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Nebular Excitation in z~2 Star-forming Galaxies from the SINS and LUCI Surveys: The Influence of Shocks and AGN  [PDF]
S. F. Newman,P. Buschkamp,R. Genzel,N. M. Forster Schreiber,J. Kurk,A. Sternberg,O. Gnat,D. Rosario,C. Mancini,S. J. Lilly,A. Renzini,A. Burkert,C. M. Carollo,G. Cresci,R. Davies,F. Eisenhauer,S. Genel,K. Shapiro Griffin,E. K. S. Hicks,D. Lutz,T. Naab,Y. Peng,L. J. Tacconi,S. Wuyts,G. Zamorani,D. Vergani,B. J. Weiner
Physics , 2013, DOI: 10.1088/0004-637X/781/1/21
Abstract: Based on high-resolution, spatially resolved data of 10 z~2 star-forming galaxies from the SINS/zC-SINF survey and LUCI data for 12 additional galaxies, we probe the excitation properties of high-z galaxies and the impact of active galactic nuclei (AGN), shocks and photoionization. We explore how these spatially-resolved line ratios can inform our interpretation of integrated emission line ratios obtained at high redshift. Many of our galaxies fall in the `composite' region of the z~0 [NII]/Ha versus [OIII]/Hb diagnostic (BPT) diagram, between star-forming galaxies and those with AGN. Based on our resolved measurements, we find that some of these galaxies likely host an AGN, while others appear to be affected by the presence of shocks possibly caused by an outflow or from enhanced ionization parameter as compared with HII regions in normal local star-forming galaxies. We find that the Mass-Excitation (MEx) diagnostic, which separates purely star-forming and AGN hosting local galaxies in the [OIII]/Hb versus stellar mass plane, does not properly separate z~2 galaxies classified according to the BPT diagram. However, if we shift the galaxies based on the offset between the local and z~2 mass-metallicity relation (i.e. to the mass they would have at z~0 with the same metallicity), we find better agreement between the MEx and BPT diagnostics. Finally, we find that metallicity calibrations based on [NII]/Ha are more biased by shocks and AGN at high-z than the [OIII]/Hb/[NII]/Ha calibration.
Star formation history of resolved galaxies. I. The Method  [PDF]
Emma E. Small,David Bersier,Maurizio Salaris
Physics , 2012, DOI: 10.1093/mnras/sts077
Abstract: We present a new method to determine the star formation and metal enrichment histories of any resolved stellar system. This method is based on the fact that any observed star in a colour-magnitude diagram will have a certain probability of being associated with an isochrone characterised by an age t and metallicity [Fe/H] (i.e. to have formed at the time and with the metallicity of that isochrone). We formulate this as a maximum likelihood problem that is then solved with a genetic algorithm. We test the method with synthetic simple and complex stellar populations. We also present tests using real data for open and globular clusters. We are able to determine parameters for the clusters (t, [Fe/H]) that agree well with results found in the literature. Our tests on complex stellar populations show that we can recover the star formation history and age-metallicity relation very accurately. Finally, we look at the history of the Carina dwarf galaxy using deep BVI data. Our results compare well with what we know about the history of Carina.
CALIFA survey: The spatially resolved star formation history of massive galaxies  [PDF]
Rosa González Delgado,Enrique Pérez,Roberto Cid Fernandes,Rubén García-Benito,André L. de Amorim,Sebastián F. Sánchez,Bernd Husemann,Rafael López Fernández,Clara Cortijo-Ferrero,Eduardo Lacerda,Damian Mast,the CALIFA collaboration
Physics , 2013, DOI: 10.1017/S1743921313005097
Abstract: The Calar Alto Legacy Integral Field Area (CALIFA) is an ongoing 3D spectroscopic survey of 600 nearby galaxies of all kinds. This pioneer survey is providing valuable clues on how galaxies form and evolve. Processed through spectral synthesis techniques, CALIFA datacubes allow us to, for the first time, spatially resolve the star formation history of galaxies spread across the color-magnitude diagram. The richness of this approach is already evident from the results obtained for the first 107 galaxies. Here we show how the different galactic spatial sub-components ("bulge" and "disk") grow their stellar mass over time. We explore the results stacking galaxies in mass bins, finding that, except at the lowest masses, galaxies grow inside-out, and that the growth rate depends on a galaxy's mass. The growth rate of inner and outer regions differ maximally at intermediate masses. We also find a good correlation between the age radial gradient and the stellar mass density, suggesting that the local density is a main driver of galaxy evolution.
IAC-pop: Finding the Star Formation History of Resolved Galaxies  [PDF]
A. Aparicio,S. L. Hidalgo
Physics , 2009, DOI: 10.1088/0004-6256/138/2/558
Abstract: IAC-pop is a code designed to solve the star formation history (SFH) of a complex stellar population system, like a galaxy, from the analysis of the color-magnitude diagram (CMD). It uses a genetic algorithm to minimize a chi2 merit function comparing the star distributions in the observed CMD and the CMD of a synthetic stellar population. A parametrization of the CMDs is used, which is the main input of the code. In fact, the code can be applied to any problem in which a similar parametrization of an experimental set of data and models can be made. The method internal consistency and robustness against several error sources, including observational effects, data sampling and stellar evolution library differences, are tested. It is found that the best stability of the solution and the best way to estimate errors is obtained by several runs of IAC-pop with varying the input data parametrization. The routine MinnIAC is used to control this process. IAC-pop is offered for free use and can be downloaded from the site http://iac-star.iac.es/iac-pop. The routine MInnIAC is also offered under request, but support can not be provided for its use. The only requirement for the use of IAC-pop and MinnIAC is referencing this paper and crediting as indicated in the site.
The 100 Myr Star Formation History of NGC 5471 from Cluster and Resolved Stellar Photometry  [PDF]
Rubén García-Benito,Enrique Pérez,ángeles I. Díaz,Jesús Maíz Apellániz,Miguel Cervi?o
Physics , 2011, DOI: 10.1088/0004-6256/141/4/126
Abstract: We show that star formation in the giant HII region NGC 5471 has been ongoing during the past 100 Myr. Using HST/WFPC2 F547M and F675W, ground based JHKs, and GALEX FUV and NUV images, we have conducted a photometric study of the star formation history in the massive giant extragalactic HII region NGC 5471 in M101. We perform a photometric study of the colour-magnitude diagram (CMD) of the resolved stars, and an integrated analysis of the main individual star forming clusters and of NGC 5471 as a whole. The integrated UV-optical-nIR photometry for the whole region provides two different reference ages, 8 Myr and 60 Myr, revealing a complex star formation history, clearly confirmed by the CMD resolved stellar photometry analysis. The spatial distribution of the stars shows that the star formation in NGC 5471 has proceeded along the whole region during, at least, the last 100 Myr. The current ionizing clusters are enclosed within a large bubble, which is likely to have been produced by the stars that formed in a major event < 20 Myr ago.
The Star Formation History of the Hubble Sequence: Spatially Resolved Colour Distributions of Intermediate Redshift Galaxies in the Hubble Deep Field  [PDF]
R. G. Abraham,R. S. Ellis,A. C. Fabian,N. R. Tanvir,K. Glazebrook
Physics , 1998, DOI: 10.1046/j.1365-8711.1999.02059.x
Abstract: We analyse the spatially resolved colours of distant galaxies of known redshift in the Hubble Deep Field, using a new technique based on matching resolved four-band internal colour data to the predictions of evolutionary synthesis models. We quantify the relative age, dispersion in age, ongoing star-formation rate, star-formation history, and dust content of these galaxies. To demonstrate the potential of the method, we study the near-complete sample of 32 I<21.9 mag galaxies with ~ 0.5 studied by Bouwens et al (1997). The dispersion of the internal colours of a sample of 0.4
A transdimensional Bayesian method to infer the star formation history of resolved stellar populations  [PDF]
J. J. Walmswell,J. J. Eldridge,B. J. Brewer,C. A. Tout
Physics , 2013, DOI: 10.1093/mnras/stt1444
Abstract: We propose a new method to infer the star formation histories of resolved stellar populations. With photometry one may plot observed stars on a colour-magnitude diagram (CMD) and then compare with synthetic CMDs representing different star formation histories. This has been accomplished hitherto by parametrising the model star formation history as a histogram, usually with the bin widths set by fixed increases in the logarithm of time. A best fit is then found with maximum likelihood methods and we consider the different means by which a likelihood can be calculated. We then apply Bayesian methods by parametrising the star formation history as an unknown number of Gaussian bursts with unknown parameters. This parametrisation automatically provides a smooth function of time. A Reversal Jump Markov Chain Monte Carlo method is then used to find both the most appropriate number of Gaussians, thus avoiding avoid overfitting, and the posterior probability distribution of the star formation rate. We apply our method to artificial populations and to observed data. We discuss the other advantages of the method: direct comparison of different parametrisations and the ability to calculate the probability that a given star is from a given Gaussian. This allows the investigation of possible sub-populations.
The Presence of Weak Active Galactic Nuclei in High Redshift Star Forming Galaxies  [PDF]
Shelley A. Wright,James E. Larkin,James R. Graham,Chung-Pei Ma
Physics , 2010, DOI: 10.1088/0004-637X/711/2/1291
Abstract: We present [OIII 5007A] observations of the star forming galaxy HDF-BMZ1299 (z=1.598) using Keck Observatory's Adaptive Optics system with the near-infrared integral field spectrograph OSIRIS. Using previous Halpha and [NII] measurements of the same source, we are able for the first time to use spatially resolved observations to place a high-redshift galaxy's substructure on a traditional HII diagnostic diagram. We find that HDF-BMZ1299's spatially concentrated nebular ratios in the central ~1.5 kiloparsec (0."2) are best explained by the presence of an AGN: log([NII]/Halpha)=-0.22+/-0.05 and 2sigma limit of log([OIII]/Hbeta)>0.26. The dominant energy source of this galaxy is star formation, and integrating a single aperture across the galaxy yields nebular ratios that are composite spectra from both AGN and HII regions. The presence of an embedded AGN in HDF-BMZ1299 may suggest a potential contamination in a fraction of other high-redshift star forming galaxies, and we suggest that this may be a source of the "elevated" nebular ratios previously seen in seeing-limited metallicity studies. HDF-BMZ1299's estimated AGN luminosity is L_Halpha = 3.7e41 erg/s and L_[OIII] = 5.8e41 erg/s, making it one of the lowest luminosity AGN discovered at this early epoch.
Spatially resolved spectroscopy and chemical history of star-forming galaxies in the Hercules cluster: the effects of the environment  [PDF]
V. Petropoulou,J. M. Vílchez,J. Iglesias-Páramo,P. Papaderos,L. Magrini,B. Cedrés,D. Reverte
Physics , 2011, DOI: 10.1088/0004-637X/734/1/32
Abstract: Spatially resolved spectroscopy has been obtained for a sample of 27 star-forming (SF) galaxies selected from our deep Halpha survey of the Hercules cluster. We have applied spectral synthesis models to all emission-line spectra of this sample using the population synthesis code STARLIGHT. We have obtained fundamental parameters of the stellar components, as the mean metallicity and age, and we have corrected the emission-line spectra for underlying stellar absorption. O/H and N/O gas chemical abundances were obtained using the latest empirical calibrations. The effects of cluster environment on the chemical evolution of galaxies and on their mass-metallicity (MZ) and luminosity-metallicity (LZ) relations were studied combining the derived gas metallicities, the mean stellar metallicities and ages, the masses and luminosities of galaxies and their existing HI data. We have found that our Hercules SF galaxies divide into three main subgroups: a) chemically evolved spirals with truncated ionized-gas disks and nearly flat oxygen gradients, witnessing the effect of ram-pressure stripping, b) chemically evolved dwarfs/irregulars populating the highest local densities, possible products of tidal interactions in preprocessing events, or c) less metallic dwarf galaxies which appear to be "newcomers" to the cluster, experiencing pressure-triggered star-formation. Most Hercules SF galaxies follow well defined MZ and LZ sequences (for both O/H and N/O); though the dwarf/irregular galaxies located at the densest regions appear to be outliers to these global relations, suggesting a physical reason for the dispersion in these fundamental relations. The Hercules cluster appears to be currently assembling via the merger of smaller substructures, providing an ideal laboratory where the local environment has been found to be a key parameter to understand the chemical history of galaxies.
The Star Formation History in Nearby Dwarf Galaxies: the Fossil Record in the Color-Magnitude Diagram  [PDF]
A. Aparicio
Physics , 1998,
Abstract: Dwarf galaxies may play a key role in the formation and evolution of bigger systems. This make a topic of major interest knowing how they form and evolve and, in particular, how their star formation histories (SFHs) have proceed since their birth. For nearby galaxies, the color-magnitude diagram (CMD) contains stars formed over all their lifetime. It is hence a fossil record of their SFHs. The analysis with synthetic CMDs provides a powerful tool to retrieve them. In this paper, I discuss the critical issues related to the computation of synthetic CMDs, present a short summary of the currently available results for the SFH extending the full life of galaxies and make a few critical considerations about the powerfulness and back-draws of the method.
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