Improving star cluster age estimates in PHANGS-HST galaxies and the impact on cluster demographics in NGC 628

We thank the referee for several useful and constructive comments that lead to improvements in the paper. Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. Support for Program number 15654 was provided through a grant from the STScI under NASA contract NAS5-26555. FB and AB would like to acknowledge funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No.726384/Empire). MB gratefully acknowledges support by the ANID BASAL project FB210003 and from the FONDECYT regular grant 1211000. EW acknowledges support from the DFG via SFB 881 ‘The Milky Way System’ (project-ID 138713538; subproject P01). FB acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No.726384/Empire). HAP acknowledges support by the National Science and Technology Council of Taiwan under grant 110-2112-M-032-020-MY3. JMDK acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme via the ERC Starting Grant MUSTANG (grant agreement number 714907). COOL Research DAO is a Decentralised Autonomous Organisation supporting research in astrophysics aimed at uncovering our cosmic origins. KG is supported by the Australian Research Council through the Discovery Early Career Researcher Award (DECRA) Fellowship DE220100766 funded by the Australian Government. KK and FS gratefully acknowledge funding from the German Research Foundation (DFG) in the form of an Emmy Noether Research Group (grant No. KR4598/2-1, PI Kreckel). PSB acknowledges financial support from the Spanish Ministry of Science, Innovation and Universities under grant number PID2019-107427GB-C31. RSK and MCS are thankful for support from the Deutsche Forschungsgemeinschaft (DFG) via the Collaborative Research Center (SFB 881, ProjectID 138713538) “The Milky Way System” (sub-projects A1, B1, B2 and B8) and from the Heidelberg Cluster of Excellence (EXC 2181 - 390900948) “STRUCTURES: A unifying approach to emergent phenomena in the physical world, mathematics, and complex data”, funded by the German Excellence Strategy. RSK and MSC also acknowledge funding from the European Research Council in the ERC Synergy Grant “ECOGAL – Understanding our Galactic ecosystem: From the disk of the Milky Way to the formation sites of stars and planets” (project ID 855130). TGW acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No. 694343).A long-standing problem when deriving the physical properties of stellar populations is the degeneracy between age, reddening, and metallicity. When a single metallicity is used for all the star clusters in a galaxy, this degeneracy can result in 'catastrophic' errors for old globular clusters. Typically, approximately 10-20 per cent of all clusters detected in spiral galaxies can have ages that are incorrect by a factor of 10 or more. In this paper, we present a pilot study for four galaxies (NGC 628, NGC 1433, NGC 1365, and NGC 3351) from the PHANGS-HST survey. We describe methods to correct the age-dating for old globular clusters, by first identifying candidates using their colours, and then reassigning ages and reddening based on a lower metallicity solution. We find that young 'Interlopers' can be identified from their H alpha flux. CO (2-1) intensity or the presence of dust can also be used, but our tests show that they do not work as well. Improvements in the success fraction are possible at the approximate to 15 per cent level (reducing the fraction of catastrophic age-estimates from between 13 and 21 per cent, to between 3 and 8 per cent). A large fraction of the incorrectly age-dated globular clusters are systematically given ages around 100 Myr, polluting the younger populations as well. Incorrectly age-dated globular clusters significantly impact the observed cluster age distribution in NGC 628, which affects the physical interpretation of cluster disruption in this galaxy. For NGC 1365, we also demonstrate how to fix a second major age-dating problem, where very dusty young clusters with E(B - V) > 1.5 mag are assigned old, globular-cluster like ages. Finally, we note the discovery of a dense population of approximate to 300 Myr clusters around the central region of NGC 1365 and discuss how this results naturally from the dynamics in a barred galaxy.Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEAssociation of Universities for Research in Astronomy, Inc. under NASA contractEuropean Research Council (ERC) under the European Union’s Horizon 2020ANID BASALFondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)DFG via SFB 881 ‘The Milky Way System’National Science and Technology Council of TaiwanERC Starting Grant MUSTANGAustralian Research Council through the Discovery Early Career Researcher Award (DECRA)German Research Foundation (DFG)Ministerio de Ciencia, Innovación y UniversidadesDeutsche Forschungsgemeinschaft (DFG) via the Collaborative Research CenterHeidelberg Cluster of Excellence funded by the German Excellence StrategyEuropean Research Council in the ERC Synergypu

PHANGS-JWST first results: a combined HST and JWST analysis of the nuclear star cluster in NGC 628

© 2023. The Author(s). Artículo firmado por 32 autores. This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 526555. These observations are associated with program 15654. This work is based on observations made with the NASA/ESA/CSA JWST. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127. The observations are associated with JWST program 02107. This research has made use of the Spanish Virtual Observatory (https://svo.cab.intacsic.es) project funded by MCIN/AEI/10.13039/ 501100011033/ through grant PID2020-112949GB-I00. N.H. and A.W.H.K. are fellows of the International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg (IMPRS-HD) and acknowledge their support. N.H. acknowledges support from Thomas Müller (HdA/MPIA) with generating part of Figure 1 and Katja Fahrion and Torsten Böker for useful discussions. A.T.B. and F.B. would like to acknowledge funding from the European Research Council (ERC) under the European Unionʼs Horizon 2020 research and innovation program (grant agreement No. 726384/Empire). E.J.W. acknowledges the funding provided by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Project-ID 138713538—SFB 881 (“The Milky Way System,” subproject P1) T.G.W. and J.N. acknowledge funding from the European Research Council (ERC) under the European Unionʼs Horizon 2020 research and innovation program (grant agreement No. 694343). J.M.D.K. gratefully acknowledges funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program via the ERC Starting Grant MUSTANG (grant agreement No. 714907). COOL Research DAO is a Decentralized Autonomous Organization supporting research in astrophysics aimed at uncovering our cosmic origins. R.S.K. acknowledges funding from the European Research Council via the ERC Synergy Grant “ECOGAL” (project ID 855130), the Deutsche Forschungsgemeinschaft (DFG) via the Collaborative Research Center “The Milky Way System” (SFB 881—funding ID 138713538—subprojects A1, B1, B2 and B8), and the Heidelberg Cluster of Excellence (EXC 2181-390900948) “STRUCTURES,” funded by the German Excellence Strategy. R.S.K. also thanks the German Ministry for Economic Affairs and Climate Action for funding in the project “MAINN” (funding ID 50OO2206). E.R. acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC), funding reference No. RGPIN-2022-03499. M.B. acknowledges support from FONDECYT regular grant 1211000 and by ANID BASAL project FB210003. K.G. is supported by the Australian Research Council through the Discovery Early Career Researcher Award (DECRA) Fellowship DE220100766 funded by the Australian Government. K.G. is supported by the Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D) through project No. CE170100013. F.N.-L. gratefully acknowledges the sponsorship provided by the Federal Ministry for Education and Research of Germany through the Alexander von Humboldt Foundation. P.S.B. acknowledges financial support from MCIN/AEI/10.13039/501100011033 under grant PID2019-107427GB-C31 A.K.L. gratefully acknowledges support by grants 1653300 and 2205628 from the National Science Foundation, award JWST-GO-02107.009-A, and a Humboldt Research Award from the Alexander von Humboldt Foundation. G.A.B. acknowledges the support from ANID Basal project FB210003.We combine archival Hubble Space Telescope and new James Webb Space Telescope imaging data covering the ultraviolet to mid-infrared regime to morphologically analyze the nuclear star cluster (NSC) of NGC 628, a granddesign spiral galaxy. The cluster is located in a 200 pc × 400 pc cavity lacking both dust and gas. We find roughly constant values for the effective radius (r_(eff) ∼ 5 pc) and ellipticity (∈ ∼ 0.05), while the Sérsic index (n) and position angle (PA) drop from n ∼ 3 to ∼2 and PA ∼ 130° to 90°, respectively. In the mid-infrared, r_(eff) ∼ 12 pc, ∈ ∼ 0.4, and n ∼ 1–1.5, with the same PA ∼ 90°. The NSC has a stellar mass of log_(10) (M^(nsc)_(*) / M_(ꙩ) = 7.06 0.31, as derived through B − V, confirmed when using multiwavelength data, and in agreement with the literature value. Fitting the spectral energy distribution (SED), excluding the mid-infrared data, yields a main stellar population age of (8 ± 3) Gyr with a metallicity of Z = 0.012 ± 0.006. There is no indication of any significant star formation over the last few gigayears. Whether gas and dust were dynamically kept out or evacuated from the central cavity remains unclear. The best fit suggests an excess of flux in the mid-infrared bands, with further indications that the center of the mid-infrared structure is displaced with respect to the optical center of the NSC. We discuss five potential scenarios, none of them fully explaining both the observed photometry and structure.Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEAssociation of Universities for Research in Astronomy, Inc., under NASA contractAssociation of Universities for Research in Astronomy, Inc., under NASA contractSpanish Virtual Observatory funded by MCIN/AEI/10.13039/ 501100011033/International Max Planck Research School for Astronomy and Cosmic Physics at the University of Heidelberg (IMPRS-HD)Thomas Müller (HdA/MPIA)European Research Council (ERC) under the European Unionʼs Horizon 2020Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)European Research Council via the ERC SynergyDeutsche Forschungsgemeinschaft (DFG) via the Collaborative Research Center “The Milky Way System”Heidelberg Cluster of Excellence “STRUCTURES,” funded by the German Excellence StrategyGerman Ministry for Economic Affairs and Climate ActionNatural Sciences and Engineering Research Council of Canada (NSERC)Australian Research Council through the Discovery Early Career Researcher Award (DECRA)Australian Research Council Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D)Federal Ministry for Education and Research of Germany through the Alexander von Humboldt FoundationMCIN/AEI/10.13039/501100011033National Science FoundationAlexander von Humboldt FoundationANID Basal projectpu

Spatially resolved star formation main sequence of galaxies in the CALIFA survey

Astrophysical Journal Letters 821.2 (2016): L26 reproduced by permission of the AASThe "main sequence of galaxies" - defined in terms of the total star formation rate ψ versus the total stellar mass M∗ - is a well-studied tight relation that has been observed at several wavelengths and at different redshifts. All earlier studies have derived this relation from integrated properties of galaxies. We recover the same relation from an analysis of spatially resolved properties, with integral field spectroscopic (IFS) observations of 306 galaxies from the CALIFA survey. We consider the SFR surface density in units of log (Mo yr-1 Kpc-2) and the stellar mass surface density in units of log (Mo Kpc-2) in individual spaxels that probe spatial scales of 0.5-1.5 Kpc. This local relation exhibits a high degree of correlation with small scatter (σ = 0.23 dex), irrespective of the dominant ionization source of the host galaxy or its integrated stellar mass. We highlight (i) the integrated star formation main sequence formed by galaxies whose dominant ionization process is related to star formation, for which we find a slope of 0.81 ± 0.02; (ii) for the spatially resolved relation obtained with the spaxel analysis, we find a slope of 0.72 ± 0.04; and (iii) for the integrated main sequence, we also identified a sequence formed by galaxies that are dominated by an old stellar population, which we have called the retired galaxies sequenceFinancial support: M.C.D. and S.F.S.: DGAPA-UNAM funding; CONACyT-180125 and PAPIIT IA- 100815 projects. Z.S.: EU Marie Curie Career Integration Grant ”SteMaGE” PCIG12-GA-2012-326466. Y.A.: RyC- 2011-09461 and AYA2013-47742-C4-3-P projects from the Spanish MINECO and the SELGIFS programme, funded by the EU (FP7-PEOPLE-2013-IRSES-612701). C.J.W.: Marie Curie Career Integration Grant 303912. R.M.G.D.: AyA2014- 57490-P and J.A. P12-FQM2828 grants. J.F.B.: AYA2013- 48226-C3-1-P from the Spanish MINECO grant. L.G.: Millennium Science Initiative through grant IC120009, and by CONICYT through FONDECYT grant 314056

Variations in the Σ_(SFR)−Σ_(mol)−Σ_(*) plane across galactic environments in PHANGS galaxies

Aims. There exists some consensus that the stellar mass surface density (Σ_(*)) and molecular gas mass surface density (Σ_(mol)) are the main quantities responsible for locally setting the star formation rate. This regulation is inferred from locally resolved scaling relations between these two quantities and the star formation rate surface density (Σ_(SFR)), which have been extensively studied in a wide variety of works. However, the universality of these relations is debated. Here, we probe the interplay between these three quantities across different galactic environments at a spatial resolution of 150 pc. Methods. We performed a hierarchical Bayesian linear regression to find the best set of parameters C_(*), C_(mol), and C_(norm) that describe the starforming plane conformed by Σ_(*), Σ_(mol), and Σ_(SFR), such that log Σ_(SFR) = C_(*) log Σ(*) + C_(mol) log Σ_(mol) + C_(norm). We also explored variations in the determined parameters across galactic environments, focusing our analysis on the C_(*) and C_(mol) slopes. Results. We find signs of variations in the posterior distributions of C(*) and C_(mol) across different galactic environments. The dependence of Σ_(SFR) on Σ_(*) spans a wide range of slopes, with negative and positive values, while the dependence of Σ_(SFR) on Σ_(mol) is always positive. Bars show the most negative value of C_(*) (−0.41), which is a sign of longer depletion times, while spiral arms show the highest C_(*) among all environments (0.45). Variations in C_(mol) also exist, although they are more subtle than those found for C_(*). Conclusions. We conclude that systematic variations in the interplay of Σ_(*), Σ_(mol), and Σ_(SFR) across different galactic environments exist at a spatial resolution of 150 pc, and we interpret these variations to be produced by an additional mechanism regulating the formation of stars that is not captured by either Σ_(*) or Σ_(mol). Studying environmental variations in single galaxies, we find that these variations correlate with changes in the star formation efficiency across environments, which could be linked to the dynamical state of the gas that prevents it from collapsing and forming stars, or to changes in the molecular gas fraction

The PHANGS-MUSE survey Probing the chemo-dynamical evolution of disc galaxies

We present the PHANGS-MUSE survey, a programme that uses the MUSE integral field spectrograph at the ESO VLT to map 19 massive (9.4< log(M/M-circle dot)< 11.0) nearby (D less than or similar to 20 Mpc) star-forming disc galaxies. The survey consists of 168 MUSE pointings (1 ' by 1 ' each) and a total of nearly 15 x 10(6) spectra, covering similar to 1.5 x 10(6) independent spectra. PHANGS-MUSE provides the first integral field spectrograph view of star formation across different local environments (including galaxy centres, bars, and spiral arms) in external galaxies at a median resolution of 50 pc, better than the mean inter-cloud distance in the ionised interstellar medium. This 'cloud-scale' resolution allows detailed demographics and characterisations of H II regions and other ionised nebulae. PHANGS-MUSE further delivers a unique view on the associated gas and stellar kinematics and provides constraints on the star-formation history. The PHANGS-MUSE survey is complemented by dedicated ALMA CO(2-1) and multi-band HST observations, therefore allowing us to probe the key stages of the star-formation process from molecular clouds to H II regions and star clusters. This paper describes the scientific motivation, sample selection, observational strategy, data reduction, and analysis process of the PHANGS-MUSE survey. We present our bespoke automated data-reduction framework, which is built on the reduction recipes provided by ESO but additionally allows for mosaicking and homogenisation of the point spread function. We further present a detailed quality assessment and a brief illustration of the potential scientific applications of the large set of PHANGS-MUSE data products generated by our data analysis framework. The data cubes and analysis data products described in this paper represent the basis for the first PHANGS-MUSE public data release and are available in the ESO archive and via the Canadian Astronomy Data Centre

NH and Mg Index Trends in Elliptical Galaxies

We examine the spectrum in the vicinity of the NH3360 index of Davidge & Clark (1994), which was defined to measure the NH absorption around 3360 \AA and which shows almost no trend with velocity dispersion (Toloba et al. 2009), unlike other N- sensitive indices, which show a strong trend (Graves et al. 2007). Computing the effect of individual elements on the integrated spectrum with synthetic stellar population integrated spectra, we find that, while being well correlated with nitrogen abundance, NH3360 is almost equally well anti-correlated with Mg abundance. This prompts the definition of two new indices, Mg3334, which is mostly sensitive to magnesium, and NH3375, which is mostly sensitive to nitrogen. Rather surprisingly, we find that the new NH3375 index shows a trend versus optical absorption feature indices that is as shallow as the NH3360 index. We hypothesize that the lack of a strong index trend in these near-UV indices is due to the presence of an old metal-poor component of the galactic population. Comparison of observed index trends and those predicted by models shows that a modest fraction of an old, metal-poor stellar population could easily account for the observed flat trend in these near-UV indices, while still allowing substantial N abundance increase in the larger galaxies.Comment: 19 pages, 6 figures, 6 table

Chemical characterisation of the X-shooter Spectral Library (XSL): [Mg/Fe] and [Ca/Fe] abundances

The X-shooter Spectral Library (XSL) is a large empirical stellar library used as a benchmark for the development of stellar population models. The inclusion of $\alpha$-elements abundances is crucial to disentangling the chemical evolution of any stellar system. The aim of this paper is to provide a catalogue of high-precision and accurate magnesium and calcium abundances from a wide variety of stars well distributed in the Hertzsprung-Russell (HR) diagram. We originally performed an analysis of the derived Mg and Ca abundances for medium-resolution spectra of 611 stars from the XSL Data Release 2. For this purpose, we used the GAUGUIN automated abundance estimation code to fit the ultraviolet-blue (UVB) and visible (VIS) spectra. We tested the consistency of the atmospheric parameters and chemical abundances with the Gaia DR3 and the AMBRE Project datasets. We have finally obtained precise [Mg/Fe] and [Ca/Fe] abundances for 192 and 217 stars respectively, from which 174 stars have measurements in both elements. The stars cover a broad range of effective temperature 4000 < T$_{\rm eff}$ < 6500K, surface gravity 0.3 < log(g) < 4.8 cm s$^{\rm -2}$, and metallicity -2.5 < [Fe/H] < +0.4 dex. We find an excellent agreement with the abundance estimates from the AMBRE:HARPS and the Gaia/RVS (Radial Velocity Spectrometer) analysis. Moreover, the resulting abundances reproduce a plateau in the metal-poor regime followed by a decreasing trend even at supersolar metallicities, as predicted by Galactic chemical evolution models. This catalogue is suitable for improving the modelling of evolutionary stellar population models with empirical $\alpha$-enhancements, which could significantly contribute to the analysis of external galaxies abundances in the near future.Comment: Accepted for publication in A&

Spatially resolved spectroscopy of early-type galaxies over a range in mass

Long-slit spectra have been obtained with the Keck telescope for a sample of 11 early-type galaxies covering a wide range in luminosity and hence mass. Rotation velocity and velocity dispersions, together with 19 Lick line-strength gradients have been measured, to, on average, two effective radii. Stellar population models taking into account the effect of the non-solar chemical composition have been used to derive ages, metallicities and α/Fe abundances along the radius. We find that line-strength gradients are due mainly to variations of the total metallicity with the radius. One galaxy out of 11 shows very strong age gradients, with a young central component, while the age gradient for the rest of the sample is very shallow or consistent with zero. We also find small variations in the [α/Fe] ratio with radius. Contrary to what is expected in simple collapse models, galaxies show both positive and negative [α/Fe] profiles. This rules out a solely inside-out, or outside-in, formation mechanism for all early-type galaxies. We do not find a correlation between the metallicity and the [α/Fe] gradients, and the local metallicity is not correlated with the local velocity dispersion for all the galaxies of our sample, which rules out scenarios where the delay in the onset of the galactic winds is the only mechanism producing the metallicity gradients. We found that metallicity gradients are correlated with the shape of the isophotes and the central mean age and metallicity of the galaxies, for galaxies younger than ∼10 Gyr. We show that the correlation between the gradients and the central values is not due to the correlation of the errors and indicates that the same process that shaped the gradient, also modified the structural parameters of the galaxies and triggered star formation in their centres. This strongly supports the merger scenario for the formation of these systems, where the degree of dissipation during those mergers increases as the mass of the progenitor galaxies decreases. Finally, we also find a dichotomy in the plane grad [α/Fe]-[α/Fe] between galaxies with velocity dispersions below and above ∼200 km s−1, which requires confirmation with larger sample