24 research outputs found
Evidence for non-axisymmetry in M31 from wide-field kinematics of stars and gas
As the nearest large spiral galaxy, M31 provides a unique opportunity to
learn about the structure and evolutionary history of this galaxy type in great
detail. Among the many observing programs aimed at M31 are microlensing
studies, which require good three-dimensional models of the stellar mass
distribution. Possible non-axisymmetric structures like a bar need to be taken
into account. Due to M31's high inclination, the bar is difficult to detect in
photometry alone. Therefore, detailed kinematic measurements are needed to
constrain the possible existence and position of a bar in M31. We obtained
220 separate fields with the optical IFU spectrograph VIRUS-W,
covering the whole bulge region of M31 and parts of the disk. We derive stellar
line-of-sight velocity distributions from the stellar absorption lines, as well
as velocity distributions and line fluxes of the emission lines H,
[OIII] and [NI]. Our data supersede any previous study in terms of spacial
coverage and spectral resolution. We find several features that are indicative
of a bar in the kinematics of the stars, we see intermediate plateaus in the
velocity and the velocity dispersion, and correlation between the higher moment
and the velocity. The gas kinematics is highly irregular, but is
consistent with non-triaxial streaming motions caused by a bar. The morphology
of the gas shows a spiral pattern, with seemingly lower inclination than the
stellar disk. We also look at the ionization mechanisms of the gas, which
happens mostly through shocks and not through starbursts.Comment: 23 pages, 39 figures; accepted for publication in A&
Re-growth of stellar disks in mature galaxies: The two component nature of NGC 7217 revisited with VIRUS-W
Previous studies have reported the existence of two counter-rotating stellar
disks in the early-type spiral galaxy NGC7217. We have obtained high-resolution
optical spectroscopic data (R ~ 9000) with the new fiber-based Integral Field
Unit instrument VIRUS-W at the 2.7m telescope of the McDonald Observatory in
Texas. Our analysis confirms the existence of two components. However, we find
them to be co-rotating. The first component is the more luminous (~ 77% of the
total light), has the higher velocity dispersion (~ 170 km/s) and rotates
relatively slowly (projected = 50 km/s). The lower luminosity second
component, (~ 23% of the total light), has a low velocity dispersion (~ 20
km/s) and rotates quickly (projected = 150 km/s). The difference in
the kinematics of the two stellar components allows us to perform a kinematic
decomposition and to measure the strengths of their Mg and Fe Lick indices
separately. The rotational velocities and dispersions of the less luminous and
faster component are very similar to those of the interstellar gas as measured
from the [OIII] emission. Morphological evidence of active star formation in
this component further suggests that NGC7217 may be in the process of
(re)growing a disk inside a more massive and higher dispersion stellar halo.
The kinematically cold and regular structure of the gas disk in combination
with the central almost dust-free morphology allows us to compare the dynamical
mass inside of the central 500pc with predictions from a stellar population
analysis. We find agreement between the two if a Kroupa stellar initial mass
function is assumed.Comment: accepted for publication by MNRA
Central rotations of Milky Way Globular Clusters
Most Milky Way globular clusters (GCs) exhibit measurable flattening, even if
on a very low level. Both cluster rotation and tidal fields are thought to
cause this flattening. Nevertheless, rotation has only been confirmed in a
handful of GCs, based mostly on individual radial velocities at large radii. We
are conducting a survey of the central kinematics of Galactic GCs using the new
Integral Field Unit instrument VIRUS-W. We detect rotation in all 11 GCs that
we have observed so far, rendering it likely that a large majority of the Milky
Way GCs rotate. We use published catalogs of the ACS survey of GCs to derive
central ellipticities and position angles. We show that in all cases where the
central ellipticity permits an accurate measurement of the position angle,
those angles are in excellent agreement with the kinematic position angles that
we derive from the VIRUS-W velocity fields. We find an unexpected tight
correlation between central rotation and outer ellipticity, indicating that
rotation drives flattening for the objects in our sample. We also find a tight
correlation between central rotation and published values for the central
velocity dispersion, most likely due to rotation impacting the old dispersion
measurements.Comment: 6 pages, 3 figures; accepted for publication in ApJ Letter
Spectroscopic decomposition of NGC 3521: unveiling the properties of the bulge and disc
We study the kinematics and the stellar populations of the bulge and disc of
the spiral galaxy NGC 3521. At each position in the field of view, we separate
the contributions of the bulge and the disc from the total observed spectrum
and study their kinematics, age, and metallicities independently. Their
properties are clearly distinct: the bulge rotates more slowly, has a higher
velocity dispersion, and is less luminous than the disc. We identify three main
populations of stars in NGC 3521: old ( Gyr), intermediate ( 3
Gyr), and young (1 Gyr). The mass and light of NGC 3521 are dominated by
the intermediate stellar population. The youngest population contributes mostly
to the disc component and its contribution increases with radius. We also study
the luminosity-weighed properties of the stars in NGC 3521. Along the
photometric major axis, we find: i) no age gradient for the stars in the bulge,
and a negative age gradient for the stars in the disc; ii) negative metallicity
gradients and sub-solar -enhancement for both the bulge and the disc.
We propose the following picture for the formation of NGC 3521: initial
formation a long time ago ( Gyr), followed by a second burst of star
formation or a merger ( 3 Gyrs ago), which contributed predominantly
to the mass-build up of the bulge. Recently ( Gyr), the disc of NGC
3521 experienced an additional episode of star formation that started in the
innermost regions.Comment: 13 pages, 11 figures, accepted for publication in MNRA
Dwarf Galaxy Dark Matter Density Profiles Inferred from Stellar and Gas Kinematics
We present new constraints on the density profiles of dark matter (DM) halos
in seven nearby dwarf galaxies from measurements of their integrated stellar
light and gas kinematics. The gas kinematics of low mass galaxies frequently
suggest that they contain constant density DM cores, while N-body simulations
instead predict a cuspy profile. We present a data set of high resolution
integral field spectroscopy on seven galaxies and measure the stellar and gas
kinematics simultaneously. Using Jeans modeling on our full sample, we examine
whether gas kinematics in general produce shallower density profiles than are
derived from the stars. Although 2/7 galaxies show some localized differences
in their rotation curves between the two tracers, estimates of the central
logarithmic slope of the DM density profile, gamma, are generally robust. The
mean and standard deviation of the logarithmic slope for the population are
gamma=0.67+/-0.10 when measured in the stars and gamma=0.58+/-0.24 when
measured in the gas. We also find that the halos are not under concentrated at
the radii of half their maximum velocities. Finally, we search for correlations
of the DM density profile with stellar velocity anisotropy and other baryonic
properties. Two popular mechanisms to explain cored DM halos are an exotic DM
component or feedback models that strongly couple the energy of supernovae into
repeatedly driving out gas and dynamically heating the DM halos. We investigate
correlations that may eventually be used to test models. We do not find a
secondary parameter that strongly correlates with the central DM density slope,
but we do find some weak correlations. Determining the importance of these
correlations will require further model developments and larger observational
samples. (Abridged)Comment: 29 pages, 18 figures, 10 tables, accepted for publication in Ap
Absorption Troughs of Lyman Alpha Emitters in HETDEX
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is designed to
detect and measure the redshifts of more than one million Ly emitting
galaxies (LAEs) between . In addition to its cosmological
measurements, these data enable studies of Ly spectral profiles and the
underlying radiative transfer. Using the roughly half a million LAEs in the
HETDEX Data Release 3, we stack various subsets to obtain the typical
Ly profile for the epoch and to understand their physical
properties. We find clear absorption wings around Ly emission, which
extend km both redward and blueward of the
central line. Using far-UV spectra of nearby () LAEs in the
CLASSY treasury and optical/near-IR spectra of LAEs in the
MUSE-Wide survey, we observe absorption profiles in both redshift regimes.
Dividing the sample by volume density shows that the troughs increase in higher
density regions. This trend suggests that the depth of the absorption is
dependent on the local density of objects near the LAE, a geometry that is
similar to damped Lyman- systems. Simple simulations of Ly
radiative transfer can produce similar troughs due to absorption of light from
background sources by HI gas surrounding the LAEs.Comment: 15 pages, 10 figures, accepted for publication in The Astrophysical
Journa
Absorption Troughs of Lyα Emitters in HETDEX
The Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) is designed to detect and measure the redshifts of more than 1 million Lyα emitting galaxies (LAEs) 1.88 < z < 3.52. In addition to its cosmological measurements, these data enable studies of Lyα spectral profiles and the underlying radiative transfer. Using the roughly half a million LAEs in the HETDEX Data Release 3, we stack various subsets to obtain the typical Lyα profile for the z ∼ 2-3 epoch and to understand their physical properties. We find clear absorption wings around Lyα emission, which extend ∼2000 km s−1 both redward and blueward of the central line. Using far-UV spectra of nearby (0.002 < z < 0.182) LAEs in the COS Legacy Archive Spectroscopic Survey treasury and optical/near-IR spectra of 2.8 < z < 6.7 LAEs in the Multi Unit Spectroscopic-Wide survey, we observe absorption profiles in both redshift regimes. Dividing the sample by volume density shows that the troughs increase in higher-density regions. This trend suggests that the depth of the absorption is dependent on the local density of objects near the LAE, a geometry that is similar to damped Lyα systems. Simple simulations of Lyα radiative transfer can produce similar troughs due to absorption of light from background sources by H i gas surrounding the LAEs
Kinematic Signatures of Bulges Correlate with Bulge Morphologies and S\'ersic Index
We use the Marcario Low Resolution Spectrograph (LRS) at the
Hobby-Eberly-Telescope (HET) to study the kinematics of pseudobulges and
classical bulges in the nearby universe. We present major-axis rotational
velocities, velocity dispersions, and h3 and h4 moments derived from
high-resolution (sigma ~ 39 km/s) spectra for 45 S0 to Sc galaxies; for 27 of
the galaxies we also present minor axis data. We combine our kinematics with
bulge-to-disk decompositions. We demonstrate for the first time that purely
kinematic diagnostics of the bulge dichotomy agree systematically with those
based on S\'ersic index. Low S\'ersic index bulges have both increased
rotational support (higher v/sigma values) and on average lower central
velocity dispersions. Furthermore, we confirm that the same correlation also
holds when visual morphologies are used to diagnose bulge type. The previously
noted trend of photometrically flattened bulges to have shallower velocity
dispersion profiles turns to be significant and systematic if the S\'ersic
index is used to distinguish between pseudobulges and classical bulges. The
correlation between h3 and v/sigma observed in elliptical galaxies is also
observed in intermediate type galaxies, irrespective of bulge type. Finally, we
present evidence for formerly undetected counter rotation in the two systems
NGC 3945 and NGC 4736.
Based on observations obtained with the Hobby-Eberly Telescope, which is a
joint project of the University of Texas at Austin, the Pennsylvania State
University, Stanford University, Ludwig-Maximilians-Universit\"at M\"unchen,
and Georg-August-Universit\"at G\"ottingen.Comment: 49 pages, 16 figures. Accepted for publication in Ap
HETDEX Public Source Catalog 1 -- Stacking 50K Lyman Alpha Emitters
We describe the ensemble properties of the Lyman Alpha
Emitters (LAEs) found in the HETDEX survey's first public data release, HETDEX
Public Source Catalog 1 (Mentuch Cooper et al. 2023). Stacking the
low-resolution ( 800) spectra greatly increases the signal-to-noise
ratio, revealing spectral features otherwise hidden by noise, and we show that
the stacked spectrum is representative of an average member of the set. The
flux limited, Ly signal-to-noise ratio restricted stack of 50K HETDEX
LAEs shows the ensemble biweight ``average" LAE to be a blue (UV
continuum slope and E(B-V) ), moderately bright
(M) star forming galaxy with strong Ly
emission (log 42.8 and (Ly)
114\AA), and potentially significant leakage of ionizing radiation. The
restframe UV light is dominated by a young, metal poor stellar population with
an average age 5-15 Myr and metallicity of 0.2-0.3 Z.Comment: 17 pages, 11 figures, 2 data files (ApJ Accepted
Prime Focus Spectrograph (PFS) for the Subaru Telescope: Overview, recent progress, and future perspectives
PFS (Prime Focus Spectrograph), a next generation facility instrument on the
8.2-meter Subaru Telescope, is a very wide-field, massively multiplexed,
optical and near-infrared spectrograph. Exploiting the Subaru prime focus, 2394
reconfigurable fibers will be distributed over the 1.3 deg field of view. The
spectrograph has been designed with 3 arms of blue, red, and near-infrared
cameras to simultaneously observe spectra from 380nm to 1260nm in one exposure
at a resolution of ~1.6-2.7A. An international collaboration is developing this
instrument under the initiative of Kavli IPMU. The project is now going into
the construction phase aiming at undertaking system integration in 2017-2018
and subsequently carrying out engineering operations in 2018-2019. This article
gives an overview of the instrument, current project status and future paths
forward.Comment: 17 pages, 10 figures. Proceeding of SPIE Astronomical Telescopes and
Instrumentation 201