1,870 research outputs found
AGB populations in post-starburst galaxies
In a previous paper we compared the SEDs of a sample of 808 K+A galaxies from
the FUV to the MIR to the predictions of the spectrum synthesis models
explicitly using AGB components. Here we use the new AGB-light models from C.
Maraston (including less fuel for the later stages of stellar evolution and
improved calibrations) to address the discrepancies between our observations
and the AGB-heavy models used in our previous paper, which over-predict the
infrared fluxes of post-starburst galaxies by an order of magnitude. The new
models yield a much better fit to the data, especially in the near-IR, compared
to previous realizations where AGB stars caused a large excess in the H and K
bands. We { also compare the predictions of the M2013 models to those with BC03
and find that both reproduce the observations equally well. } We still find a
significant discrepancy with { both sets of models} in the Y and J bands, which
however is probably due to the spectral features of AGB stars. We also find
that { both the M2013 and the BC03 models} still over-predict the observed
fluxes in the UV bands, even invoking extinction laws that are stronger in
these bands. While there may be some simple explanations for this discrepancy,
we find that further progress requires new observations and better modelling.
Excess mid-infrared emission longward of 5m is well modelled by a
Black-Body, which may arise from dust emission from the
circumstellar envelopes of Oxygen rich M stars (expected for a metal-rich
population of AGB stars).Comment: A&A accepte
Towards a Precision Cosmology from Starburst Galaxies at z>2
This work investigates the use of a well-known empirical correlation between
the velocity dispersion, metallicity, and luminosity in H beta of nearby HII
galaxies to measure the distances to HII-like starburst galaxies at high
redshifts. This correlation is applied to a sample of 15 starburst galaxies
with redshifts between z=2.17 and z=3.39 to constrain Omega_m, using data
available from the literature. A best-fit value of Omega_m = 0.21 +0.30 -0.12
in a Lambda-dominated universe and of Omega_m = 0.11 +0.37 -0.19 in an open
universe is obtained. A detailed analysis of systematic errors, their causes,
and their effects on the values derived for the distance moduli and Omega_m is
carried out. A discussion of how future work will improve constraints on
Omega_m by reducing the errors is also presented.Comment: 7 pages, 3 figures, accepted for publication in MNRA
A panchromatic survey of post-starburst mergers: searching for feedback
We consider the morphology, stellar populations, structure and AGN activity of 10 post-starburst (K+A) galaxies with Hubble Space Telescope (HST) observations, full spectral coverage in the optical, spectral energy distributions from 0.2 to 160 mu m, X-ray and radio data. Our results show that the post-starburst galaxy (PSG) phenomenon is related to mergers and interactions, and that star formation was likely triggered during close passes prior to final coalescence. We performed a detailed qualitative analysis of the observed light distribution, including low surface brightness tidal features and colour profiles, in high-resolution multiband imaging with HST. We find evidence that star formation was centrally concentrated and that quenching took place from the inside-out, consistent with the occurrence of a feedback episode. Most of our PSGs contain massive bulges and therefore should host supermassive black holes. We search for AGN activity in spectra (line ratios), optical variability, X-ray emission at 0.5-7.0 KeV and radio emission at 20 cm: all four lines of evidence show that there is no active AGN accreting at more than 0.1 per cent of the Eddington luminosity. We conclude that mergers may be a necessary, but not a sufficient condition, for AGN activity and that they are not likely to be important in our objects. If PSGs are good test cases for quenching and evolution to the red sequence, AGNs may play a smaller role than expected.</p
Evidence of Substructure in the Cluster of Galaxies A3558
We investigate the dynamical properties of the cluster of galaxies A3558
(Shapley 8). Studying a region of one square degree ( 3 Mpc) centered
on the cluster cD galaxy, we have obtained a statistically complete photometric
catalog with positions and magnitudes of 1421 galaxies (down to a limiting
magnitude of ). This catalog has been matched to the recent velocity
data obtained by Mazure et al. (1997) and from the literature, yielding a
radial velocity catalog containing 322 galaxies. Our analysis shows that the
position/velocity space distribution of galaxies shows significant
substructure. A central bimodal core detected previously in preliminary studies
is confirmed by using the Adaptive Kernel Technique and Wavelet Analysis. We
show that this central bimodal subtructure is nevertheless composed of a
projected feature, kinematically unrelated to the cluster, plus a group of
galaxies probably in its initial merging phase into a relaxed core. The cD
velocity offset with respect to the average cluster redshift, reported earlier
by several authors, is completely eliminated as a result of our dynamical
analysis. The untangling of the relaxed core component also allows a better,
more reliable determination of the central velocity dispersion, which in turn
eliminates the ``-problem'' for A3558. The cluster also shows a
``preferential'' distribution of subclumps coinciding with the direction of the
major axis position angle of the cD galaxy and of the central X-ray emission
ellipsoidal distribution, in agreement with an anisotropic merger scenario.Comment: 35 pages in latex, 17 figures in Postscript, accepted for publication
in the Astrophysical Journa
A double cluster at the core of 30 Doradus
Based on an analysis of data obtained with the Wide Field Camera 3 (WFC3) on
the Hubble Space Telescope (HST) we report the identification of two distinct
stellar populations in the core of the giant HII region 30Doradus in the Large
Magellanic Cloud. The most compact and richest component coincides with the
center of R136 and is ~1 Myr younger than a second more diffuse clump, located
~5.4 pc toward the northeast. We note that published spectral types of massive
stars in these two clumps lend support to the proposed age difference. The
morphology and age difference between the two sub-clusters suggests that an
ongoing merger may occurring within the core of 30Doradus. This finding is
consistent with the predictions of models of hierarchical fragmentation of
turbulent giant molecular clouds, according to which star clusters would be the
final products of merging smaller sub-structures.Comment: 14 pages, 5 figure
The Low End of the Initial Mass Function in Young LMC Clusters: I. The Case of R136
We report the result of a study in which we have used very deep broadband V
and I WFPC2 images of the R136 cluster in the Large Magellanic Cloud from the
HST archive, to sample the luminosity function below the detection limit of 2.8
Mo previously reached. In these new deeper images, we detect stars down to a
limiting magnitude of m_F555W = 24.7 (~ 1 magnitude deeper than previous
works), and identify a population of red stars evenly distributed in the
surrounding of the R136 cluster. A comparison of our color-magnitude diagram
with recentely computed evolutionary tracks indicates that these red objects
are pre-main sequence stars in the mass range 0.6 - 3 Mo. We construct the
initial mass function (IMF) in the 1.35 - 6.5 Mo range and find that, after
correcting for incompleteness, the IMF shows a definite flattening below ~ 2
Mo. We discuss the implications of this result for the R136 cluster and for our
understanding of starburst galaxies formation and evolution in general.Comment: 29 pages, 6 tables, 11 figures included + 3 external files, accepted
for publication by Ap.
A Strategy to Measure the Dark Energy Equation of State using the HII galaxy Hubble Relation & X-ray AGN Clustering: Preliminary Results
We explore the possibility of setting stringent constraints to the Dark
Energy equation of state using alternative cosmic tracers like: (a) the Hubble
relation using HII galaxies, which can be observed at much higher redshifts
(z~3.5) than those currently traced by SNIa samples, and (b) the large-scale
structure using the clustering of X-ray selected AGN,which have a redshift
distribution peaking at z~1.
We use extensive Monte-Carlo simulations to define the optimal strategy for
the recovery of the dark-energy equation of state using the high redshift (z~2)
Hubble relation, but accounting also for the effects of gravitational lensing,
which for such high redshifts can significantly affect the derived cosmological
constraints. Based on a "Figure of Merit" analysis, we provide estimates for
the number of 2<z<3.5 tracers needed to reduce the cosmological solution space,
presently provided by the Constitution SNIa set, by a desired factor. We find
that it is much more efficient to increase the number of tracers than to reduce
their individual uncertainties.
Finally, we propose a framework to put constraints on the dark energy
equation of state by using the joint likelihood of the X-ray AGN clustering and
of the Hubble relation cosmological analyses. A preliminary joint analysis
using the X-ray AGN clustering of the 2XMM survey and the Hubble relation of
the Constitution SNIa set provide: Omega_m= 0.31+-0.01 and w=-1.06+-0.05. We
also find that the joint SNIa-2XMM analysis provides significantly more
stringent cosmological constraints, increasing the Figure of Merit by a factor
~2, with respect to that of the joint SNIa-BAO analysis.Comment: MNRAS in press, 12 colour figure
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