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Title: QUENCHING DEPENDS ON MORPHOLOGIES: IMPLICATIONS FROM THE ULTRAVIOLET-OPTICAL RADIAL COLOR DISTRIBUTIONS IN GREEN VALLEY GALAXIES

Abstract

In this Letter, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation is distributed in these galaxies. We find that the dust-corrected u – r colors of early-type galaxies (ETGs) are flat out to R {sub 90}, while the colors monotonously turn blue when r > 0.5 R {sub 50} for late-type galaxies (LTGs). More than half of the ETGs are blue-cored and have remarkable positive NUV – r color gradients, suggesting that their star formations are centrally concentrated. The rest have flat color distributions out to R {sub 90}. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ∼50% of the ETGs have EW(Hα) >6.0 Å. Of the LTGs, 95% show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable ''blue-cores'' and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow amore » general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.« less

Authors:
;  [1]; ;  [2];  [3]
  1. Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Science, 80 Nandan Road, Shanghai 200030 (China)
  2. Center of Astrophysics, University of Science and Technology of China, Jinzhai Road 96, Hefei 230026 (China)
  3. CSIRO Astronomy and Space Science, Australia Telescope National Facility, PO Box 76, Epping, NSW 1710 (Australia)
Publication Date:
OSTI Identifier:
22365221
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 792; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTROSCOPY; COLOR; GALACTIC EVOLUTION; GALAXIES; IMAGES; MORPHOLOGY; RED SHIFT; STARS; ULTRAVIOLET RADIATION

Citation Formats

Pan, Zhizheng, Lin, Weipeng, Li, Jinrong, Kong, Xu, and Wang, Jing, E-mail: panzz@shao.ac.cn, E-mail: linwp@shao.ac.cn. QUENCHING DEPENDS ON MORPHOLOGIES: IMPLICATIONS FROM THE ULTRAVIOLET-OPTICAL RADIAL COLOR DISTRIBUTIONS IN GREEN VALLEY GALAXIES. United States: N. p., 2014. Web. doi:10.1088/2041-8205/792/1/L4.
Pan, Zhizheng, Lin, Weipeng, Li, Jinrong, Kong, Xu, & Wang, Jing, E-mail: panzz@shao.ac.cn, E-mail: linwp@shao.ac.cn. QUENCHING DEPENDS ON MORPHOLOGIES: IMPLICATIONS FROM THE ULTRAVIOLET-OPTICAL RADIAL COLOR DISTRIBUTIONS IN GREEN VALLEY GALAXIES. United States. doi:10.1088/2041-8205/792/1/L4.
Pan, Zhizheng, Lin, Weipeng, Li, Jinrong, Kong, Xu, and Wang, Jing, E-mail: panzz@shao.ac.cn, E-mail: linwp@shao.ac.cn. Mon . "QUENCHING DEPENDS ON MORPHOLOGIES: IMPLICATIONS FROM THE ULTRAVIOLET-OPTICAL RADIAL COLOR DISTRIBUTIONS IN GREEN VALLEY GALAXIES". United States. doi:10.1088/2041-8205/792/1/L4.
@article{osti_22365221,
title = {QUENCHING DEPENDS ON MORPHOLOGIES: IMPLICATIONS FROM THE ULTRAVIOLET-OPTICAL RADIAL COLOR DISTRIBUTIONS IN GREEN VALLEY GALAXIES},
author = {Pan, Zhizheng and Lin, Weipeng and Li, Jinrong and Kong, Xu and Wang, Jing, E-mail: panzz@shao.ac.cn, E-mail: linwp@shao.ac.cn},
abstractNote = {In this Letter, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation is distributed in these galaxies. We find that the dust-corrected u – r colors of early-type galaxies (ETGs) are flat out to R {sub 90}, while the colors monotonously turn blue when r > 0.5 R {sub 50} for late-type galaxies (LTGs). More than half of the ETGs are blue-cored and have remarkable positive NUV – r color gradients, suggesting that their star formations are centrally concentrated. The rest have flat color distributions out to R {sub 90}. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ∼50% of the ETGs have EW(Hα) >6.0 Å. Of the LTGs, 95% show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable ''blue-cores'' and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.},
doi = {10.1088/2041-8205/792/1/L4},
journal = {Astrophysical Journal Letters},
number = 1,
volume = 792,
place = {United States},
year = {Mon Sep 01 00:00:00 EDT 2014},
month = {Mon Sep 01 00:00:00 EDT 2014}
}
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  • We have investigated the radial g - r color gradients of early-type galaxies in the Sloan Digital Sky Survey (SDSS) DR6 in the redshift range 0.00 {<=} z {<=} 0.06. The majority of massive early-type galaxies show a negative color gradient (red-cored) as generally expected for early-type galaxies. On the other hand, roughly 30% of the galaxies in this sample show a positive color gradient (blue-cored). These 'blue-cored' galaxies often show strong H{beta} absorption-line strengths and/or emission-line ratios that are indicative of the presence of young stellar populations. Combining the optical data with Galaxy Evolution Explorer (GALEX) ultraviolet photometry, wemore » find that all blue-cored galaxies show UV-optical colors that can only be explained by young stellar populations. This implies that most of the residual star formation in early-type galaxies is centrally concentrated. Blue-cored galaxies are predominantly low-velocity dispersion systems, and tend to live in lower density regions. A simple model shows that the observed positive color gradients (blue-cored) are visible only for a billion years after a star formation episode for the typical strength of recent star formation. The observed effective radius decreases and the mean surface brightness increases due to this centrally concentrated star formation episode. As a result, the majority of blue-cored galaxies may lie on different regions in the fundamental plane (FP) from red-cored ellipticals. However, the position of the blue-cored galaxies on the FP cannot be solely attributed to recent star formation but requires substantially lower velocity dispersion. Our results based on the optical data are consistent with the residual star formation interpretation of Yi and collaborators which was based on GALEX UV data. We conclude that a low-level of residual star formation persists at the centers of most low-mass early-type galaxies, whereas massive ones are mostly quiescent systems with metallicity-driven red cores.« less
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