Star formation along the Hubble sequence Radial structure of the star formation of CALIFA galaxies

González Delgado, Rosa M. et. al.The spatially resolved stellar population content of today's galaxies holds important information for understanding the different processes that contribute to the star formation and mass assembly histories of galaxies. The aim of this paper is to characterize the radial structure of the star formation rate (SFR) in galaxies in the nearby Universe as represented by a uniquely rich and diverse data set drawn from the CALIFA survey. The sample under study contains 416 galaxies observed with integral field spectroscopy, covering a wide range of Hubble types and stellar masses ranging from M* similar to 10(9) to 7 x 10(11) M-circle dot. Spectral synthesis techniques are applied to the datacubes to derive 2D maps and radial profiles of the intensity of the star formation rate in the recent past (Sigma(SFR)), as well as related properties, such as the local specific star formation rate (sSFR), defined as the ratio between Sigma(SFR) and the stellar mass surface density (mu*). To emphasize the behavior of these properties for galaxies that are on and off the main sequence of star formation (MSSF), we stack the individual radial profiles in seven bins of galaxy morphology ( E, S0, Sa, Sb, Sbc, Sc, and Sd), and several stellar masses. Our main results are: ( a) the intensity of the star formation rate shows declining profiles that exhibit very small differences between spirals with values at R = 1 half light radius (HLR) within a factor two of Sigma(SFR) similar to 20 M-circle dot Gyr(-1) pc(-2). The dispersion in the Sigma(SFR)(R) profiles is significantly smaller in late type spirals (Sbc, Sc, Sd). This confirms that the MSSF is a sequence of galaxies with nearly constant Sigma(SFR). (b) sSFR values scale with Hubble type and increase radially outward with a steeper slope in the inner 1 HLR. This behavior suggests that galaxies are quenched inside-out and that this process is faster in the central, bulge-dominated part than in the disks. (c) As a whole and at all radii, E and S0 are off the MSSF with SFR much smaller than spirals of the same mass. (d) Applying the volume corrections for the CALIFA sample, we obtain a density of star formation in the local Universe of rho SFR = (0.0105 +/- 0.0008) M-circle dot yr(-1) Mpc(-3), in agreement with independent estimates. Most of the star formation is occurring in the disks of spirals. (e) The volume-averaged birthrate parameter, which measures the current SFR with respect to its lifetime average, b' = 0.39 +/- 0.03, suggests that the present day Universe is forming stars a about one-third of its past average rate. E, S0, and the bulge of early type spirals (Sa, Sb) contribute little to the recent SFR of the Universe, which is dominated by the disks of Sbc, Sc, and Sd spirals. (f) There is a tight relation between Sigma(SFR) and mu*, defining a local MSSF relation with a logarithmic slope of 0.8, similar to the global MSSF relation between SFR and M*. This suggests that local processes are important in determining the star formation in disks, probably through a density dependence of the SFR law. The scatter in the local MSSF is driven by morphology-related off sets, with Sigma(SFR)/mu* (the local sSFR) increasing from early to late type galaxies, indicating that the shut down of the star formation is more related to global processes, such as the formation of a spheroidal component.Support from the Spanish Ministerio de Economia y Competitividad, through projects AYA2014-57490-P, AYA2010-15081, and Junta de Andalucia FQ1580, AYA2010-22111-C03-03, AYA2010-10904E, AYA2013-42227P, RyC-2011-09461, AYA2013-47742-C4-3-P, EU SELGIFS exchange program FP7-PEOPLE-2013-IRSES-612701, and CONACYT-125180 and DGAPA-IA100815. We also thank the Viabilidad, Diseno, Acceso y Mejora funding program, ICTS-2009-10, for funding the data acquisition of this project.Peer reviewe

Star formation histories in mergers: the spatially resolved properties of the early-stage merger luminous infrared galaxies IC 1623 and NGC 6090

The role of major mergers in galaxy evolution is investigated through a detailed characterization of the stellar populations, ionized gas properties and star formation rates (SFR) in the early-stage merger luminous infrared galaxies (LIRGs) IC 1623 W and NGC 6090, by analysing optical integral field spectroscopy and high-resolution Hubble Space Telescope imaging. The spectra were processed with the starlight full spectral fitting code, and the emission lines measured in the residual spectra. The results are compared with non-interacting control spiral galaxies from the Calar Alto Legacy Integral Field Area survey. Merger-induced star formation is extended and recent, as revealed by the young ages (50–80 Myr) and high contributions to light of young stellar populations (50–90 per cent), in agreement with merger simulations in the literature. These early-stage mergers have positive central gradients of the stellar metallicity, with an average ∼0.6 Z⊙. Compared to non-interacting spirals, they have lower central nebular metallicity, and flatter profiles, in agreement with the gas inflow scenario. We find that they are dominated by star formation, although shock excitation cannot be discarded in some regions, where high velocity dispersion is found (170–200 km s−1). The average SFR in these early-stage mergers (∼23–32 M⊙ yr−1) is enhanced with respect to main-sequence Sbc galaxies by factors of 6–9, slightly above the predictions from classical merger simulations, but still possible in about 15 per cent of major galaxy mergers, where U/LIRGs belong

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

© ESO, 2015. 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 MBlack star ∼ 109 to 7 × 1011 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 (μBlack star), stellar extinction (AV), light-weighted and mass-weighted ages ('log age'L, 'log age'M), and mass-weighted metallicity ('log ZBlack star'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 MBlack star, which is evidence that quenching is related to morphology, but not driven by mass. Negative gradients of 'log age'L are consistent with an inside-out growth of galaxies, with the largest 'log age'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 MBlack star early-type galaxies have steeper gradients. The μBlack star gradients outside 1 HLR show no dependence on Hubble type. We find mildly negative 'log ZBlack star'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.Support from the Spanish Ministerio de Economia y Competitividad, through projects AYA2010-15081 (PI R.G.D.), and Junta de Andalucia FQ1580 (PI R.G.D.), AYA2010-22111-C03-03, and AYA2010-10904E (S.F.S.). We also thank the Viabilidad, Diseno, Acceso y Mejora funding program, ICTS-2009-10, for funding the data acquisition of this project. R.C.F. thanks the hospitality of the IAA and the support of CAPES and CNPq. R.G.D. acknowledges the support of CNPq (Brazil) through Programa Ciencia sem Fronteiras (401452/2012-3). A.G. acknowledges support from EU FP7/2007-2013 under grant agreement n.267251 (AstroFIt) and from the EU Marie Curie Integration Grant >SteMaGE> Nr. PCIG12-GA-2012-326466. C.J.W. acknowledges support through the Marie Curie Career Integration Grant 303912. E.P. acknowledges support from the Guillermo Haro program at INAOE. Support for L.G. is provided by the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS. L.G. acknowledges support by CONICYT through FONDECYT grant 3140566. J.I.P. acknowledges financial support from the Spanish MINECO under grant AYA2010-21887-C04-01 and from Junta de Andalucia Excellence Project PEX2011-FQM7058. I.M., J.M. and A.d.O. acknowledge support from the project AYA2013-42227-P. RAM is funded by the Spanish program of International Campus of Excellence Moncloa (CEI). J.M. A. acknowledges support from the European Research Council Starting Grant (SEDmorph; P.I. V. Wild).Peer Reviewe

Simultaneous spectroscopic and photometric analysis of galaxies with STARLIGHT: CALIFA+GALEX

We present an extended version of the spectral synthesis code STARLIGHT designed to incorporate both λ-by-λ spectra and photometric fluxes in the estimation of stellar population properties of galaxies. The code is tested with simulations and data for 260 galaxies culled from the Calar Alto Legacy Integral Field Area (CALIFA) survey, spatially matching the 3700-7000 Å optical data cubes to Galaxy Evolution Explorer (GALEX) near-ultraviolet (NUV) and farultraviolet (FUV) images. The sample spans E-Sd galaxies with masses from 10 to 10M⊙ and stellar populations all the way from star-forming to old, passive systems. Comparing results derived from purely optical fits with those which also consider the NUV and FUV data we find that the following. (1) The new code is capable of matching the input ultraviolet (UV) data within the errors while keeping the quality of the optical fit essentially unchanged. (2) Despite being unreliable predictors of the UV fluxes, purely optical fits yield stellar population properties which agree well with those obtained in optical+UV fits for nearly 90 per cent of our sample. (3) The addition of UV constraints has little impact on properties such as stellar mass and dust optical depth. Mean stellar ages and metallicities also remain nearly the same for most galaxies, the exception being low-mass, late-type galaxies, which become older and less enriched due to rearrangements of their youngest populations. (4) The revised ages are better correlated with observables such as the 4000 Å break index, and the NUV - r and u - r colours, an empirical indication that the addition of UV constraints helps mitigating the effects of age-metallicity-extinction degeneracies. © 2016 The Authors.Support from the Spanish Ministerio de Econom´ıa y Competitividad, through projects AYA2014-57490-P, AYA2010-15081 (PI RGD), Junta de Andaluc´ıa FQ1580 (PI RGD), AYA2010-22111-C03-03, AYA2010-10904E (SFS), and short-term research FPI program grants EEBB-I-2013-07071 and EEBB-I-2014-08601. SFS thanks the CONACYT-125180 and DGAPA-IA100815 projects for providing him support in this study. We also thank the Viabilidad, Diseno, ˜ Acceso y Mejora funding program, ICTS-2009-10, for funding the data acquisition of this project. Support from the Brazilian Science Galaxy spectrophotometry with STARLIGHT 199 without borders program, as well as CNPq and CAPES is duly acknowledged. This research made use of Montage. It is funded by the National Science Foundation under Grant Number ACI- 1440620, and was previously funded by the National Aeronautics and Space Administration’s Earth Science Technology Office, Computation Technologies Project, under Cooperative Agreement Number NCC5-626 between NASA and the California Institute of TechnologyPeer Reviewe

H II regions in CALIFA survey: II. The relation between their physical properties and galaxy evolution

We present here the exploration of the physical properties of the sample of H II regions and aggregations of the last H II regions catalogue of the Calar Alto Legacy Integral Field Area (CALIFA) survey. This sample comprises the optical spectroscopic properties of more than ∼26 000 ionized regions corresponding to 924 galaxies from the Integral Field Spectroscopy data, including the flux intensity and equivalent widths and the properties of their underlying stellar population. In the current study, we derive a set of physical quantities for all these regions based on those properties, including (i) the fraction of young stars; (ii) the ionization strength (using six different estimations); (iii) the oxygen abundance (using 25 different calibrators); (iv) the nitrogen and nitrogen-to-oxygen abundance; (v) the dust extinction; and (vi) the electron density. Using this data set, we explore how the loci in the classical diagnostic diagrams are connected with those quantities, the radial distributions of these parameters, and the interrelations between themselves and with the properties of the underlying stellar populations. We conclude that many properties of the H II regions are tightly related to the galactic stellar evolution at the location where those regions are observed. Those properties are modulated only as a second-order effect by the properties of the ionizing stars and the ionized nebulae that do not depend on the astrophysical context in which they are formed. Our results highlight the importance of H II regions to explore the chemical evolution in galaxies, clarifying which of their properties can be used as proxies of that evolution. © 2022 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society.CM acknowledges support from grant UNAM/PAPIIT – IN101220. We are grateful for the support of the PAPIIT-DGAPA-IG100622 and PAPIIT-DGAPA-IN112620 (UNAM) projects. RGB acknowledges additional financial support from the State Agency for Research of the Spanish MCIU through the Center of Excellence Severo Ochoa award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) grants PID2019-109067GB-I00 (MCIU) and P18-FRJ-2595 (Junta de Andalucía). LG acknowledges financial support from the Spanish Ministerio de Ciencia e Innovación (MCIN), the Agencia Estatal de Investigación (AEI) 10.13039/501100011033, and the European Social Fund (ESF) ‘Investing in your future’ under the 2019 Ramón y Cajal program RYC2019-027683-I and the PID2020-115253GA-I00 HOSTFLOWS project, and from Centro Superior de Investigaciones Científicas (CSIC) under the PIE project 20215AT016.Peer reviewe

Diffuse ionized gas in galaxies across the Hubble sequence at the CALIFA resolution

We use spatially resolved spectroscopy from the Calar Alto Legacy Integral Field Area (CALIFA) survey to study the nature of the line emitting gas in galaxies of different Hubble types, focusing on the separation of star-forming (SF) regions from those better characterized as diffuse ionized gas (DIG). The diagnosis is carried out in terms of the equivalent width of α (W). Three nebular regimes are identified. Regions where W 14 Å trace SF complexes. W values in the intermediate 3-14 Å range reflect a mixed regime (mDIG) where more than one process contributes. This three-tier scheme is inspired both by theoretical and empirical considerations. Its application to CALIFA galaxies of different types and inclinations leads to the following results: (i) the hDIG component is prevalent throughout ellipticals and S0's as well as in bulges, and explains the strongly bimodal distribution of W both among and within galaxies. (ii) Early-type spirals have some hDIG in their discs, but this component becomes progressively less relevant for later Hubble types. (iii) hDIG emission is also present above and below galactic discs, as seen in several edge-on spirals in our sample. (iv) The SF/mDIG proportion grows steadily from early- to late-type spirals, and from inner to outer radii. (v) Besides circumventing basic inconsistencies in conventional DIG/SF separation criteria based on the Hα surface brightness, our W-based method produces results in agreement with a classical excitation diagram analysis.© 2017 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society.EADL, RCF, GS, and NVA acknowledge the support from the CAPES CsF-PVE project 88881.068116/2014-01. RGD acknowledges the support of CNPq (Brazil) through Programa Ciencia sem Fronteiras (401452/2012-3). CALIFA is the first legacy survey carried out at Calar Alto. The CALIFA collaboration would like to thank the IAA-CSIC and MPIA-MPG as major partners of the observatory, and CAHA itself, for the unique access to telescope time and support in manpower and infrastructures. We also thank the CAHA staff for the dedication to this project. Support from the Spanish Ministerio de Economia y Competitividad, through projects AYA2016-77846-P, AYA2014-57490-P, AYA2010-15081, and Junta de Andalucia FQ1580.Peer Reviewe

The spatially resolved star formation history of CALIFA galaxies: Cosmic time scales

This paper presents the mass assembly time scales of nearby galaxies observed by CALIFA at the 3.5 m telescope in Calar Alto. We apply the fossil record method of the stellar populations to the complete sample of the 3rd CALIFA data release, with a total of 661 galaxies, covering stellar masses from 10 to 10M and a wide range of Hubble types. We apply spectral synthesis techniques to the datacubes and process the results to produce the mass growth time scales and mass weighted ages, from which we obtain temporal and spatially resolved information in seven bins of galaxy morphology (E, S0, Sa, Sb, Sc, and Sd) and six bins of stellar mass and stellar mass surface density. We use three different tracers of the spatially resolved star formation history (mass assembly curves, ratio of half mass to half light radii, and mass-weighted age gradients) to test if galaxies grow inside-out, and its dependence with galaxy stellar mass, stellar mass surface density, and morphology. Our main results are as follows: (a) the innermost regions of galaxies assemble their mass at an earlier time than regions located in the outer parts; this happens at any given stellar mass (M), stellar mass surface density (Σ), or Hubble type, including the lowest mass systems in our sample. (b) Galaxies present a significant diversity in their characteristic formation epochs for lower-mass systems. This diversity shows a strong dependence of the mass assembly time scales on Σ and Hubble type in the lower-mass range (10 to 10), but a very mild dependence in higher-mass bins. (c) The lowest half mass radius (HMR) to half light radius (HLR) ratio is found for galaxies between 10 and 10M, where galaxies are 25% smaller in mass than in light. Low-mass galaxies show the largest ratio with HMR/HLR ∼ 0.89. Sb and Sbc galaxies present the lowest HMR/HLR ratio (0.74). The ratio HMR/HLR is always, on average, below 1, indicating that galaxies grow faster in mass than in light. (d) All galaxies show negative (log age) gradients in the inner 1 HLR. The profile flattens (slope less negative) with increasing values of Σ. There is no significant dependence on M within a particular Σ bin, except for the lowest bin, where the gradients becomes steeper. (e) Downsizing is spatially preserved as a function of M and Σ, but it is broken for E and SO where the outer parts are assembled in later epochs than Sa galaxies. These results suggest that independently of their stellar mass, stellar mass surface density, and morphology, galaxies form inside-out on average. © ESO, 2017.CALIFA is the first legacy survey carried out at Calar Alto. The CALIFA collaboration would like to thank the IAA-CSIC and MPIA-MPG as major partners of the observatory, and CAHA itself, for the unique access to telescope time and support in manpower and infrastructures. We also thank the CAHA staff for their dedication to this project. We are grateful for the support of the IAA Computing group. Support from the Spanish Ministerio de Economia y Competitividad, through projects AYA2016-77846-P, AYA2014-57490-P, AYA2010-15081, and Junta de Andalucia P12-FQM-2828. R.C.F. acknowledges support from CNPq and FAPESC. S.F.S. thanks PAPIIT-DGAPA-IA101217 project and CONACYT-IA-180125. This research made use of Python (http://www.python.org); Numpy (Van Der Walt et al. 2011), Astropy (Astropy Collaboration et al. 2013), Pandas (McKinney 2011), Matplotlib (Hunter 2007), and Seaborn (Waskom et al. 2016). We thank the referee for very useful comments that improved the presentation of the paper.Peer reviewe

Spatially-resolved star formation histories of CALIFA galaxies: Implications for galaxy formation

This paper presents the spatially resolved star formation history (SFH) of nearby galaxies with the aim of furthering our understanding of the different processes involved in the formation and evolution of galaxies. To this end, we apply the fossil record method of stellar population synthesis to a rich and diverse data set of 436 galaxies observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, with stellar masses ranging from M ∼ 10 to 7 × 10 M. Spectral synthesis techniques are applied to the datacubes to retrieve the spatially resolved time evolution of the star formation rate (SFR), its intensity (Σ), and other descriptors of the 2D SFH in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd) and five bins of stellar mass. Our main results are that (a) galaxies form very fast independently of their current stellar mass, with the peak of star formation at high redshift (z > 2). Subsequent star formation is driven by M and morphology, with less massive and later type spirals showing more prolonged periods of star formation. (b) At any epoch in the past, the SFR is proportional to M, with most massive galaxies having the highest absolute (but lowest specific) SFRs. (c) While today, the Σ is similar for all spirals and significantly lower in early-type galaxies (ETG), in the past, the Σ scales well with morphology. The central regions of today's ETGs are where the Σ reached the highest values (> 10 M Gyr pc), similar to those measured in high-redshift star-forming galaxies. (d) The evolution of Σ in Sbc systems matches that of models for Milky Way-like galaxies, suggesting that the formation of a thick disk may be a common phase in spirals at early epochs. (e) The SFR and Σ in outer regions of E and S0 galaxies show that they have undergone an extended phase of growth in mass between z = 2 and 0.4. The mass assembled in this phase is in agreement with the two-phase scenario proposed for the formation of ETGs. (f) Evidence of an early and fast quenching is found only in the most massive (M > 2 × 10 M) E galaxies of the sample, but not in spirals of similar mass, suggesting that halo quenching is not the main mechanism for the shut down of star formation in galaxies. Less massive E and disk galaxies show more extended SFHs and a slow quenching. (g) Evidence of fast quenching is also found in the nuclei of ETG and early spirals, with SFR and Σ indicating that they can be the relic of the >red nuggets> detected at high redshift.© ESO, 2017.Support from the Spanish Ministerio de Economia y Competitividad, through projects AYA2016-77846-P, AYA2014-57490-P, AYA2010-15081, and Junta de Andalucia FQ1580, AYA2010-22111-C03-03, AYA2010-10904E, AYA2013-42227P, RyC-2011-09461, AYA2013-47742-C4-3-P, EU SELGIFS exchange programme FP7-PEOPLE-2013-IRSES-612701, CONACYT-125180, DGAPA-IA100815, and PAPIIT-DGAPA-IA101217. We also thank the Viabilidad, Diseno, Acceso y Mejora funding program, ICTS-2009-10, for funding the data acquisition of this project. A.L.d.A., E.A.D.L. and R.C.F. thanks for the hospitality of the IAA and the support of CNPq. R.G.D. acknowledges the support of CNPq (Brazil) through Programa Ciencia sem Fronteiras (401452/2012-3). C.J.W. acknowledges support through the Marie Curie Career Integration Grant 303912.Peer Reviewe