91 research outputs found
Bridging the gap in the mass-size relation of compact galaxies with MaNGA
We present the analysis of the full MaNGA DR17 sample to characterize its
population of compact galaxies. We focus on galaxies that fill the stellar mass
(M) gap between compact elliptical galaxies (cEs; ) and compact massive galaxies
(CMGs; ). We study their
stellar populations and kinematics to reveal how their properties depend on
stellar mass. We select compact galaxies in the MaNGA DR17 sample according to
their effective radius () and stellar mass. 37 galaxies fulfill our
selection criteria in the bridging region between cEs and CMGs. We derive their
kinematics and stellar population parameters from the stacked spectra at
1~ using a full spectral fitting routine. We then classify the selected
compact galaxies in three main groups based on their stellar population
properties. One of the groups shows characteristics compatible with relic
galaxies, i.e. galaxies that have remained mostly unchanged since their early
formation epoch (). Another group shows more extended and continuous
star formation histories (SFHs). The third group shows a low star-forming rate
at initial times, which increases at around Gyr. We compare the derived
properties of the selected galaxies with those of previously studied compact
galaxies at different mass ranges. The selected galaxies successfully fill the
mass gap between cEs and CMGs. Their properties are compatible with the
assumption that the scaling relations of compact galaxies at different mass
ranges are related, although galaxies in the first group are clear outliers in
the fundamental plane, suggesting different formation mechanisms for this relic
population.Comment: 16 pages, 14 figures, 2 table
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
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
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
Low-metallicity globular clusters in the low-mass isolated spiral galaxy NGC 2403
The globular cluster (GC) systems of low-mass late-type galaxies, such as NGC 2403, have been poorly studied to date. As a low mass galaxy (M∗ = 7 × 109 Mz.ast;), cosmological simulations predict NGC 2403 to contain few, if any, accreted GCs. It is also isolated, with a remarkably undisturbed HI disc. Based on candidates from the literature, Sloan Digital Sky Survey and Hyper Suprime-Cam imaging, we selected several GCs for follow-up spectroscopy using the Keck Cosmic Web Imager. From their radial velocities and other properties, we identify eight bona-fide GCs associated with either the inner halo or the disc of this bulgeless galaxy. A stellar population analysis suggests a wide range of GC ages from shortly after the big bang until the present day. We find all of the old GCs to be metal-poor with [Fe/H] ≤ -1. The age-metallicity relation for the observed GCs suggests that they were formed over many Gyr from gas with a low effective yield, similar to that observed in the SMC. Outflows of enriched material may have contributed to the low yield. With a total system of ∼50 GCs expected, our study is the first step in fully mapping the star cluster history of NGC 2403 in both space and time
Stellar velocity dispersion and dynamical mass of the ultra diffuse galaxy NGC 5846_UDG1 from the keck cosmic web imager
The ultra diffuse galaxy in the NGC 5846 group (NGC 5846 UDG1) was shown to have a large number of globular cluster (GC) candidates from deep imaging as part of the VEGAS survey. Recently, Muller et al. published a velocity dispersion, based ¨ on a dozen of its GCs. Within their quoted uncertainties, the resulting dynamical mass allowed for either a dark matter free or a dark-matter-dominated galaxy. Here, we present spectra from KCWI that reconfirms membership of the NGC 5846 group and reveals a stellar velocity dispersion for UDG1 of σ GC = 17 ± 2 km s−1. Our dynamical mass, with a reduced uncertainty, indicates a very high contribution of dark matter within the effective radius. We also derive an enclosed mass from the locations and motions of the GCs using the tracer mass estimator, finding a similar mass inferred from our stellar velocity dispersion. We find no evidence that the galaxy is rotating and is thus likely pressure supported. The number of confirmed GCs, and the total number inferred for the system (∼45), suggests a total halo mass of ∼2 × 1011 M. A cored mass profile is favoured when compared to our dynamical mass. Given its stellar mass of 1.1 × 108 M, NGC 5846 UDG1 appears to be an ultra diffuse galaxy with a dwarf-like stellar mass and an overly massive halo
The massive relic galaxy NGC 1277 is dark matter deficient. From dynamical models of integral-field stellar kinematics out to five effective radii
According to the CDM cosmology, present-day galaxies with stellar
masses should contain a sizable fraction of
dark matter within their stellar body. Models indicate that in massive
early-type galaxies (ETGs) dark matter should account for of the
dynamical mass within five effective radii (). Most massive ETGs
have been shaped through a two-phase process: the rapid growth of a compact
core was followed by the accretion of an extended envelope through mergers. The
exceedingly rare galaxies that have avoided the second phase, the so-called
relic galaxies, are thought to be the frozen remains of the massive ETG
population at . The best relic galaxy candidate discovered to date
is NGC 1277, in the Perseus cluster. We used deep integral field GCMS data to
revisit NGC 1277 out to an unprecedented radius of 6 kpc (corresponding to ). By using Jeans anisotropic modelling we find a negligible dark
matter fraction within (; two-sigma
confidence level), which is in tension with the expectation. Since the lack of
an extended envelope would reduce dynamical friction and prevent the accretion
of an envelope, we propose that NGC 1277 lost its dark matter very early or
that it was dark matter deficient ab initio. We discuss our discovery in the
framework of recent proposals suggesting that some relic galaxies may result
from dark matter stripping as they fell in and interacted within galaxy
clusters. Alternatively, NGC 1277 might have been born in a high-velocity
collision of gas-rich proto-galactic fragments, where dark matter left behind a
disc of dissipative baryons. We speculate that the relative velocities of
required for the latter process to happen were
possible in the progenitors of the present-day rich galaxy clusters.Comment: Accepted for publication in A&
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