The CALIFA survey across the Hubble sequence: Spatially resolved stellar population properties in galaxies

Various different physical processes contribute to the star formation and stellar mass assembly histories of galaxies. One important approach to understanding the significance of these different processes on galaxy evolution is the study of the stellar population content of today's galaxies in a spatially resolved manner. The aim of this paper is to characterize in detail the radial structure of stellar population properties of galaxies in the nearby universe, based on a uniquely large galaxy sample, considering the quality and coverage of the data. The sample under study was drawn from the CALIFA survey and contains 300 galaxies observed with integral field spectroscopy. These cover a wide range of Hubble types, from spheroids to spiral galaxies, while stellar masses range from M_* ∼ 10^9 to 7 x 10^11 M_⨀. We apply the fossil record method based on spectral synthesis techniques to recover the following physical properties for each spatial resolution element in our target galaxies: the stellar mass surface density (μ_*), stellar extinction (A_V), light-weighted and mass-weighted ages (_L, _M), and mass-weighted metallicity (_M). To study mean trends with overall galaxy properties, the individual radial profiles are stacked in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd). We confirm that more massive galaxies are more compact, older, more metal rich, and less reddened by dust. Additionally, we find that these trends are preserved spatially with the radial distance to the nucleus. Deviations from these relations appear correlated with Hubble type: earlier types are more compact, older, and more metal rich for a given M-star, which is evidence that quenching is related to morphology, but not driven by mass. Negative gradients of _L are consistent with an inside-out growth of galaxies, with the largest _L gradients in Sb-Sbc galaxies. Further, the mean stellar ages of disks and bulges are correlated and with disks covering a wider range of ages, and late-type spirals hosting younger disks. However, age gradients are only mildly negative or flat beyond R∼2 HLR (half light radius), indicating that star formation is more uniformly distributed or that stellar migration is important at these distances. The gradients in stellar mass surface density depend mostly on stellar mass, in the sense that more massive galaxies are more centrally concentrated. Whatever sets the concentration indices of galaxies obviously depends less on quenching/morphology than on the depth of the potential well. There is a secondary correlation in the sense that at the same M_* early-type galaxies have steeper gradients. The μ_* gradients outside 1 HLR show no dependence on Hubble type. We find mildly negative _M gradients, which are shallower than predicted from models of galaxy evolution in isolation. In general, metallicity gradients depend on stellar mass, and less on morphology, hinting that metallicity is affected by both - the depth of the potential well and morphology/quenching. Thus, the largest _M gradients occur in Milky Way-like Sb-Sbc galaxies, and are similar to those measured above the Galactic disk. Sc spirals show flatter _M gradients, possibly indicating a larger contribution from secular evolution in disks. The galaxies from the sample have decreasing-outward stellar extinction; all spirals show similar radial profiles, independent from the stellar mass, but redder than E and S0. Overall, we conclude that quenching processes act in manners that are independent of mass, while metallicity and galaxy structure are influenced by mass-dependent processes

Gran Telescopio Canarias observations of an overdense region of Lyman alpha emitters at z=6.5

We present the results of our search near the end of the Reionization Epoch for faint galaxies. This has been done using very deep OSIRIS images obtained at the Gran Telescopio Canarias (GTC). Our observations focus around two close, massive Lyman alpha emitters (LAEs) at redshift 6.5, discovered in the SXDS field within a large-scale overdense region. The total GTC observing time in three medium band filters (F883w35, F913w25 and F941w33) is over 34 h covering 7.0 x 8.5 arcmin(2) (or similar to 30 000 Mpc(3) at z = 6.5). In addition to the two spectroscopically confirmed LAEs in the field, we have identified 45 other LAE candidates. The preliminary luminosity function derived from our observations, assuming a spectroscopic confirmation success rate of 2/3 as in previous surveys, suggests this area is about 2 times denser than the general field galaxy population at z = 6.5. If confirmed spectroscopically, our results will imply the discovery of one of the earliest protoclusters in the Universe, which will evolve to resemble the most massive galaxy clusters today

Hif-1 alpha Knockdown Reduces Glycolytic Metabolism and Induces Cell Death of Human Synovial Fibroblasts Under Normoxic Conditions

Increased glycolysis and HIF-1 alpha activity are characteristics of cells under hypoxic or inflammatory conditions. Besides, in normal O-2 environments, elevated rates of glycolysis support critical cellular mechanisms such as cell survival. The purpose of this study was to analyze the contribution of HIF-1 alpha to the energy metabolism and survival of human synovial fibroblasts (SF) under normoxic conditions. HIF-1 alpha was silenced using lentiviral vectors or small-interfering RNA (siRNA) duplexes. Expression analysis by qRT-PCR and western blot of known HIF-1 alpha target genes in hypoxia demonstrated the presence of functional HIF-1 alpha in normoxic SF and confirmed the glycolytic enzyme glyceraldehyde3-phosphate dehydrogenase (GAPDH) as a HIF-1 alpha target even in normoxia. HIF-1 alpha silencing induced apoptotic cell death in cultured SF and, similarly, treatment with glycolytic, but not with OXPHOS inhibitors, induced SF death. Finally, in vivo HIF-1 alpha targeting by siRNA showed a significant reduction in the viability of human SF engrafted into a murine air pouch. Our results demonstrate that SF are highly dependent on glycolytic metabolism and that HIF-1 alpha plays a regulatory role in glycolysis even under aerobic conditions. Local targeting of HIF-1 alpha provides a feasible strategy to reduce SF hyperplasia in chronic arthritic diseases

No direct coupling between bending of galaxy disc stellar age and light profiles

We study the stellar properties of 44 face-on spiral galaxies from the Calar Alto Legacy Integral Field Area survey via full spectrum fitting techniques. We compare the age profiles with the surface brightness distribution in order to highlight differences between profile types (type I, exponential profile; and II, down-bending profile). We observe an upturn ('U-shape') in the age profiles for 17 out of these 44 galaxies with reliable stellar information up to their outer parts. This 'U-shape' is not a unique feature for type II galaxies but can be observed in type I as well. These findings suggest that the mechanisms shaping the surface brightness and stellar population distributions are not directly coupled. This upturn in age is only observable in the light-weighted profiles while it flattens out in the mass-weighted profiles. Given recent results on the outer parts of nearby systems and the results presented in this Letter, one of the most plausible explanations for the age upturn is an early formation of the entire disc(~10 Gyr ago) followed by an inside-out quenching of the star formation

Photoionization models of the CALIFA HII regions I. Hybrid models

Photoionization models of HIT regions require as input a description of the ionizing spectral energy distribution (SED) and of the gas distribution, in terms of ionization parameter U and chemical abundances (e.g., O/H and N/O). A strong degeneracy exists between the hardness of the SED and U, which in turn leads to high uncertainties in the determination of the other parameters, including abundances. One way to resolve the degeneracy is to fix one of the parameters using additional information. For each of the 20 000 sources of the CALIFA HIT regions catalog, a grid of photoionization models is computed assuming the ionizing SED to be described by the underlying stellar population obtained from spectral synthesis modeling. The ionizing SED is then defined as the sum of various stellar bursts of different ages and metallicities. This solves the degeneracy between the shape of the ionizing SED and U. The nebular metallicity (associated with O/H) is defined using the classical strong line method O3N2 (which gives our models the status of "hybrids"). The remaining free parameters are the abundance ratio N/O and the ionization parameter U, which are determined by looking for the model fitting [N II]/H alpha and [O III]/H beta. The models are also selected to fit [O II]/H beta. This process leads to a set of 3200 models that reproduce the three observations simultaneously. We find that the regions associated with young stellar bursts (i.e., ionized by OB stars) are affected by leaking of ionizing photons, the proportion of escaping photons having a median of 80%. The set of photoionization models satisfactorily reproduces the electron temperature derived from the [O III]lambda 4363/5007 line ratio. We determine new relations between the nebular parameters, like the ionization parameter U and the [OH]/[ III] or [S II]/[S III] line ratios. A new relation between N/O and O/H is obtained, mostly compatible with previous empirical determinations (and not with previous results obtained using photoionization models). A new relation between U and O/H is also determined. All the models are publicly available on the Mexican Million Models database 3MdB

The dependence of oxygen and nitrogen abundances on stellar mass from the CALIFA survey

Context. The study of the integrated properties of star-forming galaxies is central to understand their formation and evolution. Some of these properties are extensive and therefore their analysis require totally covering and spatially resolved observations. Among these properties, metallicity can be defined in spiral discs by means of integral field spectroscopy (IFS) of individual H II regions. The simultaneous analysis of the abundances of primary elements, as oxygen, and secondary, as nitrogen, also provides clues about the star formation history and the processes that shape the build-up of spiral discs. Aims. Our main aim is to analyse simultaneously O/H and N/O abundance ratios in H II regions in different radial positions of the discs in a large sample of spiral galaxies to obtain the slopes and the characteristic abundance ratios that can be related to their integrated properties. Methods. We analysed the optical spectra of individual selected H II regions extracted from a sample of 350 spiral galaxies of the CALIFA survey. We calculated total O/H abundances and, for the first time, N/O ratios using the semi-empirical routine H II-C HI-MISTRY, which, according to Perez-Montero (2014, MNRAS, 441, 2663), is consistent with the direct method and reduces the uncertainty in the O/H derivation using [N II] lines owing to the dispersion in the O/H-N/O relation. Then we performed linear fittings to the abundances as a function of the de-projected galactocentric distances. Results. The analysis of the radial distribution both for O/H and N/O in the non-interacting galaxies reveals that both average slopes are negative, but a non-negligible fraction of objects have a flat or even a positive gradient (at least 10% for O/H and 4% for N/O). The slopes normalised to the effective radius appear to have a slight dependence on the total stellar mass and the morphological type, as late low-mass objects tend to have flatter slopes. No clear relation is found, however, to explain the presence of inverted gradients in this sample, and there is no dependence between the average slopes and the presence of a bar. The relation between the resulting O/H and N/O linear fittings at the effective radius is much tighter (correlation coefficient ρ_s = 0.80) than between O/H and N/O slopes (ρ_s = 0.39) or for O/H and N/O in the individual H ii regions (ρ_s = 0.37). These O/H and N/O values at the effective radius also correlate very tightly (less than 0.03 dex of dispersion) with total luminosity and stellar mass. The relation with other integrated properties, such as star formation rate, colour, or morphology, can be understood only in light of the found relation with mass

Simultaneous optical and X-ray observations of flares and rotational modulation on the RS CVn binary HR 1099 (V711 Tau) from the MUSICOS 1998 campaign

We present simultaneous and continuous observations of the Hα, Hβ, He I D_3, Na I D_1,D_2 doublet and the Ca II H&K lines for the RS CVn system HR 1099. The spectroscopic observations were obtained during the MUSICOS 1998 campaign involving several observatories and instruments, both echelle and long-slit spectrographs. During this campaign, HR 1099 was observed almost continuously for more than 8 orbits of 2^d.8. Two large optical flares were observed, both showing an increase in the emission of Hα, Ca II H K, Hβ and He I D_3 and a strong filling-in of the Na I D_1, D_2 doublet. Contemporary photometric observations were carried out with the robotic telescopes APT-80 of Catania and Phoenix-25 of Fairborn Observatories. Maps of the distribution of the spotted regions on the photosphere of the binary components were derived using the Maximum Entropy and Tikhonov photometric regularization criteria. Rotational modulation was observed in Hα and He I D_3 in anti-correlation with the photometric light curves. Both flares occurred at the same binary phase (0.85), suggesting that these events took place in the same active region. Simultaneous X-ray observations, performed by ASM on board RXTE, show several flare-like events, some of which correlate well with the observed optical flares. Rotational modulation in the X-ray light curve has been detected with minimum flux when the less active G5 V star was in front. A possible periodicity in the X-ray flare-like events was also found

The AMY experiment: Microwave emission from air shower plasmas

You The Air Microwave Yield (AMY) experiment investigate the molecular bremsstrahlung radiation emitted in the GHz frequency range from an electron beam induced air-shower. The measurements have been performed at the Beam Test Facility (BTF) of Frascati INFN National Laboratories with a 510 MeV electron beam in a wide frequency range between 1 and 20 GHz. We present the apparatus and the results of the tests performed

Extreme magnification of an individual star at redshift 1.5 by a galaxy-cluster lens

Galaxy-cluster gravitational lenses can magnify background galaxies by a total factor of up to similar to 50. Here we report an image of an individual star at redshift z = 1.49 (dubbed MACS J1149 Lensed Star 1) magnified by more than x 2,000. A separate image, detected briefly 0.26 '' from Lensed Star 1, is probably a counterimage of the first star demagnified for multiple years by an object of greater than or similar to 3 solar masses in the cluster. For reasonable assumptions about the lensing system, microlensing fluctuations in the stars' light curves can yield evidence about the mass function of intracluster stars and compact objects, including binary fractions and specific stellar evolution and supernova models. Dark-matter subhaloes or massive compact objects may help to account for the two images' long-term brightness ratio

Observational hints of radial migration in disc galaxies from CALIFA

Context. According to numerical simulations, stars are not always kept at their birth galactocentric distances but they have a tendency to migrate. The importance of this radial migration in shaping galactic light distributions is still unclear. However, if radial migration is indeed important, galaxies with different surface brightness (SB) profiles must display differences in their stellar population properties. Aims. We investigate the role of radial migration in the light distribution and radial stellar content by comparing the inner colour, age, and metallicity gradients for galaxies with different SB profiles. We define these inner parts, avoiding the bulge and bar regions and up to around three disc scale lengths (type I, pure exponential) or the break radius (type II, downbending; type III, upbending). Methods. We analysed 214 spiral galaxies from the CALIFA survey covering different SB profiles. We made use of GASP2D and SDSS data to characterise the light distribution and obtain colour profiles of these spiral galaxies. The stellar age and metallicity profiles were computed using a methodology based on full-spectrum fitting techniques (pPXF,GANDALF, and STECKMAP) to the Integral Field Spectroscopic CALIFA data. Results. The distributions of the colour, stellar age, and stellar metallicity gradients in the inner parts for galaxies displaying different SB profiles are unalike as suggested by Kolmogorov-Smirnov and Anderson-Darling tests. We find a trend in which type II galaxies show the steepest profiles of all, type III show the shallowest, and type I display an intermediate behaviour. Conclusions. These results are consistent with a scenario in which radial migration is more efficient for type III galaxies than for type I systems, where type II galaxies present the lowest radial migration efficiency. In such a scenario, radial migration mixes the stellar content, thereby flattening the radial stellar properties and shaping different SB profiles. However, in light of these results we cannot further quantify the importance of radial migration in shaping spiral galaxies, and other processes, such as recent star formation or satellite accretion, might play a role