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Title: COLOR-MAGNITUDE RELATION AND MORPHOLOGY OF LOW-REDSHIFT ULIRGs IN SLOAN DIGITAL SKY SURVEY

Abstract

We present color-magnitude and morphological analysis of 54 low-redshift ultraluminous infrared galaxies (ULIRGs; 0.018 < z < 0.265 with z{sub median} = 0.151), a subset of the Infrared Astronomical Satellite 1 Jy sample, in the Sloan Digital Sky Survey (SDSS). The ULIRGs are both bright and blue: they are on average 1 mag brighter in M{sub {sup 0.1}r} than the SDSS galaxies within the same redshift range, and 0.2 mag bluer in {sup 0.1} g - {sup 0.1} r. They form a group in the color-magnitude diagram distinct from both the red sequence and the blue cloud formed by the SDSS galaxies: 24 out of the 52 unsaturated objects ({approx}46%) lie outside the 90% level number density contour of the SDSS galaxies. The majority (47, or {approx}87%) have the colors typical of the blue cloud, and only four ({approx}7%) sources are located in the red sequence. While ULIRGs are popularly thought to be precursors to a QSO phase, we find few (three, or {approx}6%) in the 'green valley' where the majority of the X-ray- and IR-selected active galactic nuclei (AGNs) are found. Moreover, none of the AGN-host ULIRGs are found in the green valley. For the 14 previously spectroscopic identifiedmore » AGNs ({approx}28%), we perform point-spread function subtractions and find that on average the central point sources contribute less than one-third to the total luminosity, and that their high optical luminosities and overall blue colors are apparently the result of star formation activity of the host galaxies. Visual inspection of the SDSS images reveals a wide range of morphologies including many close pairs, tidal tails, and otherwise disturbed profiles, in strong support of previous studies and the general view of ULIRGs as major mergers of gas-rich disk galaxies. A detailed morphology analysis using Gini and M{sub 20} coefficients shows that slightly less than one-half ({approx}42% in g band) of the ULIRGs are located in the merger region defined by morphology studies of local galaxies, while the remaining sources are located in the region of late-type and irregular galaxies. The heterogeneous distribution of ULIRGs in the G-M{sub 20} space is qualitatively consistent with the results found by numerical simulations of disk-disk mergers, and our study also shows that the measured morphological parameters are systematically affected by the signal-to-noise ratio and thus the merging galaxies can appear in various regions of the G-M{sub 20} parameter space. We briefly discuss the origins of the uncertainties and note that the morphology measurements should be implemented with caution for low physical resolution images. In general, our results reinforce the view that ULIRGs contain young stellar populations and are mergers in progress, but we do not observe the concentration of ULIRGs/AGN in the green valley as found by other studies. Our study provides a uniform comparison sample for studying dusty starbursts at higher redshifts such as Spitzer MIPS 24 {mu}m-selected ULIRGs at z = 1-2 or submillimeter galaxies.« less

Authors:
;  [1]
  1. Department of Astronomy, University of Massachusetts, Amherst, MA 01003 (United States)
Publication Date:
OSTI Identifier:
21394172
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 712; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/712/2/1385; Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; COLOR; COMPUTERIZED SIMULATION; GALACTIC EVOLUTION; GALAXY NUCLEI; LUMINOSITY; MILKY WAY; MORPHOLOGY; POINT SOURCES; RED SHIFT; SATELLITES; SEYFERT GALAXIES; SIGNAL-TO-NOISE RATIO; STARS; X RADIATION; DIMENSIONLESS NUMBERS; ELECTROMAGNETIC RADIATION; EVOLUTION; GALAXIES; IONIZING RADIATIONS; OPTICAL PROPERTIES; ORGANOLEPTIC PROPERTIES; PHYSICAL PROPERTIES; RADIATION SOURCES; RADIATIONS; SIMULATION

Citation Formats

Yuxi, Chen, Yun, Min S, and Lowenthal, James D., E-mail: yxchen@astro.umass.ed. COLOR-MAGNITUDE RELATION AND MORPHOLOGY OF LOW-REDSHIFT ULIRGs IN SLOAN DIGITAL SKY SURVEY. United States: N. p., 2010. Web. doi:10.1088/0004-637X/712/2/1385.
Yuxi, Chen, Yun, Min S, & Lowenthal, James D., E-mail: yxchen@astro.umass.ed. COLOR-MAGNITUDE RELATION AND MORPHOLOGY OF LOW-REDSHIFT ULIRGs IN SLOAN DIGITAL SKY SURVEY. United States. doi:10.1088/0004-637X/712/2/1385.
Yuxi, Chen, Yun, Min S, and Lowenthal, James D., E-mail: yxchen@astro.umass.ed. Thu . "COLOR-MAGNITUDE RELATION AND MORPHOLOGY OF LOW-REDSHIFT ULIRGs IN SLOAN DIGITAL SKY SURVEY". United States. doi:10.1088/0004-637X/712/2/1385.
@article{osti_21394172,
title = {COLOR-MAGNITUDE RELATION AND MORPHOLOGY OF LOW-REDSHIFT ULIRGs IN SLOAN DIGITAL SKY SURVEY},
author = {Yuxi, Chen and Yun, Min S and Lowenthal, James D., E-mail: yxchen@astro.umass.ed},
abstractNote = {We present color-magnitude and morphological analysis of 54 low-redshift ultraluminous infrared galaxies (ULIRGs; 0.018 < z < 0.265 with z{sub median} = 0.151), a subset of the Infrared Astronomical Satellite 1 Jy sample, in the Sloan Digital Sky Survey (SDSS). The ULIRGs are both bright and blue: they are on average 1 mag brighter in M{sub {sup 0.1}r} than the SDSS galaxies within the same redshift range, and 0.2 mag bluer in {sup 0.1} g - {sup 0.1} r. They form a group in the color-magnitude diagram distinct from both the red sequence and the blue cloud formed by the SDSS galaxies: 24 out of the 52 unsaturated objects ({approx}46%) lie outside the 90% level number density contour of the SDSS galaxies. The majority (47, or {approx}87%) have the colors typical of the blue cloud, and only four ({approx}7%) sources are located in the red sequence. While ULIRGs are popularly thought to be precursors to a QSO phase, we find few (three, or {approx}6%) in the 'green valley' where the majority of the X-ray- and IR-selected active galactic nuclei (AGNs) are found. Moreover, none of the AGN-host ULIRGs are found in the green valley. For the 14 previously spectroscopic identified AGNs ({approx}28%), we perform point-spread function subtractions and find that on average the central point sources contribute less than one-third to the total luminosity, and that their high optical luminosities and overall blue colors are apparently the result of star formation activity of the host galaxies. Visual inspection of the SDSS images reveals a wide range of morphologies including many close pairs, tidal tails, and otherwise disturbed profiles, in strong support of previous studies and the general view of ULIRGs as major mergers of gas-rich disk galaxies. A detailed morphology analysis using Gini and M{sub 20} coefficients shows that slightly less than one-half ({approx}42% in g band) of the ULIRGs are located in the merger region defined by morphology studies of local galaxies, while the remaining sources are located in the region of late-type and irregular galaxies. The heterogeneous distribution of ULIRGs in the G-M{sub 20} space is qualitatively consistent with the results found by numerical simulations of disk-disk mergers, and our study also shows that the measured morphological parameters are systematically affected by the signal-to-noise ratio and thus the merging galaxies can appear in various regions of the G-M{sub 20} parameter space. We briefly discuss the origins of the uncertainties and note that the morphology measurements should be implemented with caution for low physical resolution images. In general, our results reinforce the view that ULIRGs contain young stellar populations and are mergers in progress, but we do not observe the concentration of ULIRGs/AGN in the green valley as found by other studies. Our study provides a uniform comparison sample for studying dusty starbursts at higher redshifts such as Spitzer MIPS 24 {mu}m-selected ULIRGs at z = 1-2 or submillimeter galaxies.},
doi = {10.1088/0004-637X/712/2/1385},
journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 712,
place = {United States},
year = {2010},
month = {4}
}