215 research outputs found
Gravitational lens candidates in the E-CDFS
We report ten lens candidates in the E-CDFS from the GEMS survey. Nine of the
systems are new detections and only one of the candidates is a known lens
system. For the most promising five systems including the known lens system, we
present results from preliminary lens mass modelling, which tests if the
candidates are plausible lens systems. Photometric redshifts of the candidate
lens galaxies are obtained from the COMBO-17 galaxy catalog. Stellar masses of
the candidate lens galaxies within the Einstein radius are obtained by using
the -band luminosity and the color-based stellar mass-to-light ratios.
As expected, the lensing masses are found to be larger than the stellar masses
of the candidate lens galaxies. These candidates have similar dark matter
fractions as compared to lenses in SLACS and COSMOS. They also roughly follow
the halo mass-stellar mass relation predicted by the subhalo abundance matching
technique. One of the candidate lens galaxies qualifies as a LIRG and may not
be a true lens because the arc-like feature in the system is likely to be an
active region of star formation in the candidate lens galaxy. Amongst the five
best candidates, one is a confirmed lens system, one is a likely lens system,
two are less likely to be lenses and the status of one of the candidates is
ambiguous. Spectroscopic follow-up of these systems is still required to
confirm lensing and/or for more accurate determination of the lens masses and
mass density profiles.Comment: 12 pages, 5 figures, 3 tables, ApJ accepte
The MAGNUM survey: Positive feedback in the nuclear region of NGC 5643 suggested by MUSE
We study the ionization and kinematics of the ionized gas in the nuclear
region of the barred Seyfert 2 galaxy NGC~5643 using MUSE integral field
observations in the framework of the MAGNUM (Measuring Active Galactic Nuclei
Under MUSE Microscope) survey. The data were used to identify regions with
different ionization conditions and to map the gas density and the dust
extinction. We find evidence for a double sided ionization cone, possibly
collimated by a dusty structure surrounding the nucleus. At the center of the
ionization cone, outflowing ionized gas is revealed as a blueshifted,
asymmetric wing of the [OIII] emission line, up to projected velocity
v(10)~-450 km/s. The outflow is also seen as a diffuse, low luminosity radio
and X-ray jet, with similar extension. The outflowing material points in the
direction of two clumps characterized by prominent line emission with spectra
typical of HII regions, located at the edge of the dust lane of the bar. We
propose that the star formation in the clumps is due to `positive feedback'
induced by gas compression by the nuclear outflow, providing the first
candidate for outflow induced star formation in a Seyfert-like radio quiet AGN.
This suggests that positive feedback may be a relevant mechanism in shaping the
black hole-host galaxy coevolution.Comment: 9 pages, 7 figures, accepted for publication in A&
The history of star formation and mass assembly in early-type galaxies
We define a volume limited sample of over 14,000 early-type galaxies (ETGs)
selected from data release six of the Sloan Digital Sky Survey. The density of
environment of each galaxy is robustly measured. By comparing narrow band
spectral line indices with recent models of simple stellar populations (SSPs)
we investigate trends in the star formation history as a function of galaxy
mass (velocity dispersion), density of environment and galactic radius. We find
that age, metallicity and alpha-enhancement all increase with galaxy mass and
that field ETGs are younger than their cluster counterparts by ~2 Gyr. We find
negative radial metallicity gradients for all masses and environments, and
positive radial age gradients for ETGs with velocity dispersion over 180 km/s.
Our results are qualitatively consistent with a relatively simple picture for
ETG evolution in which the low-mass halos accreted by a proto-ETG contained not
only gas but also a stellar population. This fossil population is
preferentially found at large radii in massive ETGs because the stellar
accretions were dissipationless. We estimate that the typical, massive ETG
should have been assembled at z < 3.5. The process is similar in the cluster
and the field but occurred earlier in dense environments.Comment: 5 pages, 2 figures. Submitted to MNRA
The properties of SN Ib/c locations
Aims: To gain better insight on the physics of stripped-envelope
core-collapse supernovae through studying their environments. Methods: We
obtained low-resolution optical spectroscopy with the New Technology Telescope
(+ EFOSC2) at the locations of 20 Type Ib/c supernovae. We measure the flux of
emission lines in the stellar-continuum-subtracted spectra from which local
metallicities are computed. For the supernova regions we estimate both the mean
stellar age, interpreting the stellar absorption with population synthesis
models, and the age of the youngest stellar populations using the H-alpha
equivalent width as an age indicator. These estimates are compared with the
lifetimes of single massive stars. Results: Based on our sample, we detect a
tentative indication that Type Ic supernovae might explode in environments that
are more metal-rich than those of Type Ib supernovae (average difference of
0.08 dex), but this is not a statistically significant result. The lower limits
placed on the ages of the supernova birthplaces are overall young, although
there are several cases where these appear older than what is expected for the
evolution of single stars more massive than 25-30 M_{sun}. This is only true,
however, assuming that the supernova progenitors were born during an
instantaneous (not continuous) episode of star formation. Conclusions: These
results do not conclusively favor any of the two evolutionary paths (single or
binary) leading to stripped supernovae. We do note a fraction of events for
which binary evolution is more likely, due to their associated age limits. The
fact, however, that the supernova environments contain areas of recent (< 15
Myr) star formation and that the environmental metallicities are, at least, not
against the single evolutionary scenario, suggest that this channel is also
broadly consistent with the observations.Comment: Matches published version (after proofs
SN 2006oz: rise of a super-luminous supernova observed by the SDSS-II SN Survey
We study SN 2006oz, a newly-recognized member of the class of H-poor,
super-luminous supernovae. We present multi-color light curves from the SDSS-II
SN Survey, that cover the rise time, as well as an optical spectrum that shows
that the explosion occurred at z~0.376. We fitted black body functions to
estimate the temperature and radius evolution of the photosphere and used the
parametrized code SYNOW to model the spectrum. We constructed a bolometric
light curve and compared it with explosion models. The very early light curves
show a dip in the g- and r-bands and a possible initial cooling phase in the
u-band before rising to maximum light. The bolometric light curve shows a
precursor plateau with a duration of 6-10 days in the rest-frame. A lower limit
of M_u < -21.5 can be placed on the absolute peak luminosity of the SN, while
the rise time is constrained to be at least 29 days. During our observations,
the emitting sphere doubled its radius to 2x10^15 cm, while the temperature
remained hot at 15000 K. As for other similar SNe, the spectrum is best modeled
with elements including O II and Mg II, while we tentatively suggest that Fe
III might be present. We suggest that the precursor plateau might be related to
a recombination wave in a circumstellar medium (CSM) and discuss whether this
is a common property of all similar explosions. The subsequent rise can be
equally well described by input from a magnetar or by ejecta-CSM interaction,
but the models are not well constrained owing to the lack of post-maximum
observations, and CSM interaction has difficulties accounting for the precursor
plateau self-consistently. Radioactive decay is less likely to be the mechanism
that powers the luminosity. The host galaxy, detected in deep imaging with the
10 m GTC, is a moderately young and star-forming, but not a starburst, galaxy.
It has an absolute magnitude of M_g = -16.9.Comment: Contains minor changes (of editorial nature) with respect to v1 in
order to match the published version. The abstract has been modified to fit
the arXiv space requirements. 11 pages, 8 figures, 3 table
Insights on the stellar mass-metallicity relation from the CALIFA survey
We use spatially and temporally resolved maps of stellar population
properties of 300 galaxies from the CALIFA integral field survey to investigate
how the stellar metallicity (Z*) relates to the total stellar mass (M*) and the
local mass surface density (*) in both spheroidal and disk dominated
galaxies. The galaxies are shown to follow a clear stellar mass-metallicity
relation (MZR) over the whole 10 to 10 M range. This
relation is steeper than the one derived from nebular abundances, which is
similar to the flatter stellar MZR derived when we consider only young stars.
We also find a strong relation between the local values of * and Z* (the
ZR), betraying the influence of local factors in determining Z*. This
shows that both local (*-driven) and global (M*-driven) processes are
important in determining the metallicity in galaxies. We find that the overall
balance between local and global effects varies with the location within a
galaxy. In disks, * regulates Z*, producing a strong ZR whose
amplitude is modulated by M*. In spheroids it is M* who dominates the physics
of star formation and chemical enrichment, with * playing a minor,
secondary role. These findings agree with our previous analysis of the star
formation histories of CALIFA galaxies, which showed that mean stellar ages are
mainly governed by surface density in galaxy disks and by total mass in
spheroids.Comment: 6 pages, 3 figures, accepted for publication in ApJ
Stellar metallicity from optical and UV spectral indices: test case for WEAVE-StePS
Context. The upcoming generation of optical spectrographs on four meter-class telescopes, with their huge multiplexing capabilities, excellent
spectral resolution, and unprecedented wavelength coverage, will provide high-quality spectra for thousands of galaxies. These data will allow us
to examine of the stellar population properties at intermediate redshift, an epoch that remains unexplored by large and deep surveys.
Aims. We assess our capability to retrieve the mean stellar metallicity in galaxies at different redshifts and signal-to-noise ratios (S/N), while
simultaneously exploiting the ultraviolet (UV) and optical rest-frame wavelength coverage.
Methods. The work is based on a comprehensive library of spectral templates of stellar populations, covering a wide range of age and metallicity
values and built assuming various star formation histories (SFHs), to cover an observable parameter space with diverse chemical enrichment
histories and dust attenuation. We took into account possible observational errors, simulating realistic observations of a large sample of galaxies
carried out with WEAVE at the William Herschel Telescope at different redshifts and S/N values. We measured all the available and reliable indices
on the simulated spectra and on the comparison library. We then adopted a Bayesian approach to compare the two sets of measurements in order
to obtain the probability distribution of stellar metallicity with an accurate estimate of the uncertainties.
Results. The analysis of the spectral indices has shown how some mid-UV indices, such as BL3580 and Fe3619, can provide reliable constraints
on stellar metallicity, along with optical indicators. The analysis of the mock observations has shown that even at S/N = 10, the metallicity can be
derived within 0.3 dex, in particular, for stellar populations older than 2 Gyr. The S/N value plays a crucial role in the uncertainty of the estimated
metallicity and so, the differences between S/N = 10 and S/N = 30 are quite large, with uncertainties of ∼ 0.15 dex in the latter case. On the
contrary, moving from S/N = 30 to S/N = 50, the improvement on the uncertainty of the metallicity measurements is almost negligible. Our results
are in good agreement with other theoretical and observational works in the literature and show how the UV indicators, coupled with classic optical
ones, can be advantageous in constraining metallicities.
Conclusions. We demonstrate that a good accuracy can be reached on the spectroscopic measurements of the stellar metallicity of galaxies at
intermediate redshift, even at low S/N, when a large number of indices can be employed, including some UV indices. This is very promising for
the upcoming surveys carried out with new, highly multiplexed, large-field spectrographs, such as StePS at the WEAVE and 4MOST, which will
provide spectra of thousands of galaxies covering large spectral ranges (between 3600 and 9000 Å in the observed frame) at relatively high S/N
(> 10 Å−1
)
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
CALIFA : a diameter-selected sample for an integral field spectroscopy galaxy survey
JMA acknowledges support from the European Research Council Starting Grant (SEDmorph; P.I. V. Wild).We describe and discuss the selection procedure and statistical properties of the galaxy sample used by the Calar Alto Legacy Integral Field Area (CALIFA) survey, a public legacy survey of 600 galaxies using integral field spectroscopy. The CALIFA "mother sample" was selected from the Sloan Digital Sky Survey (SDSS) DR7 photometric catalogue to include all galaxies with an r-band isophotal major axis between 45 '' and 79 : 2 '' and with a redshift 0 : 005 M-r > -23 : 1 and over a stellar mass range between 10(9.7) and 10(11.4) M-circle dot. In particular, within these ranges, the diameter selection does not lead to any significant bias against - or in favour of - intrinsically large or small galaxies. Only below luminosities of M-r = -19 (or stellar masses <10(9.7) M-circle dot) is there a prevalence of galaxies with larger isophotal sizes, especially of nearly edge-on late-type galaxies, but such galaxies form <10% of the full sample. We estimate volume-corrected distribution functions in luminosities and sizes and show that these are statistically fully compatible with estimates from the full SDSS when accounting for large-scale structure. For full characterization of the sample, we also present a number of value-added quantities determined for the galaxies in the CALIFA sample. These include consistent multi-band photometry based on growth curve analyses; stellar masses; distances and quantities derived from these; morphological classifications; and an overview of available multi-wavelength photometric measurements. We also explore different ways of characterizing the environments of CALIFA galaxies, finding that the sample covers environmental conditions from the field to genuine clusters. We finally consider the expected incidence of active galactic nuclei among CALIFA galaxies given the existing pre-CALIFA data, finding that the final observed CALIFA sample will contain approximately 30 Sey2 galaxies.Peer reviewe
CALIFA, the Calar Alto Legacy Integral Field Area survey: I. Survey presentation
We present here the Calar Alto Legacy Integral Field Area (CALIFA) survey,
which has been designed to provide a first step in this direction.We summarize
the survey goals and design, including sample selection and observational
strategy.We also showcase the data taken during the first observing runs
(June/July 2010) and outline the reduction pipeline, quality control schemes
and general characteristics of the reduced data. This survey is obtaining
spatially resolved spectroscopic information of a diameter selected sample of
galaxies in the Local Universe (0.005< z <0.03). CALIFA has been
designed to allow the building of two-dimensional maps of the following
quantities: (a) stellar populations: ages and metallicities; (b) ionized gas:
distribution, excitation mechanism and chemical abundances; and (c) kinematic
properties: both from stellar and ionized gas components. CALIFA uses the PPAK
Integral Field Unit (IFU), with a hexagonal field-of-view of
\sim1.3\sq\arcmin', with a 100% covering factor by adopting a three-pointing
dithering scheme. The optical wavelength range is covered from 3700 to 7000
{\AA}, using two overlapping setups (V500 and V1200), with different
resolutions: R\sim850 and R\sim1650, respectively. CALIFA is a legacy survey,
intended for the community. The reduced data will be released, once the quality
has been guaranteed. The analyzed data fulfill the expectations of the original
observing proposal, on the basis of a set of quality checks and exploratory
analysis.
We conclude from this first look at the data that CALIFA will be an important
resource for archaeological studies of galaxies in the Local Universe.Comment: 32 pages, 29 figures, Accepted for publishing in Astronomy and
Astrophysic
- …