22 research outputs found
Identifying Blue Horizontal Branch Stars Using the z Filter
In this paper we present a new method for selecting blue horizontal branch
(BHB) candidates based on color-color photometry. We make use of the Sloan
Digital Sky Survey z band as a surface gravity indicator and show its value for
selecting BHB stars from quasars, white dwarfs and main sequence A type stars.
Using the g, r, i, and z bands, we demonstrate that extraction accuracies on
par with more traditional u, g, and r photometric selection methods may be
achieved. We also show that the completeness necessary to probe major Galactic
structure may be maintained. Our new method allows us to efficiently select BHB
stars from photometric sky surveys that do not include a u band filter such as
the Panoramic Survey Telescope and Rapid Response System.Comment: Accepted for publication in The Astronomical Journa
SDSS J122958.84+000138.0: A Compact, Optically red galaxy
We report a new compact galaxy, SDSS J122958.84+000138.0 (SDSS J1229+0001),
which has unique morphological and stellar population properties that are rare
in observations of the nearby universe. SDSS J1229+0001 has an -band
absolute magnitude (M) and half-light radius (R) of 17.75 mag
and 520 pc, respectively. Located in a fairly low density environment,
morphologically it is akin to a typical early-type galaxy as it has a smooth
appearance and red colour. But, interestingly, it possesses centrally
concentrated star forming activity with a significant amount of dust. We
present an analysis of structural and stellar population properties using
archival images and VLT/FORS2 spectroscopy. Analysis of UKIDSS H-band image
shows that the observed light distribution is better fitted with two components
S\'ersic function with inner and outer component effective radii 190 and 330
pc, respectively. Whereas, overall half-light radius measured in H-band is much
smaller compared to optical, i.e 290 pc. We prepared a Spectral Energy
Distribution (SED) from optical to FIR and interpret it to derive
star-formation rate, dust mass and stellar mass. We find that the SDSS
J1229+0001 has dust mass M = 5.1 10 M_{\sun} with a
dust to stellar mass ratio log(M/M) = 3.5. While the observed
stellar population properties are -- to some extent -- similar to that of a
typical S0 galaxy, a unified view from stellar population and structural
properties may suggests that SDSS J1229+0001 is a {\it smoking gun} example of
a compact early-type galaxy in formation.Comment: 10 pages, Accepted MNRA
Establishing a national mortality review programme for people with intellectual disabilities:the experience in England
Inferring the Andromeda Galaxy's mass from its giant southern stream with Bayesian simulation sampling
M31 has a giant stream of stars extending far to the south and a great deal
of other tidal debris in its halo, much of which is thought to be directly
associated with the southern stream. We model this structure by means of
Bayesian sampling of parameter space, where each sample uses an N-body
simulation of a satellite disrupting in M31's potential. We combine constraints
on stellar surface densities from the Isaac Newton Telescope survey of M31 with
kinematic data and photometric distances. This combination of data tightly
constrains the model, indicating a stellar mass at last pericentric passage of
log(M_s / Msun) = 9.5+-0.1, comparable to the LMC. Any existing remnant of the
satellite is expected to lie in the NE Shelf region beside M31's disk, at
velocities more negative than M31's disk in this region. This rules out the
prominent satellites M32 or NGC 205 as the progenitor, but an overdensity
recently discovered in M31's NE disk sits at the edge of the progenitor
locations found in the model. M31's virial mass is constrained in this model to
be log(M200) = 12.3+-0.1, alleviating the previous tension between
observational virial mass estimates and expectations from the general galactic
population and the timing argument. The techniques used in this paper, which
should be more generally applicable, are a powerful method of extracting
physical inferences from observational data on tidal debris structures.Comment: 27 pages, 10 figures. Accepted by MNRA
The AIMSS Project – II. Dynamical-to-stellar mass ratios across the star cluster–galaxy divide
The previously clear division between small galaxies and massive star clusters is now occupied by objects called ultra-compact dwarfs (UCDs) and compact ellipticals (cEs). Here we combine a sample of UCDs and cEs with velocity dispersions from the AIMSS project with literature data to explore their dynamical-to-stellar mass ratios. We confirm that the mass ratios of many UCDs in the stellar mass range 1
The AIMSS Project – III. The Stellar Populations of Compact Stellar Systems
In recent years, a growing zoo of compact stellar systems (CSSs) have been found whose physical properties (mass, size, velocity dispersion) place them between classical globular clusters (GCs) and true galaxies, leading to debates about their nature. Here we present results using a so far underutilized discriminant, their stellar population properties. Based on new spectroscopy from 8–10m telescopes, we derive ages, metallicities, and [α/Fe] of 29 CSSs. These range from GCs with sizes of merely a few parsec to compact ellipticals (cEs) larger than M32. Together with a literature compilation, this provides a panoramic view of the stellar population characteristics of early-type systems. We find that the CSSs are predominantly more metal rich than typical galaxies at the same stellar mass. At high mass, the cEs depart from the mass–metallicity relation of massive early-type galaxies, which forms a continuous sequence with dwarf galaxies. At lower mass, the metallicity distribution of ultracompact dwarfs (UCDs) changes at a few times 107 M⊙, which roughly coincides with the mass where luminosity function arguments previously suggested the GC population ends. The highest metallicities in CSSs are paralleled only by those of dwarf galaxy nuclei and the central parts of massive early types. These findings can be interpreted as CSSs previously being more massive and undergoing tidal interactions to obtain their current mass and compact size. Such an interpretation is supported by CSSs with direct evidence for tidal stripping, and by an examination of the CSS internal escape velocities
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 */M⊙9) 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 Astronómicas y GeofÃsicasInstituto de AstrofÃsica 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 */M⊙9) 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 Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat
The remnants of galaxy formation from a panoramic survey of the region around M31
In hierarchical cosmological models, galaxies grow in mass through the
continual accretion of smaller ones. The tidal disruption of these systems is
expected to result in loosely bound stars surrounding the galaxy, at distances
that reach times the radius of the central disk. The number,
luminosity and morphology of the relics of this process provide significant
clues to galaxy formation history, but obtaining a comprehensive survey of
these components is difficult because of their intrinsic faintness and vast
extent. Here we report a panoramic survey of the Andromeda galaxy (M31). We
detect stars and coherent structures that are almost certainly remnants of
dwarf galaxies destroyed by the tidal field of M31. An improved census of their
surviving counterparts implies that three-quarters of M31's satellites brighter
than await discovery. The brightest companion, Triangulum (M33), is
surrounded by a stellar structure that provides persuasive evidence for a
recent encounter with M31. This panorama of galaxy structure directly confirms
the basic tenets of the hierarchical galaxy formation model and reveals the
shared history of M31 and M33 in the unceasing build-up of galaxies.Comment: Published in Nature. Supplementary movie available at
https://www.astrosci.ca/users/alan/PANDAS/Latest%20news%3A%20movie%20of%20orbit.htm
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 */M⊙9) 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 Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat