840 research outputs found
The fate of spiral galaxies in clusters: The star formation history of the anemic Virgo cluster galaxy NGC 4569
We present a new method for studying the star formation history of late-type cluster galaxies undergoing gas starvation or a ram pressure stripping event by combining bidimensional multifrequency observations with multizone models of galactic chemical and spectrophotometric evolution. This method is applied to the Virgo Cluster anemic galaxy NGC 4569. We extract radial profiles from recently obtained UV GALEX images at 1530 and 2310 Å, from visible and near-IR narrow (Hα) and broadband images at different wavelengths (u, B, g, V, r, i, z, J, H, and K), from Spitzer IRAC and MIPS images, and from atomic and molecular gas maps. The model in the absence of interaction (characterized by its rotation velocity and spin parameter) is constrained by the unperturbed H-band light profile and by the Hα rotation curve. We can reconstruct the observed total gas radial density profile and the light surface brightness profiles at all wavelengths in a ram pressure stripping scenario by making simple assumptions about the gas removal process and the orbit of NGC 4569 inside the cluster. The observed profiles cannot be reproduced by simply stopping gas infall, thus mimicking starvation. Gas removal is required, which is more efficient in the outer disk, inducing radial quenching in the star formation activity, as observed and reproduced by the model. This observational result, consistent with theoretical predictions that a galaxy cluster-IGM interaction is able to modify structural disk parameters without gravitational perturbations, is discussed in the framework of the origin of lenticular galaxies in cluster
Chemical evolution of the Milky Way: the origin of phosphorus
Context. Recently, for the first time the abundance of P has been measured in
disk stars. This provides the opportunity of comparing the observed abundances
with predictions from theoretical models. Aims. We aim at predicting the
chemical evolution of P in the Milky Way and compare our results with the
observed P abundances in disk stars in order to put constraints on the P
nucleosynthesis. Methods. To do that we adopt the two-infall model of galactic
chemical evolution, which is a good model for the Milky Way, and compute the
evolution of the abundances of P and Fe. We adopt stellar yields for these
elements from different sources. The element P should have been formed mainly
in Type II supernovae. Finally, Fe is mainly produced by Type Ia supernovae.
Results. Our results confirm that to reproduce the observed trend of [P/Fe] vs.
[Fe/H] in disk stars, P is formed mainly in massive stars. However, none of the
available yields for P can reproduce the solar abundance of this element. In
other words, to reproduce the data one should assume that massive stars produce
more P than predicted by a factor of ~ 3. Conclusions. We conclude that all the
available yields of P from massive stars are largely underestimated and that
nucleosynthesis calculations should be revised. We also predict the [P/Fe]
expected in halo stars.Comment: Accepted for publication in A&A (minor changes with respect to the
submitted version
The origin of abundance gradients in the Milky Way: the predictions of different models
We aim at studying the abundance gradients along the Galactic disk and their
dependence upon several parameters: a threshold in the surface gas density
regulating star formation, the star formation efficiency, the timescale for the
formation of the thin disk and the total surface mass density of the stellar
halo. We test a model which considers a cosmological infall law. This law does
not predict an inside-out disk formation, but it allows to well fit the
properties of the solar vicinity. We study several cases. We find that to
reproduce at the same time the abundance, star formation rate and surface gas
density gradients along the Galactic disk it is necessary to assume an
inside-out formation for the disk. The threshold in the gas density is not
necessary and the same effect could be reached by assuming a variable star
formation efficiency. A cosmologically derived infall law with an inside-out
process for the disk formation and a variable star formation efficiency can
indeed well reproduce all the properties of the disk. However, the cosmological
model presented here does not have sufficient resolution to capture the
requested inside-out formation for the disk.Comment: 13 pages, 17 figures and 2 tables. Accepted for publication in
Astronomy & Astrophysic
Bird mortality related to collisions with ski–lift cables: do we estimate just the tip of the iceberg?
Collisions with ski–lift cables are an important cause of death for grouse species living close to alpine ski resorts. As several biases may reduce the detection probability of bird carcasses, the mortality rates related to these collisions are generally underestimated. The possibility that injured birds may continue flying for some distance after striking cables represents a major source of error, known as crippling bias. Estimating the crippling losses resulting from birds dying far from the ski–lift corridors is difficult and it is usually assessed by systematic searches of carcasses on both sides of the ski–lifts. Using molecular tracking, we were able to demonstrate that a rock ptarmigan hen flew up to 600 m after striking a ski–lift cable, a distance preventing its detection by traditional carcasses surveys. Given the difficulty in conducting systematic searches over large areas surrounding the ski–lifts, only an experiment using radio–tagged birds would allow us to estimate the real mortality rate associated with cable collision
Discovery of New Dwarf Galaxy near The Isolated Spiral Galaxy NGC 6503
We report the discovery of a new dwarf galaxy (NGC6503-d1) during the Subaru
extended ultraviolet (XUV) disk survey. It is a likely companion of the spiral
galaxy NGC6503. The resolved images, in B, V, R, i, and Halpha, show an
irregular appearance due to bright stars with underlying, smooth and unresolved
stellar emission. It is classified as the transition type (dIrr/dSph). Its
structural properties are similar to those of the dwarfs in the Local Group,
with a V absolute magnitude ~ -10.5, half-light radius ~400 pc, and central
surface brightness ~25.2. Despite the low stellar surface brightness
environment, one HII region was detected, though its Halpha luminosity is low,
indicating an absence of any appreciable O-stars at the current epoch. The
presence of multiple stellar populations is indicated by the color-magnitude
diagram of ~300 bright resolved stars and the total colors of the dwarf, with
the majority of its total stellar mass ~4x10^6 Msun in an old stellar
population.Comment: Published in ApJL (ApJ, 802, L24). 7 pages, 4 figure
The Universal Initial Mass Function In The XUV Disk of M83
We report deep Subaru Halpha observations of the XUV disk of M83. These new
observations enable the first complete census of very young stellar clusters
over the entire XUV disk. Combining Subaru and GALEX data with a stellar
population synthesis model, we find that (1) the standard, but
stochastically-sampled, initial mass function (IMF) is preferred over the
truncated IMF, because there are low mass stellar clusters (10^{2-3}Msun) that
host massive O-type stars; that (2) the standard Salpeter IMF and a simple
aging effect explain the counts of FUV-bright and Halpha-bright clusters with
masses >10^3Msun; and that (3) the Halpha to FUV flux ratio over the XUV disk
supports the standard IMF. The Subaru Prime Focus Camera (Suprime-Cam) covers a
large area even outside the XUV disk -- far beyond the detection limit of the
HI gas. This enables us to statistically separate the stellar clusters in the
disk from background contamination. The new data, model, and previous
spectroscopic studies provide overall consistent results with respect to the
internal dust extinction (Av~0.1 mag) and low metallicity (~0.2Zsun) using the
dust extinction curve of SMC.Comment: 11 pages, 8 figures. Accepted for publication in Ap
The properties of the Malin 1 galaxy giant disk: A panchromatic view from the NGVS and GUViCS surveys
Low surface brightness galaxies (LSBGs) represent a significant percentage of
local galaxies but their formation and evolution remain elusive. They may hold
crucial information for our understanding of many key issues (i.e., census of
baryonic and dark matter, star formation in the low density regime, mass
function). The most massive examples - the so called giant LSBGs - can be as
massive as the Milky Way, but with this mass being distributed in a much larger
disk. Malin 1 is an iconic giant LSBG, perhaps the largest disk galaxy known.
We attempt to bring new insights on its structure and evolution on the basis of
new images covering a wide range in wavelength. We have computed surface
brightness profiles (and average surface brightnesses in 16 regions of
interest), in six photometric bands (FUV, NUV, u, g, i, z). We compared these
data to various models, testing a variety of assumptions concerning the
formation and evolution of Malin 1. We find that the surface brightness and
color profiles can be reproduced by a long and quiet star-formation history due
to the low surface density; no significant event, such as a collision, is
necessary. Such quiet star formation across the giant disk is obtained in a
disk model calibrated for the Milky Way, but with an angular momentum
approximately 20 times larger. Signs of small variations of the star-formation
history are indicated by the diversity of ages found when different regions
within the galaxy are intercompared.For the first time, panchromatic images of
Malin 1 are used to constrain the stellar populations and the history of this
iconic example among giant LSBGs. Based on our model, the extreme disk of Malin
1 is found to have a long history of relatively low star formation (about 2
Msun/yr). Our model allows us to make predictions on its stellar mass and
metallicity.Comment: Accepted in Astronomy and Astrophysic
The GALEX/S4G UV-IR color-color diagram: Catching spiral galaxies away from the Blue Sequence
We obtained GALEX FUV, NUV, and Spitzer/IRAC 3.6m photometry for > 2000
galaxies, available for 90% of the S4G sample. We find a very tight "GALEX Blue
Sequence (GBS)" in the (FUV-NUV) versus (NUV-[3.6]) color-color diagram which
is populated by irregular and spiral galaxies, and is mainly driven by changes
in the formation timescale () and a degeneracy between and dust
reddening. The tightness of the GBS provides an unprecedented way of
identifying star-forming galaxies and objects that are just evolving to (or
from) what we call the "GALEX Green Valley (GGV)". At the red end of the GBS,
at (NUV-[3.6]) > 5, we find a wider "GALEX Red Sequence (GRS)" mostly populated
by E/S0 galaxies that has a perpendicular slope to that of the GBS and of the
optical red sequence. We find no such dichotomy in terms of stellar mass
(measured by ), since both massive () blue and red sequence galaxies are identified. The type that is
proportionally more often found in the GGV are the S0-Sa's and most of these
are located in high-density environments. We discuss evolutionary models of
galaxies that show a rapid transition from the blue to the red sequence on
timescale of years.Comment: 7 pages, 4 figures, 1 table. Accepted for publication in ApJ
Stellar Kinematics and Structural Properties of Virgo Cluster Dwarf Early-Type Galaxies from the SMAKCED Project. I. Kinematically Decoupled Cores and Implications for Infallen Groups in Clusters
We present evidence for kinematically decoupled cores (KDCs) in two dwarf
early-type (dE) galaxies in the Virgo cluster, VCC 1183 and VCC 1453, studied
as part of the SMAKCED stellar absorption-line spectroscopy and imaging survey.
These KDCs have radii of 1.8'' (0.14 kpc) and 4.2'' (0.33 kpc), respectively.
Each of these KDCs is distinct from the main body of its host galaxy in two
ways: (1) inverted sense of rotation; and (2) younger (and possibly more
metal-rich) stellar population. The observed stellar population differences are
probably associated with the KDC, although we cannot rule out the possibility
of intrinsic radial gradients in the host galaxy. We describe a statistical
analysis method to detect, quantify the significance of, and characterize KDCs
in long-slit rotation curve data. We apply this method to the two dE galaxies
presented in this paper and to five other dEs for which KDCs have been reported
in the literature. Among these seven dEs, there are four significant KDC
detections, two marginal KDC detections, and one dE with an unusual central
kinematic anomaly that may be an asymmetric KDC.The frequency of occurence of
KDCs and their properties provide important constraints on the formation
history of their host galaxies. We discuss different formation scenarios for
these KDCs in cluster environments and find that dwarf-dwarf wet mergers or gas
accretion can explain the properties of these KDCs. Both of these mechanisms
require that the progenitor had a close companion with a low relative velocity.
This suggests that KDCs were formed in galaxy pairs residing in a poor group
environment or in isolation whose subsequent infall into the cluster quenched
star formation.Comment: 14 pages, accepted for publication in Ap
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