Resolved Star Formation Surface Density and Stellar Mass ...

1 2014 44 Resolved star Formation Surface Density and Stellar MassDensity of Galaxies in the Local UniverseAbdurroufAstronomical Institute of Tohoku UniversityAbstractIn order to understand how the Stellar mass are distributed within the galaxies in the local Universe,where the stars are being made in high star Formation rate in them, and relation between their morphol-ogy and their activities in making stars, we are going to investigate the Surface Density of star formationrates (SFRs) and Stellar mass Surface Density by analyzing the Resolved Stellar population propertiesof 445 massive galaxies at <z< The galaxy images will be taken from SDSS DR10.

2 Onlygalaxies with Stellar mass more than will be selected. The sample will be differentiatedaccording to their morphology (elliptical, spiral, and irregular) and each galaxy s Surface will be dividedinto inner (center) and outer region. Resolved Stellar population properties, that is star Formation rate,age, Stellar mass, and extinction, will be derived by modelling the spectral energy distribution (SED) foreach spatial bin of galaxy image. Then calculation and analysis will be focused on Stellar mass Density , Density of star Formation rate, age, and extinction as a function of galactocentric IntroductionIt has been known currently that morphology ofgalaxies (elliptical, spiral, or irregular) is related totheir star Formation history (SFH).

3 How galaxieswere forming their stars in the past seems to affecttheir future appearance. Elliptical galaxies likelyformed all their stars from sudden burst in the pastwhen they was still assembled, so that they are nowdominated by red old stars and lack or almost con-tain no young blue stars. Elliptical galaxies arevery luminous and massive system with high massto light ratio which infer that this galaxies containmany dark matter halo in their outer part. Coldgas is almost not found in the elliptical galaxies, butsome of them have very small fraction of cold gasin their central region which might still be the fuelfor star Formation .

4 Different to elliptical galaxies,spiral galaxies and irregular galaxies are still form-ing their stars now as they contain many young bluestars. Spiral galaxy which prominent with their spi-ral pattern and rotational motion of their disk stars,have more young blue stars lying in the spiral armsand disk compare to the central bulge which con-tains old red stars and has high metallicity. Starforming activities inside galaxy determine by manyfactors, such as existence of cold gas, and dynami-cal fluctuation which can triggers gas shrinking dueto gravitational contraction.

5 Supernova explosionof dead stars spreads their metals contain and shedsurrounding gas which can compress gas in otherplaces and trigger next star birth. Merger or closeencounter between two galaxies also can trigger starbirth inside each galaxy by the dynamical instabil-ity produced by the merger or close encounter pro-cess. Frictional motions of orbiting gas make loss oftheir energy and eventually fall inward sum up theconcentration of gas in the central part of might cause the high star Formation activitiesin the central part of galaxy. In order to understandthis star Formation activity flow inside galaxy, weneed to know the distribution of Stellar mass den-sity and star Formation rate (SFR) Surface densityof galaxies in local Universe as well as in distantUniverse.

6 In order to calculate the distribution ofstellar mass Density and star Formation rate den-sity inside galaxy as well as other Stellar populationproperties, one method that we can used is by fit-ting the Resolved spectral energy distribution (SED)instead of integrated SED of galaxy. Resolved SEDfitting have been widely used to study the stellarmass Density as well as star Formation rate (SFR)and star Formation history (SFH) (Conti, A. et ; Welikala, N. et al. 2008; Welikala, N. et ; Zibetti, S. et al. 2009; Wuyts, S. et al. 2012;Wuyts, S. et al. 2013). In the Resolved SED fitting,multi-wavelength band photometry are calculatedfor each spatial bin, then Stellar population synthe-sis model is built in such way to fit this photom-2014 44etry SED.

7 Total Stellar mass obtained by integrat-ing Resolved Stellar mass is can be different com-pare with those obtained by unresolved photome-try (Zibetti, S. et al. 2009) which might be causedby effect of dust extinction. Total star formationrate (SFR) and other Stellar population properties(age, dust obscuration) obtained from integratingresolved SFR also different compare with those ob-tained by fitting unresolved photometry (Wuyts,S. et al. 2012). Studying Resolved Stellar popula-tion properties might give clue to more detailed un-derstanding on galaxy structure and evolution pro-cesses occurred inside Methods/Instrumentsand Data SampleIn this research we will use optical data fromSDSS Data Release 10 for massive galaxies (M> lying in redshift range of <z< is providing five-band broad band photome-try (ugriz bands), and the spectroscopic follow-upof most galaxies.)

8 In additional to the data prod-uct of SDSS, we use value-added MPA/JHU DR7galaxy catalogs. These catalogs contain informa-tion about total Stellar mass (based on Kauffman etal. 2003 and Salim et al. 2007) and star formationrate (based on Brinchmann et al. 2004) of 927552galaxies of SDSS data. Location of our sample withrespect to overall galaxies more massive than 106M lying in redshift range of <z< can beseen from Figure PSF MatchingBefore performing Resolved SED fitting to galaxyimage, we need to match the point-spread functionamong five band images of all 445 galaxies.

9 PSFmatching is done by matching the average FWHM(full width in half maximum) of PSF profile of fore-ground stars (which appears in the image) with ref-erence value of FWHM. Reference value for FWHMis taken from image band which has highest aver-age value of FWHM. For matching FWHM we useGaussian convolution in IRAF (gauss command).For calculating FWHM we use SExtractor (BertinArnouts 1996). SExtractor work by detecting theobjects (stars and galaxies) inside the image field(which might can t be seen by our eye) then cal-1: Location of data sample among galaxies moremassive than 106M which lie in <z< the parameter/physical properties (of thosedetected objects) which we want to calculate (se-lecting it from default parameter list provided bySExtractor).

10 In our case, we calculate magnitudeand FWHM of each detected object. Following fig-ure shows one example of PSF matching resultedfor one band. FWHM value is increased after beenconvolved as we can see from Figure : Comparison between FWHM value before andafter being Gaussian convolved2014 Pixel BinningFor assigning pixels to objects, we use the SExtrac-tor (Bertin Arnouts 1996) segmentation map. Wegroup pixel adopt the Voronoi two-dimensional bin-ning technique (Cappellari Copin 2003), instead ofapply multi-wavelength photometric for each Resolved SED FittingFirst we perform standard Stellar population mod-elling of five bands (ugriz) of each spatial bin indi-vidually.