30 research outputs found
Constraints from Al Measurements on the Galaxy's Recent Global Star Formation Rate and Core Collapse Supernovae Rate
Gamma-rays from the decay of Al offer a stringent constraint on the
Galaxy's global star formation rate over the past million years, supplementing
other methods for quantifying the recent Galactic star formation rate, such as
equivalent widths of H emission. Advantages and disadvantages of using
Al gamma-ray measurements as a tracer of the massive star formation rate
are analyzed. Estimates of the Galactic Al mass derived from COMPTEL
measurements are coupled with a simple, analytical model of the Al
injection rate from massive stars and restrict the Galaxy's recent star
formation rate to \hbox{5 4 M\sun yr}. In addition, we show that
the derived Al mass implies a present day \hbox{Type II + Ib} supernovae
rate of 3.4 2.8 per century, which seems consistent with other
independent estimates of the Galactic core collapse supernova rate. If some
independent measure of the massive star initial mass function or star formation
rate or \hbox{Type II + Ib} supernovae rate were to become available (perhaps
through estimates of the Galactic Fe mass), then a convenient way to
restrain, or possibly determine, the other parameters is presented.Comment: 11 pages including 1 figure, ApJ in pres
The metallicity-luminosity relation at medium redshift based on faint CADIS emission line galaxies
The emission line survey within the Calar Alto Deep Imaging Survey (CADIS)
detects galaxies with very low continuum brightness by using an imaging
Fabry-Perot interferometer. With spectroscopic follow-up observations of
MB>~-19 CADIS galaxies using FORS2 at the VLT and DOLORES at TNG we obtained
oxygen abundances of 5 galaxies at z~0.4 and 10 galaxies at z~0.64. Combining
these measurements with published oxygen abundances of galaxies with MB<~-19 we
find evidence that a metallicity-luminosity relation exists at medium redshift,
but it is displaced to lower abundances and higher luminosities compared to the
metallicity-luminosity relation in the local universe. Comparing the observed
metallicities and luminosities of galaxies at z<3 with Pegase2 chemical
evolution models we have found a favoured scenario in which the metallicity of
galaxies increases by a factor of ~2 between z~0.7 and today, and their
luminosity decreases by ~0.5-0.9mag.Comment: Accepted for publication in A&A; 12 pages, 9 figure
A quadruply imaged quasar with an optical Einstein ring candidate: 1RXS J113155.4-123155
We report the discovery of a new quadruply imaged quasar surrounded by an
optical Einstein ring candidate. Spectra of the different components of 1RXS
J113155.4-123155 reveal a source at z=0.658. Up to now, this object is the
closest known gravitationally lensed quasar. The lensing galaxy is clearly
detected. Its redshift is measured to be z=0.295. Additionally, the total V
magnitude of the system has varied by 0.3 mag between two epochs separated by
33 weeks. The measured relative astrometry of the lensed images is best fitted
with an SIS model plus shear. This modeling suggests very high magnification of
the source (up to 50 for the total magnification) and predicts flux ratios
between the lensed images significantly different from what is actually
observed. This suggests that the lensed images may be affected by a combination
of micro or milli-lensing and dust extinction effects.Comment: 4 pages, 3 figures, published in A&
The spatial clustering of mid-IR selected star forming galaxies at z ~ 1 in the GOODS fields
We present the first spatial clustering measurements of z~1, 24um-selected,
star forming galaxies in the Great Observatories Origins Deep Survey (GOODS).
The sample under investigation includes 495 objects in GOODS-South and 811
objects in GOODS-North selected down to flux densities of f_24>20 uJy and
z_AB<23.5 mag, for which spectroscopic redshifts are available. The median
redshift, IR luminosity and star formation rate (SFR) of the samples are z~0.8,
L_IR~4.4 x 10^10 L_sun, and SFR~7.6 M_sun/yr, respectively. We measure the
projected correlation function w(r_p) on scales of r_p=0.06-10 h^-1 Mpc, from
which we derive a best fit comoving correlation length of r_0 = 4.0 +- 0.4 h^-1
Mpc and slope of gamma=1.5 +- 0.1 for the whole f_24>20uJy sample after
combining the two fields. We find indications of a larger correlation length
for objects of higher luminosity, with Luminous Infrared Galaxies (LIRGs,
L_IR>10^11 L_sun) reaching r_0~5.1 h^-1 Mpc. This would imply that galaxies
with larger SFRs are hosted in progressively more massive halos, reaching
minimum halo masses of ~3 x 10^12 M_sun for LIRGs. We compare our measurements
with the predictions from semi-analytic models based on the Millennium
simulation. The variance in the models is used to estimate the errors in our
GOODS clustering measurements, which are dominated by cosmic variance. The
measurements from the two GOODS fields are found to be consistent within the
errors. On scales of the GOODS fields, the real sources appear more strongly
clustered than objects in the Millennium-simulation based catalogs, if the
selection function is applied consistently. This suggests that star formation
at z~0.5-1 is being hosted in more massive halos and denser environments than
currently predicted by galaxy formation models.[truncated]Comment: 19 pages, 15 figures. Accepted for publication in A&A. Style and
English improve
Galaxy luminosities, stellar masses, sizes, velocity dispersions as a function of morphological type
We provide fits to the distribution of galaxy luminosity, size, velocity
dispersion and stellar mass as a function of concentration index C_r and
morphological type in the SDSS. We also quantify how estimates of the fraction
of `early' or `late' type galaxies depend on whether the samples were cut in
color, concentration or light profile shape, and compare with similar estimates
based on morphology. Our fits show that Es account for about 20% of the r-band
luminosity density, rho_Lr, and 25% of the stellar mass density, rho_*;
including S0s and Sas increases these numbers to 33% and 40%, and 50% and 60%,
respectively. Summed over all galaxy types, we find rho_* ~ 3 * 10^8 M_Sun
Mpc^{-3} at z ~ 0. This is in good agreement with expectations based on
integrating the star formation history. However, compared to most previous
work, we find an excess of objects at large masses, up to a factor of ~ 10 at
M_* ~ 5*10^{11} M_Sun. The stellar mass density further increases at large
masses if we assume different IMFs for Es and spiral galaxies, as suggested by
some recent chemical evolution models, and results in a better agreement with
the dynamical mass function. We also show that the trend for ellipticity to
decrease with luminosity is primarily because the E/S0 ratio increases at large
L. However, the most massive galaxies, M_* > 5 * 10^{11} M_Sun, are less
concentrated and not as round as expected if one extrapolates from lower L, and
they are not well-fit by pure deVaucouleur laws. This suggests formation
histories with recent radial mergers. Finally, we show that the age-size
relation is flat for Es of fixed dynamical mass, but, at fixed M_dyn, S0s and
Sas with large sizes tend to be younger. Explaining this difference between E
and S0 formation is a new challenge for models of early-type galaxy formation.Comment: 42 pages, 34 figures, 9 tables. Accepted for publication in MNRA
On the optical and X-ray afterglows of gamma ray bursts
We severely criticize the consuetudinary analysis of the afterglows of
gamma-ray bursts (GRBs) in the conical-ejection fireball scenarios. We argue
that, instead, recent observations imply that the long-duration GRBs and their
afterglows are produced by highly relativistic jets of cannonballs (CBs)
emitted in supernova explosions. The CBs are heated by their collision with the
supernova shell. The GRB is the boosted surface radiation the CBs emit as they
reach the transparent outskirts of the shell. The exiting CBs further
decelerate by sweeping up interstellar matter (ISM). The early X-ray afterglow
is dominated by thermal bremsstrahlung from the cooling CBs, the optical
afterglow by synchrotron radiation from the ISM electrons swept up by the CBs.
We show that this model fits simply and remarkably well all the measured
optical afterglows of the 15 GRBs with known redshift, including that of GRB
990123, for which unusually prompt data are available. We demonstrate that GRB
980425 was a normal GRB produced by SN1998bw, with standard X-ray and optical
afterglows. We find that the very peculiar afterglow of GRB 970508 can be
explained if its CBs encountered a significant jump in density as they moved
through the ISM. The afterglows of the nearest 8 of the known-redshift GRBs
show various degrees of evidence for an association with a supernova akin to
SN1998bw. In all other cases such an association, even if present, would have
been undetectable with the best current photometric sensitivities. This gives
strong support to the proposition that most, maybe all, of the long-duration
GRBs are associated with supernovae. Though our emphasis is on optical
afterglows, we also provide an excellent description of X-ray afterglows.Comment: Includes fits to the and X-ray and optical afterglows of all GRBs
with known redshift prior to July 2001 and an alternative interpretation of
the peculiar X-ray and optical afterglows of GRB 970508. In press in
Astronomy and Astrophysic
Calibration of the distance scale from galactic Cepheids:II Use of the HIPPARCOS calibration
New estimate of the distances of 36 nearby galaxies is presented. It is based
on the calibration of the V- and I-band Period-Lumi- nosity relations for
galactic Cepheids measured by the HIPPARCOS mission. The distance moduli are
obtained in a classical way. The statistical bias due to the incompleteness of
the sample is corrected according to the precepts introduced by Teerikorpi
(1987).
We adopt a constant slope (the one obtained with LMC Cepheids). The
correction for incompleteness bias introduce an uncertainty which depends on
each galaxy. On the mean, this uncertainty is small (0.04 mag) but it may reach
0.3 mag. We show that the un- certainty due to the correction of the extinction
is small (propably less than 0.05 mag.). The correlation between the
metallicity and the morphological type of the host galaxy sug- gests us to
reduce the application to spiral galaxies in order to bypass the problem of
metallicity. We suspect that the adopted PL slopes are not valid for all
morphological types of galaxies. This may induce a mean systematic shift of 0.1
mag on distance moduli.
A comparison with the distance moduli recently published by Freedman et al.
(2001) shows there is a reasonably good agreement with our distance moduli.Comment: Accepted for Astron & Astrophys. (2002) Cepheid database available at
ftp://www-obs.univ-lyon1.fr via anonymous ftp. Directory:
pub/base/CEPHEIDES.tar.g
Star cluster catalogues for the LEGUS dwarf galaxies
We present a new Bayesian hierarchical model (BHM) named Steve for performing Type Ia supernova (SN Ia) cosmology fits. This advances previous works by including an improved treatment of Malmquist bias, accounting for additional sources of systematic uncertainty, and increasing numerical efficiency. Given light-curve fit parameters, redshifts, and host-galaxy masses, we fit Steve simultaneously for parameters describing cosmology, SN Ia populations, and systematic uncertainties. Selection effects are characterized using Monte Carlo simulations. We demonstrate its implementation by fitting realizations of SN Ia data sets where the SN Ia model closely follows that used in Steve. Next, we validate on more realistic SNANA simulations of SN Ia samples from the Dark Energy Survey and low-redshift surveys (DES Collaboration et al. 2018). These simulated data sets contain more than 60,000 SNe Ia, which we use to evaluate biases in the recovery of cosmological parameters, specifically the equation of state of dark energy, w. This is the most rigorous test of a BHM method applied to SN Ia cosmology fitting and reveals small w biases that depend on the simulated SN Ia properties, in particular the intrinsic SN Ia scatter model. This w bias is less than 0.03 on average, less than half the statistical uncertainty on w. These simulation test results are a concern for BHM cosmology fitting applications on large upcoming surveys; therefore, future development will focus on minimizing the sensitivity of Steve to the SN Ia intrinsic scatter model.AA acknowledges the support of the
Swedish Research Council (Vetenskapsradet) and the Swedish
National Space Board (SNSB). DAG acknowledges support by
the German Aerospace Center (DLR) and the Federal Ministry for
Economic Affairs and Energy (BMWi) through program 50OR1801
âMYSST: Mapping Young Stars in Space and Timeâ
Future Directions in Subglacial Environments Research
International audienceSubglacial Antarctic Lake Environments (SALE) exploration and study is poised to be a major focus of Antarctic science for the next decade or more. The foundation for an intensive period of SALE research and field efforts has been provided by substantial improvement in our understanding of these environments, the establishment of SALE research programs by the International Polar Year (IPY) Program Office and the Scientific Committee on Antarctic Research (SCAR), the funding of several national SALE programs, independent guidance on environmental stewardship issues, and a series of international workshops, meetings, and conferences that have refined SALE scientific objectives. This article summarizes recent developments in subglacial environment exploration and study and describes future research needs