Density biases and temperature relations for DESIRED HII regions

We present a first study based on the analysis of the DEep Spectra of Ionized REgions Database (DESIRED). This is a compilation of 190 high signal-to-noise ratio optical spectra of HII regions and other photoionized nebulae, mostly observed with 8-10m telescopes and containing $\sim$29380 emission lines. We find that the electron density --$n_{\rm e}$-- of the objects is underestimated when [SII] $\lambda6731/\lambda6716$ and/or [OII] $\lambda3726/\lambda3729$ are the only density indicators available. This is produced by the non-linear density dependence of the indicators in the presence of density inhomogeneities. The average underestimate is $\sim 300$ cm$^{-3}$ in extragalactic HII regions, introducing systematic overestimates of $T_{\rm e}$([OII]) and $T_{\rm e}$([SII]) compared to $T_{\rm e}$([NII]). The high-sensitivity of [OII] $\lambda\lambda7319+20+30+31/\lambda\lambda3726+29$ and [SII] $\lambda\lambda4069+76/\lambda\lambda6716+31$ to density makes them more suitable for the diagnosis of the presence of high-density clumps. If $T_{\rm e}$([NII]) is adopted, the density underestimate has a small impact in the ionic abundances derived from optical spectra, being limited to up to $\sim$0.1 dex when auroral [SII] and/or [OII] lines are used. However, these density effects are critical for the analysis of infrared fine structure lines, such as those observed by the JWST in local star forming regions, implying strong underestimates of the ionic abundances. We present temperature relations between $T_{\rm e}$([OIII]), $T_{\rm e}$([ArIII]), $T_{\rm e}$([SIII]) and $T_{\rm e}$([NII]) for the extragalactic HII regions. We confirm a non-linear dependence between $T_{\rm e}$([OIII])-$T_{\rm e}$([NII]) due to a more rapid increase of $T_{\rm e}$([OIII]) at lower metallicities.Comment: Accepted for publication in MNRA

Hierarchical Star Formation: Stars and Stellar Clusters in the Gould Belt

We perform a study of the spatial and kinematical distribution of young open clusters in the solar neighborhood, discerning between bound clusters and transient stellar condensations within our sample. Then, we discriminate between Gould Belt (GB) and local Galactic disk (LGD) members, using a previous estimate of the structural parameters of both systems obtained from a sample of O-B6 Hipparcos stars. Using this classified sample we analyze the spatial structure and the kinematic behavior of the cluster system in the GB. The two star formation regions that dominate and give the GB its characteristic inclined shape show a striking difference in their content of star clusters: while Ori OB1 is richly populated by open clusters, not a single one can be found within the boundaries of Sco OB2. This is mirrored in the velocity space, translating again into an abundance of clusters in the region of the kinematic space populated by the members of Ori OB1, and a marginal number of them associated to Sco OB2. In the light of these results we study the nature of the GB with respect to the optical segment of the Orion Arm, and we propose that the different content of star clusters, the different heights over the Galactic plane and the different residual velocities of Ori OB1 and Sco OB2 can be explained in terms of their relative position to the density maximum of the Local Arm in the solar neighborhood. Although morphologically intriguing, the GB appears to be the result of our local and biased view of a larger star cluster complex in the Local Arm, that could be explained by the internal dynamics of the Galactic disk.Comment: 23 pages, including 12 figures. Accepted for publication in MNRA

Bar pattern speeds in CALIFA galaxies: I. Fast bars across the Hubble sequence

The bar pattern speed ($\Omega_{\rm b}$) is defined as the rotational frequency of the bar, and it determines the bar dynamics. Several methods have been proposed for measuring $\Omega_{\rm b}$. The non-parametric method proposed by Tremaine \& Weinberg (1984; TW) and based on stellar kinematics is the most accurate. This method has been applied so far to 17 galaxies, most of them SB0 and SBa types. We have applied the TW method to a new sample of 15 strong and bright barred galaxies, spanning a wide range of morphological types from SB0 to SBbc. Combining our analysis with previous studies, we investigate 32 barred galaxies with their pattern speed measured by the TW method. The resulting total sample of barred galaxies allows us to study the dependence of $\Omega_{\rm b}$ on galaxy properties, such as the Hubble type. We measured $\Omega_{\rm b}$ using the TW method on the stellar velocity maps provided by the integral-field spectroscopy data from the CALIFA survey. Integral-field data solve the problems that long-slit data present when applying the TW method, resulting in the determination of more accurate $\Omega_{\rm b}$. In addition, we have also derived the ratio $\cal{R}$ of the corotation radius to the bar length of the galaxies. According to this parameter, bars can be classified as fast ($\cal{R}$ $1.4). For all the galaxies,$\cal{R}$is compatible within the errors with fast bars. We cannot rule out (at 95$\%$level) the fast bar solution for any galaxy. We have not observed any significant trend between$\cal{R}$ and the galaxy morphological type. Our results indicate that independent of the Hubble type, bars have been formed and then evolve as fast rotators. This observational result will constrain the scenarios of formation and evolution of bars proposed by numerical simulations.Comment: 17 pages, 10 figures, accepted for publication in A&

Functional upgrading in China’s export processing sector

Functional upgrading occurs when a firm acquires more sophisticated functions within an existing value chain. In this paper, we analyze if there is evidence of this type of upgrading in China’s export processing regime by investigating dynamics in the relative prevalence of Import & Assembly (IA) versus Pure Assembly (PA) processing trade over the period 2000-2013. Firms in both regimes provide similar manufacturing services to foreign companies, but IA firms also conduct the sophisticated tasks of quality control, searching, financing and storing imported materials. Consistent with a trend of functional upgrading, we show that the share of IA trade in total processing trade has increased rapidly during the period 2000-2006, both overall and within product categories. Furthermore, we find that this trend has gone hand in hand with improvements in a sector’s labor productivity and unit values. Against expectations, we find that this process has slowed down notably during the period 2006-2013.status: publishe

Quantifying the energetics of molecular superbubbles in PHANGS galaxies

Star formation and stellar feedback are interlinked processes that redistribute energy and matter throughout galaxies. When young, massive stars form in spatially clustered environments, they create pockets of expanding gas termed superbubbles. As these processes play a critical role in shaping galaxy discs and regulating the baryon cycle, measuring the properties of superbubbles provides important input for galaxy evolution models. With wide coverage and high angular resolution (50-150 pc) of the PHANGS-ALMA $^{12}$CO (2-1) survey, we can now resolve and identify a statistically representative number of superbubbles with molecular gas in nearby galaxies. We identify superbubbles by requiring spatial correspondence between shells in CO with stellar populations identified in PHANGS-HST, and combine the properties of the stellar populations with CO to constrain feedback models and quantify their energetics. We visually identify 325 cavities across 18 PHANGS-ALMA galaxies, 88 of which have clear superbubble signatures (unbroken shells, central clusters, kinematic signatures of expansion). We measure their radii and expansion velocities using CO to dynamically derive their ages and the mechanical power driving the bubbles, which we use to compute the expected properties of the parent stellar populations driving the bubbles. We find consistency between the predicted and derived stellar ages and masses of the stellar populations if we use a supernova blast wave model that injects energy with a coupling efficiency of 10%, whereas continuous models fail to explain stellar ages we measure. Not only does this confirm molecular gas accurately traces superbubble properties, but it also provides key observational constraints for superbubble models. We also find evidence that the bubbles sweep up gas as they expand and speculate that these sites have the potential to host new generations of stars.Comment: 21 pages, 15 figures, 3 tables. Accepted to A&A. Abstract abridged for arXi

Shape of the oxygen abundance profiles in CALIFA face-on spiral galaxies

Y.A. acknowledges financial support from the Ramón y Cajal programme (RyC-2011-09461). Y.A. and A.I.D. acknowledge support from the project AYA2013-47742-C4-3-P from the Spanish MINECO, as well as the “Study of Emission-Line Galaxies with Integral-Field Spectroscopy” (SELGIFS) programme, funded by the EU (FP7-PEOPLE-2013-IRSES-612701). 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. LG acknowledges support by CONICYT through FONDECYT grant 3140566. R.M.G.D. acknowledges support from the Spanish grant AYA2014-57490-P, and from the “Junta de Andalucía” P12-FQM2828 project. RAM thanks the Spanish program of International Campus of Excellence Moncloa (CEI). IM and A.d.O. acknowledge support from the Spanish MINECO grant AYA2013-42227P. JMA acknowledges support from the European Research Council Starting Grant (SEDmorph, P.I. V. Wild). Support for MM has been provided by DGICYT grant AYA2013-47742-C4-4-P. PSB acknowledges support from the Ramón y Cajal programme, grant ATA2010-21322-C03-02 from the Spanish MINECO. CJW acknowledges support through the Marie Curie Career Grant Integration 303912.We measured the gas abundance profiles in a sample of 122 face-on spiral galaxies observed by the CALIFA survey and included all spaxels whose line emission was consistent with star formation. This type of analysis allowed us to improve the statistics with respect to previous studies, and to properly estimate the oxygen distribution across the entire disc to a distance of up to 3-4 disc effective radii (re). We confirm the results obtained from classical H ii region analysis. In addition to the general negative gradient, an outer flattening can be observed in the oxygen abundance radial profile. An inner drop is also found in some cases. There is a common abundance gradient between 0.5 and 2.0 re of αO/H =-0.075 dex/re with a scatter of σ = 0.016 dex/re when normalising the distances to the disc effective radius. By performing a set of Kolmogorov-Smirnov tests, we determined that this slope is independent of other galaxy properties, such as morphology, absolute magnitude, and the presence or absence of bars. In particular, barred galaxies do not seem to display shallower gradients, as predicted by numerical simulations. Interestingly, we find that most of thegalaxies in the sample with reliable oxygen abundance values beyond ~2 effective radii (57 galaxies) present a flattening of the abundance gradient in these outer regions. This flattening is not associated with any morphological feature, which suggests that it is a common property of disc galaxies. Finally, we detect a drop or truncation of the abundance in the inner regions of 27 galaxies in the sample; this is only visible for the most massive galaxies.Publisher PDFPeer reviewe

Shape of the oxygen abundance profiles in CALIFA face-on spiral galaxies

Astronomy & Astrophysics 587 (2016): A70 reproduced with permission from Astronomy & AstrophysicsWe measured the gas abundance profiles in a sample of 122 face-on spiral galaxies observed by the CALIFA survey and included all spaxels whose line emission was consistent with star formation. This type of analysis allowed us to improve the statistics with respect to previous studies, and to properly estimate the oxygen distribution across the entire disc to a distance of up to 3-4 disc effective radii (re). We confirm the results obtained from classical H ii region analysis. In addition to the general negative gradient, an outer flattening can be observed in the oxygen abundance radial profile. An inner drop is also found in some cases. There is a common abundance gradient between 0.5 and 2.0 re of αO/H =-0.075 dex/re with a scatter of σ = 0.016 dex/re when normalising the distances to the disc effective radius. By performing a set of Kolmogorov-Smirnov tests, we determined that this slope is independent of other galaxy properties, such as morphology, absolute magnitude, and the presence or absence of bars. In particular, barred galaxies do not seem to display shallower gradients, as predicted by numerical simulations. Interestingly, we find that most of thegalaxies in the sample with reliable oxygen abundance values beyond ~2 effective radii (57 galaxies) present a flattening of the abundance gradient in these outer regions. This flattening is not associated with any morphological feature, which suggests that it is a common property of disc galaxies. Finally, we detect a drop or truncation of the abundance in the inner regions of 27 galaxies in the sample; this is only visible for the most massive galaxiesWe acknowledge financial support from the Spanish Ministerio de Economía y Competitividad (MINECO) via grant AYA2012-31935, and from the “Junta de Andalucía” local government through the FQM-108 project. We also acknowledge support to the ConaCyt funding program 180125. Y.A. acknowledges fi- nantial support from the Ramón y Cajal programme (RyC-2011-09461). Y.A. and A.I.D. acknowledge support from the project AYA2013-47742-C4-3-P from the Spanish MINECO, as well as the “Study of Emission-Line Galaxies with Integral-Field Spectroscopy” (SELGIFS) programme, funded by the EU (FP7- PEOPLE-2013-IRSES-612701). 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. LG acknowledges support by CONICYT through FONDECYT grant 3140566. R.M.G.D. acknowledges support from the Spanish grant AYA2014-57490-P, and from the “Junta de Andalucía” P12-FQM2828 project. RAM thanks the Spanish program of International Campus of Excellence Moncloa (CEI). IM and A.d.O. acknowledge support from the Spanish MINECO grant AYA2013-42227P. JMA acknowledges support from the European Research Council Starting Grant (SEDmorph, P.I. V. Wild). Support for MM has been provided by DGICYT grant AYA2013-47742-C4-4-P. PSB acknowledges support from the Ramón y Cajal programme, grant ATA2010-21322-C03-02 from the Spanish MINECO. CJW acknowledges support through the Marie Curie Career Grant Integration 30391