50 research outputs found
Detailed stellar population analysis of Early-Type galaxies with redshift to constrain their evolution
Una de las cuestiones básicas de la AstronomÃa moderna es cómo las galaxias
de las diferentes familias han evolucionado desde su formación. Una de estas
familias, las galaxias de tipos tempranos (ETGs, del inglés Early-Type Galaxy),
formadas por galaxias elÃpticas y lenticulares, que contienen la mayor parte de
la materia luminosa del Universo, ha sido profundamente estudiada durante
décadas. En esta tesis se propone esclarecer este tema, analizando las poblaciones
estelares de las ETGs masivas a trav´es del tiempo cósmico desde diferentes
puntos de vista. Para tal fin, explotamos las nuevas herramientas y métodos de
última generación, como el ajuste completo del espectro (full-spectral-fitting)
combinado con el análisis de los Ãndices espectrales mediante los diagramas
Ãndice-Ãndice. La novedad de este trabajo est´a en el estudio detallado de las
poblaciones estelares, llevado a cabo galaxia por galaxia incluso a alto desplazamiento
al rojo. Este conjunto de observaciones y métodos utilizados, permite
acotar los diferentes escenarios propuestos para la formación y evolución de las
ETGs
On the Stellar Kinematics and Mass of the Virgo Ultra-Diffuse Galaxy VCC 1287
Here, we present a kinematical analysis of the Virgo cluster ultra-diffuse
galaxy (UDG) VCC 1287 based on data taken with the Keck Cosmic Web Imager
(KCWI). We confirm VCC 1287's association both with the Virgo cluster and its
globular cluster (GC) system, measuring a recessional velocity of $1116 \pm 2\
\mathrm{km\ s^{-1}}19 \pm 6\
\mathrm{km\ s^{-1}}1.11^{+0.81}_{-0.81}
\times 10^{9} \ \mathrm{M_{\odot}}13^{+11}_{-11}$)
within the half light radius (4.4 kpc). This places VCC 1287 slightly above the
well established relation for normal galaxies, with a higher mass to light
ratio for its dynamical mass than normal galaxies. We use our dynamical mass,
and an estimate of GC system richness, to place VCC 1287 on the GC number --
dynamical mass relation, finding good agreement with a sample of normal
galaxies. Based on a total halo mass derived from GC counts, we then infer that
VCC 1287 likely resides in a cored or low concentration dark matter halo. Based
on the comparison of our measurements to predictions from simulations, we find
that strong stellar feedback and/or tidal effects are plausibly the dominant
mechanisms in the formation of VCC 1287. Finally, we compare our measurement of
the dynamical mass with those for other UDGs. These dynamical mass estimates
suggest relatively massive halos and a failed galaxy origin for at least some
UDGs.Comment: 13 pages, 10 figures with an additional 5 pages and 5 figures in
appendices. Accepted for publication in MNRAS. v2: with small updates from
publication formatting and a minor plotting fix for Fig. 1
Keck Cosmic Web Imager (KCWI) Spectra of Globular Clusters and Ultra Compact Dwarfs in the Halo of M87
Using the Keck Cosmic Web Imager we obtain spectra of several globular
clusters (GCs), ultra compact dwarfs (UCDs) and the inner halo starlight of
M87, at a similar projected galactocentric radius of 5 kpc. This enables
us, for the first time, to apply the same stellar population analysis to the
GCs, UCDs and starlight consistently to derive ages, metallicities and
alpha-element abundances in M87. We find evidence for a dual stellar population
in the M87 halo light, i.e an 80\% component by mass which is old and
metal-rich and a 20\% component which is old but metal-poor. Two red GCs
share similar stellar populations to the halo light suggesting they may have
formed contemporaneously with the dominant halo component. Three UCDs, and one
blue GC, have similar stellar populations, with younger mean ages, lower
metallicities and near solar alpha-element abundances. Combined with literature
data, our findings are consistent with the scenario that UCDs are the remnant
nucleus of a stripped galaxy. We further investigate the discrepancy in the
literature for M87's kinematics at large radii, favouring a declining velocity
dispersion profile. This work has highlighted the need for more self-consistent
studies of galaxy halos.Comment: 12 pages, 10 figures, accepted for publication in MNRA
NGC 474 as viewed with KCWI: diagnosing a shell galaxy
We present new spectra obtained using Keck/KCWI and perform kinematics and
stellar population analyses of the shell galaxy NGC 474, from both the galaxy
centre and a region from the outer shell. We show that both regions have
similarly extended star formation histories although with different stellar
population properties. The central region of NGC 474 is dominated by
intermediate-aged stars (8.3 \pm 0.3 Gyr) with subsolar metallicity ([Z/H]=
-0.24 \pm 0.07 dex) while the observed shell region, which hosts a substantial
population of younger stars, has a mean luminosity-weighted age of 4.0 \pm 0.5
Gyr with solar metallicities ([Z/H]=-0.03 \pm 0.09 dex). Our results are
consistent with a scenario in which NGC 474 experienced a major to intermediate
merger with a log mass satellite galaxy at least \sim 2
Gyr ago which produced its shell system. This work shows that the direct
spectroscopic study of low-surface brightness stellar features, such as shells,
is now feasible and opens up a new window to understanding galaxy formation and
evolution.Comment: Accepted for publication in MNRAS, 6 pages, 5 figure
Keck Spectroscopy of the Coma Cluster Ultra-Diffuse Galaxy Y358: Dynamical Mass in a Wider Context
We examine ultra-diffuse galaxies (UDGs) and their relation to non-UDGs in
mass-radius-luminosity space. We begin by publishing Keck/KCWI spectroscopy for
the Coma cluster UDG Y358, for which we measure both a recessional velocity and
velocity dispersion. Our recessional velocity confirms association with the
Coma cluster and Y358's status as a UDG. From our velocity dispersion (19
3 km s) we calculate a dynamical mass within the half-light radius which
provides evidence for a core in Y358's dark matter halo. We compare this
dynamical mass, along with those for globular cluster (GC)-rich/-poor UDGs in
the literature, to mass profiles for isolated, gas-rich UDGs and UDGs in the
NIHAO/FIRE simulations. We find GC-poor UDGs have dynamical masses similar to
isolated, gas-rich UDGs, suggesting an evolutionary pathway may exist between
the two. Conversely, GC-rich UDGs have dynamical masses too massive to be
easily explained as the evolution of the isolated, gas-rich UDGs. The simulated
UDGs match the dynamical masses of the GC-rich UDGs. However, once compared in
stellar mass -- halo mass space, the FIRE/NIHAO simulated UDGs do not match the
halo masses of either the isolated, gas-rich UDGs or the GC-rich UDGs at the
same stellar mass. Finally, we supplement our data for Y358 with other UDGs
that have measured velocity dispersions in the literature. We compare this
sample to a wide range of non-UDGs in mass-radius-luminosity space, finding
UDGs have a similar locus to non-UDGs of similar luminosity with the primary
difference being their larger half-light radii.Comment: 16 pages, 9 figures, accepted for publication in MNRA
On the stellar kinematics and mass of the Virgo ultradiffuse galaxy VCC 1287
Here, we present a kinematical analysis of the Virgo cluster ultradiffuse galaxy (UDG) VCC 1287 based on data taken with the Keck Cosmic Web Imager (KCWI). We confirm VCC 1287\u27s association both with the Virgo cluster and its globular cluster (GC) system, measuring a recessional velocity of 1116 ± 2 km s-1. We measure a stellar velocity dispersion (19 ± 6 km s-1) and infer both a dynamical mass () and mass-To-light ratio (M/L) () within the half-light radius (4.4 kpc). This places VCC 1287 slightly above the well-established relation for normal galaxies, with a higher M/L for its dynamical mass than normal galaxies. We use our dynamical mass, and an estimate of GC system richness, to place VCC 1287 on the GC number-dynamical mass relation, finding good agreement with a sample of normal galaxies. Based on a total halo mass derived from GC counts, we then infer that VCC 1287 likely resides in a cored or low-concentration dark matter halo. Based on the comparison of our measurements to predictions from simulations, we find that strong stellar feedback and/or tidal effects are plausibly the dominant mechanisms in the formation of VCC 1287. Finally, we compare our measurement of the dynamical mass with those for other UDGs. These dynamical mass estimates suggest relatively massive haloes and a failed galaxy origin for at least some UDGs
Ultra deep sub-kpc view of nearby massive compact galaxies
Using Gemini North telescope ultra deep and high resolution (sub-kpc) K-band
adaptive optics imaging of a sample of 4 nearby (z~0.15) massive
(~10^{11}M_sun) compact (R<1.5 kpc) galaxies, we have explored the structural
properties of these rare objects with an unprecedented detail. Our surface
brightness profiles expand over 12 magnitudes in range allowing us to explore
the presence of any faint extended envelope on these objects down to stellar
mass densities ~10^{6} M_sun/kpc^{2} at radial distances of ~15 kpc. We find no
evidence for any extended faint tail altering the compactness of these
galaxies. Our objects are elongated, resembling visually S0 galaxies, and have
a central stellar mass density well above the stellar mass densities of objects
with similar stellar mass but normal size in the present universe. If these
massive compact objects will eventually transform into normal size galaxies,
the processes driving this size growth will have to migrate around
2-3x10^{10}M_sun stellar mass from their inner (R<1.7 kpc) region towards their
outskirts. Nearby massive compact galaxies share with high-z compact massive
galaxies not only their stellar mass, size and velocity dispersion but also the
shape of their profiles and the mean age of their stellar populations. This
makes these singular galaxies unique laboratories to explore the early stages
of the formation of massive galaxies.Comment: Accepted for publication in ApJ Letter. Version revised to match the
accepted versio