Surface Photometry and Radial Color Gradients of Nearby Luminous Early-type Galaxies in SDSS Stripe 82
aa r X i v : . [ a s t r o - ph . C O ] S e p Research in Astron. Astrophys.
Vol. XX No. X , XX–XX R esearchin A stronomyand A strophysics Surface photometry and radial color gradients of nearby luminousearly-type galaxies in SDSS Stripe 82 ∗ Fang-Zhou Jiang , , Song Huang and Qiu-Sheng Gu Department for Intensive Instruction, Kuang Yaming Honors School, Nanjing University, Nanjing210093, China; [email protected] Department of Astronomy, Nanjing University, Nanjing 210093, China
Received 2010 July 8; accepted 2010 September 13
Abstract
We make use of the images from the Sloan Digital Sky Survey Stripe 82 (Stripe82) to present an analysis of r band surface brightness profiles and radial color gradients( g − r , u − r ) in our sample of 111 nearby early-type galaxies (ETGs). Thanks to theStripe 82 images, each of which is co-added from about 50 single frames, we are ableto pay special attentions to the low-surface-brightness areas (LSB areas) of the galaxies.The LSB areas make a difference to the S´ersic fittings and concentration indices, makingboth the indices less than the typical values for ETGs. In the S´ersic fits to all the surfacebrightness profiles, we found some S´ersic indices range from 1.5 to 2.5, much smaller thanthat of typical de Vaucouleur profiles and relatively close to that of exponential disks, andsome others much larger than 4 but still with accurate fitting. Two galaxies cannot befitted with single S´ersic profile, but once we try double S´ersic profiles, the fittings areimproved: one with a profile relatively close to de Vaucouleur law in the inner area and aprofile relatively close to exponential law in the LSB area, the other with a nice fitting inthe inner area but still a failed fitting in the outer area. There are about 60% negative colorgradients (red-core) within 1.5 R e , much more than the approximately 10% positive ones(blue-core) within the same radius. However, taking into account of the LSB areas, wefind that the color gradients are not necessarily monotonic: about one third of the red-core(or blue-core) galaxies have positive (or negative) color gradients in the outer areas. SoLSB areas not only make ETGs’ S´ersic profiles deviate from de Vaucouleur ones and shiftto the disk end, but also reveal that quite a number of ETGs have opposite color gradientsin inner and outer areas. These outcomes remind us the necessity of double-S´ersic fitting.These LSB phenomena may be interpreted by mergers and thus different metallicity inthe outer areas. Isophotal parameters are also discussed briefly in this paper: more diskynearby ETGs are spotted than boxy ones. Key words: galaxies: early-type galaxies — galaxies: surface brightness profiles andcolor gradients — techniques: photometric
Early-type galaxies (ETGs), including elliptical galaxies (Es) and bulge-dominated S0 galaxies (S0s),are generally known to be dynamically simple stellar systems of homogeneous stellar population, devoid ∗ Supported by the National Fund for Fostering Talents of Basic Sciences of China. F. Z. Jiang, S. Huang & Q. S. Gu of dust, cool gas and young blue stars. However, they are far from relaxation and their morphologicalvariety (e.g., Es’ triaxial/oblate shapes and S0s’ disks) implies that they originated by different means.The spatial distribution of stellar population properties in ETGs are the chemodynamical fossil imprintsof galaxy formation and evolution mechanisms. The study of surface brightness profiles and radial colorprofiles of ETGs sheds light on the star formation history and buildup of the stellar population, and thusprovides important clues to understand galaxy formation and evolution.As a generalization to de Vaucouleur’s R law, S´ersic’s (1963, 1968) R n model is widely usedto describe the stellar distributions in galaxies. The stellar distributions of ETGs are equivalent to thesurface brightness distributions in terms of optical observations, including Sloan Digital Sky Survey(SDSS). Even early-type stellar systems are somewhat mixtures of bulge and disk components, whichcombines to result in the intermediary form between R bulge and R disk, i.e., the R n profile. Nowexcept for decomposing an image into its separate components, galaxies are modeled with a singleS´ersic profile (e.g., Blanton et al. 2003).The colors of ETGs get bluer from the center outwards (Boroson et al. 1983; Kormendy &Djorgovski 1989; Franx & Illingworth 1990; Peletier et al. 1990a, 1990b; Michard 1999; Idiart et al.2002; de Propris et al. 2005; Wu et al. 2005; La Barbera & De Carvalho 2009). The negative color gra-dients are believed to be metallicity-dominated (Ferreras et al. 2009, Spolaor et al. 2010) in spite of thefamous age-metallicity degeneracy (Worthey 1994), although whether or not they evolve with cosmictime is still under debate (e.g., Hinkley & Im 2001). Classic collapse model (Eggen et al. 1962; Larson1974a, 1974b, 1975; Carlberg 1984) suggests that ETGs form in high redshift without subsequent sec-ondary star formation, while others (Hinkley & Im 2001) indicate that secondary bursts/accretions mayoccur at moderate redshifts. Recent studies discovered a significant fraction of positive color gradients(Michard 1999, Menanteau et al. 2001, Ferreras et al. 2005, Elmegreen et al. 2005, Suh et al. 2010),which have something to do with age gradients in addition to metallicity gradient (Silva & Elston 1994,Michard 2005). Age gradients could result from galaxy mergers (e.g., Toomre & Toomre 1972) wherestar formation events continue or occur episodically. Actually, a remarkable fraction of ETGs at highredshifts exhibit positive color gradients as results of mergers or inflows (Menanteau et al. 2001, Marcumet al. 2004, Ferreras et al. 2005, Elmegreen et al. 2005). This phenomena suggest that secondary starformation events take place at the centers of these ETGs. In consistent with these results, some post-starburst galaxies such as E+A galaxies have positive color gradients, which then evolve into negativeones as the population ages (e.g., Yang et al. 2008).This paper presents results from surface photometry of 111 nearby luminous ETGs from SDSSStripe 82 (Frieman et al. 2008, Sako et al. 2008) in three bands, u , g and r . We use S´ersic profiles to fittheir r band surface brightness profiles, and we measure their color profiles of g − r and u − r . Benefittedfrom the co-added images of SDSS Stripe 82, we pay attention to the low-surface-brightness areas (LSBareas) of the ETGs and influences from the LSB areas to the S´ersic fits and the radial color gradients.Section 2 describes the sample and the data reduction. Section 3 presents the results of the S´ersic fits,the analyses of color gradients and isophotal parameters. Section 4 is a brief discussion for the previoussection. Finally, we summarize the conclusions in Section 5. Except where stated otherwise, we assumea Λ CDM cosmology with Ω m = 0 . and H = 70 kms − Mpc − . SDSS Stripe 82 is part of the SDSS-II supernova survey (Frieman et al. 2008, Sako et al. 2008). A 2.5degree wide region along the celestial equator from − < RA < is imaged repeatedly in 303 runs(plus 2 coadd runs) for three months (September, October and November) in each of three years (2005-2007). Each image is co-added from 50 ordinary SDSS images of the same object, each of which hasthe exposure time of 52 seconds. So the co-added Stripe 82 images are about 2 magnitudes deeper thansingle frames. With the extra depth, some features invisible in single images are revealed in the LSB urface Photometry and Color Gradients of Nearby ETGs in SDSS Stripe 82 3 outer areas. Fig. 1 shows two examples of the LSB structures and Table 1 gives the information of thetwo ETGs (in our sample). Fig. 1
Left: Stripe 82 images showing shell archesor interactions in LSB areas. Right: ordinary SDSSimages for the same galaxies on their left.
Table 1
Information of the Two ETGs whose Stripe 82 Images Show LSBFeatures
SDSS Name RA DEC r Magnitudes r FracDevJ001647.00+004215.3 4.19587 0.70426 14.04 0.95J222614.62+004004.1 336.56095 0.66783 14.74 1
These are two examples of our sample of 111 ETGs, the vast majority of which are chosen from alarger sample of more than 400 galaxies according to the following criteria: Petrosian r < , z < . and FracDev r > . , which mean that they are all strictly nearby luminous early-type stellar systems.FracDev indicates how close a galaxy is in accordance with de Vaucouleur profile: 1 means typical deVaucouleur profile. The larger sample of more than 400 luminous galaxies are chosen merely accordingto r < , so it includes irregular ones, spiral ones and early-type ones. Then eyeball review adds someobvious ETGs into the sample, even if some of them has FracDev r < . . All the images that we used are corrected by the SDSS photometric pipeline (flat-fielded, sky-subtracted,etc..). SDSS pipeline may sometimes overestimate the sky background, but our scientific purpose is notabout the absolute values of the surface brightness. The × -pixel frames are sampled with F. Z. Jiang, S. Huang & Q. S. Gu ′′ . × ′′ . pixels. The PSF in r band is also ′′ . . The zero points of photometry are 24.80,25.11 and 24.63 in r , g and u band respectively.We have 111 images in each band and thus 333 frames in all the three wavebands. For each of the333 images, now that the sky background has been subtracted, we use SExtractor to generate segmentimage to mask all the sources other than the target. In order to have a neat and complete mask, we adoptthe ’automatic+manual’ scheme. First, we expand the segments appropriately, leaving the target and thesources close to the target not masked. Second, we mask any contaminations on target as well as anyother sources close to our target manually in the interactive mode of ELLIPSE. ELLIPSE is the 1Dsurface photometry task in the STSDAS ISOPHOTE package in Image Reduction Facility (IRAF). Secondly, we measure the surface brightness along elliptical annuli in r band using ELLIPSE.ELLIPSE is run twice for r band. We adopt the coordinates of the centers of the galaxies providedby SDSS, since we have tested their accuracy one by one by an extra run of ELLIPSE and find that theaverage values are no more than one pixel different from the SDSS ones. So in the first run, the centers ofall the isophotes are fixed, while the position angle (PA) and the ellipticity ( e ) are set free as functions ofradius, as well as the surface brightness ( µ ). The steps of the semi-major axis (SMA) are nonlinear withinthe upper limit of 800 pixels (ELLIPSE parameter maxsma=800). Neighboring isophotes may contact orcross each other in the first run, when the ’maximum sma length for iterative mode’ (ELLIPSE parametermaxrit) is the same with ’maxsma’. So in the second run, ’maxrit’ is reduced to such an extent that noneighboring isophotes contact or cross each other, which can be tell by the PA profile and the e profile– they should vary continuously without any jump or break. We then convert the photometric table to aspreadsheet and import its useful columns (SMA, INTENS, ELLIP, MAG, MAG LERR, MAG UERR,A4) into MATLAB to calculate isophotal parameters e , a /a and to plot the surface brightness profile. We apply single S´ersic fit to the profile to give the least-squares estimate of the three fitting parameters:S´ersic index n , effective radius R e and µ e , the surface brightness within R e . We use this R e as R and adopt R from SDSS) to calculate concentration index in r band, C r = R /R . Please note thatbefore fitting, the innermost 2PSF region of the profile is truncated as well as the outermost end of theprofile where the brightness approaches the sky level. So even if the innermost pixels are saturated, itdoes not matter.Thirdly, we apply the same set of isophotes from the photometry in r band to the photometry in u and g bands so that the surface brightness profiles in all the three bands have exactly the same stepsof radii. Hence, simple subtractions between surface brightness profiles give radial color profiles. Wedivide each color profile into two regions: the inner region 0.5 R e –1.5 R e and the outer LSB region1.5 R e –4 R e . The former region is for the convenience of comparing our analyses on color gradientswith others’ works (e.g., Suh et al. 2010), for previous statistical works discuss color profiles in thesame region more or less: within 0.5 R e is approximately the region affected by seeing, while beyond1.5 R e , single SDSS images can hardly give enough signal-to-noise ratio. The 1.5 R e –4 R e region is forour emphases on the LSB areas, beyond which noise dominates. S´ersic’s (1963, 1968) R n model is commonly expressed as an intensity profile (e.g., Sparke & Gallagher2007). I ( R ) = I e e − b n [( RR e ) n − , (1)where I e is the intensity at effective radius R e , and b n is selected to make sure Z ∞ I ( R )2 πRdR = 2 Z R e I ( R )2 πRdR, (2) http://iraf.noao.edu/ The meaning of a /a and how to calculate e and a /a are discussed in Section 3. urface Photometry and Color Gradients of Nearby ETGs in SDSS Stripe 82 5 −10 0 10 20 30 40 50 60 70 80 901416182022242628 R(arcsec) S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 18.7536R e = 7.2419Sersic Index n = 3.9051 0 5 10 15 20 25 30 35 40 451516171819202122232425 R(arcsec) S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 18.4133R e = 5.5483Sersic Index n = 3.9277 Fig. 2
Two examples of typical de Vaucouleur profiles, n ≈ . The dashed line is the S´ersic’s R n model.so that the effective radius R e encloses half of the total light from the model (Ciotti 1991, Caon et al.1993). However, the photometric results are in the units of magnitude, which by definition should beconverted from intensity with the formula µ ( R ) = − . I ( R ) . (3)So the actual format of the S´ersic’s empirical formula that are used in fitting is µ ( R ) = µ e + 2 . b n ln(10) [( RR e ) n − , (4)where b n = 2 n −
13 + 4405 n + 4625515 n + O ( n − ) , n > . . (5)The deduction and approximation of b n can be referred to Graham & Driver (2005).In Appendix Table A.1 and Table A.2, we list the photometric results. We do find quite a number ofde Vaucouleur profiles (Fig. 2) with n ≈ , but there are also several . < n < . profiles which arerelatively close to exponential disks (Fig. 3). Furthermore, a couple of profiles have S´ersic indices muchlarger than 4 but can still be fitted well with single S´ersic profile (Fig. 4), while only two profiles cannotbe fitted with single S´ersic at all (Fig. 5). However, once we try curve fitting with double S´ersic profiles,one of the two above-mentioned ones is fitted much better with an inner n = 4 . curve and an outer n = 1 . curve (Fig. 6 Left), which indicates that this ETG may be classified as elliptical galaxy withsingle SDSS image but actually turns out to be an S0 system once its LSB region is revealed. But theother one still cannot be fitted well even with double S´ersic profiles (Fig. 6 Right), no matter how wechange the initial value of n , µ e and R e or how we try different radii where the two curves meet. Thisfailure indicates that the components of this ETG can hardly be distinguished with 1D S´ersic fit or fits.In a word, we encounter the aforementioned four kinds of S´ersic fits and get a quite large range ofS´ersic indices for the sample which is supposed to contain only strict early-types whose S´ersic indicesshould be closely concentrated to 4. The histogram of S´ersic indices presents the results clearly (Fig.7 Left): the distribution of S´ersic indices has a peak at about 3-3.5 and a scatter from 1.5 to 8.5. Thehistogram of concentration indices shows a consistent result (Fig. 7 Right): most ETGs in our samplehave concentration indices smaller than 2.5 while the typical value for ETGs is C r = R /R > . . These two histograms correlate with each other to imply that the LSB areas of the ETGs makea noticeable difference in S´ersic fits. On one hand, single S´ersic profile may be misleading and thus F. Z. Jiang, S. Huang & Q. S. Gu S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 17.6128R e = 4.2918Sersic Index n = 1.9181 0 5 10 15 20 25 30 35 401516171819202122232425 R(arcsec) S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 17.9032R e = 5.0339Sersic Index n = 2.3265 Fig. 3
Two examples of the . < n < . profiles which are relatively close to exponentialdisks. The dashed line is the S´ersic’s R n model. S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 18.3591R e = 5.5938Sersic Index n = 4.6055 −20 0 20 40 60 80 100 120 14014161820222426 R(arcsec) S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 19.6807R e = 14.793Sersic Index n = 8.1225 Fig. 4
Two examples of the well-fitted single S´ersic profiles even with n much larger than 4.The dashed line is the S´ersic’s R n model.double-S´ersic fitting is needed. On the other hand, the LSB regions of the profiles make the ETGs’photometric properties shift to the disk end. Radial color gradient is defined by its slope (Wu et al. 2005, Suh et al. 2010) g g − r ≡ d ( g − r ) d log( RR e ) , g u − r ≡ d ( u − r ) d log( RR e ) . (6)We examine g − r and u − r profiles from 0.5 R e –1.5 R e and 1.5 R e –4 R e respectively in order to comparethe slopes in the two colors and to compare the slopes in the two regions, paying extra attention to theouter LSB regions. The histograms of the g − r and u − r slopes tell us two direct statistical results(Fig. 8 Upper and Lower). Firstly, there are more positive gradients in LSB regions than in inner regions urface Photometry and Color Gradients of Nearby ETGs in SDSS Stripe 82 7 S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 20.1768R e = 9.8556Sersic Index n = −11333.0919 0 5 10 15 20 25 30 35 4014161820222426 R(arcsec) S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 16.9452R e = 2.3497Sersic Index n = −30612.0698 Fig. 5
Single S´ersic profile fails to fit any of the two. The dashed line is the S´ersic’s R n model but the n values here do not make any sense. Fig. 6
Double S´ersic fits.The dashed line is the S´ersic’s R n model. Left: the LSB regionreveals that it is actually an S0 system which may be misinterpreted as an elliptical withoutLSB region. Right: double S´ersic profiles still fail to fit the curve, whose components canhardly be recognized by 1D S´ersic fit.irrespective of g − r or u − r . Secondly, there are more positive gradients in g − r than in u − r regardlessof 0.5 R e –1.5 R e or 1.5 R e –4 R e .Now that we have two colors, we can define a ’red-core’ ETG as follows: if both its g − r and u − r color in the inner region show negative gradients, we call it a ’red-core’ ETG. Similarly, we havea ’blue-core’ galaxy if its g − r and u − r colors in the inner region both show positive gradients.According to these definitions, we have 62 red-core ETGs, taking up to 60% of the whole sample and13 blue-core ones, taking up to a much smaller portion, approximately 10%. All the color gradients ofall the 108 galaxies with reliable photometric results are listed in Appendix Table A.1 and Table A.2.The outcome that there are more red-core ETGs agree with the results of Suh et al. (2010), who report11% ’red-core’ versus 4% ’blue-core’ in a large sample of 5002 ETGs, although the disagreement inthe absolute portions has something to do with our different method of defining ’red-core’/’blue-core’. F. Z. Jiang, S. Huang & Q. S. Gu f r a c t i on de Vaucoulers n=4 0.5 1 1.5 2 2.5 3 3.5 400.10.20.30.40.5 Concentration Index C r =R /R e f r a c t i on ETG typically C r >2.6 Fig. 7
Left: the histogram of S´ersic indices. The dashed line is where the peak ought to befor de Vaucouleur profiles. Right: the histogram of concentration indices. The dashed linemarks the position where the peak ought to be for typical ETGs.Since the blue-core ones are relatively rare, we would like to give an instance in Fig. 9, which may alsohelp to illustrate how our color profiles look like.When we move to the LSB regions, we find that 27 of the 62 red-core ETGs show positive u − r gradient and 31 of the 62 red-core ETGs show positive g − r gradient in their LSB regions respectively.19 of the 62 red-core ETGs show both positive u − r gradient and positive g − r gradient in their LSBregions, taking up to almost 1/3 of all the red-core ETGs. Consistently, 10 of the 13 blue-core ETGsshow positive u − r gradient and 5 of the 13 blue-core ETGs show positive u − r gradient in their LSBregions respectively. 4 of the 13 blue-core ETGs show both positive u − r gradient and positive g − r gradient in the LSB regions, also taking up to about 1/3 of the blue-core ETGs. All in all, the colorsof red-core ETGs do not get bluer outwards monotonically, and the colors of blue-core ones do notget redder outwards monotonically either. Fig. 10 presents two examples of the 19 ’abnormal’ red-coreETGs. ELLIPSE actually does not draw isophotes but a series of ellipses that approximately match theisophotes. The intensity along an ellipse is given in Fourier series: I ( θ ) = I + Σ ∞ n =1 ( A n cos nθ + B n sin nθ ) . (7)where I is the intensity averaged over the ellipse, and A n , B n are the higher order Fourier coefficients.For isophotes of perfect ellipses, these coefficients should be zeros. ’A4’, as the output of ELLIPSE,is actually A divided by SMA a , i.e., A /a . Hao et al. (2006) proved in their appendix that A /a isessentially just a /a , which is used by Bender et al. (1988, 1989) to tell whether an elliptical galaxy isdisky ( a > ) or boxy ( a < ). a /a is calculated from INTENS and A4. It is the weighted meanvalue of A4 over 2PSF to 1.5 R e with intensity counts (INTENS) as the weight. e is calculated similarly(Bender et al. 1988, 1989). From the histogram of a /a (Fig. 11), we find that there are much moredisky ETGs than boxy ones in our sample.We plot a /a versus e in Fig. 12 to see whether or not at higher e , the deviations of the isophotesfrom perfect ellipses are larger (Hao et al. 2006). But due to the fact that our sample is not meant to be acomplete and large one, we do not see clear trend in the diagram. However, it is plausible that at higher e , the ETGs are more likely to be S0s instead of Es, no wonder a /a deviates from zero. urface Photometry and Color Gradients of Nearby ETGs in SDSS Stripe 82 9 −0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.800.10.20.30.40.5 g−r gradient f r a c t i on Histogram of g−r from 0.5R e to 1.5R e and 1.5R e to 4R e positive gradient percentage: 0.5R e −1.5R e (solid line) 43.5185%1.5R e −4R e (dotted line) 62.037%−0.8 −0.6 −0.4 −0.2 0 0.2 0.4 0.6 0.800.10.20.30.40.5 u−r gradient f r a c t i on Histogram of u−r from 0.5R e to 1.5R e and 1.5R e to 4R e positive gradient percentage: 0.5R e −1.5R e (solid line) 30.5556%1.5R e −4R e (dotted line) 38.8889% Fig. 8
Upper: the histogram of g − r gradients.Lower: the histogram of u − r gradients. The solidlines are the histogram of the gradients in the innerregion of 0.5 R e –1.5 R e , while the dotted lines are thehistograms of the gradients in the outer 1.5 R e –4 R e re-gion. The dash-dot lines mark the threshold for posi-tive/negative gradient. The results in Section 3.1 remind us that S´ersic fit may not be that robust as we thought before. Inaddition, the quality of S´ersic fitting relies much on where to truncate the surface brightness profiles. Ina trial when we did not abandon the innermost 2PSF regions, we got the peak of S´ersic indices at around2.5, the typical value for S0 systems. The innermost 2PSF regions are affected by seeing effects andpossible stellar cusps. Truncating the outer region also matters: as we have tried double S´ersic profilesfor the aforementioned two ETGs in Section 3.1, if we choose not to fit the outer regions purposely, theresults of S´ersic fits may alter accordingly. Admittedly, this likelihood agrees with our discovery thatthe LSB regions matter a lot in 1D photometry and fitting.Another issue is the definition of ’red-core’/’blue-core’ ETGs. Suh et al. (2010) measured the g − r color for 5002 galaxies and set a reliable threshold for ’red-core’/’blue-core’, i.e., the . σ confidencelevel (Figure 2., Suh et al. 2010). We think that this threshold works and helps a lot in picking out theETGs with noticeable color gradient. However, we cannot use this definition in this work. Since we havea small sample of 111 luminous nearby galaxies, If we still stick to the threshold, then a large portionof our sample may fall into the category of ’no noticeable color gradient’, leaving the number of the −0.3 e ) g − r Color g−r from 0.5R e to 1.5R e y=0.074098x+1.166910 −0.3 e ) u − r Color u−r from 0.5R e to 1.5R e y=0.06567x+2.4887 10 e ) g − r Color g−r from 1.5R e to 4R e y=0.49128x+0.943310 e ) u − r Color u−r from 1.5R e to 4R e y=1.0617x+2.1608 Fig. 9
An example of the rare blue-core ETGs. −0.3 e ) g − r Color g−r from 0.5R e to 1.5R e y=−0.33807x+1.21410 −0.3 e ) u − r Color u−r from 0.5R e to 1.5R e y=−0.041933x+2.7066 10 e ) g − r Color g−r from 1.5R e to 4R e y=0.1626x+0.7996410 e ) u − r Color u−r from 1.5R e to 4R e y=0.30189x+2.6036 10 −0.3 e ) g − r Color g−r from 0.5R e to 1.5R e y=−0.038225x+1.102510 −0.3 e ) u − r Color u−r from 0.5R e to 1.5R e y=−0.081348x+2.3446 10 e ) g − r Color g−r from 1.5R e to 4R e y=0.071083x+1.056410 e ) u − r Color u−r from 1.5R e to 4R e y=0.18727x+2.2128 Fig. 10
Two examples of the red-core ETGs whose colors get redder, instead of bluer, beyond1.5 R e . Red dashed lines indicate the slopes.remaining ones not enough for statistical analyses. So we measure the u − r color in addition to g − r in the hope that the signs of the slopes of the two colors agree with each other, so that even if any singlecolor cannot give a gradient above the threshold, the consistency between the two colors still approvesa real color gradient. Fortunately, we examine all the ETGs to find that only one of them have a positive g − r gradient and a negative u − r slope. So we think that our definition of ’red-core’/’blue-core’ isalso reliable.As to the fact that one third of red-core ETGs go red (one third of the blue-core ETGs go blue) in theLSB region, we think that a plausible interpretation involves galaxy mergers. Chang et al. (2006) foundthat massive ETGs are redder than less massive ones, and color is more sensitive to metallicity ratherthan age. Spolaor et al. (2010) point out that massive ETGs have less obvious metallicity gradients.These and other discoveries both imply that the opposite color gradients between the LSB regions andthe inner regions may owe to metallicity gradients as remnant of mergers. urface Photometry and Color Gradients of Nearby ETGs in SDSS Stripe 82 11 −0.04 −0.02 0 0.02 0.04 0.0600.10.20.30.40.5 a /a f r a c t i on boxy disky Fig. 11
The histogram of a /a . The dash line is thethreshold of disky/boxy, so there are much more diskyETGs in our sample.In the future, we can investigate the spectra of the LSB areas for the ETGs with opposite colorgradients so as to resolve the age-metallicity degeneracy to see radial metallicity profiles. For problemscannot be solved by 1D photometry, we can also try 2D surface photometry with tools such as GALFIT. In this paper, we present surface photometry and radial color gradients of nearby luminous early-typegalaxies. The 2 magnitudes’ extra depth of SDSS Stripe 82 provide us the opportunity to investigate intothe low-surface-brightness areas. In the first place, we find that LSB regions make some S´ersic profilesof our high-FracDev ETGs deviate from de Vaucouleurs profile and shift to the exponential end. Thenwe find up to 60% red-core ETGs and approximately 10% blue-core ones, but red-core/blue-core ETGsdo not necessarily have monotonic color gradients. On the contrary, about one third of the red-core/blue-core ETGs show opposite color gradients between inner regions and LSB regions, which may owe togalaxy mergers and subsequent radial metallicity gradients. Finally, we find that there are more diskyETGs in our sample and we also try to use the a /a - e diagram to show that ETGs with higher e valuestend to have isophotes that deviate more from perfect ellipses. Acknowledgements
This work, as the Bachelor’s thesis of Fangzhou Jiang, is supported by theNational Fund for Fostering Talents of Basic Sciences of China. We thank all the members of thegalactic and extragalactic group in the Department of Astronomy, Nanjing University for their helpfuldiscussions. We gratefully acknowledges Lu Wei in the Department for Intensive Instruction of NanjingUniversity for her kind help with the data importation.
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Appendix A: DETAILED INFORMATION ABOUT THE SAMPLE
Table A.1
Detailed Information about the Sample, Photometric Results andColor Gradients
SDSS Name RA DEC FracDev r S´ersic Index R e R µ e C r g g − r, inner g g − r, outer g u − r, inner g u − r, outer a /a e r MagnitudesJ011248.6-001724.6 18.20252444 -0.29018160 1 3.5949 9.4562 19.33 1.8851 17.4809 -0.018715 -0.028358 -0.07705 -0.13112 0.0017 0.3259 12.95J235618.81-001820.1 359.07837711 -0.30560544 1 4.7676 6.9561 14.22 1.6732 17.3346 -0.012698 -0.0099012 -0.095444 -0.25043 0.0037 0.3138 13.23J010416.96-004553.6 16.07067765 -0.76491129 0.89 4.1974 27.28 30.67 1.293 19.2839 -0.010488 -0.091517 0.117 0.23739 -0.00090516 0.3156 13.27J011146.55-003951.5 17.94396288 -0.66432211 0.97 2.6587 4.1057 10.31 2.3159 16.2258 0.045424 -0.010903 0.014372 -0.12744 0.0019 0.2135 13.37J012943.98-011429.1 22.43327416 -1.24141730 0.93 2.8856 11.045 21.7 1.9771 17.816 0.0047963 0.044714 -0.0092825 -0.15645 -0.000063854 0.4064 13.38J030732.29-005752.3 46.88455434 -0.96453808 0.97 3.225 9.4557 21.1 2.2342 17.7391 -0.016407 0.060442 -0.12452 -0.28238 0.0034 0.2176 13.38J015441.04-000836 28.67100555 -0.14334793 0.98 4.0803 11.894 23.82 1.9683 18.2665 -0.023882 -0.093205 -0.042127 -0.23902 0.0066 0.2705 13.39J030530.84-002418 46.37852752 -0.40501239 1 3.0552 8.534 17.64 1.9687 17.5945 -0.017979 0.019746 -0.079311 0.25322 0.0019 0.3397 13.42J231808.39-002325.7 349.53496202 -0.39047265 0.8 5.3163 4.665 20.69 3.5383 19.0252 -0.031405 -0.13732 0.0093273 0.75419 0.0013 0.0382 13.5J011853.62-010007.2 19.72342956 -1.00200616 0.88 3.6808 20.9526 30.88 1.7327 19.0464 -0.021079 0.25975 0.059285 -0.019325 -0.0057 0.3335 13.53J230748.93+005625.9 346.95391663 0.94053502 1 4.0026 8.0254 16.13 1.8922 17.8216 -0.014986 -0.039578 -0.047298 0.085562 -0.00077092 0.175 13.6J232029.07-010008.7 350.12112518 -1.00242678 1 4.5442 8.8691 18.31 2.027 18.1781 -0.018996 0.045736 -0.16763 -0.44829 -0.002 0.0508 13.68J012602.51-011332.1 21.51047343 -1.22560582 0.96 3.9325 12.812 26.75 2.2357 18.6633 0.0041238 0.093578 -0.05713 -0.1852 -0.018 0.1875 13.72J011457.58+002550.9 18.73995395 0.43082652 0.79 5.3822 33.3274 23.91 0.99779 19.7342 -0.025616 0.016946 -0.2406 -0.50457 -0.0061 0.2565 13.76J012312.36-003828.2 20.80153809 -0.64116891 0.98 2.6343 8.8963 14.57 1.5459 17.6697 -0.029947 -0.017055 -0.12331 -0.33671 -0.00015011 0.5972 13.8J234430.08+001913.7 356.12533533 0.32047532 0.97 3.6178 8.1598 22 2.6638 18.1101 -0.010702 -0.0081651 -0.0052486 0.57781 0.0023 0.0888 13.81J031212.86-010342.8 48.05360848 -1.06190079 0.98 3.1603 7.2191 15.46 2.0999 17.75 -0.038225 0.071083 -0.081348 0.18727 -0.0041 0.2641 13.94J233525.66+010332.6 353.85695746 1.05907480 0.93 3.492 15.831 26.16 1.8106 19.1562 -0.0091442 -0.18197 -0.16693 0.63191 -0.0256 0.2533 13.97J001647+004215.3 4.19586472 0.70427291 0.95 3.5331 10.1844 19.4 1.896 18.5757 -0.029121 -0.040562 -0.09992 -0.34979 0.0025 0.2417 14.03J222614.63+004004 336.56097640 0.66778611 1 3.1711 6.5502 16.01 2.4751 17.6089 0.024994 0.0093977 0.13477 -0.15963 -0.0027 0.3393 14.06J220425.31+004255.5 331.10546741 0.71542132 1 2.5506 5.4687 13.01 2.181 17.309 -0.028337 -0.035825 -0.13994 -0.43243 0.0017 0.4201 14.11J204710.5+002147.8 311.79378369 0.36329981 0.81 2.0488 4.3964 11.11 2.3169 16.9985 -0.11481 -0.071288 -0.26335 1.5204 0.0011 0.243 14.11J021735.8-002936.8 34.39917627 -0.49357706 0.98 3.3831 6.7671 15.73 2.1545 18.1969 -0.017447 -0.029389 -0.77129 -0.22874 0.0014 0.0713 14.15J033601.58+010617.1 54.00660523 1.10475887 1 4.0362 8.5412 14.56 1.601 18.3207 -0.01871 0.025516 -0.047585 1.1535 0.0027 0.3738 14.16J020557.03+004624 31.48762819 0.77334047 0.98 4.4026 10.4865 18.4 1.7924 18.731 -0.016095 0.037535 -0.052994 -0.39026 0.0093 0.2007 14.16J205838.24+005445.3 314.65936086 0.91258449 0.99 4.0209 10.3188 21.31 2.0919 18.8015 -0.021973 0.069314 -0.052994 0.46902 0.0094 0.1371 14.16J231110.01-000908 347.79174779 -0.15224910 1 3.0104 5.1929 15.15 2.6967 17.6412 0.00028358 0.011971 -0.084359 -0.016687 -0.0022 0.1547 14.19J024647.79-003414.8 41.69915516 -0.57079231 0.95 5.0163 18.496 28.24 1.9574 19.4473 -0.031991 0.019586 -0.0099847 0.9781 0.000035055 0.1219 14.19J233318.7-002700.5 353.32792549 -0.45014581 1 4.5104 20.0121 25.79 1.5124 19.6328 -0.038791 -0.055995 0.14284 -0.78908 0.00077529 0.3147 14.19J005727.62-002817.6 14.36509352 -0.47157061 1 8.1125 14.793 12 0.90306 19.0577 -0.012473 -0.048233 -0.26462 -0.46491 -0.005 0.3693 14.2J014017.46-001740.8 25.07278726 -0.29467689 1 3.9869 9.6875 19.01 2.1259 18.4792 -0.008886 0.60998 0.64622 1.6074 -0.0062 0.2347 14.21J222904.69-011105.6 337.26956145 -1.18490971 0.91 2.6933 10.5183 19.23 1.8602 18.5058 0.010871 0.10962 -0.0038694 -0.76463 -0.0046 0.4284 14.21J212413.05+010706.1 321.05439566 1.11838228 1 4.4661 9.0369 12.61 1.4091 18.2644 -0.023212 0.014296 -0.025948 0.31981 0.0054 0.3878 14.22J002537.7+000212.2 6.40709052 0.03672977 1 3.5388 6.0791 13.46 1.9563 17.8479 -0.065434 0.013746 0.031839 1.0394 -0.0128 0.3443 14.22J005130.06-011511.1 12.87528325 -1.25309676 0.93 6.4237 10.0964 16.75 1.3652 19.0911 0.035644 0.67256 -0.203 -0.82407 -0.0019 0.4801 14.25J015113.38-010338.5 27.80576264 -1.06070791 0.93 7.7085 5.9679 11.92 1.1762 18.862 0.0078687 0.10491 -0.093857 -0.90778 0.0011 0.2707 14.26J222812.65+003235.6 337.05272498 0.54322348 0.95 3.8585 10.6137 21.27 2.0915 18.9029 -0.042947 -0.031789 -0.23347 -0.55431 -0.0054 0.0941 14.26J034313.96-010107.3 55.80819172 -1.01869778 0.88 2.8164 7.439 16.64 2.1299 18.3023 -0.039968 0.083739 -0.093829 0.029362 -0.0053 0.178 14.26J012235.4-003412.3 20.64751590 -0.57009991 1 3.5454 5.2537 15 3.0277 17.3873 -0.024095 0.0089256 -0.063819 0.66851 -0.0034 0.267 14.26J010425.27-001114.6 16.10529594 -0.18740242 0.97 3.1162 11.872 20.54 1.7197 18.8413 -0.0081743 0.076599 0.018154 0.49289 0.002 0.4369 14.27J022026.53-001846.2 35.11057621 -0.31283885 0.95 2.9008 9.3235 14.55 1.623 18.2389 -0.0090067 -0.010362 -0.10478 -0.28946 0.00092875 0.4641 14.29J032516.26-002432.4 51.31775271 -0.40902744 1 2.8124 8.1868 17.12 2.0769 18.3298 0.027014 -0.0033398 0.021128 -0.084288 0.009 0.477 14.29J224005.22-004827.7 340.02175136 -0.80771312 1 3.3358 5.9875 12.03 1.769 17.9762 -0.33807 0.1626 -0.041933 0.30189 -0.00091017 0.293 14.32J012802.13-004417.9 22.00888578 -0.73832185 0.92 2.945 6.5298 13.81 2.0069 18.1141 0.00088229 -0.011681 0.029804 0.18113 0.0066 0.2671 14.33J020015.67+001157.2 30.06529850 0.19923396 0.9 1.9656 5.8112 14.71 2.5827 17.6397 -0.012259 -0.04439 -0.032495 0.81589 0.006 0.3049 14.35J012117.6-003551.5 20.32335317 -0.59764847 1 3.5104 5.5602 12.64 1.9067 17.9592 -0.015385 0.036747 -0.06496 0.16729 0.0055 0.3177 14.38J030916.97-005424 47.32072761 -0.90666964 1 5.955 6.397 11.87 1.3835 18.6907 -0.019572 0.26896 -0.1261 -0.48362 -0.0045 0.2162 14.41J005716.97-004010 14.32072141 -0.66947146 0.92 1.7408 6.2232 17.06 2.8976 17.8749 0.0022425 -0.049961 0.0064705 -0.24768 0.0011 0.1315 14.48J233941.25-000204.1 354.92188685 -0.03447809 1 2.3442 5.8469 14.17 2.456 17.7817 -0.02072 -0.011135 -0.13553 -0.23719 0.00069408 0.295 14.49J212258.68+010136.1 320.74452146 1.02670285 0.97 1.8637 4.0267 10.39 2.5369 16.9602 -0.018559 -0.06997 -0.099956 -0.65464 -0.0019 0.3298 14.49J235748.57+004744.1 359.45240705 0.79558976 1 4.7676 8.843 14 1.5217 18.7963 0.034554 0.034517 0.002356 -0.48148 -0.00011651 0.211 14.49J005610.66-010700.8 14.04444799 -1.11690788 0.97 2.2418 6.1184 16.5 2.6009 17.9435 -0.016162 0.49838 -0.035228 1.0623 0.0027 0.3403 14.5J002032.94-000847 a a a The photometric results for J002032.94-000847 and J034745.73+004112.2 are not reliable, so it is not taken into theanalyses afterwards. urface Photometry and Color Gradients of Nearby ETGs in SDSS Stripe 82 15
Table A.2 (Continue) Detailed Information about the Sample, PhotometricResults and Color Gradients
SDSS Name RA DEC FracDev r S´ersic Index R e R µ e C r g g − r, inner g g − r, outer g u − r, inner g u − r, outer a /a e r MagnitudesJ002339.87-000715 5.91616577 -0.12084572 0.92 2.9463 11.7017 21.52 1.884 19.2318 -0.0089079 -0.037576 0.014278 -0.54903 -0.0035 0.5041 14.53J002900.99-011341.7 7.25412553 -1.22825889 1 3.6191 9.5859 14.24 1.5168 18.686 0.22002 -0.12594 0.19745 -0.75826 -0.0306 0.4221 14.54J213645.79+011456.3 324.19080001 1.24899874 1 4.8758 5.8036 13.33 2.0949 18.1871 -0.021301 0.037401 -0.00039655 1.1429 0.00071871 0.146 14.54J024940.69-003357.2 42.41956744 -0.56591588 0.97 2.5231 5.5643 14.16 2.4173 17.9421 -0.029371 0.00039767 -0.0728 0.35647 0.000049035 0.2622 14.54J001642.55-002643.5 4.17729552 -0.44542089 1 4.9808 8.2133 15.42 1.969 18.6272 -0.012721 0.044825 -0.066157 -0.39334 0.0007837 0.1259 14.56J015315.24+010220.7 28.31350548 1.03908428 0.78 3.4584 24.3583 24.68 1.1521 20.3325 -0.01987 -0.03403 -0.063034 -0.051731 -0.0068 0.3068 14.57J011913.49-010839.9 19.80624066 -1.14442738 0.96 1.9575 6.4876 16.19 2.5468 17.999 -0.03556 -0.01556 -0.057732 -0.25693 -0.00087108 0.3441 14.6J013132.91+003321.5 22.88714103 0.55598754 1 5.4778 39.3403 23.77 1.0447 20.3068 -0.01927 -0.27174 -0.14258 -1.1361 0.0543 0.4216 14.6J002819.3-001446.8 7.08043351 -0.24633481 1 3.3719 5.236 13.49 2.1941 18.0847 -0.6122 0.01018 -0.042758 -0.37971 -0.002 0.3641 14.64J013127.62+010947 22.86509079 1.16307996 0.96 3.5394 11.4009 19.92 1.8162 19.2226 0.071661 -0.13638 -0.029998 -0.79335 0.00083218 0.4757 14.64J020316.02-010225.1 30.81675458 -1.04031200 1 3.9051 7.2419 15.62 1.8976 18.819 -0.0072916 0.14995 -0.25452 -1.2654 0.0033 0.1889 14.65J213500.39-003041.1 323.75162529 -0.51143543 0.97 2.9277 8.1004 19.84 2.5201 18.6855 -0.03294 0.034419 -0.10639 0.053361 -0.0087 0.2628 14.67J002949.34-011405.7 7.45561756 -1.23492103 1 7.0024 12.3966 23.66 2.6859 18.8819 0.074098 0.49128 0.06567 1.0617 0.0061 0.2352 14.68J223924.03-010216 339.85014609 -1.03778562 1 3.8234 6.1246 16.1 2.339 18.477 0.0021905 0.16388 -0.12946 -0.67801 -0.0048 0.2028 14.68J014715.74+005748.1 26.81560871 0.96336361 0.93 1.9943 5.2313 16.05 3.023 17.993 -0.027968 -0.011202 0.12215 0.40489 0.0013 0.1596 14.7J024513.77-004446 41.30737872 -0.74613175 1 5.2114 10.7612 15.13 1.5141 19.1134 -0.017336 -0.054555 -0.12124 -0.45631 0.0108 0.2986 14.7J011454.25+001811.8 18.72605022 0.30327972 0.88 2.3265 5.0339 12.92 2.4188 17.9362 -0.038181 -0.062553 -0.081268 1.1149 0.00029361 0.2019 14.71J234456.11+010736.8 356.23380146 1.12691012 0.93 2.33 6.9886 18.96 2.6965 18.5893 -0.06396 0.25715 -0.13066 -0.18992 0.0061 0.157 14.73J234107.25+000542.8 355.28021641 0.09524386 1 3.3672 9.3763 16.99 1.8217 19.0061 -0.0078595 0.00049809 0.19783 1.3148 -0.0011 0.3014 14.74J011204.62-001442.3 18.01925392 -0.24511037 0.97 4.79 27.7696 25.74 1.5459 20.0675 -0.0045894 -0.11305 0.20229 -2.1856 -0.0041 0.4376 14.75J024716.96-002325.2 41.82067259 -0.39034732 1 3.2473 5.9714 14.47 2.3837 18.3683 0.00025596 -0.040222 -0.0017929 0.97321 -0.00055588 0.1566 14.75J015518.65+002912.3 28.82771889 0.48675415 1 3.0868 4.1656 12.07 2.6577 17.7805 0.0044897 0.2277 0.097484 0.072748 0.0014 0.0917 14.76J235545.2-011519.6 358.93833991 -1.25544995 0.99 2.6916 5.4229 14.53 2.7658 17.9402 0.0013852 0.062428 -0.0554438 -0.29238 -0.00091716 0.2142 14.76J220638.46+011036.8 331.66025782 1.17690392 1 2.9806 5.1769 12.51 2.1242 18.1196 -0.019533 -0.048991 -0.081213 -0.42923 0.0016 0.3023 14.77J003933.21+003550.9 9.88839858 0.59748157 0.95 4.3542 11.27 16.04 1.3079 19.3581 -0.0049445 -0.0079676 -0.20375 -0.53938 -0.0065 0.4412 14.77J032833.19+010024.2 52.13830364 1.00672494 1 6.5125 20.8425 20.67 1.1421 20.3533 -0.04183 -0.058231 -0.44186 -0.59079 -0.0012 0.2644 14.77J000730.59-004815.7 1.87746615 -0.80437922 1 3.8916 11.1471 16.69 1.4257 19.4255 0.085269 0.13012 0.35178 -1.8338 -0.0197 0.4258 14.77J034208.9-011448.2 55.53708812 -1.24674200 1 3.307 5.0052 12.81 2.2921 18.2684 0.0011853 0.043761 -0.085353 -0.58348 -0.00076894 0.1111 14.79J032305.27+002115.4 50.77198928 0.35429742 1 3.0148 6.3899 18.04 2.7836 18.4119 0.006964 0.91646 -0.33345 0.95463 -0.0019 0.2416 14.79J002901.48+002102.9 7.25616975 0.35082772 1 4.6257 6.4413 15.18 2.2701 18.6306 -0.030459 -0.040203 0.0051457 0.34502 -0.0091 0.076 14.8J005846.77-004506.5 14.69489929 -0.75182185 0.97 2.7363 5.4847 12.03 1.9598 18.1634 -0.019812 -0.053655 -0.056628 1.0168 -0.0002218 0.3852 14.8J013725.41+005838.4 24.35587777 0.97734793 1 3.9277 5.5483 12.99 2.0655 18.4488 -0.034818 0.051343 -0.13581 0.075314 -0.0015 0.1488 14.8J011612.78-000628.3 19.05328708 -0.10787758 0.99 4.2756 5.288 11.15 1.8151 18.442 -0.0089351 -0.0381 -0.17492 -0.47493 -0.0009369 0.0659 14.81J011708.94+010616.7 19.28726213 1.10464084 0.93 2.3468 4.1957 11.51 2.4913 17.7747 -0.028059 -0.020946 -0.062099 -0.46486 0.0016 0.1062 14.81J005800.46-001727.2 14.50192231 -0.29089488 0.99 2.8437 5.1734 12.25 2.1472 18.0879 0.05988 0.0097334 0.22949 -0.24307 0.0014 0.2776 14.82J213001.55-011351.4 322.50648570 -1.23094487 1 4.1145 6.167 14.76 2.2492 18.6188 0.025221 0.11569 -0.055947 -0.33062 0.00049602 0.0831 14.82J010401.73-004847 16.00723838 -0.81305974 0.95 3.318 10.1002 18.64 1.8867 19.2181 -0.01182 -0.11534 -0.088332 0.96319 -0.007 0.2942 14.83J233413.5+010148.4 353.55626412 1.03013378 1 3.2097 6.1514 14.77 2.1454 18.6026 -0.03659 -0.0080011 -0.1193 -0.15758 -0.0021 0.1956 14.83J223954.96-005919 339.97904119 -0.98861147 1 3.6077 13.2744 22.27 1.905 19.633 0.011519 0.35414 -0.16742 -1.0067 -0.00051286 0.2966 14.84J224544.74+010527.9 341.43642301 1.09108514 1 4.6055 5.5938 12.32 1.8293 18.4847 -0.028146 -0.061947 0.15546 0.89582 0.0031 0.1919 14.85J223045.48-010927.3 337.68952754 -1.15758815 0.9 3.6677 12.8301 18.77 1.6141 19.4409 0.013797 0.33252 -0.16073 -0.5191 -0.0022 0.43 14.85J024847.62-000633 42.19842593 -0.10917862 0.86 1.704 4.307 11.22 2.6051 17.4899 0.071406 0.0084674 0.18868 -0.15743 0.00095301 0.1972 14.86J001426.22+010350.8 3.60928197 1.06413569 0.93 1.9181 4.2918 11.17 2.5473 17.5994 0.00067622 -0.033878 -0.032919 -0.037764 0.0071 0.2072 14.87J015057.09+001404.2 27.73789383 0.23450808 1 3.226 7.637 16.57 2.1531 18.7384 -0.03124 0.057026 -0.055255 0.057246 0.0089 0.3795 14.88J002935.59-001406.6 7.39829902 -0.23517470 1 2.9263 5.873 15.92 2.6701 18.4369 -0.026348 -0.055164 0.012083 0.96878 0.00042886 0.145 14.88J222704.24+004517.5 336.76769142 0.75487411 0.98 3.302 7.2755 13.55 1.7749 18.6162 -0.055876 0.011286 -0.27514 -0.94251 -0.0031 0.3736 14.88J224223.94+011336.8 340.59977329 1.22691494 1 3.4292 8.824 15.78 1.7966 18.9445 0.032081 -0.18037 -0.032733 -0.83759 0.0142 0.3777 14.89J225510.03-002433.8 a a The photometric results for J225510.03-002433.8 are not reliable, so it is not taken into the analyses afterwards. −0.3 e ) g − r Color g−r from 0.5R e to 1.5R e y=0.045424x+0.9621210 −0.3 e ) u − r Color u−r from 0.5R e to 1.5R e y=0.014372x+2.0807 10 e ) g − r Color g−r from 1.5R e to 4R e y=−0.010903x+0.9778910 e ) u − r Color u−r from 1.5R e to 4R e y=−0.12744x+2.1454 10 20 30 40 501516171819202122232425 R(arcsec) S u r f a c e B r i gh t ne ss µ ( m ag / a r cs e c ) Surface Brightness Profile and Sersic Fit µ = µ e +1.0857b n [(R/R e ) −1]b n =2n−1/3+4/405n+46/25515n +O(n −3 ) µ e = 18.7217R e = 6.167Sersic Index n = 4.1145 1.5 2 2.5 3 3.5 4 4.5 500.10.20.30.40.5 Sersic Index n f r a c t i onon