Alexandre Roman-Lopes

Suppressing star formation in quiescent galaxies with supermassive black hole winds

Quiescent galaxies with little or no ongoing star formation dominate the population of galaxies with masses above 2 × 1010 times that of the Sun; the number of quiescent galaxies has increased by a factor of about 25 over the past ten billion years (refs 1, 2, 3, 4). Once star formation has been shut down, perhaps during the quasar phase of rapid accretion onto a supermassive black hole, an unknown mechanism must remove or heat the gas that is subsequently accreted from either stellar mass loss or mergers and that would otherwise cool to form stars. Energy output from a black hole accreting at a low rate has been proposed, but observational evidence for this in the form of expanding hot gas shells is indirect and limited to radio galaxies at the centres of clusters, which are too rare to explain the vast majority of the quiescent population. Here we report bisymmetric emission features co-aligned with strong ionized-gas velocity gradients from which we infer the presence of centrally driven winds in typical quiescent galaxies that host low-luminosity active nuclei. These galaxies are surprisingly common, accounting for as much as ten per cent of the quiescent population with masses around 2 × 1010 times that of the Sun. In a prototypical example, we calculate that the energy input from the galaxy’s low-level active supermassive black hole is capable of driving the observed wind, which contains sufficient mechanical energy to heat ambient, cooler gas (also detected) and thereby suppress star formation.

SDSS-IV MaNGA : spatially resolved star formation histories in galaxies as a function of galaxy mass and type

We study the internal gradients of stellar population properties within 1.5 Re for a representative sample of 721 galaxies, with stellar masses ranging between 109 M⊙ and 1011.5 M⊙ from the SDSS-IV MaNGA Integral-Field-Unit survey. Through the use of our full spectral fitting code FIREFLY, we derive light- and mass-weighted stellar population properties and their radial gradients, as well as full star formation and metal enrichment histories. We also quantify the impact that different stellar population models and full spectral fitting routines have on the derived stellar population properties and the radial gradient measurements. In our analysis, we find that age gradients tend to be shallow for both early-type and late-type galaxies. Mass-weighted age gradients of early-types arepositive [sic] (∼0.09 dex/Re) pointing to ‘outside–in’ progression of star formation, while late-type galaxies have negative light-weighted age gradients (∼−0.11 dex/Re), suggesting an ‘inside–out’ formation of discs.We detect negative metallicity gradients in both early- and late-type galaxies, but these are significantly steeper in late-types, suggesting that the radial dependence of chemical enrichment processes and the effect of gas inflow and metal transport are far more pronounced in discs. Metallicity gradients of both morphological classes correlate with galaxy mass, with negative metallicity gradients becoming steeper with increasing galaxy mass. The correlation with mass is stronger for late-type galaxies, with a slope of d(∇[Z/H])/d(log M) ∼ −0.2 ± 0.05 , compared to d(∇[Z/H])/d(log M) ∼ −0.05 ± 0.05 for early-types. This result suggests that the merger history plays a relatively small role in shaping metallicity gradients of galaxies.

Milky Way demographics with the VVV survey - II. Color transformations and near-infrared photometry for 136 million stars in the southern Galactic disk

1 Departamento de Física, Universidad de La Serena, 980 Benavente, La Serena, Chile e-mail: msoto@dfuls.cl 2 Instituto de Ciencias Astronómicas, del la Tierra y del Espacio (ICATE-CONICET), Av. España Sur 1512, J5402DSP San Juan, Argentina 3 Observatório Astronómico de Córdoba, Universidad Nacional de Córdoba, Laprida 854, x5000 BGR, Córdoba, Argentina 4 Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Vicuña Mackena 4860, Casilla 306, Santiago 22, Chile 5 Vatican Observatory, Vatican City State 00120, Italy 6 European Southern Observatory, 3107 Vitacura, Santiago, Chile 7 Department of Astrophysical Sciences, Princeton University, Princeton NJ 08544-1001, USA 8 The Milky Way Millennium Nucleus, Av. Vicuña Mackenna 4860, 782-0436 Macul, Santiago, Chile 9 Departamento de Ciencia Fisicas, Universidad Andres Bello, Avda. Republica 252, Santiago, Chile 10 Centre for Astrophysics Research, Science and Technology Research Institute, University of Hertfordshire, Hatfield AL10 9AB, UK 11 Department of Astronomy and Physics, Saint Mary’s University, Halifax, Nova Scotia, B3K 5L3, Canada 12 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK 13 Astronomy Unit, School of Physics and Astronomy, Queen Mary University of London, Mile End Road, London, E1 4NS, UK 14 Departamento de Física y Astronomía, Universidad de Valparaíso, Av. Gran Bretaña 1111, Playa Ancha, Casilla 5030, Chile 15 Instituto de Astronomía Teórica y Experimental, CONICET, Laprida 922, 5000 Córdoba, Argentina 16 Departmento de Astronomía, Universidad de Concepción, Casilla 160-C, Concepción, Chile 17 Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos 0610, Antofagasta, Chile 18 Atacama Large Millimeter Array, Alonso de Córdova 3107, Vitacura, Santiago, Chile

Two O2 If*/WN6 stars possibly ejected from the massive young Galactic cluster Westerlund 2

In this paper we report the identification of two new Galactic O2If*/WN6 stars (WR20aa and WR20c),ontheoutskirtsofthemassiveyoungstellarclusterWesterlund2.Themorphological similarity between the near-infrared spectra of the new stars with that of WR20a and WR21a (two of the most massive binaries known to date) is remarkable, indicating that probably they are also very massive stars. New optical spectroscopic observations of WR20aa suggest an intermediateO2If*/WN6spectraltype.Basedonamosaicmadefromthe3.6µmSpitzerIRAC images of the region including part of the RCW49 complex, we studied the spatial location of the new emission line stars, finding that WR20aa and WR20c are well displaced from the centre of Westerlund 2, being placed at ≈36 pc (15.7 arcmin) and ≈58 pc (25.0 arcmin), respectively, for an assumed heliocentric distance of 8 kpc. Also, very remarkably, a radius vector connecting the two stars would intercept the Westerlund 2 cluster exactly at the place where its stellar density reaches a maximum. We consequently postulate a scenario in which WR20aa and WR20c had a common origin somewhere in the cluster core, being ejected from theirbirthplacebydynamicalinteractionwithsomeotherverymassiveobjects,perhapsduring some earlier stage of the cluster evolution.

SDSS IV MaNGA - the spatially resolved transition from star formation to quiescence

FB, RM and KM acknowledge funding from the United Kingdom Science and Technology Facilities Council (STFC). RM acknowledges support from the European Research Council (ERC) Advanced Grant 695671 ‘QUENCH’. AR-L acknowledges partial support from the DIULS regular project PR15143. MB was supported by NSF/AST-1517006. KB was supported by World Premier International Research Centre Initiative (WPI Initiative), MEXT, Japan and by JSPS KAKENHI Grant Number 15K17603. AW acknowledges support from a Leverhulme Early Career Fellowship. AD acknowledges support from The Grainger Foundation.

SDSS-IV MaNGA: stellar population gradients as a function of galaxy environment

We study the internal radial gradients of stellar population properties within 1.5 Re and analyse the impact of galaxy environment. We use a representative sample of 721 galaxies with masses ranging between 109 M⊙ and 1011.5 M⊙ from the SDSS-IV survey MaNGA. We split this sample by morphology into early-type and late-type galaxies. Using the full spectral fitting code firefly, we derive the light and mass-weighted stellar population properties, age and metallicity, and calculate the gradients of these properties. We use three independent methods to quantify galaxy environment, namely the Nth nearest neighbour, the tidal strength parameter Q and distinguish between central and satellite galaxies. In our analysis, we find that early-type galaxies generally exhibit shallow light-weighted age gradients in agreement with the literature and mass-weighted median age gradients tend to be slightly positive. Late-type galaxies, instead, have negative light-weighted age gradients. We detect negative metallicity gradients in both early- and late-type galaxies that correlate with galaxy mass, with the gradients being steeper and the correlation with mass being stronger in late-types. We find, however, that stellar population gradients, for both morphological classifications, have no significant correlation with galaxy environment for all three characterizations of environment. Our results suggest that galaxy mass is the main driver of stellar population gradients in both early and late-type galaxies, and any environmental dependence, if present at all, must be very subtle.

Baade's window and APOGEE: Metallicities, ages, and chemical abundances

Context. Baades window (BW) is one of the most observed Galactic bulge fields in terms of chemical abundances. Owing to its low and homogeneous interstellar absorption it is considered the perfect calibration field for Galactic bulge studies. Aims. In the era of large spectroscopic surveys, calibration fields such as BW are necessary for cross calibrating the stellar parameters and individual abundances of the APOGEE survey. Methods. We use the APOGEE BW stars to derive the metallicity distribution function (MDF) and individual abundances for α-and iron-peak elements of the APOGEE ASPCAP pipeline (DR13), as well as the age distribution for stars in BW. Results. We determine the MDF of APOGEE stars in BW and find a remarkable agreement with that of the Gaia-ESO survey (GES). Both exhibit a clear bimodal distribution. We also find that the Mg-metallicity planes of the two surveys agree well, except for the metal-rich part ([Fe/H] > 0.1), where APOGEE finds systematically higher Mg abundances with respect to the GES. The ages based on the [C/N] ratio reveal a bimodal age distribution, with a major old population at ~ 10 Gyr, with a decreasing tail towards younger stars. A comparison of stellar parameters determined by APOGEE and those determined by other sources reveals detectable systematic offsets, in particular for spectroscopic surface gravity estimates. In general, we find a good agreement between individual abundances of O, Na, Mg, Al, Si, K, Ca, Cr, Mn, Co, and Ni from APOGEE with that of literature values. Conclusions. We have shown that in general APOGEE data show a good agreement in terms of MDF and individual chemical abundances with respect to literature works. Using the [C/N] ratio we found a significant fraction of young stars in BW. (Less)

Hundreds of new cluster candidates in the VISTA Variables in the Vía Láctea survey DR1

VISTA variables in the Via Lactea is an ESO Public survey dedicated to scan the bulge and an adjacent portion of the Galactic disk in the fourth quadrant using the VISTA telescope and the near-infrared camera VIRCAM. One of the leading goals of the VVV survey is to contribute to the knowledge of the star cluster population of the Milky Way. To improve the census of the Galactic star clusters, we performed a systematic scan of the JHKs images of the Galactic plane section of the VVV survey. Our detection procedure is based on a combination of superficial density maps and visual inspection of promising features in the NIR images. The material examined are color-composite images corresponding to the DR1 of VVV. We report the discovery of 493 new star cluster candidates. The analysis of the spatial distribution show that the clusters are very concentrated in he Galactic plane, presenting some local maxima around the position of large star-forming complexes, such as G305, RCW 95, and RCW 106. The vast majority of the cluster candidates are quite compact and generally surrounded by bright and/or dark nebulosities. IRAS point sources are associated with 59% of the sample, while 88% are associated with MSX point sources. GLIMPSE 8 mum images of the cluster candidates show a variety of morphologies, with 292 clusters dominated by knotty sources, while 361 clusters show some kind of nebulosity. Spatial cross-correlation with young stellar objects, masers, and extended green-object catalogs suggest that a large sample of the new cluster candidates are extremely young. In particular, 104 star clusters associated to methanol masers are excellent candidates for ongoing massive star formation. Also, there is a special set of sixteen cluster candidates that present clear signspot of star-forming activity having associated simultaneosly dark nebulae, young stellar objects, EGOs, and masers.

StarHorse: a Bayesian tool for determining stellar masses, ages, distances, and extinctions for field stars

Understanding the formation and evolution of our Galaxy requires accurate distances, ages and chemistry for large populations of field stars. Here we present several updates to our spectro-photometric distance code, that can now also be used to estimate ages, masses, and extinctions for individual stars. Given a set of measured spectro-photometric parameters, we calculate the posterior probability distribution over a given grid of stellar evolutionary models, using flexible Galactic stellar-population priors. The code (called {\tt StarHorse}) can acommodate different observational datasets, prior options, partially missing data, and the inclusion of parallax information into the estimated probabilities. We validate the code using a variety of simulated stars as well as real stars with parameters determined from asteroseismology, eclipsing binaries, and isochrone fits to star clusters. Our main goal in this validation process is to test the applicability of the code to field stars with known {\it Gaia}-like parallaxes. The typical internal precision (obtained from realistic simulations of an APOGEE+Gaia-like sample) are

APOGEE Chemical Abundances of Globular Cluster Giants in the Inner Galaxy

\simeq 8\%