Robust automated photometry of local galaxies from SDSS · Robust automated photometry of local...
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Robust automated photometry of local galaxies from SDSS Guido Consolandi 1 , Giuseppe Gavazzi 1 , Massimo Dotti 1 , Michele Fumagalli 2 , Matteo Fossati 3 1. The Sample 3.Petrosian magnitudes 4. The color-mass relation 6. Color gradients 5. Color profiles Conclusions: Fig. 2 Comparison of the g-band magnitudes obtained in this work and those manually obtained by Gavazzi et al. (2012). Fig. 3 Top: comparison of the g magnitudes obtained in this work with those from the DR10. Notice the lack of DR10 magni- tudes below 11 mag. Bottom: missing magnitudes from the DR10. Fig. 4 Color mass diagrams where blue dots are LTGs and red dots stand for ETGs. Left: the uncorrected colors. Center: colors, corrected for Galactic extinction. Right: colors, corrected for internal extinction. We selected a complete sample of 5851 galaxies with r < 17.7 in the local Universe. Including: The Coma supercluster selected following Gavazzi et al. (2010; 2013) in the region of Coma and A1367. The Local supercluster selected as in Gavazzi et al. (2012), based on the VCC catalog, complemented with NED, AL- FALFA (Haynes et al. 2011) data outside the Virgo cluster. Fig. 1 Sky distribution of the early (red, ETG) and late (blue, LTG) type galax- ies in the Local supercluster (left panel) and in the Coma supercluster (right panel) Based on the inspection of the template color profiles, we identify three zones: an inner region, with r≤1 kpc; an intermediate one (0.2R pet ≤ r ≤0.3R pet ); an outer, disk-dominated, region with r≥ 0.35R pet . Fig. 7 shows the color vs. total stellar mass diagram for the three zones. Fig. 7 Color magnitude diagrams of three galactic zones, where blue dots are LTGs and red dots stand for ETGs. (a) Inner zone. Green dots repre- sent AGN, Seyfert and Liner gal- axies. Notice that AGNs display a color dispersion significantly higher than normal galaxies. (b) Intermediate zone. (c) outer zone. (a) (b) (c) Fig. 8 The difference between in- ternal and outer colors as a func- tion of stellar mass for ETGs (red) and LTGs (blue). 2. The Method Images. The procedure analizes SDSS g and i images down- loaded from the IRSA and NVO “mosaic service”. Each image is cut to a width that is twice the optical diameter. Masks. The approach takes advantage of the segmentation map of SourceExtractor (Bertin and Arnouts, 1996) to mask the image. Within the galaxy radius, all stellar objects are masked, whereas outside the galaxy radius, contaminating stars and galaxies are masked. Sky-evaluation. The sky value is taken as the mode inside a region near the edges of the masked image. Petrosian radius. is the radius at which the Petrosian ratio R p (R pet ) equals an R p,lim . We set this limit to 0.2, as in SDSS. Unlike the SDSS, our procedure evaluates the Petrosian radius on a g and i combined image. Magnitudes. Magnitudes are computed inside an elliptical aperture of radius r=2R pet taken along the major axis. Color profiles. A g-i color profile is build performing aper- ture photometry within ellispses along the major axis. The radius is normalized to the Petrosian radius. Fig. 6 Template color profiles in three bins of mass and morphological type. The shredding problem affecting the SDSS pipeline has been bypassed using our semi-automated data reduction procedure. Our analysis supports a picture where: - ETGs show no large-scale color gradients at any mass. - Color profiles provide a sensitive tool for detecting circumnuclear dusty disks even in ETGs. - Spiral galaxies are composed of a blue disk dominating the outer regions plus a red bulge whose contribution increases with mass. - Disks are 0.3 mag bluer than the red se- quence but have remarkably similar slope in the color mass relation. 1 Dipartimento di fisica G.Occhialini, Università di Milano Bicocca, Italy 2 Department of Physics, Durham University, United Kingdom 3 Universitäts-Sternwarte München, Germany References: Ahn, C. P., Alexandroff, R., Allende Prieto, C., et al., 2014, ApJS, 211, 17 Bertin, E., & Arnouts, S. 1996, A&AS,117,393 Gavazzi, G., Fumagalli, M., Cucciati, O., & Boselli, A. 2010,A&A , 517, A73 Gavazzi, G., Fumagalli, M., Galardo, V., et al. 2012, A&A, 545, A16 Gavazzi, G., Savorgnan, G., Fossati, M., et al. 2013, A&A, 553, A90 Haynes, M. P., Giovanelli, R., Martin, A. M., et al. 2011, Aj, 142, 170 Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ,500, 525 Schlafly, E., F., Finkbeiner, D. P., 2011, ApJ, 737, 103 Abstract: We present a semi-automated procedure to perform reliable photometry of galaxies in SDSS images. We selected a complete sample of 5851 galaxies of the Coma and Virgo superclusters. For each galaxy, we re- cover accurate Petrosian g and i magnitudes, surface brightness and color profiles. Unlike the SDSS pipeline, our procedure is not affected by the well known shredding problem and efficiently extracts Petrosian magnitudes even from the largest objects. The g and i magnitudes are corrected for dust and internal extinction. In a color magnitude diagram the blue and red sequences are well separated, resulting in a similar slope. The analysis of the color profiles was performed either over template color profiles binned in three intervals of mass and morphological type, or by analizing color-magnitude diagrams of three zones (an inner zone (r≤1kpc); an intermediate zone (0.2R pet ≤ r ≤0.3R pet ); an outer, disk-dominated, region (r≥0.35R pet )). The two analyses consistently lead to a picture where elliptical galaxies show practically no color gradients, irrespective of their masses. Spirals - instead - display increasing color gradients with increasing mass consistently with the presence of significant bulges above 10 10 M . Galactic extinction correction. The g and i magni- tudes are corrected for Galactic extinction following Schlegel et al. (1998), re-calibrated by Schlafly et al. (2011). Internal extinction correction. (g-i) colors are further corrected for internal extinction using the empirical transforma- tion, dependent on stellar mass and inclination, derived by Gavazzi et al. (2013): (g-i) mw0 = (g-i) mw -{0.17 [1-cos(incl)][log(M * /M )- 8.19] , where incl is the disk inclination. Stellar masses. Stellar masses are derived from the i-band luminosity and the (g-i) mw0 color using log(M * /M ) = -1.94+0.59(g-i) mw0 +1.15log(L i /L ), where L i is the i-band luminosity. The blue and red sequences are well separated, although con- verging at high masses in the uncorrected color mass diagram (Fig.4, Left).They separate more in the corrected color dia- gram (Fig 4, Right) where the two distributions have nearly the same slope. The red sequence slopes of the three zones are consistent. The blue sequence instead shows significant variations be- tween the zones: at high mass, the colors are sig- nificantly bluer in the outer zone. Fig. 8 shows the color difference between the intermediate and the outer zones. While ETGs have a color residu- al of ~ 0.1 mag, independent of mass, LTGs become significantly redder toward the center. (g-i) radial profiles trace the average stellar population as well as dust reddening. In particular, we are able to detect dusty structures confirmed by archival HST observations (Fig. 5). Fig. 5 The dusty disk in the lenticular galaxy VCC 1154 detected in the color profile at r ≤ 10 arcsec. Fig. 6 shows stacked profiles of galaxies in three bins of mass and morphological type. ETGs do not show significant color gradients, irrespective of their mass. LTGs display flat color profiles at low masses while, at higher masses, their profiles show evident color gradients implying the existence of a red component in their central region whose im- portance increases with mass. In the highest mass bin, spirals are as red as ellipticals in their central parts and as blue as a dIrr in the outer parts. Magnitudes were compared to those manually (IRAF) obtained by Gavazzi et al. (2012) on the same images. Fig. 2 shows a satisfacto- ry agreement. Fig. 3 shows the comparison of our magnitudes with those from the SDSS DR10 (Ahn et al. 2014): We recover g and i magnitudes of 387 missing objects from the DR10 database, 274 are from the Local supercluster. Including the discrepant objects (see Fig. 3), 8% of the DR10 magnitudes are either unreliable or missing. In the Local supercluster, the percent- age of missing/unreliable DR10 mag- nitudes rises to the 26% and among galaxies brighter than g=11 mag it in- creases to 95% .
Transcript of Robust automated photometry of local galaxies from SDSS · Robust automated photometry of local...
Robust automated photometry of local galaxies from SDSS Guido Consolandi1, Giuseppe Gavazzi1, Massimo Dotti1, Michele Fumagalli2, Matteo Fossati3
1. The Sample
3.Petrosian magnitudes
4. The color-mass relation 6. Color gradients
5. Color pro�les
Conclusions:
Fig. 2 Comparison of the g-band magnitudes obtained in this work and those manually obtained by Gavazzi et al. (2012).
Fig. 3 Top: comparison of the g magnitudes obtained in this work with those from the DR10.Notice the lack of DR10 magni-tudes below 11 mag. Bottom: missing magnitudes from the DR10.
Fig. 4 Color mass diagrams where blue dots are LTGs and red dots stand for ETGs. Left: the uncorrected colors. Center: colors, corrected for Galactic extinction. Right: colors, corrected for internal extinction.
We selected a complete sample of 5851 galaxies with r < 17.7 in the local Universe. Including:
The Coma supercluster selected following Gavazzi et al. (2010; 2013) in the region of Coma and A1367.
The Local supercluster selected as in Gavazzi et al. (2012), based on the VCC catalog, complemented with NED, AL-FALFA (Haynes et al. 2011) data outside the Virgo cluster.
Fig. 1 Sky distribution of the early (red, ETG) and late (blue, LTG) type galax-ies in the Local supercluster (left panel) and in the Coma supercluster (right panel)
Based on the inspection of the template color profiles, we identify three zones: an inner region, with r≤1 kpc; an intermediate one (0.2Rpet ≤ r ≤0.3Rpet); an outer, disk-dominated, region with r≥0.35Rpet. Fig. 7 shows the color vs. total stellar mass diagram for the three zones.
Fig. 7 Color magnitude diagrams of three galactic zones, where blue dots are LTGs and red dots stand for ETGs.(a) Inner zone. Green dots repre-sent AGN, Seyfert and Liner gal-axies. Notice that AGNs display a color dispersion significantly higher than normal galaxies.(b) Intermediate zone.(c) outer zone.
(a)
(b) (c)
Fig. 8 The difference between in-ternal and outer colors as a func-tion of stellar mass for ETGs (red) and LTGs (blue).
2. The MethodImages. The procedure analizes SDSS g and i images down-loaded from the IRSA and NVO “mosaic service”. Each image is cut to a width that is twice the optical diameter.
Masks. The approach takes advantage of the segmentation map of SourceExtractor (Bertin and Arnouts, 1996) to mask the image. Within the galaxy radius, all stellar objects are masked, whereas outside the galaxy radius, contaminating stars and galaxies are masked. Sky-evaluation. The sky value is taken as the mode inside a region near the edges of the masked image.
Petrosian radius. is the radius at which the Petrosian ratio Rp(Rpet) equals an Rp,lim . We set this limit to 0.2, as in SDSS. Unlike the SDSS, our procedure evaluates the Petrosian radius on a g and i combined image.
Magnitudes. Magnitudes are computed inside an elliptical aperture of radius r=2Rpet taken along the major axis.
Color profiles. A g-i color profile is build performing aper-ture photometry within ellispses along the major axis. The radius is normalized to the Petrosian radius.
Fig. 6 Template color profiles in three bins of mass and morphological type.
The shredding problem affecting the SDSS pipeline has been bypassed using our semi-automated data reduction procedure.
Our analysis supports a picture where: - ETGs show no large-scale color gradients at any mass.- Color profiles provide a sensitive tool for detecting circumnuclear dusty disks even in ETGs.- Spiral galaxies are composed of a blue disk dominating the outer regions plus a red bulge whose contribution increases with mass.- Disks are 0.3 mag bluer than the red se-quence but have remarkably similar slope in the color mass relation.
1Dipartimento di fisica G.Occhialini, Università di Milano Bicocca, Italy2Department of Physics, Durham University, United Kingdom
3Universitäts-Sternwarte München, Germany
References:Ahn, C. P., Alexandroff, R., Allende Prieto, C., et al., 2014, ApJS, 211, 17 Bertin, E., & Arnouts, S. 1996, A&AS,117,393Gavazzi, G., Fumagalli, M., Cucciati, O., & Boselli, A. 2010,A&A , 517, A73Gavazzi, G., Fumagalli, M., Galardo, V., et al. 2012, A&A, 545, A16 Gavazzi, G., Savorgnan, G., Fossati, M., et al. 2013, A&A, 553, A90 Haynes, M. P., Giovanelli, R., Martin, A. M., et al. 2011, Aj, 142, 170Schlegel, D. J., Finkbeiner, D. P., & Davis, M. 1998, ApJ,500, 525 Schlafly, E., F., Finkbeiner, D. P., 2011, ApJ, 737, 103
Abstract: We present a semi-automated procedure to perform reliable photometry of galaxies in SDSS images. We selected a complete sample of 5851 galaxies of the Coma and Virgo superclusters. For each galaxy, we re-cover accurate Petrosian g and i magnitudes, surface brightness and color profiles. Unlike the SDSS pipeline, our procedure is not affected by the well known shredding problem and efficiently extracts Petrosian magnitudes even from the largest objects. The g and i magnitudes are corrected for dust and internal extinction. In a color magnitude diagram the blue and red sequences are well separated, resulting in a similar slope. The analysis of the color profiles was performed either over template color profiles binned in three intervals of mass and morphological type, or by analizing color-magnitude diagrams of three zones (an inner zone (r≤1kpc); an intermediate zone (0.2Rpet ≤ r ≤0.3Rpet); an outer, disk-dominated, region (r≥0.35Rpet)). The two analyses consistently lead to a picture where elliptical galaxies show practically no color gradients, irrespective of their masses. Spirals - instead - display increasing color gradients with increasing mass consistently with the presence of significant bulges above 1010 M .
Galactic extinction correction. The g and i magni-tudes are corrected for Galactic extinction following Schlegel et al. (1998), re-calibrated by Schlafly et al. (2011).
Internal extinction correction. (g-i) colors are further corrected for internal extinction using the empirical transforma-tion, dependent on stellar mass and inclination, derived by Gavazzi et al. (2013):
(g-i)mw0 = (g-i)mw-{0.17 [1-cos(incl)][log(M*/M )- 8.19] ,where incl is the disk inclination.
Stellar masses. Stellar masses are derived from the i-band luminosity and the (g-i)mw0 color using
log(M*/M ) = -1.94+0.59(g-i)mw0+1.15log(Li/L ),where Li is the i-band luminosity.
The blue and red sequences are well separated, although con-verging at high masses in the uncorrected color mass diagram (Fig.4, Left).They separate more in the corrected color dia-gram (Fig 4, Right) where the two distributions have nearly the same slope.
The red sequence slopes of the three zones are consistent.The blue sequence instead shows significant variations be-tween the zones: at high mass, the colors are sig-nificantly bluer in the outer zone.
Fig. 8 shows the color difference between the intermediate and the outer zones. While ETGs have a color residu-al of ~ 0.1 mag, independent of mass, LTGs become significantly redder toward the center.
(g-i) radial profiles trace the average stellar population as well as dust reddening. In particular, we are able to detect dusty structures confirmed by archival HST observations (Fig. 5).
Fig. 5 The dusty disk in the lenticular galaxy VCC 1154 detected in the color profile at r ≤ 10 arcsec.
Fig. 6 shows stacked profiles of galaxies in three bins of mass and morphological type.
ETGs do not show significant color gradients, irrespective of their mass. LTGs display flat color profiles at low masses while, at higher masses, their profiles show evident color gradients implying the existence of a red component in their central region whose im-portance increases with mass. In the highest mass bin, spirals are as red as ellipticals in their central parts and as blue as a dIrr in the outer parts.
Magnitudes were compared to those manually (IRAF) obtained by Gavazzi et al. (2012) on the same images. Fig. 2 shows a satisfacto-ry agreement.
Fig. 3 shows the comparison of our magnitudes with those from the SDSS DR10 (Ahn et al. 2014):We recover g and i magnitudes of 387 missing objects from the DR10 database, 274 are from the Local supercluster. Including the discrepant objects (see Fig. 3), 8% of the DR10 magnitudes are either unreliable or missing.
In the Local supercluster, the percent-age of missing/unreliable DR10 mag-nitudes rises to the 26% and among galaxies brighter than g=11 mag it in-creases to 95% .
