282 research outputs found
The evolution of galaxy star formation activity in massive halos
There is now a large consensus that the current epoch of the Cosmic Star
Formation History (CSFH) is dominated by low mass galaxies while the most
active phase at 1<z<2 is dominated by more massive galaxies, which undergo a
faster evolution. Massive galaxies tend to inhabit very massive halos such as
galaxy groups and clusters. We aim to understand whether the observed "galaxy
downsizing" could be interpreted as a "halo downsizing", whereas the most
massive halos, and their galaxy populations, evolve more rapidly than the halos
of lower mass. Thus, we study the contribution to the CSFH of galaxies
inhabiting group-sized halos. This is done through the study of the evolution
of the Infra-Red (IR) luminosity function of group galaxies from redshift 0 to
~1.6. We use a sample of 39 X-ray selected groups in the Extended Chandra Deep
Field South (ECDFS), the Chandra Deep Field North (CDFN), and the COSMOS field,
where the deepest available mid- and far-IR surveys have been conducted with
Spitzer MIPS and Hersche PACS. Groups at low redshift lack the brightest,
rarest, and most star forming IR-emitting galaxies observed in the field. Their
IR-emitting galaxies contribute <10% of the comoving volume density of the
whole IR galaxy population in the local Universe. At redshift >~1, the most
IR-luminous galaxies (LIRGs and ULIRGs) are preferentially located in groups,
and this is consistent with a reversal of the star-formation rate vs .density
anti-correlation observed in the nearby Universe. At these redshifts, group
galaxies contribute 60-80% of the CSFH, i.e. much more than at lower redshifts.
Below z~1, the comoving number and SFR densities of IR-emitting galaxies in
groups decline significantly faster than those of all IR-emitting galaxies. Our
results are consistent with a "halo downsizing" scenario and highlight the
significant role of "environment" quenching in shaping the CSFH.Comment: 14 pages, 10 figures, accepted for publication by A&
The role of massive halos in the Star Formation History of the Universe
The most striking feature of the Cosmic Star Formation History (CSFH) of the
Universe is a dramatic drop of the star formation (SF) activity, since z~1. In
this work we investigate if the very same process of assembly and growth of
structures is one of the major drivers of the observed decline. We study the
contribution to the CSFH of galaxies in halos of different masses. This is done
by studying the total SFR-halo mass-redshift plane from redshift 0 to redshift
z~1.6 in a sample of 57 groups and clusters by using the deepest available mid-
and far-infrared surveys conducted with Spitzer MIPS and Herschel PACS and
SPIRE. Our results show that low mass groups provide a 60-80% contribution to
the CSFH at z~1. Such contribution declines faster than the CSFH in the last 8
billion years to less than 10% at z<0.3, where the overall SF activity is
sustained by lower mass halos. More massive systems provide only a marginal
contribution (<10%) at any epoch. A simplified abundance matching method shows
that the large contribution of low mass groups at z~1 is due to a large
fraction (>50%) of very massive, highly star forming Main Sequence galaxies.
Below z~1 a quenching process must take place in massive halos to cause the
observed faster suppression of their SF activity. Such process must be a slow
one though, as most of the models implementing a rapid quenching of the SF
activity in accreting satellites significantly underpredicts the observed SF
level in massive halos at any redshift. Starvation or the transition from cold
to hot accretion would provide a quenching timescale of 1 Gyrs more consistent
with the observations. Our results suggest a scenario in which, due to the
structure formation process, more and more galaxies experience the group
environment and, thus, the associated quenching process. This leads to the
progressive suppression of their SF activity shaping the CSFH below z~1.Comment: 18 pages, 21 figures, accepted for publication by A&
Coronal properties of the EQ Peg binary system
The activity indicators of M dwarfs are distinctly different for early and
late types. The coronae of early M dwarfs display high X-ray luminosities and
temperatures, a pronounced inverse FIP effect, and frequent flaring to the
extent that no quiescent level can be defined in many cases. For late M dwarfs,
fewer but more violent flares have been observed, and the quiescent X-ray
luminosity is much lower. To probe the relationship between coronal properties
with spectral type of active M dwarfs, we analyze the M3.5 and M4.5 components
of the EQ Peg binary system in comparison with other active M dwarfs of
spectral types M0.5 to M5.5. We investigate the timing behavior of both
components of the EQ Peg system, reconstruct their differential emission
measure, and investigate the coronal abundance ratios based on emission-measure
independent line ratios from their Chandra HETGS spectra. Finally we test for
density variations in different states of activity. The X-ray luminosity of EQ
Peg A (M3.5) is by a factor of 6-10 brighter than that of EQ Peg B (M4.5). Like
most other active M dwarfs, the EQ Peg system shows an inverse FIP effect. The
abundances of both components are consistent within the errors; however, there
seems to be a tendency toward the inverse FIP effect being less pronounced in
the less active EQ Peg B when comparing the quiescent state of the two stars.
This trend is supported by our comparison with other M dwarfs. As the X-ray
luminosity decreases with later spectral type, so do coronal temperatures and
flare rate. The amplitude of the observed abundance anomalies, i.e. the inverse
FIP effect, declines; however, clear deviations from solar abundances remain.Comment: 14 pages, accepted by A&
Crystallization diagram for antisolvent crystallization of lactose : using design of experiments to investigate continuous mixing- induced supersaturation
This study investigates the effects of key process parameters of continuous mixing-induced supersaturation on the antisolvent crystallization of lactose using D-optimal Design of Experiments (DoE). Aqueous solutions of lactose were mixed isothermally with antisolvents using a concentric capillary mixer. Process parameters investigated were the choice of antisolvent (acetone or isopropanol), concentration of lactose solution, total mass flow rate, and the ratio of mass flow rates of lactose solution and antisolvent. Using a D-optimal DoE a statistically significant sample set was chosen to explore and quantify the effects of these parameters. The responses measured were the solid state of the lactose crystallized, induction time, solid yield and particle size. Mixtures of α-lactose monohydrate and β-lactose were crystallized under most conditions with β-lactose content increasing with increasing amount of antisolvent. Pure α-lactose monohydrate was crystallized using acetone as the antisolvent, with mass flow ratios near 1:1, and near saturated solutions of lactose. A higher resolution DoE was adopted for acetone and was processed using multivariate methods to obtain a crystallization diagram of lactose. The model was used to create an optimized process to produce α-lactose monohydrate and predicted results agreed well with those obtained experimentally, validating the model. The solid state of lactose, induction time, and solid yield were accurately predicted
Unravelling anomalous mass transport in miscible liquids
The dissolution dynamics between miscible liquids play a key role in many industrial, biological and environmental processes, including solvent-induced phase transformations such as the formation of polymer membranes or antisolvent crystallisation. The “common” current intuition that guides the design of diffusion processes in miscible liquids is rooted in Fick’s law. This hypothesis generally holds when the system is close to equilibrium and behaves like an ideal mixture. However, Fickian diffusion has limited applicability far from equilibrium, and many systems display “anomalous” behaviours such as uphill diffusion [1] or the Ouzo effect [2]. Despite the importance of diffusion processes, the mechanisms underlying anomalous mass transfer are still poorly understood [3]. This work provides a direct microscopic view into highly localized anomalous pathways that can occur during the mixing of miscible fluids. Results will be presented for a model system of glycine-water-ethanol that represents a typical antisolvent crystallisation process where anomalous mass transport can have significant impacts on the critical quality attributes of the resulting crystalline product. We have deployed a novel experimental setup that includes a microfluidic flow cell that is monitored using a confocal Raman microscope, enabling the measurement of spectral maps of the mixing of the solution and antisolvent streams. These maps allow for the evolution of the composition of the multicomponent fluid to be determined as mixing progresses. From the measured spectral maps, the equilibration trajectories of the mixing solution and antisolvent streams can be determined, providing information on what regions of the phase diagrams are accessed during the mixing process, while also revealing the conditions that lead to surprising diffusive behaviours. This work provides new insight into the underlying mechanisms of anomalous mass transport and a better understanding of the equilibration pathways that can occur during antisolvent crystallization. References [1] R. Krishna; Uphill diffusion in multicomponent mixtures, Chem. Soc. Rev., 44, 2812-2836 (2015). [2] S. A. Vitale, and J. L. Katz; Liquid droplet dispersions formed by homogeneous liquid-liquid nucleation: “the ouzo effect”, Langmuir, 19, 4105-4110 (2003) [3] A. Vorobev: Dissolution dynamics of miscible liquid/liquid interfaces, Curr. Opin. Colloid Interface Sci., 19, 300-308 (2014)
The AGN content in luminous IR galaxies at z\sim2 from a global SED analysis including Herschel data
We use Herschel-PACS far-infrared data, combined with previous multi-band
information and mid-IR spectra, to properly account for the presence of an
active nucleus and constrain its energetic contribution in luminous infrared
(IR) sources at z\sim2. The sample is composed of 24 sources in the GOODS-South
field, with typical IR luminosity of 10^{12} Lo. Data from the 4 Ms Chandra
X-ray imaging in this field are also used to identify and characterize AGN
emission. We reproduce the observed spectral energy distribution (SED),
decomposed into a host-galaxy and an AGN component. A smooth-torus model for
circum-nuclear dust is used to account for the direct and re-processed
contribution from the AGN. We confirm that galaxies with typical
L_{8-1000um}\sim10^{12}Lo at z\sim2 are powered predominantly by
star-formation. An AGN component is present in nine objects (\sim35% of the
sample) at the 3sigma confidence level, but its contribution to the 8-1000 um
emission accounts for only \sim5% of the energy budget. The AGN contribution
rises to \sim23% over the 5-30 um range (in agreement with Spitzer IRS results)
and to \sim60% over the narrow 2-6 um range. The presence of an AGN is
confirmed by X-ray data for 3 (out of nine) sources, with X-ray spectral
analysis indicating the presence of significant absorption, i.e.
NH\sim10^{23}-10^{24} cm^{-2}. An additional source shows indications of
obscured AGN emission from X-ray data. The comparison between the
mid-IR--derived X-ray luminosities and those obtained from X-ray data suggests
that obscuration is likely present also in the remaining six sources that
harbour an AGN according to the SED-fitting analysis.Comment: 12 pages, including 5 figures. Accepted for publication in MNRA
PEP: first Herschel probe of dusty galaxy evolution up to z~3
We exploit the deepest existing far-infrared (FIR) data obtained so far by
Herschel at 100 and 160 um in the GOODS-N, as part of the PACS Evolutionary
Probe (PEP) survey, to derive for the first time the evolution of the
rest-frame 60-um, 90-um, and total IR luminosity functions (LFs) of galaxies
and AGNs from z=0 to unprecedented high redshifts (z~2-3). The PEP LFs were
computed using the 1/Vmax method. The FIR sources were classified by means of a
detailed broad- band SED-fitting analysis and spectral characterisation. Based
on the best-fit model results, k-correction and total IR (8-1000 um) luminosity
were obtained for each source. LFs (monochromatic and total) were then derived
for various IR populations separately in different redshift bins and compared
to backward evolution model predictions. We detect strong evolution in the LF
to at least z~2. Objects with SEDs similar to local spiral galaxies are the
major contributors to the star formation density (SFD) at z< 0.3, then, as
redshift increases, moderate SF galaxies - most likely containing a
low-luminosity AGN - start dominating up to z ~= 1.5. At >1.5 the SFD is
dominated by the contributions of starburst galaxies. In agreement with
previous findings, the comoving IR LD derived from our data evolves
approximately as (1 + z)^(3.8+/-0.3) up to z~1, there being some evidence of
flattening up to z~2.Comment: Accepted for publication in the A&A Herschel first results Special
Issu
Panchromatic spectral energy distributions of Herschel sources
(abridged) Far-infrared Herschel photometry from the PEP and HerMES programs
is combined with ancillary datasets in the GOODS-N, GOODS-S, and COSMOS fields.
Based on this rich dataset, we reproduce the restframe UV to FIR ten-colors
distribution of galaxies using a superposition of multi-variate Gaussian modes.
The median SED of each mode is then fitted with a modified version of the
MAGPHYS code that combines stellar light, emission from dust heated by stars
and a possible warm dust contribution heated by an AGN. The defined Gaussian
grouping is also used to identify rare sources. The zoology of outliers
includes Herschel-detected ellipticals, very blue z~1 Ly-break galaxies,
quiescent spirals, and torus-dominated AGN with star formation. Out of these
groups and outliers, a new template library is assembled, consisting of 32 SEDs
describing the intrinsic scatter in the restframe UV-to-submm colors of
infrared galaxies. This library is tested against L(IR) estimates with and
without Herschel data included, and compared to eight other popular methods
often adopted in the literature. When implementing Herschel photometry, these
approaches produce L(IR) values consistent with each other within a median
absolute deviation of 10-20%, the scatter being dominated more by fine tuning
of the codes, rather than by the choice of SED templates. Finally, the library
is used to classify 24 micron detected sources in PEP GOODS fields. AGN appear
to be distributed in the stellar mass (M*) vs. star formation rate (SFR) space
along with all other galaxies, regardless of the amount of infrared luminosity
they are powering, with the tendency to lie on the high SFR side of the "main
sequence". The incidence of warmer star-forming sources grows for objects with
higher specific star formation rates (sSFR), and they tend to populate the
"off-sequence" region of the M*-SFR-z space.Comment: Accepted for publication in A&A. Some figures are presented in low
resolution. The new galaxy templates are available for download at the
address http://www.mpe.mpg.de/ir/Research/PEP/uvfir_temp
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