitudes towards cancer in UK adults. A population-based sample of UK adults (n=6965, age?50 years) completed the Awareness and Beliefs about Cancer scale, including six belief items: three positively framed (e.g. âCancer can often be curedâ) and three negatively framed (e.g. âA cancer diagnosis is a death sentenceâ). SES was indexed by education. Analyses controlled for sex, ethnicity, marital status, age, self-rated health, and cancer experience. There were few education-level differences for the positive statements, and overall agreement was high (all>90%). In contrast, there were strong differences for negative statements (all Ps<0.001). Among respondents with lower education levels, 57% agreed that âtreatment is worse than cancerâ, 27% that cancer is âa death sentenceâ and 16% âwould not want to know if I have cancerâ. Among those with university education, the respective proportions were 34, 17 and 6%. Differences were not explained by cancer experience or health status. In conclusion, positive statements about cancer outcomes attract near-universal agreement. However, this optimistic perspective coexists alongside widespread fears about survival and treatment, especially among less-educated groups. Health education campaigns targeting socioeconomically disadvantaged groups might benefit from a focus on reducing negative attitudes, which is not necessarily achieved by promoting positive attitudes
- âŠ