6,601 research outputs found
Multi-wavelength characterisation of z~2 clustered, dusty star forming galaxies discovered by Planck
(abridged) We report the discovery of PHz G95.5-61.6, a complex structure
detected in emission in the Planck all-sky survey that corresponds to two
over-densities of high-redshift galaxies. This is the first source from the
Planck catalogue of high-z candidates that has been completely characterised
with follow-up observations from the optical to the sub-millimetre domain.
Herschel/SPIRE observations at 250, 350 and 500 microns reveal the existence of
five sources producing a 500 microns emission excess that spatially corresponds
to the candidate proto-clusters discovered by Planck. Further observations at
CFHT in the optical bands (g and i) and in the near infrared (J, H and K_s),
plus mid infrared observations with IRAC/Spitzer (at 3.6 and 4.5 microns)
confirm that the sub-mm red excess is associated with an over-density of
colour-selected galaxies. Follow-up spectroscopy of 13 galaxies with
VLT/X-Shooter establishes the existence of two high-z structures: one at z~1.7
(three confirmed member galaxies), the other at z~2.0 (six confirmed members).
This double structure is also seen in the photometric redshift analysis of a
sample of 127 galaxies located inside a circular region of 1'-radius containing
the five Herschel/SPIRE sources, where we found a double-peaked excess of
galaxies at z~1.7 and z~2.0 with respect to the surrounding region. These
results suggest that PHz G95.5-61.6 corresponds to two accreting nodes, not
physically linked to one another, embedded in the large scale structure of the
Universe at z~2 and along the same line-of-sight. In conclusion, the data,
methods and results illustrated in this pilot project confirm that Planck data
can be used to detect the emission from clustered, dusty star forming galaxies
at high-z, and, thus, to pierce through the early growth of cluster-scale
structures.Comment: 15 pages, 13 figures. Accepted for publication in Astronomy and
Astrophysic
RX J1548.9+0851, a fossil cluster?
Fossil galaxy groups are spatially extended X-ray sources with X-ray
luminosities above L_X,bol > 10^42 h_50^-2 ergs s^-1 and a central elliptical
galaxy dominating the optical, the second-brightest galaxy being at least 2
magnitudes fainter in the R band. Whether these systems are a distinct class of
objects resulting from exceptional formation and evolution histories is still
unclear, mainly due to the small number of objects studied so far, mostly
lacking spectroscopy of group members for group membership confirmation and a
detailed kinematical analysis. To complement the scarce sample of
spectroscopically studied fossils down to their faint galaxy populations, the
fossil candidate RX J1548.9+0851 (z=0.072) is studied in this work. Our results
are compared with existing data from fossils in the literature. We use ESO VLT
VIMOS multi-object spectroscopy to determine redshifts of the faint galaxy
population and study the luminosity-weighted dynamics and luminosity function
of the system. The full-spectrum fitting package ULySS is used to determine
ages and metallicities of group members. VIMOS imaging data are used to study
the morphology of the central elliptical. We identify 40 group members
spectroscopically within the central ~300 kpc of the system and find 31
additional redshifts from the literature, resulting in a total number of 54
spectroscopically confirmed group members within 1 Mpc. RX J1548.9+0851 is made
up of two bright ellipticals in the central region with a magnitude gap of
m_1,2 = 1.34 in the SDSS r' band leaving the definition of RX J1548.9+0851
being a fossil to the assumption of the virial radius. We find a
luminosity-weighted velocity dispersion of 568 km s^-1 and a mass of ~2.5 x
10^14 M_sun for the system confirming previous studies that revealed fossils to
be massive. (abridged)Comment: 13 pages, 13 figures, accepted for publication in A&
Limits on the luminosity function of Ly-alpha emitters at z = 7.7
The Ly-alpha luminosity function (LF) of high-redshift Ly-alpha emitters
(LAEs) is one of the few observables of the re-ionization epoch accessible to
date with 8-10 m class telescopes. The evolution with redshift allows one to
constrain the evolution of LAEs and their role in re-ionizing the Universe at
the end of the Dark Ages.
We have performed a narrow-band imaging program at 1.06 microns at the CFHT,
targeting Ly-alpha emitters at redshift z ~ 7.7 in the CFHT-LS D1 field. From
these observations we have derived a photometric sample of 7 LAE candidates at
z ~ 7.7.
We derive luminosity functions for the full sample of seven objects and for
sub-samples of four objects. If the brightest objects in our sample are real,
we infer a luminosity function which would be difficult to reconcile with
previous work at lower redshift. More definitive conclusions will require
spectroscopic confirmation.Comment: 12 pages, accepted to Astronomy and Astrophysic
The host galaxy of GRB 011121: Morphology and Spectral Energy Distribution
(Abridged) We present a detailed study of the host galaxy of GRB 011121 (at z
= 0.36) based on high-resolution imaging in 5 broad-band, optical and
near-infrared filters with HST and VLT/ISAAC. The surface brightness profile of
this galaxy is best fitted by a Sersic law with index ~ 2 - 2.5 and a rather
large effective radius (~ 7.5 kpc). Both the morphological analysis and the
F450W - F702W colour image suggest that the host galaxy of GRB 011121 is either
a disk-system with a rather small bulge, or one hosting a central,
dust-enshrouded starburst. Hence, we modeled the integrated spectral energy
distribution of this galaxy by combining stellar population and radiative
transfer models, assuming properties representative of nearby starburst or
normal star-forming, Sbc-like galaxies. A range of plausible fitting solutions
indicates that the host galaxy of GRB 011121 has a stellar mass of 3.1 - 6.9
x10^9 Msun, stellar populations with a maximum age ranging from 0.4 to 2 Gyr,
and a metallicity ranging from 1 to 29 per cent of the solar value. Starburst
models suggest this galaxy to be nearly as opaque as local starbursts (with an
A_V = 0.27 - 0.76 mag). Alternatively, normal star-forming Sbc-like models
suggest a high central opacity whereas A_V = 0.12$ -- 0.57 mag along the line
of sight. For this subluminous galaxy (with L_B/Lstar_B = 0.26), we determine a
model-dependent SFR of 2.4 - 9.4 Msun/yr. The SFR per unit luminosity (9.2 -
36.1 Msun/yr/(L_B/Lstar_B)) is high compared to those of most GRB host
galaxies, but consistent with those of most of the hosts at similar low
redshift. Our results suggest that the host galaxy of GRB 011121 is a rather
large disk-system in a relatively early phase of its star formation history.Comment: accepted for publication in A&
In the whirlpool's coils: tracing substructure from combined optical/X-ray data in the galaxy cluster A1300
Structure formation is thought to act via hierarchical mergers and accretion
of smaller systems driven by gravity with dark matter dominating the
gravitational field. Combining X-ray and optical imaging and spectroscopy
provides a powerful approach to the study of the cluster dynamics and mass
assembly history. The REFLEX-DXL sample contains the most X-ray luminous galaxy
clusters (L_X > 10^45 erg/s) from the REFLEX survey at z = 0.27-0.31. We
present the photometric (WFI) and spectroscopic (VIMOS) data for the DXL
cluster RXCJ1131.9-1955 (Abell 1300); in combination with the existing X-ray
data we determine and characterise the substructure of this post-merging
system. We analyse X-ray selected groups in a 30' x 30' region encompassing the
cluster in order to study the mass assembly of A1300. The X-ray surface
brightness map of A1300 appears disturbed and exhibits the signature of a
forward shock, which is consistent with a previous analysis of radio data.
Moreover, we detect a large scale-filament in which the cluster is embedded and
several infalling groups. Comparison of the whirlpool-like features in the
entropy pseudo-map of the intra-cluster medium with the distribution of the
cluster members reveals a direct correspondence between the ICM structure and
the galaxy distribution. Moreover, comparison with existing simulations allows
us to better understand the dynamics of the cluster progenitors and to age date
their impact. A1300 is a complex massive system in which a major merging
occurred about 3 Gyr ago and additional minor merging events happen at
different times via filaments, that will lead to an increase of the cluster
mass of up to 60% in the next Gyr.Comment: Accepted for publication in MNRAS; 18 pages, 16 figures. Replaced
with revised versio
[CII] 158m Emission and Metallicity in PDRs
We study the effects of a metallicity variation on the thermal balance and
[CII] fine-structure line strengths in interstellar photon dominated regions
(PDRs). We find that a reduction in the dust-to-gas ratio and the abundance of
heavy elements in the gas phase changes the heat balance of the gas in PDRs.
The surface temperature of PDRs decreases as the metallicity decreases except
for high density ( cm) clouds exposed to weak () FUV
fields where vibrational H-deexcitation heating dominates over
photoelectric heating of the gas. We incorporate the metallicity dependence in
our KOSMA- PDR model to study the metallicity dependence of [CII]/CO line
ratios in low metallicity galaxies. We find that the main trend in the
variation of the observed CII/CO ratio with metallicity is well reproduced by a
single spherical clump, and does not necessarily require an ensemble of clumps
as in the semi-analytical model presented by Bolatto et al. (1999).Comment: 16 pages, 14 figures, accepted by A&
Multi-wavelength study of X-ray luminous clusters at z ~ 0.3 I. Star formation activity of cluster galaxies
The current paradigm of cosmic formation and evolution of galaxy clusters
foresees growth mostly through merging. Galaxies in the infall region or in the
core of a cluster undergo transformations owing to different environmental
stresses. For two X-ray luminous clusters at redshift z ~ 0.3 with opposite
X-ray morphologies, RXCJ0014.3-3022 and RXCJ2308.3-0211, we assess differences
in galaxy populations as a function of cluster topography. Cluster large-scale
structure and substructure are determined from the combined photometry in the
B, V, and R bands, and from multi-object optical spectroscopy at low
resolution. A spectral index analysis is performed, based on the [OII] and
Hdelta features, and the D4000 break, available for more than 100 member
galaxies per cluster. Combination of spectral indices and FUV-optical colours
provides a picture of the star formation history in galaxies. In spite of the
potential presence of a small fraction of galaxies with obscured star formation
activity, the average star-formation history of cluster members is found to
depend on cluster-centric distance and on substructure. There is a sharp
increase in star formation activity along two well-defined filamentary
structures of the merging cluster RXCJ0014.3-3022, out to its virial radius and
beyond, produced by luminous (L ~ L*) and sub-L* galaxies. Conversely, the
regular cool-core cluster RXCJ2308.3-0211 mostly hosts galaxies which either
populate the red sequence or are becoming passive. These results suggest the
existence of a correspondence between assembly state and overall age of the
stellar populations of galaxies inside the virialized region and in the
surrounding large scale structure of massive clusters at z ~ 0.3. (Abridged)Comment: 18 pages, 17 figures, accepted for publication in Astronomy &
Astrophysic
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Improving Information on Maternal Medication Use by Linking Prescription Data to Congenital Anomaly Registers: A EUROmediCAT Study
Research on associations between medication use during pregnancy and congenital anomalies is significative for assessing the safe use of a medicine in pregnancy. Congenital anomaly (CA) registries do not have optimal information on medicine exposure, in contrast to prescription databases. Linkage of prescription databases to the CA registries is a potentially effective method of obtaining accurate information on medicine use in pregnancies and the risk of congenital anomalies. We linked data from primary care and prescription databases to five European Surveillance of Congenital Anomalies (EUROCAT) CA registries. The linkage was evaluated by looking at linkage rate, characteristics of linked and non-linked cases, first trimester exposure rates for six groups of medicines according to the prescription data and information on medication use registered in the CA databases, and agreement of exposure. Of the 52,619 cases registered in the CA databases, 26,552 could be linked. The linkage rate varied between registries over time and by type of birth. The first trimester exposure rates and the agreements between the databases varied for the different medicine groups. Information on anti-epileptic drugs and insulins and analogue medicine use recorded by CA registries was of good quality. For selective serotonin reuptake inhibitors, anti-asthmatics, antibacterials for systemic use, and gonadotropins and other ovulation stimulants, the recorded information was less complete. Linkage of primary care or prescription databases to CA registries improved the quality of information on maternal use of medicines in pregnancy, especially for medicine groups that are less fully registered in CA registries
Intrinsic Variability of the Atlantic Meridional Overturning Circulation at Interannual-to-Multidecadal Time Scales
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