Low-resolution spectroscopy and spectral energy distributions of selected sources towards σ Orionis

Aims. We study in detail nine sources in the direction of the young σ Orionis cluster, which is considered to be a unique site for studying stellar and substellar formation. The nine sources were selected because of their peculiar properties, such as extremely-red infrared colours or excessively strong Hα emission for their blue optical colours. Methods. We acquired high-quality, low-resolution spectroscopy (R ∼ 500) of the nine targets with ALFOSC at the Nordic Optical Telescope. We also re-analysed [24]-band photometry from MIPS/Spitzer and compiled the highest quality photometric dataset available at the ViJHK_s passbands and the four IRAC/Spitzer channels, for constructing accurate spectral energy distributions between 0.55 and 24 μm. Results. The nine targets were classified into: one Herbig Ae/Be star with a scattering edge-on disc; two G-type stars; one X-ray flaring, early-M, young star with chromospheric Hα emission; one very low-mass, accreting, young spectroscopic binary; two young objects at the brown-dwarf boundary with the characteristics of classical T Tauri stars; and two emission-line galaxies, one undergoing star formation, and another whose spectral energy distribution is dominated by an active galactic nucleus. We also discovered three infrared sources associated with overdensities in a cold cloud of the cluster centre. Conclusions. Low-resolution spectroscopy and spectral energy distributions are a vital tool for measuring the physical properties and evolution of young stars and candidates in the σ Orionis cluster.

Emission-line galaxy surveys with GTC: The Hα Universe

Emission line galaxies are the most easily detected and studied objects in the high redshift Universe. They are being used to trace the evolution of critical observables of the Universe such as Star Formation Rate densities, starburst properties and abundances. Most of the research is being done using [OII]3727 and UV lines, but Hα is still one the best tracers for Star Formation Rate and physical properties of current star-forming galaxies. As a complementary contribution to studies of galaxy evolution, our team has focused into a long-term project to study the population of Hα-selected star-forming galaxies of the Universe at different redshifts. In 1995 we first determined the local Hα luminosity function, and from it the Star Formation Rate density (SFRd) of the local Universe. We then, using narrow-band imaging in the optical, extended this measurement to z ≃ 0.24 and z ≃ 0.4. Working in the near-infrared, GTC will be a very powerful tool to study the evolution of the Hα emission-line galaxy populations at different redshifts. We will both quantify the SFRd evolution and characterize the star-forming galaxy populations by directly comparing the same observables at all redshifts up to z ≃ 2.5.

Investigating evidence for different black hole accretion modes since redshift z ∼ 1

Chandra data in the COSMOS, AEGIS-XD and 4 Ms Chandra Deep Field South are combined with multiwavelength photometry available in those fields to determine the rest-frame U − V versus V − J colours of X-ray AGN hosts in the redshift intervals 0.1 < z < 0.6 (mean z¯=0.40) and 0.6 < z < 1.2 (mean z¯=0.85). This combination of colours provides an effective and least model-dependent means of separating quiescent from star-forming, including dust reddened, galaxies. Morphological information emphasizes differences between AGN populations split by their U − V versus V − J colours. AGN in quiescent galaxies consist almost exclusively of bulges, while star-forming hosts are equally split between early- and late-type hosts. The position of AGN hosts on the U − V versusV − J diagram is then used to set limits on the accretion density of the Universe associated with evolved and star-forming systems independent of dust induced biases. It is found that most of the black hole growth at z≈ 0.40 and 0.85 is associated with star-forming hosts. Nevertheless, a non-negligible fraction of the X-ray luminosity density, about 15–20 per cent, at both z¯=0.40 and 0.85, is taking place in galaxies in the quiescent region of the U − V versus V − J diagram. For the low-redshift sub-sample, 0.1 < z < 0.6, we also find tentative evidence, significant at the 2σ level, that AGN split by their U − V and V − J colours have different Eddington ratio distributions. AGN in blue star-forming hosts dominate at relatively high Eddington ratios. In contrast, AGN in red quiescent hosts become increasingly important as a fraction of the total population towards low Eddington ratios. At higher redshift, z > 0.6, such differences are significant at the 2σ level only for sources with Eddington ratios ≳ 10^− 3. These findings are consistent with scenarios in which diverse accretion modes are responsible for the build-up of supermassive black holes at the centres of galaxies. We compare these results with the predictions of theGALFORM semi-analytic model for the cosmological evolution of AGN and galaxies. This model postulates two black hole fuelling modes, the first is linked to star formation events and the second takes place in passive galaxies. GALFORM predicts that a substantial fraction of the black hole growth at z < 1 is associated with quiescent galaxies, in apparent conflict with the observations. Relaxing the strong assumption of the model that passive AGN hosts have zero star formation rate could bring those predictions in better agreement with the data.

[C II] and 12^CO(1-0) emission maps in HLSJ091828.6+514223: a strongly lensed interacting system AT z = 5.24

We present Submillimeter Array [C II] 158 μm and Karl G. Jansky Very Large Array 12^CO(1-0) line emission maps for the bright, lensed, submillimeter source at z = 5.2430 behind A 773: HLSJ091828.6+514223 (HLS0918). We combine these measurements with previously reported line profiles, including multiple 12^CO rotational transitions, [C I], water, and [N II], providing some of the best constraints on the properties of the interstellar medium in a galaxy at z > 5. HLS0918 has a total far-infrared (FIR) luminosity L_FIR(8–1000 μm) = (1.6 ± 0.1) × 10^14 L_☉ μ^–1, where the total magnification μ_total = 8.9 ± 1.9, via a new lens model from the [C II] and continuum maps. Despite a HyLIRG luminosity, the FIR continuum shape resembles that of a local LIRG. We simultaneously fit all of the observed spectral line profiles, finding four components that correspond cleanly to discrete spatial structures identified in the maps. The two most redshifted spectral components occupy the nucleus of a massive galaxy, with a source-plane separation <1 kpc. The reddest dominates the continuum map (demagnified L_FIR, component = (1.1 ± 0.2) × 10^13 L_☉) and excites strong water emission in both nuclear components via a powerful FIR radiation field from the intense star formation. A third star-forming component is most likely a region of a merging companion (ΔV ~ 500 km s^–1) exhibiting generally similar gas properties. The bluest component originates from a spatially distinct region and photodissociation region analysis suggests that it is lower density, cooler, and forming stars less vigorously than the other components. Strikingly, it has very strong [N II] emission, which may suggest an ionized, molecular outflow. This comprehensive view of gas properties and morphology in HLS0918 previews the science possible for a large sample of high-redshift galaxies once ALMA attains full sensitivity.

An extended Herschel drop-out source in the center of AS1063: a normal dusty galaxy at z=6.1 or SZ substructures?

In the course of our 870 μm APEX/LABOCA follow-up of the Herschel Lensing Survey we have detected a source in AS1063 (RXC J2248.7-4431) that has no counterparts in any of the Herschel PACS/SPIRE bands, it is a Herschel “drop-out” with S_870/S_500 ≥ 0.5. The 870 μm emission is extended and centered on the brightest cluster galaxy, suggesting either a multiply imaged background source or substructure in the Sunyaev-Zel’dovich increment due to inhomogeneities in the hot cluster gas of this merging cluster. We discuss both interpretations with emphasis on the putative lensed source. Based on the observed properties and on our lens model we find that this source may be the first submillimeter galaxy (SMG) with a moderate far-infrared (FIR) luminosity (L_FIR < 10^12 L_⊙) detected so far at z > 4. In deep HST observations we identified a multiply imaged z ~ 6 source and measured its spectroscopic redshift to be z = 6.107 with VLT/FORS. This source may be associated with the putative SMG, but it is most likely offset spatially by 10−30 kpc and they may be interacting galaxies. With a FIR luminosity in the range [5−15] × 10^11 L_⊙ corresponding to a star formation rate in the range [80−260] M_⊙ yr^-1, this SMG would be more representative of the z > 4 dusty galaxies than the extreme starbursts detected so far. With a total magnification of ~25 it would open a unique window to the normal dusty galaxies at the end of the epoch of reionization.

The evolutionary paths among galaxy types on the red sequence at 0.3 < Z < 1.5

We have studied the main evolutionary paths among the galaxy types residing on the massive end of the Red Sequence and nearby locations on the Green Valley during the last ∼9 Gyr. The morphological and star formation properties of a sample of these galaxies at 0 . 3 < z < 1 .5 with stellar masses M_∗ > 5 × 10^10 M_⊙ have been analysed. We present direct observational evidence for the first time of the existence of two main evolutionary paths among the different red galaxy types since z ∼ 1 .5, which provide some clues on the nature of the processes that have governed the assembly of present-day massive quiescent galaxies. The results are in excellent agreement with the hierarchical evolutionary framework proposed in the Eliche-Moral et al. (2010) model. Data from SHARDS (one of the ESO/GTC Large Programmes approved in 2009A) will complement and improve the present findings, shedding some light into many of the still unsettled questions concerning the migration of galaxies from the Blue Cloud to the Red Sequence at z < 1 .5.

Infrared Excess sources: Compton thick QSOs, low-luminosity Seyferts or starbursts?

We explore the nature of Infrared Excess sources (IRX), which are proposed as candidates for luminous [L_X(2–10 keV) > 10^43 erg s^−1] Compton thick (NH > 2 × 1024 cm−2) QSOs at z≈ 2. Lower redshift, z≈ 1, analogues of the distant IRX population are identified by first redshifting to z= 2 the spectral energy distributions (SEDs) of all sources with secure spectroscopic redshifts in the AEGIS (6488) and the GOODS-North (1784) surveys and then selecting those that qualify as IRX sources at that redshift. A total of 19 galaxies are selected. The mean redshift of the sample is z≈ 1. We do not find strong evidence for Compton thick QSOs in the sample. For nine sources with X-ray counterparts, the X-ray spectra are consistent with Compton thin active galactic nucleus (AGN). Only three of them show tentative evidence for Compton thick obscuration. The SEDs of the X-ray undetected population are consistent with starburst activity. There is no evidence for a hot dust component at the mid-infrared associated with AGN heated dust. If the X-ray undetected sources host AGN, an upper limit of L_X(2–10 keV) = 10^43 erg s^−1 is estimated for their intrinsic luminosity. We propose that a large fraction of the z≈ 2 IRX population is not Compton thick quasi-stellar objects (QSOs) but low-luminosity [L_X(2–10 keV) < 10^43 erg s^−1], possibly Compton thin, AGN or dusty starbursts. It is shown that the decomposition of the AGN and starburst contribution to the mid-IR is essential for interpreting the nature of this population, as star formation may dominate this wavelength regime.

Spitzer's contribution to the AGN population

Infrared selection is a potentially powerful way to identify heavily obscured AGNs missed in even the deepest X-ray surveys. Using a 24 μm-selected sample in GOODS-S, we test the reliability and completeness of three infrared AGN selection methods: (1) IRAC color-color selection, (2) IRAC power-law selection, and (3) IR-excess selection; we also evaluate a number of IR-excess approaches. We find that the vast majority of non-power-law IRAC color-selected AGN candidates in GOODS-S have colors consistent with those of star-forming galaxies. Contamination by star-forming galaxies is most prevalent at low 24 μm flux densities (~100 μJy) and high redshifts (z ~ 2), but the fraction of potential contaminants is still high (~50%) at 500 μJy, the highest flux density probed reliably by our survey. AGN candidates selected via a simple, physically motivated power-law criterion ("power-law galaxies," or PLGs), however, appear to be reliable. We confirm that the IR-excess methods successfully identify a number of AGNs, but we also find that such samples may be significantly contaminated by star-forming galaxies. Adding only the secure Spitzer-selected PLG, color-selected, IR-excess, and radio/IR-selected AGN candidates to the deepest X-ray-selected AGN samples directly increases the number of known X-ray AGNs (84) by 54%-77%, and implies an increase to the number of 24 μm-detected AGNs of 71%-94%. Finally, we show that the fraction of MIR sources dominated by an AGN decreases with decreasing MIR flux density, but only down to f_24 μ m = 300 μJy. Below this limit, the AGN fraction levels out, indicating that a nonnegligible fraction (~10%) of faint 24 μm sources (the majority of which are missed in the X-ray) are powered not by star formation, but by the central engine. The fraction of all AGNs (regardless of their MIR properties) exceeds 15% at all 24 μm flux densities.

Breaking the curve with candels: a Bayesian approach to reveal the non-universality of the dust-attenuation law at high redshift

Dust attenuation affects nearly all observational aspects of galaxy evolution, yet very little is known about the form of the dust-attenuation law in the distant universe. Here, we model the spectral energy distributions of galaxies at z ~ 1.5–3 from CANDELS with rest-frame UV to near-IR imaging under different assumptions about the dust law, and compare the amount of inferred attenuated light with the observed infrared (IR) luminosities. Some individual galaxies show strong Bayesian evidence in preference of one dust law over another, and this preference agrees with their observed location on the plane of infrared excess (IRX, L_TIR/L_UV) and UV slope (β). We generalize the shape of the dust law with an empirical model, A_ λ,σ =E(B-V)k_ λ (λ / λ v)^ σ where k_λ is the dust law of Calzetti et al., and show that there exists a correlation between the color excess E(B-V) and tilt δ with δ =(0.62±0.05)log(E(B-V))+(0.26±0.02). Galaxies with high color excess have a shallower, starburst-like law, and those with low color excess have a steeper, SMC-like law. Surprisingly, the galaxies in our sample show no correlation between the shape of the dust law and stellar mass, star formation rate, or β. The change in the dust law with color excess is consistent with a model where attenuation is caused by scattering, a mixed star–dust geometry, and/or trends with stellar population age, metallicity, and dust grain size. This rest-frame UV-to-near-IR method shows potential to constrain the dust law at even higher redshifts (z>3).

Mass assembly and morphological transformations since z ∼ 3 from CANDELS

We quantify the evolution of the stellar mass functions (SMFs) of star-forming and quiescent galaxies as a function of morphology from z ∼ 3 to the present. Our sample consists of ∼50 000 galaxies in the CANDELS fields (∼880 arcmin^2), which we divide into four main morphological types, i.e. pure bulge-dominated systems, pure spiral disc-dominated, intermediate two-component bulge+disc systems and irregular disturbed galaxies. At z ∼ 2, 80 per cent of the stellar mass density of star-forming galaxies is in irregular systems. However, by z ∼ 0.5, irregular objects only dominate at stellar masses below 10^9 M_⊙. A majority of the star-forming irregulars present at z ∼ 2 undergo a gradual transformation from disturbed to normal spiral disc morphologies by z ∼ 1 without significant interruption to their star formation. Rejuvenation after a quenching event does not seem to be common except perhaps for the most massive objects, because the fraction of bulge-dominated star-forming galaxies with M^*/M_⊙ > 10^10.7 reaches 40 per cent at z < 1. Quenching implies the presence of a bulge: the abundance of massive red discs is negligible at all redshifts over 2 dex in stellar mass. However, the dominant quenching mechanism evolves. At z > 2, the SMF of quiescent galaxies above M^* is dominated by compact spheroids. Quenching at this early epoch destroys the disc and produces a compact remnant unless the star-forming progenitors at even higher redshifts are significantly more dense. At 1 < z < 2, the majority of newly quenched galaxies are discs with a significant central bulge. This suggests that mass quenching at this epoch starts from the inner parts and preserves the disc. At z < 1, the high-mass end of the passive SMF is globally in place and the evolution mostly happens at stellar masses below 10^10 M_⊙. These low-mass galaxies are compact, bulge-dominated systems, which were environmentally quenched: destruction of the disc through ram-pressure stripping is the likely process.

Quantifying the contamination by old main-sequence stars in young moving groups: the case of the Local Association

Context. The associations and moving groups of young stars are excellent laboratories for investigating stellar formation in the solar neighborhood. Previous results have confirmed that a non-negligible fraction of old main-sequence stars is present in the lists of possible members of young stellar kinematic groups. A detailed study of the properties of these samples is needed to separate the young stars from old main-sequence stars with similar space motion, and identify the origin of these structures. Aims. Our intention is to characterize members of the young moving groups, determine their age distribution, and quantify the contamination by old main-sequence stars, in particular, for the Local Association. Methods. We used stars possible members of the young (~10-650 Myr) moving groups from the literature. To determine the age of the stars, we used several suitable age indicators for young main sequence stars, i.e., X-ray fluxes from the Rosat All-sky Survey database, photometric data from the Tycho-2, Hipparcos, and 2MASS database. We also used spectroscopic data, in particular the equivalent width of the lithium line Li I λ6707.8 Å and H_α, to constrain the range of ages of the stars. Results. By combining photometric and spectroscopic data, we were able to separate the young stars (10-650 Myr) from the old (> 1 Gyr) field ones. We found, in particular, that the Local Association is contaminated by old field stars at the level of ~30%. This value must be considered as the contamination for our particular sample, and not of the entire Local Association. For other young moving groups, it is more difficult to estimate the fraction of old stars among possible members. However, the level of X-ray emission can, at least, help to separate two age populations: stars with <200 Myr and stars older than this. Conclusions. Among the candidate members of the classical moving groups, there is a non-negligible fraction of old field stars that should be taken into account when studying the stellar birthrate in the solar neighborhood. Our results are consistent with a scenario in which the moving groups contain both groups of young stars formed in a recent star-formation episode and old field stars with similar space motion. Only by combining X-ray and optical spectroscopic data is it possible to distinguish between these two age populations.

High resolution spectroscopic characterization of the FGK stars in the Solar neighborhood

We present the most recent results of our ongoing long-term high resolution spectroscopic study of nearby (d ≤ 25 pc) FGK stars which aim is to characterize the local properties of the Galaxy, in particular the star-formation history. A through analysis has been carried out for 253 cool stars in the solar neighborhood. This includes radial and rotational velocities determinations, chromospheric activity levels inference, kinematic analysis, and age estimates. This study does not only shed new light on the issue of stellar formation history but also contributes to any present or future mission aiming to detect extra-solar planets. Exo-planets are likely to be found orbiting around nearby cool stars and their detection and characterization is highly dependent on the precise determination of fundamental stellar parameters such as age, activity levels. Therefore, our study is of paramount importance to ensure the success of any such mission.

Ammonia observations of the nearby molecular cloud MBM 12

We present NH_3(1,1) and (2,2) observations of MBM 12, the closest known molecular cloud (65-pc distance), aimed at finding evidence for on-going star formation processes, No local temperature (with a T_rot upper limit of 12 K) or linewidth enhancement is found, which suggests that the area of the cloud that we have mapped (∼ 15-arcmin size) is not currently forming stars. Therefore this nearby 'starless' molecular gas region is an ideal laboratory to study the physical conditions preceding new star formation. A radio continuum source has been found in Very Large Array archive data, close to but outside the NH_3 emission. This source is likely to be a background object.

A complete census of Herschel-detected infrared sources within the HST Frontier Fields

We present a complete census of all Herschel-detected sources within the six massive lensing clusters of the HST Frontier Fields (HFF). We provide a robust legacy catalogue of 263 sources with Herschel fluxes, primarily based on imaging from the Herschel Lensing Survey and PEP/HerMES Key Programmes. We optimally combine Herschel, Spitzer and WISE infrared (IR) photometry with data from HST, VLA and ground-based observatories, identifying counterparts to gain source redshifts. For each Herschel-detected source we also present magnification factor (mu), intrinsic IR luminosity and characteristic dust temperature, providing a comprehensive view of dust-obscured star formation within the HFF. We demonstrate the utility of our catalogues through an exploratory overview of the magnified population, including more than 20 background sub-LIRGs unreachable by Herschel without the assistance gravitational lensing.

The multiphase starburst-driven galactic wind in NGC 5394

We present a detailed study of the neutral and ionized gas phases in the galactic wind for the nearby starburst galaxy NGC 5394 based on new integral field spectroscopy obtained with the INTEGRAL fibre system at the William Herschel Telescope. The neutral gas phase in the wind is detected via the interstellar Na I D doublet absorption. After a careful removal of the stellar contribution to these lines, a significant amount of neutral gas (∼10^7 M_⊙) is detected in a central region of ∼1.75 kpc size. This neutral gas is blueshifted by ∼165 km s^−1 with respect to the underlying galaxy. The mass outflow of neutral gas is comparable to the star formation rate of the host galaxy. Simultaneously, several emission lines (Hα, [N II], [S II]) are also analysed looking for the ionized warm phase counterpart of the wind. A careful kinematic decomposition of the line profiles reveals the presence of a secondary, broader, kinematic component. This component is found roughly in the same region where the Na I D absorption is detected. It presents higher [N II]/Hα and [S II]/Hα line ratios than the narrow component at the same locations, indicative of contamination by shock ionization. This secondary component also presents blueshifted velocities, although smaller than those measured for the neutral gas, averaging to ∼−30 km s^−1. The mass and mass outflow rate of the wind is dominated by the neutral gas, of which a small fraction might be able to escape the gravitational potential of the host galaxy. The observations in this system can be readily understood within a bipolar gas flow scenario.