The Nature of LINER-like Emission in Red Galaxies

The Astrophysical Journal (Impact Factor: 5.99). 09/2011; 747(1). DOI: 10.1088/0004-637X/747/1/61
Source: arXiv


Passive red galaxies frequently contain warm ionized gas and have spectra
similar to low-ionization nuclear emission-line regions (LINERs). Here we
investigate the nature of the ionizing sources powering this emission, by
comparing nuclear spectroscopy from the Palomar survey with larger aperture
data from the Sloan Digital Sky Survey. We find the line emission in the
majority of passive red galaxies is spatially extended; the Halpha surface
brightness profile depends on radius (r) as r^(-1.28). We detect strong line
ratio gradients with radius in [N II]/Ha, [S II]/Ha, and [O III]/[S II],
requiring the ionization parameter to increase outwards. Combined with a
realistic gas density profile, this outward increasing ionization parameter
convincingly rules out AGN as the dominant ionizing source, and strongly favors
distributed ionizing sources. Sources that follow the stellar density profile
can additionally reproduce the observed luminosity-dependence of the line ratio
gradient. Post-AGB stars provide a natural ionization source candidate, though
they have an ionization parameter deficit. Velocity width differences among
different emission lines disfavor shocks as the dominant ionization mechanism,
and suggest that the interstellar medium in these galaxies contains multiple
components. We conclude that the line emission in most LINER-like galaxies
found in large aperture (>100pc) spectroscopy is not primarily powered by AGN
activity and thus does not trace the AGN bolometric luminosity. However, they
can be used to trace warm gas in these red galaxies.

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    • "The line ratios can be produced as well by shocks [3], cooling flows [4] or post-AGB stars [5]. Unresolved point sources can produce extended emission as well [6] making it even more complicated to distinguish between photoionization by an AGN or by other mechanisms. Consequently, the role of LINERs in the context of AGN evolution is not clear yet. "
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    ABSTRACT: NGC 5850 is a nearby (z=0.0085) early type spiral galaxy classified as LINER. It is considered as a prototype double-barred system. Our optical Integral Field Spectroscopic (IFS) data of the central 21x19 arcsec^2 of NGC 5850 show extended LINER-like emission which we ascribe to the presence of a hot and evolved stellar population, possibly together with a faint AGN. Additionally NGC 5850 shows extended `composite' ionization patterns, likely to stem from a mixture of LINER-like ionization and photoionization by star formation. The kinematics of the gas deviates strongly from a simple rotational structure.
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    ABSTRACT: Accurate relative spectrophotometry is critical for many science applications. Small wavelength scale residuals in the flux calibration can significantly impact the measurements of weak emission and absorption features in the spectra. Using Sloan Digital Sky Survey data, we demonstrate that the average spectra of carefully selected red-sequence galaxies can be used as a spectroscopic standard to improve the relative spectrophotometry precision to 0.1% on small wavelength scales (from a few to hundreds of Angstroms). We achieve this precision by comparing stacked spectra across tiny redshift intervals. The redshift intervals must be small enough that any systematic stellar population evolution is minimized and less than the spectrophotometric uncertainty. This purely empirical technique does not require any theoretical knowledge of true galaxy spectra. It can be applied to all large spectroscopic galaxy redshift surveys that sample a large number of galaxies in a uniform population.
    The Astronomical Journal 07/2011; 142(5). DOI:10.1088/0004-6256/142/5/153 · 4.02 Impact Factor
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    ABSTRACT: Using data drawn from the DEEP2 and DEEP3 Galaxy Redshift Surveys, we investigate the relationship between the environment and the structure of galaxies residing on the red sequence at intermediate redshift. Within the massive (10 < log10(M★/h−2 M⊙) < 11) early-type population at 0.4 < z < 1.2, we find a significant correlation between local galaxy overdensity (or environment) and galaxy size, such that early-type systems in higher density regions tend to have larger effective radii (by ∼0.5 h−1 kpc or 25 per cent larger) than their counterparts of equal stellar mass and Sérsic index in lower density environments. This observed size–density relation is consistent with a model of galaxy formation in which the evolution of early-type systems at z < 2 is accelerated in high-density environments such as groups and clusters and in which dry, minor mergers (versus mechanisms such as quasar feedback) play a central role in the structural evolution of the massive, early-type galaxy population.
    Monthly Notices of the Royal Astronomical Society 09/2011; 419(4). DOI:10.1111/j.1365-2966.2011.19938.x · 5.11 Impact Factor
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