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