J/ApJ/679/156 Extra central light in galactic nuclei. I. (Hopkins+, 2008)
Dissipation and extra light in galactic nuclei. I. Gas-rich merger remnants. Hopkins P.F., Hernquist L., Cox T.J., Dutta S.N., Rothberg B. <Astrophys. J., 679, 156-181 (2008)> =2008ApJ...679..156H
ADC_Keywords: Active gal. nuclei ; Morphology ; Magnitudes, absolute Keywords: cosmology: theory - galaxies: active - galaxies: evolution - galaxies: nuclei - quasars: general Abstract: We study the origin and properties of "extra" or "excess" central light in the surface brightness profiles of remnants of gas-rich mergers. By combining a large set of hydrodynamical simulations with data on observed mergers that span a broad range of profiles at various masses and degrees of relaxation, we show how to robustly separate the physically meaningful extra light (i.e., the stellar population formed in a compact central starburst during a gas-rich merger) from the outer profile established by violent relaxation acting on stars already present in the progenitor galaxies prior to the final stages of the merger. This separation is sensitive to the treatment of the profile, and we demonstrate that certain fitting procedures can yield physically misleading results. We show that our method reliably recovers the younger starburst population, and examine how the properties and mass of this component scale with the mass, gas content, and other aspects of the progenitors. We consider the time evolution of the profiles in different bands, and estimate the biases introduced by observational studies at different phases and wavelengths. We show that, when appropriately quantified, extra light is ubiquitous in both observed and simulated gas-rich merger remnants, with sufficient mass (∼3%-30% of the stellar mass) to explain the apparent discrepancy in the maximum phase-space densities of ellipticals and their progenitor spirals. Description: We compare our simulations with the sample of local remnants of recent gas-rich mergers from Rothberg & Joseph (RJ04, 2004AJ....128.2098R) which compile K-band imaging, surface brightness, ellipticity, and a4/a profiles, where the profiles typically range from ∼100pc to ∼10-20kpc. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 91 52 Fits to Rothberg & Joseph (RJ04, 2004AJ....128.2098R) merger remnants
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 10 A10 --- Name Source name 12 A1 --- f_Name  Source peculiarities (1) 14- 15 I2 h RAh Hour of Right Ascension (J2000) 17- 18 I2 min RAm Minute of Right Ascension (J2000) 20- 21 I2 s RAs Second of Right Ascension (J2000) 23 A1 --- DE- Sign of the Declination (J2000) 24- 25 I2 deg DEd Degree of Declination (J2000) 27- 28 I2 arcmin DEm Arcminute of Declination (J2000) 30- 31 I2 arcsec DEs Arcsecond of Declination (J2000) 33- 38 F6.2 mag KMAG Absolute K band magnitude 40- 42 F3.1 --- nsfit Outer Sersic index of two-component best-fit profile 44- 46 F3.1 --- nssim Outer Sersic index fit in the same manner to the best-fit simulations (2) 48- 50 F3.1 --- e_nssim Range in nssim 52- 56 F5.2 --- nsRJ04 Sersic index fit to the entire profile (3) 58- 61 F4.2 --- fe Fraction of light in "extra light" component of fit 63- 66 F4.2 --- fsb Fraction of light from stars produced in central, merger-induced starburst (4) 68- 71 F4.2 --- e_fsb Approximate interquartile range in fsb 73- 76 F4.2 --- fgas Initial gas fraction in the best-fitting simulation (5) 78- 81 F4.2 --- e_fgas Approximate interquartile range in fgas 83- 86 F4.2 --- Dmufit Variance about the fit 88- 91 F4.2 --- Dmusim Variance about the simulation
Note (1): Flag as follows: 0 = normal object. 7 = AGN contamination affects the central regions (i.e. estimated extra light) and prevents a good simulation fit (we only model the stellar profile here). 8 = Unrelaxed or prominent disk/bar features make the comparison with these objects uncertain. Note (2): At t∼1-3Gyr after the merger when the system has relaxed. Note (3): i.e. not decomposed into an outer Sersic and inner extra light component. Note the authors impose a maximum ns=10.0. Note (4): Note that this may be biased to high values for actively star-forming (especially LIRG and ULIRG) systems. Note (5): This is less robust (note the large interquartile range), representing a rough gas fraction of the systems ∼a few Gyr before the final merger, if they evolved in isolation.
History: From electronic version of the journal References: Hopkins et al. Paper II. 2009ApJS..181..135H. Hopkins et al. Paper III. 2009ApJS..181..486H. Hopkins et al. Paper IV. 2009ApJ...691.1424H.
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 23-Sep-2010
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