skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: LENTICULAR GALAXIES AT THE OUTSKIRTS OF THE LEO II GROUP: NGC 3599 AND NGC 3626

Abstract

We have studied unbarred S0 galaxies, NGC 3599 and NGC 3626, the members of the X-ray bright group Leo II, by means of three-dimensional spectroscopy, long-slit spectroscopy, and imaging, with the aim of identifying the epoch and mechanisms of their transformation from spirals. Both galaxies have appeared to bear complex features obviously resulting from minor merging: decoupled gas kinematics, nuclear star-forming rings, and multi-tiered oval large-scale stellar disks. The weak emission line nucleus of NGC 3599 bears all signs of Seyfert activity, according to the line-ratio diagnostics of the gas excitation mechanism. We conclude that the transformation of these lenticular galaxies took place about 1-2 Gyr ago, through gravitational mechanisms unrelated to the hot intragroup medium of Leo II.

Authors:
;  [1];  [2]
  1. Sternberg Astronomical Institute, Moscow 119992 (Russian Federation)
  2. Special Astrophysical Observatory, Nizhnij Arkhyz, Karachai-Circassia 369167 (Russian Federation)
Publication Date:
OSTI Identifier:
21443180
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astronomical Journal (New York, N.Y. Online); Journal Volume: 140; Journal Issue: 5; Other Information: DOI: 10.1088/0004-6256/140/5/1462
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EMISSION; GALACTIC EVOLUTION; GALAXIES; SPECTROSCOPY; STARS; THREE-DIMENSIONAL CALCULATIONS; X RADIATION; ELECTROMAGNETIC RADIATION; EVOLUTION; IONIZING RADIATIONS; RADIATIONS

Citation Formats

Sil'chenko, O. K., Shulga, A. P., and Moiseev, A. V., E-mail: olga@sai.msu.s, E-mail: alina.shulga@gmail.co, E-mail: moisav@gmail.co. LENTICULAR GALAXIES AT THE OUTSKIRTS OF THE LEO II GROUP: NGC 3599 AND NGC 3626. United States: N. p., 2010. Web. doi:10.1088/0004-6256/140/5/1462.
Sil'chenko, O. K., Shulga, A. P., & Moiseev, A. V., E-mail: olga@sai.msu.s, E-mail: alina.shulga@gmail.co, E-mail: moisav@gmail.co. LENTICULAR GALAXIES AT THE OUTSKIRTS OF THE LEO II GROUP: NGC 3599 AND NGC 3626. United States. doi:10.1088/0004-6256/140/5/1462.
Sil'chenko, O. K., Shulga, A. P., and Moiseev, A. V., E-mail: olga@sai.msu.s, E-mail: alina.shulga@gmail.co, E-mail: moisav@gmail.co. 2010. "LENTICULAR GALAXIES AT THE OUTSKIRTS OF THE LEO II GROUP: NGC 3599 AND NGC 3626". United States. doi:10.1088/0004-6256/140/5/1462.
@article{osti_21443180,
title = {LENTICULAR GALAXIES AT THE OUTSKIRTS OF THE LEO II GROUP: NGC 3599 AND NGC 3626},
author = {Sil'chenko, O. K. and Shulga, A. P. and Moiseev, A. V., E-mail: olga@sai.msu.s, E-mail: alina.shulga@gmail.co, E-mail: moisav@gmail.co},
abstractNote = {We have studied unbarred S0 galaxies, NGC 3599 and NGC 3626, the members of the X-ray bright group Leo II, by means of three-dimensional spectroscopy, long-slit spectroscopy, and imaging, with the aim of identifying the epoch and mechanisms of their transformation from spirals. Both galaxies have appeared to bear complex features obviously resulting from minor merging: decoupled gas kinematics, nuclear star-forming rings, and multi-tiered oval large-scale stellar disks. The weak emission line nucleus of NGC 3599 bears all signs of Seyfert activity, according to the line-ratio diagnostics of the gas excitation mechanism. We conclude that the transformation of these lenticular galaxies took place about 1-2 Gyr ago, through gravitational mechanisms unrelated to the hot intragroup medium of Leo II.},
doi = {10.1088/0004-6256/140/5/1462},
journal = {Astronomical Journal (New York, N.Y. Online)},
number = 5,
volume = 140,
place = {United States},
year = 2010,
month =
}
  • The diameters d/sub r/ of inner ring structures in disk galaxies are used as geometric distance indicators to derive the distances of 453 spiral and lenticular galaxies, mainly in the distance interval 4<..delta..<63 Mpc. The diameters are weighted means from the catalogs to Kormendy, Pedreros and Madore, and the authors. The distances are calculated by means of the two- and three-parameter formulae of Paper II; the adopted mean distance moduli ..mu../sub 0/(r) have mean errors from all sources of 0.6--0.7 mag for the well-observed galaxies.
  • We have used the full radial extent of images from the Hubble Space Telescope's Advanced Camera for Surveys and Wide Field Planetary Camera 2 to extract surface brightness profiles from a sample of six, local lenticular galaxy candidates. We have modeled these profiles using a core-Sersic bulge plus an exponential disk model. Our fast rotating lenticular disk galaxies with bulge magnitudes M{sub V} {approx}< -21.30 mag have central stellar deficits, suggesting that these bulges may have formed from ''dry'' merger events involving supermassive black holes (BHs) while their surrounding disk was subsequently built up, perhaps via cold gas accretion scenarios.more » The central stellar mass deficits M{sub def} are roughly 0.5-2 M{sub BH} (BH mass), rather than {approx}10-20 M{sub BH} as claimed from some past studies, which is in accord with core-Sersic model mass deficit measurements in elliptical galaxies. Furthermore, these bulges have Sersic indices n {approx}3, half-light radii R{sub e} < 2 kpc and masses >10{sup 11} M{sub Sun }, and therefore appear to be descendants of the compact galaxies reported at z {approx} 1.5-2. Past studies which have searched for these local counterparts by using single-component galaxy models to provide the z {approx} 0 size comparisons have overlooked these dense, compact, and massive bulges in today's early-type disk galaxies. This evolutionary scenario not only accounts for what are today generally old bulges-which must be present in z {approx} 1.5 images-residing in what are generally young disks, but it eliminates the uncomfortable suggestion of a factor of three to five growth in size for the compact, z {approx} 1.5 galaxies that are known to possess infant disks.« less
  • We present evidence for spatially extended low surface brightness emission around Lyman break galaxies (LBGs) in the V-band image of the Hubble Ultra Deep Field, corresponding to the z {approx} 3 rest-frame far-UV (FUV) light, which is a sensitive measure of star formation rates (SFRs). We find that the covering fraction of molecular gas at z {approx} 3 is not adequate to explain the emission in the outskirts of LBGs, while the covering fraction of neutral atomic-dominated hydrogen gas at high redshift is sufficient. We develop a theoretical framework to connect this emission around LBGs to the expected emission frommore » neutral H I gas, i.e., damped Ly{alpha} systems (DLAs), using the Kennicutt-Schmidt (KS) relation. Working under the hypothesis that the observed FUV emission in the outskirts of LBGs is from in situ star formation in atomic-dominated hydrogen gas, the results suggest that the SFR efficiency in such gas at z {approx} 3 is between factors of 10 and 50 lower than predictions based on the local KS relation. The total SFR density in atomic-dominated gas at z {approx} 3 is constrained to be {approx}10% of that observed from the inner regions of LBGs. In addition, the metals produced by in situ star formation in the outskirts of LBGs yield metallicities comparable to those of DLAs, which is a possible solution to the 'Missing Metals' problem for DLAs. Finally, the atomic-dominated gas in the outskirts of galaxies at both high and low redshifts has similar reduced SFR efficiencies and is consistent with the same power law.« less
  • We present a search for outlying H II regions in the extended gaseous outskirts of nearby (D < 40 Mpc) galaxies and subsequent multi-slit spectroscopy used to obtain the H II region nebular oxygen abundances. The galaxies in our sample have extended H I disks and/or interaction-related H I features that extend well beyond their primary stellar components. We report oxygen abundance gradients out to 2.5 times the optical radius for these galaxies which span a range of morphologies and masses. We analyze the underlying stellar and neutral H I gas distributions in the vicinity of the H II regionsmore » to understand the physical processes that give rise to the observed metal distributions in galaxies. These measurements, for the first time, convincingly show flat abundance distributions out to large radii in a wide variety of systems and have broad implications for galaxy chemodynamical evolution.« less
  • We have obtained long-slit spectra of 174 star-forming galaxies with stellar masses greater than 10{sup 10} M{sub Sun} from the GALEX Arecibo Sloan Digital Sky Survey (GASS) survey. These galaxies have both H I and H{sub 2} mass measurements. The average metallicity profile is strikingly flat out to R{sub 90}, the radius enclosing 90% of the r-band light. Metallicity profiles which decline steadily with radius are found primarily for galaxies in our sample with low stellar mass (log(M{sub *}) < 10.2), concentration, and/or mean stellar mass density. Beyond {approx}R{sub 90}, however, around 10% of the galaxies in our sample exhibitmore » a sharp downturn in metallicity. Remarkably, we find that the magnitude of the outer metallicity drop is well correlated with the total H I content of the galaxy (measured as f{sub HI} = M{sub HI}/M{sub *}). We examine the radial profiles of stellar population ages and star formation rate densities, and conclude that the galaxies with largest outer metallicity drops are actively growing their stellar disks, with mass-doubling times across the whole disk only one-third as long as a typical GASS galaxy. We also describe a correlation between local stellar mass density and metallicity, which is valid across all galaxies in our sample. We argue that much of the recent stellar mass growth at the edges of these galaxies can be linked to the accretion or radial transport of relatively pristine gas from beyond the galaxies' stellar disks.« less